JP3935532B2 - Wafer positioning device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wafer positioning apparatus for positioning a wafer based on information on a wafer notch formed of an orientation flat (hereinafter referred to as an orientation flat) or a notch formed on a semiconductor wafer.
[0002]
[Prior art]
Conventionally, as an example of this type of wafer positioning apparatus, there is an apparatus that detects information on an orientation flat or a notch (hereinafter referred to as orientation flat or the like when referring to both) shown in FIG. 4 in a non-contact manner. The wafer 1 has a disc shape, and a wafer notch (described later) 1a formed along a part of the outer peripheral surface along the axial direction and a wafer edge (described later) forming an arc surface other than the wafer notch. 1b. The wafer 1 is fixed to a vacuum suction pad 2, the vacuum suction pad 2 is connected to a rotary stage 3, and the wafer 1 is rotated by rotating the rotary stage 3. A light emitting diode 4 and a photodetector 5 for detecting an orientation flat of the wafer 1 are provided at the end of the wafer 1, and a detection signal of the photodetector 5 is amplified by an amplifier 6 and input to a controller 9 described below.
[0003]
The controller 9 includes an A / D converter 7 and an arithmetic processing unit 8. The A / D converter 7 converts an analog signal amplified by the amplifier 6 into a digital signal. The arithmetic processing unit 8 is an A / D converter 7. The digital signal converted by the above is input, a desired calculation process described later is performed, and a control signal is output to the rotary stage 3.
[0004]
In such a configuration, light is constantly emitted from the light emitting diode 4 toward the photodetector 5, and only light that is not shielded by the wafer 1 reaches the light receiving surface of the photodetector 5 and is converted into an electrical signal.
[0005]
When the wafer 1 is rotated as shown in FIG. 5A by rotating the rotary stage 3, the output signal of the photodetector 5 changes as shown in FIG. 5B.
When the orientation flat portion 1a of the wafer 1 is applied to the light detection portion of the photodetector 5, the amount of light shielded by the wafer edge portion 1b decreases, and the amount of light reaching the photodetector 5 increases accordingly. Further, as the rotation of the wafer 1 proceeds, the amount of light shielded by the wafer edge 1b again increases, and the amount of light reaching the photodetector 5 decreases accordingly. As a result, the temporal change in the output signal of the photodetector 5 when the orientation flat portion 1a of the wafer 1 passes through the light detection portion of the photodetector 5 is as indicated by T in FIG. The large undulation signal other than the T portion is due to the eccentricity of the wafer 1.
[0006]
The above description is for the case where the wafer 1 has the orientation flat 1a. However, when the wafer 1 has the notch 1c as shown in FIG. 6A, the output signal of the photodetector 5 is as shown in FIG. 6B. become.
[0007]
The position of the orientation flat 1a or the notch 1c is detected from the output signal of the photodetector 5 when the wafer 1 is rotated as described above, thereby positioning the wafer 1. The output signal of the photodetector 5 when the wafer 1 is rotated. Is a signal in which the signal of the orientation flat 1a or the notch 1c is included in the signal of a large swell due to the eccentricity of rotation. For this reason, even if the threshold level is set as it is, the position of the notch 1c is detected when the notch signal is smaller than the rotational eccentricity signal as in the wafer rotation signal of FIG. 6B. It becomes impossible to do. Therefore, it is necessary to separate or discriminate the rotational eccentricity signal from the notch signal using any means.
[0008]
Therefore, when the arithmetic processing unit 8 calculates the signal difference during wafer rotation, the differential signals as shown in FIGS. 5B and 6B to FIGS. 7A and 8A are obtained. . Then, even when the notch signal is buried in the rotation eccentricity signal of FIG. 6B, the notch portion is considerably emphasized as compared with the rotation eccentricity portion as shown in FIG. 8A.
[0009]
Then, with respect to the differential signal at the time of wafer rotation as shown in FIG. 8A, the threshold level is set to positive (TL +) and negative (TL−), and the position <up> where the differential signal is equal to or higher than TL +. The position of the wafer notch is determined based on the center (↑ mark) of the position <down> that is equal to or less than TL-.
[0010]
[Problems to be solved by the invention]
However, in this method, the detection positions <up> and <down> are not symmetric with respect to the center position (▽ mark) of the notch portion, and the center position (↑ mark) of the detected notch portion is shifted accordingly. Become.
[0011]
In particular, as shown in FIGS. 7A and 7B, when the notch is an orientation flat, the distance between the detection positions <up> and <down> is large. ) Greatly deviates from the actual center position of the orientation flat (marked with ▽). Therefore, when the wafer is positioned, the orientation of the wafer is shifted.
[0012]
The object of the present invention is to separate the rotation eccentricity signal and wafer notch signal at the time of wafer rotation, so that the center position of the detected wafer notch is not shifted from the actual wafer notch center position, An object of the present invention is to provide a wafer positioning apparatus capable of accurately positioning a wafer.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the invention corresponding to claim 1 is characterized in that a means for adsorbing and fixing a wafer having a notch in a part of the outer periphery thereof, a wafer rotating means for rotating the wafer, and the rotating wafer An electric signal converting means for converting a temporal position change of the wafer edge and the notch into an electric signal; and a cutoff frequency is set so as to remove a signal due to rotational eccentricity of the wafer from an output signal of the electric signal converting means. A cut-off frequency variable filter that matches the rotation frequency sent from the rotation means, and a center of the cut-out portion that detects the center position of the cut-out portion of the wafer from an electrical signal generated by the cut-out portion of the wafer separated by the cut-off frequency variable filter And a position detecting means.
[0015]
According to the present invention, the rotation eccentricity signal and the notch signal at the time of wafer rotation are passed through a cut-off frequency variable filter including a notch filter or a high-pass filter having the frequency of the rotation eccentricity signal as a cutoff frequency. Separation is possible, and the center position of the detected notch portion of the wafer does not deviate from the center position of the actual wafer notch portion. As a result, the wafer can be positioned accurately.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. FIG. 1 is a diagram for explaining a wafer positioning apparatus according to the present invention. The difference from the conventional example of FIG. 4 is that between an electric signal converting means and a notch center position detecting means, specifically, a photodetector 5. Between the amplifier 6 for amplifying the detected signal and the A / D converter 7 included in the controller 9, a cut-off frequency variable filter 11 capable of adjusting the cut-off frequency to the rotation frequency of the wafer rotating means, for example, the rotating stage 3, is provided. It is provided.
[0017]
As the cut-off frequency variable filter 11, a notch filter that filters only the rotation frequency of the rotary stage 3 is used as shown in FIG. 1B, or the rotary stage 3 as shown in FIG. A high-pass filter that outputs only the frequency exceeding the rotation frequency is used.
[0018]
In the embodiment configured as described above, the output signal of the photodetector 5 when the wafer 1 is rotated is as shown in FIGS. 5B and 6B. Thereafter, the output signal of the photodetector 5 passes through the cutoff frequency variable filter 11. In this case, the cutoff frequency of the variable cutoff frequency filter 11 matches the rotational frequency of the rotary stage 3, and the frequency of the rotation eccentricity signal of the wafer 1 matches the rotational frequency of the rotary stage 3. When the wafer 1 is rotated, the output signal of the photodetector 5 passes through the cut-off frequency variable filter 11 to remove the rotation eccentricity signal, and the wafer notch 1a as shown in FIGS. 2 (a) and 3 (a). The signal by is extracted. FIG. 2 shows the case where the notch 1a is an orientation flat, and FIG. 3 shows the case where the notch 1a is a notch.
[0019]
2A and 3A, the arithmetic processing unit 8 provides a threshold level TL, and the signal after passing through the cutoff frequency variable filter 11 becomes TL or more. <Up> is set as <up>, then the position below TL is set as <down>, and the average of <up> and <down> is detected as the center position (↑ mark) of the notch 1a.
[0020]
Since <up> and <down> are symmetric with respect to the actual center position (）) of the notch 1a as shown in FIGS. 2B and 3B, the threshold level is included in the difference data. Thus, there is no deviation from the center position of the detected notch (↑ mark), as in the conventional apparatus provided with, and the orientation of the wafer 1 is not displaced.
[0021]
According to the embodiment described above, a variable cutoff frequency filter comprising a notch filter or a high-pass filter that uses the rotation eccentricity signal and the signal of the notch 1a during wafer rotation as the cutoff frequency. 11, the wafer can be separated without passing the detected center position of the notch portion of the wafer from the center position of the actual notch portion of the wafer.
[0022]
【The invention's effect】
According to the present invention described above, the rotation eccentricity signal at the time of wafer rotation and the signal of the wafer notch can be separated, and the detected center position of the wafer notch and the actual center position of the notch of the wafer are shifted. Therefore, it is possible to provide a wafer positioning apparatus capable of accurately positioning the wafer.
[Brief description of the drawings]
FIG. 1 is a view for explaining a first embodiment of a wafer positioning apparatus of the present invention.
FIG. 2 is a diagram for explaining the function and effect of FIG. 1;
FIG. 3 is a diagram for explaining the function and effect of FIG. 1;
FIG. 4 is a view for explaining a first example of a conventional wafer positioning apparatus;
FIG. 5 is a diagram for explaining the operational effect of FIG. 4;
6 is a diagram for explaining the operational effect of FIG. 4; FIG.
7 is a diagram for explaining the problem of FIG. 4;
FIG. 8 is a diagram for explaining the problem of FIG. 4;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Wafer 2 ... Vacuum suction pad 3 ... Rotary stage 4 ... Light emitting diode 5 ... Photo detector 6 ... Amplifier 7 ... A / D converter 8 ... Arithmetic processor 9 ... Controller 11 ... Cut-off frequency variable filter

Claims (5)

Means for adsorbing and fixing a wafer having a notch part in the outer peripheral part;
Wafer rotating means for rotating the wafer;
An electrical signal conversion means for converting a temporal position change of the wafer edge and the notch into an electrical signal during rotation of the wafer;
A variable cutoff frequency filter that adjusts the cutoff frequency to the rotational frequency sent from the wafer rotating means so as to remove the signal due to the rotational eccentricity of the wafer from the output signal of the electrical signal converting means;
Notch portion center position detecting means for detecting the center position of the notch portion of the wafer from an electrical signal from the notch portion of the wafer separated by the variable cutoff frequency filter;
A wafer positioning apparatus comprising:   2. The wafer positioning apparatus according to claim 1, wherein the notch is an orientation flat or a notch formed at an edge of the wafer.   2. The wafer positioning apparatus according to claim 1, wherein the cut-off frequency variable filter is a notch filter that filters only the rotation frequency of the wafer rotating means.   2. The wafer positioning apparatus according to claim 1, wherein the cut-of-frequency variable filter is a high-pass filter that outputs only a frequency exceeding a rotation frequency of the wafer rotation means. The notch center position detection means, the position between two points of an electrical signal by the notch of the wafer to set the threshold level to an electrical signal by the notch of the wafer, corresponding to the threshold shoe Hold Level The wafer positioning apparatus according to claim 1, wherein the center of the notch portion is obtained by averaging.

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