JPH05224398A - Photomask having variable transmissivity and production of optical parts using the same - Google Patents

Abstract

PURPOSE:To provide a photomask capable of low-cost production of various diffraction gratings different from each other in cross-sectional shape and to produce optical parts with the photomask. CONSTITUTION:Groups each consisting of openings 1 and light shielding parts 2 alternately arranged at narrow intervals incapable of resolution at the time of exposure are arranged at intervals capable of resolution to obtain the objective photomask 3. The light transmissivity of the openings 1 is varied by varying the area ratio of the openings 1 to the light shielding parts 2. When this photomask 3 is used, optical parts such as a diffraction grating whose cross-sectional shape corresponds to a variation of the light transmissivity can be produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention provides a photomask capable of modulating light transmittance and a known photolithography method using the photomask to obtain optical parts such as a diffraction grating, a Fresnel lens, a microlens, and a hologram. The present invention relates to a method for manufacturing an optical component.

[0002]

2. Description of the Related Art In exposure using a normal photomask, the cross-sectional shape of a resist film formed is bilaterally symmetric and often has a rectangular cross-sectional shape. The following method is known as a method for producing a relief type diffraction grating having a left-right asymmetrical saw blade (blaze) cross section. a. A method of directly cutting a substrate using a ruling engine. b. A method in which the photoresist pattern formed on the substrate is used as a mask to perform oblique etching with an inert or active ion beam (for example, T. Aoyagi et al.
al., Appl. Phys. Letter 29, No. 5, p. 303,
See September 1976). c. A method for directly forming a blazed diffraction grating on a resist by an asymmetric two-beam interference exposure method (eg G. Schmahl e
t al., in Progress in Optics, E. Wolf, North-Ho
lland, Amsterdam. 14, p. 195, 1976).

Also, d. Electron beam (for example, see T. Shiono et al., Appl. Opt. 26, 587, 1987), or laser beam (for example, M. Haruna et al., Appl. Opt.
No. 9, p. 5120, 1990), and by directly writing on the resist on the substrate by changing the dose amount, tilting in one direction like the diffraction grating Not only the blazed diffraction grating, but also the blazed direction can be set in any direction. Utilizing this, a pattern forming method in which the direction of the blazed is changed at an arbitrary position, such as a high-efficiency Fresnel lens having a blazed pattern, is also known.

On the other hand, as a photomask whose transmittance is modulated, e. A photomask using an organic material containing a light absorber having a changed thickness (Kawatsuki et al., JP 63-2712 A).
65) is known.

[0005]

In the method (a), it takes a long time to form a diffraction grating and the cost is high. The above method b has a drawback that the device is complicated, not only the size of the device becomes large, but also etching of a large area is difficult, and therefore it is difficult to manufacture only a diffraction grating having a small area. .. The method of c above can produce a large area diffraction grating with a relatively simple device, but the diffraction grating is inevitably expensive because of low productivity. Further, since the methods a, b, and c can only create patterns in which the inclination directions of the patterns are aligned in one direction, there is a problem that the degree of freedom of the formed pattern is small.

On the other hand, in the above method d, the degree of freedom of the pattern to be formed becomes large, but the device for changing the dose is complicated, and strict production conditions are required, and the productivity is low. There is.

Further, in the above method e, the photomask formed is made of an organic material and has a problem of durability. Further, when the photomask is formed, strict production conditions are required as in the method d. There is also the problem of being done.

The present invention has been made in view of the above problems, and is a method for manufacturing an optical component having various cross-sectional shapes which is inexpensive and can be mass-produced, and a transmittance modulation type used for manufacturing the optical component. The purpose is to provide a photomask.

[0009]

In a transmittance-modulation type photomask according to the present invention, a group of apertures and light-shielding portions which are alternately arranged at a fine interval that cannot be resolved at the time of mask exposure is It is a photomask arranged with an imageable interval.

Further, the method of manufacturing an optical component according to the invention uses the photomask to perform a single exposure,
When manufacturing an optical component whose cross-sectional shape is controlled arbitrarily,
The resolution of the photomask is adjusted so as not to resolve the pattern of the openings and the light-shielding portions which are alternately arranged at a fine interval, but to resolve only the large pattern made of the aggregate. The following method is used for this adjustment.

A. When exposing with the mask aligner, the distance between the photoresist surface and the photomask is adjusted. b. A light diffusion plate is arranged between the light source and the photomask. c. The pattern image forming focus of the photomask by the projection type exposure apparatus is shifted from the photoresist surface.

Here, "unresolvable" means that the light intensity at the position corresponding to the light shielding portion of the photomask is not so high as compared with the light intensity at the position corresponding to the opening of the photomask on the photoresist surface. That is, the strength ratio does not decrease, and for example, the strength ratio is 0.95 or more. Similarly, resolvable means that, for example, the ratio of the light intensity is less than 0.95. Decrease the distance between the opening and the light shield, increase the distance between the photoresist surface and the photomask, use a light diffuser, or adjust the focus of the photomask pattern from the photomask surface. By shifting, the unresolvable state is obtained.

[0013]

In the photomask of the present invention, the light transmittance can be controlled by changing the ratio of the opening portion and the light shielding portion of the assembly, so that the light transmittance can be determined by a simple area ratio, and the mask pattern can be obtained. Can be formed by an ordinary method such as chrome etching, so that the photomask can be manufactured very easily. Moreover, the photomask made of a chromium film or the like has excellent durability.

According to the method of manufacturing an optical component using the transmittance modulation type photomask according to the present invention, the optical component is manufactured by a single exposure through the photomask, so that the manufacturing process is simplified. At the same time, mass production becomes possible, and inexpensive optical components can be obtained.

[0015]

FIG. 1 shows an example of the photomask 3 of the present invention. A large repeating pattern P is formed from an assembly of fine line-shaped openings 1 and light-shielding portions 2. In this example, the pitch of the openings 1 is constant, and the width of the openings 1 changes according to the light transmittance, and the area ratio of the openings directly becomes the light transmittance.

As shown in FIG. 2, for example, the photomask 3 is arranged so as to face a photoresist 5 formed on a glass substrate 4, and light emitted from a light source 6 is reflected by a mirror of a mask aligner 8. After being made into substantially parallel rays by the lens group 10, the photoresist 5 is irradiated through the photomask 3. At this time, if the pitch of the openings 1 is a size that cannot be resolved during mask exposure, the distribution of the amount of light irradiated onto the film surface 5a of the photoresist 5 changes smoothly, as shown in FIG. .. When the pitch of the openings 2 becomes a resolvable size, the distribution of the amount of light irradiated on the photoresist 5 at the time of mask exposure causes an unnecessary fine pattern P1 to be resolved as shown in FIG.

The pitch of the openings 1 and the exposure conditions must be determined in consideration of the size of the large pattern P to be formed and the required sharpness of the sectional shape. Generally, in order to form a finer and sharper cross-sectional pattern P, the pitch of the openings 1 must be reduced under an exposure condition with good resolution, and otherwise, the photomask 3 and the photoresist film. The parallelism of light is reduced by increasing the distance from the surface 5a, or by installing a light scattering plate 7 between the photomask 3 and the light source 6 as shown in FIG. 5, or as shown in FIG. As described above, after the image forming focus F of the pattern of the photomask 3 is shifted from the photoresist film surface 5a using the projection type exposure apparatus 8, the pitch of the openings 1 is increased.

The pitch of the light-shielding portion 2 may be changed on one photomask 3 as long as it is in a range where it is not resolved.

If a mask aligner 8 as shown in FIG. 2 is used as the exposure device, the distance between the photomask 3 and the photoresist film surface 5a should be increased, or, as shown in FIG. The resolution can be adjusted by installing a light scattering plate 7 such as frosted glass between the masks 3.

When a projection type exposure apparatus such as a mirror projection or stepper is used, a projection of a mirror projection type having a moving slit 11 as shown in FIG. 6 and a mirror / lens group 12 composed of a concave mirror and a convex mirror, for example. In the case of the exposure apparatus 9, the resolution can be adjusted by shifting the focus F formed on the photoresist film surface 5a.

FIG. 7 shows another example of the photomask 3. In this example, a large pattern P is formed by an aggregate of square dot-shaped openings 1. In this example as well, the pitch of the openings 1 is constant, and the size of the dot-shaped openings 1 changes according to the light transmittance.

It should be noted that there is no problem if the light-shielding portion 2 is formed in a dot shape instead of the opening portion 1, and the dot shape may be a circle or the like other than the quadrangle.

The photomask 3 according to the present invention as described above.
Can be easily manufactured using a normal photomask manufacturing method. For example, a method of forming a pattern on a photoresist film with an electron beam or ultraviolet rays and then removing the light-shielding metal film such as chromium by etching, or writing a pattern with light on a plate or film coated with a silver salt emulsion or the like. The photomask 3 can be produced by the method of development processing.

The present invention will be specifically described below with reference to examples. In the following Examples and Comparative Examples, the light used for exposure is light emitted from an ultra-high pressure mercury lamp that is made into substantially parallel rays by a mirror, a lens, etc.
The wavelength was 0.30 to 0.45 μm.

Example 1. A schematic view of the photomask 3 of this embodiment is shown in FIG. Example 1 is a one-dimensional lattice in which an aggregate of opening portions 1 of a line pattern whose width gradually changes at a pitch of 10 μm is arranged at a pitch of 100 μm.

In Example 1, the residual film rate curve of the commercially available positive photoresist used for pattern exposure is shown in FIG.
The aperture ratio was determined so as to correspond to the residual film ratio in FIG. For example, in the figure, when the amount of light transmitted through the maximum opening of the photomask 3 is A, the film thickness is 1 /
Since the aperture ratio where 2 becomes equal to the ratio of the exposure dose,
It is represented by B / A. By this method, the width of the opening of each of the 10 lines was determined, and the film thickness was changed linearly.

Using the photomask 3 thus obtained, the glass substrate 4 coated with the photoresist 5 to a thickness of 1 μm was used in the manner shown in FIG. 2 and the mask aligner 8 was used to form the photomask 3 and the photoresist film. The surface 5a was exposed at a distance of 200 μm. Photoresist film surface 5
The light intensity distribution on a is as shown in FIG. 10, and the cross-sectional shape of the resist pattern obtained by development with an alkaline aqueous solution is as shown in FIG. 11, with a pitch of 100 μm and a step difference of 0.9 μm.
The blazed diffraction grating of was produced.

Comparative Example 1. Same photomask 3 as in Example 1
And using a mask aligner with the distance between the photomask 3 and the photoresist film surface 5a set to 20 μm, exposure was performed with the same exposure amount as in Example 1. The light amount distribution on the photoresist film surface 5a at this time is as shown in FIG. 12, and the cross-sectional shape of the pattern obtained as a result is as shown in FIG.
There has occurred. The diffraction grating manufactured by this method has a problem that diffracted light corresponding to fine irregularities is generated.

Example 2. FIG. 14 shows a schematic diagram of the photomask 3 of this embodiment. This Example 2 is a grating in which the aggregate of the opening portions 1 of the line pattern whose width gradually changes at a pitch of 20 μm, which is larger than that of the above Example 1, is arranged at a pitch of 400 μm, and is transmitted every 200 μm. It is configured to repeat increasing and decreasing rates. The change in the transmittance of the photomask 3 was set based on FIG. 9 so that the residual film ratio changes linearly, as in Example 1.

Using the mask aligner 8 shown in FIG.
The distance between the photomask 3 and the photoresist film surface 5a is set to 100 μm, which is smaller than that in the first embodiment, and the light scattering plate 7 made of frosted glass is installed between the photomask 3 and the light source 6 to have a thickness of 1 μm. The positive resist film surface 5a was exposed. The light amount distribution on the photoresist film surface 5a is as shown in FIG. 15, and the pattern obtained after development is shown in FIG.
6 and a diffraction grating having a triangular wave-shaped cross section with a pitch of 400 μm and a step of 0.9 μm could be manufactured.

Comparative Example 2. Same photomask 3 as in Example 2
Was used, and exposure was performed under the same conditions as in Example 2 except that frosted glass was not used. As a result, a pattern P2 of fine unevenness similar to that shown in FIG. 13 was generated.

Example 3. A schematic diagram of the photomask 3 of this embodiment is shown in FIG. Example 3 is a one-dimensional grating in which the aggregate of the opening portions 1 of the line pattern whose width gradually changes at a pitch of 10 μm is arranged at a pitch of 200 μm, and the transmittance increases every 100 μm. It is configured to repeat the decrease. In this example, a commercially available negative photoresist containing cyclized rubber as a main component in which the relationship between the exposure amount and the residual film rate is as shown in FIG. 18 is used, and the opening is performed so that the residual film rate changes sinusoidally. The width of part 1 was set.

Using the projection type projection exposure apparatus 9 of the mirror projection type shown in FIG. 6, the photoresist film surface 5a is formed.
Exposure was performed by shifting the focus position F by 100 μm from the top. The light intensity distribution on the photoresist film surface 5a at this time is as shown in FIG. 19, and after immersing in xylene and rinsing with butyl acetate, as shown in FIG. 20, a sine wave having a pitch of 200 μm and a step of 0.9 μm is obtained. A diffraction grating having a wavy cross section could be produced.

Comparative Example 3. Photomask 3 as in Example 3
Was used and the exposure was performed under the same conditions as in Example 3 except that the projection type exposure apparatus was not used, a fine uneven pattern P2 similar to that shown in FIG. 13 was generated.

Example 4. A schematic view of the photomask 3 of this embodiment is shown in FIG. In Example 4, a circular pattern having a diameter of 200 μm was formed by an aggregate of patterns having square openings 1 having a pitch of 10 μm in both the X and Y directions, and the circular patterns were arranged at a pitch of 200 μm.

In this example, a photosensitive resin composition (a mixture of a copolymer of 2-butenyl ester of methacrylic acid and methyl methacrylate and m-benzoylbenzophenone) constituting a photoresist was formed in a thickness of 6 μm. It was formed on a glass substrate. The relationship between the exposure amount of the photoresist and the residual film rate is as shown in FIG. According to this FIG.
The center of the circle was set to the maximum film thickness, and the light transmittance was set so that the surface shape of the film was a part of the spherical surface in the direction outside the center.

Using the mask aligner 8 shown in FIG.
The distance between the photomask 3 and the photoresist film surface 5a is 5
The light-scattering plate 7 made of frosted glass was set between the light source 6 and the photomask 3 and exposed. The light amount distribution on the photoresist film surface 5a at this time is as shown in FIG. 23, and unreacted m-
By removing benzoylbenzophenone, as shown in FIG. 24 (a cross-sectional view taken along line 24-24 of FIG. 21), a step is 2 μm and a diameter is 2
A 00 μm spherical lens-like microlens array could be produced.

Comparative Example 4. Photomask 3 as in Example 4
When the exposure was performed under the same conditions as in Example 4 except that the same was used and no frosted glass was used, a fine uneven pattern P2 similar to that shown in FIG. 13 was generated.

The manufacturing method using the photomask of the present invention is, in addition to the above diffraction grating and microlens,
It can also be applied to the manufacture of optical components such as Fresnel lenses and holograms.

[0040]

As described above, according to the present invention,
A transmittance distribution adjustment type photomask can be easily manufactured.
Further, using this photomask, optical components having various cross-sectional shapes can be manufactured by only one exposure. As a result, an optical component having a surface relief pattern with a high degree of freedom and a precisely controlled cross-sectional shape can be produced with high productivity.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a transmittance modulation type photomask according to the present invention.

FIG. 2 is a sectional view showing an example of an exposure method using the photomask of FIG.

FIG. 3 is a view showing a cross-sectional shape of a diffraction grating manufactured using the photomask of FIG.

FIG. 4 is a diagram showing a cross-sectional shape of a diffraction grating manufactured using the photomask of FIG. 1 with a small distance from the resist film surface.

5 is a cross-sectional view showing another example of an exposure method using the photomask of FIG.

6 is a sectional view showing still another example of an exposure method using the photomask of FIG.

FIG. 7 is a diagram showing another example of the transmittance modulation type photomask according to the present invention.

FIG. 8 is a diagram showing a photomask of Example 1 of the present invention.

FIG. 9 is a characteristic diagram showing the relationship between the exposure amount of the photoresist used in Example 1 and the residual film rate.

FIG. 10 is a diagram showing a distribution of an exposure amount on the surface of the photoresist film of Example 1.

11 is a cross-sectional view of the diffraction grating manufactured in Example 1. FIG.

FIG. 12 is a diagram showing the distribution of the exposure dose of Comparative Example 1 in which the photomask of Example 1 was used and the distance between the photomask and the resist film surface was reduced.

FIG. 13 is a cross-sectional view of a diffraction grating manufactured in Comparative Example 1.

FIG. 14 is a diagram showing a photomask according to a second embodiment of the present invention.

FIG. 15 is a diagram showing a distribution of an exposure amount on the photoresist film surface of Example 2.

16 is a cross-sectional view of a diffraction grating manufactured in Example 2. FIG.

FIG. 17 is a diagram showing a photomask according to a third embodiment of the present invention.

FIG. 18 is a characteristic diagram showing the relationship between the exposure amount and the residual film rate of the photoresist used in Example 3.

FIG. 19 is a diagram showing the distribution of exposure dose on the photoresist film surface of Example 3.

20 is a cross-sectional view of a diffraction grating manufactured in Example 3. FIG.

FIG. 21 is a diagram showing a photomask of Example 4 of the present invention.

22 is a characteristic diagram showing the relationship between the exposure amount and the residual film rate of the photoresist used in Example 4. FIG.

FIG. 23 is a diagram showing a distribution of exposure amount on the photoresist film surface of Example 4.

FIG. 24 is a diagram showing a diffraction grating manufactured in Example 4;
FIG. 24 is a sectional view taken along the line 24-24 of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Opening part, 2 ... Light-shielding part, 3 ... Photomask, 5 ... Photoresist, 6 ... Light source, 7 ... Light scattering plate, 8 ... Mask aligner, 9 ... Projection exposure apparatus.

Claims (4)

[Claims] 1. A photomask comprising a set of light-shielding portions and openings which are alternately arranged at a fine interval that cannot be resolved at the time of exposure and are arranged at a large resolvable interval. Modulation photomask configured to change the light transmittance by changing the densities of the portions and the openings. 2. When the photoresist film on the substrate surface is exposed using the transmittance modulation type photomask according to claim 1, the distance between the photoresist film surface and the pattern surface of the photomask is determined by the light shielding. A method for manufacturing an optical component, wherein exposure is carried out by setting a pattern of a portion and an opening to a distance that cannot be resolved. 3. The method for manufacturing an optical component according to claim 2, wherein a light scattering plate is arranged between the light source and the photomask. 4. The projection type exposure apparatus according to claim 2, wherein the image forming focus of the pattern of the photomask is shifted from the surface of the photoresist film, and the patterns of the light shielding portion and the opening are in a state in which they cannot be resolved. A method for manufacturing an optical component, which comprises exposing the film to the original.