JPS607381B2 - Photomask pattern formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photomask pattern forming method used in manufacturing semiconductor devices.

Semiconductor technology has made remarkable progress in recent years, and LSIs are becoming more and more highly integrated.

As an important process to obtain highly integrated OSI,
There is a photolithography process, and it is necessary to faithfully reproduce the mask pattern shape on the semiconductor material, but it is quite difficult to faithfully form small-area openings on the semiconductor material substrate with steps. Now that's a problem. For example, as shown in FIG. 1, holes 4 and 5 are provided in the Si oxide film 3 at points A and B at different height levels of a semiconductor material composed of a Si substrate 1, a polycrystalline Sj 2, and a Si oxide film. In the process of exposing the surface of the polycrystalline Si2 of the Si substrate 1, as shown in FIGS. 2 and 3, for example, a positive type (hereinafter explained using an example of a positive type resist) is applied on the surface Sj oxide film 3 of the semiconductor substrate 1. After applying the photoresist 6, repattern exposure is performed using a photomask 7 by irradiation with ultraviolet light, and then the photoresist is developed and the Sj oxide film is etched to form barrier portions in the Si oxide film as shown in the figure. ing. At this time, if the substrate surface to which the photoresist is applied has a shape with uneven steps, the photoresist 6 to be applied thereon is
does not faithfully reproduce uneven steps, and the photoresist applied to the depressions is thicker than the photoresist film on the protrusions, and the surface of the photoresist is almost smooth as shown in Figure 2. This is a remarkable tendency, especially for positive type photoresists.

When exposing the pattern of the photomask 7 to the photoresist 6 having different film thicknesses as described above, in order to faithfully reproduce the mask pattern at point A in FIG.
The photoresist is exposed to light with enough energy to completely decompose the photoresist. However, if the amount of exposure becomes excessive at this time, the photoresist will be damaged to the periphery of the pattern due to the reflected light from the Si oxide film surface. It is decomposed and the pattern shape cannot be faithfully reproduced.

On the other hand, at point B, when exposed with an appropriate exposure amount corresponding to the photoresist film thickness T^ at point A, the photoresist film thickness TB at point B has the relationship TB>T^, so it is decomposed by light irradiation. This means that the area 6B that has been removed has not reached the bottom surface of the photoresist. Therefore, even after the photoresist is developed, undecomposed resist remains at point B, and if this photoresist is used as an etching mask for the Si oxide film, the Si oxide film at point B will not be etched. On the other hand, if the exposure amount is determined based on the photoresist film thickness TB at point B, overexposure will occur at point A where the photoresist film thickness is thin, and the composition of the photoresist due to light irradiation including the Si substrate and Si02 reflected light will be decomposed. The area 6A shown in FIG. 4 is as shown in FIG. 4. When the holes 4 and 5 are formed in the Si oxide film 3 using the photoresist 6 as an etching mask for the Si oxide film 3, the dimensions of the opening in the Si oxide film 3 are as follows. As shown in FIG. 5, at point B, the mask pattern dimensions can be roughly reproduced, but at point A, an opening larger than the mask pattern dimensions is formed. In particular, faithful reproduction of mask patterns is an important factor in achieving higher densities and higher integration levels of semiconductor devices, which have recently become increasingly popular, and the above-mentioned problem is one of the causes that impede higher densification. Although the above conventional example uses a positive resist, the same problem occurs when a negative resist is used.

An example of this is shown in FIG. 6. Since a pattern is formed on the negative resist 6 by polymerization and curing by light irradiation, the shadowed area (non-polymerized area) of the mask when overexposure occurs at point A in FIG. The influence of reflected and scattered light on the photoresist is opposite to that of the positive resist, and the opening of the Si oxide film 3 on the Si substrate 1 is
The hole is smaller than the pattern of the photomask 7, and in extreme cases, the hole may not be opened. As mentioned above, whether it is a positive resist or a negative resist, on a substrate with unevenness,
This means that the photomask pattern cannot be faithfully reproduced.

Therefore, an object of the present invention is to make it possible to form barrier holes that faithfully reproduce the pattern of a photomask at positions at different heights on a material substrate having uneven steps on its surface. This invention proposes a photomask pattern forming method.The present invention will be explained below based on examples together with drawings.As explained in the conventional example, the reason why the dimension of the barrier hole increases or decreases with respect to the photomask pattern 4 is due to the step. This is due to the fact that the photoresist coated on a substrate having a surface becomes substantially smooth on its surface, and the photoresist film on the concave portions of the substrate is thicker than on the convex portions.

Therefore, when forming a pattern as an etching mask that decomposes or polymerizes photoresist by irradiating it with light, exposure that provides the light energy necessary for decomposition or polymerization is performed based on the thick photoresist area. This is caused by overexposure because the photoresist layer formed on the convex portions, which has a poor thickness, is subjected to the same exposure process as the concave portions in order to perform the treatment. Figure 7 a-c
1 shows a method for manufacturing a photomask having an overexposure prevention function used in the present invention.

As shown in FIG. 7a, a translucent transmitted light amount regulating thin film layer 9 is formed on the entire surface of the glass substrate 8 using ALW or other metal thin film, and then a normal photomask pattern of chromium or the like is applied to the thin film layer 9. form 10.

Thereafter, as shown in FIG. 7b, on the same mask pattern, a photosensitive resin (hereinafter referred to as photoresist) is selectively masked only in the areas where the thin film layer 9 should remain, and the resist mask 11 and After removing the thin film layer 9 by etching using the photomask pattern 10 as a mask, the resist mask is removed to form a photomask as shown in FIG. 7c. As is clear from FIG. 7c, this photomask has a region 12 where light is completely transmitted and a region 13 where the amount of transmitted light is attenuated by the thin film layer 9. can be arbitrarily selected by adjusting the layer thickness. FIG. 8 shows another example of a photomask in which the transmitted light amount regulating thin film layer 9 is formed on the surface opposite to the main surface forming the photomask pattern 10. , FIG. 9 is a plan view of the same.

As can be seen from both sides, the formation of the transmitted light amount regulating thin film layer 9 has sufficient dimensional margin compared to a single photomask pattern, and the precision requirements for forming the same thin film layer 9 are low, making it easy to manufacture. One of its characteristics is that it is easy. FIG. 10 shows still another example of the present invention in which the transmitted light amount regulating thin film layer 9 is made of the same material as the photomask pattern 10. For example, when forming the photomask pattern 10 made of chromium, the amount of transmitted light is attenuated. Regarding the part in the transparent area 13,
Mask material (ku.

This is a photomask having a structure in which a thin film layer 9 remains to attenuate the amount of transmitted light during exposure, and the method of manufacturing the photomask is roughly the same as that shown in FIGS. 7a to 7c. FIG. 11 shows that after forming a photomask pattern 10, a transmitted light amount regulating thin film layer 9 is deposited on the entire surface, and the transmitted light amount regulating thin film layer 9 deposited on a completely transparent region 12 is selectively removed. This is an example of a photomask having two regions, a fully transparent region 12 and an attenuated transmittance region 13.

Although the transmitted light amount regulating thin film layer 9 is explained as an example composed of a metal thin film, the thin film layer 9 is not limited to a metal thin film, but is a material that attenuates and transmits the light amount, and can easily form minute patterns. It is fine as long as it is configurable.

For example, it is also possible to form a pattern using photoresist and perform ion implantation on the photoresist to control the amount of permeation. FIG. 12 shows an embodiment of the present invention in which an etching mask is formed using a positive resist 6 on a semiconductor substrate 1 to be processed having unevenness using the photomask described above.

The irradiation light amount 14 is set to be enough to decompose the photoresist film thickness TB in the region B where the resist film thickness is thick. At this time, the amount of light irradiated to the thin photoresist film thickness TA portion of the A region is exposed by the amount of light attenuated and transmitted by the transmitted light regulating film layer 9, thereby preventing the problem of over-etching seen in the conventional example. The setting of the amount of attenuation of the transmitted light by the transmitted light amount regulating thin film layer 9 is such that the appropriate exposure amount required to decompose the photoresist film thickness T^ in the A region is the same as that required to decompose the photoresist film thickness TB in the B region. Ideally, the thickness of the thin film regulating the amount of transmitted light should be formed by calculating the percentage of the exposure amount and setting the amount of attenuation of the amount of transmitted light corresponding to that.
In reality, the relationship between the photoresist film thicknesses TA and TB is not always constant and is difficult to measure, so it is difficult to prepare a large number of photomasks with different thicknesses of transmitted light amount regulating thin films that have corresponding attenuation amounts. Almost impossible.

Therefore, in the actual method of using a photomask (photoetching method), for example, the amount of attenuation of the amount of transmitted light is 20%, 40%
Prepare about 3 types of photomasks: % and 60%.
Thickness ratio T of photoresist caused by surface unevenness level difference
^/If the appropriate exposure amount ratio of A area to the appropriate exposure amount of B area by TB is approximately 60 to 80%, the attenuation amount is 20%.
% photomask, the attenuation amount is 4 in the case of 40 to 60%.
If photoetching is performed using a 0% photomask, the openings in the Si oxide film in area A may be slightly oversized, but compared to conventional photomasks, this is a significant improvement and the process yield is improved. The effect it has on improvement is significant. For convenience, the mask structure and photoetching method were explained for positive type resist, but even in the case of negative type resist, due to the difference in resist film thickness, the photomask has the function to adjust the exposure amount required to polymerize the resist. Since the idea of applying the same method to the above is the same, it is obvious that it can also be applied to masks for negative tie resists.

However, in the case of a negative type, if a photomask is used that has a light emitting film at the position corresponding to the barrier formation area of the convex photoresist and a transmitted light amount regulating thin film around it, the barrier No light due to overexposure will enter into the photoresist corresponding to the region where the portion is to be formed. As explained above, in the photomask pattern forming method of the present invention, exposure is performed through a photomask provided with a transmission amount regulating thin film at a position corresponding to a predetermined area of a convex portion of a photoresist, so that the photoresist can be properly applied to a concave portion of the photoresist. Even if exposure is performed, the convex portion will not be overexposed, and a barrier portion faithful to the mask pattern can be formed.

[Brief explanation of drawings]

1 to 6 are explanatory diagrams for explaining a conventional photomask, FIGS. 7a to 7c are process cross-sectional views showing a method of manufacturing a photomask used in the present invention, and FIGS. 8 to 11 are FIG. 12, which is an explanatory view of another example of a photomask, is a cross-sectional view showing the photomask pattern forming method of the present invention. Evening 1...Semiconductor substrate to be processed, 3...Si
Oxide film, 6... Photoresist, 6A, 6B... Soluble region of photoresist, 7... Subordinate photomask, 8
...Glass main plate, 9 ... Transmitted light amount regulating thin film layer, 10 ... Photomask pattern, 11.
. . . Mask material such as photoresist for selectively removing the zero layer of the transmitted light amount regulating thin film, 12 . . . Fully transparent region, 13 . Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12

Claims (1)

[Claims] 1. In the process of forming a photopattern on a photoresist film for photolithography formed on the entire surface of a semiconductor substrate to be processed that has a step on its main surface, the shape of the photoresist film layer is affected by the shape of the main surface of the semiconductor substrate to be processed. By exposing parts having different film thicknesses through a photomask that has a transmitted light amount regulating thin film layer as a part of which adjusts the amount of irradiated light, the amount of irradiated light corresponding to the thickness of each of the photoresist layers is applied. A photomask pattern forming method characterized by: