WO1995010073A1

WO1995010073A1 - Novolak/polyhydroxystyrene copolymer and photoresist compositions

Info

Publication number: WO1995010073A1
Application number: PCT/US1994/011253
Authority: WO
Inventors: M. Dalil Rahman; Mohammad A. Khadim; Ping-Hung Lu
Original assignee: Hoechst Celanese Corporation
Priority date: 1993-10-04
Filing date: 1994-10-04
Publication date: 1995-04-13

Abstract

A novolak/polyhydroxystyrene copolymer having a structure as shwon in formula (I), in which R = H, -CH3, -CH2CH3 or -CH2CH2CH3, n = 2 to 15, a process for producing such a copolymer, a photoresist composition containing such a copolymer, a process for producing such a photoresist and a process for producing a semiconductor device using such a photoresist.

Description

Description Novolak/Polvhvdroxystyrene Copolymer and Photoresist Compositions Background of the Invention The present invention relates to a process for producing a novolak/hydroxystyrene copolymer having a high glass transition temperature (Tg) and to a process for using such a copolymer in light-sensitive compositions. The present invention also relates to a process for making light-sensitive compositions having high thermal stability and which are useful in photoresist compositions. Further, the present invention relates to a process for coating substrates with these photoresist compositions, as well as the process of coating, imaging and developing these light-sensitive mixtures on substrates.

Photoresist compositions are used in microlithography processes for making miniaturized electronic components, such as in the fabrication of computer chips and integrated circuits. Generally, in these processes, a thin film of a photoresist composition is first applied to a substrate material, such as silicon wafers used for making integrated circuits. The coated substrate is then baked to evaporate the solvent in the photoresist composition and to fix the coating onto the substrate. The baked coated surface of the substrate is next subjected to an image-wise exposure to radiation.

This radiation exposure causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the coated surface of the substrate.

Novolak resins are frequently used as a polymeric binder in liquid photoresist formulations. These resins are typically produced by conducting a condensation reaction between formaldehyde and one or more multisubstituted phenols, in the presence of an acid catalyst, such as oxalic acid or maleic anhydride. In producing sophisticated semiconductor devices, it has become increasingly important to provide novolak resins having a high Tg, so that the photoresist compositions will have high thermal stability.

There are two types of photoresist compositions, negative-working and positive-working. When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the creation of a negative image in the coating, thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.

On the other hand, when positive-working photoresist compositions are exposed image-wise to radiation, those areas of the photoresist composition exposed to the radiation become more soluble to the developer solution (e.g. a rearrangement reaction occurs) while those areas not exposed remain relatively insoluble to the developer solution. Thus, treatment of an exposed positive-working photoresist with the developer causes removal of the exposed areas of the coating and the creation of a positive image in the photoresist coating. Again, a desired portion of the underlying substrate surface is uncovered. After this development operation, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. The etchant solution or plasma gases etch that portion of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected and, thus, an etched pattern is created in the substrate material which corresponds to the photomask used for the image-wise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining photoresist layer, after the development step and before the etching step, to increase it's adhesion to the underlying substrate and its resistance to etching solutions. Positive working photoresist compositions are currently favored over negative working resist because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity, after exposure and development. In many manufacturing applications today, resist resolution on the order of less than one micron are necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate.

Summary of the Invention

The present invention relates to a novolak/polyhydroxystyrene (PHS) copolymer having a structure as shown in Formula I and a high Tg, and to a process for producing such a copolymer.

Foπnula I

R = H, -CH₃, -CH₂CH₃, -CH₂CH₂CH₃ n = 2 to 15, preferably 2 to 10

It is known that blends of novolak resin with PHS are not useful in microlithography because the two polymers are not compatible. Physical blending of these two polymers to make a useable polymer has not been successful. The present invention relates to a process for producing a copolymer of a novolak and PHS, having the structure set forth in Foπnula I above. The novolak/PHS copolymers of the present invention have been characterized using carbon-13 NMR spectroscopy. This technique has provided detailed information on the substitution characteristics of various carbon atoms in these polymers. For example, the carbons bearing hydroxy groups are observed in the range 148-156 ppm and the methylene carbons at 25-36 ppm. The methyl groups on the aromatic ring show chemical shifts at about 16 and 20 ppm for the ortho- and para-methyl carbons, respectively. Various aromatic ring carbons are also identified based on their characteristic chemical shifts.

Model compounds using 4-hydroxystyrene and 2,4-dimethylphenol were also examined using carbon-13 NMR spectroscopy. Chemical shifts of carbons in various isomers of these compounds have been assigned to respective carbons, which confirms the structure of Formula I for this copolymer.

The invention also relates to a photoresist composition containing such a novolak/PHS copolymer and to a process for producing such photoresists compositions having high thermal stability. The invention further relates to semiconductor devices using such photoresists containing these novolak resins and one or more photosensitizers, and a process for using such photoresists in producing semiconductor devices.

The subject invention provides a water insoluble, aqueous alkali soluble novolak/PHS copolymer obtained by first condensing with formaldehyde one or more phenolic compounds, such as meta-cresol, para-cresol, ortho-cresol, 3-methyl phenol, 3,5-dimethylphenol, then polymerizing the hydroxystyrene and reacting the resulting novolak and PHS to provide such a copolymer. In a preferred embodiment of the process of the present invention, the polymerization of novolak and PHS, and subsequent crosslinking of the two components in one reaction vessel is extremely important.

The present invention provides a process for producing a novolak/PHS copolymer having a very high Tg. In one embodiment, the process comprises hydrolysing acetoxystyrene with a strong acid, such as hydrochloric acid in a low boiling solvent, such as methanol, then distilling off the excess methanol and hydrochloric acid in the presence of a high boiling solvent, such as dipropyleneglycolmethylether (DPGME). In a preferred embodiment, the process uses the resulting hydroxystyrene and/or polyhydroxystyrene oligomer which is condensed with a mixture of 3-methylphenol and 3,5-dimethylphenol mixed with formaldehyde and an acid catalyst, such as oxalic acid or maleic anhydride. The subject process comprises: a) treating acetoxystyrene having one of the following formulas:

Formula π

wherein R₁=R,=R₃=R₄=H, or ₁₌R₄=C_rC₃ alkyl or O Acetate (Ac), R₂=R₃=H, or R-=C C₃ alkyl, R₂=R₃=R₄=H;

Formula HI

wherein R,=R,=R₃=R₄=H, or

R.=R₃=H, R₂=R₄=C,-C, alkyl or OAc; or Formula IV

wherein R,=R₂=R₄=R₃=H, or

R₁₌R₂=R₄=H, R₃=C_rC₃ alkyl or OAc, or R,=R₂=H, R₃=R₄=C,-C₃ alkyl or OAc, or R,=R₄=H, R₂=R₃=C₁-C₃ alkyl or OAc; with an acid, such as dilute hydrochloric acid (HC1), in a suitable low boiling solvent, such as methanol, preferably under reflux for a period of from about 30 minutes to about 4 hours, preferably about 1 to 3 hours, adding a high boiling solvent, such as DPGME, distilling off the low boiling solvent and acid to provide a solution in the high boiling solvent, comprising hydroxystyrene oligomers; b) charging a mixture of phenols, such as a methyl phenol and a dimethyl phenol, preferably 3-methylphenol and 3,5-dimethylphenol, to the solution of hydroxystyrene oligomers at a temperature less than about 60°C, preferably from about 20°C to about 59°C; and c) condensing the formaldehyde with the mixture of phenols, preferably in the presence of an acid catalyst, most preferably oxalic acid or maleic anhydride, and crosslinking the condensate with the hydroxystyrene oligomers and thereby a water insoluble, aqueous alkali soluble novolak/PHS resin having a high Tg. The present invention further provides a photoresist composition having a very high thermal stability and a process for producing such photoresists. The subject process comprises: a) treating acetoxystyrene having one of the following formulas: Formula π

wherein R₁=R₂=R₃=R₄=H, or

R₁=R₄=C₁-C₃ alkyl or OAc, R₂=R₃=H, or R_!=C_rC₃ alkyl, R₂-=R₃=R₄=H;

Formula HI

wherein R,=R₂=R₃=R₄=H, or

R.=R₃=H, R₂=R₄=C,-C₃ alkyl or OAc; or

Formula IV

wherein R₁=R₂=R₄=R₃=H, or

alkyl or OAc, or R.=R₂=H, R_₁=R₄=C_rC₃ alkyl or OAc, or R,=R₄=H, R₂=R₃=C_rC₃ alkyl or OAc; with an acid in a suitable low boiling solvent, adding a high boiling solvent, and distilling off the low boiling solvent and acid to provide a solution, in the high boiling solvent, comprising hydroxystyrene oligomers; b) charging a mixture of phenols, such as a methyl phenol and a dimethyl phenol, preferably 3-methylphenol and 3,5-dimethylphenol, to the solution of hydroxystyrene oligomers at a temperature less than about 60°C, preferably from about 20°C to about 59°C; c) condensing the formaldehyde with the mixture of phenols and crosslinking the condensate with the hydroxystyrene oligomers and thereby producing a water insoluble, aqueous alkali soluble novolak resin having a high Tg and a structure as shown in Formula I above; and d) providing an admixture of: 1) a photosensitive component in an amount sufficient to photosensitize the photoresist composition, 2) the water insoluble, aqueous alkali soluble novolak PHS copolymer having a high Tg and 3) a suitable photoresist solvent. The invention further relates to a photoresist composition comprising admixture of a novolak/polyhydroxystyrene copolymer having a structure as shown in the following formula:

R = H, -CH₃, -CH₂CH 3' -CH₂CH₂CH n = 2 to 15; a photosensitive co poenet in an amount sufficient to photosensitize the photoresist composition and a suitable photoresist solvent.

The invention further provides a method for producing a semiconductor device by producing a photoimage on a substrate by coating a suitable substrate with a positive working photoresist composition by: a) treating acetoxystyrene having one of the following formulas:

Formula π

wherein R_!=R₂=R₃=R₄=H, or

R₁₌R₄=C_rC₃ alkyl or OAc, R₂=R₃=H, or R,=C_rC₃ alkyl, R,=R₃=R₄=H;

Formula HI

wherein R,=R,=R₃=R₄=H, or

R.=R,=H, R₂=R₄=C C₃ alkyl or OAc; or Formula IV

wherein R₁=R₂=R₄=R₃=H, or

R,=R₂=R₄=H, R₃=C,-C₃ alkyl or OAc, or R₁₌R-=H, R₃=R₄=C_rC₃ alkyl or OAc, or R,=R₄=H, R,=R₃=C C₃ alkyl or OAc; with an acid in a suitable low boiling solvent, adding a high boiling solvent, distilling off the low boiling solvent and acid to provide a solution, in the high boiling solvent, comprising hydroxystyrene oligomers; b) charging a mixture of phenols, such as a methyl phenol and a dimethyl phenol, preferably 3-methylphenol and 3,5-dimethylphenol, to the solution of hydroxystyrene oligomers at temperature less than about 60°C, preferably from about 20°C to about 59°C; c) condensing the formaldehyde with the mixture of phenols and crosslinking the condensate with the hydroxystyrene oligomers and thereby producing a water insoluble, aqueous alkali soluble novolak resin having a high Tg and the structure set forth in Formula I above; d) providing an admixture of: 1) a photosensitive component in an amount sufficient to photosensitize the photoresist composition, 2) the water insoluble, aqueous alkali soluble novolak/PHS copolymer having a high Tg and 3) a suitable photoresist solvent, to produce a photosensitive composition; e) coating a suitable substrate with photosensitive composition; and f) heat treating the coated substrate until substantially all of the photoresist solvent is removed; image-wise exposing the photosensitive composition and removing the image-wise exposed areas of such composition with a suitable developer, such as an aqueous alkaline developer; optionally one may perform a baking of the substrate either immediately before or after the removing step. It has been found that a novolak/PHS copolymer having a very high Tg and the structure set forth in Formula I above can be obtained by condensing formaldehyde with one or more phenolic compounds, in the presence of an acid catalyst, if: 1) one adds hydroxystyrene, or hydroxystyrene oligomer or a mixture thereof and crosslinks the novolak with the hydroxystyrene and/or polyhydroxystyrene or 2) simultaneously polymerizes and crosslinks the novolak and the hydroxystyrene and/or polyhydroxystyrene, such as by mixing the reactants and subsequently polymerizing and crosslinking the reaction mixture, in the same vessel.

Detailed Description of the Preferred Embodiments

Among the photosensitive components that may be utilized to produce photoresist compositions are the 2,1,4- and 2,1,5- diazonaphthoquinone sulfonic acid esters of trihydroxyphenylethane or the tri-, tetra- or hexa- hydroxybenzophenones, well known to those skilled in the art. Suitable low boiling solvents which may be used in the process of the present invention are preferably low boiling (i.e., boil below 100°C) polar organic solvents, such as methanol, ethanol or acetone, suitable high boiling solvents for use in the present process are preferably high boiling (i.e., boil at a temperature at least 25°C above the boiling point of the low boiling solvent) organic solvents having a low polarity, such as DPGME, diglyme or xylene.

The present invention provides a novolak/PHS copolymer, a photoresist composition containing such a copolymer and a process for producing: 1) such a copolymer, 2) such a photoresist and 3) semiconductor devices, using such a photoresist composition. Photoresist compositions having a high thermal stability are formed by providing an admixture of a photosensitizer; the water insoluble, aqueous alkali soluble novolak/PHS copolymer of the present invention and a suitable photoresist solvent. Suitable solvents for such photoresists and for such novolak/PHS copolymers may include one or more of propylene glycol mono-alkyl (e.g. methyl) ether, propylene glycol alkyl (e.g. methyl) ether acetate, ethyl-3-ethoxypropionate, ethyl lactate, mixtures of ethyl-3-ethoxypropionate and ethyl lactate, butyl acetate, xylene, xylenol, diglyme, ethylene glycol monoethyl ether acetate. The preferred photoresist solvents are propylene glycol methyl ether acetate (PGMEA) and ethyl-3- ethoxypropionate (EEP). The solvents may be present in the composition in an amount of up to about 95% by weight of the composition. Other optional ingredients such as colorants, dyes, anti-striation agents, leveling agents, plasticizers, adhesion promoters, speed enhancers, solvents and such surfactants as non-ionic surfactants may be added to the solution of novolak resin, sensitizer and solvent before the photoresist composition is coated onto a substrate. Examples of dye additives that may be used together with the photoresist compositions of the present invention include Methyl Violet 2B (C.I. No. 42535),

Crystal Violet (C.I. 42555). Malachite Green (C.I. No. 42000), Victoria Blue B (C.I. No. 44045) and Neutral Red (C.I. 50040) at one to ten percent weight levels, based on the combined weight of novolak and sensitizer. The dye additives help provide increased resolution by inhibiting back scattering of light off the substrate. Anti-striation agents may be used at up to about a five percent weight level, based on the combined weight of novolak and sensitizer. Plasticizers which may be used include, for example, phosphoric acid tri-(beta-chloroethyl)-ester; stearic acid; dicamphor; polypropylene; acetal resins; phenoxy resins; and alkyl resins, at about one to ten percent weight levels, based on the combined weight of novolak and sensitizer. The plasticizer additives improve the coating properties of the material and enable the application of a film that is smooth and of uniform thickness to the substrate.

Adhesion promoters which may also be used include, for example, beta-(3,4- epoxy-cyclohexyl)-ethyltrimethoxysilane; p-methyl-disilane-methyl methacrylate; vinyltrichlorosilane; and gamma-amino-propyl triethoxysilane up to about a 4 percent weight level, based on the combined weight of novolak and sensitizer. Development speed enhancers that may also be used include, for example, picric acid, nicotinic acid or nitrocinnamic acid up to about a 20 percent weight level, based on the combined weight of novolak and sensitizer. These enhancers tend to increase the solubility of the photoresist coating in both the exposed and unexposed areas, and thus they are used in applications when speed of development is the overriding consideration even though some degree of contrast may be sacrificed; i.e., while the exposed areas of the photoresist coating will be dissolved more quickly by the developer, the speed enhancers will also cause a larger loss of photoresist coating from the unexposed areas. Non-ionic surfactants that may also be used, for example, nonylphenoxy poly(ethyleneoxy) ethanol; octylphenoxy ethanol, at up to about 10% weight levels, based on the combined weight of novolak and sensitizer.

The prepared photoresist solution, can be applied to a substrate by any conventional method used in the photoresist art, including dipping, spaying, whirling and spin coating. When spin coating, for example, the resist solution can be adjusted with respect to the percentage of solids content, in order to provide coating of the desired thickness, given the type of spinning equipment utilized and the amount of time allowed for the spinning process. Suitable substrates include silicon, aluminum, polymeric resins, silicon dioxide, doped silicon dioxide, silicon nitride, tantalum, copper, polysilicon, ceramics, aluminum/copper mixtures; gallium arsenide and other such Group IIW compounds.

The photoresist coatings produced by the described procedure are particularly suitable for application to thermally grown silicon/silicon dioxide-coated wafers, such as are utilized in the production of microprocessors and other miniaturized integrated circuit components. An aluminum/aluminum oxide wafer can also be used. The substrate may also comprise various polymeric resins, especially transparent polymers such as polyesters. The substrate may also have an adhesion promoted layer of a suitable composition, such as one containing hexa-alkyl disilazane.

The photoresist composition solution is then coated onto the substrate, and the substrate is treated at a temperature from about 70°C to about 110°C for from about

30 seconds to about 180 seconds on a hot plate or for from about 15 to about 90 minutes in a convection oven. This temperature treatment is selected in order to reduce the concentration of residual solvent in the photoresist, while not causing substantial thermal degradation of the photosensitizer. In general, one desires to minimize the concentration of solvents and this first temperature treatment is conducted until substantially all of the solvents have evaporated and a thin coating of photoresist composition, on the order of one micron in thickness, remains on the substrate. In preferred embodiment the temperature is from about 85°C to about 95°C. The treatment is conducted until the rate of change of solvent removal becomes relatively insignificant. The temperature and time selection depends on the photoresist properties desired by the user, as well as the equipment used and commercially desired coating times. The coated substrate can then be exposed to actinic radiation, e.g., ultraviolet radiation, a wavelength of from about 300 nm to about 450 nm, x-ray, electron beam, ion beam or laser radiation, in any desired pattern, produced by use of suitable masks, negatives, stencils, templates, etc. The photoresist is then optionally subjected to a post exposure second baking or heat treatment, either before or after development. The heating temperatures may range from about 90°C to about 120°C, more preferably from about 100°C to about 110°C. The heating may be conducted for from about 30 seconds to about 2 minutes, more preferably from about 60 seconds to about 90 seconds on a hot plate or about 30 to about 45 minutes by convection oven.

The exposed photoresist-coated substrates are developed to remove the image- wise exposed areas by immersion in an alkaline developing solution or developed by a spray development process. The solution is preferably agitated, for example, by nitrogen burst agitation. The substrates are allowed to remain in the developer until all, or substantially all, of the photoresist coating has dissolved from the exposed areas. Developers may include aqueous solutions of ammonium or alkali metal hydroxides. One preferred hydroxide is tetramethyl ammonium hydroxide. After removal of the coated wafers from the developing solution, one may conduct an optional post-development heat treatment or bake to increase the coating's adhesion and chemical resistance to etching solutions and other substances. The post- development heat treatment can comprise the oven baking of the coating and substrate below the coating's softening point. In industrial applications, particularly in the manufacture of microcircuitry units on silicon/silicon dioxide-type substrates, the developed subsuates may be treated with a buffered, hydrofluoric acid base etching solution. The photoresist compositions of the present invention are resistant to acid-base etching solutions and provide effective protection of the unexposed photoresist-coating areas of the substrate.

Generally, blending PHS and novolak resin does not work for lithography because these two polymers are not compatible. Their synthetic procedures are very different and, consequently, making a copolymer of PHS and novolak is difficult. Recently we have been successful in making a hydroxystyrene/novolak block copolymer that is superior in lithographic performance to both novolak resins and PHS.

The following specific examples will provide detailed illustrations of the methods of producing and utilizing compositions of the present invention. These examples are not intended, however, to limit or restrict the scope of the invention in any way and should not be construed as providing conditions, parameters or values which must be utilized exclusively in order to practice the present invention.

Example 1 4- Acetoxystyrene monomer (ASM) ( Formula II) (15g) was placed in a four necked flask equipped with a condenser and a dropping funnel. Methanol (lOOg), water (25g) and HCl (lg) were added under reflux, with stirring, for 2 hours. DPGME (75g) was added; atmospheric distillation was started to remove excess methanol, HCl and water, at a temperature up to 110°C. MCC 235 (a mixture of 6.3 moles of 3-methyl phenol and 3 moles of 3,5-dimethyl phenol) (lOOg), AIBN (azo- bis-isobutyronitrile) (0.05g), and oxalic acid (l.Og) were added. Formaldehyde solution (58.94 g, C/F ratio 1/0.755) was added dropwise over a period of 90 minutes, at 95°C. The reaction was allowed to continue for 7 hours. Excess formaldehyde and water were distilled off. When the temperature reached 190°C, a vacuum was applied to remove unreacted phenols and DPGME. When the temperature reached 235°C and pressure 20 mm, the vacuum was released and the resin was poured into a tray.

Examples 2 to 5 The procedure of example 1 was repeated to make the novolak/PHS copolymers of example 2-5 with high Tg as shown in Table 1 below.

Table 1 : Properties of Novolak/PHS Copolymer

Examples HCHO A5M(s) RMW MWfGPC D.Rate Is e/ 100s Phenol μm/min

1 0.755 15.0 10.5 5032 4.1 118

2 0.800 15.0 14.3 8874 1.0 127

3 0.755 15.0 10.8 5529 3.1 117

4 0.755 15.0 10.0 5123 3.9 115

5* 0.755 15.0 10.0 5978 4.3 112

Oxalic Acid 1% used as catalyst *Maleic Anhydride 1% used as catalyst. RMW - Relative Molecular Weight D.Rate - Dissolution Rate Tg - Glass Transition Temperature (°C) MW - Molecular Weight by GPC

Example 6 A photoresist solution was prepared as follows: Into 72g of PGMEA, 22.96g of the novolak/PHS copolymer of example 1 was added. A mixture of photosensitizers, 5.04g of 2,1,5- (50%) and 2,1,4- (50%) diazonaphthoquinone sulfonic acid ester (95% esterified) of trihydroxyphenylethane was added. 25.2mg of surfactant (FC-430 available from 3M) was added. The photoresist solution was spin coated, using standard techniques, onto a silicon wafer at a constant speed, to obtain a layer of photoresist having an initial thickness of 1.29 μm. The film was soft baked on a hot plate at 100°C for 60 seconds. The film was exposed using a 0.54 NIKON i-line stepper and baked at 120°C for 60 seconds. It was puddle developed for 1 minute at 25°C, using AZ300 MIF developer available from Hoechst Celanese Corporation. The photospeed, resolution, depth of focus (DOF), and thermal stability were determined. The results are shown in Table 2 below.

Examples 7 to 11 A photoresist formulation was prepared as described in example 6 using the novolak/PHS copolymer of examples 2 to 5, respectively, and the photospeed, resolution, DOF and thermal stability were determined. The results are shown in Table 2 below.

Table 2: Lithographic Performance of Novolak/PHS Copolymer

Examples EofmJ/sq.cm) Ep(mJ/sq.cm . Resolution DOR0.5um . Thermal Stability (!C)

6 81 140 0.4μm 1.2 125

7 162 295 0.5μm 1.0 135

8 94 170 0.5μm 1.2 125

9 79 130 0.4μm 1.2 125

10 81 150 0.5μm 1.2 125

11 108 200 0.4μm 1.2 125

Eo = Energy required to clear the resist film at a given process condition. Ep = Energy required to print the defined pattern at a given process condition.

Example 12 Acetoxystyrene (lOg) was placed in a four necked flask equipped with a condenser and a dropping funnel. Methanol (lOOg), water (25g) and HCl (lg) were added with reflux and stirring over a period of 2 hours. DPGME (75g) was added; atmospheric distillation was started to remove excess methanol, HCl and water, at a temperature up to 100°C. MCC 235 (lOOg), AIBN (0.05g), and oxalic acid (l.Og) were added. Formaldehyde solution (57.05g, C/F ratio 1/0.755) was added dropwise over a period of 90 minutes, at 95°C. The reaction was allowed to continue for 7 hours. Excess formaldehyde and water were distilled off. When the temperature reached 190°C, a vacuum was applied to remove unreacted phenols and DPGME. When the temperature reached 235°C and pressure 20 mm, the vacuum was released and the resin was poured into a tray. RMW of this resin was 8.8, D.rate = 5.4 μm/min., Tg = 108°C and MW = 4241.

Example 13 Photoresist solution was prepared as follows: A total of 22.96g of the novolak/PHS copolymer of example 2 and example 12 was blended in a 1:1 ratio.

This blended novolak/PHS copolymer was added to 72g of PGMEA. A mixture of photosensitizers [5.04g of 2,1,5- (50%) and 2,1,4- (50%) diazonaphthoquinone sulfonic acid ester (95%) of trihydroxyphenylethane] was added. 25.2mg of surfactant (FC-430 available from 3M) was then added. The photoresist solution was spin coated, using standard techniques, onto a silicon wafer at a constant speed, to obtain a layer of photoresist having an initial thickness of 1.29 μm. The film was soft baked on a hot plate at 100°C for 60 seconds. The film was exposed by a 0.54 NIKON i-line stepper and baked at 120°C for 60 seconds. It was developed for 1 minute at 25°C, using an AZ300 MIF developer puddle. The photospeed, resolution, DOF, and thermal stability were determined. The results were as follows:

Eo(mJ/sq.cm) 108

Ep(mJ/sq.cm) 200

Resolution 0.4 μm

DOF(0.5μm) 1.2

Thermal Stability 125°C

Claims

Having described our invention what we desire to claim is:

1. A novolal /polyhydroxystyrene copolymer having a structure as shown in the following formula:

R = H, -CH₃, -CH,CH₃ or -CH,CH,CH₃ n = 2 to 15.

2. The copolymer of claim 1, wherein n = 2 to 10.

3. A process for producing a novolak/PHS copolymer which comprises: a) treating acetoxystyrene having one of the following formulas:

wherein R₁=R₂=R₃=R₄=H, or

R,=R₄=C₁-C₃ alkyl or OAc, R₂=R₃=H, or R_jsC_j-Cj alkyl, R,=R₃=R₄=H;

wherein R,=R,=R₃=R₄=H, or

R,=R₃=H, R₂=R₄=C_rC₃ alkyl or OAc; or

wherein R,=R₂=R₄=R₃=H, or

R₁₌R-=R₄=H, R,=C,-C, alkyl or OAc, or R-=R₂=H, R₃=R₄=C,-C₃ alkyl or OAc, or R,=R₄=H, R,=R₃=C_rC, alkyl or OAc; with an acid, in a low boiling solvent; adding a high boiling solvent; distilling off the low boiling solvent and acid to provide a solution, in the high boiling solvent, of hydroxystyrene oligomers; b) charging a mixture of phenols to the solution of hydroxystyrene oligomers, at a temperature less than about 60°C; c) condensing the formaldehyde with the mixture of phenols, in the presence of an acid catalyst and crosslinking the condensate with the hydroxystyrene oligomers and thereby producing a water insoluble, aqueous alkali soluble novolak/PHS resin.

4. The process of claim 3, wherein the low boiling solvent is a polar organic solvent having a boiling point below 100°C.

5. The process of claim 4, wherein the low boiling solvent is methanol, ethanol or acetone.

6. The process of claim 3, wherein the high boiling solvent is an organic solvent having a low polarity and a boiling point at least 25°C above that of the low boiling solvent.

7. The process of claim 6, wherein the high boiling solvent is DPGME, diglyme or xylene.

8. The process of claim 3, wherein the acetoxystyrene has formula I.

9. The process of claim 3, wherein the acetoxystyrene has formula II.

10. The process of claim 3, wherein the acetoxystyrene has formula III.

11. A photoresist composition comprising: 1) novolak/polyhydroxystyrene copolymer having a structure as shown in the following formula:

R = H, -CH₃, -CH₂CH₃ or -CH,CH₂CH₃ n = 2 to 15; 2) a photosensitive component in an amount sufficient to photosensitize the photoresist composition and 3) a photoresist solvent. 99

12. The photo composition of claim 11, wherein n = 2 to 10.

13. A process for producing a photoresist composition which comprises: a) treating acetoxystyrene having one of the following formulas:

wherein R,=R₂=R₃=R₄=H, or

R,=R₄=C,-C₃ alkyl or OAc, R₂=R₃=H, or R^C.- alkyl, R,=R₃=R₄=H;

wherein Rι=R₂=R₃=R₄=H, or

R_I=R-=H, R₂=R₄=C C₃ alkyl or OAc; or

3)

wherein R,=R₂=R₄=R₃=H, or

R₁=R₂=R₄=H, R₃=C,-C₃ alkyl or OAc, or R,=R₂=H, R₃=R₄=C,-C₃ alkyl or OAc, or R₂=R₄=H, R₂=R₃=C,-C₃ alkyl or OAc; with an acid in a suitable low boiling solvent, adding a high boiling solvent, and distilling off the low boiling solvent and acid to provide a solution, in the high boiling solvent, comprising hydroxystyrene oligomers; b) charging a mixture of phenols to the solution of hydroxystyrene oligomers at a temperature less than about 60°C; c) condensing the foπnaldehyde with the mixture of phenols and crosslinking the condensate with the hydroxystyrene oligomers and thereby producing a water insoluble, aqueous alkali soluble novolak resin; d) providing an admixture of: (1) a photosensitive component in an amount sufficient to photosensitize the photoresist composition, (2) the water insoluble, aqueous alkali soluble novolak/PHS copolymer and (3) a suitable photoresist solvent.

14. The process of claim 13, wherein the low boiling solvent is a polar organic solvent having a boiling point below 100°C.

15. The process of claim 14, wherein the low boiling solvent is methanol, ethanol or acetone.

16. The process of claim 13, wherein the high boiling solvent is an organic solvent having a low polarity and a boiling point at least 25°C above that of the low boiling solvent.

17. The process of claim 16, wherein the high boiling solvent is DPGME, diglyme or xylene.

18. The process of claim 13, wherein the acetoxystyrene has formula I.

19. The process of claim 13, wherein the acetoxystyrene has formula II.

20. The process of claim 13, wherein the acetoxystyrene has formula III.

21. A method for producing a semiconductor device by producing a photoimage on a substrate by coating a substrate with a photoresist composition by: a) treating acetoxystyrene having one of the following formulas:

wherein R_!=R₂=R₃=R₄=H, or

R_I=R₄=C,-C₃ alkyl or OAc, R,=R₃=H, or R_!=C_rC₃ alkyl, R,=R,=R₄=H;

wherein R₁=R₂=R₃=R₄=H, or

R,=R₃=H, R₂=R =C,-C₃ alkyl or OAc; or

wherein R,=R₂=R =R_;i=H, or

R.=R₂=R₄=H, R₃=C,-C₃ alkyl or OAc, or R.=R₂=H, R₃=R₄=C_rC₃ alkyl or OAc, or R₂=R₄=H, R₂=R₃=C₁-C₃ alkyl or OAc; with an acid in a suitable low boiling solvent, adding a high boiling solvent, distilling off the low boiling solvent and acid to provide a solution, in the high boiling solvent, comprising hydroxystyrene oligomers; b) charging a mixture of phenols to the solution of hydroxystyrene oligomers at temperature less than about 60°C; c) condensing the formaldehyde with the mixture of phenols and crosslinking the condensate with the hydroxystyrene oligomers and thereby producing a water insoluble, aqueous alkali soluble novolak resin; d) providing an admixture of: (1) a photosensitive component in an amount sufficient to photosensitize the photoresist composition, (2) the water insoluble, aqueous alkali soluble novolak/PHS copolymer and (3) a suitable photoresist solvent, to produce a photosensitive composition; e) coating a suitable substrate with the photosensitive composition; f) heat treating the coated substrate until substantially all of the photoresist solvent is removed; image-wise exposing the photosensitive composition and removing the image-wise exposed areas of such composition with a suitable developer.

22. The process of claim 21, wherein the low boiling solvent is a polar organic solvent having a boiling point below 100°C.

23. The process of claim 22, wherein the low boiling solvent is methanol, ethanol or acetone.

24. The process of claim 21, wherein the high boiling solvent is an organic solvent having a low polarity and a boiling point at least 25°C above that of the low boiling solvent.

25. The process of claim 24, wherein the high boiling solvent is DPGME, diglyme or xylene.

26. The process of claim 21, wherein the acetoxystyrene has formula I.

27. The process of claim 21, wherein the acetoxystyrene has formula II.

28. The process of claim 21, wherein the acetoxystyrene has formula III.