Resist composition and process for forming resist pattern thereby

Abstract: A resist composition for forming a upper resist layer and a process for forming a pattern thereby are disclosed. This resist comprises an azide compound and a polyacrylic copolymer of the following formula (1): wherein, R₁ means CH₃ , CF₃ , CN, CH₂OH, or CH₂CO₂R, wherein R means an alkyl having 1 to 5 carbon atoms R₂ means a hydrocarbon radical having at least one Si, R₃ means OH, O-C(CH₃), NH₂ , or NHCH₂OH, and, a ratio of n to m is more than 0 and is 1 or less than 1. Whereby a finely-resolved resist pattern is obtained by a preset process for forming the resist pattern.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive-working resist composition for use in double layer resist processing. 2. Description of the Related Art Due to the necessity for treating a large amount of information at a high speed an integrated semiconductor device, which plays a main role in an information treating device, has been developed and large-scale integrated circuits (LSI) and very large-scale integrated circuits (VLSI) are now in practical use. This integration is carried out by a miniaturization of unit elements and the use of a minimum line spacing of the wiring pattern on an order of submicrons, and further, a multi-layer wiring process is carried out. Therefore, many minute steps are formed on a semiconductor wafer when producing integrated circuits. When manufacturing a semiconductor integrated circuit, a resist is coated on the semiconductor substrate, and then selectively exposed and developed to dissolve the exposed portions or unexposed portions, and finally, a through hole is formed. Thereafter, a photo-etching technique (photolithography or electron-beam lithography) is conducted, whereby a conductive film or an insulating film is etched by dry-etching. Therefore, as a process for precisely forming a fine pattern while neglecting the influence of the steps, a multi-layer resist having a double-layer or triple-layer structure has been employed. Especially, a double-layer resist process having fewer process steps is generally employed. In a double-layer resist process, a novolac resist is coated on a substrate having steps, as a lower-layer resist providing a level surface, followed by coating a upper-layer resist thereon, which resist has an oxygen-plasma resistance and a high resolution. Many kinds of double-layer resist have been proposed, but an electron-beam resist which can provide a resolution on an order of sub-microns has not been developed. As a positive resist having a superior oxygen-plasma resistance, a copolymer having the following formula (1) was proposed by the present inventors (see Japanese Application No. 2-61552). wherein, R 1 means CH 3 , CF 3 , CN, CH 2 OH, or CH 2 CO 2 R, wherein R means an alkyl having 1 to 5 carbon atoms R 2 means hydrocarbon group having at least one Si, R 3 means OH, O-C(CH 3 ), NH 2 , or NHCH 2 OH, and, a ratio of n to m is more than 0 and is 1 or less than 1. The molecular weight of the copolymer is from 20,000 to 1,500,000. A cross-linking of this resin at the R 3 position is caused by heating, but since it is necessary to enlarge the ratio of α-substituted acrylate having Si as a copolymer to improve the oxygen-plasma resistance, the cross-linking density becomes too low. Accordingly, the resolution is poor, and thus it is difficult to produce a fine pattern of 0.5 µm or less. It is difficult to resolve the sub-micron pattern for the resist of the above formula (1). Therefore, there is a need to improve the resolution to make it possible to produce a pattern of 0.5 µm or less. JP-A-60138543 and JP-A-63307450 disclose a process for forming a resist pattern, wherein the resist is first cross-linked by heating a blend comprising an azide and an acrylate copolymer, and then selectively exposed to an electron beam in order to render soluble the exposed areas. The exposed areas are either vaporized or dissolved in a development solution. Summary of the Invention A novel resist composition according to this invention comprises a copolymer of formula (1) as defined above and, based on the weight of the copolymer, 0.1 to 30% by weight of an azide compound of any of formulae (2) to (7) and A process according to the invention, for forming a multi-level resist pattern, comprises the steps of: coating a semiconductor substrate with a resist, to form a lower resist layer thereon; coating the lower resist layer with the novel resist composition defined above, to form an upper resist layer thereon; heating the substrate, at a temperature above the decomposition temperature of the azide compound and below the decomposition temperature of the copolymer, to cause cross-linking of the upper resist layer; exposing the resist to a predetermined pattern of electron beam radiation, to form a latent image in the resist layer corresponding to the radiation pattern; and developing the pattern-wise exposed resist layer with a developer, to form an upper resist pattern. Description of the Invention Conventionally, the copolymer of formula (1) is heated (baked) to cause cross-linking, while splitting off R 3 as OH or NH 2 . When the novel composition is heated (hard-baked) at a temperature higher than the decomposition temperature of the azide compound but lower than the decomposition temperature of the copolymer, the cross-linking density is increased, while forming the cross-linkage at a position other than that of R 3 . The temperature of heating is preferably above 130°C, and more preferably above 180°C. The azide compound is decomposed by the heat-treatment. Further, when the highly cross-linked copolymer is subjected to electron beam radiation, the main chain is broken and becomes soluble in a solvent, as in the prior art. However, the polymer in the unexposed region is soluble, so that a strong developing agent such as methyl isobutyl ketone (MIBK) can be used, and resolution of a sub-micron pattern can be obtained. The amount of the azide is 0.1 to 30% by weight of the copolymer. If the amount is less than 0.1%, the desired results cannot be obtained, and if the amount is more than 30%, the molecular weight becomes too large due to extensive cross-linking, so that complete decomposition cannot be obtained even by electron beam radiation, so that a positive resist pattern cannot be obtained. The invention will be more clearly understood with reference to the following examples. Example 1: As the copolymer of the general formula (1), the following copolymer (M.W. = 55 x 10 4 ) of the formula (8) was employed. Also, as an azide compound, 4,4'-diazide chalcone of the formula (2) was used and this azide was added to the copolymer at the ratio of 5 weight% based on the polymer, then mixed with a MIBK solution at a ratio of 30 grams/ℓ to form a resist. This resist was coated on a silicon wafer to a thickness of about 3000 Å, then heated on a hot plate for eight minutes at 220°C. Thereafter, the formed resist film was exposed to an electron beam with an accelerated voltage of 20 KeV, and developed for three minutes in MIBK, 0.4 micron patterns were resolved. The sensitivity (E th) was 14.4 µC/cm 2 . Examples 2 - 7: As a copolymer component, the copolymer of the formula (8) was used, and as an azide compound, the compounds of the formulas (3) to (7) were respectively used, to obtain a resist in the same way as in Example 1. The thus obtained resist was coated on a silicon wafer to a thickness of about 3000 Å and a similar procedure as in Example 1 effected, to obtain similar effects. Example 8: As a copolymer component, the copolymer (M.W. = 12 x 10 4 ) of the following formula (9) was used: Also, as an azide compound, 4,4'-diazide chalcone of the formula (2) was employed, and five % by weight based on the copolymer of the azide compound was mixed with the copolymer to form a resist in the same way as in Example 1. The thus obtained resist was coated on a silicon wafer to a thickness of 3000 Å, followed by heating on a hot-plate for eight minutes at a predetermined temperature. Then, the resist layer was exposed to an electron beam at an accelerated voltage of 20 KeV, and developed for three minutes in MIBK, 0.3 micron patterns were resolved. The sensitivity (E th) was 11.2 µC/cm 2 . Example 9: As a copolymer, the copolymer (M.W. = 24 x 10 4 ) of the following formula (10) was used: As an azide compound, 4,4'-diazide chalcone was used. In accordance with the procedure described in Example 1, a finely resolved pattern of 0.45 µm having a sensitivity (E th) of 16.0 µC/cm 2 was obtained. Examples 10 - 14: As a copolymer, the copolymer of the formula (9) was used and as a diazide compound, the compounds of the formulas (3) through (7) were respectively used to form a resist. Using the same procedure as described in Example 1, a sub-micron pattern was obtained. Examples 15 - 19: As a copolymer, the copolymer of the formula (10) was used, and as a diazide compound, the compounds of the formulas (3) through (7) were respectively used to form a resist. Using the same procedure as described in Example 1, a sub-micron pattern was obtained. Example 20: A novolac-type photo resist (manufactured by Nagase Sangyo Co., Ltd.) 3 was coated to a thickness of 2.0 µm on a substrate 1, with a step having an aluminum wire 2 therein (Fig. 1A, Fig. 1B), and baked at a temperature of 220°C in an oven to form a lower resist layer. Then, a 30 g/ℓ MIBK resist solution 4 for an upper layer comprising the copolymer of the formula (8) and 5 weight% of 4,4'-diazide chalcone was coated on the substrate 1 (Fig. 1C), followed by baking at a temperature of 220°C on a hot plate for eight minutes. The thus formed resist layer was exposed to an electron beam at an accelerated voltage of 20 KeV to form a 0.4 µm line and space pattern (Fig. 1D), which was developed in MIBK for two minutes to obtain an upper resist pattern 5 (Fig. 1E). This upper resist layer was resistant to oxygen plasma. The lower resist layer was etched by oxygen-reactive ion etching (RIE) using the thus-obtained upper resist layer as a mask, to form a 0.4 µm line and space lower resist pattern (Fig. 1F). The substrate 1 was dry-etched using the upper and lower resists layers as a mask (Fig. 1G), followed by removing both resist layers to obtain a contact hole 6 (Fig. 1H). Examples 21 - 22: The compounds of the formulas (9) and (10) were respectively used, and a similar procedure as described in Example 1 was carried out, whereby a finely figured-pattern was transferred to a lower resist layer.

Claims: A resist composition, which comprises: a copolymer of formula (1): wherein R 1 is CH 3 , CF 3 , CN, CH 2 OH or CH 2 CO 2 R, wherein R is C 1-5 alkyl, R 2 is a hydrocarbon radical having at least one Si atom, R 3 is OH, OC(CH 3 ) 3 , NH 2 or NHCH 2 OH, and m and n are each integers where n/m ≤1; and based on the weight of the copolymer, 0.1 to 30% by weight of an azide compound of any of formulae (2) to (7): and A process for forming a multilevel resist pattern, which comprises the steps of: coating a semiconductor substrate with a resist, to form a lower resist layer thereon; coating the lower resist layer with a resist composition according to claim 1, to form an upper resist layer thereon; heating the substrate, at a temperature above the decomposition temperature of the azide compound and below the decomposition temperature of the copolymer, to cause cross-linking of the upper resist layer; exposing the resist to a predetermined pattern of electron beam radiation, to form a latent image in the resist layer corresponding to the radiation pattern; and developing the pattern-wise exposed resist layer with a developer, to form an upper resist pattern. A process according to claim 2, which additionally comprises baking the lower resist layer. A process according to claim 2 or claim 3, wherein said temperature is above 130°C.

Inventors: KOTACHI AKIKO, TAKECHI SATOSHI, KOTACHI, AKIKO, TAKECHI, SATOSHI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1991
Main classification: G03F7
IPC codes: G03F7