JP2003172639A - Production method for sine wave shape optical grating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method for scale of an optical encoder provided with a sine wave shape diffraction grating on a glass board. <P>SOLUTION: Resist is spread on a glass board surface which is exposed to relatively low energy using a rectangular mask. The resist after developing is baked in a temperature over the glass transition point to be softened to be sine wave shape. Then, low pressure/high density plasma etching is applied to the resist surface so that glass is ground and the sine wave shape is transcribed to the glass board. Furthermore, if the same production method is performed by changing the mask on which a pattern is arranged in two-dimensional matrix, an optical grating with two-dimensional sine wave shape can be produced. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a scale used in an optical encoder, and more particularly to a method for manufacturing a glass scale having a sinusoidal diffraction grating on its surface.

[0002]

BACKGROUND ART A linear encoder is used to measure the displacement amount and position of a drive shaft of a machine tool or a coordinate measuring machine. A photoelectric conversion method, that is, a so-called photoelectric encoder is used in many of the linear encoders. In general, this photoelectric encoder is provided with a scale having an optical grating and a detection head that is arranged so as to face the scale and is capable of relative displacement and that has a light source, an index scale, and a light receiving element inside. . Usually the above scale is
Like a scale 40 shown in FIG. 6, it is composed of a glass substrate 41 and a rectangular optical grating 42 provided on the glass substrate 41 and having a predetermined pitch.

The optical encoder has a reflection type in which light is emitted from the detection head to the optical grating and reflected by a light receiving element and photoelectrically converted, and a light is emitted from the detection head to the optical grating and transmitted. There are two types of transmission type in which a light receiving element receives light and photoelectrically converts it. In any case,
Since the optical grating provided on the scale is rectangular as described above, the detection signal obtained from the light receiving element along with the relative movement of the detection head and the scale is a triangular wave, or this triangular wave is affected by the diffracted light in the optical grating. Becomes a pseudo sine wave by adding.

This detection signal is often interpolated by an interpolation division circuit in order to improve the resolution of relative displacement detection between the scale and the detection head. For that purpose, the sine wave signal is more suitable than the triangular wave for the interpolation division processing with higher accuracy. However, since the pseudo sine wave detection signal described above is based on a triangular wave signal, it deviates from an ideal sine wave signal, that is, the waveform distortion is large, and its distortion rate is particularly affected by fluctuations in the interval between the scale and the index scale. It fluctuates greatly due to it. As a technique for reducing the measurement error due to the waveform distortion of such a detection signal, a technique in which the grid pattern on the scale itself has a sine wave shape is also proposed (see US Pat. No. 4,782,229). However, in reality, the influence of diffracted light is large and the waveform distortion cannot be eliminated so much. Also,
Since it is difficult to make this grating pattern small in manufacturing, it is not suitable for manufacturing a scale of a high resolution type optical encoder.

[0005]

Therefore, for the reason that higher diffraction efficiency can be obtained, the appearance of a sinusoidal diffraction grating having fine sinusoidal irregularities on the scale surface itself has been long awaited. Generally, lithography, machining, and a molding method using a mold are used as means for producing an optical grating having a fine pitch. Photolithography and molding methods have the advantage that multiple scales can be manufactured at one time, but since resin such as photoresist is used as the grid material, the grid material expands and contracts due to changes in temperature and humidity, and measurement accuracy deteriorates. There is a problem. Further, there is a problem that the rigidity is insufficient to be adopted as a scale for a linear encoder of a machine tool or the like that is driven at high speed. On the other hand, when an optical grating is fabricated on a glass substrate by mechanical processing, the rigidity of the scale does not pose a problem, but the problem of sine wave processing accuracy and the difficulty of mass production because individual fine grooves are processed one by one. There is. The present invention has been made to solve such problems, and an object thereof is to provide a manufacturing method for forming a sinusoidal optical grating on a glass substrate.

[0006]

In order to achieve the above object, the present invention uses a rectangular mask in which a resist is applied to a glass substrate and the resist is periodically arranged at a predetermined pitch. To expose the resist, and to bake the resist at a temperature equal to or higher than the glass transition point in order to smooth the unevenness in cross section formed after the development of the resist, and to transfer the unevenness in cross section of the resist onto the surface of the glass substrate, It is characterized in that a sinusoidal optical grating is manufactured by performing low-pressure high-density plasma etching on the resist surface.

Further, in addition to the above means, the present invention is characterized in that a sinusoidal optical grating is manufactured by forming a reflective film on the uneven surface of the glass substrate surface by a vacuum deposition method.

In addition to the above means, the present invention applies a resist to a glass substrate and exposes the resist using a mask in which islands are arranged in a two-dimensional matrix periodically at a predetermined pitch. The resist is baked at a temperature equal to or higher than the glass transition point in order to smooth the uneven profile formed after development, and a low pressure is applied to the resist surface to transfer the uneven profile of the resist onto the glass substrate surface. A sine wave shaped optical grating is manufactured by irradiating high density plasma etching.

In addition to the above-mentioned means, the present invention is characterized in that a sinusoidal optical grating is manufactured by further forming a reflective film on the uneven surface of the glass substrate by a vacuum deposition method.

As described above, the resist is once coated on the surface of the glass substrate, and the resist is exposed using a rectangular mask periodically arranged at a predetermined pitch with a relatively low energy, and the resist is periodically cross-sectioned. The resist is softened to have a smooth pseudo-sinusoidal shape by baking the resist at a temperature equal to or higher than the glass transition point after forming the uneven shape. After that, by performing low-pressure high-density plasma etching on the resist surface, the resist and the glass are gradually shaved and this pseudo sine wave shape is transferred to the glass substrate, and an optical grating having a sine wave shape is formed on the glass substrate surface. It can be manufactured. Further, it is also possible to easily attach a metal reflection film to the surface of the sine wave shaped glass substrate by a vacuum deposition method.
Furthermore, if the mask is replaced with a mask in which islands are arranged in a two-dimensional matrix and the same manufacturing method as described above is carried out, the sponge for washing dishes has a two-dimensional sinusoidal shape similar to the uneven shape provided on the surface. Optical gratings can be manufactured.

[0011]

Preferred embodiments of the present invention will be described below with reference to the drawings. In all the drawings, the same reference numerals represent the same constituent elements. (First Embodiment) FIG. 1 is a schematic view for explaining a manufacturing procedure of a sinusoidal optical grating according to the present invention. First, as shown in FIG. 1A, a resist 21 is applied on the upper surface of the glass substrate 2. By adjusting the type of resist applied here and the film thickness of the resist, the sine wave shape to be finally formed can be controlled to some extent. For example, when it is desired to make the height difference of the cross-sectional shape of the grating relatively large, that is, to make the amplitude of the sine wave shape large, it is preferable to use a high contrast type resist and also to make the film thickness relatively thick. Conversely, if you want to make the height difference of the cross-sectional shape of the grating relatively small, that is, to reduce the amplitude of the sine wave shape, it is preferable to use a low-contrast type resist, and it is not necessary to configure the film thickness too much. .

Next, as shown in FIG. 7, a glass mask 5 in which openings 51 of an elongated rectangular lattice are arranged at a predetermined pitch.
3 is used to expose the resist 21. The glass mask 53 is a mask 50 in which a metal such as Cr is deposited on the surface of the glass substrate 52 by vapor deposition so that the rectangular openings 51 are periodically arranged at a predetermined pitch on the glass substrate 52. It is configured to be equipped. Next, the resist 21 is developed to obtain a grating 22 made of the resist as shown in FIG. However, at this time, it is necessary to adjust the exposure amount so that the bottom of the grating 22 made of resist does not reach the glass substrate so that the sine wave amplitude is not saturated.

Next, the resist 21 is baked at a temperature equal to or higher than the glass transition point, and the shape of the resist cross section is shown in FIG.
It is smoothed so as to obtain the sine wave shape 23 shown in (c). This baking melts the surface of the resist 21 to obtain a smooth shape. As a result, the sinusoidal shape transferred to the glass substrate is formed by the resist.

Next, the resist shape is transferred to the glass substrate by using an anisotropic dry etching method such as low pressure high density plasma etching. That is, by irradiating the etching gas ions generated by the low-pressure high-density plasma perpendicularly to the resist surface, the resist film is gradually abraded as in the eroded sinusoidal shape 24 shown in FIG. At the same time, the glass substrate is gradually shaved in the portion where the resist is gone. Therefore, the shape of the sine wave shape 23 formed on the resist 21 is finally transferred to the glass substrate, and the sine wave shape optical grating 7 as shown in FIG. 1E is formed on the glass substrate. It is formed. CF is used for this low pressure high density plasma etching.
It is preferable to use a system gas.

The glass substrate 2 provided with the sinusoidal optical grating 7 produced as described above can be used as it is as a scale of a transmission type optical encoder, but it is also used as a main scale of a reflection type optical encoder. If
As shown in FIG. 2, a sinusoidal optical grating 7 is formed by vacuum deposition or the like.
It is preferable to provide a reflective film 26 on the upper surface of the. The material of the reflection film 26 is not particularly limited as long as a desired reflectance can be obtained, but is made of a material such as Cr which has excellent mechanical rigidity, is chemically stable, and has excellent adhesiveness to a glass substrate. Preferably.

Next, a reflective optical encoder having a scale manufactured according to the present invention will be described with reference to FIG. The reflective optical encoder 1 includes a scale 8 having a sinusoidal optical grating 7 on the surface of a glass substrate,
The detection head 3 is provided so as to face the scale 8 and to be relatively movable along the direction of the measurement axis 6 in the drawing. Irradiation light 4 is emitted from a light source (not shown) provided inside the detection head 3 toward a sine wave shaped optical grating 7 having a reflective film on the surface thereof.
The reflected light 5 reflected by is received by a light receiving element (not shown) inside the detection head 3, photoelectrically converted, and a detection signal is output. Along with the relative movement of the detection head 3 and the scale 8, a sinusoidal detection signal is output based on the pitch of the sinusoidal optical grating 7. By further interpolating and dividing this detection signal, it is possible to detect the position and displacement with high resolution and precision. Since the optical grating of the scale 8 originally has a sine wave shape, the detection signal output from the light receiving element is a substantially ideal sine wave shape signal. Therefore, compared with a triangular wave shape signal or a pseudo sine wave shape signal that contains a lot of distortion components, it is possible to perform more accurate interpolation division and to configure a high accuracy type reflective optical encoder. .

Next, a transmissive optical encoder having a scale manufactured according to the present invention will be described with reference to FIG. This transmission type optical encoder 10 includes a scale 8 having a sinusoidal optical grating 7 on the surface of a glass substrate.
And facing the scale 8 and the measuring axis 6 in the figure
Detection head 1 arranged so as to be movable relative to each other
5 is provided. A light source (not shown) provided inside the light source unit 11 of the detection head 15 emits light 13 toward the sinusoidal optical grating 7, and the transmitted light 14 transmitted through the sinusoidal optical grating 7 is opened. The detection head 15 through the part 16
The light receiving element (not shown) provided inside the light receiving section 12 receives the light, photoelectrically converts it, and outputs a detection signal. Along with the relative movement of the detection head 15 and the scale 8, a sinusoidal detection signal is output based on the pitch of the sinusoidal optical grating 7. By further interpolating this detection signal, it is possible to accurately detect the position and displacement. Since the optical grating of the scale 8 originally has a sine wave shape, the detection signal output from the light receiving element is a substantially ideal sine wave shape signal. For this reason, it is possible to perform a more accurate interpolation division compared to a triangular wave shape signal or a pseudo sine wave shape signal that contains a lot of distortion components, and thus it is possible to configure a high accuracy type transmission optical encoder. .

(Second Embodiment) In the first embodiment, a method of manufacturing a sinusoidal optical grating having a scale suitable for an optical encoder capable of measuring along one measuring axis has been described. Can be applied to manufacture a two-dimensional sinusoidal optical grating on a two-dimensional scale suitable for a so-called two-dimensional optical encoder capable of measuring along two measurement axes.

FIG. 5 shows the two-dimensional sinusoidal optical grating 31.
2 shows a two-dimensional scale 30 provided on the glass substrate 2.
The manufacturing method is substantially the same as that of the first embodiment, but the pattern of the mask used during exposure is different. That is, when manufacturing the two-dimensional sinusoidal optical grating 31, the glass mask 63 as shown in FIG. 8 is used for exposure. The glass mask 63 is formed by vapor-depositing a metal such as Cr on the surface of the glass substrate 62 so that the island-shaped openings 61 are periodically arranged in a two-dimensional matrix on the glass substrate 62 at a predetermined pitch in the vertical and horizontal directions. It is configured to include a worn mask 60. Although the square opening 61 is shown in FIG. 8, it may be a circular opening.

After this, the manufacturing method of the first embodiment is exactly the same, and the completed two-dimensional sinusoidal optical grating 3
As shown in FIG. 5, 1 has a shape in which projections are arranged vertically and horizontally at a predetermined pitch like a sponge for washing dishes. Furthermore, if a metal thin film such as Cr is attached as a reflective film on the surface of the two-dimensional sinusoidal optical grating 31 by the vacuum deposition method or the like as in the first embodiment, the two-dimensional of the reflective two-dimensional optical encoder is obtained. It can be configured as a scale.

[0021]

According to the present invention, a sinusoidal optical grating can be formed on a glass substrate having high mechanical rigidity as a scale of a reflective or transmissive optical encoder. Furthermore, 2 as a two-dimensional scale of a two-dimensional optical encoder
Dimensional sinusoidal optical gratings can also be constructed.

[Brief description of drawings]

FIG. 1 is a schematic view showing a manufacturing procedure of a sinusoidal optical grating according to the present invention.

FIG. 2 is a schematic view showing a sinusoidal optical grating provided with a reflective film according to the present invention.

FIG. 3 is a schematic view showing an example in which the sinusoidal optical grating according to the present invention is used for a scale of a reflective optical encoder.

FIG. 4 is a schematic view showing an example in which a sinusoidal optical grating according to the present invention is used as a scale of a transmissive optical encoder.

FIG. 5 is a schematic view of a two-dimensional scale equipped with a two-dimensional sinusoidal optical grating according to the present invention.

FIG. 6 is a schematic view of a scale provided with a conventional rectangular optical grating.

FIG. 7 is a schematic view of a rectangular lattice glass mask according to the first embodiment of the present invention.

FIG. 8 is a schematic view of an island-shaped grating glass mask according to a second embodiment of the present invention.

[Explanation of symbols]

1 Reflective optical encoder 2,41 glass substrate 3,15 Detection head 7 Sinusoidal optical grating 8,40 scale 10 Transmissive optical encoder 21 Resist 23, 24 sine wave shape 26 Reflective film Two-dimensional sinusoidal optical grating 53,63 glass mask

Claims (4)

[Claims] 1. A resist is applied to a glass substrate, and the resist is exposed by using a rectangular mask periodically arranged at a predetermined pitch to smooth the uneven shape of a cross section formed after the resist is developed. For this purpose, the resist is baked at a temperature equal to or higher than the glass transition point, and low-pressure high-density plasma etching is performed on the resist surface in order to transfer the uneven profile of the resist onto the glass substrate surface. Manufacturing method of sinusoidal optical grating. 2. The method of manufacturing a sinusoidal optical grating according to claim 1, further comprising forming a reflective film on the uneven surface of the glass substrate surface by a vacuum deposition method. 3. A glass substrate is coated with a resist, and the resist is exposed to light using a mask in which islands are arranged in a two-dimensional matrix periodically at a predetermined pitch. Baking the resist at a temperature above the glass transition point for smoothing, and performing low-pressure high-density plasma etching on the resist surface in order to transfer the uneven cross-sectional shape of the resist to the glass substrate surface. A method for manufacturing a characteristic sinusoidal optical grating. 4. The method for manufacturing a sinusoidal optical grating according to claim 3, further comprising forming a reflective film on the uneven surface of the glass substrate by a vacuum vapor deposition method.