CA1286905C

CA1286905C - Resist process using polysulfone polymers

Info

Publication number: CA1286905C
Application number: CA 184354
Authority: CA
Inventors: Edward Gipstein; Wayne M. Moreau
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1972-11-13
Filing date: 1973-10-26
Publication date: 1991-07-30
Also published as: JPS4979525A; GB1421805A; FR2206527B1; DE2355701A1; FR2206527A1

Abstract

RESIST PROCESS USING POLYSULFONE POLYMERS
Abstract of the Disclosure A resist mask is formed on a substrate by first forming a film of an olefin-sulfone polymer on the surface of the substrate and patterning the film to expose part of the surface. The patterning operation includes exposing portions of the film to degrading radiation.
Background of the Invention This invention relates generally to the formation of resist masks and more particularly to the formation of positive resist masks of olefin-sulfur dioxide polymers such as by electron beam exposure.
The formation of etch resistant positive resist masks using radi-ation degradable polymers and copolymers is described, for example, in United States Patent 3,535,137. A layer of polymer is applied to a sub-strate and the portions of the layer to be removed are exposed to an electron beam or other radiation which acts to reduce the molecular weight of the polymer in the energy struck areas. The polymer in the energy struck areas is then selectively removed with a solvent developer solution which preferentially dissolves the lower molecular weight material leaving a patterned protective layer of polymer covering the unexposed areas.
Such processes are especially suitable for use in the manufacture of high density, micro-miniaturized electronic integrated circuit structures because of the high resolution obtainable by the use of electron beam exposure. In order to decrease the time needed to form circuit structures using electron beam lithography, polymers having increased radiation sensitivity are desirable.

Description

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1 Brief Su~nary of the Invention 2 In accordance with this invention a positive exposure 3 resist process uses as the resist material a class of 4 polymers whose instability has heretofore made them of limite~ practical utility. These po]ymers are polysulfones 6 which can be prepared by reacting olefins with sulfur 7 dioxide.
8 A film of olefin~sulfone polymer is exposed to radiation 9 in a patternwise manner wi~h sufficient energy to cause the exposed portions of the polymer film to degrade so as ~o form 11 a positive resist image. In one aspect of the invention the 12 image is developed using a solvent which preferentially 13 dissolves the exposed portions of the film. In another aspect 14 of the invention $he exposed portions of the film are volatili~ed during the exposure so that the image is 16 simultaneously exposed and developed.
17 The polymers require as little as one-eighth ~he energy 18 dosage nèeded to expose, for example, polymethyl methaorylate 19 and yet are effective to act ~s an etch resistant mask to protect the substra$e in the unexposed areas.
21 Detailed Description 22 Polyme~s suitable for use in the process of the invention 23 are polysulfones having the repeating units of 1:1 olefin 24 monomer to SO2 and 2:1 olefin monomer to SO2 as follows:
~[monomer]n - SO2~ where n = 1 or 2. Preferred, for 26 example, are polymers of the type 27 ~[C(Rl~-C(R2H~]n5O2t where Rl = hydrogen, alkyl, aryl or .

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1 with R2 forn~ a cycloaliphatic ring and where R2 = hydrogen, 2 aryl, alkyl or with Rl forms a cycloaliphatic ring. An example 3 where n=l is poly (butene-l~sulfone); an example where 4 n=2 is poly(styrene sulfone).
The polymers can be formed by reacting olefins with sulfur 6 dioxide. The polymers are described ~Eor example in The 7 Encyclopaedia of Polymer ~echnology "Olefin Sulfur Dioxide 8 Polymers", page 460-485 and in Advances in Macromolecular 9 Chemistry Vol. 1 Polysulphones: Organic and Physical Chemistry by Ivin and Rose pages 335-406. The polymers derive their 11 usefulness in the process of the invention from the relative 12 instability of the sulfone bond and the volatile nature of 13 the degradation-products. This permits degradation of the 14 polymers at low amounts of energy so that the resist image forming process can be carried out rapidly and with less 16 energy requirement. Suitable sulfone polymers are those which 17 are stable above room temperature and whose solubility 18 characteristics permit ~he coating of films.
19 The sulfone polymers preferred for use in the invention are derived from olefins having the general formula 21 RlHC=CHR2 where Rl = Hydrogen, alkyl, aryl or wi~h R~ forms a 22 cycloaliphatic~ring and where R2 = Hydrogen, aryl, alkyl or 23 with Rl forms a cycloaliphatic ring. Examples of such olefins 24 include butene-l, butene-2, 4-bromobutene-1, pentene-l, cyclopentene~ hexene-l, and styrene. Polyisobutylene sulfone, 26 although having~the requisite instability is not sol~ble in 27 organic solvents.

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1 The polymers can be prepared by free radical polymerizations with sulfur dioxide and have molecular weights in the film forming range of from about 5000 to about 5,000,000 (weight average) with molecular weights above about 50,000 preferred.
Films of the polymers are cast from solvent solutions of the polymers containing, for example, from about 1 to about 20~ by weight of solution of the polymer. Suitable solvents should have boiling points which are below the decomposition point of the polymer to permit removal of the solvent from the cast film by heating. Ex-amples of suitable solvents are organic liquids such as, for example, toluene, cyclohexanone, benzene, chlorobenzene, butyl acetate, chloro-form, acetone, dioxane, xylene, methyl ethyl ketone, tetrahydrofuran, cellosolve* acetate, cyclohexanone, dimethyl sulfoxide, and n-butyl acetate.
The films can be cast in various thicknesses of from about 50 angstroms to about 10 microns as is conventional in the art depending upon the intended use of the resist image. For example, about 0.5 to about 2.0 microns thick for an etch process or from about 1.5 to about 3 microns thick for a lift off metallurgy process. The casting process is conventional such as by spinning or dip coat.
It is preferred to prebake the resist film in air or vacuum at a temperature usually above the glass transition temperature of the poly-mer but below the thermal decomposition temperature. The prebake re-moves traces of solvent and anneals out any strains in the film. Suit-able baking temperatures range from about 25C to a few degrees below the polymer decomposition temperature.
The resist is exposed patternwise to radiation such as, for example, ultraviolet, electron beam, x-ray~ and gamma radiation which acts to rapidly degrade the polymer. The sensitivity of the polymers makes them particularly useful in processes employing low energy focussed scanning electron beam radiation of from about 10 to about 30 KeV with charge densities of from about lxlO 6 coul/cm2 to about 1 coul/cm2 as is known in *Trade Mark - ~ -a .
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1 the art. The required dosage can be reduced by heating the polymer during exposure.
The ultimate products of the decomposition of the polysulfone polymers are the monomers, sulfur dioxide7 and various polymer fractions so that, in one aspect of -the invention, by using exposure charge densities of above about 1 x 10~5 coul/cnl2 the image can be simultaneously exposed and developed. In another aspect of the invention the image is solvent developed using solvents which preferentia11y dissolve the lower molecular weight degraded polymer in the exposed portions of the film. Suitable solvents include, for example, toluene, methyl isobutyl ketone, butyl acetate, xylene, cyclohexanone, cellosolve acetate, benzene, chlorobenzene, ethanol, methanol, butanol, cyclohexanol. The development rate can be adjusted by heading or cooling the solvent.
The solvent development is carried out preferably in ~! j - , . . . .

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1 ~ temperature range of from about 10C to about 50C.
2 Three types ~ solvent development processes can be used.
3 In the first a good solvent for both the exposed and 4 unexposed polymer is used to gain speed. The resist thickness is adjusted so that even though there i5 some 6 loss of unexposed resist, ~he remaini.ng unexposed resist 7 film is thick enough to protect the substrate during the 8 subsequent treatment. Alternately, al solvent for the 9 exposed areas only is employed. In the third type of 1~ development, a mixture of a solvent for both the exposed 11 and unexposed polymer and a solvent for the exposed polymer 12 only is used. The optimu~ development time is determined 13 for each case hy the factors of exposure dosa~e, film thickness, 14 solvent system and solvent temperature as known by one skilled in the art.
16 The patt-erned resist image requires no postbake and has 17 high resolutions of less~than the fil~ thickness. For example, la .5Q micron images line and space in a fil~ thi~kness o~ 1.0 :19 micron. The polysulfone resist is imperYious to the acids which are used, for example, in the ~abrication of integrated 21 circuits. The resist films, however, have poor etch resistance :22 to strong alkali (pH 14.0).
23 The resist films can be solvent stripped from the substrate 24 following the etch process. Suitable stripping solvents are solvents such as, for example, aliphatic and aromatic 26 hydrocarbons, ketones~ and acetates which are heated from 27 about 21C to 109C. One solvent can eerve in the proces~ as ~: , . ' ' 1 th~ casting solve~t, the developer, and the stripper by 2 adjusting the processing temperature. ~or example, toluene 3 can be used at room temperature to apply and develop the 4 resist and toluene heated at 50C can be used to strip the resist.
6 The process of the invention is further illustrated by, 7 but is not intended to be limited to the following examples B wherein parts are part~ by weight unless otherwise indicated.
g Example 1 A butene-l-sulfur dioxide copolymer is pxepaxed by the 11 following procedure.
12 Butene-l, 56.1 grams (1.0 mole) and sulfur dioxide, 13 192 grams (3.0 mole~ are condensed into a 2 litre stainless 14 steel Parr stirring autoclave at about -78C. The catalyst, 0.5 grams ~3xlO 3 mole) of azobisisobutyronitrile is then 16 added. The reactor is sealed and heated for 18 hours at about 17 45C. The reactor i5 caoled to room temperature, opened, and 18 the viscous contents are dissolved in chloroform. The 19 chloroform solution is filtered and t~en added dropwise to cold petroleum ether to precipitate a white polymer characterized 21 by elemental analysis, infrared and nuclear magnetic resonance 22 as poly(butene-l-sulfone). -23 - The procedure of Example 1 was repeated to prepare the 24 following sulfone polymers . Poly (cis-butene-2~sulfone);
poly(pentene-l-sulfone~; poly(cyclopentene sulfone);
26 poly(hexene-l-sulfone); and poly(styrene sulfone)~

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1 Example 2 2 Poly-(4-bromobutene-1-sulfone) is prep~red by the 3 followiny procedure. The monomer, 4-bromo~utene-1, 135 4 grams (1.O mole) and sulfur dioxide 192 grams (3.0 mole) were condensed into a 2 litre stainless steel Parr stirring auto-6 clave at a temperature of -78UC and the catalyst 0.8 grams 7 (4.8 x 10 3mole) a~obisisobutyronitrile was added~ The 8 autoclave was sealed and then heated at 45C for 18 hours.
9 The viscous reaction mixture waS thlen poured into 2.5 litres ~ .
of methyl alcohol to precipitata a ~white solid product. The 11 polymer was purified by repeated dissolution and precipitation 12 from chloroform/methanol and then dried at 30C under vacuum 13 to give 8 grams of white polymer. The glass transition 14 temperature was 36C. An elemental analysis was made with the following result calculated for tC~H7BrO2S)n. C, 24.13;
16 H, 3.54; Br, 40.14; S, 16.11; 0, 16.08. Found: C, 24.59, 17 H, 3.71; Br, 39.88; S, 14.37 0, 17.65.
18 The above polymers were further characterized as to their ~ ::
19 glass transltion temperatures, molecular weight, decomposition temperature ~thermo gravimetric analysis using a Du Pont 21 thermobalance) with the results being shown in Table I below:
22 Table I ~
23 Glass Transitio~Onset of Thermal 24 Polymer ~ Temp. (T~)C Decomp. C Mol Wt.
Polybutene- 64 125 MW 3,080k 26 1 sulfone) Mn 1,320k 27 Poly(cis- 47 110 MW 1,180k 28 butene-2 Mn 148k 29 sulfone) ~I 9-72-026 ~ -8 . . .
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1 Glass Transition Onset of Thermal Polymer Temp. (Tg~C _ Decomp. C Mol. Wt.

Poly~4-bromo- 36 110 --butene-l sulfone) Poly(pentene- 68 130 --1 sulfone) Poly(cyclo- 142 129 --pentene sulfone) Poly(hexene-l 60 115 Mw 611,500sulfone) 122 10Poly(styrene 78 130 Mw 366,000 sulfone) Example 3 i Poly-l-butene sulfone (Mol. Wt. Mw 3x106) was spun cast at 3000 r.p.m. to 1.25u (12~500A) thickness on 5000 A thermal oxide of silicon.
The film was prebaked in air at 95C for 1.0 hr. The film was exposed in vacuum with a 0.5u diameter beam to a dose of 3.0x10-6 coul/cm2 at 15 keV.
The film was developed in me~hyl isobutyl ketone for 90 seconds at 21C.
The exposed region was removed by the solvent to yield a positive image.
The net film thickness remaining in the unexposed region was 6200A. The ; sample was rinsed in`~methanol-~and dried at 95C for l~O minutes. The~5000A
oxide layer was etched with buf~ered HF at 21C to yield 0.5u images for diffusion dop;ng. The film was stripped in several minutes with acetone at 40C followed by aicohol and water rinse. A similar procedure was followed to etch images in silicon oxide using the polymers prepared by the procedures of Examples 1 and 2 as summarized in Table II below:

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, ' ' ` , ' ' ' . . ' '~ Wllere ~lltrathin film~ are involved, i.e. 5~.3 microns, loss of unexposed resist d~ring liquid developm~nt must be 3 avoided. One embodiment of the process of the invention 4 takes advantage of the fact that the olefin-sulfur dioxide polymers can be vapori~ed in the exposéd areas at dosage 6 levels of about 1 x 10 5coul/cm2 in vacuum. This is a means 7 of eliminating liquid development beccluse the degraded 8 monomer components of the polymer are removed simultaneously 9 with the exposure.
Although the invention has been particularly shown and 11 described with reference to preferred embodiments thereof, it 12 will be understood by those skilled in the art that the 13 foregoing and other changes in form and details may be made 14 therein without departing from the ~pirit and scvpe of the invention. ~
16 Wbat is clai~ed is:

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Claims

1. A method of forming a resist mask comprising:
forming a film of an olefin-sulfone polymer of a molecular weight of between about 5,000 to about 5,000,000 having repeating units of 1:1 olefin to sulfone or 2:1 olefin to sulfone on the surface of a substrate and patterning said film so as to expose a portion of said surface, said patterning including exposing portions of said film to degrading radiation.

2. The process of Claim 1 wherein the radiation is electrons at an energy of from about 10 to about 30 KeV.

3. The process of Claim 2 wherein the radiation is a focused, scanning electron beam with exposure dosage levels of from about 1 x 10-6 coul/cm2 to about coul/cm2 .

4. The process of Claim 3 wherein the dosage level is at least about 1 x 10-5 coul/cm2.

5. A method as set forth in Claim 1 wherein said radiation is at a dosage level sufficient to degrade said polymer in the exposed portions, and including the step of subsequently removing the exposed portions of said film.

5. Method of Claim 5 wherein removal is accomplished by dissolving the exposed portions with a solvent developer.

7. A method as set forth in Claim 1 wherein said radiation comprises electrons of an energy of from about 10 to about 30 KeV at a dosage level above about 1 x 10-5 coul/cm2 sufficient to degrade the polymer in the exposed portions into its monomeric components 8. A method as set forth in Claim 1 wherein said polymer has the repeating unit.
([C(R1H)-C(R2H)]nSO2) where n = 1 or 2 R1 = hydrogen, alkyl, aryl,or with R2 forms a cycloaliphatic ring R2 = hydrogen, aryl, alkyl or with R1 forms a cycloaliphatic ring; and wherein said radiation comprises electrons at an energy level of from about 10 to about 30 KeV and a dosage of from about 1 x 10 6 coul/cm2 to about coul/cm2 .

9. The process of Claim 8 including the steps of subsequently removing the exposed portions of the film with a solvent developer.

10. The process of Claim 9 in which the polymer is poly (butene-1 sulfone).

11. The process of Claim 9 in which the polymer is poly (cis-butene-2 sulfone).

12. The process of Claim 9 in which the polymer is poly (4-bromobutene-1 sulfone).

13. The process of Claim 9 in which the polymer is poly (pentene-1 sulfone).

14. The process of Claim 9 in which the polymer is poly (cyclopentene sulfone).

15. The process of Claim 9 in which the polymer is poly (hexene-1 sulfone).

16. The process of Claim 9 in which the polymer is poly (styrene sulfone).

17. The process of Claim 8 wherein the dosage level is above about 1 x 10 5 coul/cm2.

18. In a method of recording information whereby a modulated beam of electrons is scanned across the surface of a resist material which becomes more soluble in the developer solvent when impinged upon by the beam of electrons and the resist material is developed with a developer solvent so as to remove the solubilized portions thereof, the improvement which comprises employing as the resist material a film of a copolymer of S02 and an olefin, said copolymer having repeating units of 1:1 olefin to S02 or 2:1 olefin to S02 and a molecular weight of between about 5,000 and about 5,000,000.

19. A method of recording information in the form of a surface relief pattern in a recording medium which comprises scanning a modulated, information-containing beam of electrons across the surface of a resist material which comprises a film of a copolymer of S02 and an olefin on a support, said copolymer having repeating units of 1:1 olefin to S02 or 2:1 olefin to S02 and a molecular weight of between about 5,000 and about 5,000,000.

20. A method of recording information in the form of a surface relief pattern in a recording medium which comprises a. scanning a modulated information-containing beam of electrons across the surface of a resist material which comprises a film of a copolymer of S02 and an olefin on a support, said copolymer having repeating units of 1:1 olefin to S02 or 2:1 olefin to S02 and a molecular weight of between about 5,000 and about 5,000,000 and b. exposing the film to a developer solution to dissolve the portions of the resist film exposed to the electron beam.

21. An information storage medium which comprises a support and an electron beam sensitive film thereon, said film comprising a copolymer of S02 and olefin having information in the form of a surface relief pattern in an electron beam exposed surface, said copolymer having repeating units of 1:1 olefin to S02 or 2:1 olefin to S02 and a molecular weight of between about 5,000 and about 5,000,000.

22. A medium according to Claim 21 wherein the copolymer has vinyl unsaturation.

23. A medium according to Claim 21 wherein the olefin is butene-2.

24. A medium according to Claim 21 wherein the olefin is cyclopentene.

25. The process of Claim 1 wherein the radiation is electrons at an energy of from about 5 to about 30 KeV.

26. In a method of recording information whereby a modulated beam of electrons is scanned across the surface of a resist material which becomes more soluble in the developer solvent when impinged upon by the beam of electrons and the resist material is developed with a developer solvent so as to remove the solubilized portions thereof, the improvement which comprises employing as the resist material a film of a copolymer of S02 and an olefin, said copolymer film having a layer of an electrically conductive material in contact with a surface thereof.

27. A method of recording information in the form of a surface relief pattern in a recording medium which comprises scanning a modulated, information-containing beam of electrons across the surface of a resist material which comprises a film of a copolymer of S02 and an olefin on a support, said copolymer film having a layer of an electrically conductive material in contact with a surface thereof.

28. A method of recording information in the form of a suface relief pattern in a recording medium which comprises a. scanning a modulated information-containing beam of electrons across the surface of a resist material which comprises a film of a copolymer of S02 and an olefin on a support, said copolymer film having a layer of an electrically conductive material in contact with a surface thereof, and b. exposing said resist film to a developer solution to dissolve the portions of said film exposed to the electron beam.

29. A method according to Claim 28 wherein the film is about 350 millimicrons in thickness.

30. A method according to claim 27 in which said olefin is butene-l.

31. A method according to claim 27 in which said olefin is butene-2.

32. A method according to claim 27 in which said olefin is dodecene-1.

33. A method according to claim 27 in which said olefin is cyclopentene.

34. A method according to claim 27 in which said olefin is cyclohexene.

35. A method according to claim 27 in which said olefin is allyl benzene.

36. A method according to claim 27 in which said olefin is l-methyl cyclopentene.

37. A method according to claim 27 in which said olefin is 4-bromo-1-butene.