| PATENT ASSIGNEE'S COUNTRY | Korea |
| UPDATE | 04.00 |
| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | 18.04.00 |
| PATENT TITLE |
Copolymers containing N-vinyllactam derivatives, preparation methods thereof and photoresists therefrom |
| PATENT ABSTRACT |
Copolymers containing N-vinyllactam derivatives protected at 3-position are provided and represented by the following formula. The copolymers are used as a photoresist material suitable for deep uv process so that high sensitivity and resolution can be obtained. In addition, ultrafine circuits can be formed and an exceptional improvement in PED stability can be accomplished by use of the photoresist. ##STR1## |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | 13.03.97 |
| PATENT FOREIGN APPLICATION PRIORITY DATA | This data is not available for free |
| PATENT REFERENCES CITED | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. A phototresist copolymer comprising: N-vinyllactam derivative blocked by a protecting group represented by the following general Formula II: ##STR4## wherein: R.sub.1 is hydrogen, an alkyl group containing 1 to 10 carbon atoms, or a trialkylsilyl group containing 3 to 9 carbon atoms; R.sub.2 is a protecting group; R.sub.3 is H or the same as R.sub.2 ; R.sub.4 and R.sub.5 independently represent --OH, or --OR wherein R is an alkyl group containing 1 to 10 carbon atoms or the same as R.sub.1 ; and m is an integer of 0 to 10; wherein the protecting group is decomposed by an acid to be a functional group soluble in an alkaline developer. 2. A photoresist copolymer according to claim 1 wherein said functional group soluble in an alkaline developer is carboxylic acid, phenol or alcoholic group. 3. A photoresist copolymer according to claim 1 wherein said protecting group is selected from the group consisting of: an alkyl group containing 1 to 10 carbon atoms; a trialklylsilyl group containing 3 to 9 carbon atoms; --OR', --SO.sub.3 R', --CO.sub.2 R', --PO.sub.3 R', --SO.sub.2 R', and --PO.sub.2 R' wherein R' is an alkyl group containing 1 to 10 carbon atoms, cycloalkyl or a cyclic group containing a heteroatom selected from the group consisting of N, O, P and S. 4. A photoresist copolymer according to claim 1 wherein said protecting group is selected from the group consisting of t-butylester, t-butylcarbonate, t-butoxy, t-butoxycarbonyl, tetrahydropyranyloxycarbonyl and tetrahydrofuranyloxycarbonyl. |
| PATENT DESCRIPTION |
BACKGROUND OF THE INVENTION 1. Field of the invention The present invention relates to copolymers containing N-vinyllactam derivatives for use in microlithography, methods for preparing the same and photoresists prepared from the same. More particularly, the present invention is concerned with copolymers containing N-vinyllactam derivatives protected at 3-position, methods for preparing the copolymers, and photoresists suitable for deep uv exposure, which takes advantage of the radiation sensitivity of the copolymer to form a relief image of high sensitivity and resolution by use of deep uv. 2. Description of the Prior Art Generally, a photoresist comprises an alkali-soluble phenol- (or cresol-) formaldehyde novolak resin and a substituted naphthoquinone diazine compound as a photosensitive material (photoactive ingredient), as reported in U.S. Pat. Nos. 3,666,473, 4,115,128 and 4,173,470. While the novolak resin used in such photoresist is dissolved in an aqueous alkali solution, the naphthoquinone photosensitive material acts as a dissolution inhibitor of the resist. However, when a substrate coated with the photoresist is selectively subjected to chemical radiation, the photosensitive agent is induced to be suffered from such a structural modification that the photoresist coating is more solubilized by alkali at exposed region than at unexposed region. By virtue of such difference in solubility, a relief pattern can be formed on the coating of the substrate. That is, when the substrate is immersed in an alkaline developing solution, while the unexposed region is little affected, the exposed region of the photoresist coating is dissolved, forming a pattern. However, the above-mentioned novolak type resists were found to be unsuitable to the stepper utilizing shorter wavelength, which will be described later, because they show high optical absorbance in a range of deep ultraviolet light, 200 to 300 nm. In order to accomplish high sensitivity in the lithography process of semiconductor manufacture, chemical amplification resist has recently been developed. Indeed, the chemical amplification resist has been in the limelight since it was found to have the capacity to increase sensitivity 100-fold more comparing with conventional positive novolak resists. A chemical amplification resist, which takes advantage of the photoacid generator, is generally prepared by formulating the photoacid generator in a matrix polymer of a structure sensitively reacting to the acid. For the mechanism of the photoreaction, when the photoacid generator is exposed to light or irradiated by a high energy beam, such as X-ray beams, and electron beams, protons and strong Bronsted acid, are generated, causing the main chain or the side chain of the matrix polymer to react toward decomposition, crosslinking or a large change in polarity. This action of the acid induces, at the irradiated region, the solubility therein in the given developing solution to be altered, that is, increased or decreased. As a result, fine patterns can be formed. As the photoacid generators, onium salts which are able to respond to light and radiation are known. Typical onium salts are ammonium salts, oxonium salts and sulfonium salts. Recently, it has been reported that organic sulfonic ester can function as a photoacid generator. Available for the matrix polymer which can react with acid are those which are substituted a side chain which can be decomposed into carboxylic acid, phenol or alcoholic functional group by acid. T-Butylester, t-butylcarbonate, t-butoxy and t-butoxycarbonyl groups are known as the suitable substituents. Among these groups, t-butoxycarbonyl group is found to be best in sensitivity. Such an acid-reactive polymer in a protected state or prior to reaction with acid, can be dissolved in organic solvent but not in alkali aqueous solution. However, if the acid-reactive polymer is deprotected by reaction with acid, it is soluble in alkali aqueous solution because its polarity is largely changed. Taking advantage of this principle, the development of chemical amplification resists has been a controversial hot issue in recent years. T-Butoxycarbonyl-protected polyvinylphenol is reported to be one of the possible resins, as introduced in U.S. Pat. Nos. 4,491,628, 4,405,708 and 4,311,782. A recent trend in submicrolithography is to use deep uv (wavelength 200 to 300 nm) as a light source, preferably, a KrF excimer laser of high power (wavelength 248), rather than conventional uv, e.g. g-line (wavelength 436 nm) or i-line (wavelength 365 nm), in order to accomplish high sensitivity and resolution. However, the chemical amplification resists are readily contaminated by the base materials present in air, raising a problem of stability in the post-exposure delay (hereinafter referred to as "PED") at which T-top is formed on the course of fine pattern formation. Various methods have been suggested to improve the PED stability. Among these methods, use of base additives (mainly amines) was found to bring an improvement in PED stability, but was disadvantageous in that it caused a decrease in radiation-sensitivity of photoresist and the base additives were not uniformly distributed in film because of their diffusion into the film surface during processing. SUMMARY OF THE INVENTION Intensive research performed by the present inventors aiming to develop a photoresist for use in submicrolithography which is much improved in PED stability resulted in the finding that the chemical amplification resist polymerized with N-vinyllactam derivatives and styrenic or acrylate derivatives has high glass transition temperatures necessary for processing procedure, and is easily deprotected with little absorption of deep uv in addition to being superior in PED stability. It is a principal object of the present invention to provide a copolymer containing a N-vinyllactam derivative which is blocked at 3-position by a protecting group. It is another object of the present invention to provide a method for preparing the copolymer. It is a further object of the present invention to provide a photoresist prepared from the copolymer. DETAILED DESCRIPTION OF THE INVENTION The present invention related to copolymers containing N-vinyllactam derivatives which are substituted with a protecting group at 3-position, represented by the following chemical formula I: ##STR2## wherein, R.sub.1 is hydrogen, an alkyl group containing 1 to 10 carbon atoms, an aryl group containing 6 to 12 carbon atoms or a trialkylsilyl group containing 3 to 9 carbon atoms; R.sub.2 and R.sub.3 independently represent hydrogen, an alkyl group containing 1 to 10 carbon atoms, an aryl group containing 6 to 12 carbon atoms, a trialkylsillyl group containing 3 to 9 carbon atoms, --OR', --SO.sub.3 R', --CO.sub.2 R', --PO.sub.3 R', --SO.sub.2 R'or PO2R'wherein R'is an alkyl group containing 1 to 10 carbon atoms, cycloalkyl, a cyclic group containing a heteroatom such as N, O, P and S, or an aryl group containing 6 to 12 carbon atoms; R.sub.4 and R.sub.5 independently represent --OH, --OR wherein R is an alkyl group containing 1 to 10 carbon atoms or an aryl group containing 6 to 12 carbon atoms, or the same with R.sub.1 ; R.sub.7 and R.sub.9 independently represent hydrogen, an alkyl group containing 1 to 10 carbon atoms, an aryl group containing 6 to 12 carbon atoms, or a trialkylsillyl group containing 3 to 9 carbon atoms; R.sub.6 and R.sub.8 independently represent an aryl group containing 6 to 20 carbon atoms or an acrylate --COOR"(wherein R" is an alkyl group containing 1 to 10 carbon atoms or an aryl group containing 6 to 12 carbon atoms); m is an integer of 0 to 10; j is a molar ratio ranging from 0.005 to 0.7; and k and 1, which may be the same or different, each are a molar ratio ranging from 0.05 to 0.9. The N-vinyllactam derivatives of the present invention are represented by the following chemical formula II: ##STR3## wherein, R.sub.1 is hydrogen, an alkyl group containing 1 to 10 carbon atoms, an aryl group containing 6 to 12 carbon atoms or a trialkylsilyl group containing 3 to 9 carbon atoms; R.sub.2 and R.sub.3 independently represent hydrogen, an alkyl group containing 1 to 10 carbon atoms, an aryl group containing 6 to 12 carbon atoms, a trialkylsilyl group containing 3 to 9 carbon atoms, or --OR', --SO.sub.3 R', --CO.sub.2 R', --PO.sub.3 R', --SO.sub.2 R' or PO.sub.2 R' wherein R' is an alkyl group containing 1 to 10 carbon atoms, cycloalkyl a cyclic group containing a heteroatom such as N, O, P and S, or an aryl group containing 6 to 12 carbon atoms; R.sub.4 and R.sub.5 independently represent --OH, --OR wherein R is an alkyl group containing 1 to 10 carbon atoms or an aryl group containing 6 to 12 carbon atoms, or the same with R.sub.1 ; and m is an integer of 0 to 10. A copolymer in the present invention is prepared by polymerizing N-vinyllactam derivatives with styrenic or acrylate derivatives. Concrete examples of the N-vinyllactam derivatives used in the present invention include 1-vinyl-2-pyrrolidinone, 1-vinyl-4-butyl-2-pyrrolidinone, 1-vinyl-4-propyl-2-pyrrolidinone, 3-(t-butoxycarbonyl)-1-vinyl-2-pyrrolidinone, 3-(t-butoxycarbonyl)-1vinyl-4-butyl-2-pyrrolidinone, 3-(t-butoxycarbonyl)-1-vinyl-4-propyl-2-pyrrolidinone, 3-(tetrahydropyranyloxycarbonyl)-1-vinyl-5-ethyl-2-pyrrolidinone, 1-vinyl-4-methyl-2-piperidone, 1-vinyl-5ethyl-2-piperidone, 3-(t-butoxycarbonyl)-1-vinyl-4methyl-2-piperidone, 3-(t-butoxycarbonyl)-1-vinyl-4-propyl-2-piperidone, 1-vinyl-2-caprolactam, 1-vinyl-4-butyl-2-caprolactam, 3-(t-butoxycarbonyl)-1-vinyl-2-caprolactam, 3-(t-butoxycarbonyl)-1-vinyl-4-butyl-2-caprolactam, 3-(t-butoxycarbonyl)-1-vinyl-6-methyl-2-caprolactam, 3-(tetrahydropyranyloxycarbonyl)-1-vinyl-5-butyl-2-caprolactam, 3-tetrahydropyranyloxycarbonyl)-1-vinyl-6-propyl-2-caprolactam, 3-(tetrahydrofuranyloxycarbonyl)-1-vinyl-2-pyrrolidinone, 3-(tetrahydrofuranyloxycarbonyl)-1-vinyl-4-butyl-2-pyrrolidinone, and 3-(tetrahydropyranyloxycarbonyl)1-vinyl-6-butyl-2-caprolactam. For copolymer, another monomer is used the examples of which include 4-(t-butoxycarbonyloxy)-1-vinylcyclohexane, 3,5-(di-t-butoxycarbonyloxy)-1-vinylcyclohexane, 4-(tetrahydropyranyloxy)-1-vinylcyclohexane, 4-(tetrahydrofuranyloxy)-1-vinylcyclohexane, 3,5-(ditetrahydropyranyloxy)-1-vinylcyclohexane, 3,5-(ditetrahydrofuranyloxy)-1-vinylcyclohexane, t-butoxycarbonyloxystyrene, styrene, tetrahydropyranyloxystyrene, 4-hydroxystyrene, 4-acetoxystyrene, 3-methyl-4-hydroxystyrene, t-butyl acrylate, t-butyl methacrylate, adamantylacrylate, and adamantylmethacrylate. The copolymers of the present invention may be obtained in bulk polymerization or in a solution polymerization. As a solvent for polymerization, cyclohexanone, methylethylketone, benzene, toluene, dioxane, dimethylformamide alone or a combination thereof may be selected. Usually, the polymerization is carried out in the presence of a polymerization initiator, such as benzoylperoxide, 2,2'-azobisisobutyronitrile (AIBN), acetyl peroxide, lauryl peroxide, or t-butylperacetate. A copolymer of hydroxystyrene, t-butylacrylate and 3-(t-butoxycarbonyl)-1-vinyl-2-caprolactam (hereinafter referred to as "BCVC"), one of the copolymers of the present invention, poly(4-hydroxystyrene-co-t-butyl acrylate-co-BCVC) (hereinafter referred to as "poly(HOST-co-TBA-co-BCVC"), was found to be highly transparent as proven in the experiment in which a film 1 .mu.m thick showed an optical absorbance of 0.12 or lower at deep uv range (200 to 300 nm). Thermal gravity analysis (TGA) showed that poly(HOST-co-TBA-co-BCVC) was stable at up to 180.degree. C. At higher than 180.degree. C., rapid deprotection of t-butoxycarbonyl group occurs, producing 2-methylpropene and CO2 In the presence of acid, the t-butoxycarbonyl group was rapidly deprotected into 2-methylpropene and CO.sub.2 even at 135.degree. C. This fact means that poly(HOST-co-TBA-co-BCVC) is far superior in thermal property by virtue of its high thermal decomposition temperature and is readily deprotected at low temperatures in the presence of acid. Differential scanning calorimetry (DSC) shows that the glass transition temperature of poly(HOST-co-TBA-co-BCVC) is about 165.degree. C. Besides the transparency to deep uv and the ease of deprotection, a great improvement in PED stability is expected for a novel photoresist containing the copolymer of the present invention by virtue of appropriate photosensitivity and the introduction of the base unit (BCVC). All of the polymers of N-vinyllactam derivatives which are protected at 3-position, are high in sensitivity and contrast. Particularly, poly(HOST-co-TBA-co-BCVC), when BCVC is contained at an amount of 1 mole %, shows an appropriate sensitivity of about 10 mJ/cm.sup.2 and a high contrast. As the mole % of BCVC increases, the sensitivity decreases. For example, when BCVC is present in an amount of 2.6 mole %, the resulting copolymer shows a sensitivity of 21 mJ/cm.sup.2. However, this decrease in sensitivity is much less serious than those obtainable from the addition of conventional amine base additives. Ordinary experiment for fine pattern formation confirmed that the copolymers prepared from the N-vinyllactam derivatives and styrenic or acrylate derivatives according to the present invention could be applied for high sensitive chemical amplification resists. The thermal decomposition behavior analysis of the polymers was carried out in nitrogen atmosphere at a temperature elevation of 10.degree. C./min using DSC, commercially available from Perkin Elmer, identified as MODEL 7, and TGA. The inherent viscosities of the polymers were determined in the state of dimethylformamide solution of 0.5 g/dl at 25.degree. C. by use of a glass capillary tube. A better understanding of the present invention may be obtained in light of the following examples which are set forth to illustrate, but are not to be construed to limit, the present invention. |
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| PATENT PHOTOCOPY | Available on request |
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