KR20230100144A - Device for polishing a wafer - Google Patents

Abstract

A wafer polishing apparatus comprises: at least one first stage on which at least one first cassette each containing a plurality of wafers is loaded, wherein the first cassette has an opening through which some of the plurality of wafers are exposed; a polishing machine which polishes each of the plurality of wafers stored in the first cassette; a second stage on which a second cassette for storing wafers after polishing is loaded; a robot which delivers each of the plurality of wafers stored in the first cassette to the polishing machine; and a sensor which detects the presence or absence of each of the plurality of wafers. The sensor includes: a light emitting unit which is installed on a first side of the opening and emits light; a light receiving unit which is installed on a second side of the opening and receives the emitted light; a first bracket; second and third brackets which are fastened to the first bracket and adjust a first gap along a first direction; and fourth and fifth brackets which are fastened to the second bracket and adjust a second gap along a second direction. According to the present invention, it is possible to prevent wafers from being discarded due to incorrect determination by ensuring that a traveling path of light is located at an edge area of a wafer at all times.

Description

Wafer polishing device {Device for polishing a wafer}

The embodiment relates to a wafer polishing apparatus.

The manufacturing process of a silicon wafer includes a single crystal growth step for making a single crystal ingot, a slicing step for slicing the single crystal ingot to obtain a thin disk-shaped wafer, and cracking and distortion of the wafer obtained by the slicing step. To prevent this, an edge grinding process for processing the outer periphery, a lapping process for removing damage due to mechanical processing remaining on the wafer, a polishing process for mirror surface of the wafer, , It consists of a cleaning process to remove abrasives or foreign substances attached to the polished wafer.

As a primary polishing process for improving flatness of a wafer, a double side polishing process (DSP) may be performed, followed by a final polishing process (FP).

The finish polishing process is performed by a polishing machine.

The wafer polishing apparatus proceeds in the order of inserting the cassette --> detecting the existence of a wafer --> loading the wafer --> performing the polishing process --> taking out the cassette.

As shown in FIGS. 1 and 2 , a conventional sensor 1 for detecting the existence of a wafer is a reflective sensor 1 having a light emitting unit 2 and a light receiving unit 3 adjacent to each other. That is, the presence or absence of the wafer 10 is detected by the light emitted from the light emitting unit 2 being reflected on the edge side of the wafer 10 and the reflected light being received by the light receiving unit 3 .

However, in the conventional sensor 1, as shown in FIGS. 2 and 3A, when ultrapure water (DIW) remains on the edge side of the wafer 10, light is diffusely reflected or refracted by the ultrapure water (DIW) 11 Otherwise, the light reflected by the wafer 10 is not received by the light receiving unit 3, resulting in an error in detecting whether the wafer 10 is present or not. That is, since the wafer 10 is positioned, the light reflected by the wafer 10 is received by the light receiving unit 3 and should be detected as the presence of the wafer 10, but as described above, diffuse reflection by the ultrapure water 11 However, since the reflected light is not received by the light receiving unit 3 due to the refractive index, the absence of the wafer 10 can be detected. In this case, the wafer is not transferred to the polishing machine and polishing is not performed, so it is discarded.

In addition, in the conventional sensor 1, as shown in FIGS. 2 and 3B, when the wafer 10 is twisted and accommodated in the cassette, light is not properly reflected by the edge side of the wafer 10 or even reflected. Even if it is, it proceeds in the other direction and is not received by the light receiving unit 3, so that an error in detecting the existence of the wafer 10 occurs.

Embodiments are aimed at solving the foregoing and other problems.

Another object of the embodiments is to provide a wafer polishing apparatus capable of improving reliability because an error in detecting the existence of a wafer does not occur even if the edge side of the wafer is defective or the wafer is twisted.

The technical problems of the embodiments are not limited to those described in this section, and include those that can be grasped through the description of the invention.

According to one aspect of the embodiment to achieve the above or other object, the wafer polishing apparatus includes at least one first stage on which at least one first cassette in which a plurality of wafers are stored is loaded - the first cassette is the plurality of has an opening through which a portion of the wafer of is exposed; a polishing machine for polishing each of the plurality of wafers accommodated in the first cassette; a second stage on which a second cassette for accommodating the polished wafer is loaded; a robot transferring each of the plurality of wafers accommodated in the first cassette to the polishing machine; and a sensor for detecting the presence or absence of each of the plurality of wafers. The sensor may include a light emitting unit installed on a first side of the opening and emitting light; a light receiving unit installed on a second side of the opening to receive the emitted light; a first bracket; second and third brackets fastened to the first bracket to adjust a first interval along a first direction; and fourth and fifth brackets fastened to the second bracket to adjust a second interval along a second direction.

The first interval may be adjusted so that an amount of light corresponding to a reference value is received by the light receiving unit.

The second bracket may include a 2-1 bracket fastened to a first side of the first bracket and including a plurality of holes; and a 2-2 bracket that is bent from the 2-1 bracket and extends along the second direction and includes a plurality of holes.

The third bracket may include a 3-1 bracket fastened to a second side of the first bracket and including a plurality of holes; and a 3-2 bracket bent from the 3-1 bracket to extend along the second direction and including a plurality of holes.

The first interval is adjusted along the first direction using the plurality of holes of the first bracket and the plurality of holes of the 2-1 bracket, or the plurality of holes of the first bracket and the plurality of holes of the first bracket The first distance may be adjusted along the first direction using the plurality of holes of the 3-1 bracket.

The second interval is adjusted along the second direction using the plurality of holes of the 2-2 bracket and the plurality of holes of the 4th bracket, or the plurality of holes of the 3-2 bracket The second interval may be adjusted along the second direction using the plurality of holes of the fifth bracket.

An edge area of each of the plurality of wafers may be located on a traveling path of the light.

A second interval may be adjusted so that the light travel path is located in the edge area.

The wafer polishing apparatus includes a control unit. The control unit may generate a wafer loading command based on wafer information, and the robot may transfer each of the plurality of wafers loaded in the first cassette to the polishing machine according to the wafer loading command.

The wafer polishing apparatus includes a blocking portion installed around the light receiving portion to block ambient light.

Effects of the wafer polishing apparatus according to the embodiment are described as follows.

According to at least one of the embodiments, since the light emitting unit and the light receiving unit are positioned on the path of light, even if the edge side of the wafer is defective or the wafer is twisted, an error in detecting the existence of the wafer does not occur, thereby improving reliability. There is an advantage to being

According to at least one of the embodiments, the sensor is provided with the first to fifth brackets, and the first distance along the first direction or the second distance along the second direction is adjusted so that the traveling path of light always extends to the edge of the wafer. There is an advantage in that the wafer can be prevented from being discarded due to an erroneous decision by being located in the region.

A further scope of applicability of the embodiments will become apparent from the detailed description that follows. However, since various changes and modifications within the spirit and scope of the embodiments can be clearly understood by those skilled in the art, it should be understood that the detailed description and specific embodiments, such as preferred embodiments, are given by way of example only.

1 is a side view showing a conventional sensor.
2 is a plan view showing a conventional sensor.
3A is an exemplary view showing a wafer presence detection error.
3B is another exemplary view showing a wafer presence detection error.
4 is a diagram illustrating a wafer polishing apparatus according to an embodiment.
5 is a side view showing the sensor assembly according to the first embodiment.
6 is a plan view showing a sensor according to the first embodiment.
7 is a plan view showing a sensor according to a second embodiment.
FIG. 8 is an enlarged cross-sectional view of area A of FIG. 7 .

Hereinafter, the embodiments disclosed in this specification will be described in detail with reference to the accompanying drawings, but the same or similar components are given the same reference numerals regardless of reference numerals, and redundant description thereof will be omitted. The suffixes 'module' and 'unit' for the components used in the following description are given or used interchangeably in consideration of ease of writing the specification, and do not themselves have a meaning or role that is distinct from each other. In addition, the accompanying drawings are for easy understanding of the embodiments disclosed in this specification, and the technical idea disclosed in this specification is not limited by the accompanying drawings. Also, when an element such as a layer, region or substrate is referred to as being 'on' another element, this includes being directly on the other element or other intervening elements may be present therebetween. do.

4 is a diagram illustrating a wafer polishing apparatus according to an embodiment.

Referring to FIG. 4 , the wafer polishing apparatus 100 according to the embodiment may include at least one first stage 110 or 120, a robot 130, a polisher 140, and a second stage 150. .

The first stages 110 and 120 may be loaded with the first cassette 300 in which a plurality of wafers are accommodated.

Although two first stages 110 and 120 are shown in FIG. 4, more stages may be provided.

For example, the first cassette 300 may be loaded on one of the first stages 110 and 120 .

For example, when two or more first stages 110 and 120 are provided, at least two first cassettes 300 among the two or more first stages 110 and 120 may be loaded on corresponding first stages. there is. In this case, while the plurality of wafers stored in the first cassette 300 on one first stage are transferred or loaded to the polishing machine 140, the plurality of wafers stored in the first cassette 300 on the other first stage The wafers of may be in the air, but are not limited thereto.

The robot 130 may transfer the plurality of wafers stored in the first cassette 300 to the polishing machine 140 . For example, a plurality of wafers may be sequentially transferred to the polisher 140, but is not limited thereto.

The robot 130 may include a body 131 and an arm 132 .

The body 131 may reciprocate along the Y-axis direction. The body 131 may rotate and move in a clockwise or counterclockwise direction.

The arm 132 is installed on the body 131 and may move forward or backward along the longitudinal direction of the arm 132 . An arm plate (not shown) may be installed at an end of the arm 132 . In addition, the arm 132 may move up and down along the vertical direction (Z).

For example, by moving the body 131 along the Y-axis direction, the arm 132 may be positioned on one of the two first stages 110 and 120 . For example, the arm 132 advances along the longitudinal direction of the arm 132 and is placed under one wafer among a plurality of wafers on the first cassette 300, and the arm 132 moves backward after being raised, thereby moving the corresponding wafer. may be withdrawn from the first cassette 300 by the arm 132 . Thereafter, the arm 132 is positioned in the grinder 140 by rotating the body 131, and then the wafer may be seated on the grinder 140 by moving the arm 132 forward and downward. This description is only an example, and wafer transfer or loading is possible in various ways.

The polishing machine 140 may be housed in the first cassette 300 and polish the wafer transferred by the robot 130 . In this case, polishing may mean final polishing (FP), but is not limited thereto. Since finish polishing is a known technique, a detailed description thereof will be omitted.

The second stage 150 may be loaded with a second cassette. The second cassette may have an empty space in which wafers are not accommodated. That is, when the second cassette is loaded on the second stage 150, no wafers may be accommodated in the second cassette.

After the second cassette is loaded on the second stage 150, wafers polished in the polishing machine 140 may be accommodated in the second cassette. Although not shown, another robot is installed between the polishing machine 140 and the second stage 150, and the wafer polished by the polishing machine 140 is transferred to the second stage 150 by the robot. It can be stored in a second cassette loaded on 150.

When the set number of wafers is received in the second cassette, the second cassette may be moved from the second stage 150 to the next stage.

Meanwhile, the wafer polishing apparatus 100 according to the embodiment may include at least one or more sensors 200 and a controller 160 .

5 is a side view showing the sensor assembly according to the first embodiment. 6 is a plan view showing a sensor according to the first embodiment.

Referring to FIGS. 5 and 6 , the sensor 200 according to the first embodiment may include a motor 111 , a support shaft 112 , and the sensor 200 .

The support shaft 112 is coupled to the motor 111 and can be moved up and down in the vertical direction Z by driving the motor 111 . For example, the motor 111 may be a step motor, but is not limited thereto. For example, the support shaft 112 may be raised when the motor 111 rotates forward and the support shaft 112 may be lowered when the motor 111 rotates in the reverse direction, but is not limited thereto.

The sensor 200 is installed on one side of the support shaft 112 and may be moved up and down along with the lift of the support shaft 112 . That is, when the support shaft 112 rises, the sensor 200 also rises, and when the support shaft 112 descends, the sensor 200 may also descend.

Meanwhile, the first cassette 300 may be loaded on the first stages 110 and 120 . In order to fix the first cassette 300 to the first stages 110 and 120 , at least one fixing part 115 may be installed on the first stages 110 and 120 . The first cassette 300 may be fixed on the first stages 110 and 120 by at least one fixing part 115 . For example, when the wafers 330 stored in the first cassette 300 are transferred to the polishing machine 140 , the first cassette 300 may be removed by releasing the fixing part 115 .

Meanwhile, the sensor 200 may be raised along with the support shaft 112 that is raised by driving the motor 111 . As the sensor 200 rises, light is emitted from the sensor 200, and the presence or absence of the wafer 330 can be detected depending on whether or not the emitted light is received. That is, the sensor 200 obtains wafer information about the presence or absence of each of the plurality of wafers 330 while moving along the upward direction Z with respect to the plurality of wafers 330 stored in the first cassette 300. can do.

As shown in FIG. 6, the sensor 200 includes a light emitting unit 210, a light receiving unit 220, a first bracket 231, second and third brackets 232 and 233, and fourth and fifth brackets ( 234, 235) may be included.

For example, the light emitting unit 210 may be installed on the first side of the opening 310 of the first cassette 300 to emit light. For example, the light receiving unit 220 may be installed on the second side of the opening 310 of the first cassette 300 to receive light emitted from the light emitting unit 210 . The light emitting unit 210 and the light receiving unit 220 are positioned on the same line and may be disposed to face each other. For example, when the wafer 330 exists between the light emitting unit 210 and the light receiving unit 220, light is blocked by the wafer 330 and the light receiving unit 220 cannot receive the light of the light emitting unit 210. Wafer information in which the wafer 330 exists may be acquired. For example, when the wafer 330 does not exist between the light emitting unit 210 and the light receiving unit 220, light is not blocked by the wafer 330 and the light receiving unit 220 receives the light of the light emitting unit 210. Wafer information in which the wafer 330 does not exist may be obtained.

For example, the distance between the light emitting unit 210 and the light receiving unit 220 is greater than the diameter D of the wafer 330 so that the wafer 330 does not collide with the light emitting unit 210 and/or the light receiving unit 220. can That is, when the wafer 330 is positioned between the light emitting unit 210 and the light receiving unit 220 , each of the light emitting unit 210 and the light receiving unit 220 may be spaced apart from the side of the wafer 330 .

For example, as light emitted from the light emitting unit 210 proceeds to the light receiving unit 220 , a light traveling path 250 may be defined. That is, the light traveling path 250 may be defined as a path of light traveling from the light emitting unit 210 to the light receiving unit 220 . Of the light emitted from the light emitting unit 210, the light traveling along the light propagation path 250 is received by the light receiver 220, and since the remaining light leaves the light propagation path 250, the light is received by the light receiver 220. It doesn't work. The light receiving unit 220 may detect the presence or absence of the wafer 330 based on the amount of light traveling along the path 250 of light, that is, the amount of light.

For example, the edge region 335 of each of the plurality of wafers 330 may be positioned on the light traveling path 250 . One side of the first cassette 300 is opened to form an opening 310 , and a plurality of wafers 330 may be exposed through the opening 310 . Therefore, the path of light defined between the light emitting unit 210 and the light receiving unit 220 on the edge area 335, that is, a portion of the wafer 330 exposed by the opening 310 of the first cassette 300 By positioning the 250, the presence or absence of the wafer 330 can be accurately sensed.

For example, the edge area 335 of each of the plurality of wafers 330 forms a first straight line P1 corresponding to a position 1/8 of the diameter D of the wafer 330 from the edge side surface 331 of the wafer 330. It may be an area between and the second straight line P2 corresponding to the position of the opening 310 . When the light propagation path 250 crosses the wafer 330 that is less than 1/8 of the diameter D of the wafer 330 from the edge side surface 331 of the wafer 330, it is due to the curved surface of the wafer 330 Thus, some light is received by the light receiving unit 220, and an error may occur when the wafer 330 is not present even though the wafer 330 is present. When the path 250 of light travels out of the position of the opening 310 and crosses the side of the first cassette 300, the light from the light emitting unit 210 cannot pass through the side of the first cassette 300, and thus detects itself is impossible.

The first bracket 231 may be installed on one shaft of the support shaft 112 . For example, the first bracket 231 may serve to support all components constituting the sensor 200 . Due to the first bracket 231 fixed to the support shaft 112, all components constituting the sensor 200 may be moved together according to the elevation of the support shaft 112 . For example, the first bracket 231 may include a plurality of holes 241a and 241b formed along the first direction (X).

The second bracket 232 is fastened to the first side 231a of the first bracket 231 and the third bracket 233 is fastened to the second side 231b of the first bracket 231, so that the first direction The first interval I1 may be adjusted along (X).

The second bracket 232 is fastened to the first side 231a of the first bracket 231 and includes a 2-1 bracket 232-1 including a plurality of holes 242a, and a 2-1 bracket It may include a 2-2 bracket 232-2 bent from 232-1, extending along the second direction Y, and including a plurality of holes 242b.

The third bracket 233 is fastened to the second side 231b of the first bracket 231 and includes a 3-1 bracket 233-1 including a plurality of holes 243a, and a 3-1 bracket It may include a 3-2 bracket 233-2 bent from (233-1) and extending along the second direction (Y) and including a plurality of holes (243b).

The fourth bracket 234 is fastened to one side of the second bracket 232 and the fifth bracket 235 is fastened to one side of the third bracket 233, so that the second interval I2 along the second direction Y ) can be adjusted.

The fourth bracket 234 is fastened to one side of the 2-2 bracket 232-2 and may include a plurality of holes 244. The fifth bracket 235 is fastened to one side of the 3-2 bracket 233-2 and may include a plurality of holes 245.

For example, by using the plurality of holes 241a of the first bracket 231 and the plurality of holes 242a of the 2-1 bracket 232-1 along the first direction X, the first distance I1 is For example, by using the plurality of holes 241b of the first bracket 231 and the plurality of holes 243a of the 3-1 bracket 233-1 along the first direction X. 1 interval (I1) can be adjusted.

For example, by using the plurality of holes 242b of the 2-2 bracket 233-2 and the plurality of holes 244 of the fourth bracket 234, the second distance I2 is formed along the second direction Y. this can be adjusted For example, by using the plurality of holes 243b of the 3-2 bracket 233-2 and the plurality of holes 245 of the fifth bracket 235, the second interval I2 along the second direction Y this can be adjusted.

For example, as the first interval I1 is adjusted, the light receiving unit 220 may receive a light amount corresponding to a reference value. The reference value is a reference value for determining that there is no wafer 330, and may be set by adjusting the first interval I1 in a state in which there is no wafer 330 between the light emitting unit 210 and the light receiving unit 220. Therefore, when there is no wafer 330 between the light emitting unit 210 and the light receiving unit 220, when the amount of light received by the light receiving unit 220 is at least equal to or greater than the reference value, wafer information indicating that the wafer 330 is not present can be obtained. there is. Since ambient light such as indoor lighting is also received by the light receiving unit 220 , the amount of light received by the light receiving unit 220 may be a reference value or greater than the reference value.

For example, by adjusting the second interval I2 , the light traveling path 250 between the light emitting unit 210 and the light receiving unit 220 may be located in the edge region 335 defined on the wafer 330 .

Therefore, according to the embodiment, the sensor 200 is provided with the first to fifth brackets 231 to 235, so that the first interval I1 along the first direction X or the second direction Y By adjusting the second interval I2, the light travel path 250 is always positioned at the edge region 331 of the wafer 330, thereby preventing the wafer 330 from being discarded due to an erroneous decision.

Meanwhile, the controller 160 may generate a wafer loading command based on the obtained wafer information and transmit the generated wafer loading information to the robot 130 . The robot 130 may transfer each of the plurality of wafers 330 loaded on the first cassette 300 to the polishing machine 140 according to a wafer loading command.

Therefore, according to the embodiment, even if the edge side 331 of the wafer 330 is defective or the wafer 330 is twisted, an error in detecting the presence or absence of the wafer 330 does not occur by the sensor 200 of the embodiment. Reliability can be improved.

7 is a plan view showing a sensor according to a second embodiment. FIG. 8 is an enlarged cross-sectional view of area A of FIG. 7 .

The second embodiment is the same as the first embodiment except for the blocking part 260 . In the second embodiment, the same reference numerals are assigned to components having the same configuration, shape, and/or function as those in the first embodiment, and detailed descriptions are omitted.

Referring to FIGS. 7 and 8 , a sensor 200A according to the second embodiment may include a motor 111 , a support shaft 112 and a sensor 200 .

Also, the sensor 200A according to the second embodiment may include a blocking unit 260 .

The blocking unit 260 may be installed around the light receiving unit 220 to block ambient light. For example, the blocking unit 260 may cover the remaining area except for the front of the light receiving unit 220, but is not limited thereto. For example, the blocking unit 260 may surround the remaining area of the light receiving unit 220 except for an entrance for receiving the light of the light emitting unit 210 .

For example, the blocking part 260 may be made of a metallic material such as aluminum or a reflective material such as a mirror. For example, the blocking portion 260 may be made of a light absorbing material. For example, the blocking part 260 may be made of plastic or resin material.

Since ambient light is blocked by the blocking unit 260 , the light receiving unit 220 can only receive light from the light emitting unit 210 , and thus detection of the presence or absence of a wafer can be more accurate.

The above detailed description should not be construed as limiting in all respects and should be considered illustrative. The scope of the embodiments should be determined by reasonable interpretation of the appended claims, and all changes within the equivalent range of the embodiments are included in the scope of the embodiments.

100: wafer polishing device
110, 120: first cassette
111: motor
112: support shaft
115: fixing part
130: robot
131: body
132 arm
140: grinder
150: second stage
160: control unit
170, 170A: sensor assembly
200: sensor
210: light emitting unit
220: light receiving unit
231: first bracket
231a: first side
231b: second side
232: second bracket
233: third bracket
234: fourth bracket
235: fifth bracket
241a, 241b, 242, 243, 244, 245: hole
250: path of light
260: blocking part
300: first cassette
310: opening
330: wafer
331: edge side
335: edge area
D: diameter
I1, I2: spacing

Claims (12)

at least one first stage on which at least one first cassette accommodating a plurality of wafers is loaded, wherein the first cassette has an opening through which a portion of the plurality of wafers is exposed;
a polishing machine for polishing each of the plurality of wafers accommodated in the first cassette;
a second stage on which a second cassette for accommodating the polished wafer is loaded;
a robot transferring each of the plurality of wafers accommodated in the first cassette to the polishing machine; and
A sensor for detecting the presence or absence of each of the plurality of wafers;
The sensor,
a light emitting unit installed on a first side of the opening and emitting light;
a light receiving unit installed on a second side of the opening to receive the emitted light;
a first bracket;
second and third brackets fastened to the first bracket to adjust a first interval along a first direction; and
Including fourth and fifth brackets fastened to the second bracket and adjusting a second distance along a second direction
Wafer polishing equipment. According to claim 1,
The first interval is adjusted so that an amount of light corresponding to a reference value is received by the light receiving unit.
Wafer polishing equipment. According to claim 1,
The second bracket,
a 2-1 bracket fastened to a first side of the first bracket and including a plurality of holes; and
A 2-2 bracket bent from the 2-1 bracket and extending along the second direction and including a plurality of holes;
Wafer polishing equipment. According to claim 3,
The third bracket,
a 3-1 bracket fastened to the second side of the first bracket and including a plurality of holes; and
Including a 3-2 bracket bent from the 3-1 bracket and extending along the second direction and including a plurality of holes
Wafer polishing equipment. According to claim 4,
The first interval is adjusted along the first direction using the plurality of holes of the first bracket and the plurality of holes of the 2-1 bracket,
The first distance is adjusted along the first direction using the plurality of holes of the first bracket and the plurality of holes of the 3-1 bracket.
Wafer polishing equipment. According to claim 5,
The second interval is adjusted along the second direction using the plurality of holes of the 2-2 bracket and the plurality of holes of the fourth bracket;
The second distance is adjusted along the second direction using the plurality of holes of the 3-2 bracket and the plurality of holes of the fifth bracket.
Wafer polishing equipment. According to claim 1,
The edge area of each of the plurality of wafers is located on the traveling path of the light
Wafer polishing equipment. According to claim 7,
A second interval is adjusted so that the traveling path of the light is located in the edge area
Wafer polishing equipment. According to claim 7,
The edge area of each of the plurality of wafers is an area between a first straight line corresponding to 1/8 of the diameter of the wafer from the edge side of the wafer and a second straight line corresponding to the opening position
Wafer polishing equipment. According to claim 1,
The sensor,
Moving in a third direction with respect to the plurality of wafers to obtain wafer information about the presence or absence of each of the plurality of wafers
Wafer polishing equipment. According to claim 1,
Including a control unit,
The control unit,
Generating a wafer loading command based on the obtained wafer information;
the robot,
Transferring each of the plurality of wafers loaded in the first cassette to the polisher according to the wafer loading command.
Wafer polishing equipment. According to claim 1,
Including a blocking unit installed around the light receiving unit to block ambient light
Wafer polishing equipment.

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