JPH0620943A - Forming method for resist pattern - Google Patents

Abstract

PURPOSE:To obtain high resolution, a wide range of depth of focus and to prevent a multiple interference effect, a halation due to reflection of a step of a substrate in the case of forming a resist pattern. CONSTITUTION:The method for forming a resist pattern comprises the steps of providing a thin reflection preventive film 105 on a lower layer of a positive resist, forming a patterned positive resist 106, exposing the resist 106 to form a positive resist 107, and forming a silylated region 108 on a front surface of the resist 107 exposed by the silylation. With the resist 107 having the silylated region 108 on the front surface as a mask the film 105 is patterned, and a reflection preventive film 105a is formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a resist pattern in a lithography process in a method of manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In recent years, the demand for fine pattern formation has increased with the high integration of LSIs. At present, the main force of this fine pattern forming technique (lithography technique) is an optical exposure technique, and high integration of the resist process is being attempted along with improvement of the performance of the optical exposure apparatus. In particular, it has been pointed out that when the NA (lens numerical aperture) of the exposure apparatus is increased to improve the resolution, the depth of focus is narrowed. With the recent multi-layered wiring of devices, securing a depth of focus is becoming an important theme along with higher step height.

Further, with the recent trend of miniaturization, the demand for dimensional accuracy has become strict. For example, 0.35μ
In the case of the m rule, considering the accuracy within ± 10%, the dimensional accuracy is within ± 0.04 μm. However, when a reflective film is formed on a semiconductor substrate having a step, multiple interference effects caused by variations in the resist film thickness or resist constriction (halation) due to light reflection from the side surface of the step
Is likely to occur. Various techniques have been proposed for reducing the influence of these reflections. Proceeding of Society of Photo-Optical Instruction Engineers 1086, 242 (Proceeding of)
Society of Photo-Optical
Engineers, vol. 1086, p. 24
2, (1989)), a method using a die-containing resist and an antireflection film is presented. In this method, a resist is applied after forming an antireflection film that absorbs exposure light on a reflective substrate. Also, Journal of Vacuum Science Technology, Vol. 16, page 1620 (Journal of Va).
cum Science Technology, v
ol. 16, p. 1620, (1979), a dry development method using a multi-layer resist is reported. Proceeding of Society of Photo-Optical Instruction Engineers Vol. 920, p. 260 (Proceeding).
ofSociety of Photo-Optic
al Engineers, vol. 920, p. 26
0, (1988)) a silylation method is reported.

[0004]

Among the above conventional methods for reducing the influence of reflection, the die-filled resist method is one in which a material that does not undergo photobleaching is added to the resist as shown in FIG. Although the multiple interference effect is more effective than the normal resist without the bulk resist, the bulk effect (dimensions shown in FIG.
The relationship between the resist film thickness and the overall slope) is not much different from the usual method, and the resist shape tends to be tapered. In addition, the die-filled resist generally has a serious drawback that the depth of focus during exposure sharply decreases.

As is clear from FIG. 2, the antireflection film method can use a normal resist material having a high light transmission property, so that both the multiple interference effect and the bulk effect are small, and good resist shape and dimensional uniformity are obtained. Can be achieved.

However, this method causes a problem in removing the antireflection film after forming the resist pattern. Referring to FIG. 3, which is a cross-sectional view illustrating a method of forming a resist pattern, the above problem is as follows. First, the gate oxide film 20 is formed on the surface of the silicon substrate 201.
After forming 2 and the like, a polysilicon film 204 is deposited on the entire surface, an antireflection film is formed on the polysilicon film 204, and a positive resist is applied and formed on the entire surface. Next, a pattern of the positive resist 206a is obtained by exposure and development. Subsequently, the positive resist 206 is subjected to wet processing.
If the antireflection film in a region other than just under a is removed, an antireflection film 205a having an undercut state may be formed, or a tapered scum may occur, resulting in a significant deterioration in dimensional accuracy. Becomes [Fig. 3
(A)].

On the contrary, when the antireflection film in the above-mentioned unnecessary region is removed by dry (plasma) treatment in order to improve the dimensional accuracy, the antireflection film 205b formed as a residual has no undercut, but is positive. The mold resist 206a is transformed into a positive resist 206b [FIG. 3 (b)]. this is,
Since the dry treatment is anisotropic plasma etching mainly containing oxygen, the upper portion of the resist 206a is also etched, and in particular, the corner drop of the upper portion of the resist 206a occurs.
With the resist 206b having such a shape, there is a possibility that the dimensions of the resist 206b may change during the subsequent dry etching of the underlying polysilicon film 204. In particular, this phenomenon becomes a serious problem when the resist is thinned to improve the resolution and the depth of focus.

In the case of the multi-layer resist method, the number of lithography steps is increased and the productivity is significantly reduced. Pattern changes (bowing shape, side etch, etc.) depending on etching conditions during dry development of thicker lower layer resist
There is a problem that is likely to occur.

In the silylation method, it is necessary to sufficiently diffuse silicon into the resist in order to dry develop a thick resist film, but silylation treatment at a high temperature for a long time is required, and the quality of the resist material is deteriorated. Easy to receive. Further, since the silicon at the pattern interface essentially has a concentration gradient, there is a drawback that the dimensions gradually become smaller during dry development. More importantly, when the focus position is slightly shifted due to the substrate step, light slightly reaches the originally light-shielded portion, and as a result, silicon is diffused into that region during the silylation process. It has been observed that scum is generated during dry development.

[0010]

In order to solve the above-mentioned problems, the method of forming a resist pattern of the present invention is to form a resist pattern by applying a positive resist on a thin antireflection film, exposing it to light and developing it. After exposing the resist pattern, silicon is diffused (silylated) only in this resist pattern. Next, the underlying antireflection film is dry-etched with oxygen-based plasma.

[0011]

Next, the principle of the present invention will be described.

As shown in FIG. 2, if there is an antireflection film having a sufficient ability to absorb exposure light, both the multiple interference effect and the bulk effect can be greatly reduced. Furthermore, if there is no concern about the reflection of the underlying layer, the light transmittance of the upper resist can be increased as much as possible in order to realize a resist pattern having a vertical shape. In general, an increase in light transmittance leads to an improvement in resolution and an increase in allowable depth of focus. Further, on a substrate where reflection is likely to occur, the multiple interference effect increases as the resist film thickness decreases, but in the case of the present invention, the resist can be thinned because there is no influence of reflection. This thinning further improves the depth of focus and the resolution.

Next, after resist development, the entire surface is exposed to facilitate diffusion of silicon into the resist and reaction with the resin. Here, when a hard bake novolac resin or a polyimide resin is used as the antireflection film, the silylation reaction does not occur in these films. In the case of a novolak resist used for g, i-line exposure, a silylating agent is obtained by converting a photosensitizer, naphthoquinonediazide, into an indenecarboxylic acid by photoreacting by exposure (typically hexamethyldisilazane, hereinafter abbreviated as HMDS). Easily diffuses in the resist and reacts with the novolak resin, and oxygen of the hydroxyl group and the trimethylsilyl group are bonded. In a chemically amplified positive resist, a photo-acid generator absorbs light to generate a small amount of acid, and is then baked (100 to 150 ° C. for about several minutes) to be mainly used as a resin. Hydroxyl groups of polyvinylphenol are easily reacted with silylating agents (this is
When the silicon diffusion inhibitor added as a substance loses its function due to the acid, and when the hydroxyl group of polyvinylphenol is insoluble in the developer, for example, tert-
It may be dissociated by an acid that had been modified by a butoxycarbonyl group).

When silicon is diffused on the resist surface as described above, a silicon oxide film is formed on the surface layer of the upper resist when the underlying antireflection film is anisotropically etched by plasma mainly containing oxygen. Also, the film thickness of the resist does not decrease and the corner does not drop. In addition, since the thickness of the underlayer antireflection film is thin, the degree of silylation is sufficient. Therefore, the silylation treatment for a short time is sufficient and the resist does not drip or deteriorate. Furthermore, compared to the conventional dry development method,
Since the film thickness to be dry-etched is thin, the dimensional accuracy is remarkably improved.

By applying the present invention as described above, it is possible to secure a high developing power and a depth of focus, and at the same time, it is possible to greatly reduce the dimensional variation caused by the stepped reflective substrate, so that high dimensional accuracy can be realized.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

As a positive resist to be used, a case of a normal novolac type i-line resist will be described. MO
Referring to FIG. 1, which is a cross-sectional view of a process sequence for explaining formation of a fine polysilicon gate pattern of an S-transistor, a first embodiment of the present invention will first describe a silicon substrate 1
01 and gate oxide film 102 and field oxide film 103
And are formed by thermal oxidation, and 0.2 to 0.
A 4 μm thick polysilicon film 104 is deposited by the CVD method. Next, the underlying polysilicon film 1 having the above thickness
An antireflection film 105 having a film thickness of about 0.2 μm, to which a dye is added so as to almost completely absorb the reflection from 04, is applied. As the antireflection film 105, a hard bake novolac resin or a polyimide resin is suitable. Further, since resolution is not a problem for the antireflection film 105 itself, an arbitrary dye can be added without considering the reflectance of the underlying substrate. Next, a positive resist having an increased transparency is applied to a thickness of 0.5 to 1.0 μm, exposed and baked after exposure, and developed with an alkali developing solution to obtain a pattern of the positive resist 106 [FIG. (A)]. On this occasion,
The resist film thickness is usually 1.0 μm to 0.5 μm
The resolution and depth of focus will be greatly increased when the film is made thin.

Next, the entire surface is exposed, and the positive resist 106 is exposed to light to convert it into the exposed positive resist 107. The exposure light at that time is i-ray or deep.
Either UV may be used. Further, the exposed positive type resist 107 is subjected to silylation treatment to obtain a positive type resist 107.
A silylated region 108 is formed on the surface of the substrate [Fig. 1
(B)]. As the silylating agent, the above-mentioned HMDS, dichlorodimethylsilane or the like is used. 10 reaction chambers
^The gas is evacuated to about ^-4 torr, and a silylating agent such as HMDS is introduced therein using nitrogen gas as a carrier gas (reaction gas pressure is, for example, about 100 torr). The reaction temperature is adjusted to 120 to 150 ° C. Silylated region 10
Since the film thickness of 8 may be a thickness necessary for etching the thin antireflection film 105, the reaction time for forming this region 108 may be about 30 seconds to 3 minutes. Moreover, you may irradiate with an ultraviolet light in order to accelerate | stimulate silylation.

Next, the antireflection film 105 is etched by anisotropic dry etching to leave an antireflection film 105a. Since the antireflection film 105 has a thin film thickness of about 0.2 μm, it is relatively easy to maintain anisotropy when forming the antireflection film 105a. Parallel plate type, ECR (electron cyclotron resonance) type,
A RIE (reactive ion etching) device such as a magnetron type can be applied. Although the etching conditions vary depending on the etching apparatus, oxygen or a gas such as chlorine or bromine is mainly added to oxygen at a gas pressure of several m to 50 mtorr, and the process is completed within 1 minute, usually about 20 seconds. Next, the exposed positive resist 107 having the silylated region 108 on the surface and the remaining antireflection film 1 are formed.
Using the pattern of the two-layer structure consisting of
The polysilicon film 104 is anisotropically etched to form a polysilicon film 104a, which will be a fine polysilicon gate pattern of the MOS transistor, as shown in FIG. 1 (c).
This etching is performed by mixing a fluorocarbon type gas or a chlorine or bromine type gas.

Next, a second embodiment of the present invention in which the present invention is applied to a chemically amplified positive type resist will be described. This embodiment is basically the same as the first embodiment (in the case of a novolac resist). The only difference is that the bake treatment is added after the whole surface exposure performed after the residual formation of the resist pattern and the silylation treatment. This is because it promotes the acid-catalyzed reaction of a small amount of acid generated by exposure on the entire surface, which suppresses the diffusion of silicon and inhibits the reaction between the hydroxyl group of the resin (mainly polyvinylphenol) and the silylating agent. This is to remove the factors that cause In the case of a three-component system consisting of an acid generator, a dissolution inhibitor and a resin, the post-exposure bake treatment loses the dissolution inhibiting function (which also inhibits the diffusion of the silylating agent). On the other hand, in the case of a two-component system of a resin in which a group that prevents dissolution is added to the hydroxyl group and an acid generator, the dissolution inhibitor is removed from the resin by the above-mentioned baking treatment, and the hydroxyl group that reacts with the silylating agent is free. To

[0021]

As described above, according to the present invention, a thin antireflection film is provided on the lower surface of a positive type resist, and since exposure and development are performed, it is possible to improve the dimensional uniformity of the resist pattern, the resolution and the depth of focus. Further, after the entire surface of the resist pattern is exposed, this surface is subjected to silylation treatment to form a pattern of the lower antireflection film, so that the resist pattern is not thinned, corners are not removed, and the dimensional uniformity is further improved. It becomes possible.

[Brief description of drawings]

1A to 1D are cross-sectional views in order of processes for explaining a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a problem of the conventional technique and a graph for explaining a multiple interference effect.

FIG. 3 is a cross-sectional view for explaining the problems of the conventional technique.

[Explanation of symbols]

 101, 201 Silicon substrate 102, 202 Gate oxide film 103 Field oxide film 104, 104a, 204 Polysilicon film 105, 105a, 205a, 205b Antireflection film 106, 206a, 206b Positive resist 107 Exposed positive resist 108 Silyl Area

Claims (3)

[Claims] 1. A semiconductor substrate having a film to be processed on its surface is coated with an antireflection film that absorbs exposure light in advance, and a positive resist is coated on the antireflection film. A resist pattern made of the positive resist is formed by a development process, the resist pattern is entirely exposed, silicon is diffused only on the surface of the resist pattern, and the antireflection is performed by plasma containing oxygen using the resist pattern as a mask. A method of forming a resist pattern, characterized in that an antireflection film pattern having the same shape as the resist pattern is formed immediately below the resist pattern by anisotropically etching the film. 2. The method of forming a resist pattern according to claim 1, wherein the positive resist is a novolac resist or a chemically amplified resist. 3. The method for forming a resist pattern according to claim 1, wherein the antireflection film is a hard-baked novolac resin added with a die or a polyimide resin.