JPS62299836A - Fine pattern forming method - Google Patents

Abstract

PURPOSE:To enable light contrast to be increased again from low to high contrast without using complicated steps and patterns each in a size of <=1mum to be formed with high precision by using a specified polymer as a polymer in a photosensitive resin. CONSTITUTION:A lower resist layer is coated with a photosensitive resin comprising a light-bleachable agent of diazonium salt, water or an organic solvent, and the polymer having structural units represented by the formula shown on the right in which each of R1-R3 is H, 1-4C alkyl, halogen, or nitride; R4 is H, 1-4C alkyl, halogen, OH, or COOH; and X is H, an alkali metal, an alkaline earth metal, or ammonium. The patterns are formed by exposing the upper layer and the lower layer to light. The polymer of the upper layer may be the copolymer of the monomers themselves from which said structural units of the formula result, or one of these monomers and generally known other monomers,such as styrene or alpha-methylstyrene. It is preferred to regulate the content of the structural units each having the benzenesulfonic acid group to >=50mol% of the copolymer.

Description

Detailed Description of the Invention 3 Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a method for forming fine patterns in the semiconductor field. For more details, apply a photosensitive resin to the resist,
The present invention relates to a fine pattern forming method for improving dimensional accuracy and resolution thinning using a light exposure method.

(Problems with the Prior Art) With the increasing integration of semiconductors, the pattern dimensions are becoming increasingly finer, and in recent years there has been a demand for highly accurate processing with line widths of 1 μm or less. Various methods have been proposed to meet these demands.

For example, in terms of equipment, the following two points are expected to improve resolution based on optical theory: 1) shortening the wavelength of the light source; 2) using a lens with a large numerical aperture; and there are actually test machines on the market. However, if the wavelength of the light source is shortened, the transmittance of the lens decreases, making it impossible to obtain a sufficient amount of light. Furthermore, when a lens with a large aperture is used, problems have been pointed out, such as the depth of focus becomes shallower and the surface irregularities of the applied resist become weaker. On the other hand, in terms of resists, attempts have been made to develop resists with high contrast (hereinafter referred to as high γ resists). The resolution is certainly improved by using a high γ resist. Further, the production of high γ resists 1 to 1 can be achieved by adjusting the molecular weight and dispersion degree of the polymer in the lens. However, this method is limited by the materials used and has not been able to significantly improve resolution.

In addition, in terms of lithography, 1) a method of using a multilayer resist, 2) a method of coating a photosensitive resin on the resist ridge, etc. have been proposed.

Although the method using a multilayer resist can resolve patterns of 1 μm or less, it still has problems as an industrial method because the process is complicated, it takes too much time to manufacture semiconductors, and the yield is low.

The method of coating a photosensitive resin on a resist film is that the light immediately after passing through a mask has a high contrast, but when it passes through a space and a lens, the contrast of the light decreases. This method aims to increase contrast and improve resolution by passing through a photosensitive resin.

As a photobleaching material contained in this photosensitive resin, a nitrone compound (JP-A-59-104642) or a diazonium salt (JP-A-60-238829) has been proposed.

The method using a nitrone compound certainly improves resolution, but it requires an intermediate layer between the lower resist layer and the upper photosensitive resin layer, which complicates the process and has the problem that the yield does not improve much. .

The method using a diazonium salt has not yet achieved a sufficiently satisfactory resolution improvement effect, and furthermore, problems remain in terms of storage stability of the diazonium salt.

(Means for Solving the Problems) The object of the present invention is to solve the above-mentioned problems and relate to a method of forming fine patterns with high accuracy using a simple process.

The present inventors have determined that among the methods of providing a photosensitive layer that is bleached by light on the "-" part of the resist, a method in which the lower layer can be developed at the same time simplifies the process and can be expected to significantly improve resolution. Therefore, we investigated the use of diazonium salts as photobleaching agents.

5. The present inventors developed a method reported as a functional evaluation method for positive photoresists (IF3M, USA: F, H, Dr.
ill, et at characterization
n of positive photoresist,
IEEF transaction on select
ronDevices, vol ED-22No, 7
July 1975), it was found that the resolution could be significantly improved by increasing the A value.

Generally, the A value is expressed as A = d'' T (0) T ((Xl): final transmission sd: film thickness, and in order to improve the A value, reduce the film thickness d,
The photosensitive layer (upper layer) after bleaching has a high transmittance (that is, T
It is desirable that the value of (oo) be as close to 100% as possible) and that the initial transmittance T(o) be as small as possible. In order to reduce T(0), it is possible to increase the concentration of diazonium salt, which is a photobleaching agent, in the photosensitive layer, but if the concentration is increased, crystals of the photobleaching agent will precipitate after coating, resulting in nl to lower the resolution. Also, JP-A-60-238829
As disclosed in the above publication, the method of adding additives such as sulfonic acid derivatives or their salts to increase solubility reduces coating properties, so there is a limit to the amount added, and it is not effective. There wasn't. Furthermore, diazonium salts, which are photobleaching agents, have a problem of poor thermal stability.

Diazonium salts generally have poor stability as compounds that absorb long wavelength light. However, lithography using short wavelength light has the problem of reduced light transmittance, as described above. Furthermore, manufacturers of semiconductor integrated circuits
In order to avoid capital investment, I would like to extend the life of the exposure machine I am currently using (currently, the mainstream uses 4.36 nm light) as long as possible, so I decided to use diazonium. Improved salt stability is an important factor.

Therefore, commonly known diazonium salt stabilizers,
For example, phosphoric acid, organic phosphoric acid, citric acid.

When we investigated the stability by adding tartaric acid, etc., we confirmed that it had a slight improvement effect, so when we added a large amount of additives for further improvement, we noticed that the coating became poor and the resolution decreased. It was done.

In order to solve the above problems, the present inventors focused on the polymer used in the photosensitive resin and conducted intensive studies. As a result, by using a polymer containing a benzenesulfonic acid group, it was possible to It has been found that the solubility of the diazonium salt increases, the precipitation of crystals of the diazonium salt is inhibited during coating, and the stability of the diazonium salt can be further improved. As a result, it became possible to precisely form and cover fine patterns, and the present invention was completed.

The polymer in the photosensitive resin in the present invention is represented by the following structure.

R,R.

1.1 C-C- (However, R7-R3 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a halogen atom, a nitrile group, R4 is a hydrogen atom, an alkyl group having 1 to 4 carbon atoms) group, halogen atom, hydroxyl group, carboxyl group.

X is a hydrogen atom, an alkali metal, or an alkaline earth metal.

Each represents an ammorum group. ) Furthermore, the polymer used in the present invention may be a copolymer of compounds represented by the above-mentioned structural units or a copolymer with a generally known compound.

Examples of copolymers include styrene, α-methylstyrene, vinylpyridine, acenaphthylene, polyaniline,
Vinylnaphthalene, vinyl acetophenone, acrylic acid and its derivatives, methacrylic acid or its ester, acrylonitrile, maleic anhydride, maleic imide,
or its derivatives, allyl esters, vinyl esters,
Acrolein, acrylamide or its modified derivatives, propenylanisole, vinyl ether, indene.

Examples include copolymers with isoprene and the like.

The copolymerization ratio of the m-structured unit having a benzenesulfone group and, for example, the above-mentioned compound not having a benzenesulfone group is not particularly specified, but the content of the structural unit having a benzenesulfone group in the polymer must be 50 mol% or more. is preferred. Further, the solvent in the photosensitive resin may be any solvent as long as it does not dissolve the underlying resist, but preferably water is used. Furthermore, if necessary, a diazonium salt stabilizer may be added to the photosensitive resin.

The pattern forming method of the present invention will be described in detail below.

First, a resist commonly used with a spinner is applied to the wafer. The resist used may be any resist as long as the photosensitive resin can be dissolved at the same time in the developing solution of the resist.

After applying the resist, prebaking is performed, and then a photosensitive resin consisting of a diazonium salt, water and/or an organic solvent, and a polymer is applied using a spinner.

As the diazonium salt used at this time, any conventionally known diazonium salt can be used as long as it is a compound that absorbs well the wavelength of the light source used.

-10= For example, when exposing with 436 nm light, 2-(N,
N--dimethylamino)-5-methylthiobenzenediazonium salt, 2.4',5-triethoxy-4-biphenyldiazonium salt, 2.5-jethoxy-4-(P-
Examples include tolylthio)-benzenediazonium salt.

Further, in the case of exposure with light of 365 nm, 4-α-naphthylaminobenzenediazonium salt, 2°5-dimethoxy-4-morpholinobenzenediazonium salt, etc. can be used.

After applying the photopolymer, one layer of photopolymer.

In this method, a fine pattern is formed by exposing the underlying resist to light that sensitizes the resist, developing the resist with the used resist developer, and simultaneously peeling off and covering the photosensitive resin layer.

(Examples of the present invention) The present invention will be explained below with reference to Examples, but the present invention is not limited thereto.

11 Example 1 In order to conduct a stability test of diazonium salt, a photosensitive resin 100- having the following composition was left in a constant temperature bath at 30° C., and minor changes in the A value were measured. The results are shown in Table-1.

Composition of photosensitive resin Polystyrene sulfonate sodium salt 10 fJ
(Manufactured by Toyo Soda: PS-5) 4-Selfolino 2,5-dimethoxy 2.4g Benzenediazonium chloride 1/2 Zinc chloride double brine
90 g Example 2 The same experiment as in Example 1 was conducted using polystyrene sulfonic acid instead of the polystyrene sulfonate sodium salt used in Example 1.

As polystyrene sulfonic acid, when a 10% aqueous solution of PS-5 was gradually dropped into concentrated hydrochloric acid, polystyrene sulfonic acid was precipitated, and this precipitate was dried and used.

The results are shown in Table 1 (.

Comparative Example 1 A similar experiment was conducted using polyvinylpyrrolidone (manufactured by Gyudon Chemical Co., Ltd.) having a molecular weight of 4924500 instead of the polystyrene sulfonate sodium salt used in Example 1. For stability comparison with the photosensitive resin of Example, the amount of diazonium salt was adjusted to make the starting A values as similar as possible. Table 1 shows the results of light changes in A value.

Comparative Example 2 Tartaric acid was added to the photosensitive resin used in Comparative Example 1 as a stabilizer for the diazonium salt in an amount of 3% by weight based on the diazonium salt. An experiment similar to Example 1 was conducted using this solution. The results are shown in Table-1.

Table 1 Example 3 Positive photoresist 0FPR on silicon wafer
800 (manufactured by Tokyo Ohka Kogyo) to a film thickness of 0.9 μm. Thereafter, prebaking is performed at 80° C. for 10 minutes. Next, add 0.3% of the photosensitive resin with the following composition.
Apply to a film thickness of 5 μm.

Composition of photosensitive resin 2.5-dimethoxy-4-(N, N-4,8g dimethylamino)benzenediazonium chloride 1/2 zinc chloride double salt polystyrene sulfonate sodium salt 10 (J
water
90 (j) Next, exposure is performed using a 5:1 reduction projection exposure machine (stepper) equipped with a lens with a numerical aperture of 0.35, and after transferring the mask pattern, the developer
Development was performed for 1 minute using MD-3 (manufactured by Tokyo Ohka Kogyo).

As a result of observing the cross-sectional shape of the resist pattern with an electron microscope, it was found that it had a clear rectangular shape of 0.87. A line of zm was obtained.

Comparative Example 3 The same experiment as in Example 3 was conducted except for applying the photosensitive resin. However, the exposure time required for transfer was half that of the example. As a result of observation using an electron microscope, the resolution was 1.2 μm.

Example 4 The same experiment as in Example 3 was carried out except that polystyrene sulfonic acid was used instead of polystyrene sulfonate sodium salt, which is a polymer in the photosensitive resin used in Example 3. As a result, the resolution was 0.8 μm.

Comparative Example 4 In order to conduct a similar experiment using polyvinylpyrrolidone instead of polystyrene sulfonate sodium salt, which is a polymer in the photosensitive resin used in Example 3, a photosensitive resin was applied to the resist crotch, and diazonium Salt crystals were observed. When exposed as it was and observed the pattern with an electron microscope after visual imaging, a clear pattern could not be obtained and the resolution could not be measured.

Example 5 Instead of the diazonium salt used in Example 3, 2-(N
, N-dimethylamino)-5-methyldiobenzenediazonium chloride 1/2 zinc chloride double salt was used to carry out the same experiment as in Example 3.

The resolution was 0.9 μm.

(Effects of the Invention) According to the present invention, it is possible to increase the low contrast light to high contrast again without going through complicated steps, and it is possible to form a pattern of 1 μm or less with high precision. Furthermore, since the focal lake surface increases, the yield of semiconductors can be improved, which is of great commercial value.

Claims (2)

[Claims] (1) After coating the resist film (lower layer) with a photosensitive resin consisting of diazonium salt, a photobleach, water and/or an organic solvent, and a polymer (upper layer), both the upper and lower layers are exposed to light to form a pattern. A method for forming a fine pattern, characterized in that the polymer in the upper layer has the following structural units. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (However, R_1 to R_3 are hydrogen atoms, and the number of carbon atoms is 1 to 4.
Alkyl group, halogen atom, nitrile group, R_4
represents a hydrogen atom, an alkyl group having 1 to 4 carbon atoms, a halogen atom, a hydroxyl group, a carboxyl group, and X represents a hydrogen atom, an alkali metal, an alkaline earth metal, or an ammonium group, respectively. ) (2) The method for forming a fine pattern according to claim 1, wherein the polymer in the upper layer is a copolymer containing the structural unit described in claim 1.