JPS6220844Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a photomask, and more particularly to a photomask suitable for forming a resist pattern having a desired slope in cross section by irradiating a photoresist film with light having partially different light intensities.

As is well known, various fine patterns of magnetic bubble memory elements and various semiconductor devices are formed using a technique called photolithography.

Although this technique is useful for forming various fine patterns, it has the following problems.

For example, the cross-section of the formed photoresist pattern is generally steep. Therefore, in order to obtain a cross section with a gentle slope, heat treatment is performed after forming the photoresist pattern to soften the photoresist and make it gentle, or the distance between the photomask and the photoresist is widened during exposure to improve diffraction. Methods have been devised, such as creating a penumbra to make the cross section smoother.

However, in the heat treatment method, the range that can be smoothed depends on the thickness of the resist coating film, so it is difficult to control the range to a desired length. Furthermore, the method of widening the distance between the photoresist and the mask has the disadvantage that mask alignment cannot be carried out with high precision. Furthermore, in either method, the pattern within the same mask becomes uniformly smooth, so there is a drawback that it is difficult to partially smooth only a desired pattern.

An object of the present invention is to solve the above-mentioned problems and provide a photomask in which only a desired pattern has a gentle cross section and whose cross-sectional shape can be controlled with high precision.

In order to achieve the above object, the present invention provides a large number of fine holes below the resolution limit in the opaque film of a desired part of a photomask, and gradually changes the area of the holes to change the opaque part and transmittance. A mask pattern with semi-transparent parts is obtained.
The gist of the present invention is to provide a photomask in which a mask pattern made of an opaque film is provided on a transparent substrate, in which at least a portion of the mask pattern is provided with a plurality of holes that are finer than the pattern resolution limit, and the area of the holes is A photomask is characterized in that it becomes larger as it approaches the edge of the pattern.

Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows a cross-sectional structure of a photomask according to an embodiment of the present invention. As shown in the figure, in this embodiment, in an opaque film 2 made of a Cr film with a thickness of approximately 70 nm on a photomask substrate 1, holes 3 and patterns finer than 0.5 μm, which is the resolution limit, are formed in desired portions. 4, and the area ratio of both is gradually changing.

Since light does not pass through parts without fine pores, it acts as an opaque film. In the part having the fine holes 3, there are parts through which light passes and parts through which light does not pass. However, since hole 3 is very fine,
The light that has passed through the hole 3 is diffracted and is exposed not only to the area directly below the hole 3 but also to a portion slightly away from it. Since this amount of exposure changes depending on the area of the hole, the amount of exposure can be gradually increased by gradually increasing the area of the hole.

As is well known, when the exposed photoresist is positive type, the dissolution rate is determined by the exposure amount, so as shown in Figure 2, the resist has a film thickness corresponding to the area of the hole in the photomask. pattern 5
can be obtained on the substrate 6.

In conventional methods, it was extremely difficult to control the range in which the resist film thickness gradually decreased, but according to the present invention, it is possible to control the range in which the area of the holes on the photomask is changed. , a smooth pattern can be easily obtained. Moreover, even within the same pattern, as shown in FIG. 2, a portion 7 having a steep cross section can be formed at the same time.

In the above example, the size of the fine hole and pattern was described for the case of contact exposure and same-magnification exposure, but in reduction projection exposure, the size of the fine hole and pattern is 1/10 depending on the reduction ratio.
Needless to say, in the case of , it is 5 μm or less, and in the case of 1/5, it is 2 μm or less.

Moreover, it goes without saying that the shapes of the fine holes and patterns are not limited to circles and polygons, but also linear patterns can have similar effects.

As is clear from the above description, the present invention allows the cross section of the photoresist to be made smooth by using a photomask provided with a large number of fine holes and patterns whose area ratios are gradually changed. The shape can be controlled with high precision.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a photomask according to an embodiment of the present invention, and FIG. 2 is a sectional view of a resist pattern formed using the photomask. 1... Photomask substrate, 2... Opaque film, 3...
...hole, 4... pattern, 5, 7... resist pattern.

Claims (1)

[Scope of utility model registration request] In a photomask in which a mask pattern made of an opaque film is provided on a transparent substrate, at least a part of the mask pattern is provided with a plurality of holes that are finer than the pattern resolution limit, and the area of the holes is equal to or smaller than the edge of the mask pattern. A photomask that gets bigger the closer you get to it.