JPS608493B2 - Method for forming a positive resist image - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a positive resist image.

When a methacrylic acid ester polymer is irradiated with radiation such as X-rays, Q-rays, Y-rays, etc., a molecular cleavage reaction of the polymer occurs in the irradiated portion, so that its solubility in a solvent is improved.

Taking advantage of this property, methacrylic acid ester polymers are being studied as positive radiation-sensitive materials for use in fine image resists in the manufacture of semiconductor devices. However, although methacrylic acid ester polymers have excellent fine image forming properties, their low sensitivity poses a major obstacle to their practical application. Sensitivity can be improved by using a copolymer of methacrylic acid ester and (meth)acrylic acid having carboxylic acid in the side chain. In particular, in this case, sensitivity is significantly improved when an aqueous solution of an inorganic base, an organic base, ethanol, etc. is used for development. However, the use of such a developer results in a decrease in the ability to form fine images and a decrease in the electrical characteristics of the final product, the semiconductor device. In view of this, the present inventors conducted extensive research and found that if a medium in which a specific quaternary ammonium salt is dissolved is used (
The inventors have discovered that the sensitivity can be improved without reducing the excellent properties of meth)acrylic acid ester copolymers, such as the ability to form fine images, and have arrived at the present invention. That is, the gist of the present invention is the general formula () and the general formula (
0) (In the formula, RI and R2 represent a hydrogen atom or a methyl group, R3 represents a methyl group, a cyano group, or a halogen atom, and R4 represents a lower alkyl group). After irradiating the radiation-sensitive layer with radiation in a predetermined pattern, the radiation-sensitive layer is formed by the general formula (m) (in the formula,
One of R5, R6, R7 and R8 has 8 to 8 carbon atoms.
20 alkyl groups, the rest are lower alkyl groups having 1 to 2 carbon atoms, and x indicates a halogen atom) is treated with a medium in which a quaternary ammonium salt is dissolved to remove the radiation-exposed portion. A method of forming a positive resist image is provided.

The present invention will be described in detail below. In the method of the present invention, a copolymer having units represented by the above general formulas (1) and (b) is used as a radiation-sensitive material.

Such polymers include, for example, acrylic acid, methacrylic acid,
A monomer forming a unit represented by the general formula (1), such as crotonic acid, and a methacrylic acid ester such as methyl methacrylate, ethyl methacrylate, propyl metal acrylate, butyl methacrylate, and 2-hydroxyethyl methacrylate; methyl 1q- Q-cyanoacrylate esters such as cyanoacrylate, ethyl-Q-cyanoacrylate, and butyl-Q-cyanoacrylate; Q-halogenoacrylate esters such as methyl-Q-chloroacrylate and butyl-Q-chloroacrylate; The units forming the unit represented by (0)/
It is produced by copolymerizing with mer according to a conventional method.

Of course, the polymer is not limited to those obtained by copolymerization, but may be obtained by polymer reactions such as hydrolysis and transesterification. The method of the present invention is particularly effective for n-phthyl-Q-cyanoacrylate methacrylic acid copolymers among these copolymers.

And the molecular weight is usually 1 to 5 million, preferably about 50,000 to 50,000.
500,000 polymers are used. If the molecular weight of the polymer is too high, purification may be difficult or thin film coating on a substrate may become difficult, which is not preferable. Furthermore, if the molecular weight is too low, the sensitivity will decrease. The content of the units represented by the general formula (1) in the copolymer is usually 5 to 50 mol%, and the content of the units represented by the general formula (0) is usually 95 to 5 mol%.
It is 0 mol%. Furthermore, the copolymer contains units formed from ethylenically unsaturated monomers other than the units represented by the general formulas (1) and (0) that do not reduce radiation sensitivity or form insoluble substances when irradiated with radiation. For example, it may contain 10 mol% or less.

A radiation-sensitive layer can be formed by dissolving the copolymer in a solvent together with an additive such as a sensitizer if necessary, and applying this solution onto a substrate.

The radiation-sensitive layer can be formed according to a conventional method, and a radiation-sensitive layer having a thickness of 0.01 to 20 mm is usually formed.
A film thickness of 0.3 to 3 mm is suitable for a resist film for etching in semiconductor device manufacturing. The solvent used in forming the radiation-sensitive layer may be any solvent as long as it dissolves the copolymer, such as methyl ethyl ketone,
Methyl isobutyl ketone, xylene, cyclohexanone, 4-methoxy 4-methylbentanone-2 (bentoxone), 2-methoxyethyl acetate, 2-ethoxyethyl acetate, ethylene glycol mono/methyl ether, ethylene glycol monoethyl ether, etc. can be mentioned. Among these, ketoethers such as pentoxone are particularly preferred. The substrate on which the radiation-sensitive layer is formed may be a material commonly used in semiconductor and photomask manufacturing, such as silicon, silicon dioxide, silicon nitride, aluminum, titanium, platinum, or
chaladium, copper, tungsten, chromium, molybdenum,
Plates made of gold, phosphor glass, boron glass, chromium oxide, iron oxide, aluminum oxide, etc. are used.

Of course, after forming the radiation-sensitive layer, prebaking may be carried out according to a conventional method in order to relieve strain in the layer, remove traces of solvent, and improve adhesion. Prebaking is usually carried out at a temperature of, for example, 80 to 220 degrees, which is higher than the glass transition temperature and lower than the thermal decomposition temperature of the copolymer. A positive resist image can be obtained by irradiating such a radiation-sensitive layer with radiation in a predetermined pattern and then treating it with a developer.

As the radiation, electron beams, X-rays, Q-rays, Y-rays, etc. are used. Further, as the irradiation method, any of various well-known methods can be employed. In the present invention, it is essential to use a medium in which a quaternary ammonium salt represented by the above general formula (m) is dissolved as a developer.

In the general formula (m), R5 to R8 are a methyl group, an ethyl group, an octyl group, a nonyl group, a decyl group, a dodecyl group,
It is an alkyl group such as a hexadecyl group or an octadecyl group, and these alkyl groups must not have a hydroxyl group, a phenyl group, or any other substituent. Also, 3 of R5 to R8
One is a lower alkyl group having 1 to 2 carbon atoms. X is a halogen atom such as a chlorine atom, a bromine atom, or an iodine atom. Such quaternary ammonium salts include octyltrimethylammonium chloride, dodecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyltriethylammonium chloride, octyltriethylammonium chloride, octadecyltriethylammonium chloride, dodecyltrimethylammonium bromide, dodecyltrimethyl Examples include quaternary ammonium salts, such as ammonium iodide, in which one of R5 to R8 in the general formula (m) is an 8-20 alkyl group and the remaining are lower alkyl groups. Of course, two or more of these quaternary ammonium salts can also be used in combination. Among these quaternary ammonium salts, octyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, and octadecyltrimethylammonium chloride are particularly preferred. The medium used in the developer may be any medium as long as it dissolves the quaternary ammonium salt, and specifically includes water; alcohols such as methanol, ethanol, and isopropanol; and cyclic ethers such as dioxane and natrahydrofuran. ethers such as ethylene glycomonoethyl ether and ethylene glycomonomethyl ether; alcohols are particularly preferred.

If necessary, two or more types of media may be used in combination. The concentration of the quaternary ammonium salt in the medium varies depending on various conditions, but it is difficult to achieve the purpose of the present invention if it is too low or too high, so it is usually 0.1 to 20 m/d, preferably The range is 1 to 10 evenings/d. The positive resist image thus formed may be subjected to post-baking according to a conventional method in order to remove the medium and improve adhesion and etchant resistance.

The post-baking is carried out at a temperature lower than the melting point or pour point of the copolymer, for example from 100 to 17 pi. The present invention has been described in detail above, and the method of the present invention has the following advantages over conventional methods.

■ Copolymers containing the above units used as radiation-sensitive materials have high thermal stability and strong resistance to CF4 gas plasma, etc., so they are used in CF4 gas plasma etching, ion beam etching, sputter etching, lift-off metallization, etc. can do.
(2) Sensitivity and y value can be increased by using a medium in which the quaternary ammonium salt is dissolved as a developer.

That is, an image with high contrast can be obtained by irradiating radiation with a relatively low energy amount and a short period of time. For example, compared to using only an organic solvent such as bentoxo or methyl lysobutyl ketone as a developer,
A desired positive resist image can be sufficiently obtained with a radiation dose of 10 to 1/200, or 1/2 to 1/10 compared to when an alkaline aqueous solution of an inorganic substance is used as a developer. The method of the present invention having such advantages can be applied to the manufacture of semiconductors such as ICs and ultra-first semiconductors that require fine images.

The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to the following Examples unless it exceeds the gist thereof.

Example 1 7.5 parts of n-butyl-Q-cyanoacrylate to which 5% by weight of acetic acid was added as an anionic polymerization inhibitor and 2.0 parts of methacrylic acid purified by distillation were mixed with 0.0 parts of azobisisobutyronitrile in 38 parts of tetrahydrofuran. A copolymerization reaction was carried out for 5 hours in a 60q0 temperature tank using 038 ml as an initiator.

The resulting reaction solution was treated with petroleum ether to recover the copolymer. The reduced viscosity (SP/C) of the obtained copolymer was 1.5389, and the copolymerization composition ratio (methacrylic acid/n-butyl-Q-cyanoacrylate) was 19.3/80.7 (
molar ratio). Incidentally, the reduced viscosity is 0.2 d and the tetrahydrofuraso solution was measured at 3 d.

The above copolymer is 4-methoxy-4-methylbentanone-
2 to form a 7% by weight solution, which was purified by filtration using a 1.0 fm membrane filter. Spread this solution to a thickness of 0.
Dropped onto a silicon substrate covered with a 4mm silicon oxide film for 70 minutes. p. After spinning for 60 seconds at m,
A 0.9 m thick radiation-sensitive layer was formed on the silicon substrate by prebaking at 00q0 in 3 steps. Next, this radiation-sensitive layer was irradiated with an accelerated 20KV electron beam in a high vacuum according to the program, and then a developer having the composition shown in Table 1 was added to
Soaked for 1 minute, followed immediately by 1 minute soak in 24 oo of inpropyl alcohol. After the development was completed, the thickness of the remaining film produced by the development was measured. By changing the electron beam irradiation dose, an electron beam sensitive characteristic curve showing the relationship between the electron beam irradiation dose and the residual film rate (=film thickness after irradiation/film thickness before irradiation) is obtained, and from this curve, the residual film rate is set to 0. The electron beam irradiation amount (sensitivity) and y value required for this were determined and shown in Table 1. Note that the y value was determined from the formula below. 0.5 y: -log D.

．． 5-log D. (In the formula, ship D indicates the amount of electron beam irradiation necessary to make the residual film rate 0.5, and Do indicates the amount of electron beam irradiation necessary to make the residual film rate 0.) Table --
1 The radiation-sensitive layer prepared in Example 1 was irradiated with an electron beam of 7 x 10-7 coulombs to obtain a line pattern with a medium diameter of 2.0 mm and a length of 100 mm.

Note that ethanol in which dodecyltrimethylammonium chloride was dissolved at 89/d was used as a developer.
When this pattern image was observed with a scanning electron microscope (hereinafter referred to as SEM), there was no residual film, and the side surfaces of the line pattern were smooth and the cross section was rectangular. After post-baking this line pattern at 150qC for 3 minutes, SE
When observed with M, no change in the line pattern was observed. Comparative Example 1 A developing operation was carried out in exactly the same manner as in Example 1 except that water alone was used as the developer, but no developer was obtained.

Comparative Example 2 Development was carried out in exactly the same manner as in Example 1 except that ethanol alone was used as the developer.

In this case, as the electron beam irradiation dose increases, the residual film after development decreases, and the residual film rate that shows the minimum residual film rate at an electron beam irradiation dose of 3 × 10-6 to 3 × 10-5 coulombs/ground becomes 0. zu 0.05～
It was in the range of 0.2. Also, 6×10-6 coulombs/
After irradiating a line pattern with an electron beam, the pattern obtained by development was observed with an SEM, and a residual film was observed in the electron beam irradiated area, and the sides of the pattern had a highly uneven shape. Comparative Example 3 In Example 1, as a developer, pendyltriethylammonium chloride was dissolved in ethanol for 4 nights/d, or 2-hydroxyethyltrimethylammonium chloride was dissolved in ethanol for 8 nights/d. The developing operation was carried out in exactly the same manner except that ethanol was used.
Almost no development was performed within the average range.

Example 3 The reduced viscosity was 1.7941 and the copolymerization composition ratio (methacrylic acid/n-butyl-Q-cyanoacrylate) was 3.
Example 1 using a copolymer of 9.3/60.7 (mole ratio)
After forming a radiation-sensitive layer in the same manner as above,
Prebaked for 0 minutes.

This radiation-sensitive layer was irradiated with an electron beam in the same manner as in Example 1, and dodecyltrimethylammonium chloride was irradiated with dodecyltrimethylammonium chloride for 4 days/d.
〆When developing with dissolved ethanol and determining the sensitivity 1
．． It was 5×10-6 coulombs/me.

Comparative Example 4 Development was carried out in exactly the same manner as in Example 3 except that ethanol alone was used as the developer.

In this case, even when irradiated with an electron beam of 8×10-6 coulombs, the residual film rate did not become 0. Examples 4 to 7 In Example 1, the same procedure as in Example 1 was carried out except that the copolymer shown in Table 2 was used as the copolymer, and the one shown in Table 1 a was used as the developer. A pattern was formed.

Claims (1)

[Claims] 1 General formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ and General formula (II) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R^1 and R^5 are A radiation-sensitive layer containing a copolymer having a unit represented by hydrogen atom or methyl group, R^3 represents a methyl group, cyano group, or halogen atom, and R^4 represents a lower alkyl group is exposed to radiation. After irradiation in a predetermined pattern, the radiation-sensitive layer is formed using the general formula (I
II) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (In the formula, R^5, R^6, R^7 and R^8 represent an alkyl group, one of which is an alkyl group having 8 to 20 carbon atoms. The radiation irradiated portion is removed by treatment with a medium in which a quaternary ammonium salt represented by (the rest is a lower alkyl group having 1 to 2 carbon atoms, and X represents a halogen atom) is dissolved. A method for forming a positive resist image. 2. The method for forming a positive resist image according to claim 1, wherein the copolymer is an n-butyl-α-cyanoacrylate-methacrylic acid copolymer. 3. A method for forming a positive resist image according to claim 1 or 2, wherein the medium is alcohol. 4. The method for forming a positive resist image according to claim 1 or 2, wherein the medium is water.