US20080053478A1

US20080053478A1 - Substrate-processing method and method of manufacturing electronic device

Info

Publication number: US20080053478A1
Application number: US11/681,368
Authority: US
Inventors: Yukihiro Shibata; Naoya Hayamizu
Original assignee: Toshiba Corp
Current assignee: Toshiba Corp
Priority date: 2006-08-31
Filing date: 2007-03-02
Publication date: 2008-03-06
Also published as: JP2008058591A

Abstract

A method of manufacturing an electronic device includes dipping a substrate in a solution containing sulfuric acid, which is accommodated in a processing vessel. An aqueous solution of hydrogen peroxide supplies the sulfuric acid accommodated in the processing vessel for generating peroxomonosulfuric acid (Caro's acid). Therefore, an organic material present on the surface of the substrate is removed by the action of Caro's acid within the processing vessel. The time for supplying the aqueous solution of hydrogen peroxide into the processing vessel is set on the basis of the change with time in the concentration of Caro's acid measured in advance so as to permit the peak in the concentration of Caro's acid to appear while the substrate is kept dipped in the processing solution.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2006-235311, filed Aug. 31, 2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The present invention relates to a method of processing a substrate such as a silicon wafer and a glass substrate for a display device and to a method of manufacturing an electronic device such as a semiconductor device or a display device, particularly, relates to the technique for removing an organic material such as a photoresist material from a substrate.
2. Description of the Related Art
In the manufacture of an electronic device such as a semiconductor device, various films such as a conductive film and an insulating film are formed on a substrate, followed by forming a resist pattern on the films formed on the substrate and subsequently removing selectively the films formed on the substrate by the etching method, in which the resist pattern noted above is used as a mask. In the etching process, a wiring is formed in the case where a conductive film is selectively etched. On the other hand, a contact hole or the like is formed in the case of etching an insulating film formed on the substrate. After formation of, for example, a wiring layer, a resist material, which is an organic material remaining on the substrate, is removed so as to make the substrate surface clean and, then, the substrate is transferred into the subsequent process step.
It is known to the art that an organic material such as a resist material can be removed from the surface of the substrate by utilizing peroxomonosulfuric acid (Caro's acid: H2SO5) that is formed by a sulfuric acid/hydrogen peroxide system (SPM).
Also, it is disclosed in JP-A 2000-319689 (KOKAI) that an organic material such as a resist material can be removed from the surface of a substrate by using a washing water prepared by dissolving oxygen gas, hydrogen peroxide sulfate, and hydrogen peroxide in ultra-high-purity water.
However, in the related art utilizing Caro's acid quoted above and the related art disclosed in the Japanese patent document quoted above, the method for directly measuring the concentration of the Caro's acid has not yet been established and, thus, attentions are not paid to the index that should be controlled. Such being the situation, an excessively long processing time was required for cleaning the substrate surface by removing the organic material from the surface of the substrate. It follows that the through-put was lowered so as to lower the productivity of the electronic device such as a semiconductor device.

BRIEF SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provided a method of processing a substrate, comprising:
measuring a prescribed number of times the absorbance of a mixed liquid material containing sulfuric acid, hydrogen peroxide and an oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide during the process of mixing sulfuric acid and hydrogen peroxide;
detecting the concentration of the oxidizing material in the mixed liquid material, the concentration corresponding to the absorbance, thereby obtaining the relationship between the absorbance and the concentration of the oxidizing material;
measuring the absorbance of the mixed liquid material at a plurality of timings during the process of mixing sulfuric acid and hydrogen peroxide;
checking the absorbance of the mixed liquid material measured at each timing with the relationship between the absorbance and the concentration of the oxidizing material so as to estimate in advance the change with time in the concentration of the oxidizing material in the mixed liquid material during the mixing process; and
processing a substrate with a processing solution consisting of the mixed liquid material containing the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide, wherein the processing of the substrate with the processing solution is controlled based on the estimated change with time in the concentration of the oxidizing material contained in the mixed liquid material so as to permit the peak in the concentration of the oxidizing material in the processing solution to appear during the processing of the substrate with the processing solution.
According to a second aspect of the present invention, there is provided a method of processing a substrate, comprising:
measuring a prescribed number of times the absorbance of a mixed liquid material containing sulfuric acid, hydrogen peroxide and an oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide during the process of supplying sulfuric acid and hydrogen peroxide into a processing vessel and mixing between sulfuric acid and hydrogen peroxide in the processing vessel;
detecting the concentration of the oxidizing material in the mixed liquid material, the concentration corresponding to the absorbance, thereby obtaining the relationship between the absorbance and the concentration of the oxidizing material;
measuring the absorbance of the mixed liquid material at a plurality of timings during the process of supplying sulfuric acid and hydrogen peroxide into the processing vessel and mixing sulfuric acid and hydrogen peroxide in the processing vessel;
checking the absorbance of the mixed liquid material measured at each timing with the relationship between the absorbance and the concentration of the oxidizing material so as to estimate in advance the change with time in the concentration of the oxidizing material in the mixed liquid material during the mixing process;
accommodating in the processing vessel a processing solution consisting of the mixed liquid material containing sulfuric acid, hydrogen peroxide and the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide during the process of supplying sulfuric acid and hydrogen peroxide into the processing vessel and mixing between sulfuric acid and hydrogen peroxide in the processing vessel; and
dipping a substrate to be processed in the processing solution for processing the substrate, wherein the processing of the substrate with the processing solution is controlled based on the estimated change with time in the concentration of the oxidizing material contained in the processing solution so as to permit the peak in the concentration of the oxidizing material in the processing solution to appear during the processing of the substrate with the processing solution.
According to a third aspect of the present invention, there is provided a method of manufacturing an electronic device, comprising:
estimating in advance the change with time in the concentration of an oxidizing material contained in a mixed liquid material and produced during the mixing process between sulfuric acid and hydrogen peroxide, wherein the estimating process includes the steps of:

- (a) measuring a prescribed number of times the absorbance of the mixed liquid material containing sulfuric acid, hydrogen peroxide and the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide, wherein the absorbance is measured during the process of mixing sulfuric acid with hydrogen peroxide,
- (b) detecting the concentration of the oxidizing material in the mixed liquid material, the concentration corresponding to the absorbance, so as to obtain the relationship between the absorbance and the concentration of the oxidizing material,
- (c) measuring the absorbance of the mixed liquid material at a plurality of timings during the process of mixing sulfuric acid with hydrogen peroxide, and
- (d) checking the absorbance of the mixed liquid material measured at each timing with the relationship between the absorbance and the concentration of the oxidizing material;

forming a pattern of an organic material on a film to be processed;
processing the film to be processed by using the pattern of the organic material as a mask; and
processing the substrate having the pattern of the organic material formed thereon with a processing solution consisting of a mixed liquid material containing sulfuric acid, hydrogen peroxide and the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide, wherein the processing of the substrate with the processing solution is controlled based on the estimated change with time in the concentration of the oxidizing material contained in the mixed solution so as to permit the peak in the concentration of the oxidizing material in the processing solution to appear during the processing of the substrate with the processing solution.
Further, according to a fourth aspect of the present invention, there is provided a method of manufacturing an electronic device, comprising:
estimating in advance the change with time in the concentration of peroxomonosulfuric acid in a mixed liquid material containing sulfuric acid, hydrogen peroxide and peroxomonosulfuric acid, wherein the estimating process includes the steps of:

- (a) sampling a mixed liquid material containing sulfuric acid, hydrogen peroxide and peroxomonosulfuric acid produced by reacting between sulfuric acid and hydrogen peroxide in a processing vessel during the process of supplying hydrogen peroxide into the processing vessel having a sulfuric acid-containing solution accommodated therein for forming peroxomonosulfuric acid, and
- (b) detecting hydrogen peroxide and sulfuric acid contained in the sampled mixed liquid material by capillary zone electrophoretic analysis,

forming a film to be processed on a substrate;
forming a pattern of an organic material on the film to be processed;
processing the film to be processed by using the pattern of the organic material as a mask; and
supplying an aqueous solution of hydrogen peroxide into the processing vessel accommodating a solution containing sulfuric acid;
dipping the substrate having the pattern of the organic material formed thereon in the solution accommodated in the processing vessel; and
setting the supplying time of the aqueous solution of the hydrogen peroxide into the processing vessel based on the estimated change with time in the concentration of the peroxomonosulfuric acid so as to permit the peak in the concentration of the peroxomonosulfuric acid to appear while the substrate is kept dipped in the solution accommodated in the processing vessel, thereby removing the organic film.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 schematically shows the construction of a processing apparatus that is used for removing an organic material in the manufacturing process of an electronic device according to an embodiment of the present invention;

FIG. 2 schematically shows the construction of an analytical apparatus used in the capillary zone electrophoretic analysis of the known sample and the processing liquid sampled from the washing vessel included in the processing apparatus shown in FIG. 1;

FIGS. 3A, 3B, and 3C are cross sectional views collectively showing the manufacturing process of a semiconductor device according to an embodiment of the present invention;

FIG. 4 is a graph showing the relationship between the retention time and the absorbance of each component in the capillary zone electrophoretic analysis in respect of Example 1 of the present invention; and

FIG. 5 is a graph showing the change with time in the concentration of peroxomonosulfuric acid (Caro's acid) in the processing solution, covering the case where a silicon wafer was processed within a processing vessel for the scheduling.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.
FIG. 1 schematically shows the construction of a processing apparatus that is used for removing an organic material in the manufacturing process of an electronic device according to an embodiment of the present invention, and FIG. 2 schematically shows the construction of an analytical apparatus used in capillary zone electrophoretic analysis of the known sample and the processing liquid sampled from the washing vessel included in the processing apparatus shown in FIG. 1.
As shown in FIG. 1, the processing apparatus comprises a processing vessel 3 of a double wall structure including an inner vessel 1 and an outer vessel 2. A processing solution is accommodated in the inner vessel 1, and a wafer W accommodated in a cassette (not shown) is inserted into the inner vessel 1 so as to permit the wafer W to be dipped in the processing solution. The outer vessel 2 functions as an overflowing section of the processing solution (consisting mainly of an aqueous solution of sulfuric acid) accommodated in the inner vessel 1. The processing solution overflowing into the outer vessel 2 is allowed to flow through a pipe 4, branched pipes 5 a, 5 b and nozzles 6 a, 6 b arranged within the inner vessel 1 so as to be brought back into the inner vessel 1. An in-line heater 7, a first pump 8 and a filter 9 are mounted to the pipe 4 in the order mentioned as viewed from the outer vessel 2. A supply source 10 of an aqueous solution containing, for example, 35% by weight of hydrogen peroxide, is arranged to supply the aqueous solution of hydrogen peroxide into the inner vessel 1 through a pipe 11 and a nozzle 12 arranged within the inner vessel 1. A second pump 13 is mounted to the pipe 11. A control signal 14 for controlling the supply timing of the aqueous solution of hydrogen peroxide, which will be described herein later, is supplied to the second pump 13. Likewise, a supply source 15 of an aqueous solution containing, for example, 96 to 98% by weight of sulfuric acid is arranged to supply the aqueous solution of sulfuric acid into the inner vessel 1 through a pipe 16 and a nozzle 17 arranged within the inner vessel 1. Further, a third pump 18 is mounted to the pipe 16.
The control signal referred to above is generated from, for example, a microcomputer (not shown). The information on the change with time in the concentration of Caro's acid in the process of removing an organic material from a silicon wafer is measured in advance by the method described herein later and is supplied to the microcomputer noted above. When the control signal 14 is supplied from the microcomputer to the second pump 13 based on the information supplied to the microcomputer, the second pump 13 is driven so as to permit the aqueous solution of the hydrogen peroxide to be supplied from the supply source 10 of the aqueous solution of hydrogen peroxide into the inner vessel 1. As a result, the processing schedule is carried out so as to permit the peak in the concentration of Caro's acid generated in the inner vessel 1 to be formed during the period of time ranging between the insertion of the silicon wafer into the inner vessel 1 and the withdrawal of the silicon wafer out of the inner vessel 1.
The analytical apparatus shown in FIG. 2 comprises an anode vessel 23 and a cathode vessel 24. A buffer solution 21 is accommodated in the anode vessel 23, and another buffer solution 22 is accommodated in the cathode vessel 24. Further, a sample solution is supplied into the anode vessel 23, and an anode plate 25 is dipped in the buffer solution 21 accommodated in the anode vessel 23. Still further, a cathode plate 26 is dipped in the buffer solution 22 accommodated in the cathode vessel 24. It should be noted that the anode plate 25 is connected to a positive electrode of a high voltage power source 27, and the cathode plate 26 is connected to a negative electrode of the high voltage power source 27. A capillary tube 28 made of, for example, quartz glass is dipped at one end portion in the buffer solution 21 accommodated in the anode vessel 23 and at the other end portion in the buffer solution 22 accommodated in the cathode vessel 24. A light source 29, e.g., an ultraviolet lamp, is arranged in the vicinity of the capillary tube 28. Further, a detector 30 is arranged to face the light source 29 with the capillary tube 28 interposed therebetween.
A method of manufacturing an electronic device, e.g., a semiconductor device, according to an embodiment of the present invention will now be described with reference to FIGS. 3A to 3C. The electronic device noted above is manufactured by using the apparatuses shown in FIGS. 1 and 2.
In the first step, prepared is a silicon wafer W used for manufacturing an electronic device such as a semiconductor device. It is possible to form patterns of portions forming the electronic device on the silicon wafer W by utilizing, for example, the known technologies such as the lithography technology and the dry etching technology.
To be more specific, an insulating film 41 and a conductive film 42, which is to be processed, are formed in the order mentioned on the surface of the silicon wafer W as shown in FIG. 3A. Then, a pattern 43 of a photoresist film is formed by utilizing the lithography technology on the surface of the conductive film 42 in contact with the insulating film 41 formed on the silicon wafer W as shown in FIG. 3B. Further, the conductive film 42 formed on the silicon wafer W is selectively etched by utilizing, for example, the dry etching technology with the pattern 43 of the photoresist film used as a mask so as to form a conductive film pattern 44, as shown in FIG. 3C.
The silicon wafer W having a photoresist pattern formed thereon as described above is processed as follows by using a processing solution containing peroxomonosulfuric acid (Caro's acid).
In the first step, prepared is, for example, a calibration curve denoting the relationship between the absorbance of the mixed liquid material containing peroxomonosulfuric acid, which is produced by reacting between sulfuric acid and hydrogen peroxide, and the concentration of peroxomonosulfuric acid (Caro's acid) in the mixed liquid. The calibration curve noted above is prepared by using the capillary zone electrophoretic analytical apparatus shown in FIG. 2.
To be more specific, the buffer solutions 21 and 22 each having a desired composition are put, respectively, in the anode vessel 23 and the cathode vessel 24 included in the apparatus shown in FIG. 2. In the next step, a sample prepared by mixing an aqueous solution containing 96 to 98% by weight of sulfuric acid with another aqueous solution containing 35% by weight of hydrogen peroxide is mixed with the buffer solution 21 accommodated in the anode vessel 23. In preparing the sample, the aqueous solution containing sulfuric acid is mixed with the aqueous solution containing hydrogen peroxide at a prescribed weight ratio. In the next step, a DC voltage is applied from the high voltage power source 27 to the anode plate 25 and the cathode plate 26 so as to cause the components of the sample to be migrated into the capillary tube 28 by the electrophoresis. After application of the DC voltage, the capillary tube 28 is irradiated with an ultraviolet light emitted from the ultraviolet lamp 29, and the ultraviolet light passing through the capillary tube 28 is detected by the detector 30 so as to measure the absorbance of each of sulfuric acid, hydrogen peroxide and hydrogen peroxide/sulfuric acid system (SPM).
Capillary zone electrophoretic analysis is applied similarly to samples prepared by changing the mixing ratio of the aqueous solution of sulfuric acid to the aqueous solution of hydrogen peroxide so as to obtain the absorbance of each component relative to the retention time.
Since the concentration of Caro's acid has a correlation to the absorbance of SPM, the absorbance is measured for a plurality of samples so as to prepare a calibration curve in which the absorbance of the sample is plotted on the abscissa and the concentration of the Caro's acid is plotted on the ordinate.
In the next step, measured are the changes with time in the concentration of the Caro's acid in the process of removing the organic material attached to the surface of the substrate, e.g., a silicon wafer, by the treatment with Caro's acid. The changes with time in the concentration of the Caro's acid are measured by using the apparatus shown in FIG. 1.
In the first step, the third pump 18 is driven so as to supply at room temperature the aqueous solution containing 96 to 98% of sulfuric acid from within the supply source 15 of the aqueous solution of sulfuric acid into the inner vessel 1 through the pipe 16 and the nozzle 17 until the inner vessel 1 is filled with the aqueous solution of sulfuric acid. In the next step, the second pump 13 is driven so as to supply at room temperature a prescribed amount of the aqueous solution of hydrogen peroxide containing 35% by weight of hydrogen peroxide from within the supply source 10 of the aqueous solution of hydrogen peroxide into the inner vessel 1 through the pipe 11 and the nozzle 12. After the aqueous solution of hydrogen peroxide is supplied into the inner vessel 1, a cassette (not shown) accommodating a plurality of silicon wafers each bearing a photoresist pattern, which forms the organic material noted above, is dipped in the processing solution consisting of the aqueous solution accommodated in the inner vessel 1. The cassette is taken out of the inner vessel 1 a prescribed time later. When the silicon wafer W is dipped in the processing solution accommodated in the inner vessel 1, the organic material, i.e., the photoresist pattern, attached to the surface of the silicon wafer W is peeled off by the action of the Caro's acid formed within the inner vessel 1 by the supply of the aqueous solution of hydrogen peroxide into the inner vessel 1 accommodating an aqueous solution of sulfuric acid.
In removing the organic material from the silicon wafer W, the processing solution is sampled before and after supply of the aqueous solution of hydrogen peroxide into the inner vessel 1, during the period of time when the cassette is kept dipped in the processing solution, and after withdrawal of the cassette from within the processing solution. The absorbance of the sampled processing solution is measured by using the capillary zone electrophoretic analytical apparatus shown in FIG. 2 under the conditions equal to those for preparing the calibration curve described above. The result of the measurement of the absorbance is checked with the calibration curve prepared in advance in a manner to represent the relationship between the absorbance and the concentration of the Caro's acid. As a result, it is possible to estimate the change with time in the concentration of the Caro's acid. The information on the change with time in the Caro's acid during the process of removing the organic material from the silicon wafer W is supplied to, for example, a microcomputer (not shown).
In the next step, the organic material (photoresist pattern) is actually removed from the silicon wafer W. To be more specific, the silicon wafer W bearing the photoresist pattern is inserted into the inner vessel 1 included in the processing vessel 3 and is taken out of the inner vessel 1 a prescribed time later. In performing the particular operation, the control signal 14 is supplied from the microcomputer to the second pump 13 based on the information supplied to the microcomputer on the change with time in the concentration of the Caro's acid. As a result, the second pump 13 is driven so as to carry out the processing schedule such that the aqueous solution of hydrogen peroxide is supplied from within the supply source 10 of the aqueous solution of hydrogen peroxide into the inner vessel 1 so as to permit the peak in the concentration of the Caro's acid formed within the inner vessel 1 to appear after insertion of the silicon wafer W into the inner vessel 1 and before withdrawal of the silicon wafer W out of the inner vessel 1. In other words, the peak in the concentration of the Caro's acid noted above is allowed to appear while the silicon wafer W is kept dipped in the processing solution accommodated in the inner vessel 1.
In the embodiment of the present invention, the organic material attached to the surface of the silicon wafer W is formed of various kinds of resist materials. Also, the substrate to be processed is not limited to the silicon wafer. For example, when it comes to a display device such as a liquid crystal display device, it is possible for a glass substrate having transistors, etc. formed thereon to be processed by the method of the present invention.
It is desirable to determine appropriately the timing of supplying the aqueous solution of hydrogen peroxide into the processing vessel such that the peak in the concentration of the Caro's acid within the processing vessel is allowed to appear within 40 to 60% of the entire insertion period of the substrate into the processing vessel.
As described above, according to the embodiment of the present invention, the aqueous solution of hydrogen peroxide is supplied into the processing vessel accommodating the processing solution containing sulfuric acid. Also, the substrate bearing an organic material is inserted into the processing vessel and withdrawn therefrom a prescribed time later. The supply time of the aqueous solution of hydrogen peroxide into the processing vessel is set based on the change with time in the concentration of peroxomonosulfuric acid (Caro's acid), which is measured in advance, during the process of removing the organic material from the substrate. What should be noted is that the supply time of the aqueous solution of hydrogen peroxide is determined to permit the peak in the concentration of the peroxomonosulfuric acid (Caro's acid) to appear during the period of time ranging between the insertion of the substrate into the processing vessel and the withdrawal of the substrate out of the processing vessel. In this case, the removing efficiency of the organic material from the surface of the substrate can be markedly improved in a short processing time of, for example, about 5 minutes. As a result, the through-put of the processing can be markedly improved.
It should also be noted that it is possible to decrease the amount of the aqueous solution of hydrogen peroxide used in a single processing in the case of supplying the aqueous solution of hydrogen peroxide at the appropriate timing. As a result, it is possible to decrease the amount of the chemical solution (aqueous solution of sulfuric acid and aqueous solution of hydrogen peroxide) used for forming the Caro's acid, thereby achieving a marked cost reduction.
Examples of the present invention will now be given.

EXAMPLE 1

<Preparation of Calibration Curve Denoting the Relationship Between Absorbance Measured by the Capillary Zone Electrophoretic Analytical Apparatus and the Concentration of Peroxomonosulfuric Acid (Caro's Acid)>
Solutions were prepared by dissolving in a distilled water quinolinic acid, hexadecyl trimethyl ammonium hydroxide (10% aqueous solution) and 2-amino-2-hydroxymethyl-1,3-propane diol. The solutions thus prepared were used as buffer solutions 21 and 22, respectively, so as to be accommodated in the anode vessel 23 and the cathode vessel 24 of the apparatus shown in FIG. 2. Then, a sample was prepared by mixing an aqueous solution containing 96 to 98% by weight of sulfuric acid with another aqueous solution containing 35% by weight of hydrogen peroxide. In mixing these two aqueous solutions for preparing the sample, the mixing ratio by weight was set at 1:1. The sample thus prepared was mixed with the buffer solution 21 accommodated in the anode vessel 23. Then, a DC voltage of −10 kV, −18 μA was applied from the high voltage power source 27 to the anode plate 25 and the cathode plate 26. After application of the DC voltage, the capillary tube 28 was irradiated with an ultraviolet light emitted from the ultraviolet lamp 29, and the absorbance was measured by detecting the ultraviolet light passing through the capillary tube 28 with the detector 30.
FIG. 4 is a graph showing the absorbance of each component of sulfuric acid, hydrogen peroxide and SPM (H2SO4.H2O2) relative to the retention time by capillary zone electrophoretic analysis. Incidentally, “SPM (H2SO4.H2O2)” shown in FIG. 4 denotes the compound relating to the formation of Caro's acid.
The absorbance of each component relative to the retention time was obtained by similarly performing the capillary zone electrophoretic analysis in respect of the samples prepared by changing the mixing ratio of the aqueous solution of sulfuric acid to the aqueous solution of hydrogen peroxide.
The concentration of Caro's acid relates to the absorbance of SPM and, thus, prepared was a calibration curve in which the absorbance is plotted on the abscissa based on the result of the measurement of the absorbance of each of a plurality of samples, and the concentration of Caro's acid is plotted on the ordinate.
<Measurement of the Changes with time in the Concentration of Caro's Acid in the Process of Removing with Caro's Acid the Resist Attached to the Surface of the Silicon Wafer>
A plurality of silicon wafers W each having a novolak-based i-line resist pattern formed on the surface were accommodated in a cassette (not shown). The operation for removing the resist pattern from each silicon wafer was carried out a plurality of times by processing the silicon wafers accommodated in the cassette in the processing apparatus shown in FIG. 1. In the processing operation, the first pump 8 was driven so as to bring the processing solution overflowing from the inner vessel 1 into the outer vessel 2 and containing sulfuric acid of a high concentration back into the inner vessel 1 through the pipe 4, the branched pipes 5 a, 5 b and the nozzles 6 a, 6 b. When passing through the pipe 4, the processing solution was heated by the in-line heater 7, and fine particles were removed from the processing solution by the filter 9. Also, the third pump 18 was driven so as to supply at room temperature the aqueous solution containing 96 to 98% of sulfuric acid from the supply source 15 of the aqueous solution of sulfuric acid into the inner vessel 1 through the pipe 16 and the nozzle 17 until the concentration of sulfuric acid in the processing solution accommodated in the inner vessel 1 was increased to reach a prescribed value.
In the next step, the second pump 13 was driven so as to supply at room temperature a prescribed amount of the aqueous solution containing 35% by weight of hydrogen peroxide from the supply source 10 of the aqueous solution of hydrogen peroxide into the inner vessel 1 included in the processing vessel through the pipe 11 and the nozzle 12. After supply of the aqueous solution of hydrogen peroxide into the inner vessel 1, a cassette (not shown) accommodating a plurality of silicon wafers W each having a diameter of 300 mm and having a novolak-based i-line resist pattern formed on the surface was introduced into the inner vessel 1 and taken out of the inner vessel 1 about 5 minutes later. While the silicon wafer W was dipped in the processing solution accommodated in the inner vessel 1, the resist pattern formed on the surface of the silicon wafer W was peeled off by the action of peroxomonosulfuric acid (Caro's acid) produced within the inner vessel 1 by the supply of the aqueous solution of hydrogen peroxide into the inner vessel 1.
In peeling off the resist pattern from the surface of the silicon wafer W, the processing solution was sampled before and after supply of the aqueous solution of hydrogen peroxide into the inner vessel, during the period of time ranging between the insertion of the cassette into the inner vessel and the withdrawal of the cassette out of the inner vessel, and after withdrawal of the cassette out of the inner vessel. The absorbance of the sampled processing solution was measured by using the capillary zone electrophoretic analytical apparatus shown in FIG. 2 under the conditions equal to those for preparing the calibration curve described previously.
The change with time in the concentration of the peroxomonosulfuric acid (Caro's acid) was estimated by checking the result of the measurement of the absorbance of the sampled processing solution with the calibration curve prepared in advance for obtaining the relationship between the absorbance and the concentration of Caro's acid. FIG. 5 is a graph showing the result. The information on the change with time in the concentration of Caro's acid during the process of removing the resist pattern from the silicon wafer W was supplied into, for example, a microcomputer (not shown).
<Removal of Resist Film from the Surface of Silicon Wafer>
A plurality of silicon wafers W each having a diameter of 300 mm and having a novolak-based i-line resist pattern formed on the surface was accommodated in a cassette (not shown). In the process of inserting the cassette into the inner vessel 1 included in the processing vessel 3 and withdrawing the cassette out of the inner vessel 1 about 5 minutes later, the timing for supplying the control signal 14 to the second pump 13 was set based on the information supplied from the microcomputer. In this case, the second pump 13 was driven so as to supply the aqueous solution of hydrogen peroxide from the supply source 10 of the aqueous solution of hydrogen peroxide into the inner vessel 1 for removing the resist pattern from the surface of the silicon wafer. The timing of supplying the aqueous solution of hydrogen peroxide into the inner vessel 1 was controlled to permit the peak in the concentration of Caro's acid generated in the inner vessel 1 to appear in the central portion of the period of time ranging between the insertion of the cassette into the inner vessel and the withdrawal of the cassette out of the inner vessel 1.

COMPARATIVE EXAMPLE 1

A plurality of silicon wafers W each having a diameter of 300 mm and having a novolak-based i-line resist pattern formed on the surface was accommodated in a cassette (not shown). Then, the cassette was inserted into the processing solution accommodated in the inner vessel 1 for removing the resist pattern from the surface of the silicon wafer, followed by withdrawing the cassette out of the processing solution about 5 minutes later. In this case, the timing for driving the second pump 13 for supplying the aqueous solution of hydrogen peroxide from the supply source 10 of the aqueous solution of hydrogen peroxide into the inner vessel 1 was controlled to permit the peak in the concentration of Caro's acid generated in the inner vessel 1 to appear before the cassette was inserted into the inner vessel 1.

COMPARATIVE EXAMPLE 2

A plurality of silicon wafers W each having a diameter of 300 mm and having a novolak-based i-line resist pattern formed on the surface was accommodated in a cassette (not shown). Then, the cassette was inserted into the processing solution accommodated in the inner vessel 1 for removing the resist pattern from the surface of the silicon wafer, followed by withdrawing the cassette out of the processing solution about 5 minutes later. In this case, the timing for driving the second pump 13 for supplying the aqueous solution of hydrogen peroxide from the supply source 10 of the aqueous solution of hydrogen peroxide into the inner vessel 1 was controlled to permit the peak in the concentration of Caro's acid generated in the inner vessel 1 to appear after the cassette was taken out of the inner vessel 1.
The entire surface of the silicon wafer after removal of the resist pattern for each of Example 1 and Comparative Examples 1 and 2 was observed with a microscope including a circular view field having a diameter of 13 mm so as to count the number of particles. Table 1 shows the result.

	TABLE 1

	The number of particles

Particle size		Comparative	Comparative
(μm)	Example 1	Example 1	Example 2

Smaller than	8	13	47
0.16 μm but
not smaller
than 0.12 μm
Smaller than	3	7	23
0.20 μm but
not smaller
than 0.16 μm
Smaller than	0	4	8
0.30 μm but
not smaller
than 0.20 μm
Smaller than	0	15	11
0.50 μm but
not smaller
than 0.30 μm
Larger than	1	1	1
0.50 μm

As apparent from Table 1, the number of particles on the surface of the silicon wafer after the processing for removing the resist pattern from the silicon wafer for Example 1 was very much smaller than that for each of Comparative Examples 1 and 2, supporting that the method of the present invention is highly effective for removing the organic material from the surface of the substrate.
Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A method of processing a substrate, comprising:

measuring a prescribed number of times the absorbance of a mixed liquid material containing sulfuric acid, hydrogen peroxide and an oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide during the process of mixing sulfuric acid and hydrogen peroxide;

detecting the concentration of the oxidizing material in the mixed liquid material, the concentration corresponding to the absorbance, thereby obtaining the relationship between the absorbance and the concentration of the oxidizing material;

measuring the absorbance of the mixed liquid material at a plurality of timings during the process of mixing sulfuric acid and hydrogen peroxide;

checking the absorbance of the mixed liquid material measured at each timing with the relationship between the absorbance and the concentration of the oxidizing material so as to estimate in advance the change with time in the concentration of the oxidizing material in the mixed liquid material during the mixing process; and

processing a substrate with a processing solution consisting of the mixed liquid material containing the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide, wherein the processing of the substrate with the processing solution is controlled based on the estimated change with time in the concentration of the oxidizing material contained in the mixed liquid material so as to permit the peak in the concentration of the oxidizing material in the processing solution to appear during the processing of the substrate with the processing solution.

2. The method according to claim 1, wherein the processing of the substrate with the processing solution is performed for removing an organic material present on the substrate to be processed.

3. The method according to claim 1, wherein the oxidizing material is formed of peroxomonosulfuric acid.

4. The method according to claim 1, wherein the absorbance of the mixed liquid material containing sulfuric acid and hydrogen peroxide is measured by capillary zone electrophoretic analysis.

5. The method according to claim 1, wherein each of timings for measuring the absorbance comprises period of before and after the dipping of the substrate to be processed in the mixed liquid material and period at which the substrate is kept dipped in the mixed liquid material.

6. A method of processing a substrate, comprising:

measuring a prescribed number of times the absorbance of a mixed liquid material containing sulfuric acid, hydrogen peroxide and an oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide during the process of supplying sulfuric acid and hydrogen peroxide into a processing vessel and mixing between sulfuric acid and hydrogen peroxide in the processing vessel;

measuring the absorbance of the mixed liquid material at a plurality of timings during the process of supplying sulfuric acid and hydrogen peroxide into the processing vessel and mixing sulfuric acid and hydrogen peroxide in the processing vessel;

checking the absorbance of the mixed liquid material measured at each timing with the relationship between the absorbance and the concentration of the oxidizing material so as to estimate in advance the change with time in the concentration of the oxidizing material in the mixed liquid material during the mixing process;

accommodating in the processing vessel a processing solution consisting of the mixed liquid material containing sulfuric acid, hydrogen peroxide and the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide during the process of supplying sulfuric acid and hydrogen peroxide into the processing vessel and mixing between sulfuric acid and hydrogen peroxide in the processing vessel; and

dipping a substrate to be processed in the processing solution for processing the substrate, wherein the processing of the substrate with the processing solution is controlled based on the estimated change with time in the concentration of the oxidizing material contained in the processing solution so as to permit the peak in the concentration of the oxidizing material in the processing solution to appear during the processing of the substrate with the processing solution.

7. The method according to claim 6, wherein the processing of the substrate with the processing solution is performed for removing an organic material present on the substrate to be processed.

8. The method according to claim 6, wherein the oxidizing material is formed of peroxomonosulfuric acid.

9. The method according to claim 6, wherein the absorbance of the mixed liquid material containing sulfuric acid and hydrogen peroxide is measured by capillary zone electrophoretic analysis.

10. The method according to claim 6, wherein each of timings for measuring the absorbance comprises period of before and after the dipping of the substrate to be processed in the mixed liquid material and period at which the substrate is kept dipped in the mixed liquid material.

11. A method of manufacturing an electronic device, comprising:

estimating in advance the change with time in the concentration of an oxidizing material contained in a mixed liquid material and produced during the mixing process between sulfuric acid and hydrogen peroxide, wherein the estimating process includes the steps of:

(a) measuring a prescribed number of times the absorbance of the mixed liquid material containing sulfuric acid, hydrogen peroxide and the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide, wherein the absorbance is measured during the process of mixing sulfuric acid with hydrogen peroxide,

(b) detecting the concentration of the oxidizing material in the mixed liquid material, the concentration corresponding to the absorbance, so as to obtain the relationship between the absorbance and the concentration of the oxidizing material,

(c) measuring the absorbance of the mixed liquid material at a plurality of timings during the process of mixing sulfuric acid with hydrogen peroxide, and

(d) checking the absorbance of the mixed liquid material measured at each timing with the relationship between the absorbance and the concentration of the oxidizing material;

forming a pattern of an organic material on a film to be processed;

processing the film to be processed by using the pattern of the organic material as a mask; and

processing the substrate having the pattern of the organic material formed thereon with a processing solution consisting of a mixed liquid material containing sulfuric acid, hydrogen peroxide and the oxidizing material produced by reacting between sulfuric acid and hydrogen peroxide, wherein the processing of the substrate with the processing solution is controlled based on the estimated change with time in the concentration of the oxidizing material contained in the mixed solution so as to permit the peak in the concentration of the oxidizing material in the processing solution to appear during the processing of the substrate with the processing solution.

12. The method according to claim 11, wherein the oxidizing material is formed of peroxomonosulfuric acid.

13. The method according to claim 11, wherein the concentration of the oxidizing material is detected by capillary zone electrophoretic analysis.

14. The method according to claim 11, wherein each of timings for measuring the absorbance comprises period of before and after the dipping of the substrate having the pattern of the organic material formed thereon in the mixed liquid material and period at which the substrate is kept dipped in the mixed liquid material.

15. A method of manufacturing an electronic device, comprising:

estimating in advance the change with time in the concentration of peroxomonosulfuric acid in a mixed liquid material containing sulfuric acid, hydrogen peroxide and peroxomonosulfuric acid, wherein the estimating process includes the steps of:

(a) sampling a mixed liquid material containing sulfuric acid, hydrogen peroxide and peroxomonosulfuric acid produced by reacting between sulfuric acid and hydrogen peroxide in a processing vessel during the process of supplying hydrogen peroxide into the processing vessel having a sulfuric acid-containing solution accommodated therein for forming peroxomonosulfuric acid, and

(b) detecting hydrogen peroxide and sulfuric acid contained in the sampled mixed liquid material by capillary zone electrophoretic analysis,

forming a film to be processed on a substrate;

forming a pattern of an organic material on the film to be processed;

supplying an aqueous solution of hydrogen peroxide into the processing vessel accommodating a solution containing sulfuric acid;

dipping the substrate having the pattern of the organic material formed thereon in the solution accommodated in the processing vessel; and

setting the supplying time of the aqueous solution of the hydrogen peroxide into the processing vessel based on the estimated change with time in the concentration of the peroxomonosulfuric acid so as to permit the peak in the concentration of the peroxomonosulfuric acid to appear while the substrate is kept dipped in the solution accommodated in the processing vessel, thereby removing the organic film.

16. The method according to claim 15, wherein the supplying time of the aqueous solution of hydrogen peroxide into the processing vessel is set to permit the peak in the concentration of the peroxomonosulfuric acid to appear when the time as counted from the insertion of the substrate into the processing vessel falls within a period of 40 to 60% of the period between the insertion of the substrate bearing the organic material into the processing vessel and the withdrawal of the substrate out of the processing vessel.

17. The method according to claim 15, wherein each of timings for sampling the mixed liquid material comprises period of before and after the dipping of the substrate having the pattern of the organic material formed thereon in the mixed liquid material and period at which the substrate is kept dipped in the mixed liquid material.