United States Patent [19J
`Kikuchi et al.
`
`I lllll llllllll Ill lllll lllll lllll lllll lllll lllll lllll lllll llllll Ill lllll llll
`US005226056A
`5,226,056
`[I IJ Patent Number:
`Jul. 6, 1993
`[45) Date of Patent:
`
`[54) PLASMA ASHING METHOD AND
`APPARATUS THEREFOR
`
`[75)
`
`Inventors: Masashi Kikuchi, Fujisawa;
`Toshinari Takata, Chigasaki; Tokuo
`Watanabe, Yokosuka, all of Japan
`
`[73) Assignee: Nihon Shinku Gijutsu Kabushiki
`Kaisha, Chigasaki, Japan
`
`[21) Appl. No.: 462,380
`
`[22) Filed:
`
`Jan. 9, 1990
`Foreign Application Priority Data
`[30)
`Japan ...................................... 1-2042
`Jan. 10, 1989 [JP]
`Japan ...................................... 1-2043
`Jan. JO, 1989 [JP]
`Japan ...................................... 1-2044
`Jan. 10, 1989 [JP]
`Jan. 10, 1989 [JP]
`Japan ...................................... 1-2045
`
`Int. c1.s ............................................... H04B 7/00
`[51)
`[52) U.S. Cl. ........................................ 373/18; 373/62;
`156/345; 156/643; 156/646; 204/164;
`204/192.I; 219/121.11; 219/121.36;
`219/121.37; 219/121.4; 219/390
`[58) Field of Search ............... 156/643, 646, 668, 345;
`204/192 E, 164, 298; 373/40, 18, 22, 62;
`219/10.55 E, 10.55 M, 10.67, 121.43, 390,
`121.11, 121.36, 121.37, 121.4, 121.41, 383
`
`[56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`4,529,474 7/1985 Fujiyama et al. ........ ~ .......... 156/643
`4,533,820 8/1985 Shimizu ............................... 219/390
`4.961,812 10/1990 Baerg et al. ......................... 156/643
`4,983,254 1/1991 Fujimura et al .................... 156/643
`5,034,086 7/1991 Sato ..................................... 156/643
`Primary Examiner-Bruce A. Reynolds
`Assistant Examiner-Tu Hoang
`Attorney, Agent, or Firm-Armstrong & Kubovcik
`ABSTRACT
`[57)
`In a method for plasma ashing a resist film coated on a
`substrate, the temperature of the substrate is controlled
`initially at temperatures below that' at which explosion
`of the resist film occurs until a surface portion of a resist
`film has been removed. Thereafter, the substrate tem(cid:173)
`perature is increased to remove the remaining portions
`of the resist film. An apparatus for conducting the
`method includes a plurality of supports, which may be
`movably disposed within a vacuum treatment chamber
`for moving the substrate away from a source of heat and
`for moving the substrate into contact with the heating
`source.
`
`8 Claims, 10 Drawing Sheets
`
`52
`53
`
`--.,ioi--.i. 55
`
`-----0-Ih 7 57
`
`57
`
`56
`
`0
`
`14
`
`
`
`Page 1 of 19
`
`Samsung Exhibit 1004
`
`

`

`U.S. Patent
`
`July 6, 1993
`
`Sheet 1of10
`
`5,226,056
`
`2a
`
`-
`
`sor--
`
`13
`
`FIG. I
`
`PRIOR ART
`
`9
`
`4
`
`5
`
`3
`
`51
`
`FIG.2
`
`PRIOR ART
`
`4
`
`3
`
`2oo·c
`
`I.LI
`0::
`I.LI :::>
`t-1-
`C( C(
`0:: 0::
`I- I.LI
`CJ) Q..
`CD ::::E
`:::> I.LI
`CJ) I-
`
`A
`
`I
`I
`
`I 5 SEC
`er
`-----,----
`
`I
`
`B
`
`2oo·c
`
`I
`I
`I.LI
`0::
`JIOSEC
`:::>
`I.LI
`---,
`I- I-
`C( C(
`0:: 0::
`I
`I- I.LI
`CJ) Q..
`::::E - - - - - _L ___
`CD
`:J I.LI
`CJ) I-
`
`TIME
`
`FIG.3
`PRIOR ART
`
`TIME
`
`FIG.4
`PRIOR ART
`
`
`
`Page 2 of 19
`
`

`

`U.S. Patent
`
`July 6, 1993
`
`Sheet 2 of 10
`
`5,226,056
`
`FIG.5
`PRIOR ART
`
`FIG.6
`PRIOR ART
`
`51
`
`(µm/min)
`
`2
`
`I
`
`FIG.7
`PRIOR ART
`
`FIG.9
`PRIOR ART
`
`11
`
`IQ
`
`. rvtz~z'z~v;;:,5~
`lb
`I
`FIG.8
`PRIOR ART
`
`@> )):.iY:5s~ )~
`I l
`A
`
`I
`
`0
`LLJ
`LLJ
`&;
`~ z
`~ OL---L-~----L~~.L.-~-
`+75 mm
`-75
`O
`<[
`I
`I
`CENTER OF SUBSTRATE
`FIG. I 0
`PRIOR ART
`
`
`
`Page 3 of 19
`
`

`

`U.S. Patent
`US. Patent
`
`July 6, 1993
`July 6, 1993
`
`Sheet 3 of 10
`Sheet 3 of 10
`
`5,226,056
`5,226,056
`
`2a
`
`so/'
`
`13
`
`FI G.11
`
`
`:xssxs r
`
`4
`
`
`
`
`
`3
`
`15
`
` 200’C
`
`200°C
`
`Lu
`
`*2
`go:
`IL!
`"0.
`m:
`gm
`ml—
`
`“1
`
`2:
`ml!
`FLU
`mu-
`m2
`3‘“
`U”-
`
`TIME
`
`TIME
`
`Page 4 0f 19
`
`
`
`Page 4 of 19
`
`

`

`US. Patent
`U.S. Patent
`
`July 6, 1993
`July 6, 1993
`
`Sheet 4 of 10
`Sheet 4 of 10
`
`5,226,056
`5,226,056
`
`4
`
`17
`
`51·
`
`
`
`13
`
`'0 14
`
`l4
`
`2b
`
`FI G.14
`
`FI G.15
`
`
`
`
`"'1'.
`m
`
`
`
`14
`
`r.=s=:s::::::s:::::s:::::::s::::s:::::s;;::s::::::s:::::s:::::i::::::q 5 2
`53
`
`
`
`'12. -:.,111.- I-
`
`
`FI G.16
`
`
`
`14
`
`56
`
`Page 5 of 19
`
`
`
`Page 5 of 19
`
`

`

`U.S. Patent
`
`July 6, 1993
`
`Sheet 5 of 10
`
`5,226,056
`
`FI G.17
`
`FI G.18
`
`' 54
`
`58b
`
`64
`
`62
`
`61
`
`60
`
`'~~ )1,p~ie
`"
`
`(
`
`51
`
`12
`
`so/
`
`13
`
`2b
`
`FI G.19
`
`
`
`Page 6 of 19
`
`

`

`US. Patent
`U.S. Patent
`
`July 6, 1993
`July 6, 1993
`
`Sheet 6 of 10
`Sheet 6 of 10
`
`5,226,056
`5,226,056
`
`O)
`'II'III '—
`
`0
`C\J
`•
`l!) -
`
`N
`
`-C\J
`F.IG.2|
`(.!) --LL.
`
`•
`
`l a
`
`Page ’7 Of
`
`g.
`
`II."in
`.I-ul.‘r..—‘—-_....— .-‘
`
`“L94n n Wm
`“IIIE‘IE-lhflmmml
`
`'ii
`II
`:!J
`
`'ii
`II
`:!J
`
`0
`N
`
`
`
`Page 7 of 19
`
`

`

`U.S. Patent
`’ US. Patent
`
`July 6, 1993
`July 6, 1993
`
`Sheet 7 of 10
`Sheet 7 of 10
`
`5,226,056
`
`-
`
`'
`
`N
`
`p\Ia4
`
`“.m‘s‘g
`
`(~Oj
`
`N
`N
`• c:>
`l.J..
`
`NNdE
`
`Page 8 of 19
`
`v
`N
`• c:> -
`
`
`
`Page 8 of 19
`
`
`

`

`U.S. Patent
`
`July 6, 1993
`
`Sheet 8 of 10
`
`5,226,056
`
`FI G.23
`
`23o<23bJ
`
`,.. .. ....,
`
`I
`
`I
`
`F IG.25
`
`2b
`
`30
`
`
`
`Page 9 of 19
`
`

`

`°'
`0 en
`°'
`....
`N.
`N
`....
`en
`
`0
`~
`0 .....
`\C
`(!> a
`
`::r'
`rJ1
`
`~
`\C
`\C
`~
`
`~ = -'<
`
`~a-.
`
`""C a (D = ~
`
`~ • 00.
`
`•
`
`US. Patent
`
`July 6, 1993
`
`Sheet 9 of 10
`
`Q'
`
`FIG.27
`
`5,226,056
`
`..,J~ -1't4" ~ ':{Q,. 39b 39n JJ Ot ~ 34
`
`
`
`
`---4-v.\‘
`Ia,5I
`.i. ‘1“!VIII:
`
`
`
`
` .' i
`II'_
`'5” :
`
`
`:fl
`:
`gs
`
`
`I
`
`
`i.
`.r
`
`i\
`
`1
`
`v
`
`FIG.26
`
`Vllllllllnllnl
`
`
`‘
`
`2a
`
`
`IIIIIIIIIIIFIII
`
`J
`I I()
`
`
`
`
`) 27
`
`-
`
`-0--0-----
`@
`
`0
`
`0
`
`50
`
`<t----;----o
`Lo
`o J
`@ I I
`I
`I
`II I
`
`o
`
`o
`
`2a
`
`0 ,---
`
`~,,
`~ I 0
`
`
`
`
`
`Page 10 of 19
`
`

`

`U.S. Patent
`
`July 6, 1993
`
`Sheet 10 of 10
`
`5,226,056
`
`F IG.28
`
`43
`
`42
`
`56
`
`37
`35
`39b
`
`34
`
`FI G.29
`
`
`
`Page 11 of 19
`
`

`

`1
`
`5,226,056
`
`PLASMA ASHING METHOD AND APPARATUS
`THEREFOR
`
`2
`10 seconds as shown by the curve Bin FIG. 4. The hot
`plate 7 is maintained at a constant temperature by means
`of a thermocouple-type thermometer 10.
`Another example of the conventional dry treatment
`DETAILED DESCRIPTION OF THE
`5 apparatus is shown in FIG. 7. In the arrangement
`INVENTION
`shown in FIG. 7 a vacuum exhaust port 3 is provided
`directly under a substrate 1. In this construction, just
`1. Field of the Invention
`like in the above-described example, the substrate 1 is
`This invention relates to a method and an apparatus
`placed on a hot plate 7; oxygen radicals or radicals of a
`for removing a resist film coated on a semiconductor
`substrate by ashing utilizing plasma.
`10 reactive gas are generated by discharging of a micro-
`wave discharging member 2a connected to a micro-
`2. Background of the Invention
`wave power source 13, to generate radicals of oxygen
`In order to fabricate minute integrated circuits, a
`gas or the· reactive gas obtained by mixing oxygen gas
`resist film having a circuit pattern is placed on the sur-
`with a small quantity of CF4, N1, and Hz. The gas is
`face of a semiconductor substrate. The substrate is then
`etched, using the resist film as a template and then the 15 introduced from a reactive gas source 2b connected to
`an introduction port 2; the radicals react with a resist
`resist film is removed.
`Methods of removing the resist film can be divided
`film on the heated substrate l, and then the resist film is
`into two groups (i.e., a wet treatment method in which
`decomposed and evacuated and discharged by a vac-
`chemicals such as hydrogen peroxide, organic solvents,
`uum pump 14 via the vacuum exhaust port 3.
`and the like are used and a dry treatment method in 20 As circuits become finer, it has become frequent prac-
`tjce to utilize a resist film coated on a substrate 1 as a
`which the resist film is ashed by an oxygen plasma).
`Many of the chemicals used in the wet treatment
`mask for locally doping impurities, by ionization, on the
`method are harmful to humans and it is necessary to
`surface of the substrate 1. In this case, as shown in FIG.
`monitor the safety precautions used and the amount of
`5, the surface layer portion lla of resist film 11, utilized
`pollution caused by waste liquids. Further, the chemi- 25 as a mask, is affected and hardened by.ion beams, and
`stresses are concentrated inside the surface layer. It is
`cals used contain impurities which will cause voids in
`and contamination of the patterns of semiconductor
`difficult to remove the resist film 11 by ashing in the
`circuits. Such chemicals are therefore not suitable to the
`above-described dry treatment method and if an at-
`fabrication, on a very large-scale, of integrated circuits.
`tempt is made to remove the resist film 11 the surface
`In the dry treatment method, a resist film ofCxHyNz 30
`coated on the substrate is caused to react with oxygen
`layer lla of resist film 11 may explode due to sudden
`t d ·
`t
`thermal stresses. The flakes of the resist film 11 gener-
`d. 1
`ra 1ca s genera e m an oxygen p asma so as o remove
`1
`the resist film by decomposing and evaporating the film
`ated by the explosion would remain on the substrate 1
`into co2, NOi and HzO. This method does not generate
`or inside the vacuum treatment chamber 4 as dust parti-
`substances which are harmful to the human body and 35 cles or residual matter and become an obstacle to the
`does not contain impurities, and it is suitable to the
`hyperfine fabrication of the substrate 1.
`hyperfine fabrication of integrated circuits.
`According to findings of the inventors, the lower
`A specific example of the conventional dry treatment
`limit of temperature of explosion of the resist film 11
`method is shown in FIGS. t and 2. A substrate 1 coated
`varies with the conditions of ion doping and the type of
`with a resist film is placed either above or on heating 40 resist, but it has been found that by lowering substrate
`temperatures in the range of about 70° to 160° C. the
`means 51 inside a vacuum treatment chamber 4. The
`heating means may be an infrared lamp 5 as shown in
`surface layer portions of the resist film lla are removed
`FIG. 1 or a hot plate 7 provided with a thermally con-
`during plasma ashing without causing the resist film to
`trolled cast-in heater 6 as shown in FIG. 2. The vacuum
`explode. The inventors have also observed that the
`treatment chamber 4 contains a reactive gas introduc- 45 wider the resist film 11, the more likely an explosion
`will occur.
`tion port 2 and a vacuum exhaust port 3. Oxygen gas or
`The apparatus shown in FIGS. l, 2 and 7 is called a
`a reactive gas obtained by mixing oxygen gas with a
`small quantity of CF4, N1 or H2 to be introduced from
`downstream-type ashing apparatus because the radicals
`the reactive gas introduction port 2 is converted to
`of the reactive gas are generated outside the vacuum
`plasma by a plasma applicator 50 comprising a micro- 50 treatment chamber and flow from an upper portion
`wave discharging member 2a. The oxygen radicals or
`along the surface of the substrate together with the
`the radicals of the reactive gas are caused to react with
`reactive gas, and are discharged from the vacuum ex-
`the resist film on, the heated substrate 1. The resist film
`haust port in a lower portion of the vacuum treatment
`chamber. This apparatus is advantageous in that the
`decomposes and evaporates and then is discharged from
`vacuum treatment chamber 4 by a vacuum pump.
`55 electrically charged particles do not strike the substrate
`In the example shown in FIG. 1, the substrate 1,
`and therefore the circuit pattern formed on the substrate
`is not damaged. However, as can be seen in FIGS. 8 &
`placed on a rack 8 inside the vacuum treatment chamber
`4, is heated by the infrared lamps 5 to a predetermined
`9, it is difficult to coat the resist film 11 only on the front
`temperature in about 5 seconds as shown by the curve
`surface la of the substrate, which is a requirement of a
`A in FIG. 3. The temperature of the substrate 1 is con- 60 hyperfine circuit, as the film is often deposited on the
`trolled by an infrared thermometer 9 which detects the
`rear surface lb of the substrate 1. There is a disadvan-
`infrared rays emitted from the surface of the substrate 1.
`tage in that if the substrate 1 is heated in contact with
`The output signal of the thermometer 9 is fed back to
`the hot plate 7, to remove the resist film 11 by ashing,
`the power source of the lamp 5 to maintain the tempera-
`the reactive radicals are prevented by the hot plate 7
`ture constant by controlling the electric power.
`65 from working on that resist film 11 which is present on
`In the example shown in FIG. 2, the substrate 1 is
`the rear surface lb, and the resist film 11 partly remains
`as shown in FIG. 9. If the resist film 11 which remains
`supplied with heat by thermal contact with the hot plate
`7, and is heated to a predetermined temperature in about
`on the rear surface lb of the substrate 1 is peeled off in
`
`
`
`Page 12 of 19
`
`

`

`5,226,056
`
`3
`the following processes of fabrication, it will contami(cid:173)
`nate the semiconductor manufacturing apparatus which
`should remain clean. Poor quality integrated circuits
`through adhesion of the peeled particles on the hyper(cid:173)
`fine circuits are also produced
`Furthermore, in the apparatus as shown in FIGS. 1, 2
`and 7, the downward stream of the reactive gas flows
`along the surface of the substrate l, from one side
`towards the other side, to ash the resist film 11. As can
`be seen from the ashing speed distribution shown by the 10
`curve A of FIG. 10, the ashing speed of the resist film
`on the upstream side of the reactive gas flow is consid(cid:173)
`erably slower than that on the downstream side. There
`is, therefore, a disadvantage in that it takes a long time
`to complete the ashing process.
`A first object of this invention is to provide a method
`in which a resist film can be removed by ashing without
`an accompanying explosion of the resist.
`A second object of this invention is to provide an
`apparatus in which a resist film can be removed from 20
`not only the front surface but also the rear surface of the
`substrate.
`Another object of this invention is to provide an
`apparatus in which a resist film whose surface layer has
`been affected and hardened can be removed by ashing, 25
`and to remove the resist film by ashing without damag(cid:173)
`ing the substrate.
`A still further object of this invention is to provide an
`apparatus in which the time required for finishing the
`ashing is shortened by making the ashing speed uniform. 30
`
`4
`hardened on its surface layer, and capable of removing
`the resist film by ashing without damaging the substrate,
`there is proposed a plasma ashing apparatus which in(cid:173)
`corporates a vacuum treatment chamber for receiving a
`5 substrate coated with a resist film, the vacuum treat(cid:173)
`ment chamber having a vacuum exhaust port, heating
`means for heating the substrate, and a reactive gas intro(cid:173)
`duction port provided with a plasma applicator to
`thereby remove the resist film on the substrate by ash(cid:173)
`ing;
`wherein a front electrode is disposed in front of the
`substrate in an opposed relationship thereto at a distance
`capable of generating plasma;
`a rear electrode is disposed on the rear side of the
`15 substrate in an opposed relationship thereto at a narrow
`distance incapable of generating plasma; and
`each of the electrodes is selectively connected to a
`high-frequency power source and ground respectively.
`In this embodiment it is preferable that the front elec(cid:173)
`trode, which is disposed in an opposed relationship to
`the substrate, be comprised of a planer plate having a
`multitude of. perforations.
`An object of shortening the time required for com(cid:173)
`pleting the ashing by making the ashing speed, uniform,
`can be attained by a plasma ashing apparatus which
`includes:
`a vacuum treatment chamber for receiving a substrate
`coated with a photoresist film on a surface thereof, the
`vacuum treatment chamber having therein heating
`means to heat the substrate,
`a reactive gas introduction pipe for flowing a reactive
`gas to the vacuum treatment chamber and having in an
`intermediate portion thereof a plasma applicator to
`generate a plasma of the reactive gas,
`a vacuum exhaust pipe connected to a va_cuum pump,
`the introduction pipe and the vacuum exhaust pipe
`being connected to the vacuum treatment chamber,
`whereby the reactive gas to be introduced from the
`reactive gas introduction pipe in an ionized condition is
`caused to flow along the surface of the substrate to ash·
`the resist film on the surface thereof;
`wherein the inside of the vacuum treatment chamber
`is divided into two chambers by a shower plate, the
`shower plate having a perforated plate provided along
`the surface of the substrate;
`the vacuum exhaust pipe is connected to that side of
`the two chambers in which the substrate is located; and
`the reactive gas introduction pipe is connected to the
`other side of the two chambers.
`In this case, it is preferable tliat the shower plate be
`provided with small holes on the entire,, surface
`thereof, and a hole of relatively large diameter be
`formed in a position facing the central portion of the
`surface of the substrate. A vacuum exhaust pipe is con-
`55 nected to the vacuum treatment chamber such that it
`opens into a position facing the rear surface of the sub(cid:173)
`strate, and a thermometer is provided to measure the
`temperature of the surface of the substrate through the
`relatively large diameter hole of the shower plate.
`
`35
`
`BRIEF SUMMARY OF THE INVENTION
`In this invention, as a method of attaining the above(cid:173)
`described first object, there is provided a method which
`comprises the steps of:
`providing inside a vacuum treatment chamber a sub(cid:173)
`strate coated with a resist film;
`ashing the resist film with an oxygen plasma while
`heating the substrate to remove the resist film;
`controlling the temperature of the substrate at a low 40
`temperature until the surface layer of the resist film has
`been removed; and
`increasing the temperature thereafter to a high tem(cid:173)
`perature to remove remaining resist film.
`In order to solve the second object as described 45
`above, there is proposed a plasma ashing apparatus
`which comprises:
`a vacuum treatment chamber for receiving a substrate
`coated with a resist film, the vacuum treatment chamber
`having a vacuum exhaust port, heating means for heat- 50
`ing the substrate, and an inlet port for a reactive gas, the
`inlet port being provided with a plasma applicator to
`thereby remove the resist film on said substrate by ash(cid:173)
`ing with radicals of a reactive gas to be introduced from
`the inlet port,
`wherein a plurality of pins are provided inside the
`vacuum treatment chamber to support the substrate at a
`distance from the heating means by supporting the rear
`surface of the substrate.
`In the proposed apparatus, it is preferable to dispose 60
`the plurality of pins movably between an advanced
`position and a retracted position, the advanced position
`being such that a distance is formed between the rear
`surface of the substrate and the heating means, and the
`retracted position being such that the rear surface of the 65
`substrate contacts the heating means.
`Further, as a plasma ashing apparatus capable of
`removing a resist film which has been affected and
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIGS. 1 and 2 are sectional side views showing a
`conventional ashing method.
`FIG. 3 is a diagram showing the temperature changes
`of the substrate shown in FIG. 1.
`FIG. 4 is a diagram showing temperature changes of
`the substrate shown in FIG. 2.
`FIG. 5 is an enlarged sectional view of a resist film.
`
`
`
`Page 13 of 19
`
`

`

`5,226,056
`
`s
`FIG. 6 is also an enlarged sectional view of a resist,
`the surface thereof being heated to temperatures caus(cid:173)
`ing the upper portion thereof to explode.
`FIG. 7 is a sectional side view of a conventional
`ashing apparatus.
`FIG. 8 is a sectional view of a substrate coated with
`a resist film.
`FIG. 9 is a sectional view of a conventional substrate
`which has been treated by ashing showing remnants of
`the resist film.
`FIG. 10 is a diagram showing the distribution of the
`ashing speed of the apparatus shown in FIG. 2.
`FIG. 11 is a sectional side view showing one embodi(cid:173)
`ment of the method of this invention.
`FIGS. 12 and 13 are diagrams showing the tempera- 15
`ture changes of the substrate in the embodiments of the
`present invention.
`.
`FIGS. 14 through 16 and FIG. 19 are sectional side
`views of embodiments of this invention.
`FIG. 17 is a plane disk-shaped front electrode having 20
`a multitude of perforations.
`FIG. 18 is a perspective view showing the support for
`the substrate in the embodiment of FIG. 16.
`FIGS. 20 through 29 are further concrete embodi-
`ments of this invention wherein:
`FIG. 20 is a front view with part of the apparatus cut
`away;
`FIG. 21 a sectional side view taken along the line
`XXII-XXII of FIG. 21;
`FIG. 22 is a sectional plan view taken along the line 30
`XXIII-XXIII of FIG. 20;
`FIG. 23 is a perspective view of a cassette case;
`FIG. 24 is an enlarged view of a transfer apparatus;
`FIG. 25 is an enlarged sectional side view of a plasma
`applicator;
`FIG. 26 is a right-hand side view of FIG. 25; and
`FIGS. 27 through 29 are enlarged sectional side
`views of a vacuum treatment chamber.
`
`35
`
`6
`the reactive gas can enter the space defined by the dis(cid:173)
`tance to thereby ash the resist film on the rear surface of
`the substrate.
`When the surface portion of the resist film coated on
`5 the surface of the substrate is affected and hardened
`through radiation by ion beams, the substrate is placed
`inside the vacuum treatment chamber. The reactive gas
`is caused to flow from the reactive gas introduction port
`towards the exhaust port. A rear electrode which faces
`the rear surface of the substrate is connected to a high(cid:173)
`frequency power source, and a front electrode which is
`disposed in front of the substrate is grounded. Since the
`distance between the substrate and the rear electrode is
`set at a distance too narrow for plasma to be generated,
`the substrate becomes substantially equal in electric
`potential to that of the rear electrode, and since it be·
`comes negative in electric potential by the addition of
`high-frequency electric potential from the high-fre(cid:173)
`quency power source, -plasma discharging starts be(cid:173)
`tween the substrate and the front "electrode which is
`grounded. The ions in the plasma are moved by the
`attraction of the electric potential of the substrate and
`strike the front surface of the substrate. The resist film
`coated on the surface of the substrate is sputtered by the
`striking ions, and the surface layer portion which has
`been affected and hardened can be physically peeled off
`and removed.
`After the removal of the affected and hardened sur(cid:173)
`face layer portion is completed, the substrate is heated
`by the heating means and the connection to the rear
`electrode is changed from the high-frequency power
`source to the ground, and the plasma applicator means
`is operated. Then, the reactive gas to be introduced
`from the introduction port to the vacuum treatment
`chamber is exited by the plasma and the generated radi(cid:173)
`cals of the ·reactive gas are caused to chemically react
`with the resist film which remains on the substrate. The
`remaining resist film is ashed and is rapidly removed
`from the surface of the substrate. The decomposed and
`40 evaporated compositions are removed via the exhaust
`port.
`In case damage to the surface of the substrate is
`feared, the high-frequency power source is connected
`to the front electrode and the rear electrode is
`grounded. In this case, since the front electrode be(cid:173)
`comes negative in electric potential and the substrate is
`grounded, the ions of plasma to be generated therebe(cid:173)
`tween gently strike the surface of the substrate and do
`not damage it, and the resist film on the substrate is
`gently sputtered. When the affected and hardened sur(cid:173)
`face portion of the resist film has been peeled off by
`sputtering, the substrate is heated by the heating means.
`The connection to the front electrode is changed from
`the high-frequency power source to ground, and the
`plasma applicator is operated to rapidly remove the
`remaining resist film by ashing with the radicals in the
`reactive gas which is introduced into the vacuum treat(cid:173)
`ment chamber.
`The radicals of the reactive gas flow towards the
`front side of the substrate through the perforations in
`the front electrode, thereby uniformly ashing the entire
`resist film.
`The narrow distance between the rear electrode and
`the rear surface of the substrate is set, for example, to 1
`mm at which no plasma is generated.
`In another embodiment the inside of the vacuum
`treatment chamber is divided into two chambers by a
`shower plate. The shower plate c;.omprises a perforated
`
`JO
`
`25
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`In order to remove a resist film coated on the surface
`of a substrate the, is placed inside a vacuum treatment
`chamber and oxygen plasma is introduced into the
`chamber while heating the substrate to ash the resist 45
`film. In this case the generation of flakes by explosion of
`the resist film can be prevented by maintaining the sub(cid:173)
`strate temperature initially at temperatures lower than
`conventionally used at the beginning of the ashing pro(cid:173)
`cess, and then raising the temperature. In the first low· 50
`temperature condition, the surface layer of the resist
`film which has been affected and hardened by radiation
`of the ion beams is removed without generating sudden
`thermal stresses (i.e., without exploding the resist film).
`Then the inner portion of the resist film is rapidly 55
`heated to a high temperature and ashed at a high speed.
`The ashing of the resist film is performed by introduc(cid:173)
`ing a reactive gas in which radicals are generated
`through electric discharging with a plasma applicator,
`from the reactive gas introduction port into the vacuum 60
`treatment chamber, causing the radicals of the reactive
`gas to chemically react with the resist film of the sub·
`strate, and thus decomposing and evaporating it and
`removing it via the exhaust port. If the rear surface of
`the substrate is in contact with a heating means the resist 65
`film adhered to the rear surface thereof is not ashed. But
`by holding the substrate with a plurality of pins at a
`distance away from the heating means the radicals of
`
`
`
`Page 14 of 19
`
`

`

`25
`
`7
`plate having a large-diameter hole in its center and
`small-diameter holes about the periphery of the large(cid:173)
`diameter hole; the shower plate is disposed in front of
`the substrate which is disposed inside the vacuum treat(cid:173)
`ment chamber. Also in this construction, the vacuum 5
`exhaust pipe is connected to that side of the two cham(cid:173)
`bers in which the substrate is located, and the reactive
`gas introduction pipe is connected to the other side of
`the two chambers. Reactive gas introduced into the
`vacuum treatment chamber contacts the entire resist 10
`film through the plurality of perforations all at once
`creating a shower effect. The resist film decomposes
`and evaporates at a number of locations simultaneously
`through contact with the radicals of the reactive gas
`and can be removed uniformly at a rapid ashing speed. 15
`By providing a hole with large diameter in the center of
`the perforated plate, ashing can be performed with
`better uniformity.
`Embodiments of this invention are explained in ac(cid:173)
`cordance with the accompanying drawing FIG. 11. In 20
`this drawing reference numerals 1 through 13, 50 and 51
`denote the same elements as those of reference numerals
`1 through 13 and 50 and 51 of FIGS. 1 and 2.
`A first embodiment of the present invention incorpo-
`rates a semiconductor substrate 1 constituted by a sili(cid:173)
`con wafer coated with a resist and supported by a rack
`8 above a heating means 51 which has an infrared lamp
`5 inside a vacuum treatment chamber 4 which is pro(cid:173)
`vided with a reactive gas introduction port 2 and a 30
`vacuum exhaust port 3.
`FIG. 11 shows another embodiment in which a sub(cid:173)
`strate 1 coated with a resist is disposed on a heating
`means 51 which incorporates a hot plate 7.
`In any of the embodiments the reactive gas introduc- 35
`tion port 2 is provided with a plasma applicator 50 for
`converting the reactive gas to plasma, the plasma appli(cid:173)
`cator comprising an electric discharging means such as
`a microwave discharging member 2a, RF coil, and the
`like. Thus, oxygen gas or a reactive gas obtained by 40
`mixing oxygen gas with CF4, N1 or H2 is excited by
`plasma and is introduced into the vacuum treatment
`chamber 4. The vacuum exhaust port 3 is connected to
`an appropriate vacuum pump to exhaust the vacuum
`treatment chamber 4 to maintain an atmosphere below 45
`I0-4 Torr, for example.
`The apparatus of the first embodiment of the present
`invention is similar to the conventional apparatus
`shown in FIG. 1. However, the substrate 1 has a resist
`film 11 with a surface layer lla represented by 50
`CxHyNz which has been affected and hardened as
`shown in FIG. 5. The reactive gas excited by oxygen
`plasma and the like which is introduced from the reac(cid:173)
`tion gas introduction port 2 is caused to act on the resist
`film 11 without switching on the infrared lamp 5 at the 55
`beginning. When the surface layer portion lla has been
`removed by decomposition and evaporation through
`chemical reactions with oxygen radicals or radicals of
`the reactive gas, the lamp 5 is activated to heat the
`substrate 1 and accelerate the chemical reactions with 60
`oxygen radicals or radicals of the reactive gas to rapidly
`remove the resist film 11. The temperature of the sub(cid:173)
`strate in this process is controlled as shown by the curve
`C shown in FIG. 12; lamp 5 is activated after a lapse of
`time t1, which is required for removing the surface layer 65
`portion lla, and the substrate reaches 200° C. in about
`5 seconds, as in the conventional process, to rapidly
`remove the resist film 11.
`
`5,226,056
`
`8
`In the apparatus shown in FIG. 11, a plurality of pins
`16 are connected to and moved up and down by a lifting
`apparatus 15 which encompasses an air cylinder located
`outside the vacuum treatment chamber 4. When pins 16
`are lowered the substrate 1 is placed on the hot plate 7.
`If the apparatus in FIG. 11 is used to remove the resist
`film 11 the temperature change of the substrate is shown
`by curve D in FIG. 13. When the time t1 required for
`removing the surface layer portion lla is over, the
`substrate 1 is lowered onto the hot plate 7; the substrate
`then reaches 200° C. in about 10 seconds, as in the heat(cid:173)
`ing step of an apparatus having a conventional hot plate.
`After heating the removal of the remaining resist film 11
`is performed.
`In the apparatus of ~ach of the embodiments dis(cid:173)
`cussed above, since the resist film 11 is removed by first
`removing the surface layer portion lla at a low temper(cid:173)
`ature and then the remaining portion at a high tempera(cid:173)
`ture, the resist is removed without exploding the inter(cid:173)
`nally stressed resist film 11. It is therefore possible to
`prevent the vacuum treatment chamber from being
`contaminated with flakes of the resist film 11, and fabri(cid:173)
`cation of accurate and hyperfine circuits can be per(cid:173)
`formed.
`Two further embodiments are shown in FIGS. 14 and
`15. In these figures reference numerals 1 through 16, 50
`and 51 denote the same elements as those shown in
`FIGS. l, 2, and 11.
`In the embodiment shown in FIG. 14 a plurality of
`pins 16 are provided inside a vacuum treatment cham(cid:173)
`ber 4 such t.hat they project upwards through a heating
`means 51 which incorporates a plurality of infrared
`lamps ~· A vacuum exhaust port 3 is provided below the
`heating means. The rear surface of a substrate 1 is sup(cid:173)
`ported by the tips of the pins 16 so that a distance 17 is
`formed between the subs~rate 1 and heating means 51.
`In the embodiment shown in FIG. 15, a plurality of
`pins 16 penetrate a heating means 51 (in the direction
`shown) which encompasses a hot plate 7. As a result the
`pins are introduced into the vacuum treatment chamber
`4 from the outside thereof through a chamber wall 4a.
`Each pin 16 is connected to a lifting apparatus 15 which
`includes a cylinder provided outside the vacuum treat(cid:173)
`ment chamber 4 such that it is freely movable in the
`upward and downward directions. A vacuum exhau