JP2001057380A - Semiconductor wafer centering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately align the center of a semiconductor wafer and the position angle (orientation flat) of its flat when a semiconductor wafer is transferred. SOLUTION: This semiconductor wafer centering device is equipped with a wafer rotating means 4 which is mounted with a semiconductor wafer 1 and rotates it, an edge position detector 5 which detects data on the edge position of the wafer 1 through a non-contact manner, an A/D converter 24 which converts the output signals of the edge position detector 5 into digital signals related to the rotation angle of the wafer 1, a DMA data transfer means 26 which transfers the output of the A/D converter 24 to another circuit direct, a central processing unit(CPU) 27 which calculates the eccentric angle and eccentricity of a wafer 1 resting on the edge position signals and rotation angle signals of a wafer transferred by the DMA data transfer means 26, and a wafer drive means 4 and 22a which align the center of the wafer corresponding to the output of the central processing unit 27.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for accurately adjusting a position angle (orientation flat) of a center and a flat portion of a semiconductor wafer when a semiconductor wafer is transferred in a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art In a semiconductor wafer manufacturing apparatus, when a semiconductor wafer is stacked and stored from a cassette to another cassette, or to each stage for inspection or processing, or when transferring between stages, an accurate operation is required. Alignment of the wafer to the center (align the center position of the wafer to the reference position)
Need to do. Further, it is necessary to adjust the angle of the flat portion (or notch) of the wafer (to adjust the center line of the flat portion (or notch) of the wafer to a specific angle). Usually, a cassette or each stage does not have this centering function. Therefore, a method of adding a device for centering a wafer and aligning an angle of a flat portion (or a notch) of a wafer during transfer between the cassettes and the stages. Is being done.

Attention is paid to the fact that a wafer is preliminarily processed into a substantially circular state by an NC apparatus or the like, and the wafer is rotated and its edge position is detected and stored in accordance with the rotation angle. The eccentricity and eccentric angle of the center position of the wafer are calculated based on the maximum value and the minimum value of the detection signal, and the center of the wafer is adjusted based on the eccentricity data. For the sake of illustration, a flat portion (or notch) called an orientation flat is provided in the peripheral portion, but the edge position changes more abruptly at the start and end points of these orientation flats than at other portions. By calculating where the rate of change of the edge position signal has exceeded a certain value,
Determine the angle at which the orientation flat (or notch) exists,
The angle of the center line of the orientation flat portion (or notch portion) (a straight line connecting the center position of the wafer 1 and the center position of the orientation flat portion (or cut portion)) is corrected, and the orientation flat portion or the like is transferred to another device such as a transfer device. There has been proposed an apparatus in which the same apparatus is used so as to be at a specific position with respect to a stage.

FIG. 1 is a configuration diagram showing an example of such a conventional apparatus. In FIG. 1, reference numeral 1 denotes a semiconductor wafer to be centered, which is mounted on a turntable 2. Reference numeral 3 denotes a turntable rotating mechanism for rotating the turntable 2, which is driven by an electric motor 4.
Reference numeral 5 denotes a detector for detecting an edge position of the wafer 1, and includes a light projector 5a and an optical sensor 5b.
The output of the optical sensor 5b continuously changes while maintaining a specific relationship in accordance with the amount of received light, and includes a CCD (charge-coupled device) and a product name PSD (position sensor).
A device whose output changes linearly with respect to the amount of incident light, which is referred to as a “savedetector”, is used. Reference numeral 6 denotes an encoder for detecting the rotation amount of the electric motor 4 corresponding to the rotation angle of the turntable 2. Reference numeral 7 stores the output of the optical sensor 5b and the output of the encoder 6 as a pair of data for each fixed rotation angle of the turntable 2. Memory circuit. If the output of the optical sensor 5b is an analog signal, an A / D converter is provided between the storage circuit 7 and the optical sensor 5b to convert the signal into a digital signal. Numeral 8 writes the output signal of the A / D converter into the storage circuit 7, reads it out when necessary, calculates the amount of eccentricity and the eccentricity angle of the center position of the wafer 1, and corrects the signals (each signal of the rotation angle and the horizontal position). And a central processing circuit (hereinafter referred to as a CPU) for outputting the data. The CPU 8 uses a microcomputer to rotate the table when an edge position is detected by a program, and once receives a signal corresponding to each rotation angle of the wafer and transfers the signal to the storage circuit 7. Reference numeral 9 denotes a servo control circuit for controlling the rotation of the motor 4 for driving the turntable. The servo control circuit 9 drives the motor 4 in response to a command signal from the CPU 8 and stops the motor 4 when the rotation amount matches the command amount from the CPU 8. Is a servo control circuit. Reference numeral 10 denotes an XY table type moving mechanism for moving the turntable 2 together with its rotary drive mechanism in the XY horizontal plane in the figure, and for correcting the position of the wafer 1 by moving the table 2 according to the output of the CPU 8. And the position is controlled by the XY table driving control circuit 11. Here, before describing FIGS. 1 to 3, the positional relationship between the wafer 1 and the turntable 2 will be described with reference to FIG. 4 of the related art. FIG. 2B is a diagram in which the wafer 1 is mounted on the turntable 2 so that the center position Wc of the wafer 1 and the rotation center position Tc of the turntable 2 coincide with each other. A straight line connecting the rotation center position Tc of the table 2 is defined as an X axis.
An axis orthogonal to the axis is defined as a Y axis. Next, FIG. 4D is a view in which the wafer 1 is mounted on the turntable 2 at an arbitrary position angle, and first, the center position Wc of the wafer 1 is eccentric with respect to the rotation center position Tc of the turntable 2. In addition to the above, the X-axis (a straight line connecting the optical sensor 5b and the rotation center position Tc of the turntable 2), the center position Wc of the wafer 1 and the rotation center position Tc of the turntable 2 are added. Eccentric angle θv with a straight line connecting
(The eccentric angle of the prior art).

The operation of the apparatus shown in FIG. 1 will be described with reference to the flowchart shown in FIG. In FIG. 1, when a wafer 1 is placed on a turntable 2 by a transfer device (not shown), an electric motor 4 rotates, and the turntable rotating mechanism 3 driven by this rotates the wafer by a predetermined angle (for example, 1 degree). . At this time, the optical sensor 5b of the edge position detector 5 generates an output corresponding to the amount of light that reaches and is reduced by the wafer immediately below the sensor, and this output is output as a pair of data (θx, Lx) together with the wafer rotation amount signal. It is stored in the storage circuit 7. Further, the turntable 2 is rotated by a predetermined angle, the detection and storage of the edge position are repeated, and the process is continued until the wafer is rotated 360 degrees from the original position (θx = 0). When the detection of the edge positions on the entire circumference of the wafer is completed, the CPU 8 sequentially reads out the data stored in the storage circuit 7 and obtains the maximum value Lmax and the minimum value Lmin of the edge position signal.
And the rotation angles θmax, θ of the corresponding wafers
Calculate min. From the difference between the edge position signals Lmax and Lmin, the CPU 8 calculates the eccentricity amount signal ΔL in the radial direction with respect to the rotation center position Tc of the turntable 2 of the wafer.
(Lmax−Lmin) / 2, and θmax (or θmin)
, The eccentricity angle signal is obtained from the rotation center position Tc of the turntable 2 and the eccentricity signal (x, y) of the center position Wc of the wafer 1 on the x, y plane = (ΔLcos θmin, Δ
L sin θ min) or (x, y) = (− ΔL cos θ)
max, -ΔL sin θ max), and supplies a correction signal determined by these to the XY table control circuit 11 to perform centering.

Here, the wafer edge position detector 5 and signals obtained therefrom will be described. FIG. 3 is an enlarged explanatory view showing a part of the detector 5, and those having the same functions as those in FIG. 1 are denoted by the same reference numerals. The light from the light projector 5a is blocked by the wafer 1 as schematically shown by an arrow in the figure, a part thereof is reduced, and the rest reaches the optical sensor 5b. Therefore, if a sensor whose output changes in direct proportion to the input light quantity is used as the optical sensor 5b, the output becomes a signal proportional to the length of L which changes according to the position of the edge portion of the wafer 1. Therefore, if the center position Wc of the wafer is displaced toward the edge position detector 5 with respect to the rotation center position Tc of the turntable, the output signal is small, and if the center position Wc is displaced on the opposite side, the output signal is large. Becomes

FIG. 4 is a diagram showing how the output of the optical sensor 5b changes at this time. 12A and 12C, the horizontal axis represents the rotation angle θ of the wafer, and the vertical axis represents the output L of the optical sensor 5b.
There is. FIG. 3A shows an output when the wafer 1 is aligned with the center of the turntable 2 as shown in FIG. 3B. In this case, as described above, the wafer 1 is The output of the optical sensor 5b becomes a straight line because it is processed into a perfect circle by the above method. FIG. 3C shows that the center of the wafer 1 is displaced from the rotation center position Tc of the turntable 2 by the distance .DELTA.L at the eccentric angle .theta.v in the direction of the first quadrant of the XY table 10 as shown in FIG. The output at the time is shown. At this time, the output of the optical sensor 5b changes in a substantially sinusoidal manner as the turntable 2 rotates in the direction of the arrow in the drawing (when the turntable 2 rotates, the wafer 1 also rotates). If the maximum value of the output is Lmax and the minimum value is Lmin, the amplitude of the change is (Lmax-Lmin), which is equivalent to twice the amount of eccentricity ΔL. The angle θmin when L = Lmin corresponds to the eccentric angle θv of the wafer 1 before the rotation of the wafer 1 starts. Therefore, from these signals, the current center position of the wafer is represented by coordinates (x, y) = (ΔLcos θmin, ΔLs
inθmin). (When adopting θmax, (x, y) = (− ΔLcosθmax, −ΔLsin
θmax). Therefore, the wafer can be centered by moving the XY table by -ΔLcos θmin in the x direction and by -ΔLsinθmin in the y direction.

In the conventional apparatus shown in FIG. 1, the operation for simultaneously performing the center alignment and the alignment of the orientation flat portion (or notch portion) when the orientation flat portion (or notch portion) is provided in the peripheral portion of the wafer is as follows. Will be described.

FIG. 5A is a plan view of a wafer provided with an orientation flat (a) at a part of the peripheral edge, and FIGS. 5B to 5E show wafers having such a shape. FIG. 6 shows examples of output waveforms of the edge position detector 5 when the eccentricity is placed on a turntable in various directions. When a wafer having a shape as shown in FIG. 5A is rotated, as shown in FIGS. 5B to 5E, another circumferential portion is formed in the orientation flat portion (or cutout portion) (a). Shows a significantly different output change. In particular, since both ends show an extremely large change rate, the position of the orientation flat can be detected by monitoring the change rate of the output of the edge position detector 5. For this reason, the program of the CPU 8 is configured so that a point where the change rate of the edge position detection signal becomes equal to or more than a predetermined value is determined as the end of the orientation flat portion.

In this case, the limit of the change rate is the difference between the maximum value and the minimum value of the output signal, that is, the approximate wafer eccentricity, because the maximum change rate when the circumferential portion is detected varies depending on the eccentricity of the wafer. What is necessary is just to determine according to quantity. In addition, since the method of calculating the amount of eccentricity differs depending on the position of the orientation flat (or notch) and the eccentric angle of the wafer 1, it is necessary to determine the eccentricity.

FIGS. 6 and 7 show flowcharts for performing this operation. Steps 1 to 7 are the same as those in FIG. 4 without the orientation flat. The maximum value and the minimum value of the output signal of the optical sensor 5b may not have a true value because of the presence of the flat portion. In step 8, the maximum value Lmax and the minimum value obtained in step 7 are obtained. (Lmax-Lmin) is obtained from Lmin and the upper limit α of the rate of change is determined. Next, at step 9, the angle θ = 0 to 3
The change rate ΔLx / Δθx of the output signal L during 60 degrees is calculated, and the angle θ1 of the first position and the angle θn of the last position that satisfy {the absolute value of ΔLx / Δθx ≧ α} are searched. This θ
An intermediate angle Δθ between 1 and θn = {(θn−θ1) / 2} + θ
When 1 is obtained, the center of the flat portion exists at a position rotated by Δθ from the original rotation position.

Next, it is determined whether or not the angle θmax at which the output reaches the maximum (L = Lmax) is in the relationship of θ1 ≦ θmax ≦ θn. If θ1 ≦ θmax ≦ θn is satisfied, the wafer is first removed. Since the position corresponding to the maximum value Lmax of the step 7 obtained by the rotation is in the state shown in FIG. 5C included in the orientation flat portion, the true maximum value Lmax has not been obtained. . Therefore, the minimum value L
The angle θmin corresponding to Lmin is defined as the eccentric angle (the angle of the center deviation), and a point 90 degrees away from this (θmin + 90 degrees when θmin ≦ 270 degrees, θmin>
The output of [theta] min-90 [deg.] At 270 [deg.] Is adopted as the intermediate value Lc, and the eccentric amount [Delta] L of the center position Wc of the wafer 1 is equal to Lc.
-Lmin is obtained. From this result, the center position Wc of the wafer 1 is obtained.
Current position coordinates (x, y) = (ΔLcosθmin, ΔL
sin θmin). (However, the direction of the optical sensor 5b is + x.)

On the other hand, the angle θ at which the output L reaches the maximum value Lmax
When max is not between .theta.1 and .theta.n, the orientation flat portion is located at another position, so Lmax obtained in step 7 is adopted as the maximum eccentric amount, and .theta. is set as the angle corresponding to the eccentric angle .theta.v.
Use max. In this case, the actual center position Wc of the wafer 1 is in the direction of θmax + 180 degrees. (FIG. 5
Cases such as (b), (d), and (e). )

Next, an angle θf adjacent to +90 degrees or an angle θf adjacent to −90 degrees with respect to θmax (hereinafter referred to as a flat portion determination angle θf) is an angle (θ1) indicating the orientation flat portion (or notch portion).
To θn), and if it is within the angle indicating the orientation flat (or notch), the angle 270 degrees ahead (or 90 degrees or 270 degrees before) of θmax is set to the intermediate angle. θc, and the output value of the edge position detector 5 at that time is adopted as the intermediate value Lc. If the flat portion determination angle θf is not within the angle indicating the orientation flat portion (or notch portion), the flat portion determination angle θf is set to the intermediate angle θc, and the output value of the edge position detector 5 at that time is set to the intermediate value L.
c, the amount of eccentricity of the wafer 1 ΔL = Lmax−L
Get c. At this time, the intermediate angle θc is as shown in Table 1. That is, when the flat portion determination angle θf is not within the angle indicating the orientation flat portion (or notch portion) of the wafer 1, θ
Let c = θf. Note that the output value of the edge position detector 5 corresponding to the intermediate angle θc becomes the intermediate value Lc. However, when the flat portion determination angle θf is within the angle indicating the orientation flat portion (or notch portion) of the wafer 1, the flat portion determination angle θ
An angle that differs from f by 180 degrees is defined as an intermediate angle θc.
The edge position detector 5 corresponding to the intermediate angle θc
Becomes the intermediate value Lc. However, since the range of the angle data stored in the storage means is 0 degrees to 360 degrees, the flat portion determination angle θf and the intermediate angle θc need to be within the range of the angle data. In order to satisfy this condition, it is necessary to divide the cases as shown in Table 1.

[0015]

[Table 1]

FIG. 8 shows an example of the output waveform of the detector at this time. FIG. 3A corresponds to 1 in Table 1 (b), (c) corresponds to 2 in Table 1, and (d) corresponds to 3 in Table 1 (provided that θ1
<Θf <θn). From the above result, the current position coordinates (x, y) of the center position Wc of the wafer 1 = (− ΔLcos θ)
max, -ΔL sin θ max).

[0017]

The accuracy of the center alignment of the wafer is becoming increasingly strict at present, for example, ± 0.25 mm at the center position, and the accuracy of the angular alignment of the orientation flat portion is ± 0. Approximately 25 degrees is required. In order to satisfy such a requirement, at least 360 degrees / 0.25 degrees = 1,44 in one rotation of the wafer.
Data relating to an edge position signal of 0 or more is required.
In addition, there is a slight error in accuracy in the drive mechanism of the turntable for rotating the wafer, and the shift of the center position of the wafer and the shift of the orientation flat position angle exist simultaneously (FIG. 5A). , Or (e)), since a wafer edge position signal is obtained as a result of integrating these, the detection accuracy is further deteriorated. Therefore, it is necessary to actually secure five times or more the number of data. Is required. Therefore, usually, about 7,500 pieces of data are taken per rotation.

However, in the above-mentioned conventional apparatus, the output of the edge position detector 5 is once taken into the CPU 8 and
In accordance with the program set to 8, the data relating to the edge position signal is sequentially written and stored in the storage circuit. Here, the edge position of the wafer is detected by an edge position detector 5, the detected value is converted into a digital signal by an A / D converter, and stored in a storage circuit 7 via a CPU 8.
Consider when storing in In this case, the operation time of the A / D converter is 30 μm per data relating to the edge position signal.
and a CPU for extracting data from the A / D converter and writing the data to a predetermined address of the storage circuit 7.
Approximately 50 μs is required for processing time of 8 and a total of 80 μs
Is required as the processing time per data. Here, assuming that the wafer is rotated once (360 degrees) per second,
The speed of data detection and storage is 1 / (80 × 10 −6) = 1
The upper limit is 25,000. Normally, considering the safety of operation, the limit is about 60% of the limit, that is, about 7,500 times. With this selection, the CPU is completely occupied during the detection and storage of the required number of data, and there is no room for other operations. Therefore, the calculation of the shift amount of the center position of the wafer, the shift angle of the orientation flat position, and the correction amount thereof is performed by rotating the wafer once, storing all the data relating to the edge position signal, and reading out these data. become.

Therefore, conventionally, in order to improve the detection accuracy, the center shift is first calculated by the first edge position detecting operation, the center position shift is corrected based on the result, and then the wafer is rotated again to obtain a substantially straight line. The position data of the shape and the data of the shape in which only the orientation flat is convex upward are obtained, the orientation of the orientation flat is detected by calculating from this data, and the operation of matching the position of the orientation flat to a predetermined angle is performed based on the result. Like that. For this reason, in the conventional apparatus, 1 second.times.2 times = 2 times for detecting and storing data relating to the wafer rotation and the edge position signal.
Seconds, 1.5 seconds × 2 times = 3 seconds for reading stored data, 3 to 5 seconds are required for calculating and correcting the center position shift and the shift angle of the orientation flat portion depending on the read data, for a total of 8 to 10 seconds. Seconds were needed.

[0020]

SUMMARY OF THE INVENTION The present invention proposes an apparatus for centering a wafer which can be positioned with higher accuracy and higher speed than the above-mentioned conventional apparatus. When a wafer edge position is detected, a detection signal is converted into a digital signal. DMA data transfer means for transferring data directly to the storage circuit without going through the CPU after conversion to
In addition to speeding up memory,
By reducing the U occupancy as much as possible, the number of stored data is greatly increased, and data processing is performed during the idle time of the CPU, thereby shortening the time required for center alignment. Also, by changing the data calculation processing procedure, the detection and storage of the edge position is stopped when the necessary data is obtained without completely rotating the wafer, and the calculation and correction of the deviation amount between the center position and the orientation flat position An operation is performed.

[0021]

FIG. 9 shows an embodiment of the present invention. In FIG. 1, a wafer 1 is placed on a turntable 2, and the turntable 2 is driven to rotate around a θ-axis by an electric motor 4, and the amount of rotation is detected by a θ-axis encoder 6. The edge position of the wafer 1 is detected as an analog signal by the optical sensor 5b of the wafer edge position detector 5.
These are the same as the conventional device shown in FIG. The turntable 2 and the electric motor 4 and the encoder 6 for rotationally driving the turntable 2 are mounted on an X-axis table 21. The X-axis table 21 is an electric motor 22 for driving the X-axis table.
a and the feed screw 22b are moved in the x1-x2 directions in the figure. The amount of movement in the X-axis direction is detected by an X-axis encoder 22c connected to the electric motor 22a.
A lifter 23a lifts and separates the wafer 1 from the turntable, and is connected to an air cylinder 23c driven by a solenoid valve 23b and driven in the Z direction in the figure. An A / D converter 24 converts an analog signal output of the optical sensor 5b into a digital signal. 25
Is a storage circuit, 26 is a DMA data transfer circuit, 27
Is a central processing circuit (CPU), 28a and 28b are motor control circuits, 29a and 29b are comparators and C
The outputs of the motor control circuits 28a and 28b, which receive the motor rotation amount command signals from the PU 27 and convert them into the rotation amount signals of the respective motors 4 and 22a, are compared with the outputs of the encoders 6 and 22c. Drive.

When a pulse motor is used as an electric motor for driving the turntable 2 and the X-axis table 21, the encoders 6 and 22c are not necessary, and C
What is necessary is just to drive according to the number of drive command pulses from PU27.

Next, the DMA data transfer circuit 26 will be described. The DMA data transfer circuit 26 is an abbreviation of a direct memory access circuit, and a circuit corresponding to a CPU to be combined is commercially available in the form of an LSI. For example, when using Intel's 8085 MPU as the CPU, the DMA 8237A type, the Z80 DMA type for Zilog's Z80 MPU, and the 6844 type DM for Motorola's 6809 MPU.
A (both are model names of US manufacturers).

This DMA data transfer circuit is a circuit for directly transferring data between an input / output device, between an input / output device and a memory, and between a memory and a memory without passing through a CPU. Since the CPU only needs to exchange signals for releasing and returning the data bus, the time occupying the CPU is limited
Only a short time of less than a few percent is required when transferring via.
As a result, the wafer edge position detection / storage operation and data processing can be performed while the wafer is rotating.

Next, the embodiment of FIG. 9 will be described with reference to the flowcharts of FIGS. 10 and 11. 9 to 11, when the wafer 1 is placed on the turntable 2 by the transfer means (not shown), the centering operation of the wafer 1 and the angle adjusting operation of the orientation flat portion of the wafer 1 are started. First, .theta.x and the counter x stored in the storage circuit are set to 0, and after waiting for the output of the optical sensor 5b, it is stored in the storage circuit 25 together with the rotation angle .theta.x (= 0) at that time. Also,
Since the output of the optical sensor 5b is at least about 1 V, in step 5, the output signal Lx
Is read and input to the CPU to determine whether Lx ≠ 0. If Lx ≠ 0, it is determined that measurement has started, and the process proceeds to step 6. If Lx = 0, the output signal Lx of the optical sensor is read from the storage circuit 25 again and input to the CPU. Determine if there is. In step 6, the optical sensor 5b read from the storage circuit 25 and input to the CPU
ΔLx = Lx−Lx−1 is calculated from the output signal Lx. In step 7, ΔLx / Δθx> ΔLmax (where Δθx is the unit rotation angle, and ΔLmax is the output change rate ΔLx until then).
/ Maximum value of Δθx). When starting, of course, Lx
= Lx-1 and ΔLx = ΔLmax = 0, so ΔLx / Δθx = Δ
Lmax = 0, and the routine proceeds to step 9. If ΔLx / Δθx> ΔLmax is satisfied in step 7, this ΔLx / Δθx is set as a new ΔLmax in step 8. Thereafter, the process proceeds to step S13. In step 9, θ
It is determined whether x ≧ 360 degrees. When θx ≧ 360 degrees, since the turntable 2 is rotated by 360 degrees, the edge position signals Lx1 to Lx4 for the angles θx1 to θx4 are calculated in step 12, and thereafter, in step 21
Move on to If θx ≧ 360 degrees is not satisfied in step 9, the process proceeds to step 10. In step 10, it is determined whether or not the angles θx1 to θx4 have been selected. If the angles θx1 to θx4 have been selected, the process proceeds to step 11, and if the angles θx1 to θx4 have not been selected, the process proceeds to step 18. In step 11, it is determined whether all the edge position signals Lx1 to Lx4 corresponding to the angles θx1 to θx4 have been calculated,
If all the edge position signals Lx1 to Lx4 have been calculated, in step 12, the edge position signals Lx1 to Lx4 for the angles θx1 to θx4 are calculated. If all the edge position signals Lx1 to Lx4 have not been calculated in step 11, the process proceeds to step 18.

Next, at step 13, the sign of (x-1) is determined (whether the rotation of Δθx has been performed twice or more). At the start, x = 0, ie, x-1 = -1
Therefore, x-1> 0 is not established. for that reason,
Skipping to step 18, the turntable 2 is further rotated by Δθx, and x = x + 1 and θx = θx +
Execute Δθx. After step 18, the process returns to step 4 to store (θx, Lx) in the storage circuit. Thereafter, steps 5 to 13 are executed. At this time, since x = 1, x-1> 0 is not established in step 13. Therefore, skip to step 18 again and turntable 2
Are rotated by Δθx, and x = x + 1 and θx = θ
Execute x + Δθx. Thereafter, steps 4 to 13 are executed in the same manner as described above. At this time, since x = 2, x-1> 0 is satisfied in step 13. for that reason,
Move to step 14.

In step 14, ΔLx at this time and 1
A comparison is made with the previous ΔLx−1 to check ΔLx / ΔLx−1> k (where k is a predetermined constant).
After moving to 8, the steps after step 4 are executed.
When ΔLx / ΔLx−1> k, the change amount of the edge position is large, so it is determined that the orientation flat is the start end, and the process proceeds to step S15. In step 15, from the rotation angle θx = X · Δθx up to this point and the center angle α of the orientation flat part which is known in advance, the rotation angle is 90
Select angles (θx1, θx2, θx3, θx4) separated by degrees.
Thereafter, the process proceeds to step S16. In step 16, edge position signals Lx1, Lx2, Lx3, Lx4 corresponding to the above-mentioned θx1, θx2, θx3, θx4 are calculated. At this time, the position .theta.x1 to be adopted as Lx1 may be an edge position signal Lx corresponding to an angle .theta.x1 = .theta.x + .alpha. Obtained by adding the central angle .alpha. )
Is determined as shown in Table 2.

[0028]

[Table 2]

It is determined in step 17 whether or not all the data at these points has been obtained by the previous wafer rotation. If not, the process proceeds to step 18, where the turntable 2 is further rotated by Δθx. Steps 4 to 16 are repeated. If θx1 to θx4 and the corresponding edge position signals of Lx1 to Lx4 have been obtained, the process proceeds to step 19, where the remaining angles are rotated to 360
It stops when it has been rotated degrees. In addition, the CPU 27 reads out the edge position signals Lx1 to Lx4 corresponding to the angles θx1 to θx4, and the CPU 27 causes the rotation center position Tc of the turntable 2 to be read.
(Eccentricity) L of the center position Wc of the wafer 1 with respect to
The deviation angle (eccentric angle) θe between e and the center position Wc of the wafer with respect to the X axis is calculated by the following equation.

[0030]

(Equation 1)

(Equation 2)

(Equation 3)

However, the angle θ0 for calculating the eccentric angle is the turntable 2 when rotated 360 degrees (the same as before the start of rotation).
Is the angle formed by the straight line connecting the rotation center position Tc and the center position Wc of the wafer 1 and the straight line connecting the position corresponding to the angle θx1 and the position corresponding to the angle θx3, and θST is the X axis and the angle θx1 at this time. This is an angle formed by a straight line connecting the corresponding position and the position corresponding to the angle θx3. In the case of FIG. 12, for example, since the magnitude of θST corresponds to (360 ° −θx1), it becomes known when θx1 is determined. The rotation center position Tc of the turntable 2 and the center position Wc of the wafer, X
The relationship among the axes, θx1 to θx4, etc. is as shown in FIG. 12, and it can be easily understood from this that the above formulas hold.

When Le, θe, and θ0 are calculated in step 21, the CPU 27 issues a command to the turntable driving motor control circuit 28a to rotate the turntable 2 by -θe in step 22, and the deviation is calculated. The angle is corrected, and the center position Wc of the wafer 1 is moved on the X axis. Next, in step 23, the CPU 27 issues a command to the solenoid valve 23b to operate the air cylinder 23c, and
3a is lifted, and the wafer 1 is lifted from the turntable 2. Thereafter, the CPU 27 outputs a command to move the X-axis drive motor control circuit 28b by -Le, and the motor 22a rotates to rotate the feed screw 22b to move the X-axis table 21 by -Le. Step 25
To lower the lifter 23a to return the wafer to the turntable (centering completed).

Thereafter, in step 26, the turntable 2 is rotated to move the center line of the orientation flat portion (the center position Wc of the wafer 1 and the center position of the orientation flat portion (angle θc = θx1-1 /
The rotation is completed until the straight line connecting the position corresponding to 2.alpha.) Coincides with the predetermined angle, and the processing is terminated. When the centering is completed, the center line of the orientation flat is inclined with respect to the X-axis. When the centerline of the orientation flat is aligned with the X-axis, the eccentricity Le is usually small. 2.
The angle of the turntable 2 may be corrected by α). However, when the amount of eccentricity Le is large or when it is desired to exactly match the center line of the orientation flat with a predetermined angle, the eccentric angle calculation angle θ0 and the eccentricity Le correspond to the angles θx1 and θx1 to the end point of the orientation flat portion. The corrected angle of eccentricity θk may be mathematically calculated from the edge position signal Lx1 or the like, and the corrected angle of eccentricity θk may be used instead of the eccentric angle calculation angle θ0. That is, the turntable 2 may be rotated by (θk + ／ · α). For example, FIG.
In this case, the angle θk after the correction of the eccentricity can be calculated mathematically as follows. The eccentricity corrected angle θk is, as shown in FIG. 12, a straight line connecting the rotation center position Tc of the turntable 2 and the center position Wc of the wafer 1 (hereinafter, referred to as an eccentric angle axis), and This is an angle formed by a straight line connecting the center position Wc and a position corresponding to the angle θx1 (hereinafter, referred to as a position Px1). First, turntable 2
Distance TcPx1 from the rotation center position Tc to the position Px1 (the distance TcPx1 corresponds to Lx1. That is, the distance between the edge position detector and the turntable 2 is determined by the specification. TcPx1 can be calculated), the amount of eccentricity Le and the angle θ for calculating the eccentric angle.
With 0, the distance WcPx1 from the center position Wc of the wafer 1 to the position Px1 can be calculated by the following equation. Since the specifications of the wafer, such as the diameter and the size of the flat portion, are determined, the value of WcPx1, which is the radius of the wafer 1, can be a value determined by the specifications. ^{WcPx1 = √ (TcPx1 2 + Le} 2 -2 * TcPx1 * Le * co
s (θ0)) Further, assuming that the intersection point when a straight line perpendicular to the eccentric angle axis is drawn from the position Px1 is the position Pk, ∠PkPx1Tc can be calculated by the following equation. ∠PkPx1Tc = 180−90−θ0 [°] Further, the distance PkPx1 from the position Pk to the position Px1 can be calculated by the following equation. PkPx1 = TcPx1 * cos θ (θ = ∠PkPx1Tc) Therefore, θk can be calculated by the following equation. θk = sin-1 (PkPx1 / WcPx1) [°] Furthermore, in order to set the center line of the orientation flat to a position inclined by γ degrees with respect to the X axis, the center line of the orientation flat is positioned with respect to the X axis when the centering is completed. Since it is tilted by (θ0 + ／ · α), it may be rotated by γ- (θ0 + ／ · α). Also in this case, when the eccentricity Le is large or when it is desired to exactly match the center line of the orientation flat with the predetermined angle, the corrected eccentricity angle θk is used instead of the eccentric angle calculation angle θ0 as in the case described above. Then, the turntable 2 may be rotated by γ− (θk + ／ · α).

In steps 19 and 20, 3
Although it was rotated to 60 degrees, by changing the calculation formula at the time of position correction, the rotation for detecting the edge position was stopped at the position where the data of Lx1 to Lx4 corresponding to θx1 to θx4 was obtained in step 17. , Step 21 may be performed. In this case, since the wafer has not returned to the initial position, the rotation angle θx up to this point may be added to the calculation and correction of the shift angle and shift amount.

It should be noted that the present invention is not limited to the center alignment of wafers having the above-mentioned orientation flats and the angle adjustment of the orientation flats. It can also be applied to the alignment of plate-like objects.

[0036]

According to the apparatus of the present invention, when the edge position is detected by rotating the wafer, the data is directly stored in the storage circuit from the A / D converter by the DMA data transfer means without passing through the CPU. Therefore, there is almost no time occupied by the CPU when detecting and storing the wafer edge position. In parallel with this detection and storage, the calculation for detecting the center position shift, the shift direction (angle), and the orientation flat position is performed. This makes it possible to reduce the time required for center alignment. Also, since the CPU is hardly occupied for edge position detection and storage, the unit rotation angle for obtaining data at the same rotation speed can be reduced to a fraction of that of the conventional device even at the same rotation speed. it can. As a result, conventionally, the center position deviation of the wafer 1 is detected and detected.
The required accuracy could not be obtained unless the wafer was rotated again after the correction and the change in the edge position was detected only by the change in the orientation flat portion, so that the required accuracy could not be obtained. Even if the displacement and the detection of the orientation flat position are performed simultaneously, sufficient accuracy can be obtained.

In the apparatus according to the present invention, as in the conventional apparatus described with reference to FIG. 1, the result when the wafer is rotated at one rotation per second was examined. In this case, the rotation of the wafer for detecting the edge position is set to one time, and instead, the number of data to be collected per rotation is set to three to four of the conventional value.
As a result, the wafer rotation / detection storage and the orientation flat portion were found as a result of performing center alignment and orientation flat alignment in the procedure shown in the flowcharts of FIGS.
It took one second to select x1 to θx4, and then two to three seconds to calculate and correct θe and Le. The total was completed in three to four seconds, and the accuracy was sufficient. This required time is as short as 30 to 40% of the time required by the conventional apparatus, and a great effect of the present invention was confirmed. The difference in the required time fluctuates by a maximum of about 1 second as illustrated, for example, due to the difference in the amount of displacement between the orientation flat position and the center position from the rotation start position.

[Brief description of the drawings]

FIG. 1 is a connection diagram showing an example of a conventional device.

FIG. 2 is a flowchart for explaining the operation of the apparatus of FIG. 1;

FIG. 3 is an explanatory diagram of a detector for detecting a wafer edge position.

FIG. 4 is a diagram showing a state of an output change of an optical sensor 5b of an edge position detector 5;

FIG. 5 is a plan view of a wafer provided with a flat portion (orientation flat) and a diagram showing a change in output of an optical sensor 5b when an edge position of the wafer is detected.

FIG. 6 is a flowchart (1) of calculating a wafer eccentricity as shown in FIG. 5 in the conventional apparatus of FIG. 1;

FIG. 7 is a flowchart (2) of calculating the eccentricity of the wafer as shown in FIG. 5 in the conventional apparatus of FIG. 1;

8 is a diagram for explaining another method of adopting an edge position signal of a wafer provided with a flat portion in the conventional apparatus of FIG. 1;

FIG. 9 is a connection diagram showing an embodiment of the present invention.

FIG. 10 is a flowchart (1) for explaining the operation of the embodiment in FIG. 9;

FIG. 11 is a flowchart (2) for explaining the operation of the embodiment in FIG. 9;

FIG. 12 is an explanatory view when centering and orienting the wafer having an orientation flat portion by the procedure of the embodiment of FIG. 9 and the flowcharts of FIGS. 10 and 11;

[Explanation of symbols]

 Reference Signs List 1 wafer 2 turntable 4 turntable rotating motor 5 edge position detector 5a projector 5b optical sensor 6 encoder 21 X-axis table 22a X-axis table driving motor 22b feed screw 22c X-axis encoder 23a lifter 23b solenoid valve 23c air cylinder 24A / D converter 25 Storage circuit 26 DMA data transfer circuit 27 Central processing unit (CPU) 28a Motor control circuit for turntable drive 28b Motor control circuit for X-axis drive 29a Comparator 29b Comparator

Claims (4)

[Claims] 1. A wafer rotating means for mounting and rotating a circularly shaped semiconductor wafer, an edge position detector for detecting data on an edge position of the wafer in a non-contact manner,
An A / D converter for converting an output signal of the edge position detector into a digital signal in relation to a wafer rotation angle, and a DMA for directly transferring an output of the A / D converter to another circuit
Data transfer means, central processing means for calculating the wafer eccentricity and eccentric angle from the wafer edge position signal and rotation angle signal transferred by the DMA data transfer means, and A semiconductor wafer centering device, comprising: a wafer driving means for centering the wafer. 2. An apparatus for centering a semiconductor wafer having a circular shape and having a flat portion or a notch in a part of a circumference thereof, wherein the wafer rotating means rotates the wafer and an edge position of the wafer. An edge position detector for detecting data in a non-contact manner, an A / D converter for converting an output signal of the edge position detector into a digital signal in relation to a wafer rotation angle, and an output of the A / D converter. DMA data transfer means for directly transferring the data to another circuit; calculating the rate of change of the wafer edge position from the wafer edge position signal and the rotation angle signal transferred by the DMA data transfer means; From the position change rate signal, the wafer eccentricity,
Central processing means for calculating the eccentric angle and the center position of the flat portion or the notch; and adjusting the center of the wafer and the center line of the flat portion or the notch to a specific angle according to the output of the central processing means. A semiconductor wafer centering device comprising a wafer driving means. 3. An optical sensor when the optical sensor detects an end point of a flat portion or a notch by rotating the turntable around a rotation center position of the turntable from a state where a wafer is first placed on the wafer. Is output as the wafer edge position signal Lx1, the wafer edge position signal Lx1 is rotated by 90 degrees, 180 degrees, and 270 degrees from the detected position, and the wafer edge position signal Lx1 is rotated from the detected position to become 360 degrees or more. The output of the optical sensor at the position rotated by 360 degrees is defined as the wafer edge position signals Lx2, Lx3, and Lx4, and a straight line connecting the position of the optical sensor and the rotation center position of the turntable is defined as the X axis.
A straight line connecting the end point of the flat portion or the notch and the rotation center position of the turntable is used as the end center axis,
From the wafer edge position signals Lx1, Lx2, Lx3, and Lx4, an eccentricity Le and an eccentric angle calculation angle θ0 are calculated, and an eccentric angle calculation angle θ0 and an angle θST formed between the X axis and the end center axis are calculated. 3. The centering device for a semiconductor wafer according to claim 1, wherein the device calculates a eccentric angle θe of the difference. 4. An eccentricity Le calculated by a central processing unit.
Is 1/2 ｛(Lx3-Lx1) ² + (Lx4-Lx2) ^{2 2 1/2}
And the eccentric angle calculation angle θ0 is tan ⁻¹ ｛(Lx2
4. The semiconductor wafer centering apparatus according to claim 3, wherein -Lx4) / (Lx1-Lx3)}.