Classifications

• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/26—Processing photosensitive materials; Apparatus therefor
  • G03F7/40—Treatment after imagewise removal, e.g. baking
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/60—Organic compounds having low molecular weight
  • H10K85/649—Aromatic compounds comprising a hetero atom
  • H10K85/656—Aromatic compounds comprising a hetero atom comprising two or more different heteroatoms per ring
  • H10K85/6565—Oxadiazole compounds

Definitions

• This invention relates to an over-coating agent for forming fine patterns in the field of photolithographic technology and a method of forming fine-line patterns using such agent. More particularly, the invention relates to an over-coating agent for forming or defining fine-line patterns, such as hole patterns and trench patterns, that can meet today's requirements for higher packing densities and smaller sizes of semiconductor devices.
• the photolithographic technology which, in order to perform a treatment such as etching on the substrate, first forms a film (photoresist layer) over the substrate using a so-called radiation-sensitive photoresist which is sensitive to activating radiations, then performs exposure of the film by selective illumination with an activating radiation, performs development to dissolve away the photoresist layer selectively to form an image pattern (photoresist pattern), and forms a variety of patterns including contact providing patterns such as hole patterns and trench patterns using the photoresist pattern as a protective layer (mask pattern).
• JP-5-241348A discloses a pattern forming method comprising the steps of depositing a resin, which becomes insoluble in the presence of an acid, on a substrate having formed thereon a resist pattern containing an acid generator, heat treating the assembly so that the acid is diffused from the resist pattern into said resin insoluble in the presence of an acid to form a given thickness of insolubilized portion of the resist near the interface between the resin and the resist pattern, and developing the resist to remove the resin portion through which no acid has been diffused, thereby ensuring that the feature size of the pattern is reduced by an amount comparable to the dimension of said given thickness.
• JP-1-307228A discloses a method comprising the steps of forming a resist pattern on a substrate and applying heat treatment to deform the cross-sectional shape of the resist pattern, thereby defining a fine pattern.
• JP-4-364021A discloses a method comprising the steps of forming a resist pattern and heating it to fluidize the resist pattern, thereby changing the dimensions of its resist pattern to form or define a fine-line pattern.
• the wafer's in-plane heat dependency is only a few nanometers per degree Celsius and is not very problematic.
• JP-7-45510A An evolved version of those methods is disclosed in JP-7-45510A and it comprises the steps of forming a resist pattern on a substrate, forming a stopper resin on the substrate to prevent excessive thermal fluidizing of the resist pattern, then applying heat treatment to fluidize the resist so as to change the dimensions of its pattern, and thereafter removing the stopper resin to form or define a fine-line pattern.
• a water-soluble resin specifically, poly-vinyl alcohol is employed.
• polyvinyl alcohol is not highly soluble in water and cannot be readily removed completely by washing with water, introducing difficulty in forming a pattern of good profile. The pattern formed is not completely satisfactory in terms of stability over time.
• polyvinyl alcohol cannot be applied efficiently by coating. Because of these and other problems, the method disclosed in JP-7-45510A has yet to be adopted commercially.
• JP 2001-281886A discloses a method comprising the steps of covering a surface of a resist pattern with an acidic film made of a resist pattern size reducing material containing a water-soluble resin, rendering the surface layer of the resist pattern alkali-soluble, then removing said surface layer and the acidic film with an alkaline solution to reduce the feature size of the resist pattern.
• JP-2002-184673A discloses a method comprising the steps of forming a resist pattern on a substrate, then forming a film containing a water-soluble film forming component on said resist pattern, heat treating said resist pattern and film, and immersing the assembly in an aqueous solution of tetramethylammonium hydroxide, thereby forming a fine-line resist pattern without involving a dry etching step.
• both methods are simply directed to reducing the size of resist trace patterns themselves and therefore are totally different from the present invention in object.
• the present invention provides an over-coating agent for forming fine patterns which is applied to cover a substrate having photoresist patterns thereon and allowed to shrink under heat so that the spacing between adjacent photoresist patterns is lessened, with the applied film of the over-coating agent being removed substantially completely to form fine patterns, further characterized by containing either (i)a water-soluble polymer and an amide group-containing monomer, or (ii) a water-soluble polymer which contains at least (meth)acrylamide as its monomeric components.
• the present invention provides a method of forming fine patterns comprising the steps of covering a substrate having thereon photoresist patterns with either of the above-described over-coating agent for forming fine patterns, then applying heat treatment to shrink the applied over-coating agent under the action of heat so that the spacing between the adjacent photoresist patterns is lessened, and subsequently completely removing the applied film of the over-coating agent.
• the heat treatment is performed by heating the assembly at a temperature that does not cause thermal fluidizing of the photoresist patterns on the substrate.
• the over-coating agent of the invention for forming fine features of patterns is used to be applied to cover a substrate, having photoresist patterns (mask patterns) thereon, including patterns typified by hole patterns or trench patterns, each of these patterns are defined by spacing between adjacent photoresist patterns (mask patterns).
• the applied film of over-coating agent shrinks to increase the width of each of the photoresist patterns, thereby narrowing or lessening adjacent hole patterns or trench patterns as defined by spacing between the photoresist patterns and, thereafter, the applied film is removed substantially completely to form or define fine patterns.
• removing the applied film substantially completely means that after lessening the spacing between adjacent photoresist patterns by the heat shrinking action of the applied over-coating agent, said film is removed in such a way that no significant thickness of the over-coating agent will remain at the interface with the photoresist patterns. Therefore, the present invention does not include methods in which a certain thickness of the over-coating agent is left intact near the interface with the photoresist pattern so that the feature size of the pattern is reduced by an amount corresponding to the residual thickness of the over-coating agent.
• the over-coating agent for forming fine patterns of the invention for forming fine patterns is what either comprising a water-soluble polymer and an amide-group containing monomer (first type of the over-coating agent for forming fine patterns), or comprising a water-soluble polymer which contains at least (meth)acrylamide as its monomeric components (second type of the over-coating agent for forming fine patterns).
• the water-soluble polymer may be any polymer that can dissolve in water at room temperature and various types may be employed without particular limitation; preferred examples include acrylic polymers, vinyl polymers, cellulosic derivatives, alkylene glycol polymers, urea polymers, melamine polymers, epoxy polymers and amide polymers.
• acrylic polymers include polymers and copolymers having monomeric components, such as acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.
• Exemplary vinyl polymers include polymers and copolymers having monomeric components, such as N-vinylpyrrolidone, vinyl imidazolidinone, vinyl acetate, etc.
• Exemplary cellulosic derivatives include hydroxypropyl-methyl cellulose phthalate, hydroxypropylmethyl cellulose acetate phthalate, hydroxypropylmethyl cellulose hexahydrophthalate, hydroxypropylmethyl cellulose acetate succinate, hydroxypropylmethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetate hexahydrophthalate, carboxymethyl cellulose, ethyl cellulose, methylcellulose, etc.
• Exemplary alkylene glycol polymers include addition polymers and copolymers of ethylene glycol, propylene glycol, etc.
• Exemplary urea polymers include those having methylolurea, dimethylolurea, ethyleneurea, etc. as components.
• Exemplary melamine polymers include those having methoxymethylated melamine, methoxymethylated isobutoxymethylated melamine, methoxyethylated melamine, etc. as components.
• epoxy polymers and amide polymers those which are water-soluble may also be employed.
• Acrylic polymers are most preferred since they provide ease in pH adjustment.
• Copolymers comprising acrylic polymers and water-soluble polymers other than acrylic polymers are also preferred since during heat treatment, the efficiency of shrinking the spacing between the adjacent photo-resist patterns (mask patterns) can be increased while maintaining the shape of the photoresist pattern.
• the water-soluble polymers can be employed either singly or in combination.
• the proportions of the components are not limited to any particular values. However, if stability over time is important, the proportion of the acrylic polymer is preferably adjusted to be larger than those of other building polymers. Other than by using excessive amounts of the acrylic polymer, better stability over time can also be obtained by adding acidic compounds such as p-toluenesulfonic acid and dodecylbenzene-sulfonic acid.
• the amide group-containing monomer should have characteristics such that when added to the water-soluble polymer, it is highly soluble, is not suspended, and is compatible with the polymer component.
• amide group-containing monomer preferred one is an amide compound represented by the following general formula (I): where R 1 is a hydrogen atom, an alkyl or hydroxyalkyl group having 1-5 carbon atoms; R 2 is an alkyl group having 1-5 carbon atoms; R 3 is a hydrogen atom or a methyl group; and m is a number of 0-5.
• R 1 is a hydrogen atom, an alkyl or hydroxyalkyl group having 1-5 carbon atoms
• R 2 is an alkyl group having 1-5 carbon atoms
• R 3 is a hydrogen atom or a methyl group
• m is a number of 0-5.
• the alkyl group and the hydroxyalkyl group may be either linear of branched.
• the amide group-containing monomer of the general formula (I) is more preferred in which R 1 is a hydrogen atom, a methyl group or an ethyl group, and m is 0.
• Specific examples of the amide group-containing monomer include acrylamide, methacrylamide, N,N-dimethylacrylamide, N,N-dimethylmethacrylamide, N,N-diethylacrylamide, N,N-diethylmethacrylamide, N-methylacrylamide, N-methylmethacrylamide, N-ethylacrylamide and N-ethylmethacrylamide.
• acrylamide and methacrylamide are particularly preferred.
• the thermal shrinkage of the over-coating agent for forming fine patterns can be remarkably increased by the incorporation of the amide group-containing monomer, and thereby finer patterns can be formed.
• the content of the amide group-containing monomer added is preferably about 0.1- 30 mass %, and particularly about 1-15 mass %, based on the over-coating agent for forming fine patterns (solid content).
• the content is less than 0.1 mass %, a large thermal shrinkage cannot be obtained of the over-coating agent for forming fine patterns.
• the content exceeds 30 mass %, there is no appreciable improvement in the thermal shrinkage that justifies the increased content.
• a water-soluble polymer is a copolymer of (meth)acrylamide and at least one member selected from among monomeric components of alkylene glycol polymers, cellulosic derivatives, vinyl polymers, acrylic polymers, urea polymers, epoxy polymers and melamine polymers, provided that monomeric components of acrylic polymers are those other than (meth)acrylamide).
• acrylic polymers include acrylic acid, methyl acrylate, methacrylic acid, methyl methacrylate, N,N-dimethylaminoethyl methacrylate, N,N-diethylaminoethyl methacrylate, N,N-dimethylaminoethyl acrylate, acryloylmorpholine, etc.
• Exemplary monomeric components of vinyl polymers include N-vinylpyrrolidone, vinyl imidazolidinone, vinyl acetate, etc.
• Exemplary monomeric components of cellulosic derivatives include hydroxypropylmethyl cellulose phthalate, hydroxypropylmethyl cellulose acetate phthalate, hydroxypropyl-methyl cellulose hexahydrophthalate, hydroxypropylmethyl cellulose acetate succinate, hydroxypropylmethyl cellulose, hydroxypropyl cellulose, hydroxyethyl cellulose, cellulose acetate hexahydrophthalate, carboxymethyl cellulose, ethyl cellulose, methylcellulose, etc.
• Exemplary monomeric components of alkylene glycol polymers include ethylene glycol, propylene glycol, etc.
• Exemplary monomeric components of urea polymers include methylolurea, dimethylolurea, ethyleneurea, etc.
• Exemplary monomeric components of melamine polymers include methoxymethylated melamine, methoxymethylated isobutoxymethylated melamine, methoxyethylated melamine, etc.
• Copolymers of (meth)acrylamide and the monomeric components of the above-described polymers are preferably used in which the monomers are used in an amount of 0.1-30 mass %, more preferably about 1-15 mass %, relative to (meth)acrylamide.
• a water-soluble polymer is a copolymer or a mixture of (meth)acrylamide and at least one member selected from among polymers of alkylene glycol polymers, cellulosic derivatives, vinyl polymers, acrylic polymers (with the exception of poly(meth)acrylamide), urea polymers, epoxy polymers and melamine polymers.
• Alkylene glycol polymers, cellulosic derivatives, vinyl polymers, acrylic polymers, urea polymers, epoxy polymers and melamine polymers are preferably used the same ones having monomeric components as descried above.
• acrylic polymers particularly poly(meth)acrylate, such as poly(meth)acrylic acid
• acrylic polymers are most preferred since during heat treatment, the efficiency of shrinking the spacing between the adjacent photoresist patterns (mask patterns) can be extensively increased while maintaining the shape of the photoresist pattern. It is also preferred in terms of stability over time.
• Copolymers or mixed resins of (meth)acrylamide and each of the above polymers are preferably used in which the co-polymers are used in an amount of 0.1-30 mass %, more preferably about 1-15 mass %, relative to (meth)acrylamide.
• first and second types of over-coating agent for forming fine patters may additionally contain water-soluble amines for special purposes such as preventing the generation of impurities and pH adjustment.
• Exemplary water-soluble amines include amines having pKa (acid dissociation constant) values of 7.5-13 in aqueous solution at 25° C.
• alkanolamines such as monoethanolamine, diethanolamine, triethanolamine, 2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine, N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine, N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine, monoisopropanolamine, diisopropanolamine and truisopropanolamine; polyalkylenepolyamines, such as diethylenetriamine, triethylenetetramine, propylenediamine, N,N-diethylethylenediamine, 1,4-butanediamine, N-ethyl-ethylenediamine, 1,2-propanediamine, 1,3-propanediamine and 1,6-hex
• the water-soluble amine is to be added, it is preferably incorporated in an amount of about 0.1-30 mass %, more preferably about 2-15 mass %, of the over-coating agent for forming fine patterns (in terms of solids content). If the water-soluble amine is incorporated in an amount of less than 0.1 mass %, the coating fluid may deteriorate over time. If the water-soluble amine is incorporated in an amount exceeding 30 mass %, the photoresist pattern being formed may deteriorate in shape.
• the first and second types of over-coating agent for forming fine patterns may further optionally contain non-amine based, water-soluble organic solvents.
• any non-amine based organic solvents that can mix with water may be employed and they may be exemplified by the following: sulfoxides, such as dimethyl sulfoxide; sulfones, such as di-methylsulfone, diethylsulfone, bis(2-hydroxyethyl)sulfone and tetramethylenesulfone; amides, such as N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide, N-methylacetamine and N,N-diethylacetamide; lactams, such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone, N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone; imidazolidinones, such as 1,3-dimethyl-2-imid
• polyhydric alcohols and their derivatives are preferred for the purposes of reducing the dimensions of patterns and controlling the occurrence of defects and glycerol is particularly preferred.
• the non-amine based, water-soluble organic solvents may be used either singly or in combination.
• the non-amine based, water-soluble organic solvent is to be added, it is preferably incorporated in an amount of about 0.1-30 mass %, more preferably about 0.5-15 mass %, of the water-soluble polymer. If the non-amine based, water-soluble organic solvent is incorporated in an amount of less than 0.1 mass %, its defect reducing effect tends to decrease. Beyond 30 mass %, a mixing layer is liable to form at the interface with the photoresist pattern.
• first and second type of over-coating agent may optionally contain a surfactant for attaining special effects such as coating uniformity and wafer's in-plane uniformity.
• Suitable surfactants include N-alkylpyrrolidones, quaternary ammonium salts and phosphate esters of polyoxyethylene.
• N-alkylpyrrolidones as surfactant are preferably represented by the following general formula (II): where R 4 is an alkyl group having at least 6 carbon atoms.
• N-alkylpyrrolidones as surfactant include N-hexyl-2-pyrrolidone, N-heptyl-2-pyrrolidone, N-octyl-2-pyrrolidone, N-nonyl-2-pyrrolidone, N-decyl-2-pyrrolidone, N-undecyl-2-pyrrolidone, N-dodecyl-2-pyrrolidone, N-tridecyl-2-pyrrolidone, N-tetradecyl-2-pyrrolidone, N-pentadecyl-2-pyrrolidone, N-hexadecyl-2-pyrrolidone, N-heptadecyl-2-pyrrolidone and N-octadecyl-2-pyrrolidone.
• N-octyl-2-pyrrolidone (“SURFADONE LP 100” of ISP Inc.) is
• Quaternary ammonium salts as surfactant are preferably represented by the following general formula (III): where R 5 , R 6 , R 7 and R 8 are each independently an alkyl group or a hydroxyalkyl group (provided that at least one of them is an alkyl or hydroxyalkyl group having not less than 6 carbon atoms); X ⁇ is a hydroxide ion or a halogenide ion.
• quaternary ammonium salts as surfactant include dodecyltrimethylammonium hydroxide, tridecyltrimethylammonium hydroxide, tetradecyltrimethylammonium hydroxide, pentadecyltrimethylammonium hydroxide, hexadecyl-trimethylammonium hydroxide, heptadecyltrimethylammonium hydroxide and octadecyltrimethylammonium hydroxide.
• hexadecyltrimethylammonium hydroxide is preferably used.
• Phosphate esters of polyoxyethylene are preferably represented by the following general formula (IV): where R 9 is an alkyl or alkylaryl group having 1-10 carbon atoms; R 10 is a hydrogen atom or (CH 2 CH 2 O)R 9 (where R 9 is as defined above); n is an integer of 1-20.
• phosphate esters of poly-oxyethylene that can be used as surfactants are commercially available under trade names “PLYSURF A212E” and “PLYSURF A210G” from Dai-ichi Kogyo Seiyaku Co., Ltd.
• the first and second types of over-coating agent of the invention for forming fine patterns are preferably used as an aqueous solution at a concentration of 3-50 mass %, more preferably at 5-30 mass %. If the concentration of the aqueous solution is less than 3 mass %, poor coverage of the substrate may result. If the concentration of the aqueous solution exceeds 50 mass %, there is no appreciable improvement in the intended effect that justifies the increased concentration and the solution cannot be handled efficiently.
• the first and second types of over-coating agent of the invention for forming fine patterns are usually employed as an aqueous solution using water as the solvent.
• a mixed solvent system comprising water and an alcoholic solvent may also be employed.
• Exemplary alcoholic solvents are monohydric alcohols including methyl alcohol, ethyl alcohol, propyl alcohol and isopropyl alcohol. These alcoholic solvents are mixed with water in amounts not exceeding about 30 mass %.
• the first and second types of over-coating agent of the invention for forming fine patterns have the advantage of improving resolution beyond the values inherent in photoresist materials and it can attain wafer's in-plane uniformity by eliminating the pattern variations in the plane of the substrate. Further, the over-coating agent of the invention can form patterns of good profile by eliminating the irregularities (roughness) in the shape of patterns due, for example, to the reflection of fluorescent light from the substrate. Also it has remarkable improvement in forming finer patterns.
• the method of forming fine-line patterns according to the second aspect of the invention comprises the steps of covering a substrate having photoresist patterns thereon with either of the first and second types of the above-described over-coating agent for forming fine patterns, then applying heat treatment to shrink the applied over-coating agent under the action of heat so that the spacing between the adjacent photoresist patterns is reduced, and subsequently removing the applied film of the over-coating agent substantially completely.
• a photoresist composition of chemically amplifiable or other type is spin- or otherwise coated on a substrate such as a silicon wafer and dried to form a photo-resist layer, which is illuminated with an activating radiation such as ultraviolet, deep-ultraviolet or excimer laser light through a desired mask pattern using a reduction-projection exposure system or subjected to electron beam photolithography, then heated and developed with a developer such as an alkaline aqueous solution, typically a 1-10 mass % tetramethylammonium hydroxide (TMAH) aqueous solution, thereby forming a photoresist pattern on the substrate.
• an activating radiation such as ultraviolet, deep-ultraviolet or excimer laser light
• TMAH tetramethylammonium hydroxide
• the photoresist composition serving as a material from which photoresist patterns are formed is not limited in any particular way and any common photoresist compositions may be employed including those for exposure to i- or g-lines, those for exposure with an excimer laser (e.g. KrF, ArF or F 2 ) and those for exposure to EB (electron beams).
• an excimer laser e.g. KrF, ArF or F 2
• EB electron beams
• the over-coating agent for forming fine patterns is applied to cover entirely the substrate.
• the substrate may optionally be pre-baked at a temperature of 80-100 ° C. for 30-90 seconds.
• the over-coating agent may be applied by any methods commonly employed in the conventional heat flow process. Specifically, an aqueous solution of the over-coating agent for forming fine patterns is applied to the substrate by any known application methods including whirl coating with a spinner, etc.
• the next step heat treatment is performed to cause thermal shrinkage of the film of the over-coating agent.
• the dimensions of the photoresist pattern in contact with the film will increase by an amount equivalent to the thermal shrinkage of the film and, as the result, the photoresist pattern widens and accordingly the spacing between the adjacent photoresist patterns lessens.
• the spacing between the adjacent photoresist patterns determines the diameter or width of the patterns to be finally obtained, so the decrease in the spacing between the adjacent photoresist patterns contributes to reducing the diameter of each element of hole patterns or the width of each element of trench patterns, eventually leading to the definition of a pattern with smaller feature sizes.
• the heating temperature is not limited to any particular value as long as it is high enough to cause thermal shrinkage of the film of the over-coating agent and form or define a fine pattern. Heating is preferably done at a temperature that will not cause thermal fluidizing of the photo-resist pattern.
• the temperature that will not cause thermal fluidizing of the photoresist pattern is such a temperature that when a substrate on which the photoresist pattern has been formed but no film of the over-coating agent has been formed is heated, the photoresist pattern will not experience any dimensional changes (for example, dimensional changes due to spontaneously fluidized deforming). Performing a heat treatment under such temperature conditions is very effective for various reasons, e.g. a fine-line pattern of good profile can be formed more efficiently and the duty ratio in the plane of a wafer, or the dependency on the spacing between photoresist patterns in the plane of a wafer, can be reduced.
• the preferred heat treatment is usually performed within a temperature range of about 80-160 ° C. for 30-90 seconds, provided that the temperature is not high enough to cause thermal fluidizing of the photoresist.
• the thickness of the film of the over-coating agent for the formation of fine-line patterns is preferably just comparable to the height of the photoresist pattern or high enough to cover it.
• the remaining film of the over-coating agent on the patterns is removed by washing with an aqueous solvent, preferably pure water, for 10-60 seconds.
• an aqueous solvent preferably pure water
• rinsing may optionally be performed with an aqueous solution of alkali (e.g. tetramethyl-ammonium hydroxide (TMAH) or choline).
• alkali e.g. tetramethyl-ammonium hydroxide (TMAH) or choline.
• TMAH tetramethyl-ammonium hydroxide
• the over-coating agent of the present invention is easy to remove by washing with water and it can be completely removed from the substrate and the photoresist pattern.
• each pattern on the substrate has a smaller feature size because each pattern is defined by the narrowed spacing between the adjacent widened photoresist patterns.
• the fine-line pattern thus formed using the over-coating agent of the present invention has a pattern size smaller than the resolution limit attainable by the conventional methods. In addition, it has a good enough profile and physical properties that can fully satisfy the characteristics required of semiconductor devices.
• Steps [a.]-[c.] may be repeated several times. By repeating steps [a.]-[c.] several times, the photoresist trace patterns (mask patterns) can be progressively widened.
• the over-coating agent of the invention contains a water-soluble polymer and an amide group-containing monomer, so even if it is subjected to a plurality of washing steps, it can be completely removed each time it is washed with water. Consequently, even in the case of using a substrate having a thick film of photoresist pattern, a fine-line pattern of good profile can be formed on the substrate without causing pattern distortion or deformation.
• the technical field of the present invention is not limited to the semiconductor industry and it can be employed in a wide range of applications including the fabrication of liquid-crystal display devices, the production of magnetic heads and even the manufacture of microlens arrays.
• a substrate was whirl coated with a positive-acting photoresist TArF-7a-52 EM (product of Tokyo Ohka Kogyo Co., Ltd.), and baked at 115° C. for 90 seconds to form a photoresist layer in a thickness of 0.40 ⁇ m.
• TArF-7a-52 EM product of Tokyo Ohka Kogyo Co., Ltd.
• the photoresist layer was exposed with a laser exposure unit (Nikon S-302 of Nikon Corp.), subjected to heat treatment at 100° C. for 90 seconds and developed with an aqueous solution of 2.38 mass % TMAH (tetramethylammonium hydroxide) to form photoresist patterns which defined hole patterns with an each diameter of 161.0 nm.
• TMAH tetramethylammonium hydroxide
• the thermal shrinkage of the over-coating agent in the heat treatment can be extensively increased, and one can obtain fine-line patterns which exhibit good profiles while satisfying the characteristics required of semiconductor devices.

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