JPH09288345A - Mask for projection print - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the uniformity of illumination and of the width of lines formed in a lithographic process by eliminating the unevenness of the illumination as one of factors of the unevenness of the line width in an exposure field. SOLUTION: This mask for projection print is constituted of a transparent substrate 32 made of volosilicate glass for instance and a cover film 36 mounted on the transparent substrate 32 with a ring-like spacer 34 of desired height. An opaque pattern is plotted on the bottom surface of the transparent substrate 32 by a chrome film 38 for instance and corresponds to a conventional reticle. Further, on the cover film 36, the layout of a dot area 44 where circular opaque dot patterns 42 are regularly arranged is attained in the fixed region of the surface of a transparent thin film 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection print mask, and more particularly to a projection print mask used in an exposure step in a semiconductor process.

[0002]

2. Description of the Related Art Recent ICs (Integrated Circuits) and L
Along with high integration and high density of semiconductor devices such as SI (Large Scale Integration), the lithography technology has been developed as a center of fine processing technology. In the lithography process of such a semiconductor process, there is a problem that the line width to be formed becomes non-uniform due to uneven illuminance in the exposure field at the time of exposure.

In particular, the optical system of the current reduction projection exposure apparatus is a partial coherent illumination, and there is a considerable variation in the coherent lens factor σ which is the ratio of the NA (numerical aperture) of the reticle illumination system and the NA of the projection system. . That is, this σ
Due to variations, the light is vertically irradiated to the wafer in the central part of the exposure field, whereas the light is not vertically irradiated to the wafer in the peripheral part, and the light is irradiated at a non-uniform incident angle. Become.

On the other hand, the photodetector for measuring the illuminance of the irradiation light has a dependency on the incident angle of light, and the light is obliquely irradiated with an incident angle larger than the illuminance of the central portion of the exposure field where the light is vertically irradiated. The illuminance around the exposed field is measured low. Therefore, if it is attempted to uniformly correct the illuminance within the exposure field using such a photodetector, the illuminance around the exposure field will eventually increase. Therefore, in the exposure field, the line width becomes smaller toward the periphery of the exposure field.

In order to deal with the variation in the line width generated in the exposure field, an approach has been conventionally used to solve the problem mainly from the device side, for example, by improving or modifying the optical system of the exposure device. Came.

[0006]

However, the measures for reducing the line width variation in the exposure field by improving the optical system of the exposure apparatus as described above have the following problems. First, the pattern of a reticle used in a lithography process of a semiconductor process is usually a line pattern for forming gates, wirings, etc., and a contact for forming contact holes for connecting multi-layered wirings. There is a system pattern, but there is a problem that it is difficult to perform optical adjustment so that both the formation of the line system pattern and the formation of the contact system pattern can be compatible. Secondly, the improvement of the optical system of the exposure system
There is a problem that a huge amount of money is required for remodeling.

Therefore, the present invention has been made in view of the above problems, and improves unevenness of illuminance, which is a cause of variation in line width in an exposure field, and improves uniformity of illuminance. An object of the present invention is to provide a projection print mask capable of improving the uniformity of the line width formed in the lithography process.

[0008]

In order to solve the above-mentioned problems, a projection printing mask according to the present invention has a transparent substrate having a predetermined pattern drawn on its surface and a predetermined distance from the transparent substrate. And a cover film that locally reduces the light transmittance. in this way,
In the projection print mask according to the present invention, a transparent substrate having a predetermined pattern drawn on its surface and a cover film for locally reducing the light transmittance are arranged at predetermined intervals. This makes it possible to make the illuminance of the light passing through the projection print mask uniform. For this reason, it is possible to improve the illuminance unevenness in the exposure field without improving or modifying the optical system of the exposure apparatus, and reduce the line width variation caused by the illuminance unevenness in the exposure field. can do. Further, by changing the layout of the dot pattern, it is possible to cope with the formation of the line pattern and the contact pattern.

In the present invention, in the above projection printing mask, it is preferable that the cover film is a transparent thin film in which a dot pattern is laid out in a predetermined region on the surface. In the above projection print mask,
Since the cover film is a transparent thin film in which the dot pattern is laid out in a predetermined area, the dot pattern is laid out in correspondence with the area where the illuminance of light passing through the transparent substrate on which the predetermined pattern is drawn is high Is easily possible. Therefore, the illuminance of light passing through the projection print mask can be easily made pseudo-uniform.

In the present invention, in the above projection printing mask, the density of the dot pattern laid out on the transparent thin film is preferably different depending on the region. In the above projection print mask, the density of the dot pattern laid out on the surface of the transparent thin film differs depending on the area, so that the area where the illuminance of light passing through the transparent substrate on which a predetermined pattern is drawn is high It is possible to easily correspond to the high density area of the dot pattern. Therefore, the illuminance of light transmitted through the projection print mask can be easily and accurately pseudo-uniformized.

In the present invention, in the above projection printing mask, the cover film is preferably attached to the transparent substrate via a ring-shaped spacer. In the above projection printing mask, the cover film is attached to the transparent substrate via the ring-shaped spacer, so that the light transmittance is locally reduced with respect to the transparent substrate having a predetermined pattern drawn on its surface. Positioning with the cover film can be performed accurately and stably. For example, it is possible to accurately and stably oppose an area having a high illuminance of light passing through a transparent substrate having a predetermined pattern drawn on its surface and an area of a transparent thin film on which a dot pattern is laid out. Therefore, the illuminance of light passing through the projection print mask can be easily made pseudo-uniform.

[0012]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described. FIG. 1 is a schematic view showing an exposure apparatus that exposes an IC using a projection print mask according to one embodiment, and FIG. 2 is a perspective view showing a projection print mask used in the exposure apparatus of FIG. Is a figure,
3A and 3B are a sectional view and a plan view, respectively, showing the projection print mask.

In FIG. 1, the luminous flux radially generated from the Hg (mercury) lamp 10 as the exposure light source is efficiently condensed by the elliptical mirror 12 and then by the first mirror 14 as shown by an arrow. Reflected, collimator 1
It is incident on the integrator 18 through 6. Then, the integrator 18 measures the integrated exposure amount. Then, the light emitted from the integrator 18 is
After being reflected by the mirror 20, it is efficiently condensed by the condenser lens 22 and is incident on the projection print mask 24 according to the present embodiment. The light passing through the projection print mask 24 is applied to the surface of the wafer 30 mounted on the wafer stage 28 via the reduction projection lens 26. Therefore, the predetermined pattern drawn on the projection print mask 24 is reduced and projected on the surface of the wafer 30.

As shown in FIGS. 2 and 3, the projection printing mask 24 according to the present embodiment has a transparent substrate 32 made of, for example, borosilicate glass, and a desired height on the transparent substrate 32. The cover film 36 is attached via the ring-shaped spacer 34. An opaque pattern is drawn on the bottom surface of the transparent substrate 32 by, for example, a chromium film 38. Therefore, the transparent substrate 3 on which the opaque pattern of the chromium film 38 is drawn
2 corresponds to a conventional reticle. Further, the ring-shaped spacer 3 having a desired height is provided between the transparent substrate 32 and the cover film 36.
4, the lower surface of the ring-shaped spacer 34 is adhered onto the transparent substrate 32, and the cover film 36 is attached to the upper surface thereof, so that the transparent substrate 32 and the cover film 36 are disposed.
And are always held stably at the desired intervals.

As shown in FIG. 3, the cover film 36 forming the projection print mask 24 has circular opaque dot patterns 42 regularly arranged in predetermined areas on the surface of the transparent thin film 40. The dot areas 44 that are open are laid out. Since the dot pattern 44 is for reducing the light transmittance and should not be projected on the surface of the wafer 30 in a reduced scale, its size is required to be sufficiently small.

As described above, according to the projection print mask 24 of the present embodiment, the transparent thin film 40 surface is formed on the transparent substrate 34 on which the opaque pattern of the chromium film 38 corresponding to the conventional reticle is drawn. Since the cover film 36 in which the dot areas 44 in which the opaque dot patterns 42 are regularly arranged are laid out in a predetermined region is provided at a predetermined interval, the cover film 36 passes through the dot areas 44 of the cover film 36. The transmittance of light is locally reduced only in the area where the dot area 44 is laid out,
The illuminance at that portion relatively decreases.

Therefore, the dot area 44 in which the dot patterns 42 are arranged is laid out so as to correspond to an area where the illuminance of light passing through the transparent substrate 34 on which the opaque pattern of the chrome film 38 is drawn becomes higher than necessary. This makes it possible to make the illuminance of light passing through the projection print mask 24 pseudo-uniform within the exposure field. Therefore, the illuminance unevenness in the exposure field can be improved and the line width variation can be reduced without improving or modifying the optical system of the exposure apparatus. Moreover, by changing the layout of the dot area 44 in which the dot pattern 42 is arranged, it is possible to cope with the formation of the line pattern and the contact pattern.

Further, the cover film 3 in which the dot areas 44 in which the dot patterns 42 are arranged are laid out
Since 6 is attached to the transparent substrate 34 via the ring-shaped spacer 34 having a desired height, the dot area 44 corresponds to the region where the light transmittance is desired to be locally reduced.
The cover film 36 having the above layout can be accurately and stably aligned with the transparent substrate 34.

Next, a case of solving the problem that the line width becomes thinner toward the periphery of the exposure field by using the projection print mask 24 according to the present embodiment will be described with reference to FIG. Here, FIG. 4 is a diagram showing a comparison of the illuminance distribution in the exposure field when the conventional reticle is used and when the projection printing mask according to the present embodiment is used.

In FIG. 4, when the conventional reticle, that is, only the transparent substrate 34 on which the opaque pattern by the chromium film 38 is drawn, is used as shown in the illuminance distribution in the exposure field 46a when the conventional reticle is used. Is an area 48 where the illuminance is almost uniform in the center of the exposure field.
However, the peripheral portion of the exposure field, especially the four corner portions is a region 50 in which the illuminance is relatively higher than the central portion of the exposure field. Moreover, although not shown, the region 50 having a relatively high illuminance tends to have a higher illuminance toward the periphery.

In such a case, as shown in the figure, a cover film 36 is produced in which dot areas 44 are laid out at the four corners of the transparent thin film 40 in correspondence with the illuminance distribution in the exposure field 46a, that is, the region 48 with high illuminance. . Although not shown, the dot pattern 42 in the dot area 44 has a high illuminance region 4 in the exposure field 46a.
In order to correspond to the tendency that the illuminance increases toward the periphery in 8, the dot density increases toward the periphery.

In this way, the projection print in which the cover films 36 in which the dot areas 44 in which the dot patterns 42 are arranged so that the dot density becomes higher toward the periphery are laid out at the four corners of the transparent thin film 40 are attached to the transparent substrate 34. By using the mask 24 for
Since the transmittance of light passing through is reduced and the light illuminance in the peripheral part of the exposure field is reduced, as shown in the figure,
Almost all the area in the exposure field 46b becomes an area 52 with uniform illuminance. Therefore, it is possible to solve the problem that the line width becomes narrower toward the periphery in the periphery of the exposure field.

In the projection printing mask according to the above embodiment, a circular opaque dot pattern 42 is regularly formed in a predetermined area on the surface of the transparent thin film 40 as a cover film for locally reducing the light transmittance. Although the cover film 36 in which the dot areas 44 that are arranged in a regular manner are laid out is used, the present invention is not limited to such a cover film 36. For example, a cover film in which a film having a low transmittance, for example, a semitransparent thin film is selectively attached to a predetermined region on the surface of the transparent thin film 40 may be used.

However, as shown in the above embodiment, in the cover film 36 in which circular opaque dot patterns 42 are regularly arranged in a predetermined area on the surface of the transparent thin film 40, the dots in which the dot patterns 42 are arranged are arranged. It is possible to easily lay out the area 44 so as to correspond to a region where the light transmittance is desired to be locally reduced. Further, by changing the density of the dot pattern 42 arranged in the dot area 44 depending on the region, it is possible to easily make the density of the dot pattern 42 correspond to the illuminance distribution in the exposure field. Therefore, in order to make the illuminance of the light transmitted through the projection print mask pseudo-uniform with ease and with high accuracy, circular opaque dot patterns 42 are regularly arranged in a predetermined area on the surface of the transparent thin film 40. It can be said that the cover film 36 described above is more preferable.

Incidentally, the cover film 3 in the above embodiment.
The opaque dot pattern 42 arranged in the six dot areas 44 is circular, but it is not necessary to limit it to circular.
For example, a triangular shape, a quadrangular shape, or any other shape may be used as long as it can exhibit the function of reducing the transmittance of light passing through the dot area in which the dot pattern is arranged.

[0026]

As described above in detail, according to the mask for projection printing of the present invention, the following effects can be obtained. That is, according to the projection print mask of the first aspect, the transparent substrate having a predetermined pattern drawn on the surface thereof and the cover film for locally reducing the light transmittance are arranged at a predetermined interval. By
Since it is possible to make the illuminance of light passing through the projection print mask pseudo-uniform, it is possible to improve the illuminance unevenness in the exposure field without improving or modifying the optical system of the exposure apparatus. By reducing the variation in line width caused by uneven illumination in the field,
It is possible to improve the uniformity of the line width.

According to the projection printing mask of the second aspect, the cover film is a transparent thin film in which a dot pattern is laid out in a predetermined region, so that the surface is transparent. Since it is possible to easily lay out the dot pattern corresponding to the area where the illuminance of the light that passes through the substrate is high, it is easy to make the illuminance of the light that passes through the projection print mask uniform in a pseudo manner. The uniformity can be improved, and by changing the layout of the dot pattern, it is possible to cope with the formation of the line pattern and the contact pattern.

Further, according to the projection printing mask of the third aspect, the density of the dot pattern laid out on the surface of the transparent thin film is different depending on the region, so that the transparent pattern on which the predetermined pattern is drawn is formed. Since it is possible to change the density of the dot pattern according to the illuminance distribution of the light that passes through the substrate, the illuminance of the light that passes through the projection print mask can be easily and highly accurately pseudo-uniformized to The width uniformity can be significantly improved.

Further, according to the projection printing mask of the fourth aspect, the cover film is attached to the transparent substrate via the ring-shaped spacer, so that a predetermined pattern is drawn on the surface of the transparent substrate. Since it is possible to perform accurate and stable alignment with the cover film that locally reduces the light transmittance, it is possible to easily and pseudo-uniformize the illuminance of the light transmitted through the projection print mask. hand,
The uniformity of the line width can be improved.

[Brief description of drawings]

FIG. 1 is a schematic view showing an exposure apparatus using a projection print mask according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a projection printing mask used in the exposure apparatus of FIG.

3A and 3B are a sectional view and a plan view showing the projection print mask of FIG.

FIG. 4 is a diagram showing a comparison of illuminance distribution in an exposure field when a conventional reticle is used and when a projection printing mask according to the present embodiment is used.

[Explanation of symbols]

10 ... Hg lamp, 12 ... Elliptical mirror, 14 ... First mirror, 16 ... Collimator, 18 ... Integrator, 20 ... Second mirror, 22 ... Condenser lens, 24 ... Projection print mask, 26 ... Reduction projection lens, 28 ... Wafer stage, 30 ... Wafer, 32 ... Transparent substrate, 34 ... Ring spacer, 3
6 ... Cover film, 38 ... Chrome film, 40 ... Transparent thin film, 42 ... Dot pattern, 44 ... Dot area,
46a, 46b ... exposure field, 48 ... region with uniform illuminance, 50 ... region with relatively high illuminance, 52 ...
Area with uniform illuminance.

Claims (4)

[Claims] 1. A transparent substrate having a predetermined pattern drawn on its surface, and a cover film disposed at a predetermined distance from the transparent substrate to locally reduce the light transmittance. A mask for projection printing. 2. The mask for projection printing according to claim 1, wherein the cover film is a transparent thin film in which a dot pattern is laid out in a predetermined region on the surface. 3. The projection printing mask according to claim 2, wherein the density of the dot pattern laid out on the surface of the transparent thin film differs depending on the region. 4. The mask for projection printing according to claim 1, wherein the cover film is attached to the transparent substrate via a ring-shaped spacer. mask.