JPH0449935B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to a resist material suitable for fine pattern formation used in a phosphorography process for manufacturing high-density integrated circuits such as LSIs and VLSIs, and photomasks used in their manufacture. The present invention relates to a new negative resist material that is highly sensitive to ionizing radiation, has high resolution, and provides a resist film with excellent etching resistance after curing. Technical background of the invention and its problems As is well known, in recent years, demands for higher performance and higher integration of semiconductor integrated circuits and the like have been increasing. Therefore, instead of photolithography using conventional ultraviolet rays, lithography technology uses ionizing radiation with shorter wavelength and higher energy, such as electron beams, soft X-rays, and ion beams. Efforts are being made to establish ultra-fine pattern processing technology. On the other hand, in order to enable ultra-fine lithography technology by changing the irradiation source, the resist material used must also have properties corresponding to the changes. Generally, resist materials used in ultrafine lithography using high-energy ionizing radiation are required to have the following properties. b) It must be highly sensitive to ionizing radiation. (b) Must be of high resolution. C. It is possible to form a homogeneous thin film. (d) Excellent dry etching resistance because dry etching is applied, which is essential for forming fine, high-density patterns. E. Excellent developability. In the past, many ionizing radiation-sensitive resist materials have been developed that have the above-mentioned characteristics. and negative type, in which the crosslinking reaction is exceeded and the irradiated area becomes insolubilized by irradiation with ionizing radiation. Among these, positive types generally have the drawbacks of a narrow range of developer suitability and weak dry etching resistance. On the other hand, many negative resists are superior to positive resists in these respects. Typical ionizing radiation-sensitive negative resist materials that have been developed include polyglycidyl methacrylate systems, glycidyl methacrylate-ethyl acrylate copolymer systems, and unsaturated carboxylic acid-methacrylate copolymer systems. However, these negative resist materials also have some practical drawbacks and are not necessarily satisfactory. For example, although glycidyl methacrylate-based resist materials have high sensitivity, a lot of scum occurs at the edges of the drawn pattern, resulting in a decrease in resolution, and in practical terms only a resolution of about 2.0 μm can be obtained. Furthermore, all of the above resists have low dry etching resistance (thickness decreases significantly during dry etching), and have the drawback that it is difficult to apply the dry etching process essential for forming fine patterns with high density. In view of the above-mentioned circumstances, the present inventors have already proposed an ionizing radiation-sensitive negative resist material for the above-mentioned purpose (Patent Application No. 161430 of 1982). That is, this resist material has the general formula (In the formula, R ⁰ is a hydrocarbon residue of an aldehyde or ketone; R ² is a hydrogen atom that can be partially substituted with an acetyl group; R ³ is nothing or a polymerized unit of a monomer copolymerizable with vinyl acetate. ;, m, k are integers indicating the degree of polymerization), and is characterized by consisting of acetalized polyvinyl alcohol having a molecular weight of 10,000 to 1,000,000 alone or in a mixture with other polymers that are compatible with it. It is. Although this ionizing radiation-sensitive negative resist material has excellent properties, there has been a desire for an ionizing radiation-sensitive negative resist material that has higher sensitivity and higher resolution. OBJECTS AND SUMMARY OF THE INVENTION The present invention aims to further improve the characteristics of the above-mentioned ionizing radiation-sensitive negative resist material that the present inventors have already proposed, and has the following objects. (a) To provide an ionizing radiation-sensitive negative resist material having higher sensitivity and resolution. (b) To provide an ionizing radiation-sensitive negative resist material with excellent dry etching resistance. The ionizing radiation-sensitive negative resist material according to the present invention has structural units represented by the following general formulas () and (). (In the formula, R ¹ is a halogen-containing acyl group, and R ³
is either nothing or a polymeric unit that can be copolymerized with vinyl acetate) (In the formula, R ² is a hydrogen atom or an acetyl group, and R ³ is the same as above). halogen-containing acylated polyvinyl alcohol copolymer present in an amount of . The structure of the polymer constituting the resist of the present invention and the manufacturing method itself are known. However, the fact that this polymer is sensitive to ionizing radiation is not known, and therefore, its use as a crosslinking resin is particularly important, especially when crosslinked by irradiation with ionizing radiation to create resist films with excellent dry etching resistance. Giving was completely unknown. DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in more detail below. In the following description, "%" and "part" representing the composition are based on weight unless otherwise specified. In this specification, the term "ionizing radiation-sensitive negative resist material" refers to a material whose solubility in a solvent decreases when irradiated with ionizing radiation such as an electron beam, and which acts as a protective film during etching of a substrate. It means a moist material. The polymer constituting the resist material according to the present invention has a structural unit represented by the above general formula (), and the group R ¹ in this general formula () is a halogen-containing acyl group. More specifically, acetyl groups, propionyl groups, butyryl groups containing halogens such as fluorine, chlorine, bromine, and iodine;
isobutyryl group, valeryl group, isovaleryl group,
Examples include acryloyl group, methacryloyl group, benzoyl group, tolyl group, cyinamoyl group, and phenylacetyl group. These acyl groups may be substituted with multiple halogen atoms. Furthermore, the group R ³ in the above general formula is either nothing or a polymeric unit copolymerizable with vinyl acetate, and specifically, it is a polymeric unit such as ethylene or styrene. When styrene is present as ^R3 ,
In particular, a resist film with excellent dry etching resistance can be obtained. The polymer according to the present invention preferably contains the structural unit represented by the general formula () in an amount of 30 to 80 mol%. If the content of this structural unit is less than 30 mol %, sensitivity and solubility are undesirable, and if it exceeds 80 mol %, adhesiveness is decreased, which is undesirable. Further, the polymer constituting the resist material according to the present invention has a structural unit represented by the above general formula (), and the group R ² in this general formula () is a hydrogen atom or an acetyl group. When the group R ² is H, the structural unit represented by the general formula ( ) is vinyl alcohol, while when the group R ² is an acetyl group, the structural unit represented by the general formula ( ) is vinyl acetate. However, the polymer according to the present invention contains the structural unit represented by the general formula () in an amount of 5 to 70 mol%, and of these, the vinyl acetate unit accounts for 40 mol%.
It is preferable that it is below. Furthermore, the group R ³ has the same meaning as above. base
The polymerized units represented by R ³ are preferably present in an amount of up to 70 mol % of the polymer according to the invention. The halogen-containing acylated polyvinyl alcohol polymer according to the present invention preferably has a molecular weight of 10,000 to 1,000,000. If the molecular weight is less than 10,000, it is difficult to form a resist film, and if the molecular weight exceeds 1,000,000, the viscosity becomes too high when dissolved in a solvent, making it difficult to coat, which is not preferred. The above-mentioned halogen-containing acylated polyvinyl alcohol polymer can be synthesized by reacting polyvinyl alcohol with a halogen-substituted acid (for example, monochloroacetic acid). Further, a halogen-containing acylated polyvinyl alcohol polymer containing a polymer unit copolymerizable with vinyl acetate represented by the structural unit R ³ is first mixed with vinyl acetate,
It can be obtained by synthesizing a copolymer from vinyl acetate and a copolymerizable monomer, saponifying the resulting copolymer, and then reacting it with a halogen-substituted acid (for example, monochloroacetic acid). In the resulting halogen-containing acylated polyvinyl alcohol polymer, the structural units () and () are randomly arranged, as is clear from the manufacturing process. The resist material according to the present invention is preferably composed of a halogen-containing acylated polyvinyl alcohol polymer alone, but if necessary, it may be composed of another polymer having good compatibility and solvent solubility. A mixture can also be used. Examples of such polymers include polyvinyl acetate, polyvinyl alcohol (partially saponified polyvinyl acetate), ethylene/vinyl acetate copolymers and partially saponified products thereof, styrene/vinyl acetate copolymers, and the like. When used as a mixture, the halogen-containing acylated polyvinyl alcohol polymer represented by the above formula is preferably used in a proportion of 50% or more by weight of the total amount with other polymers. Next, a method for performing lithography using the resist material according to the present invention will be described. First, the polyvinyl alcohol copolymer according to the present invention is mixed with an aromatic solvent such as benzene or xylene, a ketone solvent such as acetone or methyl ethyl ketone, a chlorinated solvent such as chloroform or ethylene chloride, or a cellosolve such as methyl cellosolve or ethyl cellosolve. A resist solution of about 5 to 15% having a viscosity suitable for coating is prepared by dissolving it in a single solvent or a mixture of these solvents. Next, this resist solution is uniformly applied onto the semiconductor substrate or mask substrate to be processed by a conventional method such as a spinner coating method, and a pre-baking process is performed to form a coating film for resist formation with a thickness of about 0.1 to 2 μm. . Prebaking conditions depend on the type of solvent used, but in the case of lower alcohols, a temperature of 70 to 90°C and a time of 20 to 40 minutes are generally suitable. Next, on the desired part of the coating film for resist formation,
By irradiating patterns with ionizing radiation such as electron beams and soft X-rays in accordance with conventional methods to draw a pattern, and then treating with a developer to selectively dissolve and remove the resist-forming coating film in the unirradiated areas. Form a resist pattern. As the developer, the same solvents as those used for preparing the resist solution described above are preferably used. On the substrate with the resist pattern after development,
After further performing post-baking treatment and scum removal treatment as necessary, etching is performed to form an etching pattern on the exposed portion of the substrate. Post-bake treatment is for example at a temperature of 120-140℃ for a time
The scum removal process is carried out for 20 to 40 minutes.
For example, using oxygen plasma at a pressure of 0.9 to 1 Torr,
This is done by processing for 1 to 2 minutes under the condition of an output of 100W. Both wet etching and dry etching can be applied to etching, but dry etching is more suitable for forming fine patterns for processing highly integrated semiconductor substrates, mask substrates, etc. In this regard, by introducing a benzene ring into the molecular structure of the polyvinyl alcohol polymer used in the present invention, it is possible to provide a crosslinked resist film with particularly excellent etching resistance. for example,
When a patterned resist film is formed on a chrome mask substrate using a polyvinyl alcohol-based polymer with a benzene ring introduced into its molecular structure, and the exposed chromium portion is dry etched using a chlorine-based gas such as carbon tetrachloride, The film fall rate of the resist film is
A value almost equal to that of a photoresist made of a novolak phenolic resin, which has the best dry etching resistance, can be obtained. If the resist pattern remaining after etching is removed by peeling etc., it is possible to
The cycle ends. As described above, the ionizing radiation-sensitive negative resist material according to the present invention has high sensitivity and high resolution as well as excellent dry etching resistance, and is suitable for use in highly integrated semiconductor circuits that require fine patterning by dry etching or Shows extremely excellent performance in photomask manufacturing. In addition, in this specification, ionizing radiation includes electron beams, soft X-rays,
It means ion beam, etc. EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples. Example 1 10 g of polyvinyl alcohol with a degree of polymerization of 2000 and 200 g of monochloroacetic acid were mixed and reacted for 2 hours with stirring at 70°C. Next, the reaction solution was added to a large amount of water, and the resulting polymer was collected. The obtained polymer was dissolved in cellosolve and reprecipitated.
Repeat this operation to purify the general formula

The structural unit represented by [Formula] and the general formula

Monochloroacetic acid acylated polyvinyl alcohol consisting of the structural unit represented by the formula was obtained. The acylation rate in this polymer was calculated to be 45% based on elemental analysis values. Also, the molecular weight is approximately
It was 150,000 to 160,000. Next, the polymer obtained as described above was dissolved in methyl cellosolve and passed through a 0.2 μm filter to obtain a resist solution with a concentration of 5%. This resist solution was applied onto a chrome mask substrate by a spinner coating method and prebaked at 90°C for 30 minutes to obtain a uniform resist film with a thickness of 6000 Å. Next, a beam diameter of 0.25 μm was applied to this resist film.
An electron beam with an energy of 10 KeV was irradiated. After irradiating with varying exposure doses, the film was developed by immersing it in ethyl cellosolve for 60 seconds, and was further immersed in isopropyl alcohol for 30 seconds for rinsing.The residual film rate was plotted against the exposure dose to obtain a sensitivity curve. The exposure amount at which the residual film rate after development was 50% was defined as the sensitivity.
The sensitivity of this resist film was 1×10 ⁻⁶ clones/cm ² . Furthermore, using this resist, a resist film with a thickness of 6000 Å was formed on a chrome mask substrate in the same manner as above, and an electron beam with a beam diameter of 0.5 μm and an acceleration voltage of 10 kV was applied to the resist film at 1 × 10 ^-6 Coulomb/m ² The pattern was drawn by irradiating with a dose of . Furthermore, this resist film was developed by treating it with ethyl cellosolve for 1 minute, and was washed with isopropyl alcohol for 30 seconds to form a resist pattern. Next, after post-baking the substrate with the resist pattern provided in this way at 140°C for 30 minutes,
1 by oxygen plasma with a pressure of 1 Torr and an output of 100 W.
The scum was removed for 1 minute. Next, this scum-removed substrate is immersed in a ceric ammonium nitrate aqueous solution to remove the chromium film in the areas where the resist pattern is not provided.
Etched for 40 seconds. The resist pattern showed sufficient adhesion to the substrate during the wet etching. After etching, the substrate was immersed in a stripping solution made of a sulfuric acid-hydrogen peroxide mixture maintained at 70°C for 5 minutes, and the resist pattern was peeled off to a thickness of 1 μm.
A photomask with a chrome pattern consisting of lines and spaces of 1 μm was obtained. Example 2 10 g of polyvinyl alcohol with a degree of polymerization of 2000 and 200 g of dichloroacetic acid were mixed and dichloroacetic acid acylated polyvinyl alcohol was obtained in the same manner as in Example 1. The acylation rate in this polymer was calculated to be 50% based on elemental analysis values. Next, the obtained polymer was dissolved in methyl cellosolve and filtered through a 0.2 μm filter to obtain a resist solution with a concentration of 5%. This resist solution was applied by spinner coating onto a silicon wafer having a silicon oxide film with a thickness of 1500 Å, and prebaked at 90° C. for 30 minutes to form a uniform resist film with a thickness of 5000 Å. This resist film has a beam diameter of 0.25μm,
After irradiating with an electron beam having an energy of 10 KeV at 9×10 ⁻⁷ coulombs/cm ² , the resist pattern was developed by processing with acetone for 1 minute, and then washed with isopropyl alcohol for 30 seconds to form a resist pattern. Next, after performing the same post-baking treatment and scum removal treatment as in Example 1, it was immersed in an etching solution obtained by mixing a 40% ammonium fluoride aqueous solution and a 48% hydrofluoric acid aqueous solution at a ratio of 10:1. Etching was performed for 3 minutes. After etching, the substrate is etched using oxygen plasma.
When the resist was removed by processing under conditions of 5 Torr and 300 W, a silicon oxide film pattern consisting of 1 μm lines and 1 μm spaces was obtained. Example 3 Vinyl acetate containing vinyl acetate in an amount of 40 mol%/
A vinyl alcohol/styrene block copolymer was synthesized by saponifying a styrene block copolymer (molecular weight 160,000), and this copolymer was reacted with dichloroacetic acid in the same manner as in Example 1. A vinyl acetate alcohol/styrene block copolymer was obtained. The acylation rate in this polymer was calculated to be 25% based on elemental analysis values. Next, the obtained polymer was dissolved in ethyl cellosolve acetate and filtered through a 0.2 μm filter to obtain a resist solution with a concentration of 5%. This resist solution was applied onto a chrome mask substrate by a spinner coating method and prebaked at 90° C. for 30 minutes to obtain a uniform resist film with a thickness of 6000 Å. Next, the beam diameter is
3×10 ^-6 electron beam of 0.25 μm and energy of 10 KeV
Patterns were drawn by irradiating with an irradiation dose of coulomb/cm ² . Furthermore, this resist film was developed by processing with benzene for 1 minute, and then washed with isopropyl alcohol for 1 minute to form a resist pattern. Next, the substrate with the obtained resist pattern was post-baked at 140°C for 30 minutes, and then the pressure
Scum removal treatment was performed for 1 minute using oxygen plasma at 1 Torr and 100 W output. The exposed portion of the chromium film on this substrate was etched for 5 minutes by reactive sputter etching using a mixed gas of C1 ₄ and O ₂ at a pressure of 3×10 ⁻¹ Torr and an output of 300 W. The film fall rate of the resist pattern was 200 Å/min, indicating sufficient dry etching resistance. After etching, the substrate was immersed in a stripping solution consisting of a sulfuric acid-hydrogen peroxide mixture at 70° C. for 5 minutes, and then the resist pattern was peeled off to obtain a photomask having a chromium pattern consisting of 2 μm lines and spaces. Example 4 Dichloroacetic acid acylated polyvinyl alcohol was obtained in the same manner as in Example 1 using polyvinyl alcohol with a degree of polymerization of 500 and dichloroacetic acid. The acylation rate in this polymer is determined from elemental analysis values.
It was calculated to be 36%. The obtained polymer was dissolved in methyl cellosolve and filtered through a 0.2 μm filter to obtain a resist solution with a concentration of 5%. This resist solution was applied onto the substrate and dried to form a resist film with a thickness of 5000 Å.The resist solution was irradiated with a pattern of 10 KeV electron beams and developed with methyl cellosolve ^. coulomb/ ^cm2
showed a sensitivity of Example 5 Trichloroacetic acid acylated polyvinyl alcohol was obtained in the same manner as in Example 1 using polyvinyl alcohol with a degree of polymerization of 2000 and trichloroacetic acid.
The acylation rate in this polymer was 63%. When the sensitivity was measured using the obtained polymer in the same manner as in Example 4, the resist film was 1.0×
It showed a sensitivity of 10 ^-5 coulombs/cm ² . Example 6 2 parts of monochloroacetic acylated polyvinyl alcohol obtained in Example 1 and 1 part of polyacetic acid with a degree of polymerization of 1000 were dissolved in methyl ethyl ketone and mixed thoroughly to obtain a resist solution with a concentration of 6%. . When the sensitivity was measured in the same manner as in Example 4 using the obtained resist solution, the resist film was 3×
It exhibited a sensitivity of 10 ^-6 coulombs/cm ² .

Claims (1)

[Claims] 1. Constituent units represented by the following general formulas () and () (In the formula, R ¹ is a halogen-containing acyl group,
^R3 is nothing or a copolymerizable unit copolymerizable with vinyl acetate) (In the formula, R ² is a hydrogen atom or an acetyl group, and R ³ is the same as above). halogen-containing acylated polyvinyl alcohol copolymer present in an amount of Negative resist material sensitive to ionizing radiation.