JPH0331250B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resist material suitable for forming fine patterns used in a lithography process in the production of high-density integrated circuits such as LSIs and VLSIs, or photomasks used in the production thereof, and more particularly relates to resist materials that are resistant to ionizing radiation. The present invention relates to a new negative resist material that has high sensitivity and high resolution, and provides a resist film with excellent etching resistance after curing. As is well known, in recent years there has been an increasing demand for higher performance and higher integration of semiconductor integrated circuits and the like.
For this reason, lithography technology has replaced conventional photolithography using ultraviolet rays with ionizing radiation, which has a shorter wavelength and higher energy.
That is, efforts are being made to establish ultrafine pattern processing techniques using lithography using electron beams, soft X-rays, ion beams, and the like. On the other hand, in order to enable ultra-fine lithography technology by changing the radiation source, the resist material used must also have characteristics that correspond to such 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 have 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. Conventionally, many types of ionizing radiation-sensitive resists have been developed to be used for the above-mentioned purposes. It is classified as a negative type, in which a crosslinking reaction occurs when irradiated with radiation, and the irradiated area becomes insolubilized. 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 negative resists that have been developed so far include polyglycidyl methacrylate systems, glycidyl methacrylate-ethyl acrylate copolymer systems, and unsaturated carboxylic acid-methacrylate copolymer systems. However, these negative resists also have some practical drawbacks and are not necessarily satisfactory. For example, although a glycidyl methacrylate resist has high sensitivity, a large amount of scum occurs at the edges of the drawn pattern, resulting in a decrease in resolution, and in practice only a resolution of about 2.0 μm can be obtained. In addition, all of the above resists have low dry etching resistance (the film thickness decreases significantly during dry etching), and have the disadvantage that it is difficult to apply the dry etching process that is essential for creating high-density, fine patterns. ing. In view of the above-mentioned circumstances, an object of the present invention is to provide a new type of ionizing radiation-sensitive negative resist that is highly sensitive, has excellent dry etching resistance, and is capable of achieving high resolution. The present inventors have already developed one negative-tone resist sensitive to ionizing radiation for the above-mentioned purpose (Showa 56
(Patent Application No. 161430). That is, this resist 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 being composed 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. be. The resist of the present invention corresponds to one type of the above-mentioned resist, and is based on the knowledge that when the group R ⁰ in the above formula is a specific group, a significant increase in sensitivity can be obtained. That is, the ionizing radiation negative resist of the present invention has the general formula (In the formula, R ¹ is

[Formula] R ² is an acetal with a molecular weight of 10,000 to 1,000,000, represented by a hydrogen atom that can be partially substituted with an acetyl group (n is an integer of 5 or more representing the number of methylene chains; m is an integer representing the degree of polymerization) It is characterized by being made of polyvinyl alcohol polymer. The present invention will be explained in more detail below. In the following description, "%" and "part" indicating composition are based on weight unless otherwise specified. The group R ¹ contained in the acetalized moiety in the acetalized polyvinyl alcohol represented by the above formula is
It is obtained as a hydrocarbon residue derived from an aldehyde during acetalization between an aliphatic aldehyde and an alcohol. The present invention provides a resist polymer particularly highly sensitive to ionizing radiation polymerization when the number n in R ¹ , that is, -(CH ₂ )- _o H (written horizontally for convenience) is 5 or more. It is based on knowledge of what is happening. It has been found that sensitivity generally increases with increasing n. However, even if n exceeds 20, the domain structure formed by the hydrophobic bonds between the groups ^R1 of each molecule becomes too large, and no further increase in sensitivity can be expected;
From the viewpoint of synthesis of aldehyde or solubility in a suitable solvent as an acetal-reactive resist, it is considered appropriate that n is up to about 20. Although it is outside the scope of the present invention, when a methylene chain having a branched chain obtained by acetalization using a branched aldehyde or an aliphatic ketone instead of a linear aldehyde is used instead of R ¹ . It is also thought that the sensitivity of the acetalized polyvinyl alcohol produced increases as the number of carbon atoms increases. The reason why the sensitivity to ionizing radiation polymerization increases as the methylene chain length increases is not necessarily clear, but it can be explained by a) changes in the arrangement of the molecular chains;
b) The methylene chains become round (this is evidenced by the fact that the solution viscosity, etc., decreases even if the chains become longer), and c) the microdomain structure is formed by the hydrophilic polyvinyl alcohol moiety and the hydrophobic methylene chain. It is presumed that this is because factors such as the formation of a three-dimensional network structure during polymerization by ionizing radiation irradiation facilitate the development of a three-dimensional network structure. The resist of the present invention has a base of acetalized moieties.
This resist is not particularly different from the resist proposed in Patent Application No. 161430 of 1982, except that R ¹ has a relatively long methylene chain. That is, the acetalized polyvinyl alcohol described above can be obtained, for example, by acetalizing polyvinyl alcohol with an aldehyde in a homogeneous or heterogeneous system using an acid such as hydrochloric acid or sulfuric acid or a salt thereof as a catalyst. The acetalized polyvinyl alcohol polymer can also be obtained by using polyvinyl acetate or a partially saponified product thereof as a starting material and proceeding deacetic acid removal and acetalization in parallel in the same system as above. In this way, an acetalized polyvinyl alcohol polymer having the above formula is obtained. As can be seen from the above description, R ² in the formula is usually H (hydrogen), but a portion thereof may be an acetyl group (CH ₃ CO) derived from polyvinyl acetate. Further, as is clear from the manufacturing process, the acetalized polyvinyl alcohol polymer is usually a random copolymer, and the expression in the above formula does not necessarily mean a bonding mode like a block copolymer. Acetalized polyvinyl alcohol polymer is
Overall, it has a molecular weight range of 10,000 to 1,000,000. The molar content of acetalized moieties, i.e., /
(+m) preferably ranges from 20 to 80%. Also, when the number of vinyl alcohol polymerization units is m ₁ and the number of vinyl acetate polymerization units is m ₂ (m ₁ + m ₂ = m),
Vinyl alcohol polymerized unit content, i.e. m ₁ /
(+m+n) is 10 to 70 mol%, and the vinyl acetate polymerization unit content, i.e. m ₂ /(+m+n), is 40
It is preferable to set it to mol% or less. In the resist of the present invention, the above acetalized polyvinyl alcohol polymer is preferably used alone, but if necessary, it may be a mixture of this and other polymers having good compatibility and solvent solubility.
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 acetalized polyvinyl alcohol polymer represented by the above formula can be used in an amount of 50% by weight of the total amount with other polymers.
It is preferable to use the above ratio. Next, a method for performing lithography using the resist of the present invention will be described. First, the resist of the present invention is prepared using 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 solvent such as methyl cellosolve or ethyl cellosolve, either alone or in combination. A resist solution of about 5 to 15% having a viscosity suitable for coating is prepared by dissolving it in a solvent. 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 prebaking process is performed to form a resist film with a thickness of about 0.1 to 2 μm. Prebake conditions depend on the type of solvent used, but in the case of lower alcohols, the temperature
A temperature of 70 to 90°C and a time of 20 to 40 minutes is suitable. Next, a desired part of the resist film is irradiated with ionizing radiation such as an electron beam or soft X-ray to draw a pattern according to a conventional method, and then treated with a developer to selectively remove unirradiated parts of the resist film. A resist pattern is formed by dissolving and removing the resist. As a developer,
Solvents similar to those used in 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-baking treatment is for example temperature 120-140℃, time 20
The scum removal treatment can be carried out for 1 to 2 minutes at a pressure of 0.9 to 1 Torr and an output of 100 W using oxygen plasma, for example. Although both wet etching and dry etching can be applied to etching, 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 acetalized polyvinyl alcohol used in the present invention, it is possible to provide a crosslinked resist film with particularly excellent etching resistance. For example, a patterned film of the resist of the present invention thus obtained is formed on a chrome mask substrate,
When dry etching exposed chromium areas with a chlorine-based gas such as carbon tetrachloride, the film deterioration rate of the resist film is equivalent to that of a photoresist made of novolac-based phenolic resin, which has the best dry etching resistance. can get. If the resist pattern remaining after etching is removed by peeling or the like, one cycle of the lithography process is completed. As described above, the present invention has particularly high sensitivity, high resolution, and excellent dry etching resistance, so it is suitable for manufacturing highly integrated semiconductor circuits or photomasks that require dry etching for fine patterning. A suitable and highly practical ionizing radiation sensitive negative resist is provided. Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples. Example 1 1.0 g of polyvinyl alcohol with a degree of polymerization of 1500 and a degree of saponification of 98, 8 g of tetradecyl alcohol (0.057 mol),
Add 10 cc of ethanol and 1 cc of purified water to a 50 cc Erlenmeyer flask, add 2 drops of hydrochloric acid, and add while stirring.
The reaction was carried out at 40°C for 30 hours. Next, the reaction solution was added to methanol containing a neutralizing amount of NaOH, the precipitated polymer was added to chloroform and methanol, and the precipitated polymer was purified by repeating reprecipitation with chloroform and ^methanol . Acetalized polyvinyl alcohol corresponding to ( _-CH2 ) _-13H was obtained with a yield of 95%. The η _SP /C (where η _SP is the ratio and C is the concentration [g/cc]) of a 0.1 g/10 cc dichloroethane solution of the above polymer at 30° C. is 96 cm ³ /g, which is estimated to be about 170,000. Also, the acetalization rate/(+m) is approximately 70
It was in mol%. The above polymer was dissolved in ethyl cellosolve acetate and passed through a 0.2 μm filter to give a concentration of 6%.
A resist solution was obtained. 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
An electron beam of 0.25 μm and an energy of 10 KeV was irradiated.
After irradiating with varying exposure doses, the film was developed by immersing it in methyl ethyl ketone for 60 seconds, and then rinsing by immersing it in isopropyl alcohol for 30 seconds. Sensitivity was defined as the amount of remaining film at which the remaining film rate was 50%. The sensitivity of this resist film was 7.0×10 ⁻⁷ coulombs/cm ² . Furthermore, using this resist, a resist film with a thickness of 6000 Å was obtained on a chromium 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 used to coat this with 7.0 × 10 ^-7 coulombs/cm. A pattern was drawn by irradiating with a dose of ² . Furthermore, this resist film was developed by processing with methyl ethyl ketone for 1 minute, and washed with isopropyl alcohol for 30 seconds 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 was etched for 40 seconds by immersing this substrate in an aqueous ceric ammonium nitrate solution. The resist pattern showed sufficient adhesion to the substrate during the wet etching. 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 the resist pattern was stripped off to obtain a photomask with a chrome pattern consisting of lines and spaces each 1 μm in size. . Example 2 Acetalized polyvinyl alcohol was synthesized in the same manner as in Example 1 using polyvinyl alcohol with a degree of polymerization of 500 and octyl aldehyde (molecular weight approximately 90,000). The obtained polymer was dissolved in ethyl cellosolve acetate and passed through a 0.2 μm filter to obtain a resist solution with a concentration of 8%. 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. Next, apply the beam diameter to this resist film.
0.25μm, energy 10KeV electron beam 5.0×10 ^-6
After irradiating with Coulomb/cm ² , the resist pattern was developed by processing with methyl ethyl ketone for 1 minute, and was 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.
The resist was removed by processing under conditions of 5 Torr and 300 W, and a silicon oxide film pattern consisting of lines and spaces of 1 μm each was obtained. Sensitivity comparison test example Various acetalized polyvinyl alcohols were obtained in almost the same manner as in Examples 1 and 2, except that polyvinyl alcohols with different degrees of polymerization (500, 1500, 2000) and aldehydes with different methylene chain lengths were used. Sensitivity was measured in the same manner as in Example 1. The measured sensitivities are shown in the following table along with the viscosity and γ value of the resulting polymer. Also, the changes in sensitivity with respect to methylene chain length are shown in the attached drawings. These results clearly show an increase in sensitivity with increasing methylene chain length in the acetalization moiety.

【table】

【table】 [Brief explanation of drawings]

The drawing is a graph showing the change in the electron beam polymerization sensitivity of the above polymer with respect to the change in the methylene side chain length in the acetalized portion of the acetalized polyvinyl alcohol.

Claims (1)

[Claims] 1. General formula (In the formula, R ¹ is [Formula] R ² is a hydrogen atom that can be partially substituted with an acetyl group (n is a number of 5 or more representing the number of methylene chains; m is an integer representing the degree of polymerization)
An ionizing radiation-sensitive negative resist characterized by comprising an acetalized polyvinyl alcohol polymer represented by the following formula and having a molecular weight of 10,000 to 1,000,000.