JP4742793B2 - Resist substrate, resist pattern forming method, and resist substrate storage method - Google Patents

Description

  The present invention relates to a resist substrate on which a photosensitive resin used in a lithography process such as a semiconductor element manufacturing process is formed, a resist pattern forming method using the resist substrate, and a method for storing the resist substrate.

In a manufacturing process of a semiconductor device, a resist layer made of a photosensitive composition is formed on a silicon wafer, and the resist layer is patterned by lithography processing such as direct drawing using a laser or exposure using a photomask, and an etching mask. And a fine pattern is formed by etching.
Further, when manufacturing a photomask used for the lithography process, a mask material layer is formed on a transparent substrate for a mask, a resist layer made of a photosensitive composition is formed on the mask material layer, The resist layer is patterned by direct lithography using a laser or an electron beam to form an etching mask, and etching is performed to form a photomask pattern.
Further, in various fields other than semiconductor devices, fine patterns are formed by etching using an etching mask patterned by lithography processing of a resist layer.

  In recent years, with the demand for pattern miniaturization of semiconductor devices, in the pattern exposure in lithography processing, the wavelength of exposure light has been shortened. For this reason, lithography using ArF, F2, EUV, X-rays, electron beams or other charged particle beams as exposure light in addition to the currently used KrF excimer laser light has been proposed. On the other hand, for the purpose of improving throughput in pattern exposure, a highly sensitive chemically amplified photosensitive composition has been used in lithography using these exposure lights.

  The chemically amplified photosensitive composition contains an alkali-soluble resin, an acid generator that generates an acid upon exposure to exposure light, a basic compound, and the like. In this photosensitive composition, due to the presence of acid generated by exposure light exposure, a crosslinking reaction proceeds in the photosensitive composition in the negative type, and a decomposition reaction proceeds in the photosensitive composition in the positive type. . For this reason, pattern exposure with a smaller exposure amount is possible.

However, in a chemically amplified resist, since the amount of acid generated is very small, the resist characteristics are easily affected by the conditions of use of the resist. For this reason, when forming a resist pattern on a plurality of substrates when creating an actual semiconductor element, there is a problem that the sensitivity and resolution differ for each substrate, and the target pattern cannot be obtained with good reproducibility. .
For example, as described in Patent Document 1 and the like, there is a problem in that the acid in the resist layer is deactivated by a very small amount of a basic substance in the air, and the resolution changes due to a difference in exposure time after exposure. It has become. Therefore, attempts have been made to alleviate the influence of the basic substance from the outside using a resist added with a basic substance, and the above phenomenon has been partially improved.

  It is also known that the residual solvent content of the resist layer has a great influence on the resolution of the resist. In a chemically amplified resist, an acid generated by exposure diffuses from an exposed portion to an unexposed portion using a residual solvent in the resist as a diffusion path. The residual solvent in the resist layer volatilizes gradually with the passage of time, and the amount of the solvent varies. For this reason, when forming a resist pattern on a plurality of substrates when creating an actual semiconductor element, there is a problem that the sensitivity and resolution differ for each substrate, and the target pattern cannot be obtained with good reproducibility. .

As a method for solving the above problem, for example, there is a pattern forming method disclosed in Patent Document 2. According to this method, it has been attempted to control the amount of residual solvent in the resist layer to be constant by controlling the amount of solvent, pressure, temperature, etc. in the storage environment of the resist substrate. Some of the changes were improved.
Patent Document 3 describes that the resist film is subjected to heat treatment within 3 hours before drawing with an electron beam.
Further, Patent Document 4 describes a resist processing method including a step of evaporating a solvent by heating a coating film made of a resist material having a thickness of 150 nm or less while supplying a gas-downflow without a solvent. Yes.
However, these publications describe the nano-order substrate in-plane uniformity required for microfabrication with a minimum processing dimension of 200 nm or less, and the optimal residual solvent amount for obtaining a resist substrate with good storage stability. It has not been.

JP-A-6-93045 Japanese Unexamined Patent Publication No. 7-57997 Japanese Patent Laid-Open No. 11-30868 JP 2003-142390 A

  In the field of manufacturing semiconductor devices such as LSIs, the reduction of design rules is accelerating. According to the ITRS (International Technology Roadmap for Semiconductors) design rules, around 65 nm in 2010, 2010 Every year, there is a demand for fine processing technology that can achieve a minimum processing size of around 45 nm. With such miniaturization of circuit patterns and line widths (CD), in-plane uniformity (CD uniformity) of 8.0 nm is required for DRAM at 45 nm node and 5.1 nm is more severe for photomasks.

  On the other hand, in the case of VUV, EUV, X-ray, electron beam, charged particle lithography, etc. that are exposed in vacuum, in-line implementation is delayed from the point of productivity, and the time from resist application to exposure is not fixed. . For example, in mask manufacturing processes by electron beam drawing, mask blanks coated with resist are even shipped overseas, and the storage period from coating to exposure varies from several days to several months. Currently. As described above, when the period from coating to exposure is long, the variation in the content of the residual solvent contained in the resist layer has led to a decrease in the reproducibility of the resist pattern dimensions between substrates having different storage periods. .

  Therefore, the present invention has been made to solve the above-mentioned problems, and improves the dimensional accuracy of the resist pattern, and further reduces the dimensional variation of the resist pattern depending on the standing time of the resist substrate from resist coating to drawing. An object of the present invention is to provide a resist substrate capable of obtaining a dimensional accuracy of a resist pattern that can cope with further miniaturization of a photoprocess pattern that will continue to advance in the future, a storage method thereof, and a resist pattern forming method using the resist substrate. .

In order to solve the above problems, according to the present invention, a resist layer made of a photosensitive composition having a thickness of 500 nm or less contains a residual solvent compatible with the residual solvent of the resist layer, and the resist layer Pre-baked resist substrate provided on the substrate with or without direct contact with the lower layer, the resist substrate having a residual solvent amount immediately after pre-baking of the resist layer when the lower layer is not present Or when the said lower layer exists, the average residual solvent amount immediately after the prebaking which combined the resist layer and the lower layer is 0.5-20 ppm is provided.

Further, according to the present invention, after forming a lower layer in advance on two or more substrates as necessary, the photosensitive composition is applied with or without the lower layer, and a resist layer having a thickness of 500 nm or less Forming a resist substrate and pre-baking each obtained resist substrate, exposing each resist substrate after pre-baking, post-exposure baking each resist substrate, and post-exposure baking. A step of developing each completed resist substrate, and a residual solvent amount immediately after the pre- baking step in the resist layer immediately before the exposure step, or a residual solvent in the resist layer that is in direct contact with the resist layer the average amount of the residual solvent after said step of pre-baking the combination of the resist layer and the lower layer when the lower layer containing a compatibility certain residual solvent is present, smell between each of the resist substrate A resist pattern forming method characterized in that it is controlled in 0.5~20ppm is provided.

  Further, according to the present invention, the resist layer made of the photosensitive composition having a film thickness of 500 nm or less contains a residual solvent compatible with the residual solvent of the resist layer and does not go through a lower layer that is in direct contact with the resist layer. Or the resist substrate provided on the substrate, the residual solvent amount of the resist layer when the lower layer does not exist, or the average residual of the resist layer and the lower layer when the lower layer exists A method of storing a resist substrate is provided, wherein the solvent is stored after adjusting the amount of the solvent to 0.5 to 20 ppm.

Further, according to the present invention, the resist layer made of the photosensitive composition having a film thickness of 500 nm or less contains a residual solvent compatible with the residual solvent of the resist layer and does not go through a lower layer that is in direct contact with the resist layer. Or, the residual solvent amount immediately after pre-baking in the resist layer of the resist substrate that is provided on the substrate and is pre-baked , or the average residual solvent amount immediately after pre-baking combining the resist layer and the lower layer when the lower layer is present A resist substrate evaluation method is provided, wherein when the residual solvent amount or the average residual solvent amount is within a range of 0.5 to 20 ppm, it is determined to be acceptable.

The resist substrate according to the present invention limits the film thickness of the resist layer to 500 nm or less in order to prevent pattern collapse when forming a pattern with a line width of around 200 nm or finer than that.
In addition, since the residual solvent amount of the resist layer is controlled in the range of 0.5 to 20 ppm, the resist substrate is also a photomask blank or a semiconductor wafer used for manufacturing a state-of-the-art product of a semiconductor device. The diffusibility of the acid generated by exposure is optimal for the formation of a fine pattern, and sufficient sensitivity can be obtained, and the variation in pattern line width is very small.

  If the storage stability of the resist substrate is to be specifically considered, such as when photomask blanks are intended to be distributed to the market, the residual solvent amount control method described above is applied to the resist layer of the resist substrate. And it is preferable to preserve | save after adjusting the amount of the residual solvent to the range of 0.5-20 ppm.

  In addition, when it is desired to select a resist substrate in order to obtain a resist pattern dimensional accuracy that can cope with further miniaturization of a photo process pattern that will continue to advance in the future, it is preferable to select the resist substrate by the above evaluation method.

According to the present invention, the in-plane variation of the line width of the fine pattern and the variation between the resist substrates are greatly reduced, and the dimensional accuracy of the pattern is improved. Further, the exposure sensitivity varies during the storage period of the resist substrate. As a result, the reproducibility of pattern dimensions is improved regardless of the storage time from resist application to exposure.
According to the present invention, since it is possible to obtain the dimensional accuracy of a resist pattern that can cope with the miniaturization of a photo process pattern, which will continue to be further developed in the future, the fabrication of blanks for photo masks and the fine processing of semiconductor products using photo masks It is preferably applied to.

The present inventors have found that in order to control the dimensional accuracy of a chemically amplified resist on the nano order, it is important to precisely control the residual solvent amount in the resist layer on the order of ppm. Invented the invention.
The resist substrate provided by the present invention is characterized in that a resist layer made of a photosensitive composition having a film thickness of 500 nm or less and a residual solvent amount of 0.5 to 20 ppm is provided on the substrate.

  In addition, the resist pattern forming method provided by the present invention includes a step of applying a photosensitive composition to two or more substrates and forming a resist layer having a film thickness of 500 nm or less to obtain a resist substrate, and each resist obtained A step of pre-baking the substrate, a step of exposing each resist substrate after pre-baking, a step of baking after exposure of each resist substrate, and a step of developing each resist substrate after completion of post-exposure baking. The amount of residual solvent in the resist layer immediately before the step is controlled in the range of 0.5 to 20 ppm between the resist substrates.

  Further, the resist substrate storage method provided by the present invention is a method of reducing the residual solvent amount of the resist layer of the resist substrate comprising the photosensitive composition and having a resist layer having a thickness of 500 nm or less on the substrate. It is characterized by being stored after being adjusted to the range of 5 to 20 ppm.

Furthermore, in the method for evaluating a resist substrate provided by the present invention, a resist layer made of a photosensitive composition having a thickness of 500 nm or less contains a residual solvent compatible with the residual solvent of the resist layer, and the resist layer Residual solvent amount in the resist layer of the resist substrate provided on the substrate with or without direct contact with the lower layer, or the average residual solvent amount of the resist layer and lower layer when the lower layer is present Is measured, when the residual solvent amount or the average residual solvent amount is in the range of 0.5 to 20 ppm, it is determined to be acceptable.
Embodiments of the present invention are described in detail below.

In the present invention, the resist substrate is a layer of a photosensitive composition capable of forming a pattern of an etching mask by a photo process on a substrate serving as a base on which a fine pattern is to be formed, that is, a substrate in a state where a resist layer is provided. Means that.
A typical example of such a resist substrate is a photomask blank, which is an intermediate processed product for forming a photomask used in manufacturing a semiconductor device. Further, a resist layer is formed on a semiconductor wafer. An intermediate processed product for forming a semiconductor device in a state is mentioned.
In addition, intermediate processed products in various fields, such as a color filter for a liquid crystal display and a mask for a color filter (CF), also correspond to the resist substrate in the present invention as long as the substrate has a resist layer on the substrate. To do.

In the present invention, when simply referred to as “substrate”, it means a support on which a resist layer is formed, and is typically a plate, but may be a support that is not plate-shaped. Usually, a pattern forming layer to be etched, such as a light shielding layer or a conductive thin film, is provided on the substrate. However, when the surface of the substrate itself is etched, such pattern formation is performed. There may be no layer. On the other hand, the resist substrate in the present invention means a laminate in a state where a resist layer is formed on the substrate.
As the substrate used in the present invention, various inorganic substrates such as silicon wafers; blanks for photomasks in which a MoSi film and a chromium (Cr) film are laminated on glass; III-V group compound semiconductor wafers such as GaAs and AlGaAs; A chromium or chromium oxide deposition mask; an aluminum deposition substrate; an IBPSG-coated substrate; a PSG-coated substrate; an SOG-coated substrate; a carbon film sputtering substrate, or the like can be used. Furthermore, for example, an organic film such as an antireflection film may be provided on the substrate. Further, a substrate made of an organic material may be used.
These substrates may be selected and used according to the final application of the resist substrate. When self-sustaining is required like a photomask substrate, a substrate having a thickness of 1 mm or more is usually used.

A resist substrate is produced by forming a resist layer made of a photosensitive composition on the substrate as described above. Hereinafter, the method for forming the resist substrate of the present invention will be described separately for each step.
Although the photosensitive composition used for formation of a resist film is not specifically limited, In order to obtain the outstanding sensitivity of a resist layer, it is preferable to use a chemically amplified resist composition. As the chemically amplified resist composition, either a positive type or a negative type can be used.
The chemical amplification type positive resist composition is not particularly limited, and includes a conventionally known one, for example, a resin whose solubility in an alkali is changed by the action of an acid and a compound that generates an acid upon irradiation with ionizing radiation. The resist composition contained as can be mentioned. The chemically amplified negative resist composition is not particularly limited, and includes conventionally known compounds such as an alkali-soluble resin, an acid crosslinkable substance, and a compound that generates an acid upon irradiation with ionizing radiation as essential components. A resist composition can be mentioned.

In the chemically amplified positive resist composition, the resin whose solubility in alkali is changed by the action of an acid is such that at least a part of the group imparting alkali solubility such as phenolic hydroxyl group and carboxyl group in the alkali-soluble resin is present. It is protected with an acid-dissociable substituent and is hardly soluble in alkali. Examples of the alkali-soluble resins include novolak resins obtained by condensing phenols such as phenol, m-cresol, p-cresol, xylenol, and trimethylphenol with aldehydes such as formaldehyde in the presence of an acidic catalyst, hydroxystyrene Polyhydroxystyrene resins such as homopolymers of styrene, copolymers of hydroxystyrene and other styrene monomers, copolymers of hydroxystyrene and acrylic acid or methacrylic acid or derivatives thereof, acrylic acid or methacrylic acid And acrylic acid or methacrylic acid resin, which is a copolymer of styrene and its derivatives.
An alkali-soluble low molecular weight compound such as calixarene is effective when it is desired to form a very fine resist pattern. Examples of such alkali-soluble low-molecular compounds include aromatic compounds containing one or more hydroxyl groups and having a molecular weight of about 300 to 10,000, such as calixarene, JP-A-11-322656, and JP-A-11-258996. And low molecular weight compounds described in JP-A-2002-99089, JP-A-2005-75767, and the like.

  In addition, as an alkali-soluble resin having a hydroxyl group protected with an acid-dissociable substituent, hydroxystyrene having a hydroxyl group, a carboxyl group or other acidic group in the resin partially protected with an acid-dissociable substituent A polymer, a copolymer of the hydroxystyrene and another styrene monomer, a copolymer of the hydroxystyrene and acrylic acid or methacrylic acid or a derivative thereof, or acid dissociation of a part of the hydroxyl group in the carboxyl group And a copolymer of acrylic acid or methacrylic acid protected with an ionic substituent and a derivative thereof, hydroxystyrene or hydroxystyrene having a hydroxyl group partially protected with an acid-dissociable substituent. On the other hand, examples of the acid dissociable substituent include alkoxycarbonyl groups such as tert-butoxycarbonyl group and tert-amyloxycarbonyl group, tertiary alkyl groups such as tert-butyl group, ethoxyethyl group and methoxypropyl group. An acetal group such as an alkoxyalkyl group, a tetrahydropyranyl group or a tetrahydrofuranyl group, a benzyl group, a trimethylsilyl group, a 2-propenyl group having two or more substituents, or a 1-ethylcyclohexyl group. A cycloalkyl group etc. can be mentioned. The protection rate of hydroxyl groups by these acid dissociable substituents is usually in the range of 1 to 60 mol%, preferably 5 to 50 mol% of the hydroxyl groups in the resin.

On the other hand, there is no particular limitation on the compound that generates an acid upon irradiation with ionizing radiation (hereinafter referred to as an acid generator), and an arbitrary one is selected from conventionally known compounds used as an acid generator for chemically amplified resists. Can be used. Examples of such acid generators include bissulfonyldiazomethanes such as bis (p-toluenesulfonyl) diazomethane, nitrobenzyl derivatives such as 2-nitrobenzyl p-toluenesulfonate, and sulfonate esters such as pyrogallol trimesylate. , Onium salts such as diphenyliodonium hexafluorophosphate, benzoin tosylate such as benzoin tosylate, 2- (4-methoxyphenyl) -4,6- (bistrichloromethyl) -1,3,5-triazine, etc. Examples thereof include halogen-containing triazine compounds, cyano group-containing oxime sulfonate compounds such as α- (methylsulfonyloxyimino) -phenylacetonitrile, iminosulfonate compounds such as N- (isopropylsulfonyloxy) succinimide, and the like.
These acid generators may be used alone or in combination of two or more, and the blending amount thereof is 100 weight of resin whose solubility in alkali is changed by the action of the acid. The amount is 0.5 to 30 parts by weight, preferably 1 to 10 parts by weight per part. When the amount is less than this range, image formation cannot be performed, and when the amount is larger, a uniform solution is not obtained and the storage stability is lowered.

Furthermore, in the chemically amplified negative resist composition, examples of the alkali-soluble resin include phenol novolac resin, cresol novolac resin, or polyhydroxystyrene and hydroxystyrene, and a copolymerizable monomer. Examples thereof include hydroxystyrene resins such as polymers.
Hydroxystyrene resins include hydroxystyrene homopolymers, hydroxystyrene and acrylic acid derivatives, acrylonitrile, methacrylic acid derivatives, methacrylonitrile, styrene, α-methylstyrene, p-methylstyrene, o-methylstyrene, p- Copolymers with styrene derivatives such as methoxystyrene and p-chlorostyrene, hydrogenated resins of hydroxystyrene homopolymer, and hydrogenated resins of copolymers of hydroxystyrene with the above acrylic acid derivatives, methacrylic acid derivatives and styrene derivatives Etc. In addition, those obtained by protecting a part of hydroxyl groups of acidic groups such as hydroxyl groups and carboxyl groups in these resins by alkyl etherification, aryl etherification, alkenyl etherification or aralkyl etherification can be suitably used. it can.
Moreover, the mass average molecular weight (in terms of polystyrene, the same applies hereinafter) of the alkali-soluble resin is not particularly limited, but is 1,000 to 50,000, more preferably 4,000 to 30,000. If it is larger than this range, the solubility in the resist solvent will deteriorate, and if it is smaller, the resist pattern may be reduced in film thickness.

  On the other hand, as the acid crosslinkable substance, conventionally, as a crosslinking agent for a chemically amplified negative resist, at least one of a phenol derivative having an alkoxymethyl group, a methylol group, an alkoxymethyl group, and an acyloxymethyl group, which has been conventionally used. A urea compound, a melamine compound, a benzoguanamine compound, or a glycoluril compound substituted with one kind of group can be used alone or in combination of two or more kinds.

  Examples of the acid generator include the same compounds as those exemplified in the chemically amplified positive resist composition. The blending ratio of each component is usually selected in the range of 3 to 70 parts by weight of the acid crosslinkable substance and 0.5 to 20 parts by weight of the acid generator with respect to 100 parts by weight of the alkali-soluble resin. If the amount of the acid crosslinkable substance is less than 3 parts by weight, it is difficult to form a resist pattern, and if it exceeds 70 parts by weight, the developability deteriorates. Further, when the amount of the acid generator is less than 0.5 parts by weight, the sensitivity is lowered, and when it exceeds 20 parts by weight, a uniform resist is hardly obtained and the developability is also lowered.

In addition, the resist composition used in the present invention is selected from any of the known basic compounds in order to improve the resist pattern shape, stability over time in storage conditions, and the like. can do. Examples of such basic compounds include substituted or unsubstituted guanidine, substituted or unsubstituted aminopyridine, substituted or unsubstituted aminoalkylpyridine, substituted or unsubstituted aminopyrrolidine, substituted or unsubstituted indazole, Imidazole, substituted or unsubstituted pyrazole, substituted or unsubstituted pyrazine, substituted or unsubstituted pyrimidine, substituted or unsubstituted purine, substituted or unsubstituted imidazoline, substituted or unsubstituted pyrazoline, substituted or unsubstituted piperazine Substituted or unsubstituted aminomorpholine, substituted or unsubstituted aminoalkylmorpholine, and the like. Preferred substituents are amino group, aminoalkyl group, alkylamino group, aminoaryl group, arylamino group, alkyl group, alkoxy group, acyl group, acyloxy group, aryl group, aryloxy group, nitro group, hydroxyl group, cyano group It is.
These may be used alone or in combination of two or more. These amines are usually used in the range of 0.01 to 5.0 parts by mass with respect to 100 parts by mass of the alkali-soluble component.

  The chemically amplified resist composition according to the present invention further contains miscible additives as desired, for example, additional resins for improving the performance of the resist film, surfactants for improving coating properties, and dissolution inhibition. An agent, a plasticizer, a stabilizer, a colorant, an antihalation agent, and the like can be appropriately added and contained.

These resist compositions can be usually prepared by dissolving the above components in a solvent and filtering the solution as necessary.
Examples of the organic solvent used herein include ketone solvents such as cyclohexanone, acetone, ethyl methyl ketone, and methyl isobutyl ketone; cellosolv solvents such as methyl cellosolve, methyl cellosolve acetate, ethyl cellosolve acetate, and butyl cellosolve acetate; Ester solvents such as butyl acetate, isoamyl acetate, γ-butyrolactone, methyl 3-methoxypropionate; glycol solvents such as propylene glycol monomethyl ether acetate; dimethyl sulfoxide, hexamethylphosphoric triamide dimethylformamide, N-methylpyrrolidone, etc. In order to improve solubility, dimethyl sulfoxide, dimethylformaldehyde, N-methylpyrrolidinone, etc. were added to these. Mixed solvent can be used. In addition, propionic acid derivatives such as methyl methyl propionate, lactic acid esters such as ethyl lactate, PGMEA (propylene glycol monoethyl acetate), and the like have low toxicity and can be preferably used. In the present invention, such solvents can be used alone or in combination of two or more, and further, isopropyl alcohol, ethyl alcohol, methyl alcohol, n-butyl alcohol, s-butyl alcohol, t-butyl alcohol, isobutyl. An aliphatic alcohol such as alcohol or an aromatic solvent such as toluene or xylene may be contained.

  In the resist substrate of the present invention, first, a varnish of a resist composition dissolved in an organic solvent as described above is applied on a predetermined substrate by a spin coating method or a dipping method, and then usually about 60 to 160 ° C., preferably Is dried at 80 to 140 ° C. and heating time of about 1 to 30 minutes to form a resist layer. The heat drying may be performed, for example, under a reduced pressure, a dry gas atmosphere such as nitrogen, or a gas flow.

In the present invention, the thickness of the resist layer is set to 500 nm or less, particularly from the viewpoint of forming an ultrafine pattern that can correspond to the most advanced semiconductor device. For cutting-edge products of semiconductor devices, a minimum processing dimension of about 45 to 90 nm is currently required. In addition, the photomask used for that purpose usually requires a line width that is four times that of the photomask, and in particular, a line width that is one times that of the photomask. It is required to be. Therefore, when the thickness of the resist layer for forming such a pattern of advanced products exceeds 500 nm, the ratio of the pattern height to the line width of the pattern (aspect ratio) becomes too large. During the etching process, the resist pattern tends to collapse due to various effects such as the surface tension of the solvent.
The thickness of the resist layer is within a range of 500 nm or less as long as sufficient etching resistance can be obtained, that is, a thickness that can function as a resist film in the etching process. Can be determined as appropriate.
As an example, in the case of a typical photomask blank at present, a Cr thin film is formed as a light shielding layer on a transparent substrate, and a resist layer is formed thereon, the thickness of the resist layer is 50 nm. It can be made as thin as possible.

  Examples of the method for controlling the amount of residual solvent in the resist layer include a method of precisely controlling the amount of pre-baking after applying the resist composition. Even in the case of a substrate after pre-baking, the amount of residual solvent in the resist layer can be controlled to be uniform by controlling the storage environment. For example, evaporation of the solvent may be promoted to reduce the residual solvent amount to a certain amount by exposure to an air stream that does not contain a solvent, decrease the pressure, or increase the temperature. Further, by exposing the resist substrate to a gas containing solvent vapor, the amount of residual solvent can be positively increased to a saturated concentration. These techniques can be used alone or in combination.

By appropriately performing such a method, a resist substrate having a residual solvent amount of 0.5 to 20 ppm in the resist layer can be obtained.
In addition, when there is a lower layer in direct contact with the resist layer between the substrate and the resist layer, and the lower layer contains a residual solvent compatible with the residual solvent of the resist layer, the resist layer and the lower layer are combined. The average residual solvent amount is adjusted to 0.5 to 20 ppm.
In the following, the residual solvent amount of the resist layer when there is no lower layer containing a residual solvent that is in direct contact with the resist layer and compatible with the residual solvent of the resist layer, and the resist when the lower layer exists The average residual solvent amount of the layer and the lower layer is collectively referred to simply as “residual solvent amount of resist layer”.
In the present invention, the residual solvent amount of the resist layer means the ratio of the residual solvent to the volume of the resist layer (in the case of the average residual solvent amount including the lower layer, the total volume of the resist layer and the lower layer), 1 ppm = 1 ng / cm ³ .

If the residual solvent amount of the resist layer exceeds 20 ppm, the acid diffusion and movement within the resist layer becomes too active, and in applications where fine patterns are formed, in-plane variation in line width or between resist substrates The variation in is so remarkable that it cannot be ignored. On the other hand, if the residual solvent amount exceeds 20 ppm, the residual solvent amount rapidly decreases during the preservation of the resist substrate, and the variation in exposure sensitivity becomes remarkable for use in forming a fine pattern.
On the other hand, a resist substrate having a residual solvent amount of less than 0.5 ppm in the resist layer can be prepared, for example, by heating at a high temperature in a vacuum. However, it is difficult to diffuse and move the acid in the resist layer. However, a good pattern cannot be obtained. In addition, when the residual solvent amount in the resist layer is less than 0.5 ppm, it is suggested that the diffusibility of a substance intended to improve the storage stability of a basic compound or the like is lowered, and this reduces the storage stability. there is a possibility.

According to the present invention, the residual solvent amount of the resist layer is controlled in the range of 0.5 to 20 ppm, and the residual solvent amount thus controlled is used as an acceptable product. Variations and variations between resist substrates are greatly reduced, improving the dimensional accuracy of the pattern.Further, variations in exposure sensitivity during the storage period of the resist substrate are greatly reduced, and the storage time from resist application to exposure Regardless of this, the reproducibility of pattern dimensions is improved. Although depending on the storage state, a storage period of about 3 months is usually allowed after adjusting the residual solvent amount in the resist layer within the above range. During this storage period, the processing accuracy and sensitivity of the resist substrate are acceptable. Can be maintained well.
Furthermore, even when the resist substrate is a blank for a photomask or a semiconductor wafer used for manufacturing a state-of-the-art product of semiconductor devices (required line width: 45 to 90 nm), the residual solvent amount of the resist layer is 0.5 to 20 ppm. By controlling in this range, the in-plane variation of the pattern line width can be controlled so that the standard deviation 3σ is within 10 nm. Also, depending on the storage conditions, after the amount of residual solvent in the resist layer is adjusted within the above range, a storage period of about one month is normally allowed. It is possible to maintain the processing accuracy and sensitivity of the resist substrate.

  For example, in a resist substrate in which a resist layer is formed on a substrate having an organic film such as an antireflection film on the substrate, the solvent used for forming the base layer and the solvent used for forming the resist layer When the solvents are compatible with each other, the residual solvent amount indicates a residual solvent amount obtained by averaging the residual solvent amount of the resist layer and the residual solvent amount of the underlayer. Here, examples of the compatible solvent include the same resist solvents exemplified in the resist composition, and the compatible solvents for the underlayer and the resist layer may be the same or different, It may be a single solvent or a mixed solvent.

  Examples of the method for measuring the residual solvent amount include, for example, a resist substrate as an object for a predetermined volume amount of the resist layer (in the case of an average residual solvent amount including the lower layer, a predetermined volume amount of the resist layer and the lower layer). Extracted with a solvent that is not used to dissolve the resist composition (usually using a polar organic solvent), and a portion of this extract is collected for gas chromatography, liquid chromatography, nuclear magnetic resonance. Residual solvent is quantified by an analysis method such as spectral method, mass spectrometry, infrared absorption spectral method, etc., and the total residual solvent weight in the resist layer (or resist layer and lower layer) is determined by the volume of resist layer (or resist layer and lower layer). It can be calculated by dividing by (total volume).

  Further, the in-plane uniformity can be evaluated by obtaining the standard deviation 3σ for the in-plane variation of the pattern line width. For example, the line width may be measured at many points using a side-length SEM (scanning electron microscope) or the like to obtain 3σ, and the value may be evaluated against the ITRS roadmap reference.

If the storage stability of the resist substrate is to be specifically considered, such as when photomask blanks are intended to be distributed to the market, the residual solvent amount control method described above is applied to the resist layer of the resist substrate. And it is preferable to preserve | save (it contains the preservation | save state under the market distribution after shipment) after adjusting the residual solvent amount to the range of 0.5-20 ppm.
However, it is also possible to control the resist substrate after coating or purchased blanks to a desired residual solvent amount by a method such as reheating, evacuation, or exposure to solvent vapor before use.

  The resist layer thus formed is irradiated with ionizing radiation and subjected to selective exposure or drawing to form a latent image pattern. Examples of the ionizing radiation include ultraviolet rays, g-rays, i-rays, KrF excimer laser light, ArF excimer laser light, and particle beams such as electron beams. There is no restriction | limiting in particular as a method of selectively exposing by irradiating ionizing radiation, A conventionally well-known method can be used. For example, a method of irradiating ultraviolet rays, g-rays, i-rays, KrF excimer laser light, ArF excimer laser light, etc. through a desired mask pattern with a reduction projection exposure apparatus, or a method of drawing with particle beams such as electron beams Can be used. In this way, a latent image pattern is formed on the resist film.

  Finally, the resist layer having the latent image pattern is developed to visualize the latent image pattern. There is no restriction | limiting in particular as the image development processing method in this process, A conventionally well-known method can be used. For example, the development processing is performed using an alkaline aqueous solution such as a 1 to 10% by weight tetramethylammonium hydroxide aqueous solution. After the development processing, rinsing processing is usually performed using pure water or the like.

  According to the present invention, since it is possible to obtain the dimensional accuracy of a resist pattern that can cope with the miniaturization of a photo process pattern, which will continue to be further developed in the future, the fabrication of blanks for photo masks and the fine processing of semiconductor products using the photo masks It is preferably applied to.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.
Example 1
Assuming the production of photomask blanks, a negative chemically amplified resist was applied on a glass substrate to produce a resist substrate.
First, 20.1 parts by weight of an alkali-soluble resin having a structure represented by the following chemical formula, 1.5 parts by weight of hexamethylol melamine hexamethyl ether as a crosslinking agent, and N- (isopropylsulfonyloxy) succinimide as an acid generator 2 parts by weight and 0.01 part of 1,2-di (4-pyridyl) ethane as a basic compound are dissolved in 93.5 parts by weight of PGMEA (propylene glycol monomethyl ether acetate) An amplified resist was obtained.

  (In the above chemical formula, Et represents an ethyl group. M, n, and o represent the number of each repeating unit. Each repeating unit may be linked randomly.)

The resist was spin-coated on a 6-inch mask substrate so as to have a film thickness of 400 nm when dried. Thereafter, pre-baking was performed at 100 ° C. for 600 seconds to adjust the residual solvent amount immediately after pre-baking to 5.0 ppm. The obtained resist substrate was stored for 8 weeks at a constant temperature, pressure, and humidity in an environment where no solvent vapor was present, and the amount of residual solvent was measured at each of the 4th and 8th week storage points. .
Further, within 1 hour after the completion of pre-baking, the resist layer was exposed in a 100 nm line-and-space pattern by direct writing using an electron beam of 50 keV with an exposure amount of 14 μC / cm ² . Within 30 minutes after exposure, post exposure baking was performed at 100 ° C. for 500 seconds. Thereafter, development was performed using a developer containing 2.38% by weight of tetramethylammonium hydroxide (TMAH) to form a resist pattern.
Furthermore, exposure, post-exposure baking, and development were performed in the same procedure at each time point of the fourth week of storage and the eighth week of storage to form a resist pattern.

(Examples 2-5, Comparative Examples 1-2)
A resist substrate was prepared in the same procedure as in Example 1, and the pre-baking conditions (pre-baking temperature and pre-baking time) were changed to control the amount of residual solvent immediately after pre-baking. In particular, in the case of Comparative Example 2, pre-baking was performed at 100 ° C. under reduced pressure in order to set the residual solvent amount in the resist layer to 0.1 ppm.
The obtained resist substrate was stored in the same manner as in Example 1, and the amount of residual solvent was measured at each time point in the fourth week of storage and the eighth week of storage. Further, in the same manner as in Example 1, a resist pattern was formed immediately after pre-baking, at each point of 4 weeks of storage and 8 weeks of storage.

(test)
<Method for measuring amount of residual solvent in resist layer>
First, a 4 cm × 4 cm square sample was cut out from the resist substrate and extracted with 1.0 mL of acetone in a weighing bottle. A part of this solution was collected and the amount of PGMEA solvent present in the extract was measured by gas chromatography. Furthermore, the concentration was calculated by dividing the total weight of PGMEA in the resist layer by the resist volume.
The detailed measurement conditions of gas chromatography are shown below.
Equipment: HP-6890 made by HEWLETT PACKARD
Column: INERTCAP-1 (0.25 mm I.D. x 60 M, df = 0.25 μm) manufactured by GL Sciences
Inlet temperature: 200 ° C
Detector temperature: 300 ° C
Column temperature: 40 ° C x 3 min (hold) -10 ° C / min (temperature rise) -150 ° C
Sample injection volume: 2 μl

<In-plane uniformity evaluation method>
The in-plane uniformity of the pattern line width is determined by measuring the line width of a 100 nm line and space at a large number of 169 (13 × 13) points in the plane using a length measuring SEM, and taking the line and space of 100 nm as a reference. The standard deviation 3σ of the line width variation was determined. As a criterion for determining in-plane uniformity, 3σ <8 nm required for the mask at the 65 nm node in the ITRS road map is indicated as ◯, and a value higher than that is indicated as ×.

(Test results)
Table 1 shows the residual solvent amount in the resist layer and the in-plane uniformity of the pattern dimensions at each time point of the resist substrate obtained in each of Examples and Comparative Examples immediately after pre-baking, at 4 weeks of storage, and at 8 weeks of storage. Shown in

From the results shown in Table 1, the substrate having a residual solvent amount of 25 ppm immediately after pre-baking (Comparative Example 2) has a high acid diffusivity, and thus the pattern dimensional accuracy is lowered. In addition, regarding the storage stability, the amount of residual solvent after 4 weeks and 8 weeks of storage satisfies the specified range, but the sensitivity decreases significantly due to large fluctuations in the amount of residual solvent, and the same exposure as immediately after pre-baking. However, sufficient in-plane uniformity could not be obtained.
Further, the resist substrate (Comparative Example 1) having a residual solvent amount of 0.1 ppm immediately after pre-baking has good in-plane uniformity immediately after pre-baking, but the in-plane uniformity by storing for 4 weeks or more. Decreased. This is presumably because the amount of residual solvent is low, so that the diffusibility of the basic compound added for the purpose of improving the storage stability is lowered and the effect cannot be obtained sufficiently.

On the other hand, the substrate (Example 5) having a residual solvent amount of 20 ppm immediately after pre-baking was stable for storage within 4 weeks assumed in the mask process. In addition, it was shown that by controlling the amount of residual solvent immediately after pre-baking to 15 ppm or less (Examples 1 to 4), it is possible to stabilize for a longer period than expected in the above process.
For the substrate with a residual solvent amount of 0.5 ppm (Example 1), the residual solvent amount at 4 weeks and 8 weeks after storage is smaller than the specified range, but the sensitivity decreases because there is little fluctuation in the residual solvent amount. Even in the same exposure amount as that immediately after the pre-bake, in-plane uniformity was obtained.
As described above, by controlling the residual solvent amount in the resist layer immediately after pre-baking to 20 ppm or less, the in-plane variation of the line width of the fine pattern and the variation between the resist substrates are improved, and the process from resist coating to drawing is improved. The reproducibility of the pattern dimensions has been improved regardless of the storage period. However, when the substrate is stored for one month or longer, there is a possibility that the line width fluctuates due to contamination of the resist substrate due to factors other than fluctuations in the amount of residual solvent such as bases or acidic components present in the storage environment. Therefore, it is preferable to use the storage period within 4 weeks.

Claims (9)

A resist layer made of a photosensitive composition and having a film thickness of 500 nm or less is provided on the substrate without or through a lower layer containing a residual solvent compatible with the residual solvent of the resist layer and in direct contact with the resist layer. The resist substrate is a pre-baked resist substrate, and the resist substrate has a residual solvent amount immediately after pre-baking of the resist layer when the lower layer is not present, or a resist layer and a lower layer when the lower layer is present. A resist substrate, wherein the average residual solvent amount immediately after pre- baking is 0.5 to 20 ppm.   The resist substrate according to claim 1, wherein the photosensitive composition is a chemically amplified resist.   The substrate according to claim 2, wherein the chemically amplified resist is a negative chemically amplified resist.   The substrate according to any one of claims 1 to 3, wherein the substrate has a thickness of 1 mm or more. After forming a lower layer in advance on two or more substrates as required, a photosensitive composition is applied with or without the lower layer, and a resist layer having a thickness of 500 nm or less is formed to obtain a resist substrate. A step of pre-baking each resist substrate obtained, a step of exposing each resist substrate after pre-baking, a step of baking each resist substrate after exposure, and a step of developing each resist substrate after post-exposure baking A residual solvent amount immediately after the pre-baking step in the resist layer, or a lower layer containing a residual solvent that is in direct contact with the resist layer and compatible with the residual solvent of the resist layer. and wherein it is the average amount of residual solvent after said step of pre-baking the combination of the resist layer and the lower layer, is controlled to 0.5~20ppm between each resist substrate Forming a resist pattern how.   The resist pattern forming method according to claim 5, wherein a pattern having a line width of 200 nm or less is formed.   A resist layer made of a photosensitive composition and having a film thickness of 500 nm or less is provided on the substrate without or through a lower layer containing a residual solvent compatible with the residual solvent of the resist layer and in direct contact with the resist layer. In the case where the lower layer is not present, the residual resist amount of the resist layer, or when the lower layer is present, the average residual solvent amount of the resist layer and the lower layer is 0.5%. A method for storing a resist substrate, comprising adjusting to -20 ppm and then storing. A resist layer made of a photosensitive composition and having a film thickness of 500 nm or less is provided on the substrate without or through a lower layer containing a residual solvent compatible with the residual solvent of the resist layer and in direct contact with the resist layer. is, the amount of the solvent remaining after prebaking of the resist layer of the resist substrate is prebaked, or when measuring the average amount of residual solvent after prebaking the combined resist layer and the lower layer in the case where the lower layer is present, the A method for evaluating a resist substrate, wherein a pass is determined when the residual solvent amount or the average residual solvent amount is within a range of 0.5 to 20 ppm.   The method for evaluating a resist substrate according to claim 8, wherein the resist substrate is immersed in an extraction solvent, and the amount of residual solvent eluted in the extraction solvent is measured.