United States Patent [191
`Sato et a1.
`
`llllll|||||l||Illllllllllllllllllllllllllllllllllllllllllllllllllllllllllll
`5,393,374
`Feb. 28, 1995
`
`USOO5393374A
`[11] Patent Number:
`[45] Date of Patent:
`
`[54] METHOD OF AS}I[NG
`_
`.
`_
`[75] Inventors: Jumchl Sato, Tokyo; ShmgO
`Kadomura, Kanagawa, both of Japan
`[73] Assignee: Sony Corporation, Japan
`
`[21] Appl' No’: “1919
`[22] Filed:
`Aug. 26, 1993
`[30]
`Foreign Application Priority Data
`Aug. 31, 1992 [JP]
`Japan ................................ .. 4455790
`
`Int. GL6 ...................... ..
`[52] US. Cl. .................................. .. 156/643; 156/ 646;
`_
`156/651; 156/668; 134/1
`[58] Fleld of Search ............. .. 156/643, 646, 668, 651,
`156/345; 134/1
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`4,938,839 7/1990 Fujirnura et a1. ............. .. 156/ 668 X
`4,980,022 12/1990 Fujimura et a1. ............. .. 156/643
`5,030,319 7/1991 Nishino at al.
`156/643 X
`5,226,056 7/1993 Kikuchi et a1. ............... .. 156/646 X
`5,240,556 8 l9
`‘
`. ............. .. 156 345 X
`/ 93 Ishlkawa et a1
`/
`Primary Examiner-Thi Dang
`Attorney, Agent, or Firm-—Ronald P. Kananen
`[57]
`ABSTRACT
`A method of ashing comprises the steps of cooling the
`Work to a temperature of 0° C- Or therebelow and calls
`ing ashing of a photo-resist on the work. An apparatus
`for ashing Comprises a Cooling ashing chalnbery a heat
`ing ashing chamber, and a gate Valve provided between
`the two chambers. The method and apparatus as noted
`Solves prior art probl?ms and permits photo_resist
`which has heretofore been dif?cult to remove to be
`removed as well and readily and with satisfactory pro
`ductivity.
`
`4,816,638 3/1989 Ukai et a1. .................... .. 156/345 X
`
`5 Claims, 7 Drawing Sheets
`
`COOLING OF WORK
`
`~I
`
`ASHlNG
`
`~11
`
`7
`
`HEAT | NG (0U 1 CK HEATING) ~ 111
`
`
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`Page 1 of 11
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`Samsung Exhibit 1013
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`

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`US. Patent
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`Feb. 28, 1995
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`Sheet 1
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`of 7
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`5,393,374
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`FIG.1
`
`COOLING OF WORK
`
`~1
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`
`ASHlNG
`
`~II
`
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`
`HEATING<0UICK HEATING) ~IH
`
`
`
`Page 2 of 11
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`

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`US. Patent
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`Feb. 28, 1995
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`Sheet 2 0f 7
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`5,393,374
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`FIGZB
`
`FlG.2C
`
`20
`
`E‘.
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`
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`Page 3 of 11
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`U.S. Patent
`US. Patent
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`Feb. 28, 1995
`Feb. 28, 1995
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`Sheet 3 0f 7
`Sheet 3 of 7
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`5,393,374
`5,393,374
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`FIG.3
`FIG.3
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`Page 4 of 11
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`Page 4 of 11
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`US. Patent
`US. Patent
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`Feb. 28, 1995
`Feb. 28, 1995
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`Sheet 4 of 7
`Sheet 4 0f 7
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`5,393,374
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`Page 5 of 11
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`Page 5 of 11
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`US. Patent
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`Feb. 28, 1995
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`Sheet 5 of 7
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`5,393,374
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`FIG.5A
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`Page 6 of 11
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`US. Patent
`US. Patent
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`Feb. 28, 1995
`Feb. 28, 1995
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`Sheet 6 of 7
`Sheet 6 of 7
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`5,393,374
`5,393,374
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`FIG.5C
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`Page 7 of 11
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`Page 7 of 11
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`US. Patent
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`Feb. 28, 1995
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`Sheet 7 of 7
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`5,393,374
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`Page 8 of 11
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`

`

`1
`
`METHOD OF ASHING
`
`10
`
`5,393,374
`2
`satisfactory productivity, and an apparatus for ashing
`used for carrying out the same method.
`According to the invention, cooling of work, as la
`beled as step I in FIG. 1, is ?rst done. With the cooling
`of the work, the hardened ?lm of photo-resist is also
`cooled down. Thus, in this step, a stress is produced in
`the hardened ?lm to produce cracks therein (see cracks
`2c formed in hardened ?lm 2a of photo-resist as shown
`in FIG. 2B). The crack formation is promoted if a heat
`ing step (preferably a quick heating step) is also incor
`porated, as labeled as step III in FIG. 1. Subsequently,
`as ashing step, as labeled as step II in FIG. 1, is exe
`cuted, in which ashing proceeds with O radicals, for
`instance, entering through the cracks. In this way, a
`satisfactory photo-resist ashing process free from resi
`due can be realized. The hardened film that remains can
`be removed by a spin process or the like.
`According to the invention, the process can be com
`pleted by using a system like a low temperature etching
`system, so that the process is not complicated.
`Further, the throughput can be improved by effect
`ing the ashing with a system which has chambers cou
`pled to each other via a gate valve.
`In a further aspect, in a cooling chamber, accumula
`tion of the reaction by-product is liable to reduce the
`stability of ashing. Accordingly, the cooling chamber
`that has been used as such may be switched to a heating
`chamber for causing sublimation of sublimable deposits.
`By so doing, a stable process is obtainable. This permits
`maintenance cycle reduction to improve the productiv
`ity.
`Further it is effective to incorporate a supersonic
`oscillation application mechanism to apply supersonic
`oscillation to and thereby broaden the cracks formed in
`the photo-resist of the work under an ashing treatment.
`This permits more effective photoresist removal.
`According to the invention, as a speci?c means for
`the low temperature process, a method which is well
`known in low temperature etching may be used.
`
`BACKGROUND OF THE INVENTION
`1. Field of the Invention
`This invention relates to a method of and an appara
`tus for ashing away a photo-resist of a work. The inven
`tion is applicable to, for instance, photo-resist separation
`in a semiconductor integrated circuit manufacture pro
`cess and, particularly, is suitably applicable for satisfac
`torily separating a photo-resist after high dose ion im
`plantation without leaving a residue or the like.
`2. Description of the Relevant Art
`For the photo-resist separation in semiconductor
`processes, a commonly termed dry ashing process,
`which utilizes 02 plasma, has become extensively
`adopted in mass production sites as well as in place of a
`wet process using fumingnitric acid or sulfuric acid
`hydrogen peroxide (i.e., a blend solution of sulfuric acid
`and hydrogen peroxide).
`The basic mechanism of the dry ashing process is to
`remove photo-resist, which comprises an organic poly
`mer, by ashing the photo-resist into CO and CO2
`through a combustion reaction caused by providing 0
`25
`radicals, O2 radicals, and so forth, generated in plasma.
`The process permits comparatively ready separation of
`the usual photo-resist materials.
`However, there are cases where it is dif?cult to re
`move photo-resist material. For example, photo-resist
`after ion implantation can not always be readily sepa
`rated. Particularly, the problem is signi?cant when a
`high dose ion implantation is necessary as in the forma
`tion of source/drain regions for super-LS1 manufacture.
`Where a photo-resist is used as an ion implantation
`35
`mask, high dose, high energy ion implantation is made
`into the photo-resist as well. At this time, the photo
`resist surface is hardened mainly presumably due to heat
`generated by the ion bombardment. The hardened layer
`can not be readily removed with, for instance, the usual
`02 plasma alone, thus extremely deteriorating the sepa
`rability of the photo-resist.
`It is thought that the hardened surface layer is formed
`not only by heat, but also in that the ion implantation
`dopant effects substitution in the molecular structure of
`45
`the photo-resist material to cause a cross-linking reac
`tion, the reacted portion being oxidized by 02 plasma to
`remain as residue in a layer which is dif?cult to etch.
`Particularly, such a residue is liable to constitute a
`source of particle contamination to extremely reduce
`the yield of super-LS1 or like product.
`To solve this problem, a commonly termed two-step
`ashing process has been proposed, which comprises two
`steps of removing the above hardened layer in a RIE
`process incorporating an H2 type and using ion bom
`55
`bardment and then carrying out ordinary ashing
`(Fujimura et al, “Applied Physics”, spring 1989, 1P-l3,
`p. 574). This process, however, involves an additional
`step and dictates an elaborate system. Further, the H1
`RIE process requires a long time and therefore reduces
`the throughput. Accordingly, further improvement of
`the process has been demanded.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a ?ow chart illustrating the step of the
`invention;
`FIGS. 2A to 2D are sectional views of a work during
`respective steps of Embodiment 1;
`FIG. 3 is a schematic view showing an apparatus
`used in Embodiment 1;
`FIG. 4 is a schematic view showing an apparatus
`used in Embodiment 3;
`FIGS. 5A to SE are sectional views of a work during
`respective steps of Embodiment 5; and
`FIG. 6 is a view showing an apparatus used in Em
`bodiment 5.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`Preferred embodiments of the invention will now be
`described in detail with reference to the drawings. It is
`to be construed that the following embodiments are
`given for the purpose of illustration only and without
`any sense of limiting the invention.
`
`OBJECT AND SUMMARY OF THE INVENTION
`The invention seeks to provide a method of ashing,
`65
`which can solve the above problems in the prior art and
`permits photo-resist which has heretofore been dif?cult
`to remove to be removed as well and readily and with
`
`EMBODIMENT 1
`In this embodiment, the invention is applied to the
`photo-resist removal after high dose ion implantation in
`the manufacture of a highly ?nely-integrated semicon
`ductor device.
`
`
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`Page 9 of 11
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`

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`5,393,374
`3
`4
`FIG. 3 shows a magnetic ?eld microwave plasma
`In a ?rst chamber 10A, microwave 1B generated from
`ashing system used for this embodiment. Microwave 1B
`a magnetron 1A is led through a waveguide 3 to a reac
`tion chamber (i.e., a pre-treatment chamber) 5 de?ned
`generated from a magnetron 1A is led through a wave
`by a quart chamber wall 4, and a magnetic ?eld of
`guide 3 to a reaction chamber 5 de?ned by a quartz
`chamber wall 4, and a magnetic ?eld of 75x10“2 T
`8.75 X 10-2 T (tesla), which cooperates with the micro
`(tesla), which cooperates with the‘ microwave (at a
`wave (at a frequency of 2.45 GHz) to cause commonly
`termed ECR discharge, is generated by a solenoid coil
`frequency of 2.45 GHz) to cause commonly termed
`6 surrounding the reaction chamber 5, thus generating
`ECR discharge, is generated by a solenoid coil 6 sur
`rounding the reaction chamber 5. Thus, a gas plasma 7
`gas plasma 7. A wafer 8 as a work is set on a suscepter
`9 and cooled from a chiller (not shown) through a cool
`is generated. A wafer 8 as a work is set on a suscepter 9
`ing tube 10. Gas is introduced through a gas upply tube
`and is cooled from a chiller (not shown) via a cooling
`11 and discharged through a discharge tube (not
`tube 10. Desirable suscepter temperature is less than
`-10° C., and more desirably, less than —20 ° C. Gas is
`shown). A heater 12 is buried in the suscepter 9 as heat
`introduced through a gas supply tube 11 and discharged
`ing means to quickly heat the wafer. It is of course
`through a discharge tube (not shown). In the suscepter
`possible to use an IR lamp or the like for heating. The
`9; a heater 12 is buried as heating means to quickly heat
`?rst chamber 10A and a similar second chamber 10B are
`the wafer 8. It is of course possible to use an IR lamp for
`connected to each other via a gate valve 13. Parts of the
`heating.
`second chamber 10B like those of the ?rst chamber 10A
`are designated by like reference numerals or symbols
`In this embodiment, the invention was applied to a
`process of photo-resist separation after ion implantation.
`with a dash.
`FIG. 2A shows the work (i.e., wafer substrate 1) having
`In this embodiment, a work sample as shown in FIG.
`a photo-resist, which was formed after ion implantation
`2A was used. That is, in this embodiment the invention
`is applied to photo-resist separation after ion implanta
`of As+ carried out under conditions of l016/cm2 and 60
`tion, the work (i.e., wafer substrate 1) having photo
`keV. A super?cial portion of the photo-resist ?lm 2b on
`resist formed after ion implantation carried out under
`the substrate 1 was denatured into a hardened ?lm 2a.
`25
`The sample was set in the plasma asher utilizing a mi
`conditions of As+ carried out under conditions of
`1016/cm2 and 60 keV. The ?rst chamber 10A of the
`crowave discharge as shown in FIG. 3 and subjected to
`ashing under the following conditions.
`plasma asher utilizing a microwave discharge shown in
`Gas: 02, 800 sccm
`FIG. 4 was used as a cooling ashing chamber, and the
`Pressure: 266 Pa
`sample was set in this chamber and subjected to low
`temperature ashing under the following conditions.
`Microwave power: 1 kW
`Suscepter temperature: — 10° C.
`Gas: 02, 800 sccm
`Pressure: 266 Pa
`Cracks 2c as shown in FIG. 2B were formed in the
`hardened ?lm 2a, and from these cracks the ashing
`Microwave power: 1 kW
`proceeded (with introduction of radicals through the
`Suscepter: -10° C.
`cracks), whereby the inner photo-resist was removed
`Then, the work wafer substrate 8 was transferred
`through the gate valve-to the second chamber 10B,
`(FIG. 2C). Subsequently, the hardened ?lm was re
`moved using a spin processor, thus obtaining a clean
`and the chamber 10B was used as a heating ashing
`chamber for ashing under the following conditions.
`surface as shown in FIG. 2D.
`Gas: 02, 800 sccm
`Pressure: 133 Pa
`Microwave power: 1 kW
`Suscepter temperature: 250° C.
`Thus, cracks 2a as shown in FIG. 2B were formed in
`the hardened film 2a, and the inner photo-resist was
`removed (FIG. 2C). Subsequently, the hardened ?lm
`was removed with a spin processor, thus obtaining a
`clean surface as shown in FIG. 2D.
`
`20
`
`45
`
`EMBODIMENT 2
`The same work sample as in Embodiment 1 (as shown
`in FIG. 2A) was subjected to a two-step ashing process
`using the same asher as in Embodiment 1 (FIG. 3) under
`the following conditions.
`Step I
`Gas: 02, 800 sccm
`Pressure: 266 Pa
`Microwave power: 1 kW
`Suscepter temperature: — 10° C.
`Then, the conditions were switched over to the fol
`lowing.
`Step II
`Gas: 02, 800 sccm
`Pressure: 133 Pa
`Microwave power: 1 kW
`Suscepter temperature: 250 ° C.
`With such quick heating subsequent to cooling, suf?
`cient cracks as shown in FIG. 2B were formed in the
`hardened ?lm 2a, and with ashing proceeded from these
`cracks the inner photo-resist was removed (FIG. 2C).
`The hardened ?lm thus ashed was subsequently re
`moved with a spin processor to obtain a clean surface as
`shown in FIG. 2D).
`
`50
`
`55
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`60
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`65
`
`EMBODIMENT 4
`The same sample (FIG. 2A) as in the above embodi
`ments was subjected to ashing as in Embodiment 3 using
`the same asher (FIG. 4) as in Embodiment 3. First, the
`?rst chamber 10A was used as a cooling ashing chamber
`for ashing under the following conditions.
`Gas: 02, 800 sccm
`Pressure: 266 Pa
`Microwave power: 1 kW
`Suscepter temperature: — 10° C.
`Then, the wafer structure 8 as the work was trans
`ferred through the gate valve to the second chamber
`10B. Ashing was then carried out by using the chamber
`10B as a thermal ashing chamber and switching the
`ashing conditions over to the following.
`Gas: 02, 800 sccm
`Pressure: 133 Pa
`Microwave power: 1 kW
`Suscepter temperature: 250° C.
`
`EMBODIMENT 3
`In this embodiment, a microwave plasma continuous
`asher as shown in FIG. 4 was used as ashing equipment.
`
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`Page 10 of 11
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`5
`In this process, cracks 2c were formed in the hard
`ened ?lm 2a, and the inner photo-resist was removed
`(FIG. 2C). Subsequently, the hardened ?lm was re
`moved using a spin processor. In this way, a clean sur
`face as shown in FIG. 2D could be obtained.
`After processing for 100 seconds, the ?rst chamber
`10A was switched to a thermal ashing chamber while
`switching the second chamber 10B to a low tempera
`ture ashing chamber, and a similar process was carried
`out for 100 seconds. By carrying out the operation re
`peatedly a the maintenance time could be reduced to
`one half that in the prior art, and the productivity could
`be improved.
`
`15
`
`20
`
`30
`
`35
`
`EMBODIMENT 5
`In this embodiment, an ashing apparatus as shown in
`FIG. 6 was used. In this apparatus, an ashing chamber
`53 which is a main chamber is connected via a load lock
`chamber 31 and a buffer chamber 32. Gate valves 60a
`and 60b are each provided between the respectively
`adjacent adjacent chambers. In the buffer chamber 32, a
`wafer stage 34 is provided and exposed to liquid nitro
`gen circulation. The wafer as thee work thus can be
`cooled down to the liquid nitrogen temperature. That
`is, the buffer chamber wafer stage is adapted to consti
`25
`tute a low temperature cooling stage 59. The main
`chamber (i.e., ashing chamber) 53 is of a microwave
`down-stream type, and its wafer stage has a heater 58 as
`heating means. Thus, super-sonic oscillations can be
`provided with the heating up to 300° C. by the heater
`and application of DC power to an inner liquid crystal
`super-sonic oscillation element 56.
`In this embodiment, the invention was applied to a
`process of separating photo-resist 2b of a sample as
`shown in FIG. 5A, which was a wafer substrate 1 hav
`ing the photo-resist 2b after ion implantation of As+
`under coditions of 1016/cm2 and 60 keV. The photo
`resist 212 had a super?cial hardened ?lm 2a.
`By setting the sample on the wafer stage 34 in the
`bu?'er chamber 32 in the apparatus of FIG. 6, cracks 2c
`were formed in the photo-resist, as shown in FIG. 5B,
`with an effect of super-low temperature cooling.
`The sample in this state was transferred to the ashing
`chamber 53 as the main chamber of the apparatus of
`FIG. 6, and was subjected to ashing under the following
`45
`conditions.
`Gas: OZ/NZ, 950/50 sccm
`Pressure: 133 PA
`Microwave power: 1 kW
`Stage temperature: 250° C.
`DC power for super-sonic wave: 100 W
`With the super-sonic oscillation, the cracks 2c were
`broadened as shown in FIG. 5C. Thus, even at the
`elevated stage temperature, the solvent in the photore
`sist could be su?iciently gassi?ed and discharged, and
`commonly termed hopping as a source of contamina
`tion did not occur (FIG. 5D).
`The remaining hardened ?lm was removed in a wash
`ing step using a spin processor, thus realizing satisfac
`tory ashing free from residue, as shown in FIG. 5E.
`
`5,393,374
`6
`ple (FIG. 5A) was processed in the same asher (FIG. 6)
`as in Embodiment 5. The ashing was done in two steps.
`Step 1 was carried out in the same way as in Embodi
`ment 5. In this step, only the hardened ?lm 20 remained
`as shown in FIG. 5D with an effect of the super-sonic
`wave to broaden the cracks. The resultant work was
`processed under the following conditions.
`Gas: O2/S2F2, 950/50 sccm
`Pressure: 133 Pa
`Microwave power: 1 kW
`DC power: 100 W
`Stage temperature: 250° C.
`The hardened ?lm 2a, which contained an oxide of
`the dopant, was etched away in the form of AsFx with
`an effect of F separated from the added S2F2. (At this
`time, the reaction was promoted by the effect of the
`impressed super-sonic wave). In this way, the hardened
`?lm 2a could be ashed, thus obtaining a clean wafer
`surface as shown in FIG. 5B.
`As has been described in the foregoing, according to
`the invention photo-resist, which has heretofore been
`dif?cult to remove, can be separated readily and with
`satisfactory productivity. For instance, it is possible to
`obtain residue-free removal of a photo-resist after high
`dose ion implantation. It is thus possible to permit man
`ufacture of super-LSIs or the like in a stable process,
`with a high yield and with satisfactory productivity.
`What is claimed is:
`1. A method of ashing a photoresist ?lm on a work,
`comprising the steps of:
`cooling the work down to a temperature of about 0°
`C. or therebelow, and
`then heating the work to ash the photo-resist ?lm.
`2. A method of ashing according to claim 1, wherein
`the step of heating after the step of cooling is performed
`quickly.
`3. A method of ashing a photoresist ?lm on a work,
`comprising the steps of
`ashing the photo-resist ?lm while cooling the work at
`a temperature of about 0° C. or therebelow; and
`then increasing the temperatures during the ashing
`steps to remove the photo-resist.
`4. A method of ashing a photoresist ?lm on a work
`using an apparatus for ashing comprising a ?rst ashing
`chamber for cooling said work to a temperature of
`about 0° C. or therebelow, a second ashing chamber for
`heating said work, and a gate valve provided between
`said ?rst and second ashing chambers, said method
`comprising a step of ashing said photoresist ?lm on said
`work in said individual ashing chambers alternately at
`least once by transferring said work through said gate
`valve from one chamber to the other.
`5. A method of ashing a photoresist ?lm on a work
`comprising the steps of using an apparatus for ashing
`comprising: a ?rst cooling ashing chamber for cooling
`said work to a temperature of 0° C. or therebelow, a
`second heating ashing chamber for heating said work,
`and a gate valve provided between said ?rst and second
`ashing chambers, and using the cooling ashing chamber
`as a heating ashing chamber and the heating ashing
`chamber as a cooling ashing chamber, thereby remov
`ing by-product generated in the ashing chamber used as
`the cooling ashing chamber.
`
`40
`
`50
`
`55
`
`EMBODIMENT 6
`In this embodiment, the removal of the residual hard
`ened ?lm was done as well in the asher. The same sam
`
`65
`
`* * * * *
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`Page 11 of 11
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