JPS59168637A - Forming method of minute pattern - Google Patents

Abstract

PURPOSE:To prevent the generation of a standing wave by reflected rays and the lowering of resolution to occur with the generation of the standing wave and the deterioration of the controllability of pattern size by forming a layer completely absorbing rays used for exposure and obviating reflected rays from the surface of a semiconductor substrate. CONSTITUTION:A photo-resist layer 203 is formed on a semiconductor substrate 202 with a stepped section, the whole surface thereof is coated with aluminum 201 of large reflectivity, and the stepped section is flattened. An optical absorption layer 204 is shaped, and a photo-resist layer 205 is formed on a flattened surface. A desired photo-resist pattern 206 is formed through exposure and development. The optical absorption layer 204 dissolves into the developer, and an optical absorption layer pattern 207 is formed simultaneously. Reflected rays do not project to the photo-resist layer 205 because the optial absorption layer 204 completely absorbs rays of a specific wavelength. The surface is exposed by UV rays, the photo-resist layer 203 is developed and a photo-resist pattern 208 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming fine patterns using light.

In recent semiconductor-integrated circuit devices, multilayer wiring structures are commonly used to increase density, and as a result, unevenness inevitably occurs on the semiconductor substrate, and some of them are as small as 2 μm. There are many cases where there is a large step that extends even further. When forming a fine pattern on a semiconductor substrate with such a large step difference, there are many problems such as poor step coverage at the step part and variation in pattern dimensions between the bottom and top of the step. .

Multilayer resist technology has recently attracted attention as a method for solving such problems.

1 to 3 are main process diagrams of conventional multilayer resist technology. Regarding this prior art.

For example, Journal of Vacuum 5ci
ence and'1”technology magazine 1981
It is described in Volume 19, Issue 4, Page 1313. In this method, first, a thick photoresist layer 101 with a thickness of about 2 to 3 μm is placed on a semiconductor substrate 101 having a step on its surface.
The steps on the semiconductor substrate 101 are flattened by coating the semiconductor substrate 101 (FIG. 1).

As this photoresist layer 102, PMMA (poly methyl methacrylate) is mainly used.

Next, a thin photoresist layer 103 with a thickness of about 0.5 μm is coated on the upper surface of the photoresist layer 102 to open the light.
Develop and form a pattern (Figure 2).

For the photoresist layer 103, AZi370 and AZ1350J are mainly used in the case of light exposure. Next 7
De e p using Otoresist% 103 as a mask
After irradiating the entire surface with UV light (wavelength: 200-250 nm), it is developed to form a pattern of photoresist #102, and the process is completed (FIG. 3).

According to this method, the step on the surface of the semiconductor substrate 101 is flattened by the thick photoresist (ffl 102), so there is no change in the thickness of the photoresist layer 103 above and below the step.

As a result, since there is no difference in the optimum exposure amount between the two, the change in pattern dimensions is very small. Furthermore, step
Since the coverage is good, it is possible to reduce the thickness of the photoresist layer 103.

You can expect high resolution.

However, the thin upper photoresist layer 10
5 in the process of emitting light to 3 tl- and forming a pattern.
As shown in the spectral characteristics in Figure 4, for the commonly used wavelength s 436 nm, the upper layer photoresist AZ1370 has a transmittance of 60 to 70%, while the lower layer 7 photoresist PMMh has a transmittance of approximately 100%, so approximately 60 to 70% of the light used to expose the upper 7-photoresist layer 103 passes through the lower 7-photoresist layer 102 and reaches the semiconductor substrate lo1. Particularly when the semiconductor substrate 101 is covered with aluminum or the like having a high reflectance, most of the light that reaches the semiconductor substrate 101 becomes reflected light. This reflected light interferes with the incident light to generate a standing wave within the photoresist layer 103 of the -F layer. As a result, resolution is reduced and pattern dimensions become difficult to control. Therefore, according to this method, it is difficult to process fine patterns. Therefore, how to reduce the reflected light from the semiconductor substrate and prevent the generation of standing waves is a serious problem in forming fine patterns.

An object of the present invention is to provide a method for forming a 1# high-rise pattern by reducing the above-mentioned reflected light to prevent the generation of standing waves.

The present invention is characterized in that a method for forming a photoresist pattern by a light exposure method on a semiconductor substrate having a step on its surface includes a step of forming a first coating film on the semiconductor substrate to flatten the step; A second layer that absorbs glare
a step of forming a coating film on the first coating film, and a step of forming a third coating film on the second coating film in which a desired pattern is formed by a light exposure method. The pattern formation method includes

According to the present invention, by providing a layer that completely absorbs the light used for exposing the upper layer 7 photoresist, pattern formation with high resolution can be realized in order to prevent reflected light.

The following is a detailed explanation of the present invention with reference to the drawings. Figures 5 to 7 are diagrams of the main absorption process in one embodiment of the present invention, and Figure 8 is the spectral characteristics of the light absorption layer used in the present invention. It is.

First, as shown in FIG. 5, a semiconductor substrate 202 with steps is coated on the entire surface with aluminum 201 having a high reflectance. A thick photoresist layer 203 having a film thickness of about 2 μfl'l is formed to flatten this step. PMAIA is used as the photoresist layer 2 0 3 .

Next, the thickness of the upper surface of the photoresist layer 203 is approximately 470 Ω.
A light absorption layer 204 is formed. This light absorption layer 204 is, for example, manufactured by Brewer Science.
The above film thickness can be obtained by spin-coating IIC-L5 at 400 rpm and heat-treating at 148° C. for 30 minutes. As shown in FIG. 8, the spectral characteristics of the light absorption layer 204 when the film thickness is
0 surface, and as a result there is no reflected light from this surface. Next, a photoresist layer 205 is formed on the upper surface of the light absorption layer 204 to form a desired pattern. As the photoresist layer 205, for example,
Using AZ 13 70 manufactured by Silapray, its film #
li:. The thickness is approximately 0.5 μm. Photoresist layer 20
5 is formed on a flattened surface, there is no problem with step coverage at the step portion of the semiconductor substrate 202, and there is no variation in film thickness between the top and bottom of the step.

Therefore, the controllability of pattern dimensions is good, and further, high resolution can be achieved by making the film thinner.

Thereafter, as shown in FIG. 6, after exposure to light having a wavelength of 436 nm, development is performed using, for example, MF312, a developer for AZ1370 manufactured by Silaplay, to form a desired photoresist pattern 206. Since the light absorption layer 204 has a property of being dissolved in this developer, the light absorption layer pattern 207 is also formed at the same time.

As mentioned above, the wavelength used for exposure is 436
The transmittance of the photoresist layer 205 to nm light is 6
Since the ratio is 0 to 70%, this proportion of light is absorbed by the light absorption layer 204.
incident on the However, as described above, this light absorption layer 204 completely absorbs this wavelength, so no light reaches the surface of the aluminum 201, and therefore, the reflected light from this surface is transmitted to the 7Otoresist 1@204. There is no incident. Therefore, standing waves are no longer generated, and a fine photoresist pattern 206 can be formed.

Next, according to the usual method, the photoresist pattern 2
Using 06 as a mask, the entire surface was exposed to deep tJV light (wavelength 20
After exposure (0 to 250 nm), the photoresist layer 203 is developed to form a photoresist pattern 208, as shown in FIG. 7, to complete the process.

As described above, according to the present invention, a layer that completely absorbs the light used for exposure is provided to prevent light reflected from the surface of the semiconductor substrate, thereby solving the problem of conventional multilayer resist technology. It is possible to prevent the generation of standing waves due to the reflected light and the accompanying deterioration in resolution and pattern dimension controllability, thereby realizing the formation of fine patterns.

[Brief explanation of the drawing]

1 to 3 are main process diagrams of the prior art, and FIG. 4 is a diagram showing the spectral characteristics of PMMA and AZ1470. 5 to 7 are main process diagrams in one embodiment of the present invention, and FIG. 8 is a diagram showing the spectral characteristics of the light absorption layer used in the present invention. In addition, in Figure 1, 101... semiconductor base &, 10
2...Photoresist layer, 103...
Photoresist In, 201... Aluminum, 202...° Pa... Semiconductor substrate, 203...°... First resist H! j, 204... Light absorption layer, 2
05...Photoresist layer, 206...
・Photoresist pattern, 207...Light absorption layer nok turn 120B...Photoresist turn Skin length (η772) Figure 4

Claims (1)

[Claims] A method for forming a shifted resist pattern by a light exposure method on a semiconductor substrate having a step on its surface, which includes a step of forming a first coating film on the semiconductor substrate to flatten the step, and a method for preventing glare. a step of forming a second coating film having absorbency on the first coating film; and a step of forming a third coating film on the second coating film for forming a desired pattern by a light beam method. A method for forming a pattern, the method comprising the step of forming a pattern on the top.