JPH10301293A - Pattern forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover a degraded beam shape and to form a good fine pattern by forming a thin film comprising a photosensitive compsn. having inhomogeneous density distribution in the thickness direction and using a photoresist which causes photofading in the wavelengths of exposure light. SOLUTION: A photofading layer which converts a degraded beam shape of exposure light with low contrast into a good shape with high contrast is formed on a chemically amplifying photoresist. As for the photofading layer, various photofading dyes having absorption of light in the wavelengths of exposure light can be used. It is especially preferable to use a photosensitive agent as the dye used for the photofading layer, because not only the beam shape of the exposure light but development characteristics are improved. Even when the upper photofading layer is mixed into the photoresist layer, it is no problem as far as the density distribution of the photofading layer gives the highest density on the surface of the photofading layer while the density gradually decreases in the depth direction of the photoresist and becomes lowest near the substrate in the lower part of the photoresist layer. A continuous decrease in the density distribution is more preferable because reflection on interfaces in a multilayered structure is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transferring a pattern of a semiconductor integrated circuit, a liquid crystal element or the like onto a sample substrate, and more particularly to a technique for enabling use of photolithography having high resolution.

[0002]

2. Description of the Related Art A method of transferring a pattern drawn on a mask onto a sample substrate, which is called a lithography technique, is widely used for forming a pattern of a semiconductor integrated circuit or a liquid crystal element. In order to perform this pattern transfer, a reduced-projection type projection exposure apparatus for reducing and transferring a pattern on a mask is generally used.

As the pattern miniaturization of semiconductor integrated circuits and the like progresses, the projection exposure apparatus is required to transfer a fine pattern having a higher resolution than before. When the resolution limit of the exposure apparatus is approached, the light intensity distribution of a pattern to be transferred is blurred due to a light diffraction phenomenon or the like, which causes a problem that a deteriorated light pattern is formed. In general, the higher the numerical aperture (NA) of the projection lens or the shorter the wavelength of light used for exposure, the higher the resolution. However, the projection lens is also required to have a large exposure area at the same time, and there is practically a limit in improving the NA. Therefore, attempts have been made to shorten the wavelength of light used for exposure. A conventional high-pressure mercury lamp (wavelength 436 nm or 3
For example, an excimer laser (wavelength: 308 nm, 248 nm, or 1) having an emission wavelength shorter than 65 nm is used.
93 nm) is considered an effective light source.

However, in the case of an exposure light source having a short wavelength, the photosensitive composition (hereinafter, referred to as a photoresist) has a strong light absorption upon exposure, and after exposure and development, a practical fine pattern having a vertical cross-sectional shape on a substrate is formed. Difficult to form. That is, the exposure light is strongly absorbed in the upper portion of the photoresist, and the exposure light hardly reaches near the substrate below the photoresist. As a result, the photochemical reaction in the photoresist frequently occurs on the photoresist surface, and hardly occurs on the side in contact with the substrate.

When developing a latent image pattern by such exposure, in the case of a negative type photoresist which becomes resistant to development due to a photochemical reaction, the upper portion of the photoresist protrudes, and the lower portion of the photoresist is eroded laterally during development. In other words, it becomes a so-called reverse tapered shape and becomes a pattern that is not suitable for practical use.

Further, when the photo-absorption of the photoresist is stronger, since the photo-chemical reaction of the photoresist near the substrate does not occur, the entire lower portion of the photoresist is dissolved and removed at the time of development, and the pattern may be lost.

[0007] Similarly, even in the case of a positive type photoresist which becomes soluble in a developer due to a photochemical reaction, a fine pattern cannot be formed if the photoresist has a strong light absorption.

The light-absorbing main components of a photoresist include a polymer as a binder and a photosensitive agent. In particular, the photosensitive agent has a so-called photobleaching property, in which light absorption is strong before exposure and light transmittance increases upon exposure. Due to the photobleaching property, the light reaches the inside of the photoresist as the exposure amount increases.

The high-resolution photoresist has an important characteristic that an exposure shape deteriorated by light diffraction or the like is improved by a photobleaching effect in the inside of the photoresist to recover an exposure shape having a high contrast. Image quality is obtained.

A normal photoresist contains about 30% of a photosensitive agent which absorbs light for exposure, and has a strong absorption in short-wavelength exposure, so that a normal photoresist cannot be used. That is, even if the exposure wavelength is shortened in order to obtain higher resolution, a practical pattern cannot be obtained with an ordinary photoresist.

Therefore, a chemically amplified photoresist has been studied as a photosensitive composition that absorbs less light during exposure. A chemically amplified photoresist is highly sensitive because it utilizes a chain reaction of a catalyst generated by a photochemical reaction. Since the content of the photosensitive component that absorbs light for exposure can be reduced to several percent, there is a feature that light absorption can be reduced. However, in the case of a chemically amplified photoresist, since the content of the photosensitive component was small, the change in the transmittance of the photoresist at the start and end of the exposure was small, and the light shape of the exposure was deteriorated without the photobleaching effect. As it is, there is a disadvantage that the resolution is poor.

[0012]

In the case of a chemically amplified photoresist, since the content of the photosensitive component is small, the change in the transmittance of the photoresist at the start of exposure and at the end of exposure is small. Therefore, there is no characteristic of recovering the deteriorated light shape while the light shape of the exposure remains deteriorated.

An object of the present invention is to provide a pattern forming method for recovering a degraded light shape and forming a good fine pattern.

[0014]

The object of the present invention is to provide a thin film comprising a photosensitive composition having a non-uniform concentration distribution in a thickness direction.
It is also achieved by using a photoresist that undergoes photobleaching at the wavelength of the exposure light.

In a conventional pattern forming method using a chemically amplified photoresist, when a fine pattern close to the resolution limit of an exposure apparatus is optically transferred, the light pattern shape is deteriorated due to light diffraction. Was exposing the photoresist. Therefore, the resolution was poor.

On the other hand, in the present invention, a photobleaching layer is provided above the chemically amplified photoresist to convert an exposure shape having low contrast and degraded into a good light shape with high contrast. For this photobleaching layer, various photobleachable dyes having light absorption at the exposure wavelength can be used. When a photosensitive agent is used as a dye for the photobleaching layer, not only the exposure shape is improved, but also the development characteristics are improved.
Particularly preferred.

The photobleaching layer may not have a two-layer structure in which the photobleaching layer is overlaid on a photoresist. Even if the upper photobleaching layer is mixed with the photoresist layer, the concentration distribution of the photobleaching agent is the highest on the surface of the photobleaching layer, gradually decreases in the depth direction of the photoresist, and becomes the highest near the substrate below the photoresist layer. Good if it is low. Such a continuous decrease in the concentration distribution is more preferable because reflection at the boundary surface of the multilayer structure disappears. High resolving power can be obtained even when photobleaching is performed inside the photoresist. In particular, it is more desirable that the surface concentration is at least twice the concentration near the substrate in order to recover the deteriorated light shape.

As a method for forming a thin film having such a non-uniform concentration distribution, a usual method may be used. For example, there is a multi-coating method in which a photoresist solution is applied and dried, and then a solution containing a photobleaching agent is spin-coated. Both layers are appropriately mixed to form a thin film having a non-uniform concentration gradient in which the concentration of the photobleaching agent is high on the surface and low on the substrate side.

Alternatively, a thin film having a non-uniform concentration gradient may be produced by infiltrating a photobleaching agent from the photoresist surface. Of course, it is also possible to produce a thin film having a non-uniform concentration gradient by accumulating layers having different concentrations using the Langmuir-Blodgett method.

The concentration distribution in the depth direction in a thin film having a non-uniform concentration gradient is determined by photoelectron spectroscopy with ion milling, 2
It can be easily measured directly by secondary ion mass spectrometry, total reflection spectroscopy, etc.

Even when a photosensitive agent is used as a dye for the photobleaching layer, the concentration distribution of the photosensitive agent in the depth direction needs to be high at the surface and low near the substrate. In particular, it is more desirable that the surface concentration is at least twice the concentration near the substrate in order to recover the deteriorated light shape. When a photosensitive agent is used, the concentration of the photosensitive agent decreases with exposure. It is efficient to perform exposure at an exposure amount at which the density distribution of the photosensitive agent in the depth direction after exposure is constant. It is particularly efficient and efficient that the exposure amount matches the exposure amount required for forming a photoresist pattern.

Although the above description has been made with reference to a chemically amplified photoresist as an example, a photoresist having a light-transmitting photosensitive material can be used as the photoresist to be used. Among such photoresists, highly sensitive photoresists such as chemically amplified photoresists are particularly preferred.

The structure of the present invention is particularly preferable in the case of a chemically amplified photoresist from the viewpoint of preventing contamination by basic components in the atmosphere.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION

Example 1 100 parts by weight of poly (p-hydroxybenzylmethylsilsesquioxane) partially protected with a t-butyloxycarbonyl group was mixed with 7 parts by weight of diphenyliodotrifluoromethanesulfonic acid to obtain a mixture. The resulting mixture was dissolved in ethyl acetate cellosolve. This resist solution is spin-coated on a silicon substrate,
Heated and dried for minutes. The thickness of the resist film was 0.8 μm. A solution of 100 parts by weight of poly (p-hydroxybenzylmethylsilsesquioxane) partially protected with t-butyloxycarbonyl group and 10 parts by weight of naphthoquinonediazide was spin-coated on the chemically amplified photoresist thin film, Heat drying at 10 ° C. for 10 minutes. The thickness of the entire thin film was 1 μm.

When this thin film was measured by total reflection spectroscopy and photoelectron spectroscopy with ion milling, the concentration distribution of naphthoquinonediazide in the thin film was high on the air side surface, and continuously decreased monotonically toward the substrate side interface. Was. The surface concentration was 2.5 times the substrate concentration.

The resist is irradiated with a pattern of ultraviolet light having a wavelength of 248 nm at an exposure amount of 40 mJ / cm ² , and
Heated at 00 ° C. for 10 minutes. After completion of the heating, the resist film was treated with tetramethyl ammonium hydroxide 1.
Developed with a 2% aqueous solution for 60 seconds. The pattern size is 0.2
In the case of μm, a good positive resist pattern having a vertical cross-sectional shape was formed.

When the thin film after exposure was measured by total reflection spectroscopy and photoelectron spectroscopy with ion milling, the concentration distribution of naphthoquinonediazide in the thin film was substantially uniform with only a 5% or less increase or decrease in the depth direction. there were.

Example 2 Diphenyliodotrifluoromethanesulfonic acid was mixed with 100 parts by weight of poly (p-hydroxybenzylmethylsilsesquioxane) partially protected with t-butyloxycarbonyl group at a ratio of 7 parts by weight. The resulting mixture was dissolved in ethyl acetate cellosolve. This resist solution is spin-coated on a silicon substrate,
It was dried by heating at 80 ° C. for 10 minutes. The thickness of the resist film was 1 μm.

On this chemically amplified photoresist thin film,
A naphthoquinonediazide solution was added dropwise, contacted for 10 minutes and removed.

When this thin film was measured by total reflection spectroscopy and photoelectron spectroscopy with ion milling, the concentration distribution of naphthoquinonediazide in the thin film was high on the air side surface and decreased monotonically continuously toward the substrate side interface. Was. The concentration at the surface was twice as high as that at the substrate.

The resist was irradiated with a pattern of ultraviolet light having a wavelength of 248 nm at an exposure amount of 30 mJ / cm ² ,
Heated at 00 ° C. for 10 minutes. After completion of the heating, the resist film was treated with tetramethyl ammonium hydroxide 1.
Developed with a 2% aqueous solution for 60 seconds. The pattern size is 0.2
μm, a positive resist pattern having a good cross-sectional shape was formed.

Example 3 The procedure described in Example 1 was repeated. However, in the case of this embodiment, the photoresist film thickness was changed from 0.8 μm to 0.4 μm, and the exposure wavelength was changed to 2 μm.
The test was performed by changing from 48 nm to 193 nm. As a result,
A clear positive resist pattern having a size of 2 μm was formed. The exposure amount was 30 mJ / cm ² .

[0033]

According to the present invention, a high-resolution fine pattern can be formed by exposure using light having a short wavelength. In other words, a fine pattern can be formed since the deteriorated light shape can be recovered and a good exposure shape can be obtained for exposure. As a result, finer processing can be realized than before, and high integration of a semiconductor integrated circuit or the like can be easily performed.

Claims (6)

[Claims] 1. A thin film made of a photosensitive composition has a non-uniform density distribution in a thickness direction, and the light intensity of exposure is controlled by photobleaching at the wavelength of exposure light. Pattern forming method. 2. The pattern forming method according to claim 1, wherein the photobleachable substance is a photosensitive agent. 3. The pattern forming method according to claim 1, wherein the thin film made of the photosensitive composition is a chemically amplified photoresist. 4. A pattern forming method according to claim 1, wherein the concentration distribution of the photobleaching substance for controlling the light intensity of the exposure is large at the upper part of the film, and the concentration of the photobleaching substance is large in the substrate part of the film. A pattern forming method characterized by decreasing as approaching. 5. The pattern forming method according to claim 4, wherein the concentration of the photobleachable substance for controlling the light intensity of exposure at the upper portion of the film is at least twice the concentration at the substrate portion of the film. Pattern forming method. 6. A pattern forming method according to claim 4, wherein after the exposure, the light bleaching substance is exposed at an exposure amount such that a substance concentration distribution in an unbleached state becomes uniform.