JPS61284923A - Pattern forming method - Google Patents

Abstract

PURPOSE:To enable a resist pattern to be formed as per the designed size regardless of the size and shape of the pattern by changing the optical transmittance of the optically transmissive portion of a mask in dependence on the pattern size and shape. CONSTITUTION:Using an apparatus comprising a substrate wafer coated with a resist, a light source for exposure, and a mask for pattern transfer, a latent image is formed by projecting an exposure light from the light source for exposure through the mask to expose the resist film, and thereafter development is carried out to form a pattern. In such pattern forming method, the optical transmittance of the optically transmissible portion of the mask is changed in dependence on the pattern size and shape. Exposure is performed using a mask (reticle) which has the respective patterns in the shape of a lattice, isolated line or hole having a pattern size of, e.g., 0.6-5mum, the optical transmittances of which respective patterns have the values as shown. In this case, a thin film of Cr is evaporated on the reticle, and the optical transmittances are changed by changing the film thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a pattern forming method, and more particularly to a pattern forming method 5 which is particularly useful for forming fine patterns in semiconductor integrated circuits and magnetic bubble elements having a high degree of integration.

[Background of the invention]

In order to manufacture semiconductor circuits, it is necessary to form patterns of various thicknesses and shapes all at once, and these patterns are required to have high dimensional accuracy.

Since optical lithography is affected by optical diffraction, the size of the actually formed pattern shifts from the design value, as shown in Figure 2, depending on the shape and size of the pattern.This phenomenon is referred to as dimensional conversion difference. ). This phenomenon is particularly noticeable near the resolution limit. Since patterns with various sizes and shapes are formed simultaneously, the dimensional accuracy between patterns inevitably decreases due to dimensional conversion differences.

Conventionally, the minimum dimension of the pattern to be formed was about 2 μm, which was larger than the limit resolution of the optical system.

Moreover, since the required accuracy was approximately ±0.2 μm,
This dimensional conversion difference was not a very big problem.

However, as semiconductors become more highly integrated, the required pattern dimensions become finer, and it becomes necessary to form patterns with a minimum dimension of about 0.6 μm. In other words, it is necessary to form a pattern with dimensions very close to the resolution limit, and the dimensional accuracy is also about ±
0.1 μm, and dimensional conversion differences have been highlighted as a major problem. Note that the discussion regarding this type of dimensional conversion difference can be found in the Technical Research Report 5S of the Institute of Electronics and Communication Engineers.
It was done by Nakase in D83-182.

If the dimensional conversion difference is small, this dimensional conversion difference can be corrected by correcting the mask-like pattern size. However, when the dimensional conversion difference is large, dimensional correction on the mask is insufficient and there is almost no margin.

Therefore, in order to accurately form a pattern whose dimensions shift from the design value due to the difference in dimension conversion, each button must be exposed separately for each pattern. However, this method of correcting dimensional conversion differences by changing the exposure time for each exposure not only makes the process longer and more complicated, but also requires a margin for alignment between each exposure, which hinders high integration. There was a problem.

[Object of the Invention] An object of the present invention is to solve the problems of the prior art described above and to provide a method for forming a resist pattern according to the designed dimensions regardless of the size and shape of the pattern.

[Summary of the invention]

The phenomenon in which the pattern dimensions shift from the design values depending on the pattern dimensions and shape is mainly due to changes in the light intensity distribution and light intensity of the exposure light that has passed through the pattern formed on the mask due to the effects of light diffraction, etc. arise. In order to sufficiently correct the dimensional shift from the design value, it is necessary to correct both the light intensity and the light intensity distribution of the exposure light mentioned above, but after thorough consideration, we found that the dimensions can be corrected by only correcting the light intensity distribution. It has been found that the correction can be carried out satisfactorily for practical purposes. Then, in order to correct the light intensity, the transmittance of the screen was changed according to the pattern.

[Embodiments of the invention]

The present invention will be explained below using examples.

As the exposure device, a reduction projection exposure device having a reduction ratio of 10 times was used. The numerical aperture (NA) of the lens is 0.
315, and the exposure wavelength is mercury i-line (365 nm).

grid-like pattern with pattern size from 0.6 to 5 μm;
Exposure was carried out using a mask (reticle) having isolated line and hole autumn/winter patterns, and the light transmittance of each of these patterns having the values shown in Figure WE1. A thin film of reticle VCCr was deposited, and the light transmittance was varied by varying the film thickness.

Furthermore, by forming an antireflection film against exposure light on the Cr surface, the adverse effects of optical interference caused by forming a thin Cr film were eliminated. In addition to Cr vapor deposition, Ag is a method for changing the light transmittance of a reticle.

Examples include vapor deposition of At or the like, formation of a film containing a dye that absorbs exposure light, or doping of a reticle with a dye that absorbs exposure light.

A substrate on which a photoresist was formed on a Si wafer was exposed to light using the method button described above, and then developed. The amount of deviation of the formed pattern dimensions from the design value was within the range of ±O, OS μm regardless of the shape and size of the grid, isolated line, and hole autumn/winter patterns.

In the above example, a Si wafer was used as the substrate, but since it hardly depends on the substrate material, oaAs, w, A
4 T t, S A02.5i3N4jpolys i
, WS i, Mo5it, polyimide film, etc. substrates also have no good luck. In addition, although a NAo, 315 lens was used, the wavelength is not limited to this, and the wavelength may also be not only the i-line but also the mercury g-line (436nm'>) or the h-line (405nm).For example, if the wavelength is the g-line and the lens is When the NA was 0.28, when the light transmittance of each pattern on the mask was set to the value shown in FIG. 3, the dimensional conversion difference between patterns of 0.9 μm or more could be reduced to about ±065 μm or less.

Further, the reduction ratio of the reduction projection exposure apparatus is not limited to 10 times, but may be 5 times or 7 times without any problem. Furthermore, this method can also be applied to scanner exposure methods and contact exposure methods.

〔Effect of the invention〕

According to the present invention, it was possible to form a pattern whose dimensions were as designed, regardless of the size and shape of the pattern. As a result, circuit design has become easier.

In addition, it has become possible to coexist fine patterns and relatively large patterns while maintaining high precision, making it possible to reduce the number of masks and significantly reducing the number of semiconductor manufacturing processes.9.

[Brief explanation of drawings]

FIG. 1 and the tXa diagram are curve diagrams of the relationship between the design dimensions and light transmittance of a mask according to an embodiment of the present invention, and FIG. 2 is a diagram of the relationship curve between the design dimensions and the amount of deviation in a conventional mask. etc. 1 Curse *;l h 3 'u & (/1Ara) Toru 2 figure o, 4- o, b oJ5/, o 2
．． o 3.0 4.0 bell needle bruise (p phantom 13 mouth

Claims (1)

[Claims] Using an apparatus consisting of a substrate wafer coated with at least a resist, an exposure light source, and a pattern transfer mask, exposure light is irradiated from the exposure light source through the mask to expose the resist film to form a latent image. 1. A pattern forming method in which a pattern is formed by forming a pattern and then developing the pattern, the method comprising changing the light transmittance of a light-transmitting part of the mask according to the pattern size and shape.