WO2014101586A1

WO2014101586A1 - Wafer prealignment method

Info

Publication number: WO2014101586A1
Application number: PCT/CN2013/087387
Authority: WO
Inventors: 张波; 刘品宽; 朱晓博; 张帆; 梁家欣
Original assignee: 上海交通大学
Priority date: 2012-12-27
Filing date: 2013-11-19
Publication date: 2014-07-03
Also published as: CN103050427A

Abstract

A wafer prealignment method comprises: a high-precision transmission laser sensor calculating, according to circumferential edge data of a wafer and by building a mathematical model for detecting the centroid of the wafer, position coordinates (x̅, y̅) of the centroid, a radial displacement maximum eccentricity vector e_max, and an angle θ̅ between a radial displacement maximum eccentric position and the horizontal Y-direction, and actuating the wafer to rotate by the angle θ̅ to make the radial displacement maximum eccentricity vector e_max and the horizontal Y-direction in a straight line, so as to accomplish the positioning of the centroid of the wafer; and positioning a notch of the wafer precisely according to the centroid algorithm. The method uses a light transmission sensor to detect an edge of a wafer, and uses a centroid algorithm to determine the positions of a centroid and a notch of the wafer, thereby effectively enhancing the precision of the positioning method, reducing time and space occupied by the prealignment apparatus, and lowering the cost.

Description

Wafer pre-alignment method

The present invention relates to semiconductor fabrication, and in particular to a wafer pre-alignment method.

Background technique

With the development of lithography, higher requirements are placed on the accuracy of wafer alignment and exposure systems. In order to reduce the time for precise alignment of randomly searched mark locations and improve wafer utilization, pre-alignment processes must be added during wafer transfer prior to precise alignment to ensure accurate wafer alignment in a short period of time. .

Current wafer pre-alignment has evolved from initial mechanical pre-alignment to optical pre-alignment, with accuracy from 200 microns to 1 micron or even sub-micron, and requires high productivity. Therefore, high requirements are placed on the accuracy of the detection, manufacture and installation of the pre-alignment device. The main function of the wafer pre-alignment device in the lithography machine is to pre-align the wafer before the leveling and lithography process (fine alignment in the leveling and pre-focusing subsystem), to minimize the crystal The round repeatability error is taken from the wafer cassette by the robot and then placed at the precision alignment station. There are two main deviations in wafer pre-alignment adjustment: one is the offset of the centroid in the horizontal plane (which can be defined as the degree of freedom in the X and Y directions), and the other is the angle of the wafer groove (notch). Error (can be defined as) Θ rotational direction freedom).

Current wafer pre-alignment methods typically employ optical pre-alignment, or a combination of optical and mechanical means. Conventional optical pre-alignment devices use a linear charge-coupled device (CCD) sensor to detect wafer edges. One of its pre-alignment methods is to find the alignment information by comparing the actual waveform of the linear CCD signal with the standard waveform. For example, in the method of US Patent: US7042568, the wafer is rotated. When the wafer is eccentric, the actual waveform of the linear CCD signal behaves like a sinusoid, otherwise it appears as a standard waveform. This allows the eccentricity of the wafer to be obtained by comparing the two waveforms. Then the turntable drives the wafer to rotate again, and finds the wafer to the minimum where the CCD is covered, that is, the bottom of the wafer gap, and then performs the notch positioning. The accuracy of the method is not high, especially the notch part is positioned by a single sampling point, and the accuracy is greatly affected by the sampling frequency and interference.

Another pre-alignment method is to collect edge data during wafer rotation by CCD sensor, and obtain the radius of the wafer and the coordinates of the center center by least square fitting. For example, in Chinese patent CN 1787200A, the centering mechanism moves the wafer so that its wafer coincides with the center of rotation, and then uses the data according to the previous circumference, and uses the edge conversion rate to find the approximate position of the gap, and rotates the notch to the vicinity of the scanning line of the CCD sensor. The gap is sampled in a small range, the same The notch is fitted by the least squares algorithm to obtain the center coordinates of the notch circle. The intersection of the center of the notch and the center of the rotation and the edge of the wafer is the center of the gap, and the center of the gap is rotated to a specified angle to complete the wafer notch positioning. The method uses the least squares circle fitting algorithm to find the center of the wafer and the center of the notch. However, the wafer contains a gap, which is not a standard circle. Therefore, the data of the notch has to be removed during the calculation, which not only increases the workload, but also requires CCD. The acquired wafer edge data must be evenly distributed, and the amplitude of the acquired adjacent data cannot be changed too much, which requires high precision of the hardware device.

The pre-alignment positioning method adopted above uses a linear CCD sensor to detect the edge of the wafer, and the sampling frequency of the sensor is small, thereby limiting the number of sampling points per week of the wafer, and the space occupied is large, throughout the pre-alignment device. In the case where the space size is limited, the space size of the CCD sensor often fails to meet the requirements.

Summary of the invention

SUMMARY OF THE INVENTION A primary object of the present invention is to overcome the deficiencies of the prior art described above and to provide a wafer pre-alignment method based on a high precision laser transmissive sensor. According to an aspect of the invention, a wafer pre-alignment method is provided, comprising the steps of:

Step 1: Let the external wafer transfer robot hand over the wafer to the wafer pre-alignment device, and use the visual inspection unit 5 to detect whether the wafer has been placed on the vacuum adsorption unit 4 by detecting the rate of change of the received light intensity. When it is detected that the wafer has been placed, the motion control unit 7 is triggered to cause the vacuum adsorption unit 4 to fix the wafer; and the vacuum adsorption unit 4 is driven by the Θ-Υ two-degree-of-freedom motion unit 2 to rotate the wafer for one week, in the visual detection unit 5 The laser transmission sensor detects the edge position of the wafer, and the data acquisition unit 6 synchronously collects the data of the wafer edge obtained by the laser transmission sensor;

Step 2: Let the motion control unit 7 calculate the centroid position coordinate (y) of the wafer by using the mathematical model of the crystal center of the wafer by using the data of the wafer edge acquired from the data acquisition unit 6, and the radial displacement is maximum. The eccentric amount ^ and the angle between the maximum eccentricity of the radial displacement and the horizontal Y direction;

Step 3: The motion control unit 7 issues an instruction to cause the tilting platform of the θ-Y two-degree-of-freedom motion unit 2 to drive the wafer rotation angle so that the radial displacement maximum eccentricity e is in line with the horizontal Y direction, and the diameter is The displacement maximum eccentricity _{emax is} adjusted to the Y-axis, and the vertical transition unit 3 is raised to move the wafer away from the θ-Y two-degree-of-freedom motion unit 2 θ - γ two-degree-of-freedom motion unit 2 in the Y-direction linear motion platform, Θ Coordinate with the centroid wafer of the wafer toward the center of the rotating platform to complete the centroid positioning of the wafer;

Step 4: Lowering the vertical transition unit 3 and fixing the vacuum adsorption unit 4 to the wafer, θ-γ two-degree-of-freedom motion The unit 2 drives the vacuum adsorption unit 4 to rotate the wafer once, the visual detecting unit 5 detects the edge position of the wafer, the data collecting unit 6 synchronously collects the data of the wafer edge for one week, and the motion control unit 7 analyzes the wafer edge one week to complete the gap. Positioning the data segment and issuing an instruction to cause the θ-Y two-degree-of-freedom motion unit 2 to rotate the notched data segment to the vicinity of the laser-transmissive sensor for small-scale fine sampling, and the data acquisition unit 6 synchronously collects data; the motion control unit 7 Using the data acquired from the data acquisition unit 6, the actual notch centroid position of the wafer is calculated, and the angle β between the notch position of the wafer and the Y direction is obtained;

Step 5: The motion control unit 7 issues an instruction to rotate the wafer in the θ-Υ2-DOF motion unit 2 to rotate the wafer to a specified angle to complete the wafer notch positioning.

Preferably, in the step 2, the motion control unit 7 calculates the centroid position coordinate (y) of the wafer, the maximum eccentricity of the radial displacement, and the maximum eccentricity of the radial displacement and the level Y by using a centroid positioning algorithm. The angle of the orientation, wherein the centroid localization algorithm is specifically: determining the eccentricity, the eccentric rotation in the 9-Y two-degree-of-freedom motion unit 2 by the displacement value of the wafer edge measured by the laser transmission sensor A functional relationship between the corner of the platform and the edge displacement to accurately calculate the centroid of the wafer.

Preferably, in the step 4, the motion control unit 7 calculates the actual notch centroid position of the wafer by using a centroid localization algorithm, wherein the centroid localization algorithm is specifically: measured by a laser transmissive sensor The displacement value of the edge of the wafer determines the relationship between the eccentricity, the rotation angle and the edge displacement. The notch centroid is calculated, the notch centroid and the center line of the rotating platform are the notch direction, and the notch direction is rotated to a specified angle. That is, the precise positioning of the wafer notch can be completed.

Preferably, the data acquisition unit 6 synchronously acquires the wafer edge one-week data obtained by the laser transmission type sensor, specifically: the encoder signal of the twisting platform is used as an external clock, and is rotated during the rotation of the tilting platform. The data acquisition unit 6 controls the data acquisition unit 6 to synchronize the data acquisition of the laser transmission sensor by the encoder pulse signal to the rotary platform, so that the analog or digital quantity measured by the laser transmission sensor can correspond to the corresponding rotation angle of the tilting platform. .

Preferably, in the step 4, the motion control unit 7 uses the data acquired from the data acquisition unit 6 to analyze the mathematical characteristics of the difference in circumference and notch curvature, and calculates the actual notch centroid position of the wafer.

Preferably, a point on the edge of the wafer having a curvature of less than 3° is identified as a point on the wafer notch, otherwise it is identified as a point on the circumference of the wafer.

Preferably, the centroid position coordinate ( y ) of the circular circular heart O ' is calculated by the following formula:

Where x is the X-axis coordinate of the circular circular heart O ', and y is the Y-axis coordinate of the circular circular heart O ', which is the distance from the center of the 9-way rotating platform to the edge of the wafer, which is the turret angle of the center of the rotating platform , is a function of the radius of the silicon wafer with respect to the angle.

Calculate the maximum eccentricity of the radial displacement by calculating the position coordinate ( , ) of the circular circular heart O ' by the following formula.

Calculate the angle between the maximum eccentricity of the radial displacement and the Υ direction by the following formula

Θ = arctan=

X

Preferably, in the step 4, the positioning of the notched data segment is specifically as follows: the inflection point at which the curvature change rate of the notch is the largest is the start and end point of the notch; the data acquisition unit 6 collects the laser transmission sensor. In addition to the analog output signal, the LOW digital output signal of the laser-transmitted sensor is also acquired synchronously; then the LOW digital output signal data is searched, and the inflection point from 1 to 0 is the starting point of the gap, and the inflection point changing from 0 to 1 is the gap. The end point, thus finding the gap data segment.

Preferably, the laser transmissive sensor comprises a laser emitter, a receiver, and a sensor holder, the laser emitter is for emitting a laser beam, the receiver is for receiving the light intensity signal, and the laser emitter and the receiver are fixed on the sensor bracket, There is a gap between the laser emitter and the receiver, and the relative position remains unchanged.

The X Υ Θ Θ refers to the three coordinate axes of the Cartesian Cartesian coordinate system.

The centroid localization algorithm: according to the gravity center coordinate algorithm of the mechanical particle system, the displacement value of the wafer edge measured by the laser transmission sensor is used to determine the function relationship between the eccentricity, the rotation angle and the edge displacement, thereby Accurate calculation of the center of the wafer and the location of the gap. The algorithm has high precision and is suitable for the detection of standard gardens and non-standard circles (such as wafer gaps).

The data acquisition method of the data acquisition unit 6 is: taking the encoder signal of the rotating platform as an external clock, and controlling the data acquisition card to the laser transmission type by the encoder pulse signal of the rotating platform during the rotation of the rotating platform Sensor synchronous data acquisition, the analog or digital quantity measured by the laser transmission sensor can correspond to the corresponding rotation angle of the turntable. Therefore, in the edge data acquisition process, the rotating platform does not need to rotate at a constant speed, and does not need to exceed the rotation of the full circle in order to avoid the data of the acceleration and deceleration phase of the rotating platform.

The degree of freedom adjustment method of the present invention: Since the position of the wafer is random when it is transmitted to the pre-alignment device, there are positional errors in the three directions of eccentricity and notch of X and Y. The purpose of pre-alignment is to adjust these deviations. Theoretically, to adjust these deviations requires three degrees of freedom to compensate. Considering the detection method and accuracy problem, a degree of freedom Z is required to transfer the wafers, which requires a total of four degrees of freedom. The method obtains the angle between the maximum eccentricity of the radial displacement and the Y direction, and the rotation angle makes the maximum eccentricity with the radial displacement adjust to a line with the horizontal Y direction, thereby achieving a reduction of one degree of freedom and achieving a reduced mechanism. Improve the purpose of centering efficiency.

The laser transmissive sensor: A novel transmissive laser discriminating sensor, which is composed of a transmitter and a receiver, the transmitter emits a laser beam, and the receiver receives the light intensity signal. The transmitter and receiver are fixed on a special profile bracket with a 30cm pitch and the relative position remains unchanged. Different sizes of wafers can be detected by adjusting the mounting position of the sensor bracket. The laser-transmitted sensor has a sampling rate of up to 80 s, a discrimination accuracy of up to 5 μm, a full mounting size of no more than 10 cm, and automatic adjustment to reduce maintenance.

The motion control unit: adopts a new multi-axis motion control card, which can precisely control the rotation of the stepping motor and the servo motor.

The data acquisition unit adopts a high-speed data acquisition AD module, which can synchronously collect the position signal of the rotating unit and the edge data signal output by the laser transmission type sensor.

The invention has the following beneficial features and effects:

(1) A high-precision transmission type laser sensing system mainly composed of a laser-transmissive sensor, which can be embedded in the frame of the entire pre-alignment device, does not occupy the actual space size. At the same time, because its frequency of use is much higher than the sampling frequency of the linear CCD, in the same case, the number of sampling points per week at the edge of the wafer is increased, thereby improving the measurement accuracy.

(2) A new wafer pre-alignment method based on centroid algorithm is used to improve the positioning accuracy of the circular center and the notch position.

(3) Adopting an efficient data acquisition method, the rotating platform does not need constant rotation speed during the detection process, and it does not need to skip the rotation of the rotating platform during the acceleration/deceleration phase and exceeds the rotation of the full circle, which greatly saves the positioning time. The centroid algorithm provides good acquisition data. (4) Calculate the angle between the maximum eccentricity of the radial displacement and the Y direction, and rotate the angle so that the maximum eccentricity of the radial displacement is in line with the horizontal Y direction, effectively reducing one degree of freedom and thus reducing The complexity of the organization has improved the efficiency of the heart and shortened the time for the heart.

DRAWINGS

Other features, objects, and advantages of the present invention will become more apparent from the Detailed Description of Description

1 is a schematic view showing the overall structure of a corresponding device of the method provided by the present invention;

2 is a schematic diagram of a general implementation flow of the present invention;

3 is a schematic diagram of a mathematical model of wafer eccentricity according to the present invention;

4 is a schematic diagram of solving a circular circular polar coordinate of the present invention;

5 is a schematic diagram of a mathematical model of a wafer notch edge according to the present invention;

6 is a schematic diagram of the polar coordinate solution of the notch core of the present invention;

7 is a schematic structural view of a θ-Y two-degree-of-freedom motion unit in the apparatus shown in FIG. 1;

Figure 8 is a schematic structural view of a vacuum adsorption unit in the apparatus shown in Figure 1;

9 is a schematic structural view of a vertical transition unit and a visual detecting unit in the apparatus shown in FIG. 1. FIG. 10 is a general working flow chart of the apparatus shown in FIG.

detailed description

The invention will now be described in detail in connection with specific embodiments. The following examples are intended to further understand the present invention by those skilled in the art, but are not intended to limit the invention in any way. It should be noted that a number of variations and modifications may be made by those skilled in the art without departing from the inventive concept. These are all within the scope of protection of the present invention.

As shown in FIG. 1 , in order to realize a wafer pre-alignment device of the method provided by the present invention, the wafer pre-alignment device comprises a work surface, a Θ-Υ two-degree-of-freedom motion unit 2, a vertical transition unit 3, The vacuum adsorption unit 4, the visual detection unit 5, the data acquisition unit 6, and the motion control unit 7. Wherein: the Θ-Υ two-degree-of-freedom motion unit 2 is used for adjusting the eccentricity and the notch position of the wafer, and is fixed on the work surface 1; the vertical transition unit 3 is vertically fixed on the work surface 1 for temporarily placing the wafer The wafer and the θ-Y two-degree-of-freedom motion unit 2 can be completely separated to achieve the purpose of adjusting the eccentricity; the vacuum adsorption unit 4 is coaxially fixed on the θ-Y two-degree-of-freedom motion unit 2 for fixing the crystal The circle is arranged to enable centering and notch positioning; the visual detecting unit 5 is configured to detect the edge position and the notch position of the wafer, and is fixed on the work surface 1 in parallel with the vertical transition unit 3; the data acquisition unit 6 is used for collecting the crystal The circular edge data, the motion control unit 7 is used to process the wafer edge data, and the data acquisition unit 6 and the motion control unit 7 are all placed outside the external controller, which will not be described in detail in the present invention.

Preferably, the θ - Y two-degree-of-freedom motion unit 2 comprises a connected Y-direction linear motion platform and a tilting rotary platform, wherein:

The linear motion platform includes a two-dimensional precision ball screw 10, a high-resolution stepping motor 6, a linear guide 9, and a slider

11. The coupling 7, wherein: the symmetrical center line of the linear motion platform is overlapped with the axis of the ideal alignment position of the wafer and fixed on the work surface 1; the two-dimensional precision ball screw 10 and the slider 11 are connected to each other to form two The plane 11 is linearly moved; the slider 11 is connected to two parallel linear guides 9; the linear guide 9 is fixed on the work surface 1; the 2D precision ball screw 10 is connected through the coupling 7 and the high resolution step The input motor 6 is connected, and when the high-resolution stepping motor 6 rotates, the slide table 11 is driven to move in a Y direction along the linear guide 9;

The slewing platform includes a turret connecting plate 12, a turret gantry 13, and a direct drive brushless servo motor 14, wherein: the direct drive brushless servo motor 14 and the turret gantry 13 are coaxially mounted for single-axis rotary motion, Y-direction linear motion The platform and the cymbal are fixed to the rotating platform by a turret connecting plate 12, that is, the turret connecting plate 12 is fixed on the slider 11, and the turret gantry 13 is disposed on the turret connecting plate 12.

Preferably, the twisting platform has a hollow design, and the vacuum air tube of the vacuum adsorption unit 4 is coaxially mounted with the direct drive brushless servo motor 14.

Preferably, the vacuum adsorption unit 4 includes an adsorption sleeve 15, an adsorption connection member 16, a vacuum suction head 17, and a hexagon socket fastening screw 18, wherein: the adsorption sleeve 15 is coaxially fixed on the turntable gantry 13, and the adsorption connection is The member 16 is used as a connecting member of the vacuum suction head 17 and the suction sleeve 15, and is fixed by a plurality of hexagon socket fastening screws 18; vacuum suction head

17 is used to fix the wafer and transmit the torque to the rotating platform.

Preferably, the surface shape of the vacuum nozzle 17 adopts an irregular fan shape design.

Preferably, the vertical transition unit 3 includes a base bracket 19, a vertical bracket 20, and a Z-direction linear motion platform.

21. The L-shaped transition tray 25 and the plurality of tabs 26, wherein: the Z-direction linear motion platform 21 is fixed on the base bracket 19 by the vertical bracket 20 for completing the Z-direction linear motion; the entire vertical transition unit 3 is placed at work. On the table top 1; the L-shaped transition tray 25 is vertically fixed on the slide table of the Z-direction linear motion platform 21 for vertical movement in the Z direction, and is designed with a circular opening for the vacuum suction unit 4 to pass through; the plurality of tab columns 26 It is fixed in a square shape on the L-shaped transition tray 25.

Preferably, the top of the tab 26 is provided with an annular sealing ring to prevent damage to the wafer, and a hollow design is used for both vacuum suction and wafer placement and transition placement of the wafer.

Preferably, the visual detection unit 5 comprises a sensor holder 22, a laser emitter 23 and a receiver 24, Medium: The laser emitter 23 is used to emit a laser beam, the receiver 24 is used to receive the light intensity signal, and the laser emitter 23 and the receiver 24 are fixed on the sensor holder 22 with a gap between the laser emitter and the receiver.

Preferably, the distance between the laser emitter and the receiver is 30 cm.

Preferably, the data acquisition unit 6 and the motion control unit 7 are further included, wherein: the data acquisition unit 6 is configured to synchronously acquire the position signal of the tilting platform and the edge data signal output by the visual detecting unit 5 in real time; The rotation of the high-resolution stepping motor and the direct-drive brushless servo motor 14 is precisely controlled by the digital signal output from the calculation data acquisition unit 6.

The main parts of the wafer pre-alignment device will be described in detail below.

As shown in FIG. 7, the Θ-Υ two-degree-of-freedom motion unit 2 includes: a Y-direction linear motion platform and a tilting rotary platform. Wherein: the linear motion platform is mainly composed of a two-dimensional precision ball screw 10, a high-resolution stepping motor 6, a linear guide 9, a slider 11, and a coupling 7, and the symmetrical center line of the linear motion platform is ideally aligned with the wafer. The axis of the position is combined and fixed on the work surface 1. Wherein: the two-dimensional precision ball screw 10 and the slider 11 are connected to each other to form a linear motion in a two-dimensional plane direction, the slider 11 and the two parallel linear guides 9 are connected to each other, and the linear guide 9 is fixed on the profile 8, two-dimensional The precision ball screw 10 - end is connected to the stepping motor 6 through the coupling 7 , and when the stepping motor 6 rotates, the slide table 11 is driven to move in the Y direction linearly along the linear guide 9 . The slewing rotary platform is mainly composed of a turntable connecting plate 12, a turntable stand 13, and a direct drive brushless servo motor 14. Wherein: the direct drive brushless servo motor 14 and the turntable gantry 13 are coaxially mounted to realize a single-axis rotary motion, and the Y-direction linear motion platform and the tilting rotary platform are fixed by a turntable connecting plate 12, that is, the turntable connecting plate 12 is fixed at On the slider 11. The slewing platform adopts a hollow design, so that the vacuum air pipe can be installed coaxially with the motor, which solves the problem that the entire Θ-Y two-degree-of-freedom moving unit vibrates due to the tracheal drag when the rotating motor rotates at a large scale.

As shown in Fig. 8, the vacuum suction unit 4 is mainly composed of a suction cup sleeve 15, a suction cup connecting member 16, a vacuum suction head 17, and a hexagonal fastening screw 18. The suction cup sleeve 15 is coaxially fixed to the turntable gantry 13, and the suction cup connecting member 16 serves as a connecting member of the vacuum suction head 17 and the suction cup sleeve 15, and is fixed by three hexagon socket fastening screws 18. Among them: The vacuum nozzle 17 is used to fix the wafer and transmit the torque to the rotating platform. The structural design is mainly focused on the shape of the surface of the tip. The vacuum deformation of the wafer will be deformed when the force is applied. The shape of the surface of the nozzle is different, and the deformation caused by the wafer is different. Most of the designs adopt a circular circular hole design, which easily causes the vacuum contact portion of the wafer to collapse. Therefore, the surface shape of the vacuum nozzle 17 in this embodiment adopts an irregular fan shape design, which can effectively avoid deformation of the edge of the wafer, improve the edge measurement accuracy of the wafer, and ensure the process of adsorbing and releasing the wafer. Produces a small impact.

As shown in FIG. 9, the vertical transition unit 3 is mainly transported by the base bracket 19, the vertical bracket 20, and the Z straight line. The movable platform 21 L-shaped transition tray 25 is composed of four tab columns 26. Wherein: the Z-direction linear motion platform 21 is the same as the Y-direction linear motion platform, and is fixed on the base bracket 19 by the vertical bracket 20 for completing the Z-direction linear motion. The entire vertical transition unit 3 is placed on the work surface 1. The L-shaped transition tray 25 is vertically fixed on the slide table of the Z-direction linear motion platform 21 for vertical movement in the Z direction, and is designed with a circular opening to enable the vacuum suction unit 4 to pass through, thereby effectively saving installation space; the L-shaped transition tray The design of the 25 is capable of being fixed to the vertical bracket at the same time as the visual inspection unit 5, thereby effectively reducing the installation size, making the whole device compact, wide-ranging, flexible, and simple. The four tabs 26 are fixed in a square shape on the L-shaped transition tray 25. Since the wafers are directly in contact with the wafer, the top of the four tabs 26 is provided with an annular sealing ring to prevent damage to the wafer, and a hollow design is adopted. , for vacuum suction and wafer placement and transition placement wafers.

As shown in Fig. 9, the visual detecting unit 5 is mainly composed of a sensor holder 22, a laser transmitter 23 and a receiver 24. Wherein: the laser beam is emitted by the laser emitter 23, and the receiver 24 receives the light intensity signal. The laser transmitter 23 and the receiver 24 are fixed to the special sensor holder 22 with a vertical spacing of 30 cm, and the relative position remains unchanged. The mounting position of the sensor holder 22 can be adjusted to detect wafers of different sizes. The laser emitter 23 uses a transmission lens, and the laser light emitted as a parallel beam is concentrated on the light receiving element (high sensitivity PD) after passing through the light receiving lens. When the parallel beam is blocked, the beam will decrease in proportion to the amount of light that is blocked and incident on the light-receiving element; at this point, the receiver 24 captures the amount of light that passes through the edge of the wafer and the gap, and the amount of data converted by the amount of light is For the distance from the edge of the wafer to the center of rotation, the data at several points on the edge are combined, and the center position and the direction of the gap of the wafer can be calculated by the corresponding algorithm.

As shown in FIG. 2, the overall flow of implementing the method provided by the present invention using the above wafer pre-alignment apparatus includes the following steps:

Step (a): The external wafer transfer robot transfers the wafer to the wafer pre-alignment device, and the visual inspection unit 5 determines whether the wafer has been placed on the vacuum adsorption unit by detecting the rate of change of the received light intensity. When the wafer has been placed, the motion control unit 7 is triggered to fix the wafer by the vacuum adsorption unit 4; the Θ-Υ two-degree-of-freedom motion unit 2 drives the vacuum adsorption unit to rotate the wafer for one week, and the laser light in the visual detection unit 5 is transmitted. The sensor detects the edge position of the wafer, and the data acquisition unit 6 synchronously acquires the wafer edge one-week data obtained by the laser transmission sensor; Step (b): The motion control unit 7 uses the data acquired from the data acquisition unit 6, by constructing The mathematical model of the circular circular heart is detected, and the actual centroid coordinate, radius, maximum radial eccentricity 6 of the wafer and the angle between the maximum eccentricity of the radial displacement and the Y direction are calculated;

Step (c): the motion control unit 7 issues an instruction to cause the θ-Y two-degree-of-freedom motion unit 2 to rotate toward the platform The rotation angle of the wafer is driven so that the maximum radial eccentricity is in line with the horizontal yaw direction, the maximum eccentricity of the radial displacement is adjusted to the Υ axis, and the vertical transition unit 3 is raised to lift the wafer out of θ - Υ two degrees of freedom. The moving unit 2 moves toward the linear motion platform, and the center of the rotating platform coincides with the centroid wafer of the wafer to complete the centroid positioning of the wafer; step (d): Θ - Υ two degrees of freedom motion unit 2 again The vacuum adsorption unit 4 is driven to rotate the wafer for one week, the visual detecting unit 5 detects the edge position of the wafer, the data collecting unit 6 synchronously collects data, and the motion control unit 7 analyzes the data to complete the positioning of the notched data segment, and issues an instruction to make θ - The Y two-degree-of-freedom motion unit 2 rotates the data segment to the vicinity of the laser-transmissive sensor for small-scale fine sampling, and the data acquisition unit 6 synchronously collects data; the motion control unit 7 uses the data acquired from the data acquisition unit to construct The wafer notch detection mathematical model calculates the actual notch centroid position of the wafer;

Step (e): The motion control unit issues an instruction to cause the wafer to rotate at an angle of Θ-Y two-degree-of-freedom motion unit 2 to complete the wafer gap positioning.

The overall process of implementing the method of the present invention by using the above-mentioned wafer pre-alignment device mainly includes two main parts of the positioning detection of the crystal circular center and the positioning detection of the wafer notch, which are respectively described below as follows:

The method flow of the circular center positioning detection of the present invention comprises the following steps:

Step (1): Verify whether the wafer edge data is correct or not: As shown in FIG. 3, the ft robot is sent to the center of the rotating platform to send the wafer to the vacuum adsorption unit 4, and the circular center is located at ^, and the eccentricity is e, the eccentricity e is that when the wafer is eccentrically rotated, the displacement variation of the laser-transmitted sensor to the edge of the wafer can be analogized to the displacement of the rod on the rotating cam; the ideal outer diameter of the wafer is A through Θ A rectangular coordinate system is established to the center of the rotating platform, and the actual geometric center coordinate of the wafer after the rotation angle is (x, }, and the X-coordinate offset of the detection detecting unit 5 in the fixed X-axis direction is fe z, and the calculation formula is as follows:

. X = ecos O

y = e sin 0

Ox ' = e cos 0 + (R ² - e ² sin ² Θ) ¹¹²

The above formula is the mathematical function relationship between the eccentricity ^turn angle 边缘 and the edge displacement when the wafer is eccentrically rotated under ideal conditions, and can be used to verify whether the data is correct or not during the detection process.

Step (2): Edge data acquisition and processing of the wafer: In actual detection, the wafer can be regarded as stationary, and the laser-transmissive sensor rotates around the center of rotation of the turntable. Usually, the centroid of the wafer is calculated by the least squares method. However, since the roundness error of the wafer is large, about ± 0.1, and the data at the positioning gap needs to be processed separately, so a preferred example of the present invention is Instead of using this method, a method based on centroid calculation is designed. As shown in Figure 4, data mining The collecting unit 6 synchronously collects the digital signal of the laser transmitting sensor under the pulse control of the rotating platform encoder, and obtains the distance S between the sensor and the edge of the wafer and the corresponding turn angle e of the wafer during the rotation of the wafer 360. The distance from the center of the rotating platform to the edge of the wafer is the distance from the next sampling point P w ^ w) Δ θ The distance from the laser head of the sensor to the axis of the rotating platform is L′, then ^=Ζ-&_; From the centroid calculation method of a two-dimensional arbitrarily shaped object, the centroid position coordinates ( y ) of the circular circle ^ can be obtained. o For continuous measurement, the formula is as follows: p ² cos OOdpde

Άθάράθ

ρ sin θ^άράθ

Ρθάράθ where χ is the X-axis coordinate of the circular center, y is the Υ-axis coordinate of the circular center, and P is the distance from the center of the rotating platform to the edge of the wafer, which is the turret angle of the center of the rotating platform. (For the function of the wafer radius as a function of angle.

The maximum eccentricity of the radial displacement can be obtained from the position coordinate ( ~y ) of the circular center 0 '.

Step (3): _Centroid positioning: The rotation Θ angle adjusts the radial displacement maximum eccentricity _emax to a line with the horizontal Y-direction linear motion unit, thus achieving a reduction in one degree of freedom, only one Y-direction adjustment Deviation can achieve the purpose of centroid positioning. The vertical transition unit 3 rises to drive the wafer away from the vacuum adsorption unit, and then the axis motion platform compensates the wafer for eccentricity 6 to complete the positioning of the circular center of the crystal. At the same time, by analyzing the collected data, the starting position of the gap can also be found, which lays a foundation for the re-acquisition of the gap data segment.

The method flow of the wafer notch location detection of the present invention comprises the following steps:

Step (1): Identification of the notch edge: In the process of the crystal circular center positioning detection, the identification of the notch edge is also completed, and the gap data segment is prepared. The angle of change of the edge of the wafer can be represented by the angle between adjacent three points. As shown in FIG. 5, the present invention utilizes the mathematical characteristics of the difference in curvature of the circumference and the notch to identify the notch data of the wafer. The cosine theorem can be used to obtain the edge variation of the wafer gap:

It can be seen from the analysis of the edge change rate of the wafer after the solution of a set of sampled data that the edge transition rate of the gap is very different from that of the circumference. The edge non-notch edge change rate is very small, the angle is about 3°; the rate of change of the notch edge is relatively large, and the maximum angle does not exceed 2. 4°, so the gap can be identified by selecting the appropriate domain value. Sampling point. The domain value set in the preferred embodiment of the present invention is 3°, and if ", <3°, it is determined as a point on the notch.

(1) Positioning of the data segment of the gap: When the centroid of the wafer is adjusted, the amount of data change in the non-notched portion of the laser-transmissive sensor becomes very small, and the amount of data change in the notched portion It is still very large, and the entire data will reflect the shape characteristics of the gap. The trend of sensor data changes is shown in Figure 6. When the gap enters the laser-transmitted sensor, the data will be significantly reduced until the lowest point of the gap arrives, and then increase significantly until the gap completely leaves the sensor. Back to normal. The point at which the rate of change of the notch has the largest rate of change is the start and end of the gap. According to the mathematical model of the structural crystal circular heart, the notch is at an angle of about 2. 4° to the center of the wafer, and the lower limit of the laser transmission sensor can be set in advance. The laser transmissive sensor controller provides a LOW digital signal output. When the detected data is less than the sensor's defined lower limit value, the LOW terminal digital output is 0, otherwise the output is 1. Therefore, in addition to collecting the laser-transmitted sensor analog output signal, we also synchronously acquire its LOW digital output signal. Then the latter data is searched. The inflection point from 1 to 0 is the starting point of the gap. The inflection point from 0 to 1 is the end point of the gap, so that the data segment of the actual notch centroid calculation is found.

(2) Precise positioning of the notch: The shape of the data segment calculated by the notch centroid obtained by the notch data segment is actually a small segment of the outer contour of the notch, as shown in Fig. 6, at this time, the notch centroid of the wafer The calculation can be performed in the same way as the centroid calculation method of the wafer. Only the circular center of the circle calculates a circle, and the notch centroid calculates a small fan shape, that is, their calculation formula is similar, but the integral angle range is inconsistent, and the coordinates of the notch centroid can be obtained. The intersection of the notch centroid and the center of rotation and the edge of the wafer is the center of the gap sought.

The invention proposes a novel pre-alignment using a high-precision laser transmission sensor and a centroid-based algorithm for the conventional wafer pre-alignment positioning method in the IC manufacturing process, which has low pre-alignment precision and insufficient space. Positioning method. The method uses a light-transmissive sensor to detect the edge of the wafer, and uses a centroid algorithm to determine the position of the circular center and the notch, thereby effectively improving the accuracy of the positioning method, reducing the time space occupied by the pre-alignment device, and reducing the time. cost. The specific embodiments of the present invention have been described above. It is to be understood that the invention is not limited to the specific embodiments described above, and various modifications and changes may be made by those skilled in the art without departing from the scope of the invention.

Claims

A wafer pre-alignment method, comprising the steps of:

Step 1: Let the external wafer transfer robot hand over the wafer to the wafer pre-alignment device, and use the visual inspection unit (5) to determine whether the wafer has been placed in the vacuum adsorption unit by detecting the rate of change of the received light intensity (4) Above, when it is detected that the wafer has been placed, the motion control unit (7) is triggered to fix the wafer by the vacuum adsorption unit (4); the vacuum adsorption unit (4) is driven by the θ-Y two-degree-of-freedom motion unit (2) Rotating the wafer for one week, the laser transmission sensor in the visual inspection unit (5) detects the edge position of the wafer, and the data acquisition unit (6) synchronously acquires the wafer edge one-week data obtained by the laser transmission sensor;

Step 2: Let the motion control unit (7) calculate the centroid position coordinates of the wafer using the data of the wafer edge obtained from the data acquisition unit (6) (;, y, the maximum eccentricity of the radial displacement ^ and the radial direction The angle between the maximum eccentricity of the displacement and the horizontal Y direction;

Step 3: The motion control unit (7) issues an instruction to cause the 旋转-Υ two-degree-of-freedom motion unit (2) to drive the wafer rotation angle to make the radial displacement maximum eccentricity ^ in line with the horizontal Y direction. Upper, the radial displacement maximum eccentricity _{emax is} adjusted to the Y-axis, and the wafer is separated from the Θ-Υ two-degree-of-freedom motion unit (2) by the vertical transition unit (3), and the θ-γ two-degree-of-freedom motion unit (2) The Y moves in the linear motion platform, and the center of the rotating platform coincides with the centroid wafer of the wafer to complete the centroid positioning of the wafer;

Step 4: Lower the vertical transition unit (3) and fix the wafer to the vacuum adsorption unit (4). The θ-γ two-degree-of-freedom motion unit (2) drives the vacuum adsorption unit (4) again to rotate the wafer for one week. The unit (5) detects the edge position of the wafer, the data acquisition unit (6) synchronously collects one week of wafer edge data, and the motion control unit (7) analyzes the wafer edge one week data to complete the location of the gap data segment, and issues an instruction to make - Υ two-degree-of-freedom motion unit (2) Rotate the notched data segment to the vicinity of the laser-transmissive sensor for small-scale fine sampling, the data acquisition unit (6) synchronously collects data; the motion control unit (7) utilizes data acquisition from the data The data obtained by the unit (6) calculates the actual notch centroid position of the wafer, and obtains the angle between the notch position of the wafer and the Y direction.

Step 5: The motion control unit (7) issues an instruction to cause the wafer in the Θ-Υ two-degree-of-freedom motion unit (2) to rotate the wafer to a specified angle to complete the wafer notch positioning.

2. The wafer pre-alignment method according to claim 1, wherein in the step 2, the motion control unit (7) calculates a centroid position coordinate of the wafer by using a centroid positioning algorithm (;, y , maximum radial displacement The eccentricity amount 6> and the angle between the maximum eccentricity of the radial displacement and the horizontal Y direction, wherein the centroid localization algorithm is specifically: determining the eccentricity by the displacement value of the wafer edge measured by the laser transmission sensor The relationship between the rotation angle of the 旋转-rotating platform and the edge displacement in the θ-γ two-degree-of-freedom motion unit (2), so that the centroid of the wafer can be accurately calculated.

3. The wafer pre-alignment method according to claim 1, wherein in the step 4, the motion control unit (7) calculates the actual notch centroid position of the wafer by using a centroid positioning algorithm, wherein The centroid localization algorithm is specifically: determining the relationship between the eccentricity, the rotation angle and the edge displacement by the displacement value of the wafer edge measured by the laser transmission sensor, and calculating the notch centroid, the notch centroid and the orientation The center line of the rotating platform is the direction of the notch, and the direction of the notch is rotated to a specified angle, that is, the precise positioning of the wafer notch can be completed.

The wafer pre-alignment method according to claim 1, wherein the data acquisition unit (6) synchronously acquires a wafer edge data obtained by the laser transmission sensor, specifically: The encoder signal to the rotating platform acts as an external clock, and the encoder pulse signal is controlled by the encoder pulse signal of the rotating platform during the rotation of the rotating platform to synchronize the data acquisition by the laser transmitting sensor, so that the laser transmits The analog or digital quantity measured by the sensor can be in one-to-one correspondence with the corresponding rotation angle of the tilting platform.

5. The wafer pre-alignment method according to claim 1, wherein in the step 4, the motion control unit (7) utilizes data acquired from the data acquisition unit (6), utilizing circumferential and notch curvature Different mathematical characteristics are analyzed to calculate the actual notch center position of the wafer.

6. The wafer pre-alignment method according to claim 5, wherein a point on the edge of the wafer having a curvature of less than 3[deg.] is identified as a point on the wafer notch, otherwise, it is determined as a point on the circumference of the wafer. .

7. The wafer pre-alignment method according to claim 1, wherein the centroid position coordinate (y) of the circular center O' is calculated by the following formula:

ς

^ £ ρΟΙράθ ρ sin ΘΟΙράθ

Ρΰάράθ where ^ is the axis coordinate of the circular center Ο, ^ is the Υ axis coordinate of the circular center 0', which is the distance from the center of the rotating platform to the edge of the wafer, which is the turntable at the center of the rotating platform The corner, P (is a function of the radius of the wafer; Calculate the maximum eccentricity of the radial displacement by the positional coordinates of the circular circular heart O ' by the following formula (x, y

Calculate the angle between the maximum eccentricity of the radial displacement and the Y direction by the following formula

Θ = arctan =.

x

The wafer pre-alignment method according to claim 1, wherein in the step 4, the positioning of the notched data segment is specifically: the bevel edge in which the curvature change rate of the notch is the largest is defined The start and end points of the gap; the data acquisition unit (6) collects the analog output signal of the laser-transmitted sensor, and simultaneously acquires the LOW digital output signal of the laser-transmitted sensor; and then searches for the LOW digital output signal data, from 1 The inflection point to the zero change is the starting point of the gap, and the inflection point that changes from 0 to 1 is the end point of the gap, thereby finding the gap data segment.

9. The wafer pre-alignment method according to claim 1, wherein the laser-transmitted sensor comprises a laser emitter, a receiver, and a sensor holder, the laser emitter is for emitting a laser beam, and the receiver is used for Receiving the light intensity signal, the laser emitter and the receiver are fixed on the sensor holder, wherein there is a gap between the laser emitter and the receiver, and the relative position remains unchanged.