JP2729297B2 - Semiconductor wafer centering equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention accurately aligns a center portion of a wafer and a flat portion or notch indicating a crystal direction at a predetermined angle when a semiconductor wafer is transferred in a semiconductor manufacturing apparatus. And a device for the same. 2. Description of the Related Art In a semiconductor wafer manufacturing apparatus, a wafer is accurately centered when transferring a semiconductor wafer from a stacked cassette to another cassette, to each stage for inspection or processing, or between stages. Need to be matched. Usually, since the cassette and each stage are not provided with this centering function, a method of adding a centering device during transfer between them is performed. FIG. 10 is an external view showing an example of such a conventional apparatus, and FIG. 10 (a) shows a case where a wafer 102 is dropped into a container 101 called a centering cup whose inner diameter changes in a tapered shape. FIG. 2B shows a case in which the center is adjusted by holding the wafer 102 with the scroll chuck 103. [Problems to be Solved by the Invention] In the conventional apparatus as described above, since the center is adjusted while rubbing the edge or the back surface of the thin wafer, the generation of dust which is most disliked in the semiconductor manufacturing apparatus is generated. There is a drawback that the wafer cannot be saved, and there is a risk of damaging the wafer. In order to prevent the damage, it is necessary to perform a centering operation slowly and softly, so that the speed cannot be increased. [Means for Solving the Problems] The present invention focuses on the fact that a wafer is preliminarily processed by an NC device or the like into a substantially circular state, and rotates the wafer to rotate its edge position. Detected and stored in correspondence with the angle, the eccentricity and direction of the wafer position 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. . Further, the wafer is provided with flat portions (or notches) in the peripheral portion to indicate the crystal direction, but at the start point and the end point of these flat portions, etc., the edge position is smaller than in other portions. Since the change becomes steep, by calculating the point where the change rate of the edge position data is equal to or more than a certain value, the flat portion or the like is located at a specific position with respect to another stage such as a transfer device. This is performed by the device described above. [Operation] According to the present invention, as described above, the center and the position of the flat portion (or notch) of the wafer are detected by rotating the wafer only by one rotation, and the position of the wafer mounted table or the other The center and the flat part (or notch) are aligned when the stage is transferred to the stage. Embodiment FIG. 1 is a configuration diagram showing an embodiment of the apparatus of the present invention. In FIG. 1, reference numeral 1 denotes a semiconductor wafer to be centered, which is mounted on a turntable 2. 3
Is a turntable rotating mechanism for rotating the turntable 2, and is driven by the 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. This optical sensor
5b is a type in which the output changes continuously according to the amount of received light while maintaining a specific relationship. The output is linear with respect to the amount of incident light called a CCD (Charge Coupled Device) or a trade name PSD (Position Sensitive Detector). It is desirable that it changes dynamically.
Reference numeral 6 denotes an encoder for detecting a rotation amount of the electric motor 4 corresponding to the rotation angle of the turntable 2 and outputting a digital signal. Reference numeral 7 denotes an output of the optical sensor 5b and an output of the encoder 6 as one.
This is a storage circuit that stores, as a pair of data, for each fixed rotation angle of the turntable 2. Here, when the output of the optical sensor 5b is an analog signal, an A / D converter may be provided between the storage circuit 7 and the optical sensor 5b. An arithmetic circuit 8 reads out the output of the storage circuit 7, calculates the deviation amount and direction of the center position of the wafer 1, and outputs correction signals (signals of the rotation angle and the horizontal position). Available. When a microcomputer is used for the arithmetic circuit, the table can be rotated when the edge position is detected, and a command signal or the like for storing a signal corresponding to each rotation angle of the wafer can be output. 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 accordance with a command signal from the arithmetic circuit 8 and stops the motor 4 when the rotation amount matches the output of the encoder 6. This is a normal servo control circuit. Reference numeral 10 denotes an XY table type moving mechanism for moving the turntable 2 together with its rotation drive mechanism in the XY horizontal plane shown in the figure.
The position of the wafer 1 is corrected by moving the table 2 in accordance with the output of the arithmetic circuit 8, and the position is controlled by the XY table driving control circuit 11. An example of centering a wafer having no flat portion or notch in the apparatus of FIG. 1 will be described with reference to the flowchart of 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 to a predetermined angle ( (For example, once). At this time, the optical sensor 5b of the edge position detector 5 generates an output in accordance with the amount of light that arrives after being reduced by the wafer immediately below the optical sensor. This output is output together with a wafer rotation amount signal and a pair of data (θx, Lx) 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 position of the entire circumference of the wafer is completed, the arithmetic circuit 8 sequentially reads out the data stored in the storage circuit 7 and determines the maximum value Lmax and the minimum value Lmin of the edge position signal and the rotation angle of the wafer corresponding to each. Calculate θmax and θmin. The arithmetic circuit 8 also calculates the edge position signal Lmax
From the difference from Lmin, an eccentricity amount signal ΔL = (Lmax−Lmin) / 2 in the diameter direction with respect to the rotation center of the turntable 2 of the wafer is obtained, and the eccentricity angle signal θv corresponds to θmin in FIG. Assuming that the coordinates of the center position of the turntable 2 on the XY plane with respect to the rotation center are (x, y) = (0, 0), the X coordinate = ΔLcosθv = ΔLcosθmin Y coordinate = ΔLsinθv = ΔLsinθmin, and a deviation signal (x, y) on the X and Y planes of the center position of the wafer with respect to the rotation center of the turntable 2 can be obtained as (ΔLcosθmin, ΔLsinθmin). Since θmax = θmin + 180 degrees, substituting this into the above equation gives (x, y) = (− ΔLcosθmax ′, −ΔLsinθmax). With these, a position correction signal is supplied to the XY table control circuit to perform centering. Here, the wafer edge position detector 5 and signals obtained therefrom will be described. FIG. 3 is an explanatory diagram showing the detector 5 in an enlarged manner. In the drawing, components 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, when 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 wafer 1 is deviated toward the edge position detector 5 with respect to the center of the turntable 2, the output signal is small, and if the wafer 1 is deviated to the opposite side, the output signal is large. Here, in order to simplify the description, first, a wafer 1 having a circular shape without a flat portion or a notch will be described. The state of the output change of the optical sensor 5b at this time is shown in the diagram of FIG. In the figure, the horizontal axis represents the rotation angle θ of the wafer, and the vertical axis represents the output L of the optical sensor 5b. FIG. 3A shows the output when the wafer 1 coincides with the center of the turntable 2 as shown on the left side. In this case, as described above, the wafer 1 is transferred to an NC machine or the like. Therefore, the output of the optical sensor is linear because it is processed into a perfect circle. FIG. 3B shows the output when the center of the wafer 1 is displaced from the rotation center of the turntable 2 in the direction of the first quadrant of the XY plane of the XY table 10 by an angle θv and a distance ΔL. At this time, the output of the optical sensor 5b changes in a substantially sinusoidal manner as the wafer 1 rotates in the direction of the arrow in the figure. The amplitude of the change is (Lmax−Lmin), where Lmax is the maximum value of the output and Lmin is the minimum value, which is equivalent to twice the eccentricity ΔL. The angle θmin when L = Lmin corresponds to the eccentric angle θv of the wafer 1 from the direction of the optical sensor 5b on the XY plane before the rotation of the wafer starts. Therefore, it can be seen from these signals that the center position of the wafer before the start of rotation is at coordinates (x, y) = (ΔLcosθmin, ΔLsinθmin). (When θmax is adopted, θmax = θmin + 180 degrees, so when this is substituted, (x, y) = (− ΔLcosθmax, −ΔLsinθmax).) Therefore, the XY tail is shifted in the X direction by −ΔLcosθmin, Y
-ΔLsinθmin in the direction (or + ΔLcosθmax in the X direction,
If the wafer is moved by + ΔL sin θ max in the Y direction, the wafer can be centered. According to the present invention, the center of the flat part (or notch) and the position of the flat part (or notch) when the flat part (or notch) is provided at the peripheral portion of the wafer are simultaneously adjusted by devising the contents of the arithmetic circuit. Yes, and will be described in detail below with reference to FIGS. FIG. 5 (a) is a plan view of a wafer provided with a flat portion (a) at a part of the peripheral portion, and FIGS. 5 (b) to (e).
Shows an example of an output waveform of the edge position detector when the wafer having such a shape is placed on the turntable 2 while being eccentric in various directions. When a wafer having a shape as shown in FIG. 5 (a) is rotated, its flat portion or notch portion (a) as shown in FIGS. 5 (b) to (e) is obtained.
Shows a change in output that is significantly different from other circumferential portions. In particular, since both ends show an extremely large change rate, the position of the flat portion can be detected by monitoring the change rate of the output of the edge position detector. Therefore, in the present invention, the arithmetic circuit 8 is configured so that a point where the rate of change of the edge position detection signal becomes equal to or more than a predetermined value is determined as both ends of the flat portion. In this case, the limit of the rate of change is the left of the maximum value and the minimum value of the output signal, that is, the approximate amount of wafer eccentricity, because the maximum rate of change when detecting the circumference is different depending on the eccentricity of the wafer. , May be determined according to. In addition, since the method of calculating the amount of eccentricity differs depending on the position of the flat portion (or the notch) and the eccentric direction of the wafer, it is necessary to determine the eccentric amount. FIG. 6 shows a flowchart for performing this. Steps 1 to 7 are the same as those in FIG. 4 having no flat portion. Here, 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, but in step 8, the maximum value obtained in step 7 is input. From Lmax and minimum value Lmin (Lmax-Lmin)
To determine the upper limit α of the rate of change. Next, in step 9, the rate of change dL / dθ of the output signal L from the angle θ = 0 ° to 360 ° is calculated, and the first position θ1 where the absolute value of (dL / dθ)｝ ≧ α is obtained. Find the last position θn. This θ
When the intermediate point Δθ = {(θn−θ1) / 2} + θ1 between 1 and θn 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) satisfies the relationship of θ1 ≦ θmax ≦ θn. If θ1 ≦ θmax ≦ θn, the wafer is rotated first. The maximum value Lmax of step 7 obtained by
Is in a state as shown in FIG. 5 (c) included in the flat portion, so that the true maximum value has not been obtained.
Therefore, a minimum value Lmin is adopted as a reference, and an angle θmin corresponding to Lmin is defined as a deviation direction θv (a direction of center shift),
90 ° away from this (θmin + 9 when θmin ≦ 270 °)
0 °, θmin> 270 °, θmin−90 °) is adopted as the middle point Lc, and the center deviation ΔL = Lc−Lmin of the wafer is obtained. From this result, the position coordinates (x, y) before rotation of the wafer center = (ΔLcosθmin, ΔLsinθmin) are obtained. (However, the direction of the optical sensor 5b is + X.) On the other hand, when the angle θmax at which the output L reaches the maximum value Lmax is not between θ1 and θn, the flat portion is located at another position, and thus the maximum deviation amount Lmax obtained in step 7 is adopted, and θmax is adopted as a value corresponding to the deviation direction θv. In this case, the actual wafer center direction is the direction of θmax + 180 degrees. (Cases as shown in FIGS. 5 (b), (d), and (e)) Next, it is determined whether or not the point θf adjacent to θmax by 90 degrees is in the flat portion, and the inside of the flat portion, that is, θ1 to If it is between θn, the output of the point 270 degrees ahead (or 90 degrees before) is used, and if it is not a flat portion, the output of that point is used as the middle point Lc, and the deviation amount of the wafer ΔL = Lmax−Lc Get. At this time, the angle θc of the midpoint position is θmax
Table 1 shows the position θf at which the presence of a flat portion is to be determined based on the value of θ and the corresponding angle θc of the output to be adopted as the middle point. FIG. 7 shows an example of the output waveform of the detector at this time. FIG. 3A shows Table 1 (1), and FIGS. 2B and 2C show Table 1 2.
(D) corresponds to 3 in Table 1 (provided that θ1 <θf <θn). From the above result, the current position coordinates (x, y) of the wafer center = (− ΔLcosθ′max, −ΔLsinθmax) are obtained. Thus, the XY table is driven to perform centering, and the turntable is rotated so that the center of the flat portion is at a predetermined angle by the flat portion center position angle Δθ obtained earlier. Note that the above is an example of a method of calculating the wafer deviation amount and the deviation direction based on the θmin position. This calculation method is based on θmax and can be compared with a standard sine wave. However, any method may be used, such as a method of predicting the position data of the flat portion and calculating Lmax, Lmin, Lc, θv, and Δθ. In the above description, an example has been described in which centering is performed by moving the entire wafer turntable 2 two-dimensionally in the XY plane according to the output of the arithmetic circuit 8 using the XY table. It is not limited to a device having a simple structure. For example, a table that can move only in one axis direction (for example, the X axis) may be used instead of the XY table. In this case, similarly to the above description, the wafer is rotated once to calculate the deviation amount ΔL and the direction θv at the center of the wafer, and when aligning the center, the wafer turntable is first corrected in the direction (−θv) for correcting the deviation angle. ), And the entire turntable is moved by −ΔL after the deflection direction is made to coincide with the X-axis direction. (However, the order may be reversed, and the rotation and the X-axis direction correction may be performed simultaneously.) In this case, the turntable position can be corrected by only one axis, so that the structure is simplified and the control is simplified. Become. Further, in the embodiment shown in FIG. 1, the center alignment and the alignment are performed by moving and rotating the entire wafer turntable in the horizontal direction. However, the present invention is not limited to this. After calculating the amount, the wafer may be once lifted off the turntable, separated from the turntable, moved in the horizontal direction in this state, and re-mounted on the turntable using three-dimensional handling means. Further, in the case where the wafer is transferred to another stage for processing after being centered, only the center position of the wafer is calculated following the edge detection. If the processing is performed by correcting the distance signal between apparatuses, the centering step and the transfer step can be performed in one step, so that the wafer moving means of the centering apparatus can be omitted and the tact time can be reduced. . FIG. 8 is an external view showing another embodiment of the present invention as described above, in which a three-dimensional robot is used as wafer handling means. In FIG. 1, reference numeral 21 denotes a wafer stocker, which stores wafers assembled on another stage (not shown). Reference numeral 22 denotes a processing stage, which is provided with a processing device for performing predetermined processing on the centered wafer.
Reference numeral 23 denotes a robot having three axes (X axis = horizontal direction, Φ axis = rotation direction, Z axis = vertical direction), and has a claw for transferring a wafer at the tip of an arm. Numeral 24 denotes a wafer center detecting mechanism for detecting the center position, which comprises the turntable 2, the edge detector 5 and their accessories in the embodiment of FIG. 27 is a base equipped with these. In the figure, the control device is not shown. The operation of the apparatus in FIG. 8 will be described with reference to the flowchart in FIG. In the apparatus shown in FIG. 8, first, the robot 23 rotates the arm to take out one wafer from the wafer stocker 21 and rotates it about 180 degrees clockwise to drop it on the turntable 2 of the wafer center detecting mechanism 24. After the arm of the robot 23 retreats, the wafer rotates once by the turntable 2 of the wafer center detecting mechanism, and the center position is calculated by the output of the edge position detector 5 as described above. The calculation result is supplied to a control circuit of the robot 23 (not shown). In addition, in order to align the flat portion and the notch portion provided on the wafer 1 in a certain direction, the flat portion position direction signal (θ1 and θn in the flowchart of FIG. 6) obtained by the above-described edge position detection operation. Then, the turntable 2 is further rotated until the flat portion reaches a predetermined position by an angle Δθ = {(θn−θ1) / 2} + θ1 between the wafer and the wafer. The robot is lifted from the table, rotated left by about 90 degrees, and transferred to the processing stage 22. At this time, the amount of movement of the wafer by the robot 22 is first determined with respect to the true positional relationship between the wafer center detection mechanism 24 and the processing stage 22. If it is determined based on a signal corrected based on a signal calculated at the time of detecting the center position, the wafer transferred to the processing stage has a position accurately centered with respect to the processing stage. Equipment After the eccentricity signal is obtained by the center position detecting operation, the wafer is once lifted from the turntable by the robot 23 and moved by the Φ axis and the X axis of the robot 23 according to the eccentricity signal. [Effect of the Invention] As described above, in the present invention, a change in the edge position can be obtained in a non-contact manner by simply rotating the wafer by one rotation. , The eccentricity of the wafer, the eccentric direction and the direction of the center of the flat portion or the notch are calculated at the same time, and the wafer is moved in accordance with the calculation result. And the wafer does not slide, so that no dust is generated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 explains an operation when only the centering of the apparatus of FIG. 1 is performed on a wafer having no flat portion. Flowchart for the third
FIG. 4 is an enlarged view of a part of the detector 5 in the embodiment of FIG. 1, and FIGS. 4A and 4B are diagrams showing changes in the output of the optical sensor 5b with respect to a circular wafer. , Fifth
FIG. 5A is a plan view showing an example of a wafer in which a flat portion is provided in a part of the peripheral portion. FIGS. 5B to 5E show various types of wafers having the shape shown in FIG. FIG. 6 is a diagram showing an example of an output waveform of an edge position detector when placed on a turntable eccentrically in the direction of FIG. 7 (a) to 7 (d) are diagrams showing examples of output waveforms of the edge position detector when the flat portion is included in one of the middle points, and FIG. 8 is a diagram showing the present invention. FIG. 9 is an external view showing another embodiment, FIG. 9 is a flowchart for explaining the operation of the apparatus shown in FIG. 8, and FIG. 10 is an external view showing an example of a conventional apparatus. 1 ... wafer, 2 ... turntable, 5 ... wafer edge detector, 5a ... light emitter, 5b ... light sensor, 6 ... encoder, 7 ... memory circuit, 8 ... arithmetic circuit, 9 ... servo Control circuit, 10: XY table, 11: XY table position control circuit, 21: Wafer stocker, 23: Robot, 24: Wafer center detection mechanism.

Claims (1)

(57) [Claims] What is claimed is: 1. A centering device for a semiconductor wafer having a flat portion (or a notch portion) formed in a circular shape and having a flat portion (or a notch portion) in a part of the circumference, comprising: a wafer rotating means for rotating the wafer; and a signal relating to an edge position of the wafer. An edge position detector that obtains the data in a non-contact manner, storage means for storing an output signal of the edge position detector as data corresponding to a wafer rotation angle for each predetermined rotation angle, and reading the wafer edge position data stored in the storage means Calculating a maximum value Lmax, a minimum value Lmin, and a rate of change dLx / dθ of the wafer edge position signal to calculate an eccentric amount ΔL, an eccentric direction θv, and a direction Δθ of the center of a flat portion (or a notch) of the wafer. A semiconductor driving means for adjusting the center of the wafer and the center of the flat portion (or notch) to a specific angle in accordance with the output of the arithmetic means. Wafer of the center alignment apparatus. 2. 2. The semiconductor wafer centering apparatus according to claim 1, wherein said wafer driving means is means for horizontally moving the entire rotating means on which said wafer is mounted. 3. The wafer driving means is a mechanism for transferring the wafer from the wafer rotating means to another, and the centering of the wafer is performed by correcting a wafer moving amount at the time of transferring the wafer by an output of the calculating means. 2. An apparatus for centering a semiconductor wafer according to claim 1, wherein said means is a means for performing said operation. 4. The calculating means is means for calculating the eccentric direction of the wafer as an angle θv with respect to the original rotation position of the wafer, and the wafer rotating means rotates the wafer to detect an edge position of the wafer and then rotates the wafer. Means for rotating the wafer by −θv further until the specific axis direction of the wafer driving means coincides with the eccentric direction according to the calculated eccentric direction signal θv, and the centering of the wafer is performed by the driving means. Only by the specific axis of-
2. The apparatus for centering a semiconductor wafer according to claim 1, wherein the apparatus is moved horizontally by ΔL.