JP2005091001A - Scale manufacturing method and photoelectric encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for scales having an optical grating made of chrome with a uniform machined depth. <P>SOLUTION: A first chrome layer 21 is deposited onto a substrate 17 through the use of an ion plating system. A second chrome layer 23 is deposited by lowering the power of the system. The first chrome layer 21 having a low etching rate is used as an etching stopper, the second chrome layer 23 having a higher etching rate is selectively etched to form an optical grating 19. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a photoelectric encoder used for precision measurement and a method for producing a scale as a component of the photoelectric encoder.

  Conventionally, a photoelectric encoder (hereinafter also referred to as “encoder”) has been used for precise measurement of linear displacement and angular displacement. The encoder is mounted on a coordinate measuring machine or an image measuring machine. The measurement by the encoder will be briefly described as follows.

  While moving the light source unit and the light receiving unit relative to the scale, the optical grating of the scale is irradiated with light from the light source unit through the index grating. A plurality of (for example, four) sinusoidal optical signals generated in this manner are received by a plurality of photodiodes (light receiving portions) corresponding to the respective phases, and electric signals generated by photoelectric conversion are used. Then, the amount of displacement such as a straight line is measured.

  Now, in the encoder, (a) the light applied to the optical grating is transmitted through the scale, and the transmitted light is used for measurement, and (b) the light applied to the optical grating is reflected by the scale, There is a reflection type that uses this reflected light for measurement. Chromium is often used as a material for reflective optical gratings. This is because chromium has an advantage of excellent adhesion to glass, moderate light reflectance, good workability, and difficult oxidation.

  The reflection type optical grating has a structure in which irregularities are regularly provided on a light reflection layer such as a chromium layer. If unevenness occurs in the processing depth when the irregularities are formed in the light reflecting layer, the in-plane distribution and the variation in repeatability increase. Here, the variation in the in-plane distribution means that the processing depth varies depending on the position in one optical grating. In addition, the variation in repeatability means that the processing depth differs between a plurality of optical gratings. Since the optical signal received by the light receiving unit is generated by the optical grating of the scale, the above variation hinders improvement in measurement accuracy.

As a method of making the processing depth of the diffraction grating (optical grating) uniform, a silicon oxide film formed on the silicon substrate using the difference in etching rate between the silicon substrate and the silicon oxide film and using the silicon substrate as an etching stopper There is a technique for forming unevenness to be a diffraction grating by selectively etching (see Patent Document 1).
Japanese Patent Laid-Open No. 7-113905 (paragraph [0043], FIG. 1)

  However, since the silicon oxide film is transparent, it is necessary to further form a reflective film on the optical grating in order to make it reflective.

  An object of this invention is to provide the manufacturing method of the scale which has a chromium-made optical grating with uniform processing depth, and a photoelectric encoder provided with this scale.

  A photoelectric encoder according to the present invention includes a first chrome layer and a reflective optical grating having a second chrome layer that is selectively formed on the first chrome layer and has a higher etching rate than the first chrome layer. , A light source unit that generates light to irradiate the optical grating, light received from the light source unit reflected or diffracted by the optical grating, and movable relative to the scale together with the light source unit A light receiving unit.

  According to the photoelectric encoder of the present invention, since the second chrome layer has a higher etching rate than the first chrome layer, the second chrome layer is patterned using the first chrome layer as an etching stopper to form an optical grating. Can be formed.

  In the photoelectric encoder according to the present invention, the second chrome layer can have a light reflectance lower than that of the first chrome layer. When the first and second chromium layers are formed by, for example, an ion plating method, the chromium layer having a low light reflectance (second chromium layer) is a chromium layer having a high light reflectance (first chromium layer). ), The etching rate is increased.

  In the photoelectric encoder according to the present invention, the scale may be formed with a light reflecting layer covering the first and second chromium layers. According to this, even if the light reflectance differs between the first chromium layer and the second chromium layer, the light reflectance of the optical grating can be made uniform.

  The photoelectric encoder scale manufacturing method according to the present invention includes a first step of forming a first chromium layer on a substrate by using an ion plating method, and lowering the power of the film forming apparatus than the first step. A reflective optical grating by selectively etching the second chromium layer using the first chromium layer as an etching stopper, and a second step of forming a second chromium layer on the first chromium layer. And a third step of forming.

  According to the scale manufacturing method of the present invention, the second chromium layer is formed by lowering the power of the film forming apparatus than the formation of the first chromium layer. Thereby, the etching rate of the second chromium layer can be made larger than that of the first chromium layer. Therefore, when a reflective optical grating is formed by selectively etching the second chrome layer using the first chrome layer as an etching stopper, the processing depth of the groove (second chrome layer) of the optical grating can be reduced. It can be made uniform.

  In the scale manufacturing method according to the present invention, the first and second chromium layers can be formed in the same vacuum. According to this, since the first and second chromium layers can be formed without taking the scale substrate out of the chamber, the adhesion between the first chromium layer and the second chromium layer is excellent. Become.

  In the scale manufacturing method according to the present invention, a sputtering method may be used for the film formation in the second step. According to this, while making the etching rate of the second chromium layer larger than that of the first chromium layer, the light reflectance of these chromium layers can be made equal. Therefore, it is possible to produce a scale including an optical grating with uniform light reflectance while eliminating variations in the processing depth of the grooves of the optical grating.

  According to the present invention, the optical grating can be formed by patterning the second chromium layer using the first chromium layer as an etching stopper. Therefore, the processing depth of the grooves of the optical grating can be made uniform.

  Hereinafter, an embodiment of the present invention (hereinafter referred to as the present embodiment) will be described with reference to the drawings. First, the configuration of the photoelectric encoder 1 according to this embodiment will be described. FIG. 1 is a diagram illustrating a schematic configuration of the encoder 1. The encoder 1 includes a light source unit 3, a scale 5 including an optical grating irradiated with the light generated here, and a light receiving unit 7 that receives light reflected or diffracted by the optical grating.

  The light source unit 3 includes a light emitting diode (LED) 9. Further, the light source unit 3 includes an index grating 11 disposed at a position where light from the light emitting diode 9 is irradiated. The index grating 11 is formed on the surface of the long transparent substrate 13 opposite to the surface facing the light emitting diode 9 side. The index lattice 11 has a plurality of light shielding portions 15 arranged in a linear manner with a predetermined pitch.

  A scale 5 is disposed on the transparent substrate 13 on the index grating 11 side with a predetermined gap from the grating 11. The scale 5 has a dimension in the longitudinal direction larger than that of the index lattice 11, and a part of the scale 5 appears in FIG. FIG. 2 is an enlarged sectional view of a part of the scale 5. The structure of the scale 5 will be described in detail with reference to FIGS. 1 and 2.

  The scale 5 includes a long substrate 17 made of glass, silicon or the like. One surface of the substrate 17 faces the index grating 11. An optical grating 19 is disposed on this one surface. Light from the light source unit 3 is applied to the optical grating 19 via the index grating 11. The optical grating 19 includes a first chrome layer 21 as a base and a second chrome layer 23 selectively formed thereon. The first chrome layer 21 and the second chrome layer 23 form an uneven pattern. The second chrome layer 23 has a higher etching rate than the first chrome layer 21. This is because the formation conditions of these chromium layers are different, as will be described later.

  Next, the light receiving unit 7 will be described with reference to FIG. The light receiving unit 7 is arranged with a predetermined gap on the surface side of the transparent substrate 13 on which the optical grating 19 is formed. The light receiving unit 7 includes a plurality of photodiodes 25 arranged such that the light receiving surface faces the optical grating 19 side. Thereby, the light from the light source unit 3 reflected or diffracted by the optical grating 19 is received by the photodiode 25. The plurality of photodiodes 25 are arranged on the transparent substrate 13 in a linear manner with a predetermined pitch. Therefore, in this embodiment, the light receiving unit 7 and the index grating 11 are formed on the same transparent substrate 13. In addition to the structure in which the plurality of photodiodes 25 are arranged, a structure in which an index grating is provided on the entire surface of one large light receiving element may be used. In this case, the index lattice 11 is not necessary.

  The transparent substrate 13 including the light receiving unit 7 and the index grating 11 and the light emitting diode 9 are housed in a housing (not shown), and this housing can be moved along the measurement axis x corresponding to the longitudinal direction of the scale 5. ing. The scale may be movable and the housing may be fixed. That is, the scale 5 is movable relative to the casing along the measurement axis x.

  Next, the measurement operation of the photoelectric encoder 1 will be described. When light is emitted from the light emitting diode 9 to the index grating 11, diffracted light is generated by the grating 11. And if the said housing | casing containing the light source part 3 and the light-receiving part 7 is moved along the measurement axis x, the change of a light-dark pattern (sine wave-like optical signal) will arise by interference. Specifically, the brightness of the light interfered by the phase difference between the light reflected by the first chrome layer 21 (for example, light L1) and the light reflected or diffracted by the second chrome layer 23 (for example, light L2). A signal is generated. The optical grating 19 functions as a phase grating.

  This signal is an A phase (0 degree) optical signal, a B phase (90 degree) optical signal that is 90 degrees out of phase with the A phase, and an AA phase (180 degree) that is 180 degrees out of phase with the A phase. And an optical signal of BB phase (270 degrees) whose phase is shifted by 270 degrees from the A phase, and are detected by the photodiodes 25 corresponding thereto.

  An electrical signal generated by each photodiode 25 is sent to an IC chip (not shown). In the IC chip, a predetermined amount of processing (DC component removal or the like) is performed on the A phase and the B phase, and then the displacement amount is calculated based on the processed A phase and B phase. The result is output to a display unit (not shown). The above is the operation of the photoelectric encoder 1.

  In the present embodiment, the first and second chromium layers 21 and 23 are formed by an ion plating method. FIG. 3 is a schematic diagram of an ion plating apparatus 51 (an example of a film forming apparatus) used for forming the first and second chromium layers 21 and 23. The apparatus 51 includes a vacuum chamber 53 and a susceptor 55 that is disposed in the upper portion of the chamber 53 and holds the scale substrate 17. The susceptor 55 is connected to a direct current power source 57 disposed outside the vacuum chamber 53. In the lower part of the vacuum chamber 53, a crucible 61 containing a vapor deposition source (chrome) 59 is disposed. A spiral electrode 63 is disposed between the crucible 61 and the susceptor 55. The spiral electrode 63 is connected to a high frequency power supply 65 provided outside the vacuum chamber 53 via a high frequency matching circuit 67.

  An example of a method for manufacturing the scale 5 according to the present embodiment using the device 51 will be described in detail. 4 to 6 are process diagrams for explaining this, and correspond to the sectional view of FIG.

  First, the substrate 17 shown in FIG. 4 is held by the susceptor 55 shown in FIG. An inert gas is introduced into the vacuum chamber 53. Then, the evaporation source (chromium) 59 is heated and evaporated by an electron beam or induction heating. In this state, the high frequency power supply 65 supplies a high frequency of 13.56 MHz and power (that is, power) of 500 to 1000 W to the spiral electrode 63. As a result, a discharge is generated in the vacuum chamber 53 and the evaporated chromium is ionized. This is deposited on the substrate 17 by being drawn toward the susceptor 55 to which a DC voltage is applied from the DC power source 57. As a result, as shown in FIG. 4, a first chromium layer 21 having a thickness of 0.05 to 0.2 μm is formed on the substrate 17.

  Subsequently, the power of the device 51 is lowered, and a second chromium layer 23 having a thickness of 0.1 to 0.3 μm is formed on the first chromium layer 21 as shown in FIG. Specifically, to reduce power, do as follows. For example, the high frequency power supplied from the high frequency power supply 65 to the spiral electrode 63 is set to 100 to 0 W.

  Next, the substrate 17 in the state of FIG. 5 is taken out from the vacuum chamber 53, and a photoresist 27 is formed on the second chromium layer 23. Development is performed after exposing the photoresist 27 so as to correspond to the pattern of the optical grating. Then, the optical grating 19 is formed by selectively dry etching the second chromium layer 23 using the photoresist 27 as a mask and the first chromium layer 21 as an etching stopper. Etching conditions are, for example, as follows.

  Finally, the photoresist 27 remaining on the second chromium layer 23 is peeled off by an ordinary method, thereby completing the scale 5 shown in FIG.

  The effect of this embodiment will be described in comparison with a comparative example. FIG. 7 is an enlarged cross-sectional view of a part of the scale 71 according to the comparative example, and corresponds to FIG. In the scale 71, an optical grating 75 composed of a chromium layer 73 is formed on the substrate 17.

  The scale 71 is produced as follows. A chromium layer 73 is formed on the substrate 17 by an arbitrary film forming method such as an ion plating method or a sputtering method. The film forming conditions of the chromium layer 73 are constant, and the power is not changed midway as in the present embodiment. Then, the photoresist 27 shown in FIG. 6 is formed on the chromium layer 73 as in the present embodiment. Using the photoresist 27 as a mask, the chrome layer 73 is selectively dry-etched until the target processing depth is reached.

  However, since the etching speed varies depending on the position on the substrate 17, if there is no etching stopper as in the comparative example, the processing depth d of the groove of the optical grating 75 varies (in-plane distribution variation). In addition, since it is difficult to control etching accurately at a target processing depth, when there is no etching stopper as in the comparative example, the optical grating 75 is compared with an optical grating formed by the same method. , Processing depth d is different (variation in repeatability).

  On the other hand, according to the present embodiment, the second chromium layer 23 having an etching rate larger than that of the first chromium layer 21 is selectively etched using the first chromium layer 21 as an etching stopper. Therefore, by making the thickness of the second chromium layer 23 the same as the processing depth, as shown in FIG. 2, the optical grating 19 made of chromium having a uniform processing depth d of the groove of the optical grating 19 is produced. Can do. Therefore, since it is possible to eliminate large variations in the in-plane distribution and the repeatability of the optical grating 19, the measurement accuracy of the photoelectric encoder 1 can be improved.

  The first chromium layer 21 functions as an etching stopper. For this reason, the case where the first chromium layer 21 is not etched is included in the second chromium layer 23 having a higher etching rate than the first chromium layer 21.

  When both the first and second chromium layers 21 and 23 are formed by the ion plating method, the second chromium 23 has a light reflectance lower than that of the first chromium layer 21. The light reflectance of the second chromium 23 is, for example, 40%, whereas the light reflectance of the first chromium 21 is, for example, 55%. Thereby, it is estimated that the film quality of the 1st chromium layer 21 is dense, and the film quality of the 2nd chromium layer 23 is coarse. Therefore, when the first and second chromium layers 21 and 23 are formed by the ion plating method having different powers, the reason why the etching rates are different is considered to be due to the density. Here, the light reflectance can be defined by spectral reflectance (reflectance with respect to monochromatic light). The light reflectance is 40%. When the wavelength of incident light is, for example, 600 to 650 nm, the spectral reflectance is It means 40%.

  In the present embodiment, the first chrome layer 21 and the second chrome layer 23 have different light reflectivities. Therefore, as shown in FIG. 8, a third chromium layer 29 (an example of a light reflecting layer) is formed by ion plating or sputtering so as to cover the first and second chromium layers 21 and 23. Also good. Thereby, the reflectance of the light of the optical grating 19 can be made uniform, and the measurement accuracy can be further improved. The light reflecting layer is not limited to a chromium layer, and may be any material that has good adhesion with Cr, such as gold, has high light reflectivity, and is not easily oxidized.

  In the present embodiment, the first and second chromium layers 21 and 23 are formed in the vacuum chamber 53 (same vacuum) shown in FIG. Therefore, the first and second chromium layers 21 and 23 can be formed without taking the substrate 17 out of the chamber 53. Therefore, the adhesion between the first chromium layer 21 and the second chromium layer 23 is excellent.

  As a modification of the present embodiment, the second chromium layer 23 may be formed by a sputtering method. Hereinafter, modified examples will be described. FIG. 9 is a schematic view of a sputtering apparatus 81 that can be used in a modification. In the vacuum chamber 83 of the apparatus 81, a lower electrode 85 on which a substrate 17 on which a first chromium layer 21 (not shown) is formed is placed, an upper electrode 87 holding chromium as a target, Is arranged. The lower electrode 85 is connected to the high frequency power supply 89, and the upper electrode 87 is connected to the high frequency electrode 91. A gas introduction pipe 93 is connected to the vacuum chamber 83.

  The formation of the second chromium layer 23 using the sputtering apparatus 81 will be described. First, an inert gas is introduced from the gas introduction pipe 93 into the vacuum chamber 83 to make the inside of the chamber 83 an inert atmosphere. The high frequency power supply 91 supplies a high frequency with a frequency of 13.56 MHz and a power of 200 to 1000 W to the upper electrode 87. Thus, the second chromium layer 23 is formed on the first chromium layer 21 by sputtering as shown in FIG.

  According to the sputtering method, the etching rate of the second chromium layer 23 can be made larger than that of the first chromium layer 21, and the light reflectivity of these layers 21 and 23 can be made equal. Therefore, it is possible to produce the scale 5 including the optical grating 19 having a uniform light reflectance while eliminating variations in the processing depth of the grooves of the optical grating 19.

It is a figure which shows schematic structure of the photoelectric encoder which concerns on this embodiment. It is a partial expanded sectional view of the scale with which the photoelectric encoder which concerns on this embodiment is equipped. It is the schematic of the ion plating apparatus which can be used for manufacture of the scale which concerns on this embodiment. FIG. 3 is a first process diagram of a method for manufacturing the scale shown in FIG. 2. FIG. 3 is a second process diagram of the method for manufacturing the scale shown in FIG. 2. FIG. 4 is a third process diagram of the scale manufacturing method shown in FIG. 2. It is a partial expanded sectional view of the scale which concerns on a comparative example. In the photoelectric encoder which concerns on this embodiment, it is a partially expanded sectional view of the scale in which the 3rd chromium layer was formed. It is the schematic of the sputtering device which can be used with the modification of the manufacturing method of the scale which concerns on this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photoelectric encoder, 3 ... Light source part, 5 ... Scale, 7 ... Light-receiving part, 9 ... Light emitting diode, 11 ... Index grating | lattice, 13 ... Transparent substrate, 15 ... Light-shielding part, 17 ... Substrate, 19 ... Optical grating, 21 ... First chromium layer, 23 ... Second chromium layer, 25 ... Photodiode, 27 ... Photoresist, 29 ... third chromium layer, 51 ... ion plating apparatus, 53 ... vacuum chamber, 55 ... susceptor, 57 ... DC power supply, 59 ... evaporation source, 61 ... Crucible, 63 ... Spiral electrode, 65 ... High frequency power supply, 67 ... High frequency matching circuit, 71 ... Scale, 73 ... Chromium layer, 75 ... Optical grating, 81 ..・ Sputtering equipment, 83 ... Vacuum chamber, 85 ... Lower part Pole, 87 ... upper electrode, 91 ... high frequency power source, 93 ... gas inlet tube, d ... machining depth

Claims (6)

A scale on which a reflective optical grating having a first chromium layer and a second chromium layer selectively formed on the layer and having a higher etching rate than the first chromium layer is disposed;
A light source unit that generates light to irradiate the optical grating;
A light receiving unit that receives light from the light source unit reflected or diffracted by the optical grating and is movable relative to the scale together with the light source unit;
A photoelectric encoder comprising: The second chrome layer has a lower light reflectivity than the first chrome layer,
The photoelectric encoder according to claim 1. The scale is formed with a light reflecting layer covering the first and second chromium layers.
The photoelectric encoder according to claim 1, wherein the photoelectric encoder is a photoelectric encoder. A first step of forming a first chromium layer on the substrate using an ion plating method;
A second step of forming a second chromium layer on the first chromium layer by lowering the power of the film forming apparatus than in the first step;
A third step of forming a reflective optical grating by selectively etching the second chromium layer using the first chromium layer as an etching stopper;
A method for producing a scale of a photoelectric encoder, comprising: Sputtering is used for the film formation in the second step.
The method for manufacturing a scale of a photoelectric encoder according to claim 4. Forming the first and second chromium layers in the same vacuum;
The method for producing a scale of a photoelectric encoder according to claim 4 or 5.

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