JPH02122516A - Exposure method - Google Patents

Abstract

PURPOSE:To prevent the opening of a resist pattern from scattering by providing a light-reducing film which weakens irradiation light transmitting a photomask at a transmission area of a mask pattern corresponding to the area where a photo resist is thin due to steps in a substrate. CONSTITUTION:In a photomask 3A, a light-reducing film 3c is provided at one part of a light transmission area 4 of a photomask 3 and the light transmission area 4 corresponding to part corresponds to the area of a projecting part 1a of a substrate 1. The light-reducing film 3c weakens an irradiation light 5 which penetrates the photomask 3A and abates its strength. The thickness of a light-reducing film 3c is determined by the arrangement of thickness of the thick area and thin area of a photo resist 2. Thus, if exposure is made by the photomask 3A, the size a of an opening 7 on the projecting part 1a of a resist pattern 6A formed on the substrate 1 by development becomes nearly the same as the size b of other opening 7, thus eliminating scattering of the opening 7.

Description

[Detailed Description of the Invention] [Summary] An exposure method in which a photomask is placed opposite to a substrate coated with a photoresist on the surface thereof, and light is irradiated from the photomask side to transfer a mask pattern of the photomask onto the photoresist. In order to prevent variations in the openings of the resist pattern formed from the photoresist due to the steps, the mask pattern is transparent in areas where the photoresist is thinned due to the steps. A photomask is used in which a light-attenuating film is provided in the region to weaken the irradiation light that passes through the photomask.

[Industrial application field]

The present invention relates to an exposure method for transferring a mask pattern of a photomask onto a photoresist by placing a photomask facing a substrate coated with a photoresist on the surface and irradiating light from the photomask side, and particularly relates to a method when the substrate surface has a step.

In the manufacture of semiconductor devices, the above-mentioned exposure is often used to form a resist pattern that serves as a mask for substrate processing. In that case, if there are steps on the surface of the substrate due to prior processing, thick and thin regions will be created in the photoresist, which will cause variations in the openings of the resist pattern formed from the photoresist. Some effort is needed.

[Conventional technology]

FIG. 4 is a side view illustrating the conventional example of exposure, and FIG. 5 is a side sectional view of a resist pattern formed by the conventional example.

In FIG. 4, 1 is a substrate, 2 is a photoresist, 3 is a photomask, and 5 is irradiation light.

The substrate 1 is a semiconductor wafer to be exposed or a processed product thereof, and here has a convex portion 1a with a height of about 0.4 μm, and has a step 1b on the surface depending on the height.

The photoresist 2 is of a positive type applied to the surface of the substrate 1 and has a thickness of about 1.6 μm, but the thickness on the convex portion la is about 1.2 μm due to the step 1b.

The photomask 3 has a substrate 3a made of a transparent plate such as quartz glass, and a light-shielding film 3b made of chromium or the like deposited thereon.
A mask pattern is formed in which a light-transmitting region 4 is provided, and the light-transmitting region 4 is a plurality of windows of about 1 μm square, some of which are convex portions 1a? Compatible with iN area.

In the exposure, the photomask 3 is opposed to the substrate 1 and the irradiation light 5 is irradiated from the photomask 3 side, and the photoresist 2 is partially exposed by the irradiation light 5 that has passed through the light-transmitting area 4. By subsequent development, a resist pattern 6 having an open lower part from which the photosensitive area 2a has been removed is formed on the substrate l, as shown in FIG. Ru.

[Problem to be solved by the invention]

However, in the above exposure, the thickness of the photoresist 2 is thin on the convex portion 1a and thick on other areas, so if the exposure intensity is adjusted to the thick area, the thin area will be overexposed. As shown in FIG. 5, the size a of the open lower portion on the convex portion la is approximately 0.2 μm larger than the size b of the other open lower portions, and there is a problem in that the open lower portions vary.

This hinders the miniaturization of patterns required for higher integration of semiconductor devices.

Therefore, the present invention aims to solve the problem in that when there is a step on the surface of the substrate, in an exposure process in which a photomask is opposed to a substrate coated with photoresist on the surface and light is irradiated from the photomask side to transfer the mask pattern of the photomask onto the photoresist, when there is a step on the substrate surface. It is an object of the present invention to prevent variations in the openings of a resist pattern formed from the photoresist.

[Means to solve the problem]

The above object is solved by the exposure method of the present invention, which uses a photomask that is provided with a light-attenuating film that weakens the irradiation light that passes through the photomask in the light-transmitting area of the mask pattern corresponding to the area where the photoresist is thinned due to the step. Ru.

[For production]

By suitably weakening the irradiation light using the light attenuation film, it is possible to prevent overexposure in thin areas even if the exposure intensity is adjusted to thicker areas of the photoresist. It is possible to achieve alignment for both thick and thin regions.

From this, it is possible to prevent variations in the openings of the resist pattern formed from the photoresist due to differences in level on the substrate surface.

〔Example〕

Embodiments of the exposure method according to the present invention will be described below with reference to FIGS. 1 to 3. FIG. 1 is a side view explaining the example, FIG. 2 is a sectional side view of a resist pattern formed in the example, and FIGS. 3(a) to (e) are manufacturing process diagrams of the photomask used in the example. , and the same reference numerals throughout the figures indicate the same objects.

In the exposure example shown in FIG. 1, the conventional photomask 3 described in FIG. 4 is replaced with a photomask 3A.

The photomask 3A has a light-attenuating film 3c provided in a part of the light-transmitting region 4 of the photomask 3, and the light-transmitting region 4 corresponding to the part corresponds to the convex portion 1ajJ area of the substrate 1. It is. The light attenuation film 3c is a chromium oxide film with a thickness of 100 mm and weakens the irradiation light 5 that passes through the photomask 38, making its intensity approximately 80% of that without the light attenuation film 3c.

This value of 80% means that the exposure intensity can be reduced to 1 thickness without attenuation.
．． When matched with 6 μm photoresist 2, the thickness is 1.2
This is a value that matches the exposure intensity to the photoresist 2 of μm.

From this, when exposed using the photomask 3A, a resist pattern 6^ formed on the substrate 1 by development in the same manner as the conventional resist pattern 6 is formed in the opening on the convex portion la, as shown in FIG. The size a of the lower part is approximately equal to the size b of the other open lower parts, and there is almost no variation in the opened lower parts.

The photomask 3A can be manufactured, for example, as follows.

That is, in FIG. 3, first, a conventional photomask 3 is manufactured as shown in (a), then a light-attenuating film 3c is deposited on the light-shielding film 3b side as shown in (b), and the convex portions of the base vi1 are formed on it. A resist mask 8 corresponding to 1a is formed as shown in (C),
After selectively removing the light attenuation film 3c as shown in (d), (e
) If the mask 8 is removed as shown in FIG.
is completed. Needless to say, the light attenuation film 3 is placed at the desired location.
It is also possible to provide c using a known lift-off method.

It is easy to understand that the thickness of the light attenuation film 3c is determined by the thickness distribution of the thick and thin regions of the photoresist 2, and that the material of the light attenuation film 3c is not limited to chromium oxide. It will be.

〔Effect of the invention〕

As explained above, according to the configuration of the present invention, a step is formed on the surface of the substrate during exposure in which a photomask is placed opposite to a substrate coated with photoresist on the surface, and light is irradiated from the photomask side to transfer the mask pattern of the photomask onto the photoresist. When using a photoresist, it is possible to prevent variations in the openings of the resist pattern formed from the photoresist due to the step difference, thereby facilitating the miniaturization of patterns required for higher integration of semiconductor devices. It has the effect of making it easier.

[Brief explanation of drawings]

Figure 1 is a side view explaining the example, Figure 2 is a side sectional view of a resist pattern formed in the example, and Figures 3 (a) to (e) are manufacturing process diagrams of the photomask used in the example. , FIG. 4 is a side view illustrating a conventional example, and FIG. 5 is a side sectional view of a resist pattern formed by the conventional example. In the figure, ■ is the substrate, 1a is the convex part, 1b is the step, 2 is the photoresist, 2a is the photosensitive area, 3.3A is the photomask, 3b is the light-shielding film, 3c is the light-reducing film, 4 is the light-transmitting area, and 5 is the light-transmitting area. The irradiation light is 6.6A, and the register is an aperture. Do pattern, 2 spellings! 1 day, 1aL day 8 child ps (ffil!
1Figure 1

Claims (1)

[Claims] In exposure in which a photomask is placed opposite to a substrate coated with photoresist on the surface and light is irradiated from the photomask side to transfer the mask pattern of the photomask onto the photoresist, when the substrate surface has a step, the step An exposure method characterized by using a photomask provided with a light-attenuating film that weakens irradiation light transmitted through the photomask in a light-transmitting region of a mask pattern corresponding to a region where the photoresist is thinned.