`
`11111444. States Patent
`
`
`Higashikawa et a1.
`
`
`[19]
`
`
`
`[11] Patent Number::
`
`
`[45] Date of Patent:
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`
`
`
`
`4,474,447
`
`
`
`Sep. 25, 1984
`
`[54] DRY ETCHING METHOD FOR ORGANIC
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`
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`MATERIAL LAYERS
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`[75]
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`
`Inventors:
`
`*
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`
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`Iwao Higashikawa; Tsunetoshi
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`
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`
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`Arilmdo, both of Tokyo, Japan
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`[73] Assignee:
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`Tokyo Shibaura Denld Kabushiki
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`
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`Kaisha, Kanagawa, Japan
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`[21] App]. No.: 552,254
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`[22] Filed:
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`Nov. 116, 1903
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`[30]
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`Foreign Application Priority Data
`Mar. 8, 1983 [JP]
`............................. .. 58-37938
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`Japan
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`[51]
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`[52]
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`[58]
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`1161. cm ...................... .. 4446: 1/22; co3c 15/00;
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`co3c 25/06; B29C 17/08
`10.5.01. .................................. .. 156/643; 156/646;
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`156/655; 156/659.1; 156/668; 156/345;
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`
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`204/192 E; 204/298; 252/791
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`
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`14614 of Search .......... .. 156/643, 646, 655, 659.1,
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`156/668, 345; 204/164, 192 E, 298; 252/791;
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`427/38, 39, 43.1
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`4,374,699
`4,381,967
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`
`[56]
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`
`
`
`
`References Cited
`U. S. PATENT DOCUMENTS
`
`
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`2/1983 Sanders et al. ...................... 156/643
`5/1983 Sanders etal. .................... .. 156/643
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`OTHER PUBLICATIONS
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`M. Hatzakis, “Multilayer Resist Systems for Lithogra-
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`phy”, Solid State Technology, Aug. 1981, pp. 74-80.
`
`
`
`
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`
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`J. Moran et al., “High Resolution, Steep Profile, Resist
`Patterns”, The Bell System Technical Journal, vol. 58,
`
`
`
`
`
`
`
`
`
`
`
`
`
`No. 5, May—Jun. 1979, pp. 1026—1036.
`Primary Examiner—William A. Powell
`
`
`
`Attorney, Agent, or Firm—Banner, Birch, McKie &
`
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`
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`
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`Beckett
`
`
`[57]
`
`ABSTRACT
`
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`‘ A dry etching method for organic material layers is
`disclosed which utilizes a parallel plate electrode type
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`plasma etching apparatus. An etching gas containing
`nitrogen as its primary constituent is introduced into the
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`apparatus, and then the organic material layers are an-
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`isotropically etched by applying a high frequency eleca
`tric power to the electrodes to produce a plasma.
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`6 Claims, 8 Drawing Figures
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`77
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`Q
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`g.
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` a.
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`Page 1 of 10
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`TSMC Exhibit 1038
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`TSMC v. IP Bridge
`IPR2016-01379
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`Page 1 of 10
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`TSMC Exhibit 1038
`TSMC v. IP Bridge
`IPR2016-01379
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`

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`US, Pmm Sep. 25, 1984.
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`Sheet 1 of5
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`4,473,437
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`US” Pawn Sep. 25, 1984-
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`494739437
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`USO Pmm
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`US. P333333:
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`Sep. 25, 1984
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`Page 5 0f 10
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`US. Patent
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`Sep. 25, 1984
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`Sheet 5 of5
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`$473,437
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`

`

`ll
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`DRY ETCHING METHOD FOR ORGANIC
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`MATERIAL LAYERS
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`4,473,437
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`2
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`SUMMARY OF THE INVENTION
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`It is an object of the present invention to provide a
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`dry etching method for organic material layers which
`can etch the same substantially anisotropically to im-
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`prove processing accuracy.
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`The above and other objects are achieved according
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`to the invention by utilizing an etching gas containing
`nitrogen.
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`In the present invention, it was recognized that the
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`problems of side-etching of the organic material layer
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`and recession of the mask material layer in dry etching
`of an organic material layer occurred because of the use
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`of an 02 gas. Oxygen ions accelerated by the cathode
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`drop voltage in a parallel plate electrode type dry etch-
`ing apparatus bombard the surface of an organic mate-
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`rial layer to decompose the organic material into carbon
`or hydrocarbon fragments containing one to three car-
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`bon atoms such as C, CH2, C2H5, etc. Furthermore, the
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`fragments produced through the decomposition are
`oxidized by oxygen radicals 0* in the vicinity of the
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`surface of the organic material layer to produce H20,
`C0, C02, etc. At the same time, a chemical action oc‘
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`curs between 0* and unbombarded portions of the
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`organic material
`layer so that side<etching occurs.
`However, the inventors of the present invention be-
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`lieved that anisotropic etching can be attained without
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`side-etching, even under a high gas pressure with rich
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`radicals, by applying such radicals as react with the
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`aforementioned carbon or hydrocarbon fragments but
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`not with the unbombarded portions of the organic mate-
`rial layer. In addition, since the: fragments are radicals
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`with one unpaired electron, carbons with two unpaired
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`electrons, ions, etc. which are active themselves, the
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`present inventors further believed that these fragments
`would react even with rather inert species.
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`Accordingly, in the present invention, nitrogen has
`been found to be an ideal dry etching gas for organic
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`layer materials because it produces an anisotropic etch-
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`ing. A nitrogen radical N" has an electron disposition of
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`2822P3 in an outer shell in ground state and has a maxi-
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`mum number of unpaired electrons in a valence orbital
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`nutshell. Therefore, electron repulsion does not occur
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`in the N*, so that in comparison with an oxygen radical
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`0*, it is stable and its reactivity is remarkably small to
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`unbombarded organic materials. It has been discovered
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`in the present invention that nitrogen gas etching causes
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`neither side—etching under a high gas pressure nor reces-
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`sion- of a mask material layer. Moreover it was also
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`discovered that carbon or hydrocarbon fragments, i.e.,
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`C, CH2, Csz, etc., which are produced through de-
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`composition of organic material layers by ion bombard-
`ment, react well with N* to produce CN, HCN, etc.
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`Also, it has been discovered that the etching speed of
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`nitrogen is sufficient.
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`On the basis of the above discoveries, the present
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`invention provides a dry etching method for organic
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`material layers comprising the steps of placing a work-
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`piece having an organic material layer and an etching
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`mask pattern on a cathode electrode facing an anode
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`electrode in an etching chamber, and then introducing a
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`gas containing nitrogen as the primary constituent into
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`the etching chamber while simultaneously applying a
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`high frequency electrical voltage between the elec-
`trodes to produce a plasma to thereby selectively and
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`anisotropically etch the organic. material layer.
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`5
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`10
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`15
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`BACKGROUND OF THE INVENTION
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`This invention relates to an improved dry etching
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`method, especially a dry etching method for etching
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`organic material layers anisotropically.
`DESCRIPTION OF THE PRIOR ART
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`For the purpose of fabricating integrated circuit de-
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`vices of very high density, a microprocessing technique
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`of high precision is required. For example, various types
`of multi—layered resist processes, which are disclosed in
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`“Solid State Technology,” August 1981, pages 74—80,
`by M. Hatzakis, can be used to overcome the difficulty
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`of forming a high resolution resist pattern on an etching
`workpiece with an uneven surface. The principle of
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`some of the processes is illustrated in FIG. 1. In FIG.
`20
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`1(a), layer 1 of aluminum or other suitable material to be
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`etched, has an uneven surface. Organic material layer 2,
`for example a resist layer,
`is applied over layer 1 in '
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`solution form and solidified by heating to form a level
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`25
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`layer. Next, mask material layer 3 having an etching
`rate different than organic material layer 2 is formed on
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`layer 2 and covered by resist layer 4. Resist layer 4 is
`substantially flat so that a high resolution etching pat-
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`tern can be obtained by a conventional photo engraving
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`process. Using the pattern of resist layer 4 as an etching
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`mask, mask material layer 3 is patterned as shown in
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`FIG. 1(a). Subsequently, using mask material layer 3 as
`an etching mask, organic material layer 2 is etched off
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`anisotropically and resist layer 4 is removed as shown in
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`FIG. 11(b). Moreover, using patterned organic material
`layer 2 as an etching mask, aluminum layer l is etched
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`precisely.
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`_ A known drying etching method for organic material
`layer 2, which levels etching layer 1, uses an 02 gas as
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`disclosed in “Proceedings of 4th Dry Process Sympo-
`sium,” Tokyo 1982, by T. Arikado. According to this
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`dry etching method, a workpiece with an organic mate-
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`rial layer is placed on a cathode electrode of a parallel
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`plate electrode type plasma etching apparatus. By prop-
`45
`erly setting the gas pressure in the etching chamber
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`where the workpiece is placed and the electric power of
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`a high frequency electric power source connected
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`across the cathode and anode, a plasma is produced
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`which then etches the organic material layer.
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`However, in the above organic material dry etching
`method, it is difficult to etch the organic material layer
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`accurately because of side—etching of the organic mate-
`rial layer, recession of the mask material thereon, etc.
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`When 02 gas is used in this dry etching process, the
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`density of oxygen radicals 0* is high under a high gas
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`pressure condition in the etching chamber, which pro-
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`duces side-etching of organic material layer 2 as shown
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`in FIG. 2(a). On the other hand, under a low gas pres—
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`sure condition, increased ion sputtering occurs due to
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`60
`an increase in the cathode drop voltage of the parallel
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`plate electrode type dry etching apparatus. Though
`side—etching does not occur under this low gas pressure
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`condition, a pattern transfer error does occur because of
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`recession of mask material layer 3 as shown in FIG.
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`2(b). Side-etching of organic material layer 2 and reces—
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`sion of mask material layer 3 are undesirable because
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`they diminish processing accuracy and result in serious
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`defects in the microprocessing technique.
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`Page 7 of 10
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`3
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`4,473,437
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`FIGS. 1(a) and 1(b) show sectional views of a work-
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`piece in two steps of a conventional multi-layered resist
`process.
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`FIGS. 2(a) and 2(b) show sectional views of a'work-
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`piece which illustrate problems of a conventional dry
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`etching method using oxygen gas.
`FIG. 3 shows a schematic view of a parallel plate
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`electrode type dry etching apparatus utilized in the
`invention.
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`FIG. 4 is a graph illustrating the relationship among
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`the gas pressure, the cathode drop voltage and the re-
`cession of a mask material layer when a nitrogen gas is
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`used in the apparatus of FIG. 3.
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`FIG. 5 shows the characteristic curves denoting the
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`relationship between the high frequency electric power
`and the gas pressure when a nitrogen gas is used in the
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`apparatus of FIG. 3.
`FIGS. 6(a)—6(f) show sectional views of a workpiece
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`in each step of an embodiment of the invention applied
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`to the process of patterning interconnections of an MOS
`transistor.
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`FIGS. 7(a)—7(c) show sectional views of a workpiece
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`in each step of another embodiment of the invention
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`applied to the process of forming a gate electrode of an
`MOS transistor.
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`DETAILED DESCRIPTION OF THE
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`PREFERRED EMBODIMENTS
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`FIG. 3 is a schematic view showing a parallel plate
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`electrode type dry etching apparatus utilized in the
`invention. In FIG. 3, a pair of electrodes 12, 13 face
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`each other in etching chamber 10 of housing 11. Upper
`electrode 12 constitutes an anode, which is grounded.
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`45
`Lower electrode 13 constitutes a cathode, to which
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`high frequency electric power is supplied from high
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`frequency electric source 15 via matching circuit 16.
`The lower electrode is fixed on support member 22, and
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`thereon is placed workpiece 14 having an organic mate-
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`‘rial layer. An insulator film may be placed between
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`workpiece 14 and lower electrode 13. These electrodes
`12, 13 are electrically isolated from each other by insu-
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`55
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`lator 27. Cooling pipe 23 runs through support member
`22. An etching gas is introduced into etching chamber
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`11 through gas supply pipe 19 connected to pipes 17, 18
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`which are provided with valves 25, 26. The etching gas
`is exhausted from etching chamber 11 through gas ex-
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`haust pipes 20, 21.
`FIG. 4 shows the relationship among the gas pres-
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`sure, the cathode drop voltage and the recession of a
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`mask material layer formed on a positive type resist
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`layer of the novolac resin group having the following
`chemical formula:
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`50
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`Page 8 of 10
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`CH2
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`CH2
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`In the case of FIG. 4, the workpiece was etched by
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`introducing a N2 gas into the dry etching apparatus
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`shown in FIG. 3. A high frequency electric power of
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`500 W was applied between the pair of electrodes 12,
`13. In FIG. 4, the mark (.) represents no recession of the
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`mask material layer, and the mark (x) represents the
`occurrence of recession. As shown in FIG. 4, the cath-
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`ode drop voltage decreases in accordance with an in-
`crease of the gas pressure and recession of the mask
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`material layer does not occur at a cathode drop voltage
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`less than 1000 V. Thus, high accuracy etching can be
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`achieved if the cathode drop voltage is kept at or below
`1000 V, since recession of the mask material layer is
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`prevented.
`FIG. 5 shows characteristic curves denoting the rela-
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`tionship between the high frequency electric power and
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`the gas pressure for different cathode drop voltages
`when a N2 gas was introduced into the apparatus of
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`FIG. 3. In FIG. 5, the curves A, B and C correspond to
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`cathode drop voltages of 1100 V, 1000 V and 800 V,
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`respectively. From FIGS. 4 and 5, it is understood that
`recession of the mask material layer can be prevented
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`by setting the high frequency electric power and the gas
`pressure in the area above the curve B of FIG. 5 in
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`order to maintain the cathode drop voltage at or below
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`1000 V. Under this condition, side-etching also does not
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`occur.
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`Two illustrative embodiments of the present inven-
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`tion will now be described.
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`EXAMPLE 1
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`FIGS. 6(a)—6(/) are sectional views of a workpiece in
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`each step of an embodiment of the invention applied to
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`the process of patterning interconnections of an MOS
`transistor.
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`FIG. 6(a), a N-channel MOS transistor is formed on
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`workpiece 30 in a conventional manner. This transistor
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`is provided with source 33, drain 34, gate oxide film 35
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`and gate electrode 36 surrounded by field oxide film 32.
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`Workpiece 30 further includes insulator film 40 having
`contact holes and aluminum-silicon alloy film 41 having
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`an uneven surface. As described below, this alloy film
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`41 is selectively etched by a multi-layered resist process
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`which includes the dry etching method according to the
`invention.
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`In the dry etching method, a positive type resist solu-
`tion of the novolac resin group first is applied over the
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`surface of aluminum-silicon alloy film 41. The novolac
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`resin group has the following formula:
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`4 .5
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`02
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`I0
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`Page 8 of 10
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`

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`4,473,437
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`5
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`h)
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`N2
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`6
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`0
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`N2
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`‘
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`3'02
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`0
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`'
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`CH2 0 CH2
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`CH3
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`10
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`15
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`,
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`n
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`5'02
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`0
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`CH2
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`CH2
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`CH3
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`n
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`The resist solution over alloy film 41 has a thickness of
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`approximately 2 pm on the average. Subsequently, the
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`resist solution is solidified by heating so that the surface
`of alloy film 411 is leveled and resist layer 43 is formed as
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`shown in FIG. 6(b). Si02 film 44 is formed on resist
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`layer 43. Furthermore, over the surface of Si02 film 44,
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`a positive type resist solution of the novolac resin group ‘
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`is applied and solidified by heating, so that resist layer
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`45 of 1 pm thickness if formed (FIG. 6(b)). Next, as
`shown in FIG. 6(c), resist pattern 45a is formed by a
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`conventional photolithography process including an
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`electron beam exposure technique and a resist develop-
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`ment technique by KOH. The resolution rate of resist
`30
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`pattern 45a is remarkably high because of the flatness of
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`resist layer 45.
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`Subsequently SiO2 film 44 is etched using resist pat-
`tern 45a as a mask by an anisotropic dry etching method
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`utilizing a CF4 gas (FIG. 6(d)). Thereafter, resist layer
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`43 is anisotropically etched using a N2 gas by placing
`workpiece 30 on a quartz plate on cathode electrode 13
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`as shown in FIG. 3. A N2 gas is supplied to etching
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`chamber 10 by opening valve 25. Results show that,
`when the gas pressure in etching chamber 10 was 0.3
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`Torr and the high frequency electric power was 500 W
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`at 13.56 MHz, an etching speed of 3000 Angstrom/mi-
`nute was obtained. Thus, in an etching time of 8 min-
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`utes, resist pattern 4311 was formed as shown in FIG.
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`6(e). On observing the sectional shape and the surface
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`configuration of the workpiece by a scan microscope, it
`was found that resist layer 43 was etched according to
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`the shape of Si02 film pattern 440 with fidelity, and
`with very minimal side-etching of layer 43 and reces-
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`sion of pattern 440.
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`Next, SiO2 film pattern 44a is removed as shown in
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`FIG. 6(f), and aluminum-silicon alloy film 41 is aniso-
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`tropically etched using resist pattern 430 as a mask and
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`using a mixture of CCl4 and C12 as an etching gas. Thus,
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`interconnection pattern 41a is completed as shown in
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`FIG. 6(f).
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`35
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`45
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`Thereafter, resist pattern 75a of a 1 pm thickness is
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`formed by a conventional photolithography technique
`as shown in FIG. 7(b). Using resist pattern 75a as an
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`etching mask, SiO2 film 74 is anisotropically etched by
`a CH4 gas to form a Si02 film pattern 740.
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`Next, the workpiece shown in FIG. 7(b) is placed
`directly on cathode 13 of the apparatus in FIG. 3. An
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`etching gas primarily containing nitrogen then is intro-
`duced into the apparatus. This etching gas may be a
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`mixture of N2 and 02 at a mixture rate of N2 to the total
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`under 30 mol %. The mixture can be controlled by
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`regulating the opening of valves 25 and 26. With a gas
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`pressure of 0.3 Torr and a 'high frequency electric
`power of 500 W at 13.56 MHz, in an etching time of 5
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`minutes, resist pattern 730 is formed as shown in FIG.
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`7(a) by an anisotropic etching of resist layer 73. At that
`time, any side-etching of resist layer 73 and any reces-
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`sion of Si02 film pattern 74a were scarcely visible. Sub-
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`sequently, polysilicon film 66 is etched using a mixture
`of C12 and H2 and using resist pattern 730 as an etching
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`mask in order to form a gate electrode.
`_
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`The above invention can be applied in various forms
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`other than the above examples. Various organic mate-
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`rial layers, for example a polystyrene layer of a low
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`melting point or a polyimide layer of thermohardening,
`may be used instead of resist layers 43, 73. Furthermore,
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`mask material layers 44 and 740 may be formed of Si,
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`SiN, MoSi2, etc. as well as SiO2, all of which show a
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`high etching selectivity rate to the above organic mate-
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`rial layers. The etching gas containing nitrogen may be
`a gas containing not only N2 but also such additives as
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`02, 112,503, C0, C02, etc. Preferably, the amount of
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`the additives should be at or below 30 mol % of the
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`total to accomplish an efficient etching by nitrogen.
`Furthermore, for the etching gas, at least one selected
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`from the group of N2, N20, NO, N02 may be used. In
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`any case, the amount of oxygen should be set at 30 mol
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`% of the total or less for the purpose of preventing
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`side-etching during the condition of attainment of anis-
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`tropic etching.
`We claim:
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`1. In a parallel plate electrode type dry etching appa-
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`ratus for etching a workpiece, said apparatus including
`an etching chamber containing an anode and a cathode
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`facing said anode, a dry etching method for etching an
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`organic material layer of said workpiece comprising the
`steps of:
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`mounting said workpiece on said cathode facing said
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`anode in said etching chamber, said workpiece
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`having an etching mask layer formed on an organic
`material layer;
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`50
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`55
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`EXAMPLE 2
`
`FIGS. 7(a)—7(c) show sectional views of a workpiece
`
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`in each step of another embodiment of the invention
`
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`applied to the process of patterning a gate electrode.
`As first shown in FIG. 7(a), workpiece 60 includes
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`field oxide film 62 and gate oxide film 65 formed on
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`silicon substrate 61. Polysilicon film 66 containing N-
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`type impurities is deposited over the entire surface.
`Then, a resist layer 73 of the novolac resin group having
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`an average thickness of 2 pm and Si02 film 74 are
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`formed over the entire surface. The novolac resin group
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`has the following chemical formula:
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`Page 9 of 10
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`60
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`65
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`Page 9 of 10
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`

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`4,473,437
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`7
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`introducing a gas containing nitrogen as its primary
`constituent into said etching chamber; and
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`7 applying a high frequency electric power between
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`said anode and said cathode while introducing said
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`gas to produce a plasma to thereby selectively etch
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`the organic material layer.
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`2. A dry etching method for etching an organic mate-
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`rial layer according to claim 1 wherein the high fre-
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`quency electric power and the gas pressure in said etch-
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`ing chamber are set to keep the cathode drop voltage
`between said anode and said cathode at or below 1000
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`volts.
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`3. A dry etching method for etching an organic mate-
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`rial layer according to claim 1 wherein the gas contain-
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`8
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`ing nitrogen contains nitrogen and an additive at or
`below 30 mol % of the total.
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`4. A dry etching method for etching an organic mate-
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`rial layer according to claim 1 wherein said gas contains
`at least one selected from the group of N2, N20, NO
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`and N02.
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`5. A dry etching method for etching an organic mate-
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`rial layer according to claim 1 wherein said gas further
`contains at least one additive selected from the group of
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`H2, 502, CO and C02.
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`6. A dry etching method for etching an organic mate-
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`rial layer according to claim 1 wherein said gas consists
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`of a mixture of N2 and 02, the amount of 02 being equal
`to or less than 30 mol %.
`
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`t
`t
`t
`t
`*
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`10
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`15
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`20
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`25
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`30
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`35
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`45
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`50
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`55
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`60
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`65
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