WO1994013010A1 - Process of shaping features of semiconductor devices - Google Patents

Process of shaping features of semiconductor devices Download PDF

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Publication number
WO1994013010A1
WO1994013010A1 PCT/US1992/010151 US9210151W WO9413010A1 WO 1994013010 A1 WO1994013010 A1 WO 1994013010A1 US 9210151 W US9210151 W US 9210151W WO 9413010 A1 WO9413010 A1 WO 9413010A1
Authority
WO
WIPO (PCT)
Prior art keywords
iodine
ion beam
process according
chamber
region
Prior art date
Application number
PCT/US1992/010151
Other languages
French (fr)
Inventor
Lynwood W. Swanson
John M. Lindquist
Original Assignee
Fei Company
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to US07/685,844 priority Critical patent/US5188705A/en
Priority claimed from US07/685,844 external-priority patent/US5188705A/en
Application filed by Fei Company filed Critical Fei Company
Priority to PCT/US1992/010151 priority patent/WO1994013010A1/en
Priority to US08/021,481 priority patent/US5376791A/en
Publication of WO1994013010A1 publication Critical patent/WO1994013010A1/en

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
    • H01J37/305—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating or etching
    • H01J37/3053—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating or etching for evaporating or etching
    • H01J37/3056—Electron-beam or ion-beam tubes for localised treatment of objects for casting, melting, evaporating or etching for evaporating or etching for microworking, e.g. etching of gratings, trimming of electrical components
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
    • H01L21/30604—Chemical etching
    • H01L21/30612—Etching of AIIIBV compounds
    • H01L21/30621—Vapour phase etching
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/302—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to change their surface-physical characteristics or shape, e.g. etching, polishing, cutting
    • H01L21/306—Chemical or electrical treatment, e.g. electrolytic etching
    • H01L21/3065—Plasma etching; Reactive-ion etching
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/04—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer
    • H01L21/18—Manufacture or treatment of semiconductor devices or of parts thereof the devices having at least one potential-jump barrier or surface barrier, e.g. PN junction, depletion layer or carrier concentration layer the devices having semiconductor bodies comprising elements of Group IV of the Periodic System or AIIIBV compounds with or without impurities, e.g. doping materials
    • H01L21/30—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26
    • H01L21/31—Treatment of semiconductor bodies using processes or apparatus not provided for in groups H01L21/20 - H01L21/26 to form insulating layers thereon, e.g. for masking or by using photolithographic techniques; After treatment of these layers; Selection of materials for these layers
    • H01L21/3205—Deposition of non-insulating-, e.g. conductive- or resistive-, layers on insulating layers; After-treatment of these layers
    • H01L21/321—After treatment
    • H01L21/3213—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer
    • H01L21/32133—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only
    • H01L21/32135—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only
    • H01L21/32136—Physical or chemical etching of the layers, e.g. to produce a patterned layer from a pre-deposited extensive layer by chemical means only by vapour etching only using plasmas
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J2237/00—Discharge tubes exposing object to beam, e.g. for analysis treatment, etching, imaging
    • H01J2237/006—Details of gas supplies, e.g. in an ion source, to a beam line, to a specimen or to a workpiece

Definitions

  • the present invention relates to a micro- machining method employing a focused ion beam and particularly to such a method for micromachining solid materials, for example on semiconductor devices, in a selective and environmentally acceptable manner .
  • Focused ion beam systems are used in forming, shaping or altering microscopic structures in semi ⁇ conductor devices, or in other solid materials, including semiconductor or insulating surfaces and metal areas providing electrical connection.
  • the focused ion beam can be directed to a very small point on a semiconductor device and then scanned, raster fashion, over a surface where material is to be removed.
  • sputtering As an ion impinges on the semiconduc ⁇ tor device surface, its momentum is transferred resulting in the removal of one or more surface atoms according to a process called sputtering.
  • a raster pattern of a given overall shape for example a horizontal raster pattern, a correspondingly shaped area of surface material can be removed. Often several successive layers of a semiconductor device are removed in a given area in order to reach and possibly sever an underlying layer.
  • a chemically reactive gas i.e., fluorine or chlorine.
  • the gas is adsorbed on the surface of the semiconductor device prior to arrival of the ion beam and the gas reacts chemically with the surface material to produce an area of material that is more easily sputtered away.
  • a gas such as chlorine chemically reacts with the surface and forms chlorides which are more easily removed by the ion beam, resulting in a substantial increase in sputtering rates.
  • an enhancement factor in sputtering of silicon has been reported of approximately fourteen, i.e., the gaseous enhanced sputtering occurs approximately fourteen ° times as fast as without the introduction of the gas. Gas enhanced sputtering is also less subject to redeposition of sputtered material.
  • the enhancement factor for metal surfaces such as conductive layers in the semiconductor device may 5 be even greater.
  • chlorine gas for example, is often chemically reactive with the whole surface of the object being formed and may undesirably attack areas adjacent to the ion beam position resulting ° in a lack of contrast between machined and non- machined areas.
  • Iodine vapor is supplied within the same chamber and is directed toward the object's surface in order to enable a chemical reaction between the iodine and the surface material in the area where the ion beam is aimed. Because of its limited chemical reactivity, as compared with fluorine or chlorine, iodine would not be expected to produce significant results in regard to increased sputtering yield. However, we have discovered the effectiveness of iodine vapor is substantially equal to that of chlorine while the use of iodine eliminates the manufacturing difficulties and safety hazards heretofore encountered.
  • Iodine is a solid at room temperature and can be easily conveyed from place to place.
  • Solid iodine crystals can be placed in a container or crucible within the enclosure of the focused ion beam system where the solid iodine is heated to slightly above room temperature to produce a still relatively small vapor pressure but which is never ⁇ theless effective.
  • the safety problems are significantly reduced or eliminated.
  • the machining process is more accurate. Because of iodine's reduced chemical reactivity as compared with chlorine, the sputtering of material can be more selective.
  • the ion beam itself can more clearly delineate the area being machined inasmuch as adjacent areas are not attacked by the vapor to nearly the same extent.
  • FIG. 1 is a schematic representation of a focused ion beam system adapted for carrying out the process of the present invention
  • FIG. 2 is a partially broken away, cross sectional view illustrating in greater detail a vapor source for the system of FIG. 1;
  • FIG. 3 is a sectional view of a portion of a semiconductor device;
  • FIG. 4 is a sectional view of the FIG. 3 device having a portion thereof removed by ion beam sputtering;
  • FIG. 5 is a sectional view of a portion of a block of semiconductor material having a portion of the top surface thereof machined away.
  • an evacuated envelope 10 includes an upper neck portion 12 within which are located a liquid metal ion source 14 and a focusing column 16 which includes extractor electrode means and an electrostatic optical system.
  • Ion beam 18 passes from source 14 through column 16 and between electrostatic deflection means schematically indi- cated at 20 toward sample 22, which comprises a semiconductor device positioned on movable X-Y stage 24 within lower chamber 26.
  • An ion pump 28 is employed for evacuating neck portion 12.
  • the chamber 26 is evacuated with turbomolecular and mechanical pumping system 30 under the control of vacuum controller 32.
  • a high voltage power supply 34 is connected to liquid metal ion source 14 as well as to appro ⁇ priate electrodes in focusing column 16 for forming an approximately 25 keV ion beam 18 and directing the same downwardly.
  • Deflection controller and amplifier 36 operated in accordance with a prescribed pattern such as a raster pattern provided by pattern generator 38, is coupled to deflection plates 20 whereby beam 18 may be controlled to trace out a corresponding pattern on the upper surface of sample 22.
  • the source 14 typically provides a beam of gallium ions although other ions could be used such as inert gas ions or other metallic ions, for example indium, aluminum, or silicon.
  • the source is capable of being focused into a sub 0.1 micron width beam at sample 22 for either modifying the surface 22 or for the purpose of imaging the surface 22.
  • An electron multiplier 40 used for detecting secondary emission for imaging is connected to video circuit and amplifier 42, the latter supplying drive for video monitor 44 also receiving deflection signals from controller 36.
  • the focused ion beam system is further provided with a source 46 for supplying iodine vapor.
  • the source is located inwardly of the side of chamber 26 by trans ⁇ lation device 48 adapted for positioning the source via support means within bellows 52.
  • the source 46 in particular comprises a reservoir or crucible 50.
  • a heater 54 which may comprise a membrane type heater, is utilized for raising the temperature of iodine crystals located within reservoir or crucible so to a temperature for providing a suitable vapor pressure, i.e., a temperature between approximately 30° C. and 50° C.
  • a transfer tube or nozzle 56 extends from reservoir 50 and is connected thereto via control valve 58 adapted for releasing iodine vapor.
  • the nozzle is extended and translated in orthogonal directions substantially perpendicular to its axis employing translation apparatus 48, so that iodine vapor can be aimed directly toward a region on the top surface of sample 22 wherein material is to be removed by scanning ion beam 18.
  • a door 60 is opened for inserting sample 22 on stage 24, and also for inserting iodine crystals within reservoir or crucible 50.
  • the door is interlocked so that it cannot be opened if the temperature in reservoir 50 is substantially above room temperature.
  • a gate valve, schematically illustrated at 62, is closed before door 60 can be opened to seal off the ion source and focusing column apparatus.
  • the base pressure within chamber 26 is 1 X 10" 6 Torr. With the emission of the iodine from the vapor source 46, the chamber back ⁇ ground pressure is 1 X 10 "5 Torr.
  • Vapor source 46 illustrated schematically in FIG. 1, is depicted in greater detail in FIG. 2.
  • a valve shaft tube 64 is supported by a translation apparatus or manipulator (not shown in FIG. 2) and extends inwardly toward sample chamber 26 through bellows 52 where it joins bellows header 66.
  • the bellows 52 is disposed generally coaxially about tube 64 between header 66 and apertured end plate 68 through which tube 64 also passes.
  • End plate 68 is located outwardly from the wall of chamber 26 forming the cover of cylindrical chamber extension 70 aligned with and positioned over an aperture 72 in the sidewall of chamber 26.
  • the cylindrical chamber extension 70 is joined to a radial flange 74 that is secured to the wall of chamber 26 by means not shown.
  • An O-ring seal 76 is fitted within a circular groove in flange 74 to bear against the sidewall of the sample chamber.
  • Valve shaft tube 64 communicates with a header tubular housing portion 78 which is aligned with tube 64 and ends in a necked down portion or nozzle 80 received within an upper horizontal passage in container cap 82.
  • Tubular housing portion 78 is provided with a plurality of apertures so that the vacuum within chamber 26 is also maintained within tube 64.
  • Crucible 50 receives solid iodine as indicated at 84 and has an upper radial flange captured within an annular retainer 86 internally threaded and securable onto cap 82.
  • An 0-ring 88 is inter ⁇ posed between the radial flange of crucible 50 and the lower threaded portion of the cap 82.
  • an electrical heater element 54 Secured to the top of cap 82 is an electrical heater element 54 provided control current for the purpose of maintaining crucible 50 at a predetermined temperature.
  • Cap 82 is further supplied with a delivery tube 90 communicating with the interior of the cap and the crucible, and which slideably receives therewithin tapered end valve member 58.
  • Valve member 58 is carried at one end of valve shaft 92 that passes through valve shaft tube 64, tubular housing portion 78, the upper part of cap 82, and the delivery tube 90.
  • Valve member 58 is adapted to be extended and withdrawn by means of longi ⁇ tudinal movement of valve shaft 92, the latter being secured to header 94 of bellows 96 attached to the end of tube 64 farthest from the chamber 26.
  • a handle 98 extending from header 94 can be manipu ⁇ lated in a longitudinal direction either manually or by mechanical means not shown for operating the valve.
  • the shaft 92 also passes through an O-rin ⁇ seal 100 in a vertical wall at the top of cap 82 where the shaft 92 then extends into the vapor atmosphere from crucible 50.
  • Nozzle 56 takes the form of a hypodermic needle 102 received in a bayonet joint at the inner end of a tubular fitting 104 threadably received over the end of delivery tube 58.
  • An O-ring seal or valve seat 105 is located at the juncture between delivery tube 90 and fitting 104 such that the tapered end of valve member 58 is positionable thereagainst for closing the valve and preventing delivery of the vapor to the interior of chamber 26.
  • door 60 In order to place the iodine crystals 84 within crucible 50, door 60 (in FIG. 1 ⁇ is opened and annular retainer 86 is threadably disengaged from cap 82 whereby the crucible 50 can be removed downwardly. Iodine crystals 84 can then be placed in crucible 50 after which the crucible is again positioned below cap 82 and retainer 86 is employed to secure the crucible in the position shown.
  • Door go can be opened and material can be inserted in crucible 50 only when the temperature thereof (measured by means not shown) is approximately room temperature, e.g. 29° C. or less.
  • door 60 can be operated only when chamber 26 is returned to ambient pressure, with gate valve 62 in place to seal off the upper part of the apparatus.
  • the chamber is suitably evacuated employing pumping means 28 and 30 under the control of means 32.
  • the valve 58 is maintained in an open position during initial chamber evacuation in order to evacuate the crucible, but is returned to a closed position when a predetermined vacuum level is reached.
  • heater 54 may be operated to raise the temperature of the iodine crystals whereby iodine vapor is generated for direction toward the sample 22 by means of nozzle 56.
  • valve 58 may be opened as the nozzle 56 is directed towards the desired area of the sample.
  • Bellows 52 accommodates movement of the entire nozzle assembly and crucible relative to the sample, while bellows 96 permits extension and retraction of valve 58 without affecting the vacuum within chamber 26.
  • sample 22 is placed on stage 24 while solid iodine is deposited in crucible 50, after which the chamber 26 is closed and evacuated and gate 62 is opened so that an ion beam 18 can be generated and directed toward the sample.
  • the sample can be positioned by movement of stage 24 in a well understood manner.
  • Nozzle 56 is positioned so that iodine vapor can be directed towards the raster area as crucible 50 is heated by element 54 to an approximate range between 30° C. and 50° C. and valve 58 is opened to permit escape of the iodine vapor.
  • Pattern generator 38 is programmed to deflect ion beam 18 in a raster pattern corres ⁇ ponding to a specific area of sample 22 where mate ial is removed or machined away by ion beam sputtering.
  • FIGS. 3-5 various portions of a semiconductor integrated circuit device or the like are illustrated as may be microscopically machined in accordance with the present invention.
  • body 106 of semiconductor material e.g. silicon
  • a layer 108 suitably comprising an insulating material such as silicon dioxide.
  • a metal conductor 110 which may comprise an aluminum connecting lead is located upon layer 108 and is covered by a second insulating or passivation layer 112.
  • the device may be placed in the apparatus as illustrated in FIG. 1 at the location of sample 22, and ion beam 18 is deflected in a raster pattern corresponding to a rectangular area encompassing metal conductor 110 while iodine vapor is delivered from nozzle 56.
  • FIG. 4 illustrates the device after the machining operation depicting the depression 114 milled away by the scanning ion beam. It should be observed that the underlying insulating layer 108 can also be machined if so desired, but in this case conduc ⁇ tor 110 thereabove was removed.
  • an area 118 is milled by means of an ion beam accom ⁇ panied by iodine vapor directed toward surface 118.
  • the process according to the present invention is suitable for micromachining of various objects in addition to integrated circuit devices, for instance an ion beam according to the present invention may be employed for machining laser facets or optical elements used in directing infrared radiation.
  • iodine vapor is directed toward the surface of a sample (e.g. sample 22 in FIG. 1), iodine is adsorbed on such surface for enabling chemical reaction to take place between iodine and the material of said surface.
  • the reaction product of iodine and silicon i.e., Sil 4
  • the reaction product of iodine and silicon i.e., Sil 4
  • Gal 2 is generated as well as compounds of arsenic and iodine.
  • a reaction product comprises Al I 3 .
  • iodine vapor In the course of removal of surface material by sputtering it is desirable to provide sufficient iodine vapor to the surface to form a saturated roonolayer before impingement of the ion beam. If the ion beam is scanned in a regular raster pattern, sufficient iodine vapor is provided so that a given point on the surface of the sample where material is to be removed will receive such onolayer during one raster period, or the time it takes the ion beam to return to a given point in the raster after its prior interception of the same point.
  • the vapor pressure and flux provided in a given area is proportional to the temperature of crucible 50 which is in turn controlled by means of electrically operated heater 54. Such control is conveniently accomplished in an automatic manner.
  • etching enhancement by approximately a factor of fifteen has been observed for silicon, as well as an enhancement factor of approximately twenty-seven for aluminum.
  • gas assisted physical sputtering achieved in accordance with the present invention is very selective and allows accurate machining of desired areas without as much affect on surrounding areas. Furthermore, the absence of redeposition is observed. Thus, rapid and accurate machining of surfaces including metal conductors in integrated circuit devices is selectively carried out in accordance with the present invention, this even though prior attempts at metal machining employing chlorine or fluorine have produced unsatisfactory results.
  • iodine is a solid at room tempera- ture with a very low vapor pressure and can be handled in the open before placement in a heatable crucible such as crucible 50 hereinbefore described.
  • the crucible can then be placed inside the vacuum system where, even though the tempera- ture of the crucible is raised to produce a higher vapor pressure, the small amount of vapor is exhausted via the vacuum system already present in the focused ion beam apparatus to a remote location and/or gas treatment means.
  • the chamber 26, if operating properly, cannot be opened until the crucible returns to the ambient temperature level at which the iodine vapor pressure is very low.
  • the method according to the present invention has considerable utility as applied to the rapid modification, repair and analysis of semiconductor devices. It is also of considerable utility in other micromachining applications, but has the advantage of convenience and economy of operation without the dangers of potential toxicity.

Abstract

Semiconductor devices are modified and/or repaired by a gas enhanced physical puttering process. A sample (22) is positioned on a movable X-Y stage (24) located within a lower chamber (26) which is evacuated and under the control of vacuum controller (32). In an evacuated envelop (10) a focused ion beam (18) passes from a liquid metal ion source (14) through column (16) and deflection means (20) and is scanned over an area to be removed on the sample (22). Iodine vapor from source (46) is directed toward the same area to aid in the selective sputtering by enabling a chemical reaction at the scanned area. The iodine may be initially handled in a solid state and is then heated inside the focused ion beam system without presenting a toxic hazard.

Description

PROCESSOFSHAPINGFEATURESOFSEMICONDUCTORDEVICES
Background of the Invention The present invention relates to a micro- machining method employing a focused ion beam and particularly to such a method for micromachining solid materials, for example on semiconductor devices, in a selective and environmentally acceptable manner . Focused ion beam systems are used in forming, shaping or altering microscopic structures in semi¬ conductor devices, or in other solid materials, including semiconductor or insulating surfaces and metal areas providing electrical connection. The focused ion beam can be directed to a very small point on a semiconductor device and then scanned, raster fashion, over a surface where material is to be removed. As an ion impinges on the semiconduc¬ tor device surface, its momentum is transferred resulting in the removal of one or more surface atoms according to a process called sputtering. By selecting a raster pattern of a given overall shape, for example a horizontal raster pattern, a correspondingly shaped area of surface material can be removed. Often several successive layers of a semiconductor device are removed in a given area in order to reach and possibly sever an underlying layer.
It has been discovered heretofore that the above described physical sputtering process can be enhanced by the introduction of a chemically reactive gas, i.e., fluorine or chlorine. The gas is adsorbed on the surface of the semiconductor device prior to arrival of the ion beam and the gas reacts chemically with the surface material to produce an area of material that is more easily sputtered away. Thus a gas such as chlorine chemically reacts with the surface and forms chlorides which are more easily removed by the ion beam, resulting in a substantial increase in sputtering rates. For instance, an enhancement factor in sputtering of silicon has been reported of approximately fourteen, i.e., the gaseous enhanced sputtering occurs approximately fourteen ° times as fast as without the introduction of the gas. Gas enhanced sputtering is also less subject to redeposition of sputtered material. The enhancement factor for metal surfaces such as conductive layers in the semiconductor device may 5 be even greater.
However, the introduction of chlorine or fluorine gas creates a safety hazard because of the combined toxicity and high vapor pressure of the gas. Consequently the use thereof is outlawed in 0 many industrial settings. Moreover, handling of tanks of toxic gas at high pressures is awkward even in a carefully monitored laboratory environment.
Furthermore it is difficult to confine the area which is to be machined only to the area upon 5 which the focused ion beam impinges. As indicated above, chlorine gas, for example, is often chemically reactive with the whole surface of the object being formed and may undesirably attack areas adjacent to the ion beam position resulting ° in a lack of contrast between machined and non- machined areas.
Summary of the Invention In accordance with the present invention, the 5 process of shaping an object such as a semiconduc- tor device comprises directing a focused ion beam onto the surface of the object for the removal of material by sputtering. Iodine vapor is supplied within the same chamber and is directed toward the object's surface in order to enable a chemical reaction between the iodine and the surface material in the area where the ion beam is aimed. Because of its limited chemical reactivity, as compared with fluorine or chlorine, iodine would not be expected to produce significant results in regard to increased sputtering yield. However, we have discovered the effectiveness of iodine vapor is substantially equal to that of chlorine while the use of iodine eliminates the manufacturing difficulties and safety hazards heretofore encountered.
Iodine is a solid at room temperature and can be easily conveyed from place to place. Solid iodine crystals can be placed in a container or crucible within the enclosure of the focused ion beam system where the solid iodine is heated to slightly above room temperature to produce a still relatively small vapor pressure but which is never¬ theless effective. Thus, while introduction of iodine in this manner results in the enhancement of the ion beam machining to substantially the same extent as hereinbefore encountered with gaseous chlorine, the safety problems are significantly reduced or eliminated. At the same time the machining process is more accurate. Because of iodine's reduced chemical reactivity as compared with chlorine, the sputtering of material can be more selective. The ion beam itself can more clearly delineate the area being machined inasmuch as adjacent areas are not attacked by the vapor to nearly the same extent.
It is accordingly an object of the present invention to provide an improved method for micro- machining semiconductor devices and other solid materials, said method being characterized by enhanced contrast between machined areas and non- machined areas.
It is a further object of the present inven- tion to provide an improved method for enhanced physical sputtering of semiconductor devices and the like which method is non-hazardous to operating personnel.
It is another object of the present invention to provide an improved method for micromachining semiconductor devices and the like wherein said method is characterized by economy of construction and ease of operation.
The subject matter of the present invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. However, both the organization and method of opera¬ tion of the invention, together with further advan¬ tages and objects thereof, may best be understood by reference to the following description taken in connection with accompanying drawings wherein like reference characters refer to like elements.
Drawings FIG. 1 is a schematic representation of a focused ion beam system adapted for carrying out the process of the present invention;
FIG. 2 is a partially broken away, cross sectional view illustrating in greater detail a vapor source for the system of FIG. 1; FIG. 3 is a sectional view of a portion of a semiconductor device;
FIG. 4 is a sectional view of the FIG. 3 device having a portion thereof removed by ion beam sputtering; and
FIG. 5 is a sectional view of a portion of a block of semiconductor material having a portion of the top surface thereof machined away.
Detailed Description
Referring to FIG. 1, illustrating a focused ion beam system for carrying out the process according to the present invention, an evacuated envelope 10 includes an upper neck portion 12 within which are located a liquid metal ion source 14 and a focusing column 16 which includes extractor electrode means and an electrostatic optical system. Ion beam 18 passes from source 14 through column 16 and between electrostatic deflection means schematically indi- cated at 20 toward sample 22, which comprises a semiconductor device positioned on movable X-Y stage 24 within lower chamber 26. An ion pump 28 is employed for evacuating neck portion 12. The chamber 26 is evacuated with turbomolecular and mechanical pumping system 30 under the control of vacuum controller 32.
A high voltage power supply 34 is connected to liquid metal ion source 14 as well as to appro¬ priate electrodes in focusing column 16 for forming an approximately 25 keV ion beam 18 and directing the same downwardly. Deflection controller and amplifier 36, operated in accordance with a prescribed pattern such as a raster pattern provided by pattern generator 38, is coupled to deflection plates 20 whereby beam 18 may be controlled to trace out a corresponding pattern on the upper surface of sample 22.
The source 14 typically provides a beam of gallium ions although other ions could be used such as inert gas ions or other metallic ions, for example indium, aluminum, or silicon. The source is capable of being focused into a sub 0.1 micron width beam at sample 22 for either modifying the surface 22 or for the purpose of imaging the surface 22. An electron multiplier 40 used for detecting secondary emission for imaging is connected to video circuit and amplifier 42, the latter supplying drive for video monitor 44 also receiving deflection signals from controller 36. in accordance with the present invention, the focused ion beam system is further provided with a source 46 for supplying iodine vapor. The source is located inwardly of the side of chamber 26 by trans¬ lation device 48 adapted for positioning the source via support means within bellows 52. The source 46 in particular comprises a reservoir or crucible 50. A heater 54, which may comprise a membrane type heater, is utilized for raising the temperature of iodine crystals located within reservoir or crucible so to a temperature for providing a suitable vapor pressure, i.e., a temperature between approximately 30° C. and 50° C. A transfer tube or nozzle 56 extends from reservoir 50 and is connected thereto via control valve 58 adapted for releasing iodine vapor. The nozzle is extended and translated in orthogonal directions substantially perpendicular to its axis employing translation apparatus 48, so that iodine vapor can be aimed directly toward a region on the top surface of sample 22 wherein material is to be removed by scanning ion beam 18. A door 60 is opened for inserting sample 22 on stage 24, and also for inserting iodine crystals within reservoir or crucible 50. The door is interlocked so that it cannot be opened if the temperature in reservoir 50 is substantially above room temperature. A gate valve, schematically illustrated at 62, is closed before door 60 can be opened to seal off the ion source and focusing column apparatus. The base pressure within chamber 26 is 1 X 10"6 Torr. With the emission of the iodine from the vapor source 46, the chamber back¬ ground pressure is 1 X 10"5 Torr.
Vapor source 46, illustrated schematically in FIG. 1, is depicted in greater detail in FIG. 2. A valve shaft tube 64 is supported by a translation apparatus or manipulator (not shown in FIG. 2) and extends inwardly toward sample chamber 26 through bellows 52 where it joins bellows header 66. The bellows 52 is disposed generally coaxially about tube 64 between header 66 and apertured end plate 68 through which tube 64 also passes. End plate 68 is located outwardly from the wall of chamber 26 forming the cover of cylindrical chamber extension 70 aligned with and positioned over an aperture 72 in the sidewall of chamber 26. The cylindrical chamber extension 70 is joined to a radial flange 74 that is secured to the wall of chamber 26 by means not shown. An O-ring seal 76 is fitted within a circular groove in flange 74 to bear against the sidewall of the sample chamber.
Valve shaft tube 64 communicates with a header tubular housing portion 78 which is aligned with tube 64 and ends in a necked down portion or nozzle 80 received within an upper horizontal passage in container cap 82. Tubular housing portion 78 is provided with a plurality of apertures so that the vacuum within chamber 26 is also maintained within tube 64.
Crucible 50 receives solid iodine as indicated at 84 and has an upper radial flange captured within an annular retainer 86 internally threaded and securable onto cap 82. An 0-ring 88 is inter¬ posed between the radial flange of crucible 50 and the lower threaded portion of the cap 82. Secured to the top of cap 82 is an electrical heater element 54 provided control current for the purpose of maintaining crucible 50 at a predetermined temperature.
Cap 82 is further supplied with a delivery tube 90 communicating with the interior of the cap and the crucible, and which slideably receives therewithin tapered end valve member 58. Valve member 58 is carried at one end of valve shaft 92 that passes through valve shaft tube 64, tubular housing portion 78, the upper part of cap 82, and the delivery tube 90. Valve member 58 is adapted to be extended and withdrawn by means of longi¬ tudinal movement of valve shaft 92, the latter being secured to header 94 of bellows 96 attached to the end of tube 64 farthest from the chamber 26. A handle 98 extending from header 94 can be manipu¬ lated in a longitudinal direction either manually or by mechanical means not shown for operating the valve. The shaft 92 also passes through an O-rinς seal 100 in a vertical wall at the top of cap 82 where the shaft 92 then extends into the vapor atmosphere from crucible 50.
Nozzle 56 takes the form of a hypodermic needle 102 received in a bayonet joint at the inner end of a tubular fitting 104 threadably received over the end of delivery tube 58. An O-ring seal or valve seat 105 is located at the juncture between delivery tube 90 and fitting 104 such that the tapered end of valve member 58 is positionable thereagainst for closing the valve and preventing delivery of the vapor to the interior of chamber 26.
In order to place the iodine crystals 84 within crucible 50, door 60 (in FIG. 1} is opened and annular retainer 86 is threadably disengaged from cap 82 whereby the crucible 50 can be removed downwardly. Iodine crystals 84 can then be placed in crucible 50 after which the crucible is again positioned below cap 82 and retainer 86 is employed to secure the crucible in the position shown. Door go can be opened and material can be inserted in crucible 50 only when the temperature thereof (measured by means not shown) is approximately room temperature, e.g. 29° C. or less. Also, door 60 can be operated only when chamber 26 is returned to ambient pressure, with gate valve 62 in place to seal off the upper part of the apparatus. After placement of material in crucible 50 (and presumably after placement of sample 22 on stage 24) , the chamber is suitably evacuated employing pumping means 28 and 30 under the control of means 32. The valve 58 is maintained in an open position during initial chamber evacuation in order to evacuate the crucible, but is returned to a closed position when a predetermined vacuum level is reached. Then, heater 54 may be operated to raise the temperature of the iodine crystals whereby iodine vapor is generated for direction toward the sample 22 by means of nozzle 56. When crucible 50 is raised to a desired temperature between 30° and 50° C., valve 58 may be opened as the nozzle 56 is directed towards the desired area of the sample. Bellows 52 accommodates movement of the entire nozzle assembly and crucible relative to the sample, while bellows 96 permits extension and retraction of valve 58 without affecting the vacuum within chamber 26.
Summarizing the method according to the present invention, sample 22 is placed on stage 24 while solid iodine is deposited in crucible 50, after which the chamber 26 is closed and evacuated and gate 62 is opened so that an ion beam 18 can be generated and directed toward the sample. The sample can be positioned by movement of stage 24 in a well understood manner. Nozzle 56 is positioned so that iodine vapor can be directed towards the raster area as crucible 50 is heated by element 54 to an approximate range between 30° C. and 50° C. and valve 58 is opened to permit escape of the iodine vapor. Pattern generator 38 is programmed to deflect ion beam 18 in a raster pattern corres¬ ponding to a specific area of sample 22 where mate ial is removed or machined away by ion beam sputtering.
Referring to FIGS. 3-5, various portions of a semiconductor integrated circuit device or the like are illustrated as may be microscopically machined in accordance with the present invention. In FIG. 3, body 106 of semiconductor material, e.g. silicon, is covered by a layer 108, suitably comprising an insulating material such as silicon dioxide. A metal conductor 110 which may comprise an aluminum connecting lead is located upon layer 108 and is covered by a second insulating or passivation layer 112. Assuming it is desired to sever or disconnect the conducting metal layer 110, the device may be placed in the apparatus as illustrated in FIG. 1 at the location of sample 22, and ion beam 18 is deflected in a raster pattern corresponding to a rectangular area encompassing metal conductor 110 while iodine vapor is delivered from nozzle 56.
FIG. 4 illustrates the device after the machining operation depicting the depression 114 milled away by the scanning ion beam. It should be observed that the underlying insulating layer 108 can also be machined if so desired, but in this case conduc¬ tor 110 thereabove was removed.
Also, regions of semiconductor material are readily removed. Referring to FIG. 5, illustrating a portion of a block 116 of semiconductor material, an area 118 is milled by means of an ion beam accom¬ panied by iodine vapor directed toward surface 118. The process according to the present invention is suitable for micromachining of various objects in addition to integrated circuit devices, for instance an ion beam according to the present invention may be employed for machining laser facets or optical elements used in directing infrared radiation.
As the iodine vapor is directed toward the surface of a sample (e.g. sample 22 in FIG. 1), iodine is adsorbed on such surface for enabling chemical reaction to take place between iodine and the material of said surface. As the focused ion beam scans a surface of silicon for example, the reaction product of iodine and silicon, i.e., Sil4, is removed. In the case of a semiconductor sample formed of gallium arsenide, Gal2 is generated as well as compounds of arsenic and iodine. When a metal layer such as an integrated circuit conductor formed of aluminum is being removed, a reaction product comprises Al I3. In the course of removal of surface material by sputtering it is desirable to provide sufficient iodine vapor to the surface to form a saturated roonolayer before impingement of the ion beam. If the ion beam is scanned in a regular raster pattern, sufficient iodine vapor is provided so that a given point on the surface of the sample where material is to be removed will receive such onolayer during one raster period, or the time it takes the ion beam to return to a given point in the raster after its prior interception of the same point. The vapor pressure and flux provided in a given area is proportional to the temperature of crucible 50 which is in turn controlled by means of electrically operated heater 54. Such control is conveniently accomplished in an automatic manner.
Although unexpected because of the lower reactivity of iodine compared with chlorine, etching enhancement by approximately a factor of fifteen has been observed for silicon, as well as an enhancement factor of approximately twenty-seven for aluminum. Moreover, the gas assisted physical sputtering achieved in accordance with the present invention is very selective and allows accurate machining of desired areas without as much affect on surrounding areas. Furthermore, the absence of redeposition is observed. Thus, rapid and accurate machining of surfaces including metal conductors in integrated circuit devices is selectively carried out in accordance with the present invention, this even though prior attempts at metal machining employing chlorine or fluorine have produced unsatisfactory results.
Moreove , iodine is a solid at room tempera- ture with a very low vapor pressure and can be handled in the open before placement in a heatable crucible such as crucible 50 hereinbefore described. The crucible can then be placed inside the vacuum system where, even though the tempera- ture of the crucible is raised to produce a higher vapor pressure, the small amount of vapor is exhausted via the vacuum system already present in the focused ion beam apparatus to a remote location and/or gas treatment means. As also noted above, the chamber 26, if operating properly, cannot be opened until the crucible returns to the ambient temperature level at which the iodine vapor pressure is very low. It will be appreciated the method according to the present invention has considerable utility as applied to the rapid modification, repair and analysis of semiconductor devices. It is also of considerable utility in other micromachining applications, but has the advantage of convenience and economy of operation without the dangers of potential toxicity.
While a preferred embodiment of the present invention has been shown and described, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from the invention in its broader aspects. The appended claims are therefore intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.

Claims

Claims
1. The process of shaping features of a solid object comprising the steps of: positioning said object within an enclosed chamber, supplying iodine vapor within said chamber so that iodine is adsorbed on an exposed surface of said object for enabling chemical reaction between iodine and the material at said surface, generating a focused ion beam, and directing said ion beam toward said surface for removal through sputtering of at least a portion of said surface comprising the reaction products of iodine and surface material.
2. The process according to claim 1 wherein said iodine vapor is provided within said chamber by heating solid iodine within said chamber.
3. The process according to claim 1 wherein said object comprises a semiconductor device.
4. The process according to claim 1 wherein said exposed surface is metal.
5. The process according to claim 1 wherein said ion beam is generated employing a liquid metal ion source.
6. The process according to claim 1 wherein said metal comprises gallium.
7. The process according to claim 1 including substantially evacuating said chamber for main- taining the interior of the chamber at a low pressure
8. The process according to claim 1 including directing said iodine vapor toward the surface of said object.
9. The process according to claim 1 including deflecting said ion beam according to a pattern of movement wherein the configuration of the material removed corresponds to the deflection pattern.
10. The process of shaping features of a semiconductor device comprising the steps of: positioning said device on a stage within a substantially gas tight chamber of a focused ion beam system, positioning solid iodine within said chamber and heating said iodine to a temperature in excess of 30° C. for generating iodine vapor, directing said iodine vapor towards a region of said device where machining is desired for enabling chemical reaction between iodine and material from which said device is formed, generating a focused ion beam by means of said focused ion beam system and directing said ion beam toward said region of said device where machining is desired while scanning said beam in a raster pattern over said region for removal through ion beam sputtering of at least a portion of said region, and removing reaction products of iodine and material from which said device is formed by evacuating said chamber.
11. The process according to claim 10 wherein the region of said device toward which said iodine vapor and said ion beam are directed for machining said region comprises metallic material.
12. The process according to claim 10 wherein the region of said device toward which said iodine vapor and said ion beam are directed for machining said region comprises insulating material.
13. The process according to claim 10 wherein the region of said device toward which said iodine vapor and said ion beam are directed for machining said region comprises semiconductor material.
14. The process according to claim 10 wherein the region of said device toward which said iodine vapor and said ion beam are directed for machining said region comprises plural layers.
PCT/US1992/010151 1991-04-15 1992-11-25 Process of shaping features of semiconductor devices WO1994013010A1 (en)

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US08/021,481 US5376791A (en) 1991-04-15 1993-02-22 Secondary ion mass spectometry system

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