United States Patent i
`Hwanget al.
`
`[54]
`
`METHOD FOR REMOVAL OF
`PHOTORESIST OVER METAL WHICH
`ALSO REMOVESOR INACTIVATES
`CORROSION-FORMING MATERIALS
`REMAINING FROM PREVIOUS METAL
`ETCH
`
`[75]
`
`Inventors:
`
`Jeng H. Hwang, Cupertino; Steve Y.
`Mak,Pleasanton, both of Calif.
`
`[73]
`
`[21]
`
`[22]
`
`[51]
`[52]
`
`[58]
`
`Assignee: Applied Materials, Inc., Santa Ciara,
`Calif.
`
`Appl. No.: 749,733
`
`Filed:
`
`Aug. 26, 1991
`
`Int. CLS acess B44C 1/22; B29C 37/00
`US. C1. eecccceeescteeerteeeteetenneees 156/643; 134/1;
`156/651; 156/655; 156/668
`Field of Search............... 156/643, 646, 651, 655,
`156/657, 659.1. 662. 668, 345; 204/192.36,
`298.33; 134/1, 19, 31
`References Cited:
`
`U.S. PATENT DOCUMENTS
`
`4.980.022 12/1990 Fujimura et al. vice 134/1 X
`5.057.187 10/1991 Shinagawa etal. we 136/643
`
`FOREIGN PATENT DOCUMENTS
`
`63-216346
`2-140923
`
`9/1988 Japan vee 156/643
`3/1990)
`Japan ..ccccceccceereeeeceeene 156/643
`
`AUTRE CATERAA
`
`US005174856A
`(11] Patent Number:
`[45] Date of Patent:
`
`5,174,856
`Dec. 29, 1992
`
`OTHER PUBLICATIONS
`
`Toy, David A., “Choose the Right Process to Strip
`Your Photoresist”, Semiconductor International, Feb.,
`1990, pp. 82-87.
`
`Primary Examiner—William A. Powell
`Attorney, Agent, or Firm—John P. Taylor
`
`ABSTRACT
`[57]
`A processis described for removing from an integrated
`circuit structure photoresist remaining after a metal
`etch which also removes or inactivates a sufficient
`amount of any remaining chlorine residues remaining
`from the previous metal etch to inhibit corrosion of the
`remaining metal for at least 24 hours. The process in-
`cludes a first stripping step using either Oz gas or a
`combination of O2 gas and N2 gas and/ora fluorocarbon
`gas associated with a plasma followed by a subsequent
`step using a combination of O2 and NH; gases associated
`with a plasma. When fluorocarbon gas is used in the
`first stripping step, a flushing step may be used prior to
`introduction of the NH: gas to flush out any remaining
`fluorocarbon gas. Preferably, the plasma is generated in
`a microwave plasma generator located upstream of the
`stripping chamber and the stripping gases pass through
`this generator so that reactive species produced from
`the gases in the plasma enter the stripping chamber.
`
`20 Claims, 1 Drawing Sheet
`
`
`
`
`
`
`
`
`
`
`
`FLOWING A MIXTURE OF OXYGEN GAS,
`NITROGEN GAS, AND A FLUOROCARBON
`GAS THROUGH A MICROWAVE PLASMA
`GENERATOR INTO A STRIPPING CHAMBER
`CONTAINING AN INTEGRATED
`CIRCUIT STRUCTURE COMPRISING A
`PREVIOUSLY ETCHED PATTERNED METAL
`LAYER AND A PHOTORESIST MASK
`OVER THE UNETCHED METAL
`
`
`
`
`
`
`
`IGNITING A PLASMA IN THE GENERATOR
`WHILE THE GASES ARE FLOWING THROUGH
`THE GENERATOR INTO THE CHAMBER
`
`
`
`
`
`
`
`EXTINGUISHING THE PLASMA AND
`SHUTTING OFF THE FLOW OF NITROGEN GAS
`
`
`AND FLUOROCARBON GAS WHILE FLUSHING
`
`THE CHAMBER WITH OXYGEN GAS TO
`REMOVE ANY REMAINING FLUOROCARBON
`GAS AND HEATING THE STRUCTURE TO A
`TEMPERATURE OF ABOUT 245°C
`
`
`
`
`
`
`FLOWING AMMONIA GAS AND OXYGEN GAS
`THROUGH THE PLASMA GENERATOR INTO THE
`
`CHAMBER AND IGNITING A PLASMA IN
`
`
`
`THE GENERATOR AFTER ABOUT 10 SECONDS
`OF GAS FLOW TO COMPLETE THE REMOVAL
`OF PHOTORESIST AND REMOVAL OR
`INACTIVATION OF CHLORINE RESIDUES
`
`
`
`
`
`
`
`Page 1
`
`of 6
`
`Samsung Exhibit 1018
`
`Page 1 of 6
`
`Samsung Exhibit 1018
`
`

`

`U.S. Patent
`
`Dec. 29, 1992
`
`5,174,856
`
`
`
`
`
`
`
`
`
`
`
`FLOWING A MIXTURE OF OXYGEN GAS,
`NITROGEN GAS, AND A FLUOROCARBON
`GAS THROUGH A MICROWAVE PLASMA
`GENERATOR INTO A STRIPPING CHAMBER
`CONTAINING AN INTEGRATED
`CIRCUIT STRUCTURE COMPRISING A
`PREVIOUSLY ETCHED PATTERNED METAL
`LAYER AND A PHOTORESIST MASK
`OVER THE UNETCHED METAL
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`FLOWING AMMONIA GAS AND OXYGEN GAS
`THROUGH THE PLASMA GENERATOR INTO THE
`
`
`
`
`CHAMBER AND IGNITING A PLASMA IN
`THE GENERATOR AFTER ABOUT 10 SECONDS
`OF GAS FLOW TO COMPLETE THE REMOVAL
`OF PHOTORESIST AND REMOVAL OR
`
`
`INACTIVATION OF CHLORINE RESIDUES
`
`
`
`IGNITING A PLASMA IN THE GENERATOR
`WHILE THE GASES ARE FLOWING THROUGH
`THE GENERATOR INTO THE CHAMBER
`
`EXTINGUISHING THE PLASMA AND
`SHUTTING OFF THE FLOW OF NITROGEN GAS
`AND FLUOROCARBON GAS WHILE FLUSHING
`THE CHAMBER WITH OXYGEN GAS TO
`REMOVE ANY REMAINING FLUOROCARBON
`GAS AND HEATING THE STRUCTURE TO A
`TEMPERATURE OF ABOUT 245°C
`
`
`
`
`
`Page 2 of 6
`
`Page 2 of 6
`
`

`

`1
`
`5,174,856
`
`METHOD FOR REMOVAL OF PHOTORESIST
`OVER METAL WHICH ALSO REMOVES OR
`INACTIVATES CORROSION-FORMING
`MATERIALS REMAINING FROM PREVIOUS
`METAL ETCH
`
`BACKGROUNDOF THE INVENTION
`1. Field of the Invention
`This invention relates to a process for removing pho-
`toresist remaining over a metal layer after etching of the
`metal layer. More particularly, this inventionrelates to
`a dry process for removing photoresist and also remov-
`ing or inactivating corrosion-forming etch residues re-
`maining over a metal layer after etching of the metal
`layer.
`2. Description of the Related Art
`A photoresist mask, which remains over portions of
`one or more metal layers on an integrated circuit struc-
`ture after patterning such metal! layers through the pho-
`toresist mask, has been conventionally removed by dry
`etch techniques using plasmas of oxygen and fluorocar-
`bon gases. Such dry etch techniques are preferred over
`wet etch techniques since the underlying metals are not
`attacked, and because the dry etching is sometimes
`more effective in removal of photoresist residues, par-
`ticularly when the photoresist has been altered byreac-
`tive ion etching, high temperature post bakes, or the
`like.
`However, such dry etch techniques have been found
`to be Jess than satisfactory in removing or inactivating
`certain sidewall etch residues remaining from the previ-
`ous metal etch (patterning) step. Such metal etch pro-
`cesses conventionally use chlorine-based chemistry.
`e.g., Claand BCla, which mayleave chlorine-containing
`residues on/in sidewalls of the photoresist mask and
`underlying metal layer portions after the metal etch.
`If such chlorine-containing residues (regardless of
`their source) in the sidewall residues, remaining after
`the metal etch step, are not removed or inactivated
`during the subsequent removal of the photoresist mask,
`such chiorine-containing residues may cause corrosion
`of the underlying metal prior to subsequent downstream
`processing steps which may include washing (solvent
`rinse) steps resulting in removal of such chlorine-con-
`taining residues.
`Sinceit is knowthat such subsequent processing steps
`can result in removal of any chlorine-containing resi-
`dues remaining in sidewalls from the metal etch step,it
`has become conventional to judge the effectiveness of
`the photoresist removal step in also removing orinacti-
`vating such chlorine-containing residues based on how
`much corrosion occurs during a 24 hour period follow-
`ing the photoresist removal step. If no corrosion of the
`underlying metal occurs within 24 hours after the pho-
`toresist removal step, the photoresist removal step is
`judged to have successfully removed or inactivated a
`sufficient amount of such corrosion-causing residues,
`since it is assumed that within 24 hours the integrated
`circuit structure will have been subjected to subsequent
`processing which will include at least one subsequent
`washing step which will remove any remaining chlo-
`rine-containing residues.
`re-
`However,
`the currently practiced photoresist
`moval process using O2 and CFy, has not succeeded in
`providing this desired 24 hours of protection from cor-
`
`Page 3 of 6
`
`2
`rosion of the metal by such chlorine-containing resi-
`dues.
`It would, therefore, be desirable to provide an im-
`proved process for the removal of photoresist remain-
`ing after a metal etch step which would not only re-
`move the photoresist mask, but also removeor inacti-
`vate a sufficient amount of any remaining chlorine-con-
`‘taining residues from the metal etching step so that the
`remaining metal or metals will be passivated or free
`from corrosion for at least 24 hours after such process-
`ing.
`
`SUMMARYOF THE INVENTION
`
`The invention comprises a process for removing pho-
`toresist remaining after a metal etch which also removes
`or inactivatesa sufficient amount of any remaining chlo-
`rine-containing residues, in sidewall residues from the
`metal etch step, to inhibit corrosion of the remaining
`metal or metals for at least 24 hours. The process in-
`cludesa first stripping step using either O2 or a combina-
`tion of and a fluorocarbon gas and/or nitrogen gas,
`associated with a plasma; and followed by a subsequent
`step using a combination of O2 and NH; gasesalso asso-
`ciated with a plasma. When a fluorocarbon gasis used
`in the first stripping step, a flushing step may be used
`prior to introduction of the NH3 gasto flush out any
`remaining fluorocarbon gas.
`BRIEF DESCRIPTION OF THE DRAWING
`
`The sole FIGUREis a flow sheet
`process of the invention.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`illustrating the
`
`The process of the invention is utilized on an inte-
`grated circuit structure whereon a metal
`layer, or a
`composite of metal layers, previously deposited on an
`integrated circuit structure, and which, for example,
`may comprise a titanium nitride barrier layer and an
`overlying aluminum layer, has just been etched through
`a photoresist mask, leaving titanium nitride barrier por-
`tions and aluminum portions under the photoresist
`mask. After the metal etch step, sidewall etch residues
`remain on the sidewall surfaces of the photoresist mask,
`and on the sidewall surfaces of the remaining underly-
`ing metal layer portions. These sidewall etch residues,
`in turn, contain chlorine etch materials or residues
`therein which can cause corrosion of such metal por-
`tions.
`
`30
`
`50
`
`In accordance with the invention, the chlorine-con-
`taining residues in such sidewalls are removedor inacti-
`vated and remaining metal portions of the metal layers
`are passivated during the process for the removalof the
`photoresist mask portions.
`The metal layer or layers, partially removed during
`the preceding metal etch step to leave the patterned
`metal portions, may comprise any metal conventionally
`. used in the formation of integrated circuit structures,
`60 such as, for example, aluminum, titanium, tungsten,etc.
`When multiple metal layers are etched to form metal
`portions, the upper metal portions will usually comprise
`aluminum and the underlying metal portions will usu-
`ally comprise a metal compound such astitanium ni-
`tride which serves as a barrier layer to prevent spiking
`of aluminum to underlyingsilicon contacts. Such under-
`lying electrically conductive metal-containing barrier
`materials will be referred to herein as metal
`layers,
`
`Page 3 of 6
`
`

`

`3
`regardless of whether they comprise pure metals. metal
`alloys, or metal compounds.
`The process of the invention finds greatest utility
`when the upper metal portions over the barrier layer
`comprise aluminum or any other metal which maybe
`subject to corrosion by chlorine-containing residues, or
`other corrosion-forming metal etch step residues,
`if
`such residues are not removed during the photoresist
`removal step. By aluminum is meant either pure alumi-
`num or an aluminum alloy such as, for example, an
`aluminum alloy containing 1-2 wt. % silicon and 0-4
`wt. % copper.
`The integrated circuit structure (wafer) is removed
`from the metal etch chamber and placed in a vacuum
`stripping chamber, unless the same chamberis to be
`used for both processes. The stripping chamberis main-
`tained at a pressure ranging from about 0.5 to about 3
`Torr, typically about 2 Torr. The temperature of the
`waferat this stage is within a range of from about 40° C.
`to about 100° C.
`,
`During thefirst stripping stage, O2 gas may be used
`alone or in combination with a fluorocarbon and/or N2
`gas. When a fluorocarbon gas is used in this step, the
`fluorocarbon gas may comprise,
`for example, CFs,
`CHF:3, CoFs. C3Fe¢. C2H4F>. or the like. However, the
`use of CFy gas is preferred.
`The rate of flow of such gas or gasesin thisfirst step
`wil] be at a rate equivalent to a rate of from about 1000
`to about 2000 standard cubic centimeters per minute
`(sccm). typically about 1400 sccm. of O2: from about 0 3
`to about 150 sccm. typically about 100 sccm, of No; and
`from about 0 sccm to about 80 sccm, typically about 45
`sccm, of the fluorocarbon gas into a 5 liter stripping ©
`chamber.
`A plasma having a powerlevel of about 500 watts to
`about 2500 watts, typically about 1400 watts,
`is then
`ignited in the gas flow, preferably upstream ofthe strip-
`ping chamber, and maintained for about 10 seconds
`after which the plasmais extinguished and the flowof
`the fluorocarbon gas such as CFyis shut off. The flowof
`Nz: into the chamber mayalso optionally be shut off at
`this time.
`While any type of conventionally generated plasma
`may, in general, be used in the practice of the invention,
`preferably the plasma used in the process of the inven-
`tion is generated by a microwave plasma generator such
`as, for example, a Mode] AURAplasma generator com-
`mercially available from the GaSonic division of Ato-
`mel Corporation of Sunnyvale, Calif., which is located
`upstream of the stripping chamber.
`In this type of apparatus, the gas flowing toward the
`stripping chamberfirst passes through the microwave
`plasma generator located upstream of the stripping
`chamber and the plasma generated therein produces
`reactive species from the gases flowing through the
`plasma generator to the stripping chamber, and such
`reactive species then flow into the stripping chamber.
`After the plasma is extinguished, and the flow of
`fluorocarbon gasinto the chamberis shut off, at the end
`of the first step, the flow of O2 may be increased from
`1400 sccm (or its equivalence in a larger or smaller
`chamber) up to from about 2000 sccm to about 4000
`sccm, typically about 3000 sccm, to flush out any re-
`maining fluorocarbon gas prior to the next step of the
`process. This flushing step, which need only be carried
`out if fluorocarbons are used in the first step, is carried
`out fora minimum timeperiod ofat least about 10 sec-
`onds.
`
`5_
`
`20
`
`40
`
`45
`
`50
`
`4
`the temperature of the
`During this flushing step,
`wafer may be slowly ramped up. at a rate of about 10°
`C./second, to a temperature of from about 150° C. to
`about 400° C.. typically about 245° C., at which temper-
`ature the wafer is maintained during the remainder of
`the process.
`,
`While the wafer is heating up to the desired operating
`temperature, e.g., 245° C., ammonia gas is
`flowed
`through the plasma generator into the stripping cham-
`ber at a rate equivalent to from about 10 to about 300
`sccm, and typically about 65 sccm,into a 5 liter cham-
`ber, while the O2 is flowed through the plasma genera-
`tor into the stripping chamber at an equivalent rate
`within the range of from about 2000 to about 5000 sccm,
`typically about 3000 sccm. Theratio of NH3 gas to O2
`gas flowing into the stripping chamber should range
`from about 0.5 volume % NH: to about 10 volume %
`NHa, with the balance O2 gas.
`The O2 and NH3 gasesare flowed through the plasma
`generatorinto the stripping chamberfor a period ofat
`least about 10 seconds,after which a plasmais ignited in
`the plasma generator and maintained for a period ofat
`least about 40 seconds, preferably at least about 60 sec-
`onds, during which the flow of the O2 and NH3gases
`through the plasma generator into the stripping cham-
`ber is maintained. Longer periods of time can be used,
`both for the gas flow prior to the plasma ignition, as
`well as the period during which the plasma remains on,
`but such longer periods are deemed to be unnecessary.
`After the plasmais extinguished and the flow of gases
`shut off. the wafer may be removed from the stripping
`chamberand subject to further processing,e.g., topside
`processing, as desired. The process of the invention
`removesall of the photoresist and also removesorinac-
`tivates a sufficient amount of any chlorine-containing
`residues remaining from prior metal etching to provide
`freedom from any corrosion forat least 24 hours follow-
`ing the resist removal process of the invention.
`Tofurtherillustrate the invention, a silicon wafer was
`provided with a layer of oxide thereon, a layer of alumi-
`num containing 1 wt. % silicon and 0.5 wt. % copper
`deposited over the oxide layer, and a photoresist mask
`formed over the metal layer. The metal layer wasfirst
`conventionally etched through the photoresist mask
`using a mixture of BCl3 and Cl) etchant gases in a 11.5
`liter vacuum etch chamber.
`The wafer wasthen placed ina 5 liter stripping cham-
`ber where the photoresist mask was then stripped and
`the underlying metal passivated by removal or inactiva-
`tion of any etch residues remaining from the metal etch
`step by first flowing a mixture of O2, CF4, and N2
`through a microwave plasma generator located up-
`stream of the stripping chamber, and then into the
`chamberat a rate of 1400 sccm O2, 45 scem CFy, and
`100 sccm No, for a period of about 10 seconds during
`which a plasma wasignited in the plasma generator and
`maintained at a powerlevel of about 1400 watts.
`The plasma was then extinguished and the flow of
`CF, and N2 shut off, while the flow of O2 was increased
`to 3000 sccm to flush out any remaining CF, gases.
`During this flushing period the wafer was ramped upto
`a temperature of about 245° C.at a rate of about 10° C.
`per second, e.g., over about a 25 second period.
`After the wafer reached 245° C., as measured by a
`thermocouple contacting the back of the wafer, NH;
`was flowed through the plasma generator into the
`chamber at a rate of about 65 sccm. After about 10
`seconds, the plasma wasreignited in the plasma genera-
`
`5,174,856
`
`60
`
`65
`
`Page 4 of 6
`
`Page 4 of 6
`
`

`

`9,174,856
`
`6
`12. The process of claim 10 wherein a fluorocarbon
`gas flows through said plasma generatorinto said strip-
`ping chamberduring said step a) and which includes the
`additional step of continuing to flow O2 through said
`plasma generator into said stripping chamberafter ex-
`tinguishing said plasma and shutting offthe flow ofsaid
`fluorocarbon gas into said chamber during said step a)
`to thereby purge said stripping chamberof any fluoro-
`carbon gas in said stripping chamber prior to com-
`mencement of step b).
`13. The process of claim 1 wherein said wafer is main-
`tained at a temperature of from about 100° C. to about
`400° C. during said step b).
`14. The process of claim 13 wherein said wafer is
`maintained at from about 40° C. to about 100° C. during
`said step a) and then heated to said step b) temperature
`range at a rate of about 10° C. per second.
`15. The process of claim 1 wherein said stripping
`chamberis maintained at a pressure of from about 0.5
`Torr to about 3 Torr during said process.
`16. A process for removing, from an integrated cir-
`cuit structure, photoresist remaining after a metal etch
`which comprises:
`a) flowing through a microwave plasma generator
`into a stripping chambercontaining said integrated
`circuit structure a mixture of Oo, Na, and fiuorocar-
`bon gases for a period of at least about 10 seconds
`at a rate equivalent to. flowing from about 1000
`sccm to about 2000 sccm ofsaid O2 gas, from about
`50 sccm to about 150 sccm of said N2 gas, and from
`about 20 sccm to about 80 sccm ofsaid fluorocar-
`bon gas into a 5 liter chamber;
`b) igniting a plasma in said plasma generator while
`said Or, No, and fluorocarbon gases are flowing
`through said plasma generator into said stripping
`chamber;
`c) then extinguishing said plasma and shuttingoff said
`flowof said N> gas and said fluorocarbon gasinto
`said stripping chamber while maintaining said flow
`of O2 into said chamber to purge said chamber of
`fluorocarbon gas;
`then flowing NH3 and QO: gases through said
`plasma generator into said stripping chamberat a
`rate equivalent to a flow of from about 10 sccm to
`about 300 sccm of NH3 and from about 2000 sccm
`to about 5000 sccm of O2into a 5 liter chamber; and
`e) igniting a plasma in said plasma generatorat least
`about 10 secondsafter said NH; and Q2gases begin
`flowing through said plasma generator into said
`stripping chamber.
`17. The process of claim 16 wherein said hydrocar-
`bon gas comprises CF4.
`18. The process of claim 16 wherein said plasmais
`maintained at a powerlevel of from about 500 watts to
`about 2500 watts while said O2, N2, and CF4 gases are
`flowing through said plasma generator into said strip-
`ping chamber.
`19. The process of claim 16 wherein said plasma is
`maintained at a powerlevel of from about 500 watts to
`about 2500 watts for a period of at least about seconds
`while said O2 and NHgases are flowing through said
`plasma generatorinto said stripping chamber.
`20. A process for removing. from an integrated cir-
`cuit structure, photoresist remaining after a metal etch,
`which process also removes or inactivates chlorine
`residues remaining from said previous metal etch, com-
`prising:
`
`d)
`
`tn
`
`5
`
`20
`
`35
`
`40
`
`50
`
`60
`
`65
`
`5
`tor and maintained for about 60 seconds following
`which the flow of NH: was shut off and the plasma
`extinguished.
`The wafer was then removed from the stripping
`chamberand allowed to stand in the open atmosphere
`for 24 hours. The wafer surface was then examined,
`using 500 X light field and dark field optical micro-
`scopes, and a 50,000 x scanning electron microscope
`(SEM). All of the photoresist was removed and no
`evidence of corrosion was found on the exposed metal
`surfaces.
`Thus, the process of the invention results in complete
`removal of photoresist from the surface of an integrated
`circuit structure after patterning of a metal layer be-
`neaththe resist mask and the remaining metalis passiv-
`ated by removal or inactivation of any corrosion-pro-
`ducing residues remaining from the prior meta! etch
`step.
`Having thus described the invention whatis claimed
`
`is:
`
`1. A process for removing from an integrated circuit |
`structure, in a stripping chamber. photoresist remaining
`after a metal etch which comprises:
`a) exposing said structure to O2 gas for a period of at
`least about 10 seconds; and
`b) then exposing said structure to O2 gas and NH: gas
`for a period of at least about 40 seconds.
`2. The process of claim 1 which further comprises
`igniting a plasma associated with said stripping chamber
`during said step b).
`3.:The process of claim 2 wherein said plasma ignited
`during said step b) is maintained at a power level of
`from about 500 to about 2500 watts.
`4. The process of claim 3 wherein said plasmais gen-
`erated in a microwave plasma generator upstream of
`said stripping chamber.
`5. The process of claim 4 wherein said NH; gas is
`flowed through said plasma generatorinto said strip-
`ping chamber at a rate equivalent to a flow of from
`about 10 sccm to about 300 sccm into a 5 liter chamber.
`6. The process of claim 4 wherein said O2 gas is
`flowed through said plasma generator into said strip-
`ping chamberduring said step b) at a rate equivalent to
`a flow of from about 2000 sccm to about 5000 sccm into
`a 5 liter chamber.
`7. The process of claim 4 wherein the ratio of NH3
`gas to O2 gas flowing through said plasma generator
`into said stripping chamber during said step b) should
`range from about 0.5 volume % NH: to about 10 vol-
`ume % NH3.
`8. The process of claim 7 which further comprises
`igniting a plasma in said plasma generator during said
`step a).
`9. The process of claim 8 wherein said step a) further
`comprises exposing said wafer to a combination of O2
`gas and N2gas or a fluorocarbon gas.
`10. The process of claim 8 wherein O:, and optionally
`N2 gas and/or a fluorocarbon gas,
`is flowed through’
`said plasma generator into said stripping chamber dur-
`ing said step a) at a rate equivalent to flowing from
`about 1000 sccm to about 2000 sccm ofsaid O2 gas, from
`0 sccm to about 150 sccm of said N2 gas, and from 0
`sccm to about 80 sccm ofsaid and from 0 sccm to about:
`80 sccm ofsaid fluorocarbon gasinto a 5 liter chamber.
`11. The process of claim 8 wherein said plasma during
`said step a) is maintained at a powerlevel of from about
`500 to about 2500 waits.
`
`Page 5 of 6
`
`Page 5 of 6
`
`

`

`5,174,856
`
`7
`8
`a) flowing through a microwave plasma generator
`ping chamber while maintaining said flow of O2
`into a stripping chamber containing said integrated
`into said chamberto purgesaid stripping chamber
`circuit structure a mixture of Ox. Na, and CF4 gases
`of said CFy gas:
`for a period of at least about 10 seconds at a rate
`d) then flowing NH; and O2gases into said through
`equivalent
`to flowing from about 1000 sccm to
`said plasma generator into said stripping chamber
`about 2000 sccm ofsaid O: gas. from about 50 sccm
`at a rate equivalent to a flowof from about 10 sccm
`to about 150 sccm ofsaid No gas, and from about 20
`to about 300 sccm of NH: and from about 2000
`sccm to about 80 sccm of said CF4 gas into a5liter
`sccm to about 5000 sccm of O2into a 5 liter cham-
`chamber;
`ber; and
`b) igniting a plasma in said microwave plasma genera-
`igniting a plasmain said microwaveplasma genera-
`tor and maintaining said plasmain said generatorat
`tor at least about 10 secondsafter said NH3 and O2
`a powerlevel of from about 500 watts to about
`gases begin flowing through said generator into
`2500 watts while said O2, N2, and CF4 gases are
`said stripping chamber and maintaining said plasma
`flowing through said plasma generator into said
`at a powerlevel of from about 500 watts to about
`stripping chamber;
`c) then extinguishing said plasma and shutting offsaid
`2500 watts for a period of at least about 40 seconds.
`*
`*
`*
`&€
`.
`flow of said N2 gas and said Cf4 gas into said strip-
`
`€)
`
`20
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`Page 6 of 6
`
`Page 6 of 6
`
`€
`