A wafer automatic centering method

Abstract

The present invention discloses a wafer automatic centering method. When the robot retrieves the wafer, the sensor collects the wafer edge signal, and the current wafer center position is obtained through an algorithm. The position is compared with the wafer teaching center position. If there is a deviation, the robot compensates in the next wafer delivery process; when the wafer notch happens to fall within one of the sensor detection areas, the algorithm can discard the sensor measurement result of the notch area. According to this method, the machine does not need to add additional workstations, and the robot can measure and compensate for the wafer offset during the wafer transmission process, which does not affect the equipment production capacity at all, and the cost is much lower than traditional mechanical centering units and optical centering units.

Description

Technical Field

[0001] The invention belongs to the field of electronic semiconductors, and in particular relates to an automatic wafer centering method. Background Art

[0002] In electronic semiconductor production and processing equipment, the wafer handling robot is responsible for the transfer of wafers between various workstations. It is the core moving part of the machine. Its positioning accuracy directly determines the accuracy of the wafer placement, and the accuracy of the wafer placement determines the yield of chip processing. Therefore, it is particularly important to improve the accuracy of the robot's wafer placement. In order to improve the accuracy of the robot's placement of wafers, before the wafer is sent to the key process unit, such as the glue unit, the wafer is first placed in a mechanical or optical centering unit. This unit can ensure that each chip sent to the process unit is located at the center of the suction cup, correct the offset of the wafer when it enters the glue unit, and ensure the uniformity of glue coating, EBR deviation and stable wafer transmission.

[0003] 1) The mechanical centering unit is centered by mechanical clamping, and its disadvantage is low accuracy (±0.2mm).

[0004] 2) The optical centering unit mainly uses optical measurement methods to center the wafer, but its disadvantage is that the centering speed is slow.

[0005] 3) Whether mechanical alignment or optical alignment is used, several workstations will be added, which will not only increase the equipment cost, but also reduce the equipment production capacity and equipment space utilization rate, and it is impossible to achieve real-time monitoring of the wafer transfer position each time. Summary of the invention

[0006] In view of the above technical problems, the purpose of the present invention is to provide a wafer automatic centering method. The centering device is installed on the robot body, and the machine does not need to add additional workstations. The robot can measure and compensate for the wafer offset during the wafer transfer process, which does not affect the equipment production capacity at all, and the cost is much lower than that of traditional mechanical centering units and optical centering units.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a wafer automatic centering method, comprising the following steps:

[0008] The robot drives the wafer to move toward the wafer target position in the R-axis direction;

[0009] By setting a fiber optic counter-radiation sensor in the direction of wafer movement, signal interruption and recovery are generated;

[0010] Record the wafer position coordinates at the time when the interruption and recovery signals are generated and latch the corresponding encoding position of the robot drive motor;

[0011] According to the wafer position coordinates of the interrupt and recovery signals, it is judged in real time whether the current wafer center deviates from the teaching position. If so, position correction is performed, otherwise no correction is performed;

[0012] According to the center coordinate position of the wafer after correction, the encoding position of the robot drive motor after correction is calculated, and the robot is controlled to drive the wafer to move.

[0013] The optical fiber counter-radiation sensors are in two groups, and two sensors in each group are placed opposite to each other and are respectively arranged on both sides of the wafer moving plane, one of which is arranged on the target station and the other is arranged on the sensor fixing frame, and the sensor fixing frame is arranged on the target station.

[0014] The end of the robot is connected to the wafer by suction through a suction cup.

[0015] The calculation of the teaching position is:

[0016] Assuming that no deviation occurs, the distances traveled by sensors A and B in the wafer moving direction are chord lengths LA and LB respectively, and the two end points of the chord lengths are positions Y1 and Y2, positions Y3 and Y4 respectively; interruption signals are generated at positions Y1 and Y3, and recovery signals are generated at positions Y2 and Y4;

[0017] According to formulas (1), (2), and (3), the coordinates (x A ,y A )

[0018]

[0019] x A =d A (3)

[0020] Among them, d A is the chord-center distance, and the wafer center coordinates are (0, y A );

[0021] Similarly, the coordinates (x B ,y B ), wafer center coordinates (0, y B ) Chord center distance d B ;

[0022] Select (0,yA), (0,y B ) One of them is used as the teaching position for automatic wafer centering.

[0023] The position correction includes two parts: compensation correction of the R axis and compensation correction of the TH axis.

[0024] The compensation and correction of the R axis includes:

[0025] 1) After the robot picks up the wafer, the actual position of the wafer will shift relative to the taught position. At this time, the current wafer center measured by the two sensors is O An (x An ,y An ) and O Bn (x Bn ,y Bn ), the chord-center distances are d An and d Bn ;

[0026] Δd n =|d Bn -d An |-|d A -d B | (4)

[0027] 2) The wafer detected by this method is a notched wafer; the sensor with the shortest chord-center distance is defined as A, and according to formula (4): if Δd n >0, sensor B may encounter a wafer notch, and the wafer center measured by sensor A is selected; if Δd n <0, sensor A may encounter a wafer notch, so the wafer center measured by sensor B is selected;

[0028] If sensor B encounters a wafer notch, the wafer center O measured by sensor A is selected. An (x An ,y An ), then the wafer center O is calculated according to equations (5) and (6): An Relative to the taught position (0, y A ) Deviation value Δx in X and Y directions An , Δy An ;

[0029] Δx An =x An (5)

[0030] Δy An =y An -y A (6)

[0031] Among them, considering that the robot cannot interfere with other units when placing the film after compensation, the compensation range is limited to |Δx An |≤2.5mm,|Δy An |≤2.5mm, no compensation will be performed outside this range.

[0032] The compensation and correction of the TH axis includes:

[0033] According to formula (7), the TH axis deviation angle Δθ is calculated An :

[0034]

[0035] Among them, L O L is the distance between the center of the teaching wafer and the rotation center of TH. R It is the distance between the zero point of the arm coordinate system and the R-axis teaching position.

[0036] A wafer automatic centering system comprises a controller, a sensor group, a drive motor, and a mechanical arm; the sensor groups are respectively arranged on both sides of a wafer moving plane, and are used to collect wafer edge signals during wafer movement; the drive motor is used to receive instructions from the controller to control the movement of the mechanical arm; a wafer is arranged at the end of the mechanical arm; the controller loads a program to execute the method steps as described above, calculates and corrects the position deviation of the wafer, converts it into a coded position of the drive motor, and controls the mechanical arm to perform position correction and automatic centering.

[0037] It also includes an amplifier module for amplifying the wafer edge signal collected by the sensor group and sending it to the controller.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. Automatic compensation of wafer offset is achieved during the robot’s wafer picking and delivery process. Unlike traditional centering units, which require additional centering time, the overall productivity of the machine can be improved.

[0040] 2. The centering accuracy of this system is higher than that of traditional mechanical centering units;

[0041] 3. The system has a compact structure and can be integrated into the robot. It can save space and improve the space utilization of the machine after replacing the traditional centering unit;

[0042] 4. The system costs only one tenth of the traditional optical centering unit;

[0043] 5. The system can identify wafer notches during the measurement process, eliminating the need for an additional wafer notch identification unit.

[0044] 6. Achieve contactless alignment to prevent process defects caused by particles generated by wafer edge collision. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 is a flow chart of the method of the present invention;

[0046] Figure 2 is a diagram showing the relationship between the positions of the manipulator and the sensor of the present invention;

[0047] Figure 3 is a diagram of the sensor and amplifier positions of the present invention;

[0048] Figure 4 It is a schematic diagram of the wafer position detection principle of the present invention;

[0049] Figure 5 It is a schematic diagram of wafer position offset and compensation calculation of the present invention; DETAILED DESCRIPTION

[0050] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific implementation method of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the invention, so the present invention is not limited by the specific implementation disclosed below.

[0051] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0052] Two fiber optic sensors are installed at the front end of the robot arm. One end of the sensor is installed on the base of the R-axis of the robot, and the other end is installed on the sensor fixing seat. The sensor fixing seat is fixed to the R-axis base. When the robot retrieves the wafer, the sensor collects the edge signal of the wafer, and the current center position of the wafer is obtained through the algorithm. This position is compared with the teaching center position of the wafer. If there is a deviation, the robot will compensate for it in the next wafer delivery process; when the wafer notch happens to fall within one of the sensor detection areas, the algorithm can be used to discard the sensor measurement results of the notch area. The automatic centering system has a compact structure and is integrated with the robot body, and does not take up machine space. The detection accuracy of this wafer automatic centering system is ±0.05mm, which is much higher than the traditional mechanical centering unit.

[0053] Measuring principle

[0054] This method is suitable for wafers with notches, but not for wafers with flat edges (small size). Since a single sensor may encounter a wafer notch, two sensors will be needed to measure, calculate the wafer center position independently, and compare them to determine whether a sensor encounters a wafer notch. If so, use the measurement value of the other sensor.

[0055] When the robot retracts its hand after taking the wafer, the sensor starts to collect signals when the wafer approaches the sensor. The time when sensor A is blocked and leaks out is recorded as TA0 and T A1 , the time when sensor B is blocked and leaked by Wafer is recorded as T B0 and T B1 . T A0 and T B0 Collect rising edge signals at all times, T A1 and T B1 The falling edge signal is collected at all times. The sensor A signal is connected to the arm motor driver probe 1 interface, and the sensor B signal is connected to the arm motor driver probe 2 interface. The two signals of each sensor trigger the probe function of the arm motor driver in turn, latch the motor position at this time, and upload it to the controller.

[0056] like Figure 1 As shown, sensor A will record the motor positions at position points Y1 and Y2, and sensor B will record the motor positions at position points Y3 and Y4.

[0057] According to formulas (1), (2), and (3), the coordinates (x A , yA)

[0058]

[0059] x A =d A (3)

[0060] Where dA is the chord-center distance, and the wafer center coordinates are (0, yA).

[0061] Similarly, the coordinates (x B ,y B ), wafer center coordinates (0, y B ) Chord center distance d B .

[0062] Use the teaching tool to fix the wafer at the center of the robot. During the wafer transfer process, two sensors record the center position of the wafer at this time, as shown in the above formula (0, y A )、(0,y B ), which is the teaching position of the wafer automatic centering system.

[0063] like Figure 2 As shown in the figure, after the robot picks up the wafer, the actual position of the wafer will shift relative to the taught position. At this time, the center of the wafer measured by the two sensors is O An (x An ,y An ) and O Bn (x Bn ,y Bn), the chord-center distances are d An and d Bn .

[0064] Δd n =|d Bn -d An |-|d A -d B | (4)

[0065] According to formula (4), if Δd n >0, sensor B may encounter a wafer notch, and the wafer center measured by sensor A is selected; if Δd n <0, sensor A may encounter a wafer notch, so the wafer center measured by sensor B is selected;

[0066] If sensor B encounters a wafer notch, the wafer center O measured by sensor A is selected. An (x An ,y An ), then according to formula (5) (6) the wafer center O can be calculated An Deviation Δx in the X and Y directions relative to the taught position of the wafer automatic centering system An , Δy An .

[0067] Δx An =x An (5)

[0068] Δy An =y An -y A (6)

[0069] Considering that the robot cannot interfere with other units when placing the film after compensation, the compensation range is limited to |Δx An |≤2.5mm,|Δy An |≤2.5mm, no compensation will be performed outside this range.

[0070] Since the calculation of the wafer center only involves the R axis, it only needs to be performed in the robot arm coordinate system. However, when performing wafer placement compensation, the TH axis needs to be rotated, and the Δx calculated in the robot arm coordinate system needs to be An , Δy An Bring it into the TH axis rotation center coordinate system to calculate the TH axis compensation angle.

[0071] According to formula (7), the TH axis deviation angle Δθ can be calculated: An .

[0072]

[0073] When the robot arm delivers the film next time, the deviation compensation is performed, the sensor signal collection is turned off, and the compensation value of the hand extension direction is Δy An , the TH axis compensation angle is Δθ An .

[0074] If sensor B is selected, the wafer offset position can be calculated by the above formula and compensated when feeding the wafer.

[0075] During the transmission process, each wafer will be repeatedly picked up by the robot and placed in different units for process processing. The wafer offset will be measured by the sensor each time the wafer is taken out, and compensation will be made the next time the wafer is sent.

[0076] The embodiments described in the above description will help those skilled in the art to further understand the present invention, but do not limit the present invention in any form. It should be noted that, for those of ordinary skill in the art, several changes and improvements can be made without departing from the concept of the present invention. These all belong to the protection scope of the present invention.

Claims

1. A wafer automatic centering method, characterized in that: The following steps are involved: The robot drives the wafer to move toward the wafer target position in the R-axis direction; By setting a fiber optic counter-radiation sensor in the direction of wafer movement, signal interruption and recovery are generated; Record the wafer position coordinates at the time when the interruption and recovery signals are generated and latch the corresponding encoding position of the robot drive motor; According to the wafer position coordinates of the interrupt and recovery signals, it is judged in real time whether the current wafer center deviates from the teaching position. If so, position correction is performed, otherwise no correction is performed; According to the center coordinate position of the wafer after correction, the encoding position of the robot drive motor after correction is calculated, and the robot is controlled to drive the wafer to move; Two fiber optic sensors are installed at the front end of the robot arm. One end of the sensor is installed on the base of the R axis of the robot, and the other end is installed on the sensor fixing seat. The sensor fixing seat is then fixed to the R axis base. During the transfer process, each wafer will be repeatedly picked up and placed in different units by the robot for process processing. Each time the wafer is taken out, the sensor will measure the wafer offset and compensate it when the wafer is sent next time. The calculation of the teaching position is: Assuming that no deviation occurs, let the distances traveled by sensors A and B in the wafer moving direction be chord lengths LA and LB respectively, and the two end points of the chord lengths be position points Y1 and Y2, position points Y3 and Y4 respectively; An interrupt signal is generated at the position point Y1 and the position point Y3, and a recovery signal is generated at the position point Y2 and the position point Y4; According to formulas (1), (2), and (3), the coordinates (x A ,y A ) XA=dA(3) Among them, d A is the chord-center distance, and the wafer center coordinates are (0, y A ); Similarly, the coordinates (x B ,y B ), wafer center coordinates (0, y B ) Chord center distance d B ; Select (0, y A )、(0,y B ) one of which is used as a teaching position for automatic wafer centering; The position correction includes two parts: R-axis compensation correction and TH-axis compensation correction; The compensation and correction of the R axis includes: 1) After the robot picks up the wafer, the actual position of the wafer will shift relative to the taught position. At this time, the current wafer center measured by the two sensors is O An (x An ,y An ) and O Bn (x Bn ,y Bn ), the chord-center distances are d An and d Bn ; Δd n =|d Bn -d An |-|d A -d B |(4) 2) The wafer detected by this method is a notched wafer; the sensor with the shortest chord-center distance is defined as A, and according to formula (4): if Δd n >0, sensor B may encounter a wafer notch, and the wafer center measured by sensor A is selected; if Δd n <0, sensor A may encounter a wafer notch, so the wafer center measured by sensor B is selected; If sensor B encounters a wafer notch, the wafer center O measured by sensor A is selected. An (x An ,y An ), then the wafer center O is calculated according to equations (5) and (6): An Relative to the taught position (0, y A ) Deviation value Δx in X and Y directions An , Δy An ; Δx An =x An (5) Δy An =y An -y A (6) Among them, considering that the robot cannot interfere with other units when placing the film after compensation, the compensation range is limited to |Δx An |≤2.5mm,|Δy An |≤2.5mm, no compensation will be performed if it exceeds this range; The compensation and correction of the TH axis includes: According to formula (7), the TH axis deviation angle Δθ is calculated An : Among them, L O L is the distance between the center of the teaching wafer and the rotation center of TH. R It is the distance between the zero point of the arm coordinate system and the R-axis teaching position.

2. The wafer automatic centering method according to claim 1, characterized in that: The optical fiber counter-radiation sensors are in two groups, and two sensors in each group are placed opposite to each other and are respectively arranged on both sides of the wafer moving plane, one of which is arranged on the target station and the other is arranged on the sensor fixing frame, and the sensor fixing frame is arranged on the target station.

3. The wafer automatic centering method according to claim 1, characterized in that: The end of the robot is connected to the wafer by suction through a suction cup.

4. The wafer automatic centering system according to claim 1, characterized in that: It includes a controller, a sensor group, a drive motor, and a robotic arm; the sensor groups are respectively arranged on both sides of the wafer moving plane, and are used to collect wafer edge signals during the wafer movement process; the drive motor is used to receive instructions from the controller to control the movement of the robotic arm; a wafer is arranged at the end of the robotic arm; the controller loads a program to execute the method steps described in any one of claims 1-3, calculates the position deviation of the wafer and corrects it, converts it into the encoded position of the drive motor, and controls the robotic arm to perform position correction and automatic centering.

5. The wafer automatic centering system according to claim 1, characterized in that: It also includes an amplifier module for amplifying the wafer edge signal collected by the sensor group and sending it to the controller.

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