JP2557817B2 - Ionizing radiation sensitive negative resist - Google Patents

Description

The present invention relates to a resist material suitable for forming a fine pattern used in a lithographic process for manufacturing a photomask used for manufacturing high-density integrated circuits such as LSI and VLSI, or for manufacturing them. More specifically, the present invention relates to a novel negative resist material which is highly sensitive to ionizing radiation and has high resolution and, after curing, gives a resist film having excellent etching resistance.

As is well known, in recent years, high performance of semiconductor integrated circuits,
The demand for higher integration is ever increasing. Therefore, as a lithographic technique, photolithography using conventional ultraviolet rays is replaced with ionizing radiation having a shorter wavelength and higher energy, that is, lithography using electron beams, soft X-rays, ion beams, etc. Efforts are being made to establish fine pattern processing technology.

On the other hand, in order to enable the ultrafine lithographic technique by changing the radiation source as described above, the resist material used must also have characteristics corresponding to it. Generally, the following characteristics are required for a resist material used for ultrafine lithography using high-energy ionizing radiation.

B) High sensitivity to ionizing radiation.

B) High resolution.

C) A homogeneous thin film can be formed.

D) Excellent dry etching resistance because dry etching, which is essential for high-density fine patterning, is applied.

E) Excellent developability.

Conventionally, many types of ionizing radiation sensitive resists having the above-mentioned characteristics have been developed. These are positive type which is solubilized in the irradiated part by causing a disintegration reaction by the irradiation of ionizing radiation. , Negative type in which the irradiation part is insolubilized by a crosslinking reaction caused by irradiation with ionizing radiation.

Among them, the positive type generally has a drawback that the suitable range of the developing solution is narrow and the dry etching resistance is weak. On the other hand, many negative resists are superior to positive resists in these respects.

Typical examples of negative resists sensitive to ionizing radiation that have been conventionally developed include polyglycidyl methacrylate type, glycidyl methacrylate-ethyl acrylate copolymer type, and unsaturated carboxylic acid-methacrylate copolymer type. However, these negative resists also have some drawbacks in practical use, and it is difficult to say that they are always satisfactory. For example, a glycidyl methacrylate-based resist has a high sensitivity, but the resolution is lowered because scum is often generated at the edge of the drawing pattern,
Practically, only a resolution of about 2.0 μm can be obtained. Further, each of the above resists has a drawback that the dry etching resistance is low (the film thickness is largely reduced during dry etching), and it is difficult to apply the dry etching process which is indispensable for forming a high-density fine pattern.

In view of the above-mentioned circumstances, it is an object of the present invention to provide a new type of ionizing radiation sensitive negative resist which has high sensitivity and excellent dry etching resistance and can achieve high resolution.

The present inventors have already developed one ionizing radiation sensitive negative resist for the above-mentioned purpose (Japanese Patent Application No. 16/1981
No. 1430). That is, this resist has the general formula (In the formula, R ⁰ represents a hydrocarbon residue of an aldehyde or a ketone; R ²
Is a hydrogen atom which can be partially substituted with an acetyl group; R ³ is absent or is a polymer unit of a monomer copolymerizable with vinyl acetate; l, m and k are integers indicating the degree of polymerization) The acetalized polyvinyl alcohol having a molecular weight of 10,000 to 1,000,000, or a mixture of the acetalized polyvinyl alcohol and another polymer compatible with the acetalized polyvinyl alcohol.

The present inventors further developed a series of research on the above resists, synthesized various polymers having an acetal group as a side chain as an ionizing radiation sensitive group, and examined the ionizing radiation reactivity of these polymers. The inventors have found that they have extremely excellent performance and have completed the present invention.

That is, the negative resist sensitive to ionizing radiation according to the present invention has the general formula (In the formula, R ¹ is a hydrogen atom or an alkyl group, R ² is a hydrocarbon residue of an aldehyde or a ketone and contains an aromatic hydrocarbon group, and m is an integer of 1 or more showing a methylene chain length. , N is 1 or 2), a polymer having a molecular weight of 10,000 to 1,000,000, which comprises a structural unit having an acetal structure in the side chain, or a copolymer or a polymer having a molecular weight of 10,000 to 1,000,000 containing the structural unit. It is characterized in that it is composed of a mixture with another polymer compatible with.

The structure of the polymer constituting the resist of the present invention and the production method itself are known. However, the fact that this polymer is sensitive to ionizing radiation is not known, and therefore, its use as a crosslinkable resin, especially a resist film excellent in dry etching resistance which is crosslinked by irradiation of ionizing radiation is used. It was never known to give.

Hereinafter, the present invention will be described in more detail. In the following description, “%” and part indicating composition are based on weight unless otherwise specified.

The resist according to the present invention is represented by the above general formula,
In the formula, R ₁ is a hydrogen atom or an alkyl group, for example, a methyl group,
Examples thereof include ethyl group and n-propyl group.

The group R ² included in the acetal structure of the side chain is a hydrocarbon residue derived from an aldehyde or a ketone during the acetalization between an aldehyde or a ketone and an alcohol, which is a hydrocarbon group containing an aromatic group. is there. That is, in the present specification, the term “acetalization” includes not only acetalization in a narrow sense by dehydration condensation between aldehyde and alcohol but also dehydration condensation between ketone and alcohol (so-called ketalization). Is used to mean Specific examples of such a hydrocarbon residue of an aldehyde or a ketone include an aromatic hydrocarbon group, (In the formula, R ³ represents hydrogen or a substituent other than hydrogen) and the like.

The above group R ² may contain halogen such as chlorine.

On the other hand, in the formula, m is a number of 1 or more representing the methylene chain length, n is a number of 1 or 2, and indicates that the acetal structure is a 5-membered ring or a 6-membered ring.

Of these, those containing an aromatic group as the R ² group are preferably used in order to provide a resist film having excellent dry etching resistance.

The polymer having an acetal structure in the side chain as described above preferably has a molecular weight of 10,000 to 1,000,000, and preferably 10,000 to 15,000. Generally, high sensitivity is obtained as the molecular weight increases, but if the molecular weight becomes too large, the coating suitability is impaired, which is not preferable.

The resist of the present invention is a homopolymer consisting of a structural unit having an acetal structure in the side chain represented by the above general formula, or a copolymer containing the structural unit, or good compatibility with the homopolymer and It is composed of a mixture with another polymer having good solvent solubility. Among these, a homopolymer composed of a structural unit having an acetal structure in the side chain represented by the above general formula is preferable.

The copolymer containing a structural unit having an acetal structure in the side chain represented by the above general formula, the structural unit and other structural units such as styrene, vinylnaphthalene, α-methylstyrene, chloromethylated styrene, parogenization Examples thereof include styrene, isopropenyl naphthalene, chloromethylated vinyl naphthalene, methyl acrylate, ethyl acrylate, butyl acrylate, glycidyl methacrylate, trifluoroethyl methacrylate ethylene, vinyl acetate unit and the like.

The other constitutional units as described above are present in the copolymer in an amount of 20 to 80 mol% in order to impart suitability as an ionizing radiation resist such as high sensitivity, etching resistance, and high resolution to the resist. be able to. Such a copolymer has 10,0
It preferably has a molecular weight of 100 to 100,000,000.

Further, as described above, the resist according to the present invention has a homopolymer composed of a structural unit having an acetal structure in the side chain represented by the above general formula, and good compatibility with the homopolymer and good solvent solubility. It may be a mixture with another polymer. Such polymers include polyvinyl acetate, polyvinyl alcohol (partially saponified polyvinyl acetate), ethylene / vinyl acetate copolymers and partially saponified products thereof,
Examples thereof include styrene / vinyl acetate copolymer. It is preferable that these copolymers have a molecular weight of 10,000 to 1,000,000. When used as a mixture, the homopolymer composed of a structural unit having an acetal structure in the side chain represented by the above formula is preferably used in a proportion of 50% by weight or more based on the total amount of the other polymers.

The above-mentioned polymer can be produced by a known method. For example, acrylic acid chloride or methacrylic acid chloride and an alcohol having an acetal ring are subjected to dehydrochlorination reaction to synthesize a monomer, which is obtained by polymerizing in a homogeneous system or a heterogeneous system by a catalyst such as azoisobutylnitrile or thermal polymerization. To be

Next, a method of performing lithography using the resist according to the present invention will be described.

First, the resist according to the present invention is used alone or in an aromatic solvent such as benzene or xylene; a ketone solvent such as acetone or methyl ethyl ketone; a chlorine solvent such as chloroform or ethylene chloride; a cellosolve solvent such as methyl cellosolve or ethyl cellosolve. By dissolving in these mixed solvents, a resist solution of about 5 to 15% having a viscosity suitable for coating is prepared.

Then, the resist solution is uniformly applied to a semiconductor substrate or a mask substrate to be processed by a conventional method such as a spinner-coating method, and a pre-baking treatment is performed to a thickness of 0.
A resist film of about 1 to 2 μm is formed. 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.

Subsequently, a desired portion of the resist film is irradiated with a pattern of ionizing radiation such as an electron beam or a soft X-ray according to a conventional method to draw a pattern, which is further treated with a developing solution to select a resist film of an unirradiated portion A resist pattern is formed by physically removing it. As the developing solution, the same solvents as those used for preparing the resist solution described above are preferably used.

The substrate having the resist pattern after development is further subjected to post-baking treatment and scum removal treatment, if necessary, and then etching is performed to form an etching pattern on the exposed portion of the substrate. The post-baking treatment is performed, for example, at a temperature of 120 to 140 ° C. for a time of 20 to 40 minutes, and the scum removal treatment is performed using oxygen plasma at a pressure of 0.9 to 1 To.
It is performed by processing for 1 to 2 minutes under the condition of rr and output of 100W.

Either wet etching or dry etching can be applied, but dry etching suitable for fine patterning is more suitable for processing highly integrated semiconductor substrates, mask substrates and the like. In this respect, by introducing a benzene ring into the molecular structure of the resist used in the present invention, a crosslinked resist film having particularly excellent etching resistance can be provided. For example, when the patterned film of the resist of the present invention thus obtained is formed on a chromium mask substrate and the chromium exposed portion is dry-etched by a chlorine-based gas such as carbon tetrachloride, the resist film The sliding speed is almost the same as that of a photoresist made of a novolak-based phenol resin, which has the best dry etching resistance.

If the resist pattern remaining after etching is removed by peeling or the like, one cycle of the lithographic process is completed.

As described above, the ionizing radiation-sensitive negative resist according to the present invention has high sensitivity and high resolution and is excellent in dry etching resistance, and has a highly integrated semiconductor circuit or photomask that requires fine patterning by dry etching. Shows extremely excellent performance in the production of In the present specification, ionizing radiation means an electron beam or soft X.
A line, an ion beam, etc. are meant.

 Hereinafter, the present invention will be described more specifically by way of examples.

Reference Example 1 60 g of (2,2-dimethyl-1,3-dioxolan-4-yl) methyl acrylate (DMDMA) was dissolved in 300 g of toluene, and 8 × 10 ^-2 g of azoisobutyronitrile (AIBN) was dissolved therein.
Was added and reacted at 50 ° C. for 4 hours under a nitrogen atmosphere. The reaction solution obtained after the reaction was added to a large amount of methanol to recover the polymer, and the obtained polymer was reprecipitated and purified twice with a benzene-ethanol system, and dried to obtain poly (2,2-dimethyl-
1,3-dioxolan-4-yl) methyl acrylate (P
DMDMA) got. This PDMDMA was dissolved in chlorobenzene and passed through a 0.2 μm filter to obtain a resist solution having a concentration of 5%.

This resist solution was applied onto a chromium mask substrate by a spinner coating method, and prebaked at 90 ° C. for 30 minutes to obtain a uniform resist film having a thickness of 6,000Å. Next, a beam diameter of 0.25 μm and energy of 10 KeV were applied to this resist film.
Was irradiated with an electron beam of 4 × 10 ⁻⁸ coulomb / cm ² to draw a pattern. Further, this resist film was treated with methyl ethyl ketone for 1 minute, developed, and washed with isopropyl alcohol for 1 minute to form a resist pattern.

Next, the substrate provided with the resist pattern is heated to 140 ° C.
After 30 minutes of post-baking, a scum removal treatment was performed for 1 minute with oxygen plasma having a pressure of 1 Torr and an output of 100 W.

Wet this substrate with a chromium mask wet etching solution (165 g of ceric ammonium nitrate, 43 ml of 70% perchloric acid,
Immerse in pure water (1000 ml) for 1 minute, etch, wash with water,
The substrate was immersed in a stripping solution consisting of sulfuric acid-hydrogen peroxide mixture at 70 ° C for 5 minutes, and then the resist pattern was stripped to 2 μm.
A photo mask having a chrome pattern consisting of lines and spaces was obtained.

Reference Example 2 (2,2-Dimethyl-1,3-dioxolan-4-yl) methyl methacrylate (50 g) and styrene (50 g) were reacted in a benzene solvent with AIBN (0.1 g) as a catalyst at 52 ° C. for 12 hours (2,2-
A copolymer of dimethyl-1,3-dioxolan-4-yl) methyl methacrylate and styrene was obtained.

The obtained copolymer was dissolved in chlorobenzene and filtered to obtain a resist solution having a concentration of 5%.

This resist solution was applied onto a chromium mask substrate by a spinner coating method, and prebaked at 80 ° C. for 30 minutes to form a uniform resist film having a thickness of 0.6 μm. Next, this resist film was irradiated with an electron beam having an energy of 10 KeV at 1 × 10 ⁻⁶ coulomb / cm ² , and then developed with methyl cellosolve and washed with isopropyl alcohol to form a resist pattern.

Then, post-baking treatment and scum removal treatment similar to those in Reference Example 1 were performed, and then the pressure of this substrate was 3 × 10 ^−1.
The exposed portion of the chromium film was etched for 5 minutes by reactive sputtering using a mixed gas of Cl ₄ and O ₂ at Torr and an output of 300 W. The film sliding speed of resist pattern is 200Å /
Therefore, it showed sufficient dry etching resistance.

After etching, the resist pattern was peeled off in the same manner as in Reference Example 1 to obtain a photomask having a chrome pattern composed of 1 μm lines and spaces.

Reference Example 3 In the same manner as in Reference Example 1 using (2-oxo-1,3-dioxolan-4-yl) methyl acrylate, poly (2
-Oxo-1,3-dioxolan-4-yl) methyl acrylate (PODMA) was prepared. Dissolve this PODMA in chlorobenzene and filter through a 0.2 μm filter to obtain a concentration of 6
% Resist solution was obtained.

This resist solution is applied on a silicon wafer having a silicon oxide film with a thickness of 1500 Å by a spinner coating method, and prebaked at 90 ° C for 30 minutes,
A uniform resist film with a thickness of 5000Å was formed. Next, this resist film was irradiated with an electron beam having a beam diameter of 0.25 μm and an energy of 10 KeV at 1 × 10 ⁻⁷ clone / cm ² , and then treated with methyl ethyl ketone for 1 minute and developed, and washed with isopropyl alcohol for 30 seconds to form a resist. A pattern was formed.

Then, after the same post-baking treatment and scum removal treatment as in Reference Example 1, 40% ammonium fluoride aqueous solution and 48% hydrofluoric acid aqueous solution were mixed at a ratio of 10: 1 and immersed in an etching solution, Etching was carried out for 3 minutes.

After etching, the substrate was exposed to oxygen plasma for 5 Torr, 3
The resist was peeled off by processing under the condition of 00 W, and a pattern of a silicon oxide film consisting of lines and spaces of 1 μm each was obtained.

Example having a benzene ring in the acetal part (2-phenyl-1,3-dioxane-4,6-cyclohexenemethylene-4
-Yl) Methyl acrylate was used to obtain a copolymer with styrene by the same method as in Reference Example 2. The obtained copolymer was dissolved in chlorobenzene and passed through a 0.2 μm filter to obtain a resist solution having a concentration of 6%.

This resist solution was applied by a spin coating method on a silicon wafer obtained by growing 3000 Å polysilicon on a silicon oxide film, and prebaked at 90 ° C. for 30 minutes to obtain a uniform resist film with a thickness of 5000 Å. Next, this resist film was irradiated with an electron beam having a beam diameter of 0.25 μm and an energy of 10 KeV so that the irradiation amount was 1.0 × 10 ^-6 coulomb / cm ² and a pattern was drawn. After the drawing, it was treated with methyl ethyl ketone for 1 minute. Develop and with isopropyl alcohol
It was washed for 30 seconds to form a resist pattern.

Next, the silicon wafer on which the resist pattern was formed
After post-baking at 140 ° C. for 30 minutes, scum removal was performed by plasma in the same manner as in Example 1, and then treated with CF ₄ mixed with 2% O ₂ under the conditions of 2 Torr and 300 W output. The exposed portion of the polysilicon film was dry etched.

After dry etching, the substrate was exposed to oxygen plasma for 5T.
Treated under the conditions of orr and 300W to remove the resist, width 2.0μ
A polysilicon pattern in which a line of m and a gap of 2.0 μm in width were repeated in sequence was obtained.

Claims (1)

(57) [Claims] 1. A general formula (In the formula, R ¹ is a hydrogen atom or an alkyl group, R ² is a hydrocarbon residue of an aldehyde or a ketone and contains an aromatic hydrocarbon group, and m is an integer of 1 or more showing a methylene chain length. , N is 1 or 2), the molecular weight of the constituent unit having an acetal structure in the side chain is 10,000 to 10,000.
1,000,000 polymer, or molecular weight including the above structural unit 1
A negative resist sensitive to ionizing radiation, which comprises a copolymer of 0,000 to 1,000,000 or a mixture of the above polymer and another polymer compatible with the ionizing radiation.