JPH0844042A - Transmittancee modulation type photomask and its production and production of optical element formed by using the same - Google Patents

Abstract

PURPOSE:To provide a transmittance modulation type photomask which is easily producible while having the performance equivalent to the performance of the conventional photomasks and a process for production thereof and an optical element formed by using the same. CONSTITUTION:A light absorption layer 3 having absorptivity to light of a prescribed wavelength region is formed on at least one surface of a substrate 2 for the photomask which is substantially plane on both surfaces and is substantially transparent to light of the prescribed wavelength region. This light absorption layer 3 is formed to a shape having a prescribed depth distribution. As a result, the transmittance of light is given according to the depth distribution when the light of the prescribed wavelength region is transmitted through this layer. The transmittance of the light is higher at the points where the depth is deeper and the transmittance of the light is lower at the points where the depth is shallower and, therefore, this photomask acts as the transmittance modulation type photomask 1. The photomask is more easily producible than the photomask formed with the prescribed shape on the substrate itself for the photomask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmittance modulation type photomask, a method of manufacturing the same, and a method of manufacturing an optical element using the same.

[0002]

2. Description of the Related Art In recent years, diffractive optical elements and aspherical lenses have attracted attention due to the demand for smaller and lighter optical systems. A diffraction grating is often used as a low pass filter. There are various methods for manufacturing a diffractive optical element, but a method using a transmittance modulation type photomask, that is, after applying a resist on the optical element substrate, exposure through the transmittance modulation type photomask and A method is known in which a predetermined pattern is formed on a resist by performing a development process, and then the pattern shape of the resist is transferred to a substrate for an optical element by dry etching. Since this method requires only one exposure, it can be easily and efficiently manufactured even if the optical element substrate is glass, and mass production is also possible. In addition, if the mask has a blazed transmittance distribution, it is possible to easily manufacture a diffractive optical element having a high diffraction efficiency as compared with the binary method in which the blazed shape is approximated by steps.

By the way, as a method of manufacturing a transmittance modulation type photomask, For example, as disclosed in Japanese Patent Laid-Open No. 63-271265, a groove is formed in a transparent photomask substrate or a photomask substrate containing a light absorber by using a cutting device equipped with a diamond tool, a ruling engine, or the like. And a surface on which the groove is formed is coated with a light absorber or a transparent material and polished. B. For example, as disclosed in Japanese Unexamined Patent Publication No. 1-200258, a transparent photomask substrate is subjected to plastic working using a ruling engine or a diamond tool to form irregularities on the transparent photomask substrate, A method of lapping a convex portion to remove it, embedding an ultraviolet absorber in the concave portion and polishing it to flatten it. C. For example, as disclosed in Japanese Unexamined Patent Publication No. 63-271265, a predetermined pattern is formed on a resist by an asymmetric two-beam exposure method, and this pattern is transferred to a photomask substrate by plasma etching or the like to form the pattern. A method in which the formed surface is coated with a light absorber or a transparent material and polished. D. For example, as disclosed in Japanese Unexamined Patent Publication No. 63-271265, a predetermined pattern is formed on a resist by irradiating the resist on a transparent photomask substrate while changing the dose of various beams. A method in which a pattern is transferred to a photomask substrate by plasma etching or the like, and the surface on which the pattern is formed is coated with a light absorber or a transparent material and polished. E. For example, as disclosed in Japanese Patent Application Laid-Open No. 63-271265, a pattern is formed on a resist on a photomask substrate by an arbitrary method, and the pattern is used as a mask to perform oblique etching with various beams. A method in which a predetermined pattern is transferred to a substrate for coating, a surface on which the pattern is formed is coated with a light absorbent or a transparent material, and then polished. F. For example, as disclosed in JP-A-2-82202, a method of obtaining a density filter using an electron beam drawing plotter. Etc. are known.

[0004]

There are various problems in each of the above methods. First, in the above methods (a) and (b), since the photomask substrate is directly processed, there is a problem that the tool is significantly worn when glass is used for the photomask substrate, and the processing efficiency is high. Since it is low, it takes a large amount of money and an enormous amount of time to manufacture a photomask having a practical area. Therefore, the material of the photomask substrate is limited to a material with good workability. There is. Secondly, with the method (c) described above, a photomask having a large area can be manufactured, but there is a problem that the shape of the photomask is limited.

Thirdly, in the above method (2), since the exposure amount must be precisely controlled in accordance with the resist characteristics, the apparatus becomes complicated and expensive, and it becomes difficult to manufacture a large-area photomask. There is a problem of becoming. Fourthly, in the above method (d), the pattern shape may be largely deviated from the design value in the fine pattern portion due to scattering of electron beams used for exposure, far-ultraviolet light, ultraviolet light, or the like in the resist or proximity effect. However, there is a problem that it becomes difficult to efficiently manufacture a photomask with high precision.

Fifth, the method (e) has a problem that, when an ion beam is used as the beam, the processing speed is slow, and therefore the processing takes a very long time. Sixth, the above method has a problem that the device is complicated and expensive. Seventh, the above method has a problem that the desired shape is estimated from the residual film characteristic curve of the resist and the electron beam is used to draw the desired shape, so that the manufacturing work is complicated and takes time.

Eighth, in the above methods (a) to (e), since the manufactured photomask is made of two kinds of materials, there is a possibility that the photomask may be peeled off at the boundary between both materials during repeated use.
Ninth, in the above methods (a) to (e), reflection occurs at the boundary portion between the two kinds of materials and interferes with the incident light, so that the formed pattern may be destroyed.

As is apparent from the above problems, when an optical element is manufactured by using the transmittance modulation type photomask manufactured by the conventional method, it takes time and cost to manufacture the photomask, and the optical element also becomes expensive. Will end up. Further, when the accuracy of the photomask becomes low, the accuracy of the optical element also becomes low.

The present invention has been made in view of the above-mentioned various problems, and it is a first object of the present invention to provide a transmittance modulation type photomask which has the same performance as the conventional one and is easy to manufacture. And A second object of the present invention is to provide a manufacturing method of a transmittance modulation type photomask which can easily manufacture a highly accurate transmittance modulation type photomask.

A third object of the present invention is to provide a manufacturing method of a transmittance modulation type photomask which can easily manufacture a highly accurate and excellent transmittance modulation type photomask. Further, a fourth object of the present invention is to provide a method of manufacturing an optical element which can easily manufacture a highly accurate optical element with good reproducibility by using the transmittance modulation type photomask of the present invention.

[0011]

In order to achieve the above-mentioned first object, the transmittance modulation type photomask of the first invention is substantially flat on both sides and is substantially effective for light in a predetermined wavelength range. On at least one surface of the transparent photomask substrate, a light absorbing layer having absorptivity for light in the predetermined wavelength range is formed, and the light absorbing layer is formed in a shape having a predetermined depth distribution. It is characterized by being formed.

In order to achieve the above-mentioned second object, in the method of manufacturing a transmittance modulation type photomask of the second invention, both surfaces are substantially flat and are substantially transparent to light in a predetermined wavelength range. On at least one surface of the photomask substrate is a light absorption layer which is easier to machine than the photomask substrate and has absorptivity for light in the predetermined wavelength range, and the light absorption layer is formed. It is characterized by being machined into a shape having a predetermined depth distribution.

In order to achieve the above-mentioned third object, the method of manufacturing a transmittance modulation type photomask of the third invention is such that the photomask substrate having absorptivity for light in a predetermined wavelength range is formed on the photomask substrate. A processed layer made of a material that is easier to machine than a mask substrate is formed, the processed layer is formed into a shape having a predetermined depth distribution by machining, and the shape formed on the processed layer is anisotropic. It is characterized in that the pattern is transferred to the photomask substrate in a similar manner by means of reactive etching.

In order to achieve the above-mentioned fourth object, in the method for manufacturing an optical element of the fourth invention, a photosensitive resin layer is formed on an optical element substrate, and both surfaces are formed on the photosensitive resin layer. A light absorption layer having an absorption property for light in the predetermined wavelength range is formed on a photomask substrate that is substantially flat and substantially transparent for light in the predetermined wavelength range, and the light absorption layer is A transmittance modulation type photomask formed in a shape having a predetermined depth distribution is closely contacted or closely arranged with a slight gap, and the photosensitive resin layer is exposed through the transmittance modulation type photomask. The shape of the photosensitive resin layer remaining after the development is transferred to the optical element substrate in a similar manner by anisotropic etching.

In order to achieve the above-mentioned fourth object, the method for manufacturing an optical element according to the fifth aspect of the present invention is such that a photosensitive resin layer is formed on an optical element substrate, and both surfaces are substantially flat and predetermined. A light-absorbing layer having absorptivity for light in the predetermined wavelength range is formed on a photomask substrate that is substantially transparent to light in the wavelength range, and the light-absorbing layer has a predetermined depth distribution. The photosensitive element is exposed to light through a transmittance modulation type photomask formed on the substrate and a projection optical system, developed, and the shape of the photosensitive resin layer remaining after development is anisotropically etched to obtain the optical element. It is characterized in that the transfer is similar to the substrate for use.

[0016]

According to the first aspect of the invention, since the light absorption layer having absorptivity for the light in the predetermined wavelength range is formed in the shape having the predetermined depth distribution, the light in the predetermined wavelength range is transmitted. When this is done, the light transmittance is given according to the depth distribution. That is, the light transmittance is higher at a deeper place and lower at a shallower place. Therefore, it acts as a transmittance modulation type photomask.

According to the second aspect of the present invention, the photomask substrate supports the light absorption layer which is easier to machine than the photomask substrate and has the absorptivity for the light in the predetermined wavelength range. The light absorption layer also functions as a machining layer, and is formed by machining into a shape having a predetermined depth distribution.

According to the third aspect of the present invention, even when it is substantially impossible to directly machine the photomask substrate, the photomask substrate is made of a machinable material. Since a processing layer is provided and the processing layer is subjected to a predetermined mechanical processing, the shape formed on the processing layer is transferred to the photomask substrate by anisotropy in an anisotropic manner. It is possible to give a shape having a predetermined depth distribution.

According to the fourth aspect, a photosensitive resin layer is provided on the optical element substrate, and the photomask substrate is substantially transparent to light in a predetermined wavelength range on the photosensitive resin layer. A light absorption layer having an absorptivity for light in the predetermined wavelength region is formed on the light absorption layer, and the light absorption layer is formed into a shape having a predetermined depth distribution. Of the photosensitive resin according to the transmittance distribution of the transmittance modulation type photomask by exposing and developing the photosensitive resin layer through the transmittance modulation type photomask. A pattern is formed. Since this pattern is transferred analogously to the optical element substrate by anisotropic etching, even if it is practically impossible to directly machine the optical element substrate, a predetermined pattern is formed on the optical element substrate. A shape having a depth distribution of can be provided.

According to the fifth aspect of the invention, a photomask substrate is provided in which a photosensitive resin layer is provided on the optical element substrate, and both surfaces are substantially flat and substantially transparent to light in a predetermined wavelength range. A transmittance modulation type photomask having a light absorption layer having an absorptivity for light in the predetermined wavelength region formed thereon, and the light absorption layer having a shape having a predetermined depth distribution, and a projection optical system. By exposing and developing the photosensitive resin layer through the, a pattern of the photosensitive resin according to the transmittance distribution of the transmittance modulation type photomask is formed. Since this pattern is transferred analogously to the optical element substrate by anisotropic etching, even if it is practically impossible to directly machine the optical element substrate, a predetermined pattern is formed on the optical element substrate. A shape having a depth distribution of can be provided.

[0021]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a transmittance modulation type photomask of the present invention, in which 1 denotes a transmittance modulation type photomask (hereinafter referred to as a photomask). The photomask 1 is a substrate for a photomask that is substantially transparent to light in a predetermined wavelength range, such as g-line, h-line, i-line, and other ultraviolet rays of a mercury lamp, and has substantially flat surfaces on both sides. 2 and a light absorption layer 3 formed on the photomask substrate 2 and having a shape having a predetermined depth distribution while absorbing the light in the predetermined wavelength range.

Generally, when light is incident on a layer that absorbs light, the following relationship is established between the transmittance T of the layer and the thickness of the layer. 1n (1 / T) ∝ (layer thickness) That is, the cross-sectional shape of the light absorption layer, that is, the depth distribution is related to the transmittance. For example, in the case of the photomask 1 of FIG. 1, the depth distribution of the light absorption layer 3 has a sawtooth shape,
When light in a predetermined wavelength range is incident on the photomask 1, the transmittance distribution for the light has a sawtooth-like shape reflecting the depth distribution of the light absorption layer 3, so that the transmitted light intensity distribution also has a sawtooth-like shape. . The present invention is not limited to the case where the depth distribution of the light absorption layer 3 as shown in FIG. 1 has a sawtooth shape, but is applicable to various depth distributions.

The photomask 1 of this embodiment has the same effect as the conventional transmittance modulation type photomask in which the photomask substrate 2 has a predetermined depth distribution during exposure.
Since the light absorption layer 3 formed on the photomask substrate has a predetermined depth distribution, it can be manufactured more easily than the conventional one. By the way, generally, when an optical element is manufactured using a photomask, the shorter the exposure light is, the higher the resolution can be, and the fine pattern can be formed on the optical element. Therefore, it is desired to manufacture a photomask that transmits light of short wavelength. Here, the short wavelength is preferably 450 nm or less. On the other hand, when light with a wavelength of 190 nm or less is used, it is absorbed by air, and there are almost no usable optical materials. Therefore, as the exposure light,
Light having a wavelength in the range of 450 nm or less and 190 nm or more is particularly suitable. Therefore, if a photomask that transmits light having a wavelength in the above range is produced according to the present invention and an optical element is produced using light in the above range as exposure light, an optical element having a finer pattern can be produced.

Next, a method of manufacturing the transmittance modulation type photomask of the present invention will be described with reference to FIGS.
2A to 2F are views for explaining an embodiment in which the present invention is applied to manufacture of a transmittance modulation type photomask corresponding to a diffractive optical element. First, as shown in FIG. 2A, one surface of the photomask substrate 2 which is substantially transparent to light in a predetermined wavelength range, for example, g-rays or ultraviolet rays of a mercury lamp is polished on both sides of the photomask substrate 2 as shown in FIG. 2A. By comparison, the light absorption layer 3 which is easier to process is formed with a predetermined thickness t. Here, as the value of the thickness t, a value larger than the maximum processing depth d _max described later is used. Further, "easy to machine" means that the tool is less worn and the machining rate is good. Photomask substrate 2
As the material, any material that transmits light in the predetermined wavelength range can be used. For example, when ultraviolet rays are used as exposure light, quartz, synthetic quartz, SiO ₂ type glass, LiF, MgF ₂ ,
CaF ₂ , BaF ₂ , sapphire, KBr, KI and the like are preferable. In addition, synthetic quartz, SiO ₂ -based glass, and CaF ₂ are particularly preferable in terms of isotropy and environment resistance.

As the material of the light absorption layer 3, a material having an absorptivity for the light in the predetermined wavelength range and easier to machine than the photomask substrate 2 can be used. For example, when using ultraviolet light as exposure light, polymer materials, glass,
There are metal oxides, nitrides and the like, and it is desirable that the refractive index thereof is substantially equal to the refractive index of the photomask substrate 2 in order to prevent reflection at the boundary surface between the light absorption layer 3 and the photomask substrate 2. Hereinafter, the case of using ultraviolet rays will be described in more detail.

When the light absorption layer 3 is a polymer material, a polymer material suitable as a binder material, for example, an ultraviolet absorber suitable for a resin, such as a salicylic acid derivative or a 2-hydroxybenzophenone derivative, or glass or a metal oxide. And particles of nitride or the like are mixed, a film is formed on the photomask substrate 2 by a dip coating method, a spin coating method, or the like, and the organic solvent is scattered by heating. At that time, the refractive index can be made equal to that of the photomask substrate 2 by appropriately selecting the binder material. Further, the absorption coefficient of the light absorption layer 3 can be adjusted by changing the amount of the ultraviolet absorber to be mixed, and the depth distribution determined from the viewpoint of the transmittance can be adapted to the depth suitable for processing. You can

When the light absorption layer 3 is glass, for example, S
io ₂ glass and chalcogenide glass are suitable. The light absorption layer 3 may be formed by a sol-gel method or L method.
There is a method of forming a film by using a PD method (liquid phase deposition method), a CVD method (chemical vapor deposition method) or the like. When using the sol-gel method, the material of the film can be synthesized at a low temperature. In addition, because it is easy to make high-purity materials and a uniform thickness can be obtained,
A high quality film can be easily obtained. Also, since there are so many elements that can be applied to the coating, various films can be formed, and by appropriately selecting the material,
The refractive index of the light absorption layer 3 can be made equal to that of the photomask substrate 2.

When the LPD method is used, the film can be formed at a low temperature, and the refractive index of the light absorption layer 3 can be made equal to that of the photomask substrate 2 by appropriately setting the heating temperature. . Furthermore, since the LPD method has a good film-forming property and a film with few impurities can be obtained, a high-quality film with few defects can be obtained even if the photomask substrate 2 has a complicated irregular surface. Also, since the structure is dense, the change in film thickness due to heat treatment is small,
The layer can be formed with high accuracy. The features of the CVD method are that a high-melting point substance can be synthesized at a low temperature, that a film can be formed efficiently and uniformly regardless of the shape of the photomask substrate, that impurities can be reduced by using a high-purity source gas, and the composition of the deposit and It is easy to control the structural form. Therefore, when the CVD method is used, a highly pure and uniform layer can be easily formed at a low temperature. When the light absorption layer 3 is a metal oxide or a nitride, the light absorption layer 3 can be formed by a vacuum deposition method, a sputtering method, a CVD method or the like.

Although the case where the predetermined wavelength range is the ultraviolet range has been described above, an appropriate material is selected as the material for the photomask substrate 2 and the light absorbing layer 3 other than the ultraviolet range, for example, the visible range and the infrared range. By doing so, the same effect can be obtained. Further, in particular, the predetermined wavelength range is 450 nm or less and 190 n
When it is in the range of m or more, it is possible to manufacture a photomask which can be exposed so that the resolution is further improved for the above-mentioned reason.

Next, mechanical processing is performed to form the light absorption layer 3 into a shape having a desired depth distribution. For example, FIGS.
As shown in E, the light absorption layer 3 is processed into a desired shape by a processing machine such as a numerically controlled lathe type processing machine, a numerically controlled milling machine type processing machine, or a ruling engine type processing machine. Alternatively, as shown in FIG. 2F, the light absorbing layer 3 is processed into a desired shape by pressing the mold 4 against the light absorbing layer 3. At this time, since the light absorption layer 3 that is easier to machine than the photomask substrate 2 is machined, the photomask substrate 2 can be machined more easily than when directly processed. A material that is difficult to machine can be used as 2. Further, since the light absorption layer 3 is used as it is as a transmittance modulation type photomask after processing, it is not necessary to coat or polish another material. Furthermore, there is no exposure step and the light absorption layer 3 can be formed only by machining.
Since the predetermined shape is formed on the substrate, the processing accuracy does not deteriorate due to the proximity effect or the like that occurs during exposure.

Next, a description will be given of a case of manufacturing a concentric diffractive optical element, for example, a transmittance modulation type photomask corresponding to a blazed diffractive lens, in the step of machining the light absorption layer 3 into a desired shape. To do. If a cutting machine, for example, a numerically controlled lathe type machine (not shown) is used,
As shown in B, the photomask substrate 2 having the light absorption layer 3 formed thereon is attached as a work. Then, while rotating the work, the cutting tool 5 is moved based on the design data of the photomask to be manufactured, and the light absorption layer 3 is cut into a desired shape. At this time, since the photomask substrate 2 is not directly processed, cutting can be performed easily and at high speed regardless of the workability of the photomask substrate 2. Therefore, even a large-area photomask can be easily manufactured. Further, even those having different cross-sectional shapes can be easily dealt with by changing the processing data, and photomasks corresponding to optical elements of various shapes can be manufactured.

Here, when the ring depth is different for each ring, such as a diffractive optical element optimized for a plurality of wavelengths, the photomask corresponding thereto also has a different ring depth for each ring. In that case, it is preferable that t> d _max , where d _max is the maximum working depth of the ring. When the thickness t of the light absorption layer 3 is made slightly larger than the maximum processing depth d _max , even if there is some error in the movement of the cutting tool 5,
It is possible to effectively prevent the cutting tool 5 from coming into contact with the photomask substrate 2.

On the other hand, in the case of manufacturing a linearly shaped diffractive optical element, for example, a transmittance modulation type photomask corresponding to a diffraction grating, a cutting machine, for example, a numerical control milling machine type machine or a ruling engine type machine is used. Using FIG. 2C
As shown in FIG. 2E, the cutting tool 5 is fixed and the work is moved vertically and horizontally, or the work is fixed and the cutting tool 5 is moved vertically and horizontally to cut the light absorption layer 3 into a desired shape. At this time, since the photomask substrate 2 is not processed, it can be easily and rapidly cut regardless of the workability of the photomask substrate 2 as in the case of the concentric circular diffractive optical element. Therefore, even a large-area photomask can be easily manufactured. Moreover, by changing the processing data, it is possible to easily manufacture photomasks corresponding to optical elements of various shapes.

By cutting the light absorption layer 3 as described above, a shape having a desired depth distribution can be easily obtained. Further, recent numerical control processing machines have a processing accuracy of submicron, and can obtain a desired shape with high accuracy. Furthermore, by changing the processing data,
Not limited to the shapes illustrated in FIGS. 2B to 2E, it is possible to easily manufacture photomasks corresponding to optical elements of various shapes, such as aspherical lenses, Fresnel lenses, and diffractive cylindrical lenses. Further, for example, a lathe type processing machine, a milling machine type processing machine, and a ruling engine type processing machine are versatile, and the same processing machine can be used for various purposes, so that the cost for manufacturing a photomask can be suppressed. .

Next, description will be given of the case where the die machining is performed in the step of machining the light absorption layer 3 into a shape having a desired depth distribution. As shown in FIG. 2F, a mold 4 having a predetermined shape, for example, a mold is pressed against the light absorption layer 3,
A desired shape is formed on the light absorption layer 3. In this case, it is possible to form a desired shape with good reproducibility by performing the mold processing. Moreover, since a desired shape can be easily and efficiently formed, mass production can be easily performed. As is clear from the above description, according to the present embodiment, it is possible to easily manufacture the transmittance modulation type photomask having various patterns with high accuracy.

Next, an example in which the present invention is applied to manufacture of a transmittance modulation type photomask corresponding to a diffractive optical element will be described with reference to FIGS. First, as shown in FIG. 3A, a processing layer 7 is formed with a predetermined thickness t on one surface of a photomask substrate 6 whose both surfaces are absorptive to light in a predetermined wavelength range. Here, the value of the thickness t is set to a value larger than the maximum working depth d _max as described in the above embodiment. As the photomask substrate 6, all materials having absorptivity for the light in the predetermined wavelength range can be used. For example, when ultraviolet rays are used as the exposure light, general materials that absorb ultraviolet rays, particularly SiO ₂ glass, chalcogenide glass, UV filters, etc. are preferable in terms of durability and etching.

As the material of the processing layer, a material that can be machined more easily than the photomask substrate 6, for example, a resin or a metal that can be machined easily can be used. As the metal that can be easily machined, for example, Al or P—Ni (electroless nickel) can be used. The processing layer 7 is formed by
When the processed layer 7 is made of resin, it can be performed using a spin coater or the like. By selecting the baking conditions, the hardness suitable for the subsequent process can be obtained.
When the processing layer 7 is made of metal, the processing layer 7 can be formed by vacuum vapor deposition, sputtering, plating or the like.

Next, the processed layer 7 is machined into a desired shape. For example, as shown in FIG. 3B, a photomask substrate 6 on which a processing layer 7 is formed as a work is attached to a cutting machine, for example, a numerically controlled lathe type machine (not shown), and a photo to be manufactured while rotating the work. The tool 5 is moved based on the mask design data to process the processing layer 7 into a predetermined shape. Alternatively, when the processing layer 7 is made of resin, as shown in FIG. 3C, the processing layer 7 is formed into a desired shape by pressing a mold 4a (for example, a mold) having a predetermined shape against the processing layer 7. To do. At this time, since the processing layer 7 is processed, it is possible to easily form the processing layer 7 into a desired shape even if it has a large area, as compared with the case where the processing layer 7 is formed into a desired shape by an asymmetric two-beam exposure method or beam exposure. You can Further, since a processing layer that is easier to machine than the photomask substrate 6 is processed, a material that is difficult to machine can be used as the photomask substrate 6. Furthermore, since a predetermined shape is formed in the processed layer 7 only by mechanical processing without an exposure step, processing accuracy does not decrease due to the proximity effect or the like that occurs during exposure.

In the case of cutting, since the numerical control processing machines of recent years have extremely high processing accuracy, the processing layer 7 can be processed into a desired shape with extremely high accuracy. Further, by changing the processing data, as shown in FIGS. 4A to 4E, photomasks corresponding to various optical elements such as aspherical lenses and Fresnel lenses can be easily manufactured. Further, by using a milling machine type processing machine, a ruling engine type processing machine or the like, it is possible to easily manufacture a photomask corresponding to a linear diffractive optical element or the like. Further, since these processing machines have versatility and can be used for other purposes, the cost for manufacturing a photomask can be suppressed. In the case of die processing, processing layer 7
Since it can be reproducibly formed into a desired shape efficiently in a short time, mass production is possible.

After the mechanical processing is completed, the photomask substrate 6 and the processing layer 7 are eroded. For erosion processing, see Fig. 3D.
Anisotropic etching as shown in, for example, reactive ion etching is suitable. As a result, the shape of the processed layer 7 is transferred to the photomask substrate 6 in a similar manner in the depth direction. By performing erosion processing until the shape of the processing layer 7 is transferred to the photomask substrate 6, a transmittance modulation type photomask as shown in FIG. 3E can be manufactured. At this time, by adjusting the composition of the etching gas 8,
The etching selection ratio of the photomask substrate 6 and the processing layer 7 can be changed, and if the selection ratio is set to 1: 1, the shape of the processing layer 7 is directly transferred to the photomask substrate 6. When the selection ratio is other than 1: 1, the shape of the processing layer 7 is enlarged or reduced in the depth direction and is transferred to the photomask substrate 6 in a similar manner. The value in the depth direction of the pattern to be formed may be determined.

In the above, since the shape formed on the processing layer 7 is transferred to the photomask substrate 6 by erosion processing, the photomask material is only the material of the photomask substrate 6. Therefore, if this photomask is used, there is no reflection that occurs at the boundary between different materials during exposure, and the resist pattern does not collapse due to interference between reflected light and incident light. Therefore, it is possible to obtain a photomask with high performance capable of forming a resist pattern with high accuracy. In addition, a photomask having excellent durability can be manufactured without peeling at the boundary between different materials. Further, especially when the photomask substrate 6 has absorptivity for light having a wavelength of 450 nm or less and 190 nm or more, a photomask which can be exposed so that the resolution is further improved for the reasons described above. You can

This embodiment is not limited to the production of a photomask suitable for producing a diffractive optical element, and for example, as shown in FIGS. 4A to 4E, a photomask suitable for an aspherical lens, a Fresnel lens, etc. It can also be applied to production.
As is clear from the above description, according to the present embodiment, it is possible to easily and highly accurately manufacture a high-performance, large-area transmittance modulation type photomask having excellent durability.

Next, an embodiment in which the present invention is applied to manufacture of an optical element will be described with reference to FIGS. First, as shown in FIG. 5A, the photosensitive resin layer 10 is formed on one surface of the optical element substrate 9 made of a predetermined material, for example, optical glass.
Is formed with a predetermined thickness. After that, pre-baking is performed under appropriate conditions.

Next, as shown in FIG. 5B, the photosensitive resin layer 1
Transmittance modulation type photomask 1 so as to be in close contact with the upper surface of 0.
1 is arranged, and the photosensitive resin layer 10 is exposed through the transmittance modulation type photomask 11 with the exposure light 12 having a wavelength that the photosensitive resin layer 10 is exposed to. When the development is performed after exposure, when the photosensitive resin layer 10 is made of a positive type photosensitive resin, the residual film thickness of the photosensitive resin layer 10 becomes thin in the portion where the intensity of the exposure light 12 is strong, or the film is formed. It does not remain. On the other hand, exposure light 1
In the portion of 2 where the intensity is weak, the residual film thickness becomes thicker and the exposure light 12
5C according to the intensity distribution of the photosensitive resin layer 1
A depth profile is formed at 0. On the other hand, when the photosensitive resin layer 10 is made of a negative type photosensitive resin, the residual film thickness is large in a portion where the intensity of the exposure light 12 is strong and the remaining film thickness is weak in a portion where the intensity of the exposure light 12 is opposite to the positive type. The photosensitive resin layer 10 becomes thinner and has a depth shape opposite to that of the negative type.

After the post-baking, anisotropic etching such as reactive ion etching is performed as shown in FIG. 5D.
As a result, the shape of the photosensitive resin layer 10 is transferred to the photomask substrate 9 in a similar manner in the depth direction. Photosensitive resin layer 1
By performing etching until the shape of 0 is completely transferred to the optical element substrate 9, an optical element as shown in FIG. 5E can be manufactured. At this time, by adjusting the composition of the etching gas 8a, the value of the etching selection ratio between the optical element substrate 9 and the photosensitive resin layer 10 can be changed.

At the time of exposure, the photomask 11 may be placed close to the photosensitive resin layer 10 with a slight gap between them to perform exposure. When they are brought into close contact with each other, exposure can be performed with good resolution, and when they are slightly separated, the photosensitive resin layer 1
It is possible to perform exposure without damaging 0 or the photomask 11. Further, when a photomask having an absorptivity for light having a wavelength of 450 nm or less and 190 nm or more is used, and exposure is performed with light having a wavelength of this range, the resolution is further improved for the above reason. It can be exposed.

According to the manufacturing method of this embodiment, when the blazed shape as shown in FIG. 5C is formed by using the binary method, only the approximate blazed shape can be obtained. A blazed shape as shown in FIG. 5C can be obtained without stepwise approximation. Moreover, since the photosensitive resin layer 10 is formed into a desired shape by one exposure using the photomask 11, the number of steps is smaller than that of the binary method. Also, there are no mask overlay errors,
It is possible to accurately form a predetermined shape. Therefore,
A large number of optical elements can be accurately duplicated in a short time.

In this embodiment, the transmittance modulation type photomask shown in FIG. 1 is used, but the transmittance modulation type photomask manufactured by the manufacturing method shown in FIGS. 2 to 4 is used. Good. As is clear from the above description, according to this embodiment, the optical element can be easily manufactured. Further, optical elements having various shapes such as a diffractive optical lens, a diffraction grating, an aspherical lens, and a Fresnel lens can be easily manufactured according to the photomask.

Next, referring to FIGS.
Another embodiment in which the present invention is applied to manufacture of an optical element will be described. First, as shown in FIG. 5A, a photosensitive resin layer 10 is formed with a predetermined thickness on one surface of an optical element substrate 9 made of a predetermined material, for example, optical glass. After that, pre-baking is performed under appropriate conditions.

Next, the photosensitive resin layer 10 is projected and exposed with exposure light. FIG. 6 is a diagram showing a configuration when a lens is used as a projection exposure system. An illumination system 13 illuminates the transmittance modulation type photomask 11. Photo mask 1
1 and the photosensitive resin layer 10 are in a conjugate relationship, and the image of the photomask 11 is formed on the photosensitive resin layer 10 by the projection lens 14 having a very small aberration, and the photosensitive resin layer 10 is separated from the image of the photomask 11 by the projection lens 14. Exposure is performed according to the transmittance distribution. At this time, the image on the photosensitive resin layer 10 becomes an image of equal size or reduced size according to the magnification of the projection lens 14. In the case of reduction projection, the photomask becomes large according to the magnification, and the photomask 11 is easily manufactured. For example, the pitch of the pattern formed on the photosensitive resin layer 10 is 10 μm.
m, and when the magnification of the projection lens is 1/5, the pitch of the photomask is 50 μm. Further, the wavelength of the exposure light used is within the wavelength range where the photosensitive resin is exposed. Especially as the exposure light, the wavelength is 450 nm or less 1
When the light in the range of 90 or more is used, it is possible to perform exposure so that the resolution is further improved due to the above reason.

After the exposure, the photosensitive resin layer 10 is developed in the same manner as in the above-described embodiment to form a depth shape. And
Post-baking and anisotropic etching are performed to transfer the shape of the photosensitive resin layer 10 to the optical element substrate 9 in a similar manner in the depth direction to manufacture an optical element.

In this embodiment, a desired shape can be obtained without stepwise approximation as in the above-described embodiments. Further, since the photomask 11 and the photosensitive resin layer 10 do not come into contact with each other, there is no defect such as peeling of the resist. Further, damage to the mask due to contact with the optical element substrate 9 can be prevented. Moreover, since the photosensitive resin layer 10 is formed into a desired shape by one exposure using the photomask 11, the number of steps is smaller than that of the binary method.
Further, it is possible to form a predetermined shape with high accuracy without a mask overlay error. Therefore, a large number of optical elements can be accurately duplicated in a short time. Further, by changing the photomask, optical elements of various shapes can be easily manufactured.

In the present embodiment, the case where the projection lens is used as the projection optical system has been described, but a mirror projection using a mirror may be used as the projection optical system. As is clear from the above description, according to this embodiment, the optical element can be easily manufactured. Also, for example, a diffractive optical lens, a diffraction grating, an aspherical lens,
Optical elements of various shapes such as a Fresnel lens can be easily manufactured.

It should be noted that the present invention is not limited to the above-described embodiments, and various modifications or changes can be added. For example, in the transmittance-modulated photomask according to claim 1, the predetermined wavelength range is wavelength 450.
It is preferable that the thickness is in the range of not more than 190 nm and not less than 190 nm. In that case, the predetermined wavelength range is 450 nm.
Since the light absorption layer having an absorptivity for light in the range of 190 nm or more is formed in a shape having a predetermined depth distribution, when light having a wavelength in the above range is transmitted, the light absorption layer is changed according to the depth distribution. Light transmittance is imparted, and the light transmittance increases as the depth increases, and the light transmittance decreases as the depth decreases, and the light transmittance acts as a transmittance modulation photomask. Therefore, in addition to the effect of the first aspect, it is possible to perform the exposure by using the light in the above range as the exposure light, so that it is possible to perform the exposure so as to improve the resolution.

Further, in the method of manufacturing a transmittance modulation type photomask according to claim 2, it is preferable that the light absorption layer is machined using a lathe machine.
In that case, the photomask substrate supports a light absorption layer that is easier to machine than the photomask substrate, and the light absorption layer also functions as a machining layer, as in the case of claim 2. By rotating the work using a lathe type processing machine, the light absorption layer is formed into a shape having a predetermined depth distribution. Therefore, in addition to the effect of claim 2, by processing the light absorption layer by using a lathe type processing machine with high processing accuracy, a transmittance modulation type corresponding to a concentric diffractive optical element, an aspherical lens, or the like can be obtained. The photomask can be easily manufactured with high precision. Further, the photomask can be manufactured efficiently and inexpensively. Further, photomasks of various shapes can be easily manufactured.

Further, in the method of manufacturing a transmittance modulation type photomask according to claim 2, it is preferable that the light absorption layer is machined by using a milling machine type machine or a ruling engine type machine. . In that case, similarly to claim 2, the photomask substrate supports a light absorption layer that is easier to machine than the photomask substrate, and the light absorption layer also functions as a machining layer. Use a milling machine type processing machine or a ruling engine type processing machine to fix the cutting tool and move the work up, down, left or right, or fix the work and move the cutting tool up, down, left or right to move the light absorption layer to a predetermined depth distribution. It is formed into a shape having. Therefore, in addition to the effect of the second aspect, by processing the light absorption layer using a milling lathe type processing machine or a ruling engine type processing machine with high processing accuracy, the transmission corresponding to a linear diffractive optical element or the like can be achieved. A rate modulation type photomask can be easily manufactured with high precision. Further, the photomask can be manufactured efficiently and inexpensively. Further, photomasks of various shapes can be easily manufactured.

Further, in the method of manufacturing a transmittance-modulated photomask according to claim 2, it is preferable that the machining of the light absorption layer is die machining. In that case, claim 2
Similarly, the photomask substrate supports a light absorption layer that is easier to machine than the photomask substrate, and the light absorption layer also functions as a machining layer. The layers are shaped to have a predetermined depth distribution. Therefore, in addition to the effect of the second aspect, by processing the light absorption layer by mold processing, it is possible to mass-produce the transmittance modulation type photomask with high accuracy and reproducibility with mold accuracy. Further, photomasks of various shapes can be easily manufactured.

Further, in the method of manufacturing a transmittance modulation type photomask according to claim 2, it is preferable that the predetermined wavelength range is in the range of 450 nm to 190 nm. In that case, the photomask substrate is easier to machine than the photomask substrate and has a wavelength range of 45 nm.
The light absorbing layer has a shape having a predetermined depth distribution because it supports a light absorbing layer having an absorptivity for light in the range of 0 nm or less and 190 nm or more, and the light absorbing layer also functions as a machining layer. Thus, a predetermined distribution can be given to the transmittance of the photomask substrate with respect to light having a wavelength in the above range. Therefore, in addition to the effect of claim 2, the wavelength of the exposure light is 450 nm or less and 190 nm or less.
Since exposure can be performed using light in the above range, a photomask that can be exposed so as to improve resolution can be manufactured.

In the method of manufacturing a transmittance-modulated photomask according to the third aspect, it is preferable that the machining layer is machined by using a lathe machine. In that case, in the machining of the machining layer according to the third aspect, the machining layer is formed into a predetermined shape by rotating the work using a lathe type machining machine. Therefore, in addition to the effect of claim 3, in order to efficiently process the processing layer using a lathe type processing machine with high processing accuracy, a transmittance modulation type corresponding to a concentric diffractive optical element, an aspherical lens or the like. The photomask can be easily manufactured with high precision and at low cost. Further, photomasks of various shapes can be easily manufactured.

Further, in the method of manufacturing a transmittance modulation type photomask according to claim 3, it is preferable that the machining layer is machined by using a milling machine type machine or a ruling engine type machine. In that case, in the machining of the machining layer according to claim 3, a milling machine type machine or a ruling engine type machine is used to fix the bite to move the work up and down, left and right, or to fix the work and move the bite up, down, left and right. The processed layer is formed into a predetermined shape by moving to. Therefore, in addition to the effect of claim 3, since the processing layer is processed by using the milling lathe type processing machine or the ruling engine type processing machine with high processing accuracy, the transmittance modulation corresponding to the linear diffractive optical element or the like is performed. The mold photomask can be easily manufactured with high precision and at low cost. Further, photomasks of various shapes can be easily manufactured.

Further, in the method of manufacturing a transmittance-modulated photomask according to the third aspect, it is preferable that the machining of the machining layer is die machining. In that case, in the machining of the working layer according to claim 3, the working layer is formed into a predetermined shape by pressing the die. Therefore, in addition to the effect of the third aspect, since the processing layer is processed by the mold processing, the transmittance modulation type photomask can be mass-produced easily with good mold accuracy and reproducibility. Further, photomasks of various shapes can be easily manufactured.

Further, in the method for manufacturing a transmittance modulation type photomask according to claim 3, it is preferable that the predetermined wavelength range is within a range of 450 nm to 190 nm. In that case, a machining layer made of a machinable material is provided on a photomask substrate having absorptivity for light having a wavelength of 450 nm or less and 190 nm or more, and the machining layer is subjected to predetermined machining, Since the shape formed on the processed layer by the isotropic etching is transferred to the photomask substrate in a similar manner, it is possible to give the photomask substrate a shape having a predetermined depth distribution, and the wavelength is within the above range. A predetermined distribution can be given to the transmittance of the photomask substrate with respect to the light. Therefore,
In addition to the effect of claim 3, the exposure light has a wavelength of 450 n.
Since exposure can be performed using light in the range of m or less and 190 nm or more, a photomask that can be exposed so as to improve resolution can be manufactured.

Further, in the optical element manufacturing method according to any one of claims 4 and 5, the transmittance modulation type photomask is
It is preferable to manufacture by using the manufacturing method according to claim 2 (and a configuration to which the above-mentioned machining or the like is limited) or claim 3 (and to which the above-mentioned mechanical-processing or the like is limited). . In that case, in Claim 4 or 5, a highly accurate transmittance modulation type photomask which is easily manufactured by using the manufacturing method of Claim 2 (and a structure in which the limitation such as the above machining is added), or Claim 4. 3 (and a configuration in which the above-mentioned machining process and the like are added) are used to easily expose the photosensitive resin by exposure using a highly durable transmittance-modulated photomask manufactured with high precision. A predetermined shape is formed on the layer. Therefore, by exposing using the above transmittance modulation type photomask, an easy and accurate optical element can be manufactured inexpensively. Moreover, various optical elements can be easily manufactured.

[0064]

According to the first aspect of the invention, since the light absorbing layer of the photomask substrate has a predetermined shape, the photomask substrate itself has a predetermined shape. It can be manufactured more easily.

According to the second aspect of the invention, since the light absorption layer formed on the photomask substrate is processed more easily than the photomask substrate, it depends on the workability of the photomask substrate. Without doing so, the light absorption layer can be easily formed into a shape having a predetermined depth distribution.

According to the third aspect, since the processed layer of the photomask substrate is processed, the transmittance modulation type photomask can be easily manufactured without depending on the processability of the photomask substrate. In addition, since a predetermined shape is formed on the processing layer by machining, problems due to exposure do not occur, and machining can be performed with the accuracy of machining. Further, since the pattern shape of the processed layer is transferred to the photomask substrate, it is possible to easily manufacture a transmittance modulation type photomask which has excellent durability and in which the pattern shape does not collapse due to interference during exposure.

According to the fourth aspect of the invention, since the exposure is performed using the transmittance modulation type photomask of the first aspect of the invention, the optical element can be easily manufactured. Moreover, various optical elements can be easily manufactured by changing the photomask.

According to the fifth aspect of the invention, since exposure is performed using the transmittance modulation type photomask of the first aspect of the invention, an optical element can be easily manufactured. Moreover, various optical elements can be easily manufactured by changing the photomask. Furthermore, since there is a projection optical system between the photomask and the photosensitive resin and the mask and the photosensitive resin layer do not come into contact with each other, defects such as resist peeling and damage to the mask do not occur, and it is cheap and easy. The optical element can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram for explaining one embodiment of a transmittance modulation type photomask of the present invention.

2A to 2F are views for explaining an example in which the present invention is applied to manufacture of a transmittance modulation type photomask corresponding to a diffractive optical element.

3A to 3E are diagrams for explaining an example in which the present invention is applied to manufacture of a transmittance modulation type photomask corresponding to a diffractive optical element.

4A to 4E are diagrams for explaining an example in which the present invention is applied to manufacture of an optical element.

5A to 5E are views for explaining another embodiment in which the present invention is applied to manufacture of an optical element.

FIG. 6 is a diagram for explaining another embodiment of the present invention.

[Explanation of symbols]

 1 Photomask Substrate 2 Light Absorption Layer 3 Transmittance Modulation Photomask 4,4a Type 5 Byte 6 Photomask Substrate 7 Processing Layer 8, 8a Etching Gas 9 Optical Element Substrate 10 Photosensitive Resin Layer 11 Transmittance Modulation Type Photomask 12 Exposure light 13 Illumination system 14 Projection lens

Claims (5)

[Claims] 1. A photomask substrate, both surfaces of which are substantially flat and which is substantially transparent to light in a predetermined wavelength range, has absorptivity for light in the predetermined wavelength range on at least one surface of the substrate. A transmittance modulation type photomask, wherein a light absorption layer is formed, and the light absorption layer is formed in a shape having a predetermined depth distribution. 2. A photomask substrate that is substantially flat on both sides and is substantially transparent to light in a predetermined wavelength range, and is easier to machine than the photomask substrate. And a step of forming a light absorbing layer having absorptivity for the light in the predetermined wavelength range, and a step of forming the light absorbing layer into a shape having a predetermined depth distribution by machining. Method for manufacturing a transmittance modulation type photomask. 3. A step of forming a processing layer made of a material that is easier to machine as compared with the photomask substrate, on the photomask substrate having absorptivity for light in a predetermined wavelength range, and the processing layer. A step of forming a shape having a predetermined depth distribution by machining, and a step of analogously transferring the shape formed on the processed layer to the photomask substrate by anisotropic etching. And a method for manufacturing a transmittance-modulated photomask. 4. A step of forming a photosensitive resin layer on a substrate for an optical element, wherein both surfaces of the photosensitive resin layer are substantially flat and are substantially transparent to light in a predetermined wavelength range. A transmittance-modulation-type photomask in which a light-absorbing layer having absorptivity for light in the predetermined wavelength range is formed on a photomask substrate, and the light-absorbing layer is formed in a shape having a predetermined depth distribution. Are closely contacted or closely arranged with a slight gap therebetween, a step of exposing and developing the photosensitive resin layer through the transmittance modulation type photomask, and a shape of the photosensitive resin layer remaining after the development. Is transferred to the optical element substrate by anisotropic etching in a similar manner, and a method for manufacturing an optical element. 5. A step of forming a photosensitive resin layer on a substrate for an optical element, and the step of forming a photosensitive resin layer on a substrate for a photomask, both surfaces of which are substantially flat and substantially transparent to light in a predetermined wavelength range. A light absorption layer having an absorptivity for light in a predetermined wavelength range is formed, and the light absorption layer is formed into a shape having a predetermined depth distribution. It is characterized by including a step of exposing and developing the photosensitive resin layer, and a step of analogously transferring the shape of the photosensitive resin layer remaining after the development to the optical element substrate by anisotropic etching. Optical element manufacturing method.