JPH09211871A - Formation of resist pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to form fine patterns having good shapes with high dimensional accuracy and good reproducibility by first baking a chemical amplification type resist at its phase transition temp. or above after exposure, then baking this resist at the phase transition temp. or below after the next exposure. SOLUTION: The photoresist film 12 of the chemical amplification type is formed on a semiconductor substrate 11 and is irradiated with UV rays through a mask plotted with desired semiconductor integrated circuit patterns. The resist film is then subjected to development by using an alkaline developer after the post-exposure baking. The post-exposure baking is divided to two stages; the first baking is executed for 5 to 15 seconds at the phase transition temp. of the resist film 12 or above and the second baking at the phase transition temp. of the resist film or below. The diffusion length of acids increases in the first baking and, therefore, the distribution of the generated acid quantity in the film thickness direction by standing waves is made uniform. Since the baking is short in time, the softening of the resist to the extent of degrading the resolution does not arise. The chemical amplification reaction is completely progressed by the second baking to be executed for about 60 to 120 seconds at the phase transition temp. of the resist or below.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a fine resist pattern.

[0002]

2. Description of the Related Art Conventional photolithography uses g (436 nm) and i (365 nm) rays as its exposure light. As its resist, a novolak resin is used as a base resin and naphthoquinone diazide is used as a photosensitizer. Dissolution-inhibiting positive resists using were the mainstream. However, excimer laser light (248 nm), which is far-ultraviolet light advantageous for further miniaturization, is used.
nm, 193 nm, etc.) is required. As a resist for the conventional g-line and i-line, light absorption is too large, and a good resist pattern cannot be obtained.
In addition, the sensitivity was also significantly reduced.

However, a photo-acid generator (PAG; Photo)
A chemically amplified resist utilizing an acid-catalyzed sensitization reaction generated from Acid Generator was devised (Ito et al. 1982 Symposium).
on VLSI Technology), and is now the mainstream resist for excimer laser lithography. In the case of a positive resist, this chemically amplified resist is composed of a resin having a dissolution inhibiting group introduced and PAG. When this positive resist is exposed, P
Acid is generated from AG, and the acid acts as a catalyst on the dissolution inhibiting group by baking after exposure, and the dissolution inhibiting group is eliminated. As a result, the exposed portion becomes alkali-soluble, so that a positive pattern is formed. On the other hand, the negative resist is composed of a resin, a cross-linking agent and PAG. When this negative resist is exposed, an acid is generated from PAG in the exposed portion, and the acid generated by baking after exposure acts as a catalyst on the crosslinking agent,
Crosslinking of the resin occurs. As a result, the exposed part becomes sparingly soluble in alkali, so that a negative pattern is formed.

As described above, in the chemically amplified resist, the post-exposure bake plays an important role in pattern formation,
As the baking method, a chemical amplification reaction sufficiently occurs as proposed in JP-A-5-216233.
60 seconds or more at a temperature above ℃ and below the resist phase transition temperature
It is generally performed for about 120 seconds.

[0005]

On the other hand, when the exposure wavelength is shortened from i-line to excimer light, the reflectance from the underlying substrate is greatly increased. The light incident on the resist is reflected at the interface with the substrate, and the reflected light interferes with the incident light to form a standing wave in the resist film. Therefore, the light intensity in the resist film changes periodically in the film thickness direction. Therefore, as shown in FIG. 2, the generated acid concentration in the resist film has a periodic distribution in the film thickness direction. In the case of a single-step post-exposure bake that is performed below the conventional resist phase transition temperature, since the acid diffusion length is small, the acid concentration distribution due to the standing wave is not averaged. As shown, wavy unevenness (hereinafter referred to as “sidewall standing wave”) is formed on the side wall of the resist pattern 33, which causes a problem that dimensional accuracy is deteriorated.

An object of the present invention is to solve the above-mentioned problems and to provide a method for forming a chemically amplified resist pattern having high resolution and good rectangularity and dimensional accuracy without standing waves on the side wall.

[0007]

According to the present invention, a chemically amplified photoresist film is formed on a semiconductor substrate, ultraviolet rays are radiated through a mask on which a desired semiconductor integrated circuit pattern is drawn, and after post-exposure bake, In a method of forming a resist pattern in which development is performed using an alkali developing solution, post-exposure baking is performed in two steps, and first baking is performed at a temperature of the phase transition temperature of the resist film or higher and a baking time of 5 seconds or more and 15 seconds or less The second baking is performed at a temperature not higher than the phase transition temperature of the resist film.

In the first baking performed at a high temperature, the diffusion length of the acid increases, so that the distribution of the amount of acid generated by the standing wave in the film thickness direction becomes uniform. Since the baking is performed at a temperature equal to or higher than the phase transition temperature, the softening of the resist slightly promotes uniform acid concentration distribution. First bake time is 5 seconds or more 15
Since it is as short as a second or less, the resist is not softened so much that the resolution is lowered. Here, since the short baking time of 15 seconds or less is insufficient for completing the chemical amplification reaction, the second baking is performed.

The second bake corresponds to a conventional single-step post-exposure bake, which is performed at a temperature below the resist phase transition temperature for a bake time of about 60 seconds to 120 seconds, and the second bake causes a chemical amplification reaction. Will progress completely.

[0010]

Next, the present invention will be described with reference to the drawings. 1A and 1B are cross-sectional views illustrating a method of forming a resist pattern according to an embodiment of the present invention. As the base resin, polyvinylphenol (PVP) having an average molecular weight of 15,000 is used, and about 30% of the phenolic hydroxyl groups are tertiary butoxycarbonyl groups (t-B).
OC), and about 4% by weight (ratio to resin) of triphenylsulfonium hexafluoroantimonate was added as an acid generator to prepare a resist solid component.
The phase transition temperature of these resist solid components was about 120 ° C. A resist solution was prepared by dissolving the resist solid component in propylene glycol methyl ether acetate.

This resist solution was spin-coated on a Si substrate 11 and baked at 120 ° C. for 90 seconds before exposure to form a chemically amplified positive resist film 12 having a thickness of 0.7 μm. Subsequently, pattern exposure through a mask was performed using a KrF excimer laser stepper (FIG. 1).
(A)).

After the pattern exposure, a first post-exposure bake at 150 ° C. for 10 seconds was performed, and a second post-exposure bake at 100 ° C. for 90 seconds was subsequently performed. Then, 2.38% tetramethylammonium hydroxide (TMA
H) Development was performed with an aqueous solution. As a result, a rectangular 0.25 μmL / S resist pattern without standing waves on the side wall was obtained (FIG. 1 (b)).

On the other hand, when a single step post-exposure bake was performed at 100 ° C. for 90 seconds, a large standing wave was observed on the side wall of the pattern as shown in FIG. Also, 150
When the single step post-exposure bake was performed at 90 ° C. for 90 seconds, the resolution was lowered and the film loss was greatly rounded, resulting in a pattern as shown in FIG.

[0014]

As described above, according to the method of the present invention, it is possible to eliminate the standing wave on the side wall which is observed in the chemically amplified resist pattern by the conventional post-exposure bake method.
A fine resist pattern of 0.30 μm or less having a good shape can be obtained. Further, it is possible to improve the resolution, the depth of focus, and the dimensional accuracy by 10% or more.

[Brief description of drawings]

1A and 1B are cross-sectional views illustrating a method of forming a resist pattern according to an embodiment of the present invention.

FIG. 2 is a diagram showing an acid concentration distribution in a resist film in a film thickness direction.

FIG. 3 is a sectional view of a resist pattern formed by a conventional post-exposure bake (100 ° C., 90 seconds).

FIG. 4 is a cross-sectional view of a resist pattern after baking after exposure at 150 ° C. for 90 seconds.

[Explanation of symbols]

 11, 31, 41 Silicon substrate 12 Chemically amplified resist film 13, 33, 43 Resist pattern

Claims (2)

[Claims] 1. A chemically amplified photoresist film is formed on a semiconductor substrate, irradiated with ultraviolet rays or deep ultraviolet rays through a mask on which a desired semiconductor integrated circuit pattern is drawn, and post-exposure bake is followed by using an alkali developing solution. In the method of forming a resist pattern in which development is performed by development, baking after exposure is performed by 2
And a second post-exposure bake is performed at a temperature not lower than the phase transition temperature of the resist film, and a second post-exposure bake is performed at a temperature not higher than the phase transition temperature of the resist film. 2. The baking time of the first post-exposure bake is 5
The resist pattern forming method according to claim 1, wherein the resist pattern forming time is not less than 2 seconds and not more than 15 seconds.