Photoresist composition

Abstract: A chemical amplifying type positive photoresist composition, excellent in various properties, and not form necking at the potion where the bottom antireflective coating and the resist film contact, which comprises (A) a resin which is converted to alkali-soluble from alkali-insoluble or alkali slightly soluble by the action of an acid, (B) an acid generator, (C) a tertiary amine compound and (D) a diphenyl sulfone compound, and a fine photoresist pattern can be formed in high precision using the photoresist composition.

Description: The present invention relates to a photoresist composition suitable for lithography utilizing high-energy radiation such as a far ultraviolet radiation including eximer laser, electron beam or X-ray radiation. Recently, with development of higher integration of an integrated circuit, formation of a submicron pattern is required. Eximer laser lithography has attracted special interest for such a requirement, particularly because it enables production of 64 MDRAM and 256 MDRAM. As a resist suitable for such eximer laser lithography process, a so-called chemical amplifying type resist has been suggested which utilizes an acid catalyst and chemical amplifying effect. In the chemical amplifying type resist, solubility of portion irradiated with a radiation in an alkaline developer is changed through a reaction utilizing an acid catalyst generated from an acid generator in the irradiated portion, and by this, a positive or negative pattern is obtained. In the chemical amplifying type positive resist, an acid generated in the irradiated portion diffuses by post heat treatment (post exposure bake: hereinafter, abbreviated as PEB), and acts as a catalyst for changing solubility of the irradiated portion in a developer. Such a chemical amplifying type resist has a defect that the acid generator is liable to be decomposed by the light reflected from the substrate. For example, when the irradiated light is reflected to a lateral direction due to a difference in level on the substrate, the reflected light of a lateral direction causes so-called halation effect, which makes the line width of a part of the pattern narrower and makes it difficult to obtain a defined line width of the pattern. A bottom antireflective coating is generally used as the undercoating in order to suppress such halation effect. That is, generally, a bottom antireflective coating is formed on the substrate, and a resist film is formed on it, followed by irradiation and developing to form a pattern. As a bottom antireflective coating, e.g. "DUV-18" manufactured by Brewer Science is known. However, there is a defect that a bottom antireflective coating causes a phenomenon called "necking" in which the pattern become narrower at the portion where the bottom antireflective coating and the resist film contact, and the pattern is liable to fall down or resolution lowers. The object of the present invention is to provide a chemical amplifying type positive photoresist composition excellent in various properties such as sensitivity, resolution, film retention ratio, applicability and heat resistance, particularly excellent in profile on a bottom antireflective coating. This object could be achieved by the provision of a positive photoresist composition comprising (A) a resin which is obtainable by at least partially protecting the phenolic hydroxyl groups in an alkali-soluble resin having a phenol skeleton with 1-ethoxyethyl groups, and which is converted to alkali-soluble from alkali-insoluble or only slightly alkali soluble by the action of an acid, (B) an acid generator, (C) a tertiary amine compound and (D) a diphenyl sulfone compound. The resin (A) which is a main component of the photoresist component is by itself alkali-insoluble or only slightly alkali soluble, and becomes alkali-soluble by a chemical reaction caused by the action of an acid. There is used a resin obtained by protecting at least a part of the phenolic hydroxyl groups in an alkali soluble resin having a phenol skeleton with 1-ethoxyethyl groups which have solution inhibiting ability against alkaline developers and are unstable against acid. Examples of the alkali soluble resin used for producing the resin (A) include novolak resins, polyvinylphenol resins, polyisopropenylphenol resins, copolymers of vinylphenol with styrene, acrylonitrile, methyl methacrylate or methyl acrylate, and copolymers of isopropenylphenol with styrene, acrylonitrile, methyl methacrylate or methyl acrylate. Positional relation between a hydroxy group and a vinyl group or an isopropenyl group in vinylphenol and isopropenylphenol is not particularly limited, however, in general, p-vinylphenol or p-isopropenylphenol is preferred. Hydrogen may also be added to these resins for improving transparency. For example an alkyl group or alkoxy group may be introduced into a phenol nucleus of the above-described resins, as long as the resulting resin is alkali-soluble. Among these alkali soluble resins, polyvinylphenol-based resins, namely a homopolymer of vinylphenol or copolymer of vinylphenol with other monomer are preferably used. The ratio of the phenolic hydroxyl groups substituted by the protecting group to the all phenolic hydroxyl groups in the alkali soluble resin (protective group introducing ratio) is preferably from 10 to 50%, in general. Particularly preferred is a resin obtained by partially protecting a phenolic hydroxyl group in the polyvinylphenol-based resin with a 1-ethoxyethyl group. The acid generator (B) can be selected from various compounds which generate an acid by irradiation to the substance itself or a resist composition containing the substance. The acid generator (B) can be used as a mixture of two or more compounds. Examples thereof include onium salts, organic halogen compounds, compounds having a diazomethanedisulfonyl skeleton, disulfone compounds having an aromatic group, orthoquinone diazide compounds and sulfonic acid compounds. In the present invention, as the acid-generator, compounds having a diazomethanedisulfonyl skeleton are preferably used. Examples of the compounds having a diazomethanedisulfonyl skeleton as the acid generator include bis(benzenesulfonyl)diazomethane, bis(4-chlorobenzenesulfonyl)diazomethane, bis(p-toluenesulfonyl)diazomethane, bis(4-tert-butylbenzenesulfonyl)diazomethane, bis(2,4-xylenesulfonyl)diazomethane and bis(cyclohexanesulfonyl)diazomethane. A tertiary amine compound(C) is added to the composition of the present invention as a quencher. It is known that performances of a chemical amplifying type resist change depending on the standing time from irradiation to PEB, so-called time delay effect, which is caused by deactivation of an acid generated in a resist by a small amount of ammonia or amines existing in environmental atmosphere. The tertiary amine compound(C) is used in order to prevent the deactivation of an acid. It is preferable that the tertiary amine compound (C) is a compound which does not vaporizes at pre-baking temperature, so that it remains in a resist film formed on a substrate even after pre-baking of the resist film and exhibits its effect. Therefore, in general, a compound having the boiling point of 150°C or higher is used as the tertiary amine compound (C). In addition to the above-described resin (A), the acid generator (B) and the tertiary amine compound (C), the photoresist composition of the present invention comprises (D) a diphenyl sulfone compound. Necking on a bottom antireflective coating is suppressed by incorporating the diphenyl sulfone compound (D). The diphenyl sulfone compound (D) has two phenyl groups which are linked through a sulfonyl group(-SO 2 -). The two phenyl groups may be same to or different from each other and may be optionally substituted. The diphenyl sulfone compound (D) may be, for example, a compound represented by the following formula (I): wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 each independently represent hydrogen or a group which can bond to phenyl, provided that R 1 and R 10 may optionally be linked directly. Examples of the group which can bond to phenyl include alkyl having 1-4 carbon atoms, alkoxy having 1-4 carbon atoms, halogen, nitro and hydroxyl. Specific examples of the diphenyl sulfone compound (D) include diphenyl sulfone, 4-chlorodiphenyl sulfone, 4,4'-dichlorodiphenyl sulfone, 4-fluorodiphenyl sulfone, 4,4'-difluorodiphenyl sulfone, 4-bromodiphenyl sulfone, 4,4'-dibromodiphenyl sulfone, 4,4'-dihydroxydiphenyl sulfone and dibenzothyophenesulfone. Preferably, the amount of the resin (A) is from 20 to 99% by weight, the amount of the acid-generator (B) is from 0.05 to 20% by weight, the amount of the tertiary amine compound is from 0.001 to 10% by weight and the amount of the diphenyl sulfone compound(D) is 0.01 to 20 % by weight based on the weight of total solid component of this composition. The photoresist composition of the present invention may optionally comprise other components, for example, various additives conventionally used in this field such as a dissolution inhibitors, sensitizers, dyes, adhesion improvers and electron donors. A resist solution is prepared by mixing the above respective components with a solvent so that the concentration of the total solid content in this positive photoresist composition is within the range from 10 to 50% by weight. The solution is coated on a substrate such as silicon wafer. The solvent used may be any one which can dissolve the respective components and may be those which are normally used in this field. Examples thereof include glycol ether esters such as ethylcellosolve acetate, methylcellosolve acetate, propylene glycol monomethyl ether acetate and propylene glycol monoethyl ether acetate, glycol mono or diethers such as ethylcellosolve, methylcellosolve, propylene glycol monometyl ether, propylene glycol monoethyl ether and diethylene glycol dimethyl ether, esters such as ethyl lactate, butyl lactate and ethyl pyruvate, ketones such as 2-heptanone, cyclohexanone and methyl isobutyl ketone, and aromatic hydrocarbons such as xylene. These solvents may be used alone or in combination of two or more. A positive pattern is formed from the resist film coated on a substrate, usually via respective processes such as pre-baking, patterning exposure, PEB, developing with an alkali developer. The following example further illustrates the present invention in detail, but does not limit the scope thereof. In example, reference example and comparative example, all "part" or "parts" is by weight unless otherwise stated. Reference Example (protection of resin) Into a nitrogen-purged 500 ml four-necked flask were charged 25 g (208 mmol in terms of p-vinylphenol unit) of poly(p-vinylphenol) having a weight average molecular weight (Mw) of 23,900 and a polydispersion (Mw/Mn) of 1.12 [VP-15000 manufactured by Nippon Soda Co., Ltd.) and 0.021 g(0.109 mmol) of p-toluenesulfonic acid, and they were dissolved in 250 g of 1,4-dioxane. To this solution was added dropwise 7.88 g (109 mmol) of ethylvinyl ether, then, the mixture was reacted at 25°C for 5 hours. Thereafter, the reaction solution was added dropwise into 1500 ml of ion-exchanged water, then filtered to obtain a white wet cake. This wet cake was again dissolved into 200 g of 1,4-dioxane, then the solution was added dropwise to 1500 ml of ion-exchanged water, and filtered. The resulted wet cake was washed by stirring in 600 g of ion-exchanged water, and filtered to take a wet cake. Thereafter, this washing operation using this ion-exchanged water was repeated twice. The resulted white wet cake was dried under reduced pressure to obtain a resin in which a hydroxyl group of poly(p-vinylphenol) was partially 1-ethoxyethyl etherified. This resin was analyzed by 1 H-NMR to find that 35% of the hydroxy group was protected by a 1-ethoxyethyl group. This resin had a weight average molecular weight of 31,200 and a polydispersion of 1.17. Example 1 13.5 parts of the resin synthesized in the Reference Example, 0.5 parts of bis(cyclohexanesulfonyl)diazomethane as an acid generator, 0.02 parts of tris[2-(2-methoxyethoxy)ethyl]amine and 0.5 parts of diphenyl sulfone were dissolved in 67 parts of propylene glycol monomethyl ether acetate. The resulting solution was filtrated through a filter made of a fluorine resin having a pour size of 0.1 µm to prepare a resist solution. On a silicone wafer washed by a conventional method, "DUV-18", an organic composition for bottom antireflective coating manufactured by Brewer Science was coated, and the silicone wafer was baked at 205 °C for 1 minute to prepare a silicone wafer with a bottom antireflective coating having a thickness after drying of 570 Å. Then, the resist solution obtained-above was coated using a spin coater so that the thickness after drying was 0.7 µm. Thereafter, this silicone wafer was pre-baked at 90°C for 90 seconds on a hot plate. The film after the pre-baking was subjected to exposure treatment using KrF eximer laser stepper having an exposure wavelength of 248 nm [NSR-1755 EX8A manufactured by Nikon Corp., NA = 0.45) with changing exposure amount stepwise, through a chromium mask having a pattern. After the exposure, the wafer was heated for 90 seconds at 100°C on a hot plate for conducting PEB to effect de-protective group reaction in the exposed portion. This was developed with 2.38% by weight aqueous solution of tetramethylaminium hydroxide to obtain a positive pattern. The pattern thus formed was observed by an electron microscope. A fine pattern of 0.23 µm was resolved in good profile at an exposure of 46 mJ/cm 2 . No necking was observed at the portion where the bottom antireflective coating and the resist film contact. Example 2 The same procedure as in Example 1 was conducted except that tris[2-(2-methoxyethoxy)ethyl]amine, the quencher, was replaced by N-methyl-di-n-octylamine, and the PEB was conducted at 100 °C for 1 minute. A fine pattern of 0.22 µm was resolved in good profile at an exposure of 75 mJ/cm 2 . No necking was observed at the portion where the bottom antireflective coating and the resist film contact. Example 3 The same procedure as in Example 1 was conducted except that diphenyl sulfone was replaced by 4,4'-dichlorodiphenyl sulfone. A fine pattern of 0.24 µm was resolved in good profile at an exposure of 38 mJ/cm 2 . No necking was observed at the portion where the bottom antireflective coating and the resist film contact. Using the photoresist composition according to the present invention which comprises a diphenyl sulfone compound, no necking was formed at the portion where the bottom antireflective coating and the resist film contact, and a pattern in good profile was obtained with excellent resolution and sensitivity. Therefore, a fine photoresist pattern can be formed in high precision using the photoresist composition of the present invention.

Claims: A positive photoresist composition comprising (A) a resin which is obtainable by at least partially protecting the phenolic hydroxyl groups in an alkali soluble resin having a phenol skeleton with 1-ethoxyethyl groups, and which is converted to alkali-soluble from alkali-insoluble or only slightly alkali soluble by the action of an acid, (B) an acid generator, (C) a tertiary amine compound and (D) a diphenyl sulfone compound. The composition according to Claim 1, wherein the diphenyl sulfone compound (D) is a compound represented by the following formula (I): wherein R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , R 9 and R 10 each independently represent hydrogen or a group which can bond to phenyl, provided that R 1 and R 10 may optionally be linked directly. The composition according to Claim 1, wherein the amount of the resin (A) is from 20 to 99% by weight, the amount of the acid-generator (B) is from 0.05 to 20% by weight, the amount of the tertiary amine compound (C) is from 0.001 to 10% by weight and the amount of the diphenyl sulfone compound (D) is 0.01 to 20 % by weight based on the weight of total solid component of this composition.

Inventors: YAKO YUKO, YAKO, YUKO
Applicants: SUMITOMO CHEMICAL CO, SUMITOMO CHEMICAL COMPANY, LIMITED
Application year: 1998
Main classification: G03F7
IPC codes: G03F7, H01L21