JPH0541442A - Wafer counting method and apparatus - Google Patents

Abstract

PURPOSE:To exactly obtain a wafer position reference point, when wafers accommodated in a cassette of a semiconductor manufacturing equipment are counted. CONSTITUTION:A cassette 5 in which a necessary number of wafers 4 are continuously loaded is relatively scanned by a wafer sensor 15 in the direction vertical to the wafer surface. On the basis of a wafer ON-OFF signal and the position information of ON-OFF signal generation point, wafer intervals and wafer positions are obtained, and the wafer detection starting position is calculated from the wafer intervals and the wafer positions. Thereby the actual states of wafers is judged, and the reference position for counting the wafers is obtained from the actual state of wafers by calculation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer counting method and apparatus for detecting the state of wafers in a cassette in a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art Generally, in a semiconductor manufacturing apparatus, wafers are handled while they are loaded in a cassette. In addition, when actually processing the wafers, the wafers are processed or transferred one by one, so how many wafers are loaded in the cassette, and how the wafers are loaded such as the presence or absence of missing teeth Need to detect.

In response to such a request, the present applicant has filed Japanese Patent Application No. 1-1.
No. 98171 and Japanese Patent Application No. 2-34469 propose a wafer number counting device.

This wafer number counting device uses a beam of light or ultrasonic waves to emit light toward the peripheral edge surface of the wafer and detect a reflected signal from the peripheral edge surface. Move it in the vertical direction of the plane,
The beam emitted from the sensor is crossed over the peripheral edge of the wafer. The wafer storage pitch of the cassette itself is known. As shown in FIG. 5, a wafer detection width ZS smaller than the storage pitch is set, and whether or not the wafer is present is determined by whether or not the reflection signal is present within the detection width ZS. Is determined.

Adjacent wafer detection widths ZS are separated by a wafer storage pitch excluding the wafer detection width ZS and a wafer non-detection width Zd. Therefore, assuming the wafer detection start reference position PS, the presence / absence of a wafer is determined with respect to the first wafer detection width, and the second wafer presence / absence determination is performed from the position moved by the wafer undetected width Zd. Detection width ZS of. This detection procedure is repeated for all the planned detection widths to complete the wafer detection work.

By properly setting the start reference position as described above, the presence / absence of the wafer can be detected. If the start reference position is not correct, the wafer is detected by the detection width Z.
It means that it is out of S and cannot be detected. Conventionally, this wafer start reference position has been manually set.

[0007]

However, the manual setting of the starting reference position depends on the sense of the operator, and therefore the setting itself takes time and the setting accuracy varies. Further, there is a problem that the setting time and the setting accuracy are greatly influenced by the skill of the setter, and as a result, the reliability of the detection result is low.

Further, since the reflection signal from the end face of one wafer is detected, the beam emission axis of the sensor and the wafer are completely arranged so that the reflection signals from the end faces of other wafers do not coexist. The wafer must be parallel and completely perpendicular to the direction of sensor travel.

Alternatively, the positional relationship between the sensor and the wafer, that is, the cassette must be confirmed for the reason that an accurate reflection signal cannot be obtained unless the beam emission axis and the tangent line of the wafer peripheral end surface are at right angles. .. Conventionally, since these confirmation operations have been performed manually and by human senses, there is a problem that it takes time and reliability is low.

In view of the above situation, the present invention aims to provide a wafer number counting method and apparatus capable of checking the detection state of the sensor and the positional relationship between the sensor and the cassette and automatically setting the wafer detection position. It is a thing.

[0011]

SUMMARY OF THE INVENTION According to the present invention, a wafer sensor is made to relatively scan in a direction perpendicular to a wafer surface with respect to a cassette in which a required number of wafers are continuously loaded, and a wafer ON-OFF signal is generated. The wafer interval and the wafer position are obtained based on the position information of the ON-OFF signal generation point, and the wafer detection start position is calculated from the wafer interval and the wafer position.

[0012]

Since the actual state of the wafer is automatically judged and the reference position for counting the wafer is calculated and obtained from the result of the judgment, there is no variation and there is no human error, so the reference position can be set accurately. ..

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a cassette loader, 2 is a cassette shelf, and 3 is a control device.

The cassette loader 1 transfers the cassette 5 loaded with the wafers 4 to the cassette shelf 2.
The cassette pedestal 6 on which the cassette 5 is mounted is screwed onto the lifting screw rod 7, and is lifted and lowered by the rotation of the lifting screw rod 7 by the lifting motor 8.

The cassette shelf 2 is provided so as to face the cassette loader 1 and accommodates the cassettes 5 in multiple stages.

The control device 3 mainly comprises a main control unit 9, a motor control unit 10, a motor drive unit 11, and a wafer detection unit 1.
2. The operation unit 13 and the storage unit 16 are configured to drive and control the lifting motor 8, and a position signal from an encoder 14 provided in the lifting motor 8 is fed back to the motor driving unit 11. ..

The cassette loader 1 of the cassette shelf 2
A reflection detection type wafer sensor 15 such as an ultrasonic sensor is attached at a position opposite to the above position and at a position where the cassette 5 completely passes when the cassette 5 moves up and down.

The wafer measuring operation will be described below.

First, the cassette 5 in which three wafers are continuously stored from the lowermost part is set on the cassette pedestal 6 and the elevating motor 8 is driven to set the cassette 5 to the wafer sensor 15. Pass through. Further, detection of the presence or absence of the wafer is started from the required position Pa before passing the wafer 4.

ON from the wafer sensor 15 at this time
The OFF signal is taken in by the wafer detection unit 12,
At the same time, the change point of ON-OFF signal (from ON signal to OFF
The position information of the signal or the point where the OFF signal changes to the ON signal) is detected based on the signal from the encoder 14.
Based on this position information, in the main control unit 9, the wafer sensor signal ON sections T1, T2, T3, the wafer sensor signal OFF sections T4, T5, the wafer sensor signal ON section average TON, the wafer sensor signal OFF section average TOFF, Wafer sensor signal ON-OFF ratio DR, wafer center positions PZ1, PZ2, PZ3, and inter-wafer distances Za and Zb are calculated as follows. However, P1, P2, and P3 are points at which the signal is switched from ON to OFF, and P1 ', P2', and P3 '.
Is the point at which the signal switches from OFF to ON.

Sensor signal ON section T1 = P3'-P3 T2 = P2'-P2 T3 = P1'-P1 Sensor signal OFF section T4 = P2-P3 'T5 = P1-P2' Average of sensor signal ON section TON = ( T1 + T2 + T3) / 3 Average of sensor signal OFF section TOFF = (T4 + T5) / 2 Sensor signal ON-OFF ratio DR = {TON / (TON + TOFF)} × 100 Wafer center position PZ1 = (P3 ′ + P3) / 2 PZ2 = (P2 '+ P2) / 2 PZ3 = (P1' + P1) / 2 Wafer distance Za = PZ2-PZ1 Zb = PZ3-PZ2 Judgment result for judging whether the wafer sensor adjustment state is good or not from the data calculated above To decide.

One of the judgment results is determined by the following Table 1 from the value of DR obtained above. Further, the table 1 is previously input to the storage unit 16, and the storage unit 16 is set with a criterion for quality judgment, for example, status # 2 in Table 1. Further, a cassette slot pitch interval Z described later
2 is also entered in advance.

[0024]

[Table 1]

The determination result 2 is determined by whether or not the values of the inter-wafer distances Za and Zb obtained above are within the permissible range with respect to the wafer detection width set as a parameter in advance. Therefore, the cassette slot pitch interval is Z2, and the allowable range is ± of the cassette slot pitch interval.
When it is 10%, it becomes as follows.

Tolerable range Upper limit: Z2 ′ = Z2−Z2 × 0.1 Upper limit: Z2 ″ = Z2 + Z2 × 0.1 Allowable range: Z2 ′ ≦ Za, Zb ≦ Z2 ″, and the determination results are that both wafer distances Za and Zb are allowable. If it is within the range, it is "1", and if not, it is "0".

Only when the judgment result 1 matches a preset value and the judgment result 2 is "1", the result is judged to be good, and when the result is good, the wafer detection start described below is started. The position PS is calculated.

The wafer detection start position PS is a position half the wafer detection width below the center position PZ3 of the lowermost wafer, and is as follows.

Wafer detection start position PS = PZ3 + (ZS / 2) When the above series of processing is completed and the result is good, the judgment result and the wafer detection start position are shown, and otherwise, only the judgment result is obtained by the main control unit 9 And outputs the result to the operation unit 13
To display. The flow of the above series of processing is shown in FIG.

As described above, when the determination of the sensor adjustment state is good and the values of the inter-wafer distances Za and Zb are within the allowable range, the cassette loaded with the wafers to be processed is placed on the cassette receiving table 6, The pedestal 6 is moved up and down, and in the main controller 9 based on the detection signal (ON-OFF signal) from the wafer sensor 15 and the position information from the encoder 14,
The number of wafers 4 and the positions of missing teeth are counted and used as information for subsequent wafer processing.

If it is impossible to determine the sensor adjustment state, the adjustment is performed again, but the adjustment state of the wafer sensor is displayed on the display unit, so that the readjustment can be easily performed.

The wafer sensor may be an optical sensor instead of the ultrasonic sensor, and may be a passage type instead of a reflection type. In order to detect the adjustment state of the wafer sensor, three wafers from the bottom of the cassette are used. Although wafers are loaded, the positions of wafers to be loaded and the number of wafers are not limited to this. Furthermore, if a wafer is continuously loaded without setting a special cassette for detecting the adjustment state of the wafer sensor, the cassette loaded with the wafer to be actually processed may be used. Good.

The cassette may be a horizontal type instead of the vertical type, and in this case, the cassette and the wafer sensor may be moved relative to each other in the horizontal direction.

[0034]

As described above, in the present invention, the adjustment state of the wafer sensor is judged, and if the judgment is good, the wafer position reference point is automatically set. There is no variation due to the skill level, etc., and the setting accuracy is improved. Further, even if the adjustment state of the sensor is impossible, the adjustment state is known, so that an excellent effect that readjustment can be easily performed is exhibited.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an abbreviated example of the configuration of an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a change point of a wafer and a wafer detection signal.

FIG. 3 is a diagram showing a change point of a wafer and a wafer detection signal.

FIG. 4 is a flowchart showing a flow of operation.

FIG. 5 is an explanatory diagram showing a cassette, a wafer, and a detection width.

[Explanation of symbols]

 1 Cassette Loader 2 Control Device 4 Wafer 5 Cassette 9 Main Control Unit 14 Encoder 15 Wafer Sensor 16 Storage Unit

Claims (4)

[Claims] 1. The position of a wafer ON-OFF signal and an ON-OFF signal generation point is obtained by scanning a wafer sensor relative to a cassette in which a required number of wafers are continuously loaded in a direction perpendicular to the wafer surface. A wafer counting method, wherein a wafer interval and a wafer position are obtained based on information, and a wafer detection start position is calculated from the wafer interval and the wafer position. 2. Wafer ON signal section, wafer OFF
2. The wafer counting method according to claim 1, wherein a signal section is obtained, a ratio between the ON signal section and the OFF signal section is calculated, and the wafer sensor adjustment state is judged based on the ratio. 3. Wafer ON signal section, wafer OFF
The signal section is calculated, the ratio between the ON signal section and the OFF signal section is calculated, and the wafer sensor adjustment state is determined based on the ratio, and it is determined whether the wafer interval is within the allowable range with respect to the preset wafer detection width. The wafer counting method according to claim 1, wherein the wafer detection start position is calculated when the determination result is good. 4. A wafer loaded in a cassette,
A wafer sensor that is relatively movable in the direction perpendicular to the wafer surface, a position detector that detects the relative movement position, a wafer interval and a wafer position are calculated from the wafer sensor and the position detector, and a wafer detection start position is calculated. A wafer counting device comprising: a control unit for calculating.