JP2006267312A - Gray scale mask - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a gray scale mask wherein a difference (or a ratio) between the maximum transmittance and the minimum transmittance which can be actually obtained can be made larger than that of a conventional gray scale mask. <P>SOLUTION: The difference between a numerical aperture when pitch P is 2.5 μm and a gap G is 0.3 μm and a numerical aperture when the pitch P is 2.5 μm and the gap G is 2.0 μm, for example, is only 57.7%, in the conventional gray scale mask wherein circular patterns are arranged in a squarer shape as shown in (a) and on the other hand, the difference between numerical apertures when pitch P is 2.5 μm and a gap G is 0.3 μm and a numerical aperture when the pitch P is 2.5 μm and the gap G is 2.0 μm can be expanded to 66.6% in this gray scale mask wherein circular patterns are arranged in a hexagonal shape as shown in (b). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a gray scale mask used for the purpose of manufacturing a microlens using a lithography process.

  Microlenses (including microlens arrays in this specification) are fabricated using photolithography techniques. As these methods, there is a method as described in JP-A-9-008266 (Patent Document 1). However, as a method for producing a precise microlens, JP-A-8-504515 ( A method as disclosed in Patent Document 2) is generally used. This is because the resist formed on the surface of the optical substrate is exposed to light using a gray scale mask (a mask having a change in light transmittance that can be regarded as analog), and the resist is developed. Form a three-dimensional resist pattern in the shape and use it as a microlens, or, as described above, further etch the lens-shaped resist together with the optical substrate to form a lens-shaped resist pattern Is transferred to an optical base material to form a microlens made of the optical base material.

  As described above, for example, a gray scale mask in which the transmittance can be regarded as changing in an analog manner according to the exposed part is described in, for example, “The Institute of Electrical Engineers of Japan, E, Sensor Micromachine Sub-division, Vol. , P410-415, (Research of gray scale lithography using micro chrome pattern) "(Non-Patent Document 3), circular patterns are arranged at a predetermined pitch, and according to the desired transmittance. Thus, it is formed by changing the size of the circular pattern. As described above, conventionally, a circular pattern is exclusively used as the pattern, and a square arrangement is also used as the pattern arrangement.

JP-A-9-008266 JP-T 8-504515 IEEJ Transactions, E, Sensor Micromachine Sub-division, Vol.128, No.10, P410-415, (Grayscale Lithography Using Microchrome Patterns)

  However, the minimum diameter of the circular pattern that can be formed is limited by the influence of the resolution of the stepper and aligner used when manufacturing the gray scale mask, the influence of the γ characteristics of the resist, etc., and the distance between adjacent patterns is also limited. As a result, the maximum diameter of the circular pattern that can be formed is also limited. Therefore, as long as a conventional circular pattern and a rectangular array of patterns are used, there is a limit to the difference (or ratio) between the maximum transmittance and the minimum transmittance that can be realized.

  The present invention has been made in view of such circumstances, and provides a gray scale mask capable of making the difference (or ratio) between the maximum transmittance and the minimum transmittance that can be realized larger than that of a conventional gray scale mask. Is an issue.

  A first means for solving the above problem is a gray scale mask formed by arranging rectangular patterns in a rectangular pattern on the entire surface or a part of the effective area.

  A second means for solving the above-mentioned problem is a gray scale mask characterized in that a circular pattern is formed in a hexagonal arrangement on the entire surface or a part of the effective area.

  A third means for solving the above problem is a gray scale mask formed by arranging hexagonal hexagonal patterns on the entire surface or a part of the effective area.

  ADVANTAGE OF THE INVENTION According to this invention, the gray scale mask which can make the difference (or ratio) of the maximum transmittance | permeability which can be implement | achieved larger than a conventional gray scale mask can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a diagram comparing a conventional example and an example of an embodiment of the present invention when a pattern formed on a gray scale mask is circular. In the following embodiments including this embodiment, the description will be made assuming that the pattern portion becomes a hole and transmits light.

  FIG. 1A shows a conventional pattern arrangement method, in which circular patterns are squarely arranged with a pitch P and a gap G between patterns. FIG. 1B shows a pattern arrangement method as an example of an embodiment of the present invention. A circular pattern having a radius P according to a gray scale is arranged in a hexagonal manner with a pitch P and a gap G between patterns. It is a thing.

  The pattern density (aperture ratio) in FIG.

It is expressed. On the other hand, the pattern density (aperture ratio) in FIG.

It is expressed.

  FIG. 2A shows a pattern arrangement method, which is another example of the embodiment of the present invention, and is a square having a pitch P and a gap G between patterns, each side having a different length depending on the gray scale. The pattern is a square array. In this case, due to the influence of the resolution of the stepper that manufactures the gray scale mask, the corners of each square pattern are circular. Let R be the radius of this circle.

  The pattern density (aperture ratio) in such a pattern is

It becomes.

  FIG. 2B shows a pattern arrangement method which is an example of the embodiment of the present invention, and is a regular hexagon having a pitch P and a gap G between patterns, the length of one side of which varies depending on the gray scale. The pattern is a hexagonal arrangement. Also in this case, due to the influence of the resolution of the stepper that manufactures the gray scale mask, the corners of each regular hexagonal pattern are circular. Let R be the radius of this circle.

  The pattern density (aperture ratio) in such a pattern is

It becomes.

  When a gray scale mask is manufactured using a general G-line stepper, the minimum value of the gap G is about 0.4 μm due to the influence of the resolution. Further, the minimum value of the radius R of rounded corners is about 0.3 μm. Therefore, in the case of a circular pattern, the minimum radius of the pattern is also about 0.3 μm. When the maximum value of the gap G is 2.0 μm, the pattern density (aperture ratio) for the pattern in the prior art and each pattern in the example of the present invention is calculated based on the equations (1) to (4). Is shown in Table 1.

  As can be seen from Table 1, in the pattern of the prior art shown in FIG. 1A, the aperture ratio width (difference between the maximum value and the minimum value of the aperture ratio) is 57.7%. In the embodiment, the circular pattern shown in FIG. 1B is 66.6%, the square pattern shown in FIG. 2A is 73.4%, and the regular hexagonal pattern shown in FIG. 2B is 73.4%. The width can be increased. If the aperture ratio width is large, it is possible to increase the number of gradations of the gray scale mask, and it is possible to realize a smoother shade change. In addition, the shape manufactured using such a gray scale mask is also smooth and closer to the design shape.

  In the above embodiment, light is transmitted through the pattern portion, but it goes without saying that the same can be said for a gray scale mask in which light is blocked by the pattern portion.

  In an actual gray scale mask, all of the effective portions (portions actually used for resist exposure) may be formed in the same pattern, or FIG. 1 (b) and FIG. 2 (a). A pattern as shown in FIG. 2B may be mixed in the effective portion. Further, a part of the effective portion may be formed in a conventional pattern as shown in FIG.

  It should be noted that a pattern and arrangement in which the aperture ratio width can be larger than other portions may be employed in the region where the gray scale changes sharply. Further, the pitch of each pattern does not necessarily have to be the same for all the effective portions, and the pitch may be appropriately changed in each portion.

  Such a grayscale mask of the present invention is used for all lenses manufactured using photolithography such as a cylindrical lens, a Fresnel lens, a diffraction grating, etc. in addition to a normal spherical microlens and an aspherical microlens lens. Applicable as appropriate.

It is a figure which compares and shows one example of embodiment of this invention, when a pattern formed in a gray scale mask is circular. It is a figure which shows the arrangement | sequence method of the pattern which is another example of embodiment of this invention.

Claims (3)

A gray scale mask formed by arranging rectangular patterns in a rectangular pattern on the whole or part of the effective area. A gray scale mask formed by arranging hexagonal patterns in a hexagonal pattern on the whole or part of the effective area. A gray scale mask formed by arranging hexagonal patterns in a hexagonal pattern on the whole or part of the effective area.

Images