US20120186745A1

US20120186745A1 - Plasma processing apparatus

Info

Publication number: US20120186745A1
Application number: US13/035,159
Authority: US
Inventors: Go Miya; Masaru Izawa; Takumi Tandou
Original assignee: Hitachi High Technologies Corp
Current assignee: Hitachi High Tech Corp
Priority date: 2011-01-26
Filing date: 2011-02-25
Publication date: 2012-07-26
Also published as: JP2012156277A; JP5703038B2

Abstract

Provided is a plasma processing apparatus in which accuracy or reliability of processing is improved. This plasma processing apparatus includes a sample stage in a processing chamber arranged in a vacuum vessel and in which plasma is generated. The sample stage has a cylindrical shape and operates as an evaporator through which a refrigerant of a refrigerating cycle flows. Further, the apparatus includes refrigerant passages which are concentrically arranged inside of the sample stage, one or more detectors which detect vibrations of the sample stage, and an control unit which controls a temperature of the refrigerant flowing into the sample stage based on detection results of a dryness of the refrigerant flowing through the passages obtained from an output of the detectors.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a plasma processing apparatus which processes a substrate-shaped sample such as a semiconductor wafer mounted on a sample stage arranged in a processing chamber in a vacuum vessel by using plasma formed in this processing chamber and which processes the sample while controlling a temperature of the sample stage including passages of a refrigerant circulating through a refrigerating cycle in the sample stage.
In a manufacturing process of a semiconductor device, a plasma processing is conventionally performed to samples such as semiconductor wafers by using a plasma etching apparatus or a plasma CVD apparatus. In the above-described plasma processing, a temperature of the sample has a significant impact on processing results. Specifically, in the plasma etching processing, it has an impact on a size of a processing pattern or processed profiles formed on a sample surface by etching. On the other hand, in the plasma CVD processing, it has an impact on quality of a film formed on a sample surface or a deposition rate. Therefore, for the purpose of improving quality of a processing performed on a surface of a sample substrate in the above-described plasma processing, it is extremely important to manage the sample temperature.
In the above-described plasma processing, there is adopted a technology of controlling a temperature of an internal portion of the sample stage and that of a sample holding surface to control a sample temperature by using a temperature control unit arranged in the sample stage for holding the sample. For example, an apparatus system is used in which a passage of a refrigerant is formed in the sample stage and a liquid refrigerant flows through this passage to control a temperature of the sample stage by exchanging heat based on a heat transfer between the refrigerant and a passage wall surface contacted by it so that the sample is controlled to a desired temperature. In this case, a refrigerant temperature control unit (e.g., chiller unit) is connected to the sample stage via piping, the refrigerant controlled to a predetermined temperature by using a cooling device or a heating device in the refrigerant temperature control unit is supplied to the passage in the sample stage to exchange heat, and then is returned to the refrigerant temperature control unit again.
The above-described refrigerant temperature control unit has a configuration in which this liquid refrigerant is stored in a tank for storage once to control its temperature and, then, the refrigerant is supplied to the sample stage. In this configuration, a heat capacity of the refrigerant becomes large since a large amount of the refrigerant is used to control a temperature. As a result, it is advantageous in keeping a sample temperature constant even when the amount of heat entering the sample and the sample stage changes. However, when a temperature of the sample and the sample stage is intended to change notably and rapidly, on the other hand, a rate of a temperature change fails to be increased because of a large heat capacity of the refrigerant. Further, only heat is transferred in the heat exchange between the liquid refrigerant and the passage and, therefore, the amount of heat transfer is small so that the temperature change of the sample stage and the sample can not be quickened.
On the other hand, in the fabrication of semiconductor devices, power applied to the sample during processing tends to increase along with an increase in the diameter of a semiconductor wafer as a sample in the above-described plasma processing. As a result, the amount of heat entering the sample and the sample stage is larger than before. Therefore, there is demanded a technology of stably performing a temperature control of a semiconductor substrate with high speed and high accuracy to this large heat input. Further, due to a complication of a semiconductor device structure and a multilayer film on a semiconductor substrate surface, a temperature of the sample is expected to be controlled speedily and appropriately according to each processing step for processing each of a plurality of films.
Further, in the conventional refrigerant temperature control unit, since a heat transfer between a passage wall and the liquid refrigerant is performed while the liquid refrigerant flows through the passage in the sample stage, a temperature of the liquid refrigerant gradually rises up from entering an inlet of the passage until exiting to an outlet thereof. There is a possibility that an in-plane temperature distribution of sample stage surface is deteriorated due to this temperature change of the refrigerant since a surface temperature of the sample stage receives an influence of the temperature of the refrigerant flowing through the passage. As a result, the in-plane temperature distribution of the sample may be deteriorated and deterioration of the in-plane distribution of the plasma processing can be attributed.
To solve the above-described problem, there is proposed a technology in which the passage through which the refrigerant for cooling the sample stage circulates is configured as a refrigerating cycle including a compressor, a condenser, an expansion valve, and an evaporator and the refrigerant is caused to boil and evaporate in the refrigerant passage in the sample stage to cool the sample stage; that is, the sample stage is operated as an evaporator of the refrigerating cycle and a temperature of the sample stage is controlled by using a refrigerant temperature control unit of the so-called direct expansion system. As examples of the above-described technology, those disclosed in JP-A-6-346256 and JP-A-2005-89864 are known.
As the above-described conventional technology, there is disclosed a technology of configuring a refrigerating cycle for introducing chlorofluorocarbon substitute R410a (hydrofluorocarbon), for example, as the refrigerant to the refrigerant passage in the sample stage and operating the sample stage as an evaporator, using evaporative latent heat of the refrigerant for heat exchange between the refrigerant and the passage wall surface, and controlling the temperature with respect to the large amount of heat entering the sample and the sample stage. Further, there is disclosed a technology in which by controlling a opening degree of the expansion valve a pressure of the refrigerant in the passage is quickly controlled to thereby change a refrigerant temperature quickly and, as a result, a temperature of the sample stage and the sample is changed to a desired temperature to thereby improve accuracy and reproducibility of processing of the sample.

SUMMARY OF THE INVENTION

In a temperature control mechanism of a sample stage using a refrigerant temperature control unit of a direct expansion system disclosed in JP-A-6-346256 and JP-A-2005-89864, even though the heat enters the sample stage from plasma, when refrigerant in a passage is in a state of a gas-liquid mixed flow, a temperature of the refrigerant becomes constant. On the other hand, when the refrigerant is in a state referred to as dryout that a liquid portion of the refrigerant completely evaporates and the entire refrigerant changes into a gas, a temperature of the refrigerant rises up.
Therefore, in the middle of entering a refrigerant inlet of the sample stage, circulating through the passage in the sample stage, and exiting from a refrigerant outlet, dryness gradually rises up due to the heat transferred from the plasma and thus dryout occurs in the sample stage. In this case, at the downstream side further than a position in which the dryout occurs, the refrigerant temperature becomes higher than that of the upstream side. As a result, a temperature distribution of the sample stage becomes inhomogeneous or a desired distribution cannot be accomplished and, therefore, reproducibility and accuracy of the sample processing are impaired. To prevent the problem, the aforementioned dryout of the refrigerant or a sign of its occurrence need to be detected. However, the above-described problem is not considered in the conventional technology.
Further, in the refrigerant temperature control unit of the direct expansion system disclosed in JP-A-6-346256 and JP-A-2005-89864, a refrigerating cycle is configured in the sample stage. Therefore, a pressure of the circulating refrigerant becomes higher as compared with a case where a refrigerant of which a temperature is controlled at the outside of the sample stage is supplied and the sample stage is not used as a part of the refrigerating cycle. In the configuration in which the liquid refrigerant circulates by the above-described chiller unit, for example, the refrigerant has a pressure of approximately 0.4 to 0.8 MPa (4 to 8 atmospheric pressure). On the other hand, in the technology disclosed in JP-A-6-346256 and JP-A-2005-89864, when using chlorofluorocarbon substitute R410a, for example, the refrigerant has a high pressure of approximately 2.0 to 4.0 MPa (20 to 40 atmospheric pressure).
In addition, one metal disk whose surface is milled in a groove shape to configure the refrigerant passage and another metal disk are joined with each other, thereby generally manufacturing the sample stage which mounts the sample. Accordingly, a force applied to the refrigerant passage by a pressure of the refrigerant acts on it so as to separate both of these metal disks. Therefore, when the refrigerant has a pressure of approximately 0.4 to 0.8 MPa, strength of the junction can be easily secured. On the other hand, when the refrigerant has a high pressure of approximately 2.0 to 4.0 MPa, there is a problem that a risk that the junction is separated and the sample stage is broken becomes high. Further, as described above, the refrigerant in the sample stage flows while boiling. Since vibrations are generated in the sample stage along with the boiling, the risk increases such that the separation in the junction of two metal disks configuring the sample stage occurs.
The plasma processing is generally performed in the processing chamber decompressed to approximately several Pa; when the junction of an peripheral portion of the sample stage arranged in the processing chamber is separated and the refrigerant leaks out of the sample stage, the refrigerant evaporates to raise a pressure of the processing chamber and as a result a problem for the plasma processing is posed. In addition, when a chlorofluorocarbon substitute is used as the refrigerant, since it is a compound of hydrogen, fluorine, and carbon, their components diffuse in the plasma to thereby pose a problem for the plasma processing. Moreover, even if the junction of the peripheral portion of the sample stage is effectively joined and the refrigerant is prevented from leaking out of the sample stage, the refrigerant flows through an area except the provided passage when the junction of an internal portion is separated and a short circuit of the refrigerant passage occurs. Since the passage in the sample stage is strictly designed, when the refrigerant flow changes, a temperature distribution of the sample stage changes into an originally unintended one. As a result, an in-plane temperature distribution of the plasma processing on a sample surface changes.
As can be seen, consideration is not made in the above-described conventional technology with regard to a detection unit for the dryout of the refrigerant while flowing through the passage in the sample stage and a problem to detect separation in the junction of the sample stage and breakage of the sample stage. As a result, consideration is not made with regard to a problem that accuracy, reproducibility, and reliability of the processing by using the plasma processing apparatus are impaired.
It is an object of the present invention to provide the plasma processing apparatus in which accuracy or reliability of the processing is improved.
The above-described objects are accomplished by a plasma processing apparatus including a processing chamber which is arranged in a vacuum vessel and in which plasma is generated; a sample stage which is arranged inside toward the bottom of this processing chamber, of which a sample is mounted on an upper surface, which has a shape of a cylinder, and which operates as an evaporator by flowing a refrigerant of a refrigerating cycle through therein; a refrigerant passage which is arranged in the sample stage and concentrically at a center of the cylinder; one or more of detectors which are arranged under the sample stage and detect vibrations of this sample stage; and an control unit which controls an operation of a compressor or an expansion valve configuring the refrigerating cycle based on a detection result of a dryness of the refrigerant flowing through the passage obtained from an output from this detector.
Further, they are accomplished by a plasma processing apparatus includes an control unit which is arranged between the compressor on the refrigerating cycle and the sample stage and controls a temperature of the refrigerant flowing into the sample stage based on a detection result of a dryness of the refrigerant flowing through the passage obtained from an output from this detector.
Further, they are accomplished by the plasma processing apparatus in which one or more of the detectors are arranged on a bottom surface of the sample stage and are connected to a position near an inlet of the refrigerant to inside of the sample stage.
Further, they are accomplished by the plasma processing apparatus in which additional one or more of the detectors are arranged on a bottom surface of the sample stage and are connected to a position near an outlet of the refrigerant from the sample stage.
Further, they are accomplished by the plasma processing apparatus in which the refrigerant passage includes a plurality of passages of shapes of circular arcs which are concentrically arranged in a multiple manner at different radial distances from the center in the sample stage; and a connection passage connecting two passages among these passages of shapes of circular arcs and in which additional one or more of the detectors are arranged on the bottom surface of the sample stage and near the connection passage.
Further, they are accomplished by the plasma processing apparatus in which plan-view shape of the connection passage has a curvature radius smaller than plan-view shape of the passages of shapes of circular arcs.
Further, they are accomplished by the plasma processing apparatus in which the passage in the sample stage is configured by joining two upper and lower members, and a defect in the junction of the upper and lower members is detected from an output from the one or more detectors arranged to be connected to a position near the connection passage on the bottom surface of the sample stage.
Further, they are accomplished by the plasma processing apparatus which further includes a member having electrical insulation arranged to be contacted with the bottom surface of the sample stage, in which the one or more detectors are arranged to be contacted with the member having the insulation.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view illustrating a schematic of a configuration of a plasma processing apparatus according to a first embodiment of the present invention;

FIGS. 2A and 2B are enlarged lateral and longitudinal sectional views illustrating a configuration of the sample stage according to the first embodiment illustrated in FIG. 1;

FIGS. 3A to 3E are graphs illustrating outputs of detection by each vibration sensor arranged on the sample stage according to the first embodiment illustrated in FIG. 1;

FIGS. 4A and 4B are lateral and longitudinal sectional views illustrating a schematic of a configuration of the sample stage according to a second embodiment;

FIG. 5 is a longitudinal sectional view illustrating a schematic of a configuration of the sample stage according to a third embodiment;

FIG. 6 is a longitudinal sectional view illustrating a schematic of a configuration of the sample stage according to a fourth embodiment; and

FIGS. 7A and 7B are graphs illustrating time-series output of detection by a pressure gauge according to the fourth embodiment illustrated in FIG. 6.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will be described below with reference to the accompanying drawings.

First Embodiment

A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3E.
FIG. 1 is a longitudinal sectional view illustrating a schematic of a configuration of a plasma processing apparatus according to the first embodiment of the present invention. In particular, in the present embodiment, FIG. 1 illustrates a configuration of the plasma processing apparatus which forms ECR plasma by using an electric field by microwave and a magnetic field and etches a substrate-shaped sample such as a semiconductor wafer arranged in a processing chamber in a vacuum vessel.
In the present embodiment, there is arranged a processing chamber lid 2 configuring an upper part of the vacuum vessel and made of plate-shaped quartz for tightly sealing the inner and outer parts of the processing chamber on a processing chamber wall 1 configuring the vacuum vessel and having a cylindrical shape, thereby configuring the processing chamber 3 in which a pressure is internally reduced. A sample stage 4 having a cylindrical shape is provided inside toward the bottom of the processing chamber 3, and a sample 5 (a semiconductor wafer in the present embodiment) is held on a mounting surface, which is an upper surface of the sample stage 4.
An opening of a gas-introducing tube 6 is provided on an upper portion of the processing chamber 3 and a processing gas 7 being a highly reactive gas for performing etching processing is introduced into the processing chamber 3 from the opening. An evacuate port 8 is provided under the processing chamber 3 and the processing gas 7 introduced into the processing chamber 3, plasma, and particles of reaction products generated by the etching processing are exhausted. Ahead of the evacuate port 8, a pressure control valve 9 and a turbo molecular pump 12 as a type of a vacuum pump are provided. When an opening degree of the pressure control valve 9 is controlled, a pressure of the processing chamber 3 is controlled to approximately several Pa.
Microwave 10 is applied via the processing chamber lid 2 being an upper part of the processing chamber 3 and generates plasma 11 by the interaction with a magnetic field caused by a solenoid coil (not illustrated) arranged around the processing chamber wall 1. When the sample 5 is exposed to this plasma 11, a plasma etching processing is performed.
Further, in the present embodiment, in order to control a temperature of the sample 5, which is a circular semiconductor wafer, a refrigerant passage 20 is provided in the sample stage 4. To this refrigerant passage 20, a refrigerant temperature control unit 21 using a refrigerating cycle of a direct expansion system is connected and chlorofluorocarbon substitute as a refrigerant flows through the passage 20.
The refrigerant temperature control unit 21 has a compressor 22, a condenser 23, expansion valves 24-1 and 24-2, and an evaporator 26. The refrigerant fed from the sample stage 4 is introduced to the evaporator 26 via the expansion valve 24-2 having controlled therein an opening degree and is evaporated until a dryness becomes equal to approximately zero therein. Thereafter, the refrigerant is introduced to the compressor 22 and compressed therein, and then is introduced to the condenser 23.
To the condenser 23 coolant water 25 is introduced and the refrigerant introduced to the condenser 23 is cooled to be condensed. The condensed refrigerant is introduced to the expansion valve 24-1 having controlled therein an opening degree. After being controlled to a desired pressure by the opening degree, the refrigerant is introduced to the refrigerant passage 20 and circulates while boiling and evaporating.
Based on the above-described configuration of the refrigerating cycle, the sample stage 4 is controlled to a desired temperature. Incidentally, the refrigerant introduced into the sample stage 4 controls a temperature of the sample stage 4 while boiling. Therefore, the sample stage 4 functions as a first evaporator as it were and the evaporator 26 inside of the refrigerant temperature control unit 21 functions as a second evaporator.
Further, although not illustrated, piping between the expansion valve 24-1 and the sample stage 4 and another piping between the expansion valve 24-2 and the sample stage 4 are covered with insulation, thereby insulating the piping.
Incidentally, when an opening degree of the expansion valve 24-1 is reduced, since the pressure of the refrigerant in the refrigerant passage 20 is lowered, the temperature is lowered. On the contrary, when an opening degree of the expansion valve 24-1 is increased, since the pressure of the refrigerant is raised, the temperature is raised. Besides, when an opening degree of the expansion valve 24-2 is reduced, since the pressure of the refrigerant in the refrigerant passage 20 is raised, the temperature is raised. On the contrary, when an opening degree of the expansion valve 24-2 is increased, since the pressure of the refrigerant in the refrigerant passage 20 is lowered, the temperature is lowered.
When the number of rotations of the compressor 22 is increased, since a flow rate of the refrigerant introduced to the sample stage 4 is increased, the pressure is increased and the temperature is increased. When the opening degrees of these expansion valves 24-1 and 24-2, and the number of rotations of the compressor 22 are controlled, the sample stage 4 is controlled to a desired temperature. As a result, the sample 5 is controlled to a target temperature suitable for the plasma etching processing.
At a plurality of places on the bottom surface of the sample stage 4 according to the present embodiment, vibration sensors 37-1 to 37-3 as detectors for detecting vibrations are arranged to thereby detect vibrations near the arranged places. In addition, in the present embodiment, as the vibration sensors, AE sensors (acoustic emission sensors) are used.
FIGS. 2A and 2B are enlarged lateral and longitudinal sectional views illustrating a configuration of the sample stage according to the present embodiment illustrated in FIG. 1. FIG. 2A illustrates a top view of a section of the sample stage 4.
In the sample stage 4 according to the present embodiment, a planar shape in which the refrigerant passages are approximately concentrically arranged in a multiple manner in a plurality of positions with different radii as illustrated in this figure has a plurality of circular arc portions. Here, there is arranged a passage in which, in order to cause the refrigerant to flow from an arbitrary circular arc passage in a certain radial position to a circular arc passage in a different radial position in the outside or in the inside, both the passages are connected and arranged and having a circular arc planar shape with a smaller curvature radius. This portion of the passage or that of the sample stage 4 having arranged therein the passage is called as a bend section.
The refrigerant introduced from a refrigerant inlet 30 circulates through the refrigerant passage 20 while being divided into two directions as indicated by arrows and further flows through an inside passage via the bend sections 31. As described above, the refrigerant circulates through via the approximately concentric passages and the bend section 31 and then joins together near the refrigerant outlet 32. The refrigerant is ejected from the refrigerant outlet 32 to the outside of the sample stage 4 and returned to the refrigerant temperature control unit 21 as illustrated in FIG. 1. The above-described configuration makes it possible to improve an azimuthal uniformity of a temperature of a sample or a sample stage in different radial positions.
Further, FIG. 2B illustrates a configuration near the sample stage 4. The sample stage 4 is composed of two metallic circular plates 35-1 and 35-2 (e.g., made of aluminum base alloy). In a bottom surface of the circular plate 35-1, rectangular grooves with a section of the planar-shaped passage viewed from the upper side as illustrated in FIG. 2A are arranged. Then, a surface in which the groove is not formed in the bottom surface of the circular plate 35-1 is joined with the upper surface of the circular plate 35-2, thereby configuring the refrigerant passage 20. Therefore, an area in which the plates are joined is illustrated by using a hatched portion in FIG. 2A.
In the present embodiment, the vibration sensors are arranged on the bottom surface of the sample stage 4 and vibrations caused by the refrigerant are measured, thereby detecting a state of the refrigerant. Also, vibrations associated with separation between the joined circular plates 35-1 and 35-2 are detected.
Hereinafter, arrangement places of the vibration sensors will be described with reference to FIG. 2B. In addition, to assist understanding the arrangement places, the arrangement places of the vibration sensors 37-1 to 37-3 are illustrated also in FIG. 2A by using a broken line.
The vibration sensor 37-1 is arranged on the bottom surface of the sample stage 4 and near the refrigerant inlet 30 and the vibration sensor 37-3 is arranged on the bottom surface of the sample stage 4 and near the refrigerant outlet 32, respectively. Further, the vibration sensors 37-2 are arranged on the bottom surface of the sample stage 4 and near the bend sections 31. When the vibration sensors are arranged at the above-described places, respectively, vibrations near the respective places can be detected. For example, since the vibration sensor 37-1 is arranged near the refrigerant inlet 30, the vibrations near the refrigerant inlet 30 can be detected. Further, signals of the vibrations detected by these vibration sensors 37-1 to 37-3 are transmitted to a signal processor 39 for processing.
Hereinafter, a specific evaluation and processing method for the vibrations detected by the vibration sensors 37-1 to 37-3 will be described. In the present embodiment, an object in which the vibration sensors 37-1 to 37-3 are arranged on the bottom surface of the sample stage 4 is to mainly detect the vibrations associated with boiling of the refrigerant in a gas-liquid mixture phase. However, vibrations detected on the bottom surface of the sample stage 4 are present in addition to the above-described vibrations. Examples of such vibrations include vibrations from a floor of a place in which the plasma processing apparatus is arranged and vibrations caused by the turbo molecular pump 12 attached to the processing chamber wall 1. These vibrations are a noise component in the detection according to the present embodiment.
Therefore, the vibrations associated with boiling of the refrigerant and the noise component are separated; a spectral analysis using a fast Fourier analysis generally used for the analysis of data on vibrations such as sound is performed to convert into a frequency of vibration data and a power spectrum indicating intensity of the frequency. Further, by decibel conversion of the acquired power spectrum, a sound pressure level is acquired. The decibel conversion is a method which represents the power spectrum by the common logarithm of a ratio to a reference value and, in general, a sound pressure level Lp is acquired from an intensity p at a certain frequency by using an equation (1).
Lp=20×log₁₀(p/p ₀) (1)
Here, p₀=20×10⁻⁶[Pa] (Pascal).
Since the acquired sound pressure level is data including noise components, a component less than a certain threshold is considered as noise. A component more than or equal to the certain threshold is used for the analysis of the vibrations associated with boiling of the refrigerant. In the present embodiment, the threshold is set to zero. A weak component is eliminated from among the noise components of the data acquired by the vibration sensors by the above-described operation. For example, the vibrations from a floor of the place in which the plasma processing apparatus is arranged, which is one of the above-described noises is eliminated by this operation.
Results detected by the vibration sensors 37-1 and 37-3 and arranged by using the above-described method are illustrated in FIGS. 3A and 3C, respectively. Further, detection results of one of the plurality of vibration sensors 37-2 are illustrated in FIG. 3B. FIGS. 3A to 3E are graphs illustrating outputs of detection by the respective vibration sensors arranged on the sample stage 4 according to the first embodiment illustrated in FIG. 1. Moreover, these graphs are acquired at a state in which plasma 11 is generated in the processing chamber 3 and at a state in which the refrigerant is supplied to the refrigerant passage 20 by the refrigerant temperature control unit 21. The abscissa represents the frequency and the ordinate represents the sound pressure level.
Here, particularly, FIG. 3C illustrates detection results acquired in the case where dryout does not occur at the refrigerant outlet 32. In the graph of FIG. 3A, peaks 40-a appear at frequencies of 450 Hz, 900 Hz, and 1350 Hz. These are matched with a fundamental frequency of 450 Hz, its second harmonic of 900 Hz, and its third harmonic of 1350 Hz with respect to the number of rotation of 27000 rpm of the turbo molecular pump 12. Therefore, the peaks are determined to be caused by the operation of the turbo molecular pump 12.
Also, in the detection results of the vibration sensors 37-2 and 37-3 respectively illustrated in FIGS. 3B and 3C, the peaks respectively illustrated in the peaks 40-b and 40-c appear at exactly the same frequencies (namely, 450 Hz, 900 Hz, and 1350 Hz) as those of the peak 40-a. Further, the sound pressure levels of these peaks 40-a to 40-c are approximately the same as each other. The reason is as follows. Since the sample stage 4 is mechanically connected to the processing chamber wall 1, vibrations of the turbo molecular pump 12 are propagated with approximately the same intensity to the vibration sensors 37-1 to 37-3 arranged on the bottom surface of the sample stage 4. As a result, the vibrations are detected with approximately the same sound pressure levels.
Further, in FIGS. 3A to 3C, peaks 41-a to 41-c appear at approximately 650 Hz in addition to the peaks 40-a to 40-c, respectively. Here, in FIG. 3D, there are illustrated the detection results of one of the vibration sensors 37-2 in a state in which the turbo molecular pump 12 is operated, operations of the refrigerant temperature control unit 21 is stopped, and supply of the refrigerant to the refrigerant passage 20 is stopped. When the refrigerant flows, the peak 41-b appears at approximately 650 Hz as illustrated in FIG. 3B whereas, when the refrigerant does not flow, there only appear peaks 40-d associated with the operation of turbo molecular pump 12 and no peak appears at approximately 650 Hz as illustrated in FIG. 3D. Further, although not illustrated here, when the refrigerant does not flow, there appears no peak at approximately 650 Hz also in the detection results of the vibration sensors 37-1 and 37-3 in the same manner as in FIG. 3D. Therefore, the peaks 41-a to 41-c are determined to appear only when the refrigerant flows through.
Here, when comparing the peaks 41-a to 41-c at approximately 650 Hz of FIGS. 3A to 3C at a state in which the refrigerant flows, differences between sizes of the peaks 41-a to 41-c arise. Here, since a size of the peak 41-a detected by the vibration sensor 37-1 arranged near the refrigerant inlet 30 is extremely small, this peak is generated due to the vibrations associated with boiling of the refrigerant. The reason is as follows. Near the refrigerant inlet 30, it is immediately after the introduction of the refrigerant at a state in which dryness of the refrigerant is equal to approximately zero to the refrigerant passage 20 and, therefore, the refrigerant does not nearly receive heat from the plasma 11. Accordingly, boiling does not nearly occur, and as a result, vibrations are not nearly generated.
Further, based on the detection results of one of the vibration sensors 37-2 arranged near the bend sections 31 illustrated in FIG. 3B, the refrigerant receives heat from the plasma 11 in a process of flowing from the refrigerant inlet 30 to the bend section 31. Accordingly, the vibrations become greater due to the fact that boiling violently occurs and, as a result, the peak 41-b at approximately 650 Hz becomes larger than the peak 41-a. Further, in the detection result (FIG. 3C) of the vibration sensor 37-3 arranged near the refrigerant outlet 32, which is further downstream than the bend sections 31, the peak 41-c is lower than the peak 41-b in the sound pressure level. The reason is as follows. When the refrigerant receives heat from the plasma 11 in a process of flowing from the bend section 31 to the refrigerant outlet 32, boiling is continued and the dryness becomes high. Specifically, since a ratio of the liquid is reduced in the refrigerant in a gas-liquid mixture phase, a size of the vibrations caused by the boiling becomes small.
As discussed above, the peaks 41-a to 41-c at approximately 650 Hz in FIGS. 3A to 3C are determined to depend on the vibrations generated by the boiling.
Next, in FIG. 3E, there is illustrated the detection result of the vibration sensor 37-3 at a state in which the dryout occurs before the refrigerant reaches the refrigerant outlet 32 and, as a result, all the refrigerant at the refrigerant outlet 32 turns into a gas completely. Incidentally, the dryout at the refrigerant outlet 32 occurs in the case where the amount of heat entering the sample stage 4 from the plasma 11 is excessively large or a flow rate of the refrigerant introduced to the refrigerant passage 20 is excessively small. When the dryout occurs, as illustrated in FIG. 3E, the peak at approximately 650 Hz does not appear while there appear peaks 40-e associated with the operation of turbo molecular pump 12.
The vibrations due to the boiling indicated as the peaks 41-a to 41-c of FIGS. 3A to 3C are generated when bubbles are generated in the liquid and the bubbles rise up to a gas-liquid interface and burst. Therefore, as illustrated in FIG. 3E, when the dryout occurs at the refrigerant outlet 32, since all the refrigerant evaporates and only a gas is present, vibrations are not generated and the peak at approximately 650 Hz does not appear.
As can be seen from the above, in the detection result of the vibration sensor 37-3 arranged near the refrigerant outlet 32, in the case where the peak 41-c indicating boiling of the refrigerant appears, the dryout is considered not to occur. On the other hand, in the case where the peak 41-c does not appear, the dryout is considered to occur.
As described above, the signal processor 39 performs processings in which respective vibration data detected by the vibration sensors 37-1 to 37-3 is subjected to spectrum analysis using fast Fourier analysis to convert to a power spectrum, a sound pressure level is calculated by decibel conversion, peaks having the sound pressure levels of zero or more are extracted, a peak indicating boiling of the refrigerant is identified, and the presence or absence of the dryout is determined based on a height of the peak.
In the present embodiment, operations in the case where the signal processor 39 determines that a sign of the dryout is detected will be here described. In the present embodiment, when a sound pressure level of the peak 41-c indicating boiling of the refrigerant is lower than a certain threshold (e.g., three decibel) in the detection result of the vibration sensor 37-3, a flow rate of the refrigerant is increased. As a result, since a flow rate of the refrigerant is increased and the refrigerant is ejected from the refrigerant outlet 32 before it completely evaporates, the dryout is avoided.
To cope with the above-described problem, the number of rotation of the compressor 22 in the refrigerant temperature control unit 21 is increased. Note that, when the number of rotation of the compressor 22 is increased, a temperature of the refrigerant in the refrigerant passage 20 is raised and temperatures of the sample stage 4 and the sample 5 are raised. As a result, since the temperature of the sample 5 rises up above the target temperature, a harmful influence is exerted on the etching processing.
To prevent this phenomenon, in the refrigerant temperature control unit 21 while the number of rotation of the compressor 22 is increased, at the same time, an opening degree of the expansion valve 24-1 is decreased or an opening degree of the expansion valve 24-2 is increased. By this operation, increase of the temperature of the refrigerant is prevented while increasing a flow rate of the refrigerant. Further, by performing the above-described operation, in the case where the dryness at the refrigerant outlet 32 is lowered and a sound pressure level of the peak 41-c of the detection result of the vibration sensor 37-3 becomes larger than a certain threshold, it can be determined that the dryout is suppressed and the number of rotation of the compressor 22 and opening degrees of the expansion valves 24-1 and 24-2 may be maintained. By the above-described operation, a temperature of the sample 5 is controlled and maintained in the desired range while the dryout is suppressed; accuracy and reliability of the processing of the sample are improved.
When performing the above-described control of the flow rate and temperature of the refrigerant, it is preferred to find out correlations among the number of rotation of the compressor 22, the opening degrees of the expansion valves 24-1 and 24-2, and either the temperature of the refrigerant or that of the sample stage 4 by using experiments and the like and records data on the correlations in advance. In the present embodiment, the refrigerant temperature control unit controller 33 transmit command signals to the refrigerant temperature control unit 21 via an input and output interface so as to cause a computing unit to read out data memorized in an not-illustrated, internal memory device, to select a value of the temperature of the refrigerant to be set using the above-described data according to a program similarly memorized in the memory device, and to control to the set value of the temperature of the refrigerant.
The number of rotation of the compressor 22 and the opening degrees of the expansion valves 24-1 and 24-2 of the refrigerating cycle, which receives the command signals, are controlled by their drive units, which are not illustrated, and the temperature of the refrigerant is controlled to a desired value. Further, the refrigerant temperature control unit controller 33 may transmit above-described commands of operating the compressor 22 and the like so as to keep the temperature of the refrigerant measured by using a thermometer arranged on the sample stage 4 or a thermometer 27 arranged in the refrigerant temperature control unit 21 in the predetermined range.
Moreover, in the present embodiment, the peak of the vibrations associated with boiling of the refrigerant appears at approximately 650 Hz; however, it does not necessarily appear at the above-described frequency. The vibrations are caused by generation and disappearance of the bubbles as described above and, therefore, are influenced by dryness and physical properties of the refrigerant such as viscosity, density, and surface tension. Further, since the physical properties are influenced by a type of the refrigerant and the temperature, it is difficult to predict in advance at which frequency the peak of the vibrations due to boiling of the refrigerant appears. However, the vibrations of the turbo molecular pump 12 having the possibility of confusing its vibrations with those due to boiling of the refrigerant can be determined because their sound pressure levels are very high as described above and the frequency of the peaks appear at integral multiplies of the number of rotation.
Consequently, in the present embodiment, the vibrations associated with boiling of the refrigerant and the vibrations of the turbo molecular pump 12 are distinguished and a spectrum of the vibrations associated with boiling of the refrigerant is detected. Further, as described above, by comparing the detection result (FIG. 3B) at a position in which boiling of the refrigerant occurs and the detection result (FIG. 3D) in the case where the operation of the refrigerant temperature control unit 21-1 is stopped and the supply of the refrigerant to the refrigerant passage 20 is stopped, it becomes easy to determine the frequency of the peak indicating the vibrations associated with boiling of the refrigerant.
Incidentally, in the sample stage 4 according to the present embodiment, a total of 8 vibration sensors 37-1 to 37-3 are arranged as one each at the refrigerant inlet 30, at the refrigerant outlet 32, and near the bend sections 31 of six places, respectively; however, the number of the arrangement is not limited thereto. In the configuration of the refrigerant passage 20 according to the present embodiment, the refrigerant is not cooled and flows through while receiving heat from a wall surface of the refrigerant passage 20 and boiling. Therefore, as a distance in which the refrigerant flows is longer, namely, it is nearer the refrigerant outlet, the dryness becomes higher in general. Accordingly, when the vibration sensor 37-3 is arranged at only one position near the refrigerant outlet 32 and the vibrations associated with boiling of the refrigerant are detected, a minimum of dryout can be detected.
Further, by using the vibration sensors 37-2 arranged near the bend sections 31 to detect vibrations at the relevant bend sections 31, it can be determined with high accuracy whether the refrigerant evaporates properly while the refrigerant flows through or whether the sample stage 4 is cooled or in an abnormal state. Further, by detecting the vibrations near the refrigerant inlet 30 with the vibration sensor 37-1, it can be determined with high accuracy whether the dryness of the refrigerant near the refrigerant inlet 30 is equal to zero (0%) or a value close to zero (the refrigerant is laid in a saturated liquid state). Then, necessity and accuracy of the control in the temperature of the refrigerant with the refrigerant temperature control unit 21 can be improved.
Further, when the heat amount received from the plasma 11 by the sample 5 or the sample stage 4 is extremely large and the flow rate of the refrigerant is low, the dryout might occur before the refrigerant introduced from the refrigerant inlet 30 reaches the bend sections 31. In that case, the peak indicating the vibrations associated with boiling of the refrigerant is detected not by the vibration sensors 37-2 and 37-3 but by only the vibration sensor 37-1. In that case, the flow rate of the refrigerant need to be increased more compared with the case where the dryout occurs between the bend sections 31 and the refrigerant outlet 32 as described above. Therefore, the number of rotation of the compressor 22 is increased further along with the opening degree of the expansion valve 24-1 is lowered or the opening degree of the expansion valve 24-2 is raised so that the refrigerant is maintained at the target temperature while raising the flow rate of the refrigerant. As seen above, by determining at which position of the refrigerant passage 20 the dryout occurs, reliability in the control of the flow rate of the refrigerant is improved. Therefore, the plurality of vibration sensors are preferably arranged as shown in the present embodiment.
Further, the vibration sensors are arranged at positions under the passage as described above and between the refrigerant inlet 30 and the refrigerant outlet 32 so that a detection accuracy of a sign of the occurrence of the dryout and its position and the effects of reduction in standing of bubbles generated by evaporation with the supply control of the refrigerant performed based on these detection results and suppression of the dryout are improved. In addition, these detection units are preferably arranged near the bend sections 31 and the like.
The reason is that in the refrigerant passage 20, since the curvature radii of each passage become smallest at the bend sections 31, concentrations of stress to separate the circular plates 35-1 and 35-2 from each other due to an internal pressure of the refrigerant are easy to occur at the junction near the bend section 31 and there is a high possibility that junction defects such as separation and crack are generated. Therefore, by arranging the vibration sensors 37-2 near the bend sections 31, not only the vibrations due to boiling of the refrigerant but also those associated with the separation of the junction when it occurs are detected and, therefore, the occurrence of the separation can be detected.
In such a configuration, the respective vibration sensors 37-1 and 37-2 and the like transmit the detection result of the vibrations to the signal processor 39. When the computing unit of this signal processor 39 determines the vibrations are associated with the separation of the junction, the processing result is transmitted to an apparatus controller 43 via a communication unit. Then, according to a program memorized in advance in an internal memory unit the apparatus controller 43 informs of occurrence of an abnormality using an information unit equipped on the plasma processing apparatus or displays it on the monitor of a command input unit of the user. For example, a warning is displayed on a control screen which is displayed in a CRT monitor for the command input and the user can be notified.
As described above, an output is received from the detection unit arranged on the bottom surface of the sample stage 4 and the dryness of the refrigerant flowing or the occurrence of the dryout is detected; by controlling operations of the refrigerating cycle, flow of the refrigerant, and the temperature of the refrigerant introduced to the refrigerant passage 20 in the sample stage 4 to a desired value based on the result the refrigerant temperature control unit 21 suppresses the occurrence of the dryout and maintains the temperature of the sample 5 during the processing in the desired range so that accuracy, yield, and reproducibility of the processing are improved. Further, by early detection of the occurrence of the separation at the bend sections 31 in which the separation in the junction of the sample stage 4 is easy to occur, the amount and the time of work required for maintenance/inspection is reduced and reliability of the plasma processing apparatus and efficiency of the processing with it are improved.

Second Embodiment

In the above-described embodiment, it is configured so that the refrigerant passage 20 in the sample stage 4 has one system; that is, the refrigerant to be supplied to the refrigerant passage 20 is controlled to one condition and the sample stage 4 is substantially controlled to one temperature. In that case, the temperature of the surface of the sample stage 4 or that of the sample 5 is approximately uniform in the surface.
In contrast, when a plurality of systems, for example, two systems of the refrigerant passages are formed in the sample stage 4 and the refrigerant with temperature higher than that of an outer system is introduced to an inner system, the sample stage 4 or the sample 5 can be made into a convex-shaped temperature distribution which is higher in the inner side.
In an etching processing for forming a gate electrode, a density in a reaction product generated in the processing becomes high in an inner portion. Therefore, by setting the temperature of the sample 5 higher in the inner side and lowering an attachment coefficient of the reaction product to the gate, the processing is generally conducted so as to make dimensions of the gate electrode be uniform in the plane of the sample 5. A configuration in which for controlling temperature distributions of the sample 5 and the sample stage 4 as described above the plurality of systems of the refrigerant passages are formed in the sample stage 4 will be described as a second embodiment with reference to FIGS. 4A and 4B.
Hereinafter, FIGS. 4A and 4B illustrate lateral and longitudinal sectional views illustrating a schematic of a configuration of the sample stage according to the second embodiment. FIG. 4A illustrates a plan view of the section of the sample stage 4. In order to have a temperature distribution in a radial direction, an inner refrigerant passage 20-1 and an outer refrigerant passage 20-2 are provided in the sample stage 4, each of which has approximately concentric passages and bend sections in the similar manner as in the first embodiment. Further, to the inner refrigerant passage 20-1 and the outer refrigerant passage 20-2, the refrigerant temperature control units 21-1 and 21-2 of the direct expansion system described in the first embodiment are connected, respectively.
In the inner refrigerant passage 20-1, the refrigerant introduced from an inner refrigerant inlet 30-1 is divided into two directions, circulates through the inner refrigerant passage 20-1, and further flows through the passage on the outside via a bend section 31-1. The above-described refrigerant which flows as being divided into two directions joins together near an inner refrigerant outlet 32-1, is ejected from the inner refrigerant outlet 32-1 to the outside of the sample stage 4, and returns to the refrigerant temperature control unit 21-1 as illustrated in FIG. 4B.
Similarly, also in the outer refrigerant passage 20-2, the refrigerant introduced from an outer refrigerant inlet 30-2 is divided into two directions, circulates through the outer refrigerant passage 20-2, and further flows through the passage on the inside via a bend section 31-2. The above-described refrigerant which flows as being divided into two directions joins together near an outer refrigerant outlet 32-2 and is ejected from the outer refrigerant outlet 32-2 to the outside of the sample stage 4.
Further, FIG. 4B illustrates a configuration near the sample stage 4. In the same manner as in the first embodiment, the vibration sensor 37-1 is arranged on the bottom surface of the sample stage 4 and near the inner refrigerant inlet 30-1, the vibration sensor 37-3 is arranged on the bottom surface of the sample stage 4 and near the inner refrigerant outlet 32-1, a vibration sensor 37-4 is arranged on the bottom surface of the sample stage 4 and near the outer refrigerant inlet 30-2, and a vibration sensor 37-6 is arranged on the bottom surface of the sample stage 4 and near the outer refrigerant outlet 32-2. Further, the vibration sensors 37-2 are arranged on the bottom surface of the sample stage 4 and near the bend sections 31-1 and vibration sensors 37-5 are arranged on the bottom surface of the sample stage 4 and near the bend sections 31-2.
The vibration sensors are arranged at these places, respectively, thereby detecting vibrations near them in the same manner as in the first embodiment. Then, signals of the vibrations detected by these vibration sensors 37-1 to 37-6 are transmitted to the signal processor 39 for processing.
A detection method using these vibration sensors 37-1 to 37-6 is the same as in the first embodiment. That is, vibrations of the refrigerant at the inner refrigerant inlet 30-1, the bend sections 31-1, the inner refrigerant outlet 32-1, the outer refrigerant inlet 30-2, the bend sections 31-2, and the outer refrigerant outlet 32-2 are detected using the vibration sensors 37-1 to 37-6. Further, the signal processor 39 performs processings in which respective vibrations data detected by the vibration sensors 37-1 to 37-6 are subjected to spectrum analysis using the fast Fourier analysis, sound pressure levels are calculated using power spectrum conversion and decibel conversion, the peaks having the sound pressure levels of zero or more are extracted, the peak indicating boiling of the refrigerant is identified, and the presence or absence of the dryout is determined based on a height of the peak. Further, it is determined whether the dryout of the refrigerant occurs at the inner refrigerant outlet 32-1 or the outer refrigerant outlet 32-2.
Also, when the signal processor 39 determines that a sign of the dryout is detected, the refrigerant temperature control unit controller 33 controls the number of rotation of the compressor 22 and the opening degrees of the expansion valves 24-1 and 24-2 in the refrigerant temperature control units 21-1 or 21-2 in the same manner as in the first embodiment. So, while preventing the dryout, the refrigerant temperatures in the inner refrigerant passage 20-1 and the outer refrigerant passage 20-2 can be controlled to desired values. Further, when the separation in the junction of the sample stage 4 is detected using the vibration sensors 37-1 to 37-6, the apparatus controller 43 issues a warning indicating that an abnormality occurs to a plasma etching apparatus.
When configuring the apparatus and performing the operations as described above, the temperatures of the refrigerants to be introduced, respectively, are controlled to desired values while preventing the dryout and, as a result, a temperature distribution of the sample 5 can be controlled to perform preferable etching processing in the same manner as in the first embodiment even when a plurality of systems of the refrigerant passages, namely, the inner refrigerant passage 20-1 and the outer refrigerant passage 20-2 are provided on the sample stage 4. Also in the same manner as in the first embodiment, occurrence of the separation at the bend sections 31-1 and 31-2 in which the separation of the junction in the sample stage 4 is easy to occur can be detected.
Here, a positional relationship between the inner refrigerant inlet 30-1 and the inner refrigerant outlet 32-1 according to the present embodiment will be described. In the present embodiment, the inner refrigerant inlet 30-1 is arranged on the inner circumference than the inner refrigerant outlet 32-1.
Also in the present embodiment, in order for the temperature of the sample 5 to be made into a convex-shaped distribution that a central part is higher than an outer periphery, the temperature of the refrigerant to be introduced to the inner refrigerant passage 20-1 is made higher than that of the outer refrigerant passage 20-2. Then, the refrigerant with the dryness of approximately zero introduced from the inner refrigerant inlet 30-1 boils by receiving heat from the plasma 11. It circulates through the passage on the inner circumference of the inner refrigerant passage 20-1 with the dryness rising up. After the bend sections 31-1, the refrigerant circulates through the passage on the outer circumference of the inner refrigerant passage 20-1 while being heated by the plasma 11 and cooled by the outer refrigerant passage 20-2 adjacent to the passage on the outer circumference to be ejected from the inner refrigerant outlet 32-1.
In that case, by making the dryness of the refrigerant sufficiently high at the bend sections 31-1, even if the heat quantity to the outer refrigerant passage 20-2 is larger than the heat quantity from the plasma 11 and the refrigerant circulates through the passage on the outer circumference of the inner refrigerant passage 20-1 with the dryness being lowered, the dryness is suppressed from being reduced to zero before the refrigerant reaches the inner refrigerant outlet 32-1. Therefore, before the refrigerant introduced to the inner refrigerant passage 20-1 is ejected from the inner refrigerant outlet 32-1, the dryness will not become equal to zero. When the dryness of the refrigerant in a gas-liquid mixture phase is not equal to zero as described above, the temperature of the refrigerant does not change; the refrigerant temperature does not change at a process in which the refrigerant flows through the inner refrigerant passage 20-1. As a result, a temperature distribution which is even in an azimuthal direction can be realized in the sample stage 4 and the sample 5.
On the other hand, in opposition to the present embodiment, when the inner refrigerant inlet 30-1 is arranged on the outer circumference than the inner refrigerant outlet 32-1, in the example of FIG. 4A the refrigerant is introduced from the inner refrigerant outlet 32-1 and is ejected from the inner refrigerant inlet 30-1. When the temperature of the refrigerant to be introduced to the inner refrigerant passage 20-1 is made higher than that of the refrigerant to be introduced to the outer refrigerant passage 20-2, the refrigerant with the dryness of approximately zero introduced from the inner refrigerant outlet 32-1 receives heat from the plasma 11 and simultaneously circulates while being cooled from the passage of the innermost circumference of the outer refrigerant passage 20-2 adjacent to the outer circumference to reach the bend sections 31-1.
In this case, when the heat quantity to the outer refrigerant passage 20-2 is larger than the heat quantity from the plasma 11, the refrigerant circulates through the passage on the outer circumference of the inner refrigerant passage 20-1 with the dryness remaining to be zero and the refrigerant temperature being dropped and reaches the bend sections 31-1. Therefore, the temperature distribution in the azimuthal direction in the inner refrigerant passage 20-1 becomes non-uniform so that the temperature distribution in the azimuthal direction of the sample stage 4 and the sample 5 becomes non-uniform. As a result, uniformity in an in-plane distribution of the plasma processing of the sample 5 is remarkably impaired.
Incidentally, when the inner refrigerant inlet 30-1 is arranged on the inner circumference than the inner refrigerant outlet 32-1 as in the present embodiment, an optimal value of the dryness of the refrigerant in the bend sections 31-1 is influenced by both of the heat quantity to the outer refrigerant passage 20-2 and the heat quantity from the plasma 11. If the former is larger than the latter, for example, while the refrigerant after the bend sections 31-1 circulates through the passage on the outer circumference of the inner refrigerant passage, the dryness is gradually lowered. Therefore, the dryness at the bend sections 31-1 needs to be made sufficiently high such that the dryness of the refrigerant will not be equal to zero before it is ejected from the inner refrigerant outlet 32-1.
On the contrary, if the heat quantity to the outer refrigerant passage 20-2 is smaller than the heat quantity from the plasma 11, while the refrigerant after the bend sections 31-1 circulates through the passage on the outer circumference of the inner refrigerant passage, the dryness gradually rises. Therefore, the dryness at the bend sections 31-1 needs to be sufficiently low such that the dryness of the refrigerant is prevented from becoming equal to one, that is, the dryout is prevented from occurring before the refrigerant is ejected from the inner refrigerant outlet 32-1. When the amount of heat entering from the plasma 11 and the amount exiting to the adjacent refrigerant passage as described above are found out in advance by calculations or experiments and, further, the optimal dryness at the bend sections 31-1 is found out, it can be checked whether the dryness is the optimal value by the vibration sensor 37-2 during the plasma processing. Specifically, when the optimal value of the dryness at the bend sections 31-1 is high and close to unity (100%), a liquid portion of the refrigerant ought to be small and the peak 41-b illustrated in FIG. 3B ought to be low.
On the other hand, when the optimal value of the dryness at the bend sections 31-1 is small, since the liquid portion of the refrigerant is large and boils violently, the peak 41-b illustrated in FIG. 3B ought to be high. As described above, during the plasma processing, the vibrations at the inner refrigerant inlet 30-1 and the inner refrigerant outlet 32-1 are detected using the vibration sensors 37-1 and 37-3 and at the same time the vibrations at the bend section 31-1 are detected using the vibration sensor 37-2 to prevent the dryness from becoming equal to zero or to prevent the dryout from occurring in the entire area of the inner refrigerant passage 20-1.
Moreover, with regard to the arrangement of the refrigerant passages, when the plurality of systems of the refrigerant passages are provided in the sample stage 4 and the refrigerants with different temperatures are introduced to the respective systems, as described in the present embodiment, it is preferable that the dryness is raised by heating from the plasma 11 before the refrigerant reaches the passage adjacent to the refrigerant passage through which the refrigerant with lower temperature circulates. With this non-uniformity of the temperature distribution in the azimuthal direction of the sample stage 4 and the sample 5 is eliminated, and as a result, an in-plane distribution of the plasma etching processing of the sample 5 can be made uniform.

Third Embodiment

A third embodiment of the present invention will be described below with reference to FIG. 5. In the second embodiment, the vibration sensors 37-1 to 37-6 are arranged directly on the bottom surface of the sample stage 4. However, in the etching processing, in order that ions in the plasma 11 are pulled in toward the sample 5 as a workpiece, a radio-frequency power source 53 is connected to the sample stage 4 to apply a radio frequency power in many cases. In that case, since a radio frequency power exerts a harmful influence on the vibration sensors 37-1 to 37-6, they cannot be arranged directly on the bottom surface of the sample stage 4. The third embodiment of the present invention copes with the above-described problem. In the same manner as in the first embodiment, the vibrations due to boiling of the refrigerant introduced to the sample stage 4 are detected using the vibration sensors and the dryout of the refrigerant is detected. Unlike the first embodiment, piping made of electrically insulating materials (e.g., alumina ceramics) is arranged under the sample stage 4 and the vibration sensors are arranged on the insulating piping to thereby detect vibrations.
FIG. 5 illustrates a vicinity of the sample stage used in the present embodiment and components connected to it. Here, although a top view of the cross section of the sample stage 4 is not illustrated, a sample stage same as the sample stage 4 illustrated in the second embodiment of the present invention is used. Circular holes are formed at portions in which the circular plate 35-2 configuring the lower side of the sample stage 4 is connected to the inner refrigerant inlet 30-1, the inner refrigerant outlet 32-1, the outer refrigerant inlet 30-2, and the outer refrigerant outlet 32-2 and electrically insulating piping 51-1 to 51-4 are inserted into and connected to the holes, respectively. 0 rings 57 are installed at respective upper parts of these insulating piping 51-1 to 51-4 to form a shaft sealing structure so that the refrigerant introduced to or ejected from the inner refrigerant passage 20-1 is sealed so as not to leak. Further, the vibration sensors 37-1, 37-3, 37-4, and 37-6 are arranged directly at the insulating piping 51-1 to 51-4, respectively. Also, although not illustrated, areas of the insulating piping 51-1 to 51-4 in which the vibration sensors 37-1, 37-3, 37-4, and 37-6 are not arranged are covered with thermally insulating materials, thereby performing heat insulation.
The above-described insulating piping 51-1 to 51-4 is tightly contacted with and fixed on the bottom surface of the sample stage 4 and the vibrations due to the refrigerant at the inner refrigerant inlet 30-1, the inner refrigerant outlet 32-1, the outer refrigerant inlet 30-2, and the outer refrigerant outlet 32-2 can be detected using the vibration sensors 37-1, 37-3, 37-4, and 37-6 through the insulting piping 51-1 to 51-4, respectively.
Further, electrically insulating members 55-1 and 55-2 made of electrically insulating materials are tightly contacted with and fixed on the bottom surface of the sample stage 4 under the bend sections 31-1 of the inner refrigerant passage 20-1 and the bend sections 31-2 of the outer refrigerant passage 20-2, respectively. Vibration sensors 37-2 and 37-5 are tightly contacted with and fixed on the insulating members 55-1 and 55-2, respectively. By this, the vibrations of the refrigerant at the bend sections 31-1 and 31-2 can be detected with the vibration sensors 37-2 and 37-5. In this configuration, since the insulating members 55-1 to 55-4 are tightly contacted with and fixed on the sample stage 4, respectively, even if the vibration sensors 37-1, 37-3, 37-4, and 37-6 are arranged at any position of the insulating members 55-1 to 55-4, vibrations can be detected. However, when the respective vibration sensors are arranged away from the sample stage 4 and in a position near the refrigerant temperature control unit 21-1 or 21-2, since vibrations of driving components such as the expansion valves 24-1 and 24-2 and the compressor 22 are also detected, an S/N ratio is lowered. Therefore, the respective vibration sensors are preferably arranged at areas of the respective insulating members near the sample stage 4.
The detection method using the vibration sensors 37-1 to 37-6 is the same as in the first embodiment. That is, the vibration sensors 37-1 to 37-6 detect the vibrations of the refrigerant at the inner refrigerant inlet 30-1, the bend sections 31-1, the inner refrigerant outlet 32-1, the outer refrigerant inlet 30-2, the bend sections 31-2, and the outer refrigerant outlet 32-2. With the data processed by the signal processor 39 it is determined whether the dryout of the refrigerant occurs at the inner refrigerant outlet 32-1 or the outer refrigerant outlet 32-2. Also, when the signal processor 39 determines that a sign of the dryout is detected, by controlling the number of rotation of the compressor 22 and the opening degrees of the expansion valves 24-1 and 24-2 in the refrigerant temperature control unit 21-1 or 21-2 in the same manner as in the first embodiment, the refrigerant temperature in the inner refrigerant passage 20-1 and the outer refrigerant passage 20-2 can be controlled to a desired value while preventing the dryout.
When configuring the apparatus and performing the operations as described above, also in the case of applying radio frequency power to the sample stage 4, the temperatures of the refrigerants to be introduced to the inner refrigerant passage 20-1 and the outer refrigerant passage 20-2 are controlled to desired values while preventing the dryout and, as a result, a temperature distribution of the sample 5 can be controlled to perform preferable etching processing in the same manner as in the first embodiment. Also in the same manner as in the first embodiment, occurrence of the separation at the bend sections 31-1 and 31-2 in which the separation of the junction in the sample stage 4 is easy to occur can be detected.

Fourth Embodiment

In the first and second embodiments, it is configured so that the separation in the junction of the sample stage 4 is detected by using the vibration sensors 37-1 to 37-6. In contrast, in the fourth embodiment, a pressure gauge is arranged on the piping between the refrigerant temperature control unit 21-1 or 21-2 and the sample stage 4 to detect pressure of the refrigerant and the separation of the junction of the sample stage 4 and the occurrence of the refrigerant leakage are detected. A fourth embodiment will be described below with reference to FIGS. 6, 7A, and 7B.
FIG. 6 illustrates a vicinity of the sample stage 4 used in the present embodiment and components connected to it. Further, a configuration of this sample stage 4 is the same as that of the one of which the top-view section is shown in FIG. 2A and the same reference numerals as in FIG. 2A are used to explain.
To the inner refrigerant passage 20-1 and the outer refrigerant passage 20-2, the refrigerant temperature control units 21-1 and 21-2 are connected, respectively, and the refrigerants are supplied to the respective passages. Here, a pressure gauge 60-1 is connected to the piping at a downstream of the expansion valve 24-1 in the refrigerant temperature control unit 21-1 and between the expansion valve 24-1 and the inner refrigerant inlet 30-1; approximately the same pressure as that of the refrigerant in the inner refrigerant passage 20-1 can be measured.
In the above-described configuration, a time change of the refrigerant pressure detected by the pressure gauge 60-1 is illustrated in FIG. 7A. When a preset temperature of the refrigerant is not changed up or down and the amount of heat entering the sample 5 and the sample stage 4 from the plasma 11 is not changed, the refrigerant pressure does not change and constant with time as in a stable-pressure region 72-1. When the separation occurs in the junction of the sample stage 4 under such a state, since a volume of the refrigerant passage suddenly increases, the refrigerant pressure drops and a pressure change 72-2 arises. Then, when a progress of the separation stops, a change in the volume stops so that the pressure change 72-2 of the refrigerant also stops and the pressure becomes constant again as in a stable-pressure region 72-3. This phenomenon appears as a time-series pressure change such that a pressure is reduced and recovered within a specific time or a pressure suddenly drops from a stable value and then recovers to the same value as or a value close to that of the previous pressure. The above-described detection result of the refrigerant pressure is transmitted to the signal processor 39.
When the pressure change 72-2 appears between the stable-pressure regions 72-1 and 72-3 as illustrated in FIG. 7A and its size is larger than or equal to a predetermined threshold, the signal processor 39 judges that the separation occurs and the processing result is transmitted to the apparatus controller 43. Alternatively, based on a signal from the signal processor 39, which receives signals of the pressure change, the computing unit of the apparatus controller 43 judges. Based on this, a warning indicating that an abnormality occurs is issued to the plasma etching apparatus. For example, the warning is displayed on a control screen of the plasma etching apparatus and is informed to an operator.
Further, since in a plasma etching apparatus a plurality of wafer processings are generally repeated using the same processing conditions, the detection results of the refrigerant pressure are saved at the processings and a change in the refrigerant pressure may be detected by comparison with the past detection result of the refrigerant pressure at the processing of the same type. The detection result 75-1 of the refrigerant pressure in the case where the plasma etching processing is properly performed as illustrated by a broken line in FIG. 7B and the detection result 75-2 in the case where the pressure change 72-2 appears as illustrated by a solid line in the same figure are compared and thereby the pressure change associated with the separation of the junction of the sample stage 4 can be detected more certainly.
Incidentally, in the present embodiment, the pressure gauge 60-1 is arranged downstream of the expansion valve 24-1 and between the expansion valve 24-1 and the inner refrigerant inlet 30-1; however, a place for the arrangement is not limited thereto. Since an object of the arrangement of the pressure gauge 60-1 is to detect the refrigerant pressure in the refrigerant passage 20-1, a place in which the pressure can be measured as close to that in the passage as possible is preferable. Therefore, it is necessary there is no component with low conductance such as a valve like between the expansion valve 24-1 and the inner refrigerant inlet 30-1. Accordingly, the pressure gauge 60-1 may be arranged downstream of the inner refrigerant outlet 32-1 and between the inner refrigerant outlet 32-1 and the expansion valve 24-2.
Further, in the present embodiment, in order to detect the pressure of the refrigerant flowing through the inner refrigerant passage 20-1, the pressure gauge 60-1 is arranged between the inner refrigerant inlet 30-1 and the refrigerant temperature control unit 21-1; in the same manner, when the pressure gauge 60-2 is arranged between the outer refrigerant inlet 30-2 and the refrigerant temperature control unit 21-2, the pressure of the refrigerant flowing through the outer refrigerant passage 20-2 can be detected and the separation in the junction of the sample stage 4 can be detected to inform an operator of the abnormality with the signal processor 39 and the apparatus controller 43. Moreover, when there are the plurality of systems (two systems in the present embodiment) of the refrigerant passages of the inner refrigerant passage 20-1 and the outer refrigerant passage 20-2 in the sample stage 4 as in the present embodiment, it is preferable that all the systems have the pressure gauges arranged between the refrigerant passages and the refrigerant temperature control units.
As seen above, by arranging the pressure gauges between the sample stage 4 and each of the refrigerant temperature control units 21-1 and 21-2, detecting the refrigerant pressure, and capturing the time change, the separation of the junction in the sample stage 4 can be detected and an operator can be notified of the abnormality.
When the first to fourth embodiments as described above are applied, the dryout and the separation of the junction in the sample stage 4 both of which are possible when a temperature control unit of the direct expansion system is used in a plasma processing apparatus.
According to the above-described embodiments, the dryness of the refrigerant in the sample stage can be detected with high accuracy and a flow of the refrigerant is controlled so that a temperature value of the sample or sample stage during the processing or a temperature distribution in the azimuthal direction or in the radial direction of the sample can be made close to a desired temperature value or distribution. In addition, separation in portions in which members configuring the passage in the sample stage are joined can be detected early with high accuracy. Through the above-described effects, accuracy, reproducibility, and reliability of the processing of the sample in a plasma processing apparatus can be improved.
It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.

Claims

1. A plasma processing apparatus comprising:

a processing chamber which is arranged in a vacuum vessel and in which plasma is generated;

a sample stage which is arranged inside toward the bottom of said processing chamber, of which a sample is mounted on an upper surface, which has a shape of a cylinder, and which operates as an evaporator by flowing a refrigerant of a refrigerating cycle through therein;

a refrigerant passage which is arranged in said sample stage and concentrically at a center of said cylinder;

one or more of detectors which are arranged under said sample stage and detect vibrations of said sample stage; and

an control unit which controls an operation of a compressor or an expansion valve configuring said refrigerating cycle based on a detection result of a dryness of said refrigerant flowing through said passage obtained from an output from said detector.

2. The plasma processing apparatus according to claim 1,

wherein one or more of said detectors are arranged on a bottom surface of said sample stage and are connected to a position near an inlet of said refrigerant to inside of said sample stage.

3. The plasma processing apparatus according to claim 2,

wherein additional one or more of said detectors are arranged on a bottom surface of said sample stage and are connected to a position near an outlet of said refrigerant from said sample stage.

4. The plasma processing apparatus according to claim 2,

wherein said refrigerant passage comprises

a plurality of passages of shapes of circular arcs which are concentrically arranged in a multiple manner at different radial distances from said center in said sample stage; and

a connection passage connecting two passages among said passages of shapes of circular arcs, and

wherein additional one or more of said detectors are arranged on the bottom surface of said sample stage and near said connection passage.

5. The plasma processing apparatus according to claim 4,

wherein plan-view shape of said connection passage has a curvature radius smaller than plan-view shape of said passages of shapes of circular arcs.

6. The plasma processing apparatus according to claim 4,

wherein said passage in said sample stage is configured by joining two upper and lower members, and a defect in the junction of said upper and lower members is detected from an output from said one or more detectors arranged to be connected to a position near said connection passage on the bottom surface of said sample stage.

7. The plasma processing apparatus according to claim 1, further comprising a member having electrical insulation arranged to be contacted with the bottom surface of said sample stage,

wherein said one or more detectors are arranged to be contacted with said member having the insulation.

8. A plasma processing apparatus comprising:

a control unit which is arranged between a compressor on said refrigerating cycle and said sample stage and controls a temperature of said refrigerant flowing into said sample stage based on a detection result of a dryness of said refrigerant flowing through said passage obtained from an output from said detector.