JPH07104444B2 - Method of manufacturing diffraction grating and exposure apparatus used therefor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a diffraction grating that diffracts a light wave by phase control, and more specifically, to a method for manufacturing a diffraction grating with reduced high-order diffracted light intensity of ± 2nd order or higher, and It relates to an exposure apparatus used for it.

[Conventional technology]

Optoelectronic products such as a three-beam type CD player and a video camera use a diffraction grating for dividing a laser beam at a predetermined ratio. Generally, in a three-beam type CD player, the reading signal and the focusing control signal are detected by the 0th-order diffracted light, and the tracking control signal is detected by the ± 1st-order diffracted light.
Higher-order diffracted light higher than the second order is not necessary, and the generation of higher-order diffracted light higher than the ± 2nd order reduces the utilization efficiency of the laser light and causes stray light. Further, even in a single-tube type or a single-plate type and a diffraction grating used as an optical low-pass filter in a video camera, only 0th order diffracted light and ± 1st order diffracted light are necessary, and high order diffracted light of ± 2nd order or more is required. This is a cause of deterioration of low frequency MTF (Modulation Transfer Function) characteristics.

From the above, in the diffraction grating used for optoelectronic products such as CD players and video cameras, it is desired to reduce the high-order diffracted light intensity of ± 2nd order or higher. As a method, it is known to make the cross-sectional shape of the diffraction grating trapezoidal or sinusoidal.

A method of manufacturing a diffraction grating, which has been widely used in the past, will be described with reference to FIG. Conventionally, on a transparent substrate 11 such as glass, MgFe ₂ , S
After depositing a transparent dielectric film 13 such as iO ₂ and forming a photosensitive film 12 by applying a photosensitive resin composition onto the film by a spin coating method or the like, a photomask 14 having a predetermined diffraction grating pattern is formed. Exposure is carried out, and undeveloped portions of the photosensitive film are removed by development to open a window. After that, the diffraction film 17 was produced by etching the dielectric film in the window and removing the unnecessary photosensitive film. Therefore, since the cross-sectional shape of the diffraction grating manufactured by such a method is limited to the rectangular wave shape, it is impossible to reduce the high-order diffraction intensity of ± 2nd order or higher.

[Problems to be solved by the invention]

The present invention has been made in view of the above problems, and an object thereof is to provide a method of manufacturing a diffraction grating having a triangular wave shape, a trapezoidal wave shape, a sine wave shape, or the like.

[Means and Actions for Solving Problems]

In the method for producing a diffraction grating according to the present invention, a light scattering plate having a function of scattering light such as frosted glass is installed between the light source and the photomask, or between the photomask and the photosensitive film,
By adjusting the distance between the photo mask and the photosensitive film to expose the light intensity distribution to a triangular wave shape, a trapezoidal wave shape, a sine wave shape, or the like, exposure is performed to form a triangular wave shape, a trapezoidal wave shape, or a sine wave shape diffraction grating.

The present invention will be described below with reference to FIG.

FIG. 1 (b) is a cross-sectional view showing the concept of the exposure apparatus of the present invention, and FIGS. 1 (a) to 1 (c) are process cross-sectional views for explaining the steps of producing a diffraction grating using the exposure apparatus. It was In the figure, reference numeral 7 denotes an exposure apparatus of the present invention, which comprises a light source 3, a light scattering plate 5 and a photomask 4.

After a photosensitive resin film 2 is applied on a transparent substrate 1 such as glass or plastic by a coating method or the like (FIG. 1a), a light source 3, a light scattering plate 5 and a photomask 4 for a diffraction grating having a predetermined periodic structure are formed. It is installed in the equipped exposure apparatus (Fig. 1b). The distance g between the photomask 4 and the photosensitive resin film can be adjusted by a distance adjusting device not shown in the drawing, and the intensity distribution of light reaching the photosensitive resin film can be adjusted by adjusting the distance g. It can be adjusted as desired. For example, by gradually increasing the distance g, the intensity distribution of light can be changed from a trapezoidal wave shape to a sine wave shape to a triangular wave shape. Although the light-scattering plate is installed between the photomask and the light source in FIG. 1b, the same function can be achieved if it is installed between the photomask and the photosensitive resin film or both of them.

Next, a desired diffraction grating can be obtained by irradiating a light having a desired intensity and wavelength for exposing the photosensitive resin film from the light source, exposing, and then developing. The photosensitive resin used can be arbitrarily selected as long as it is a material having transparency and durability that can form a diffraction grating after development. Dry developable materials are particularly preferable, for example, acrylics having a photoreactive carbon-carbon double bond disclosed in, for example, EPA 220652, JP-A-62-95225, JP-A-62-95226 and the like. An acid polymer,
A composition with a low molecular weight compound consisting of an aromatic aldehyde or ketone which may have a substituent capable of photoreacting with the double bond, or a polymer having a cinnamoyl group as a side chain and cinnamic acid or a derivative thereof. A photosensitive resin composition composed of a combination of

The light-scattering plate used in the present invention may be any as long as it has a capability of transmitting parallel light emitted from a light source in a scattered state, and other materials such as frosted glass having the surface of a transparent substrate as a scattering surface. Alternatively, it may be a transparent plate in which a light-scattering substance such as particulate titanium oxide is dispersed.

〔Example〕

As a photosensitive resin, an equimolar copolymer of methylmethacrylate and crotylmethacrylate was synthesized, and the crotylmethacrylate component in this copolymer was added to an equimolar amount of benzophenone to prepare a 4% by weight benzene solution. This solution was applied to the glass substrate 1 by spin coating to form the photosensitive film 2. Next, a frosted glass 5 is installed between the ultra-high pressure mercury lamp 3 which is a light source and the photomask 4, and the benzophenone is bonded to the crotylmethacrylate component by proximity exposure for 3 minutes with the gap g between the photomask 4 and the photosensitive film 2 set to 200 μm. Let By this method, the intensity distribution of ultraviolet rays on the surface of the photosensitive film becomes sinusoidal. Finally, the sample was heated under reduced pressure at 0.2 mmHg and 100 ° C. to sublimate the unreacted benzophenone, and the sinusoidal diffraction grating 6 was produced.

In the above embodiment, the distance between the photomask and the photosensitive film is 200 μm.
However, the cross-sectional shape of the diffraction grating can be made into a trapezoidal wave shape, a sine wave shape, a triangular wave shape or the like by changing this interval.

〔The invention's effect〕

As described above, by installing a light scattering plate having a function of scattering light between the light source and the photomask or between the photomask and the photosensitive film, a diffraction grating having a trapezoidal or sinusoidal cross section is produced. As a result, the light intensity of high-order diffracted light of ± 2nd order or higher can be reduced, which can be useful for improving the characteristics of optoelectronic products such as CD players and video cameras.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of a method for producing a diffraction grating according to the present invention, and FIG. 2 shows a conventional method for producing a diffraction grating. 1, 11 ... Transparent substrate 2, 12 ... Photosensitive film 3 ... Light source 4, 14 ... Photo mask 5 ... Light scattering plate 6, 17 ... Diffraction grating 13 ... Transparent dielectric film

Claims (4)

[Claims] 1. An exposure device provided with a light scattering plate having a function of scattering light between a light source and a photomask, or between a photomask and a photosensitive film, wherein light generated by the light source is used as a photomask for a diffraction grating and a light. A method for producing a diffraction grating, which comprises exposing a photosensitive resin selectively by passing through a scattering plate, and then developing. 2. The cross-sectional shape of the obtained diffraction grating is a triangular plate shape or a trapezoidal wave shape by adjusting the distance between the photomask and the photosensitive film to make the light intensity distribution triangular, trapezoidal or sinusoidal. Alternatively, the method for producing a diffraction grating according to claim 1, wherein the diffraction grating has a sinusoidal shape. 3. An exposure apparatus, wherein a light scattering plate having a function of scattering light is provided between the light source and the photomask or between the photomask and the photosensitive film. 4. A distance between a photomask and a photosensitive film can be adjusted, and by adjusting the distance, the intensity distribution of light reaching the photosensitive film can be adjusted to a trapezoidal wave shape, a sine wave shape, a triangular wave shape, or the like. The exposure apparatus according to claim 3, which is characterized in that.