JPH07104590B2 - Transmittance modulation type photomask, its manufacturing method and diffraction grating manufacturing method using the same - Google Patents

Description

TECHNICAL FIELD The present invention relates to a photomask in which light transmittance is three-dimensionally formed along a pattern of a diffraction grating, and manufacturing using the photomask using a known photoresist. The present invention relates to a method of manufacturing a diffraction grating which obtains the diffraction grating by a method.

[Prior Art] As a method of manufacturing a relief type grating having a blaze shape,
For example, the following method is known.

a. Method of cutting the substrate directly with a ruling engine b. Using electron beam and its dose
By directly writing on the resist on the substrate by changing the value (see, for example, T. Fujita et al., Opt. Lett., Vol. 7, No. 12, page 578, December 1982) c. Apply a photoresist and create a periodic resist pattern by exposing through a mask,
A method of forming by performing oblique etching with an inert or active ion beam using the resist pattern as a mask (for example, T. Aoyagi et al., Appl. Phys. Letter 29, No. 5, p. 303, September 1976). D) Exposing a thin resist by the asymmetric two-beam interference exposure method.
A method of directly obtaining a blazed diffraction grating by developing (eg G. Schmahl et al., In Progress in Optics, EW
olf issue, North-Holland, Amsterdam, 14, p. 195, 1976) [Problems to be solved by the invention] In the method of the above-mentioned a, it takes a long time and expensive to manufacture a diffraction grating.

The above method b has the drawbacks that the device for changing the dose becomes complicated, the device becomes large, and it is difficult to draw a large area, and it is difficult to manufacture only a diffraction grating having a small area. .

The method of the above-mentioned c has a drawback that the apparatus is complicated as in the case of the above-mentioned b and becomes expensive due to the increase in size.

On the other hand, in the manufacturing method of d, a large area diffraction grating can be manufactured by a relatively simple apparatus as compared with the manufacturing method of b, but since the productivity is low, the diffraction grating is inevitably expensive. Furthermore, there are restrictions on the shape of the diffraction grating.

As described above, since the productivity is low in any of the methods, the diffraction grating has to be expensive. Further, it is also possible to make a mold based on the morphological modulation type diffraction grating manufactured by the method of a. To d., And to make a replica from this by molding,
The process is difficult, cumbersome and expensive.

The present invention has been made in view of the above points, and a main object of the present invention is to provide a form-modulation type diffraction grating having various blazed shapes that is inexpensive and can be mass-produced. Another object is to provide a transmittance modulation type photomask for this purpose. Still another object of the present invention is to provide another type (refractive index modulation type) diffraction grating using the photomask.

[Means and Actions for Solving Problems] Therefore, in the present invention, a morphological modulation type (relief type) diffraction grating is prepared as a photomask, and the morphological modulation surface of the diffraction grating is referred to as a grating side. ) Is coated with a layer of a light absorber having substantially the same refractive index as that of the substrate of the above-mentioned morphology modulation type diffraction grating to form a photomask. And
Using this photomask, a form-modulation type diffraction grating is manufactured by one exposure.

Therefore, the manufacturing process is simplified and mass production is possible.

Example As shown in FIG. 1, the photomask of the present invention comprises a blaze-shaped diffraction grating 2 made of a transparent material and a blaze-shaped diffraction grating 4 made of a material containing a light absorber. It is a transmittance modulation type photomask in which gratings form a structure in which they are fitted to each other via the grating surfaces.

Generally, the relationship between the thickness of the layer containing the light absorber and the light transmittance T has the following relationship as shown in FIG.

log (1 / T) ∝thickness Therefore, the transmittance-modulated photomask constructed as shown in FIG. 1 has a light transmittance along the original diffraction grating pattern as shown in FIG. Will form a photomask that changes into a sawtooth shape.

The preferred method for producing the photomask of the present invention will be described below.

FIG. 2 is an enlarged sectional view showing a part of the original blazed diffraction grating 1 in which a blazed grating surface 3 is formed on a surface of a substrate 2 of Pyrex glass by a ruling engine or the like. The material forming the substrate 2 may be any material as long as it can transmit light rays such as ultraviolet rays. Further, the method of forming the diffraction grating surface is not particularly limited, and may be formed by any other method shown in the above-mentioned conventional technique in addition to the cutting by the ruling engine.

For example, (1) electron beam, ion beam
A method of forming a diffraction grating surface by directly drawing on a resist on a substrate by changing the dose using various beams such as a laser beam and an X-ray beam, and (2) a resist pattern on the substrate by an arbitrary method. After the formation of the resist pattern, the resist pattern is used as a mask to cause the various beams to act, and oblique etching is performed to form a diffraction grating surface, (3)
There is a method of directly forming a blazed diffraction grating surface by an asymmetric two-beam interference exposure method by a combination of parallel light and obliquely incident light or a combination of parallel light and divergent light.

Here, in general, photoresists are often inferior in light resistance, moisture resistance, and mechanical properties such as mechanical strength.

Therefore, when forming the above-mentioned original diffraction grating surface, the above-mentioned diffraction grating surface is formed on a substrate having practical durability as a photomask, and then the plasma etching method or sputter etching method is used. It is preferable to etch the diffraction grating surface made of photoresist by an arbitrary dry etching method such as a reactive ion beam etching method and transfer it to a durable material surface. The base material having durability can be arbitrarily selected from materials suitable for etching. A glass substrate provided with an arbitrary polymer material containing or not containing a light absorber by a technique such as coating is preferably used because it is easily etched by oxygen plasma.

Next, as shown in FIG. 1, a light absorber having a refractive index n substantially equal to the refractive index N of the substrate 2 or a composition 4 containing the same is placed on the blazed lattice surface 3 of the substrate 2. Surface 4 '
To be parallel to the surface 2'of the substrate 2. The layer 4 of the light absorbing agent is made of a material having a desired light absorbing agent, and is applied, for example, in a form in which an ultraviolet absorbing agent such as 2,2-dihydroxy-4-methoxybenzophenone is contained in a suitable binder resin. To be done. Here, as a suitable binder resin, it is important that its refractive index n is substantially the same as the refractive index N of the transparent substrate 2. If the difference in refractive index is 0.01 or less, there is no practical problem, but the difference in refractive index is preferably 0.00
It should be 1 or less. When the refractive index difference increases beyond the above range, light is diffracted at the interface 3 between the original diffraction grating 1 and the light absorber layer 4, and it becomes difficult to obtain a diffraction grating with high accuracy.

It is important to improve the adhesion between the original diffraction grating 1 and the light absorber layer 4, and this interface can be subjected to any treatment for increasing the adhesion. They are various surface treatment agents and adhesives. It is preferable to perform heat treatment after applying the light absorber layer 4. When the material is a synthetic resin, the temperature is preferably near the glass transition point (Tg). Here, the vicinity of the glass transition point is Tg ± about
The range of 50K is shown. The heat treatment significantly increases the adhesion.

As the light absorber and the binder resin, any inorganic or organic material may be used as long as the transparency is maintained.

As a method for applying the light absorber layer, in addition to coating, an arbitrary force method such as a vacuum deposition method can be adopted.

The parallelism between the upper and lower surfaces of the photomask can be achieved by, for example, polishing after applying the light absorber.

When the original diffraction grating itself shown in FIG. 2 is composed of a light-absorbing material, the material to be coated may be a transparent material containing no light-absorbing agent. For the diffraction grating composed of the light absorbing material, for example, adopt the above-mentioned transfer method in which dry etching is performed from the upper surface of the diffraction grating made of an arbitrary photoresist formed on the upper surface of the light absorbing material. Can be easily obtained by.

In the above example, the lattice plane 3 of the substrate 2 on which the transmittance modulation type photomask 5 is formed is described as having a triangular cross section, but the following configuration is also available. Good.

That is, as shown in FIG. 10, the blazed diffraction grating of the transmittance modulation type photomask 20 is formed by forming a curved grating surface 16 on a substrate 15 made of a material that transmits light. This lattice plane 16 is also formed by an arbitrary method such as cutting with a ruling engine as in the above example.

Next, a light absorbing agent 17 having a refractive index n'which is substantially the same as the refractive index N'of the substrate 15 is placed on the blazed lattice surface 16 of the substrate 15 so that its surface 17 'is parallel to the surface 15' of the substrate 15. Coat so that Then, as shown in FIG. 12, it is possible to form a photomask in which the light transmittance T'by the light absorbing agent 17 changes in a sawtooth shape along the original diffraction grating pattern.

Next, a method of manufacturing a blazed diffraction grating by exposing and developing using this transmittance modulation type photomask will be described.

As shown in FIG. 6, a solution of a photosensitive resin 7 adjusted so that a dose amount (exposure amount) and a residual film rate after exposure and development are formed on a transparent substrate 6 as shown in FIG. Prepared by coating and drying 8 by spin coating so as to have a film thickness of about 1 μm. Next, a transmittance modulation type photomask 5 formed as shown in FIG. 1 is placed on this. Then, as shown in FIG. 7, the photomask 5 is exposed by exposing the light 9 in parallel and uniformly in an appropriate amount.

Next, this is developed to obtain a blazed diffraction grating 10 in which the photosensitive resin 7 is formed in a sawtooth shape 7 on the substrate 6 as shown in FIG.

If a transparent material is used as the photosensitive resin 7, the transmission type diffraction grating is used as it is. Further, as shown in FIG. 9, a reflective diffraction grating 12 can be easily formed by forming a reflective film 11 thereon by vapor deposition or the like.

The resulting grating can have any surface finish. For example, an antireflection film applied to a known optical component can be provided. Further, when the photosensitive resins 7 and 7 ′ are mechanically weak, SiO ₂ , TiO ₂ or the like may be attached thereon as a protective film by a method such as a vapor deposition method or a sputtering method.

The pitch of the blazed diffraction grating can be made by ordinary photolithography, for example, about 1 μm is sufficiently possible.

In the above example, when the transmittance modulation type photomask shown in FIG. 10 is used, the relationship between the dose amount (exposure amount) and the residual film rate after exposure and development is shown in FIG. 16 as the photosensitive resin. Use a photoresist adjusted to change linearly as shown in FIG. Then, the diffraction grating shown in FIG. 8 is obtained.

The method for producing the blazed diffraction grating has been described above. For example, instead of the blazed diffraction grating 1 shown in FIG.
A sine-wave diffraction grating is obtained by producing a photomask using the sine-wave diffraction grating 18 shown in the figure and performing the same operation thereafter.

Thus, according to the present invention, a diffraction grating of any shape can be obtained. Further, since the pitch and / or the depth of this diffraction grating need not necessarily be uniform, various form modulation type diffraction gratings such as Fresnel lenses and zone plate lenses can be obtained.

Using the photomask of the present invention, the photosensitive resin showing the relationship between the dose amount (exposure amount) and the refractive index after exposure and development as shown in FIG. 14 in place of the photosensitive resin having the relationship shown in FIG. If a resin is used, a refractive index modulation type diffraction grating can be obtained. The feature that the pitch and / or the change in the refractive index can be arbitrarily selected is the same as in the case of the form modulation type diffraction grating.

The present invention will be specifically described below with reference to examples.

(Example of Manufacturing Photomask) Example 1 A blaze-shaped lattice plane 3 is formed on one surface of a substrate 2 of Pyrex glass having a refractive index N = 1.47 by a ruling engine or the like. (See FIG. 2) Cellulose acetate 0.87 g, methyl methacrylate / 4 fluoroethyl methacrylate copolymer 0.13 g, 2,2-dihydroxy-4-methoxybenzophenone (ultraviolet absorber) 0.01
g, a solution consisting of DMF (dimethylformamide) 20 g,
A triangular Pyrex blaze diffraction grating 2 shown in FIG. 2 having a pitch of 6 μm and a depth of about 1 μm was spin-coated. In order to improve the adhesion between the substrate 2 and the ultraviolet absorber layer 4, baking was performed at 50 ° C. for about 2 hours after spin coating.
At this time, the film thickness was about 6 μm at a thick portion and about 5 μm at a thin portion, and the surface was smooth. (See FIG. 1) Then, the transmittance T of ultraviolet rays of the ultraviolet absorbent 4 has a relationship of log (1 / T) ∝thickness as shown in FIG.

Further, the refractive index of glass is 1.470 and the refractive index of the absorbent layer is 1.4.
Since it is adjusted to 71, almost no diffraction occurs between the original glass lattice and the polymer layer.

Therefore, the blazed diffraction grating 5 configured as shown in FIG. 1 forms a photomask in which the ultraviolet transmittance changes in a sawtooth shape along the pattern of the original diffraction grating as shown in FIG. Will be done.

Example 2 An ultraviolet absorber 2, on a light transmitting substrate 19 such as a quartz glass substrate,
8'of 2'-dihydroxy-3-methoxybenzophenone
After coating a mixture of copolymers of methyl methacrylate and glycidyl methacrylate contained by weight% by a spin coating method, solvent resistance in a photolithography process was imparted by a photocrosslinking reaction. The refractive index of this coat layer A is
It was 1.51. (Refer to FIG. 15) Subsequently, a photoresist AZ-1400 manufactured by Shipley Co., Ltd. is coated on the coat layer A to form the coat layer B. As shown by the solid arrow in FIG. The blazed grating was patterned by the two-beam interference method using the obliquely incident light shown by. Then, etching was performed by oxygen plasma etching, and the blazed lattice of the coat layer B was transferred to the coat layer A. Next, on the coating layer A having a blaze-like form, a material having almost the same refractive index (a composition ratio of glycidyl methacrylate was increased to adjust the refractive index to 1.51 Copolymer) was coated by a spin coating method so that the surface became flat, and a transmittance-modulated photomask in which the light transmittance was continuously changed was obtained.

Example 3 In Example 2, as the coating layer B, using a photoresist adjusted so that the exposure amount in photolithography and the residual film rate satisfy the relationship of FIG. A beam was irradiated to pattern a blazed grating having a shape as shown in FIG. 10 and a pitch of 6 μm. Subsequently, by oxygen plasma etching, a blazed grating having a pitch of 6 μm and a height of 1 μm was transferred, and subsequently, a photomask was manufactured by the same operation as in Example 2.

When the ultraviolet transmittance of this photomask was measured,
It was confirmed that the photomask was a transmittance modulation type photomask as shown in FIG.

(Production Example of Diffraction Grating) Example 4 A photosensitive resin composition (2-butenyl ester of methacrylic acid and methyl ester of methacrylic acid) in which the relationship between the exposure amount and the film thickness after exposure is in a proportional relationship on a glass substrate. Of a copolymer and m-benzoylbenzophenone) of about 3 μm
m and dried. On top of this, the photomask of Example 3 was used to expose ultraviolet rays to 10 j / cm at the 95% transparent portion of the photomask.
After irradiating so that it became ² , high temperature decompression treatment was performed. As a result, a blazed diffraction grating having a pitch of 6 μm and a height of 1 μm was obtained.

[Effects of the Invention] As described above, according to the present invention, a transmittance distribution control type analog photomask can be formed, and a blazed diffraction grating can be easily formed on a substrate by only one exposure. Since it can be formed, it can offer the possibility of mass production in combination with simplification of the manufacturing process.

[Brief description of drawings]

FIG. 1 is an enlarged sectional view of an essential part of a photomask comprising a blazed diffraction grating according to an embodiment of the present invention, and FIG. 2 is an enlarged sectional view of an essential part of a blazed diffraction grating used in the present invention. 3 is a diagram showing the relationship between the thickness and the transmittance of the ultraviolet absorbent used in the photomask of FIG. 1, FIG. 4 is a diagram showing the transmittance of the photomask of FIG. 1, and FIG. The figure is a diagram showing the relationship between the exposure amount of the photosensitive resin exposed through the photomask of FIG. 1 and the residual film rate, and FIGS. 6 to 9 show the photomask of the present invention. FIG. 10 is a diagram for explaining a process of manufacturing a diffraction grating by using FIG. 10, FIG. 10 is an enlarged sectional view of an essential part of a photomask according to another embodiment of the present invention, and FIG. 11 is a photomask shown in FIG. Diagram showing the relationship between the thickness and transmittance of the ultraviolet absorber used, Figure 12 is the photomass shown in Figure 10. FIG. 13 is a sectional view showing the main part of a sine wave diffraction grating used in the present invention, and FIG. 14 is a diagram showing the relationship between the exposure amount of photosensitive resin and the change in refractive index. FIG. 15 is a schematic diagram showing an exposure method for producing a transmittance modulation type photomask according to the present invention, and FIG. 16 is a diagram showing the relationship between the exposure amount of the photosensitive resin and the residual film rate. is there. 2 ... Morphological modulation type diffraction grating (transparent material) 3 ... Blazed grating surface 4 ... Blazed diffraction grating (UV absorber)

Claims (8)

[Claims] 1. A form-modulation diffraction grating (A) made of a transparent material,
A blazed diffraction grating (B) made of a material containing a light absorbing agent, wherein the diffraction grating (A) made of the transparent material and the diffraction grating (B) containing the light absorbing agent are disposed with their grating surfaces interposed therebetween. A transmittance modulation type photomask forming a fitted structure. 2. The refractive index of the material forming the morphology-modulating diffraction grating (A) and the material forming the blazed diffraction grating (B) are substantially equal to each other. Photo mask. 3. The photomask according to claim 1, wherein the shape-modulation diffraction grating (A) or the blazed diffraction grating (B) has a triangular or sawtooth cross-sectional shape. 4. The light transmittance according to claim 1, wherein the light transmittance changes in a triangular shape or a sawtooth shape along the pattern of the diffraction grating.
The photomask described in the item. 5. A transparent material containing or not containing a light absorber, wherein the grating surface of the form-modulating diffraction grating (A) contains or does not contain a light absorber (the light absorber is contained in the diffraction grating (A)). A method of manufacturing a transmittance modulation type photomask, which comprises forming a layer (B) made of a transparent material having a refractive index substantially the same as that of the diffraction grating. 6. The method of manufacturing a photomask according to claim 5, wherein the form-modulation diffraction grating (A) is formed by a lithography method. 7. (a) A photosensitive resin layer is formed on a substrate, and (b) a form-modulation type diffraction grating (A) made of a transparent material thereon.
And a blazed diffraction grating (B) made of a material containing a light absorber, wherein the diffraction grating made of the transparent material and the diffraction grating containing the light absorber are fitted to each other via a lattice plane. A transmittance modulation type photomask forming the above is closely mounted, and (c) a method of manufacturing a diffraction grating by exposing and developing the photomask. 8. A photosensitive resin in which the relationship between the exposure amount as a photosensitive resin and the residual film rate after exposure and development is substantially equal to the relationship between the light transmittance and the thickness of a light absorber of a diffraction grating used as a photomask. The method for manufacturing a diffraction grating according to claim 7, wherein a photosensitive resin is used.