JP2002350188A - Optical encoder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve an optical encoder where a semiconductor mobile plate having a light transmission lattice and a light receiving element can be manufactured with an improved yield by a manufacturing process. SOLUTION: The optical linear encoder 1 has the mobile plate 5 made of a silicon substrate where the light transmission lattice 3 and lattice-shaped photodiodes 4A and 4B are formed. The light transmission lattice 3 of the mobile plate 5 is formed by laminating a light-shielding film 42 made of an aluminum thin film on the surface of a light transmission thin-film section 41 being formed by etching the mobile plate 5. As compared with a case where the light transmission lattice is set to a slit formed on the semiconductor substrate, the etching process in the semiconductor substrate is simplified, and the decrease in the strength at the semiconductor substrate section where the light transmission lattice is formed can be inhibited. As a result, the mobile plate 5 can be manufactured by a simple process having an improved yield, thus manufacturing the optical linear encoder inexpensively and easily by that amount.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical encoder based on a three-grating theory, and more particularly, to an optical encoder configured so that a semiconductor substrate having a light transmission grating and a light receiving element can be easily manufactured. is there.

[0002]

2. Description of the Related Art One of the applicants of the present invention has previously disclosed in
Japanese Patent Publication No. 321097 proposes an optical encoder based on a three-grating theory. In this optical encoder, an LED as a light source, a moving plate made of a semiconductor substrate in which a light transmission grating and a light receiving element (photodiode) are formed at a constant pitch, and a reflection grating at a constant pitch are formed. LED with reflection grating plate
A moving plate is disposed between the reflection grating plate and the moving plate.

In the optical encoder having this configuration, the moving plate is integrated with the object to be measured, and is moved in a direction perpendicular to the optical axis of the light emitted from the LED, and in the direction in which the light transmission grating and the photodiode are arranged. . The light emitted from the LED first irradiates the back surface of the moving plate, passes through the light transmission grating formed on the moving plate, and irradiates the surface of the reflection grating plate in a checkerboard shape. Since the reflection gratings are also formed with the reflection gratings at a constant pitch, only the components of the light illuminating the reflection grating plate that are irradiated on the respective reflection gratings are reflected.
The reflection grating image irradiates the moving plate again, and is received by the vertically striped photodiode formed at a constant pitch and a constant width.

A light transmission grating in the form of a vertical stripe and a photodiode formed on a moving grating plate function as two grating plates.
Therefore, based on the theory of three gratings using a reflection grating, the amount of light received by the photodiode changes in a sinusoidal manner corresponding to the relative movement between the reflection grating plate and the moving grating plate. Therefore, a pulse signal corresponding to the relative moving speed can be obtained based on the photocurrent of the photodiode, and the relative moving speed can be calculated based on the pulse rate of the pulse signal.

If the photodiodes are arranged so that A-phase signals and B-phase signals having phases different from each other by 90 degrees can be obtained, the moving direction of the moving grating plate can be determined based on these two-phase signals.

As described above, in the optical encoder disclosed in the above publication, the light transmission grating and the light receiving element are manufactured by the semiconductor manufacturing technology, so that a grating with a minute pitch can be manufactured. A high-resolution encoder can be realized. In addition, since the light receiving elements formed in the form of vertical stripes at a constant pitch function as a grating, and the grating itself has a lens effect, it is not necessary to use a lens optical system, and the device can be downsized. Furthermore, according to the theory of the three lattices, the gap between the reflection grating and the light transmission grating is not widened and the fluctuation of the gap does not adversely affect the resolution, so that the mounting accuracy of the members in which these are formed is ensured. Adjustment work can be simplified, and restrictions on the mounting location are reduced. In addition, since the distance between the reflection grating and the light transmission grating can be increased, there is an advantage that, for example, the side of the reflection grating can be housed in a protective case or the like to improve environmental resistance.

[0007]

Here, the light transmission grating formed on the movable plate made of a semiconductor substrate has a structure in which the semiconductor substrate is etched to form fine light transmission grating slits at a fine pitch. It is said.

In order to form such a slit in a semiconductor substrate, for example, two-stage etching is required as follows. That is, it is necessary to form a thin film portion by performing anisotropic etching on the semiconductor substrate, and further perform dry etching such as ICP on the formed thin film portion to form a fine slit with high accuracy. It is preferable that the slit manufacturing process can be simplified because the production efficiency can be increased and the cost can be reduced.

In addition, since fine slits are formed at minute intervals in the thin film portion of the semiconductor substrate, there is a problem that the strength of this portion is weak and the yield is deteriorated.

[0010] The object of the present invention is to solve the above problems.
It is an object of the present invention to propose an optical encoder configured so that a light transmission grating can be formed in a semiconductor substrate by a simple process.

Another object of the present invention is to propose an optical encoder configured to suppress a decrease in strength of a portion of a semiconductor substrate on which a light transmission grating is formed.

[0012]

In order to solve the above-mentioned problems, the present invention provides a light source, a reflection grating having a predetermined shape arranged at a constant pitch, and a light beam having a predetermined shape arranged at a constant pitch. A transmission grating, having a light receiving element that receives the reflected light image emitted from the light source and transmitted through the light transmission grating and reflected by the reflection grating, based on a detection signal obtained from each light receiving element, at least, In an optical encoder for detecting a relative speed between the reflection grating and the light transmission grating: a reflection grating plate on which the reflection grating is formed, and a semiconductor substrate on which the light transmission grating and the light receiving element are formed. The semiconductor substrate has a light-transmitting region in which the light-transmitting gratings are arranged at a predetermined interval, and a first light-receiving element in which the light-receiving elements are formed at one side of the light-transmitting region and arranged at a predetermined interval. region A second light-receiving region formed on the other side of the light-transmitting region, wherein the light-receiving elements are arranged at predetermined intervals; and the light-transmitting grating is a light-transmitting thin-film portion formed on the semiconductor substrate. And a light shielding film arranged at a constant pitch on the surface of the thin film portion.

Here, the semiconductor substrate is generally a silicon substrate. In this case, the thickness of the thin film portion is 10 μm.
m.

In this case, if the central wavelength of the light emitted from the light source is 900 nm or more, the thin film portion can be a light transmitting portion substantially transparent to the emitted light.

Here, the light shielding film can be a metal thin film, for example, an aluminum thin film.

As described above, in the optical encoder of the present invention, instead of forming a slit as a light transmission grating in a semiconductor substrate, a thin film portion substantially transparent to emitted light is formed, and the thin film portion is formed. A light-transmitting grating is formed by forming a light-shielding film having openings patterned at a constant pitch on the surface. The thin film portion only needs to be subjected to etching such as wet etching once for the semiconductor substrate. Therefore, the manufacturing process of the light transmission grating can be simplified. Further, the strength of the portion of the semiconductor substrate on which the light transmission grating is formed is higher than that in the case where slits are formed at minute intervals, and the yield can be improved.

Next, an optical encoder according to the present invention has a light emitting diode as the light source and a holding substrate holding the light emitting diode, and the holding substrate has the light emitting diode mounted on a surface thereof. With a concave part,
It is desirable that the semiconductor substrate be laminated and adhered to the surface of the holding substrate. According to this configuration, a small and compact optical encoder can be realized.

On the other hand, a first detection signal obtained from each of the light receiving elements included in the first light receiving area is a second detection signal obtained from the light receiving element included in the second light receiving area.
It is desirable to set the relative positional relationship of the light receiving elements between the two light receiving regions so that the phase is shifted by 90 degrees with respect to the detection signal. This makes it possible to detect the relative movement direction between the reflection grating plate and the semiconductor substrate based on the two types of detection signals having different phases.

Here, in each of the first and second light receiving regions, light receiving elements may be arranged so that detection signals having a phase difference of 90 degrees can be obtained.

Next, since the light receiving elements are arranged at minute intervals, crosstalk between adjacent light receiving elements may increase. In order to prevent or suppress crosstalk, it is desirable to use a light receiving element having a pin structure. When a light receiving element having a pn structure is used, the distance between the light receiving elements is preferably at least 40 μm.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an optical linear encoder to which the present invention is applied will be described below with reference to the drawings.

FIG. 1 is a schematic configuration diagram showing an optical linear encoder of this embodiment. As shown in this figure, an optical linear encoder 1 has an LED 2 as a light source, a moving plate 5 composed of a semiconductor substrate on which a light transmission grating 3 and photodiode groups 4A and 4B are built, and a reflection grating 6 having a surface. And a control circuit section 8. The moving plate 5 of the present embodiment is a light source-integrated moving plate unit in which the LEDs 2 are integrated, as described later. The light emitted from the LED 2 passes through the light transmission grating 3 formed on the moving plate 5 and
The reflection grating 6 is irradiated. The reflected light image reflected by the reflection grating 6 is received by the photodiode groups 4A and 4B, and the detection signals of the respective photodiode groups 4A and 4B are transmitted to the control circuit unit 8.
Supplied to

The control circuit section 8 includes a photodiode group 4A,
A signal processing unit 9 for forming an A-phase signal and a B-phase signal whose phases are shifted by λλ based on the 4B detection signal, and the moving speed and the moving direction of the moving plate 5 based on these A-phase and B-phase signals; The system includes a calculation unit 10 for calculating movement information, a display unit 11 for displaying a calculation result, and a lamp drive unit 12 for feedback-controlling the driving of the LED 2.

FIGS. 2A to 2C are a schematic plan view showing a movable plate unit integrated with a light source, a schematic sectional view taken along line bb, and a schematic sectional view taken along line cc. It is an outline sectional view.

Referring to these drawings, the moving plate unit 20 of the present embodiment includes an LED holding plate 21 made of a silicon substrate and a silicon substrate laminated and adhered to the surface of the LED holding plate 21. And a moving plate 5 comprising: A recess 22 having a constant depth is formed on the surface of the LED holding plate 21, and the LED 2 is mounted therein. LED2 of this example is a surface light emitting diode,
For example, it has a structure in which a light emitting layer of GaAlAs is formed on an AuZn substrate. An infrared light emitting diode having a center wavelength band in a region of 900 nm or more.

The moving plate 5 is also formed of a silicon substrate, and its surface 23 has a light transmitting region 2 in which light transmitting gratings 3 having a constant width and a constant width are arranged at regular intervals in a central portion.
4 are formed. On the upper side of the light transmitting area 24,
First light receiving region 25 in which photodiode group 4A is arranged
Is formed, and a second light receiving region 26 in which the photodiodes 4B are arranged is also formed below the light transmitting region 24.

Photodiode group 4 in first light receiving area 25
A includes first and second photodiodes 31 and 32 arranged alternately, an A-phase signal is obtained from the first photodiode 31, and an inversion of the A-phase whose phase is inverted from the second photodiode 32. A signal is obtained. Similarly, the photodiode group 4 in the second light receiving region 26
B also includes third and fourth photodiodes 33 and 34 alternately arranged. From the third photodiode 33, a B-phase signal shifted by 90 degrees from the A-phase signal is obtained. An inverted signal of the B-phase signal is obtained from the photodiode 34.

Electrode wiring layers 35, 36, 37, and 38 made of an aluminum thin film are formed on the moving plate surface 23. The electrode wiring layers 35 are connected to the respective photodiodes 31 from which an A-phase signal can be obtained. The layer 36 is connected to each photodiode 32 from which an A-phase inverted signal is obtained, the electrode wiring layer 37 is connected to each photodiode 33 from which a B-phase signal is obtained, and the electrode wiring layer 38 is obtained from a B-phase inverted signal. It is connected to a photodiode 34.

Next, FIG. 3 is an enlarged partial sectional view of the light transmitting region 24 formed at the center of the moving plate surface 23. As can be seen from this figure, the light transmission region 24 of the present example
Is a thin film portion 41 formed by performing wet etching from the back surface side of the moving plate 5;
And the light-shielding film 42 laminated on the surface. The thin film portion 41 has a thickness of about 10 μm, and is substantially transparent to infrared light, particularly light having a wavelength of 900 nm or more.

On the surface of the thin film portion 41, the light transmission grating 3
The light-shielding film 42 in which the opening corresponding to is patterned. Therefore, the portion of the thin film portion 41 exposed from the opening of the light shielding film 42 functions as the light transmission grating 3. In this example, an aluminum thin film is used as the light shielding film 42. Metal thin films other than aluminum thin films can also be used.

FIG. 4 is an enlarged partial cross-sectional view showing the photodiodes 31 and 32 formed in the first light receiving region 25. The same applies to the case of the second light receiving region 26. As can be seen from this figure, a pin-junction photodiode 3 having a boron-doped layer 51 formed by doping boron from the surface of a moving plate 5 made of a silicon substrate.
1, 32 are built. Each photodiode 31,
The electrode wiring layers 35 and 36 made of aluminum are connected to the 32 boron-doped layer 51, and the common electrode layer 53 made of aluminum is connected to the n-layer side of the moving plate 5. The electrode wiring layers 35 and 36 are insulated from the movable plate 5 by an insulating layer 54 made of a silicon oxide film. Also,
The exposed surface of the moving plate 5 is covered with a silicon oxide film 55 to ensure durability. Similarly, the surface of the boron doped layer 51 is also covered with the silicon oxide film 56.

FIG. 5 is an explanatory diagram showing an arrangement relationship of the photodiodes 31 to 34 in the first and second light receiving regions 25 and 26. As shown in this figure, when the pitch of the light transmission grating 3 is P, the first light receiving region 2
5, the photodiodes 31 for outputting the A-phase signal are arranged at a pitch P, and between them, the photodiodes 32 for outputting the inverted signal of the A-phase are arranged at the same pitch P, and the pitch of the photodiodes 31 and 32 is P / P. It is 2.

Similarly, also in the second light receiving area 26, the photodiodes 33 for outputting the B-phase signal are arranged at a pitch P, and the photodiodes 34 for outputting the inverted signal of the B-phase are similarly arranged at the pitch P. And the pitch of the photodiodes 33 and 34 is P / 2.

Further, the first and second light receiving areas 2
Between the points 5 and 26, the distance between the photodiode 31 and the photodiode 33 is P / 4, and therefore, the distance between the photodiode 32 and the photodiode 34 is also P / 4.
It has become. Therefore, the A-phase signal and its inverted signal are obtained from the photodiodes 31 and 32, and the B-phase signal and its inverted signal are obtained from the photodiodes 33 and.

In the thus configured optical linear encoder 1 of the present embodiment, the movable plate 5 is connected to the object to be measured (not shown).
And moved in a direction perpendicular to the optical axis L and in the direction in which the slits and photodiodes are arranged.
The light emitted from the LED 2 first irradiates the back surface of the moving plate 5, passes through the light transmission grating 3 formed on the moving plate 5, and causes the reflection grating plate 7 arranged at a fixed position to form a grid stripe. Irradiation. Since the reflection gratings 6 having the same width are formed at a constant pitch also on the reflection grating plate 7, the reflection grating plate 7
Is reflected, only the component irradiated on each reflection grating 6 is reflected. The reflection grating image irradiates the moving plate 5 again, and is received by the photodiode groups 4A and 4B.

As described above, the vertical stripe light transmission grating 3 and the photodiode groups 4A and 4B formed on the moving plate 5 function as two grating plates. Therefore, based on the theory of three gratings using the reflection grating 6, the photodiode groups 4A, 4B
, The amount of received light changes in a sinusoidal manner corresponding to the relative movement between the fixed-side reflection grating 6 and the moving-side light transmission grating 3.
Therefore, a pulse signal corresponding to the relative moving speed can be obtained based on the photocurrents of the photodiode groups 4A and 4B,
The relative moving speed can be calculated based on the pulse rate of the pulse signal.

The A-phase signal can be obtained with high accuracy based on the outputs of the photodiodes 31 and 32 in the first light receiving area 25, and the photodiode 3 in the second light receiving area 26 can be obtained.
The B-phase signal can be obtained with high accuracy based on the outputs of the signals 3 and 34. The moving direction of the moving plate 5 can also be determined based on these two-phase signals.

Here, the optical linear encoder 1 of this embodiment
Then, the light transmitting thin film portion 41 is formed by etching the moving plate 5 which is a semiconductor substrate.
By laminating a light-shielding film 42 in which openings corresponding to the light transmission grating are patterned on the surface of
Is formed.

Therefore, it is not necessary to perform a plurality of etching steps as in the case where the through hole formed in the semiconductor substrate is used as a light transmission grating. Further, the light-shielding film 42 may be formed simultaneously with the formation of the aluminum thin film used as the wiring layer. Therefore, the manufacturing process of the movable plate 5 having the light transmission grating can be simplified.

Further, since the portion where the light transmission grating is formed is a thin film portion, a decrease in strength can be suppressed as compared with the case where a through hole is formed. Therefore, compared with the case where a through hole is formed,
A moving plate can be manufactured with good yield.

Further, in this embodiment, the photodiodes 31 to 34 having a pin structure are used, and there is an advantage that crosstalk can be suppressed as compared with the case where a pn structure photodiode is used.

That is, when a long-wavelength light is used as in this example, if a photodiode having a pn structure is used, more than 10% of the power reaches even at a depth of about 40 μm from the silicon surface. When the pitch of the photodiodes is about 10 μm, the carriers generated by light irradiation are directed toward the light receiving portion on the surface by diffusion, so that the separation characteristics between the photodiodes arranged adjacently deteriorate, and so-called crosstalk increases. I will.

However, in this embodiment, since a photodiode having a pin structure is used, such crosstalk can be suppressed. For example, in the photodiodes 31 to 34 of this example, the n-layer has a high concentration of about 1E17 cm −3 or more, the i-layer has a concentration of about 2E13 cm −3 at a maximum and a thickness of about 30 μm, and a reverse bias of about 15 V is applied. Shall be. In this case, the i-layer is depleted, so that carriers generated in the i-layer do not cause crosstalk. Carriers generated by the incident power that reaches the n-layer through the i-layer disappear in a relatively short time because the n-layer has a high concentration. Therefore, crosstalk hardly occurs.

The photodiode pitch is 40 μm.
In the case where it is sufficiently larger than the above, there is no need to worry about crosstalk, and for example, a pn junction photodiode as shown in FIG. 6 can be used. In FIG. 6, parts corresponding to the parts shown in FIG. 4 are given the same numbers.

(Other Embodiments) In the above example, the reflection grating plate on which the reflection grating is formed is the fixed side. However, the reflection grating plate side is the moving side, and the moving plate side is the fixed side. It may be.

Although an LED is used as a light source in the above example, other light sources such as a laser light source can be used.

Further, the above example relates to a linear encoder, but the present invention is similarly applicable to a rotary encoder. In this case, the light transmission grating and the photodiode may be formed at regular angular intervals in the circumferential direction.

[0048]

As described above, according to the present invention, based on the three-grating theory, a light-receiving element receives a reflection grating image capable of detecting information relating to the relative movement between the reflection grating and the light transmission grating. In such an optical encoder, the light transmission grating and the light receiving element are formed on a common semiconductor substrate, and an opening corresponding to the light transmission grating is formed on the surface of the light transmitting thin film portion formed on the semiconductor substrate. The light-transmitting grating is formed by laminating a light-shielding film in which the portions are patterned.

Therefore, according to the present invention, the process of forming the light transmission grating can be simplified as compared with the case where the slit formed in the semiconductor substrate is used as the light transmission grating. Further, it is possible to suppress a decrease in the strength of the semiconductor substrate portion where the light transmission grating is formed.

Therefore, according to the present invention, a semiconductor substrate having a light transmission grating and a light receiving element can be manufactured with a high yield by a simple manufacturing process, and accordingly, an optical encoder can be manufactured simply and inexpensively. Becomes possible.

[Brief description of the drawings]

FIGS. 1A and 1B are schematic structural views showing an optical linear encoder based on a three-lattice theory to which the present invention is applied.

2 (a), (b) and (c) are schematic plan views showing a movable plate unit integrated with a light source in FIG. 1, a schematic sectional view of a portion cut along line bb, and cc. It is a schematic sectional drawing of the part cut | disconnected by the line.

FIG. 3 is an enlarged partial sectional view showing a portion of a light transmission grating formed on the moving plate of FIG.

FIG. 4 is an enlarged partial cross-sectional view showing a photodiode portion formed on the moving plate of FIG. 1;

FIG. 5 is an explanatory view showing an arrangement relationship of photodiodes formed on the moving plate of FIG. 1;

FIG. 6 is a partial cross-sectional view of the moving plate shown in FIG. 1 when a photodiode having a pn structure is used as the photodiode.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Optical linear encoder 2 LED 3 Light transmission grating 4A, 4B Photodiode group (light receiving element) 5 Moving plate 6 Reflection grating 7 Reflection grating plate 8 Control circuit unit 20 Light source integrated type moving plate unit 21 LED holding plate 22 Depression 23 Substrate Surface 24 Light transmitting area 25 First light receiving area 26 Second light receiving area 31 to 34 Photodiode 41 Thin film part 42 Light shielding film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor: Kenji Kobayashi 3-2-3 Marunouchi, Chiyoda-ku, Tokyo F-term in Nikon Corporation (reference) 2F103 BA00 BA31 BA37 CA01 CA02 CA03 DA01 DA12 EA00 EA17 EA20 EB06 EB12 EB16 EB32 EB37 FA12 GA15

Claims (10)

[Claims] 1. A light source, a reflection grating having a predetermined shape arranged at a constant pitch, a light transmission grating having a predetermined shape arranged at a constant pitch, and a light emitted from the light source and transmitted through the light transmission grating. A light receiving element for receiving a reflected light image reflected by the reflection grating; and an optical encoder for detecting at least a relative speed of the reflection grating and the light transmission grating based on a detection signal obtained from each light receiving element. And a reflection grating plate on which the reflection grating is formed, and a semiconductor substrate on which the light transmission grating and the light receiving element are formed. A light-transmitting region arranged in a first light-receiving region formed on one side of the light-transmitting region, the light-receiving elements are arranged at predetermined intervals, and formed on the other side of the light-transmitting region; The light receiving element A light-transmitting grating defined by a light-transmitting thin-film portion formed on the semiconductor substrate and a light-shielding film laminated on the surface of the thin-film portion. An optical encoder, comprising: 2. The optical encoder according to claim 1, wherein the semiconductor substrate is a silicon substrate, and the thickness of the thin film portion is approximately 10 μm. 3. The optical encoder according to claim 2, wherein the central wavelength of the light emitted from the light source is 900 nm or more. 4. The optical encoder according to claim 1, wherein the light shielding film is a metal thin film. 5. The optical encoder according to claim 4, wherein the metal thin film is an aluminum thin film. 6. The light-emitting device according to claim 1, further comprising: a light-emitting diode as the light source; and a holding substrate holding the light-emitting diode, wherein the holding substrate includes a concave portion on a surface of which the light-emitting diode is mounted, An optical encoder, wherein the semiconductor substrate is laminated and bonded to the surface of the holding substrate. 7. The light receiving element according to claim 1, wherein a first detection signal obtained from each light receiving element included in the first light receiving area is obtained from the light receiving element included in the second light receiving area. An optical encoder characterized in that the relative positional relationship of the light receiving elements between the two light receiving areas is set so that the phase is shifted by 90 degrees with respect to the second detection signal obtained. 8. The relative position of each light receiving element according to claim 1, wherein the first and second light receiving element regions are set such that detection signals having phases shifted by 90 degrees from each other are obtained. An optical encoder, comprising: 9. The optical encoder according to claim 1, wherein the light receiving element has a pin structure. 10. The optical encoder according to claim 1, wherein the light receiving element has a pn structure, and an interval between the light receiving elements is 40 μm or more.