JP2731177B2 - Photo mask - Google Patents

Description

The present invention relates to a photomask, and more particularly, to a photomask used for forming a fine pattern.

(Prior Art) Through a mask formed with a desired light shielding pattern,
The technique of irradiating light onto a substrate to transfer a fine pattern is a technique widely used in the field of semiconductor manufacturing.

Such a pattern transfer technique has been remarkably developed in recent years, and a fine pattern can be obtained. However, for a pattern requiring a resolving power near the performance limit of the transfer device, there is a problem that the fidelity to the pattern is reduced.

For example, when irradiating light through a mask on which a desired light-shielding pattern is formed on the surface of a semiconductor substrate coated with a photoresist, transferring a fine pattern, and forming fine holes, etc., the pattern size Exposure dose may change significantly compared to patterns with large
There has been a problem that a resist pattern having a good sectional shape cannot be obtained.

In particular, in pattern processing such as forming a hole using a positive resist, depending on the pattern dimensions,
There is a problem that the dimensional error of the formed pattern changes significantly.

This is presumably because in the case of forming a fine hole having a small pattern size, the amount of light transmitted through the opening region (light-transmitting region) of the light-shielding pattern is not sufficient.

Further, even in a pattern having a relatively large dimension, a pattern edge cannot be formed sharply, and when this transfer pattern is etched using an etching-resistant mask, there is a problem that pattern defects are likely to occur. Was.

(Problems to be Solved by the Invention) As described above, when a pattern having a fine dimension is formed, not only a defect occurs but also a pattern edge cannot be formed sharply even in a pattern having a relatively large dimension. there were.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a photomask capable of performing faithful pattern transfer with a constant light amount without depending on pattern dimensions.

[Configuration of the invention]

(Means for Solving the Problems) In order to achieve the above object, the invention according to claim 1 includes: a light-transmitting substrate; a mask pattern made of a light-shielding material disposed on the light-transmitting substrate; A recess formed on the light-transmitting substrate and covering the opening of the mask pattern; and a material having a higher refractive index than the material forming the light-transmitting substrate filled in the recess. The opening surface has a shape larger than the bottom surface.

The invention according to claim 2 is a light-transmitting substrate, a mask pattern made of a light-shielding material disposed on the light-transmitting substrate, and an opening of the mask pattern formed on the light-transmitting substrate. And a concave portion covering the portion, wherein the concave portion has a shape whose bottom surface is larger than the opening surface.

(Operation) According to the first configuration of the present invention, by forming the opening and the vicinity of the outer edge thereof with the second material having a larger refractive index than the first light-transmitting material forming the substrate, the original structure is obtained. If
Light that strikes the light-shielding material and does not pass through the mask is also refracted when entering from the first material to the second material, and is condensed on the periphery of the opening. This makes it possible to form a sharp image of a pattern edge, and to form a faithful pattern even for a fine pattern.

Further, according to the second configuration of the present invention, by forming the concave portion on the substrate surface in the vicinity of the opening and the outer edge thereof, light that would otherwise hit the light-shielding material and does not pass through the mask can be transmitted. When the light enters the air (in many cases, it is exposed under a condition close to a vacuum, but in that case, in a vacuum), it is reflected and condensed on the periphery of the opening, so that more area becomes the pattern edge. The light amount can be condensed, a sharp image of a pattern edge can be formed, and a faithful pattern can be formed even for a fine pattern.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a cross section of a photomask according to an embodiment of the present invention.

This photomask comprises a light-shielding film pattern 2 formed of a laminated film of a chromium thin film and a chromium oxide thin film formed on the surface of a light-transmitting quartz substrate 1, and an opening of the light-shielding film pattern 2 and an outer edge thereof. A recess h is formed on the surface of a nearby substrate, and the novolak resin 3 is filled in the recess.

Next, a manufacturing process of this photomask will be described.

First, as shown in FIG. 2A, a light-shielding film 2 'composed of a laminated film of a chromium thin film and a chromium oxide thin film is formed on the surface of a translucent quartz substrate 1 by a sputtering method, and then an electron beam is applied. A resist pattern R is formed by an exposure method.

Next, as shown in FIG. 2B, the light-shielding film 2 'is patterned by isotropic etching using the resist pattern as a mask. At this time, conditions are set so as to be slightly over-etched, and the opening of the light-shielding film pattern 2 and the substrate surface near the outer edge thereof are also etched to form a concave portion h.

After that, as shown in FIG. 2 (c), after removing the resist pattern R, a novolak resin film 3 is applied to the entire surface of the substrate 1 so as to have a film thickness of 1 μm and is cured.

Hereinafter, a case will be described in which a resist pattern for patterning a silicon oxide film formed on a silicon substrate is formed using a photomask formed as described above.

First, a positive photoresist film is formed on a surface of a silicon substrate 10 having a 0.8 μm thick silicon oxide film 11 formed thereon by spin coating so as to have a thickness of 1.41 μm.
After applying 12 (for example, PFR-7750: made of Japan Synthetic Rubber) on the base of the reduction projection exposure apparatus, and installing the photomask formed in the above-described process on the mask base and performing positioning, Irradiation with light having an energy of 475 mJ / cm ² is performed to expose the photoresist film 12 as shown in FIG. 3 (a).

After that, a developer (for example, NMD-W: manufactured by Tokyo Ohka)
And developed for 60 seconds.

In this way, as shown in FIG. 3B, a highly accurate resist pattern 12 is formed on the silicon oxide film 11 on the surface of the silicon substrate 10.

And finally, using this resist pattern as a mask,
As shown in FIG. 3C, the silicon oxide film is etched by anisotropic etching.

As a result, it was found that the hole pattern H having a thickness of 0.55 μm was also formed accurately with high fidelity to the pattern of the photomask.

This is because, as shown in FIG. 1, the light L is refracted at the interface between the quartz substrate 1 and the novolak resin having a higher refractive index than the light L, and is converged toward the opening h of the light shielding film pattern. 4
As shown in FIG. 7A, the relationship between the energy intensity received on the resist surface and the mask pattern is considered to be because the light intensity near the periphery of the opening is increased as compared with the conventional case.

For comparison, FIG. 4B shows the relationship between the energy intensity received on the resist surface and the mask pattern of the photomask when a conventional photomask is used.

As is clear from the comparison between FIGS. 4A and 4B, in the case of the photomask of the present invention, the light energy intensity received near the light-shielding film pattern edge of the photomask is significantly larger than that of the conventional photomask. It can be seen that it has increased.

In the above-described embodiment, an example was described in which the novolak resin 3 was applied not only to the concave portions but also to the surface of the light-shielding film pattern. However, as shown in FIG. Alternatively, only the concave portions may be filled with the novolak resin 3.

Further, as shown in FIG. 6, the recess is not filled with the novolak resin 3 and only the recess h2 is formed in the opening of the light-shielding film pattern and the quartz substrate surface at the periphery thereof. You may.

This photomask may be formed by etching a concave portion in the same manner as in the first embodiment. However, in order to sharpen the edge E of the concave portion, a fluorine-based gas or a chlorine-based gas is used when etching the substrate for forming the concave portion. Reactive ion etching using gas, argon sputtering, or the like is used.

In the case of this photomask, the light L near the periphery of the opening is reflected by the concave portion on the surface of the quartz substrate and condensed in the opening, the light energy intensity near the pattern edge is increased, and the dimensional accuracy is improved even for a fine pattern. And a good pattern can be formed.

In these examples, the cross-sectional shape of the concave portion on the surface of the quartz substrate can be appropriately changed as needed.

Further, the materials of the light-transmitting substrate and the light-shielding film pattern can be appropriately changed without being limited to the examples.

〔The invention's effect〕

As described above, according to the present invention, the opening of the light-shielding film pattern and the vicinity of the outer edge thereof are formed of the second material having a higher refractive index than the first light-transmitting material forming the substrate. Therefore, a large amount of light can be condensed in a region serving as a pattern edge, and a sharp image of the pattern edge can be formed. In addition, a faithful pattern can be formed even for a fine pattern. .

Further, according to the second configuration of the present invention, since the concave portion is formed on the substrate surface in the vicinity of the opening of the light-shielding film pattern and the outer edge thereof, more light is condensed in the region serving as the pattern edge. It is possible to form a sharp image of the pattern edge,
A faithful pattern can be formed even for a fine pattern.

[Brief description of the drawings]

FIG. 1 is a view showing a photomask of an embodiment of the present invention, FIGS. 2 (a) to 2 (c) are manufacturing process diagrams of the photomask of the embodiment of the present invention, and FIGS. 3 (a) to 3 (c). FIG. 4C is a view showing a process of forming a resist pattern using the photomask of the embodiment of the present invention. FIGS. 4A and 4B show the photomasks of the embodiment of the present invention and the conventional example, respectively. FIG. 5 shows the relationship between the light intensity on the substrate surface and the pattern in the case, and FIGS. 5 and 6 show the photomasks of the second and third embodiments of the present invention, respectively. DESCRIPTION OF SYMBOLS 1 ... Quartz substrate, 2 ... Light shielding film, 3 ... Novolak resin, 10 ... Silicon substrate, 11 ... Silicon oxide film, 12 ...
... resist film, h, h2 ... recess, H ... hole pattern,
L ... Light.

Claims (2)

(57) [Claims] 1. A light-transmitting substrate, a mask pattern made of a light-shielding material disposed on the light-transmitting substrate, and a concave portion formed on the light-transmitting substrate and covering an opening of the mask pattern. A material having a higher refractive index than a material of the light-transmitting substrate filled in the concave portion, wherein the concave portion has a shape having an opening surface larger than a bottom surface. 2. A light-transmitting substrate, a mask pattern made of a light-shielding material disposed on the light-transmitting substrate, and a concave portion formed on the light-transmitting substrate and covering an opening of the mask pattern. A photomask, comprising: a concave portion having a shape in which a bottom surface is larger than an opening surface.