JPH07137804A - Semiconductor wafer cassette reference position determining method - Google Patents

Abstract

PURPOSE:To determine the insertion reference position of a cassette without the confirmation of an operator by visual observation. CONSTITUTION:While operating a vacuum pump, a horizontal arm 24 is moved up from the lower side of a semiconductor wafer 12 inserted in the specified stage of a cassette 10, and pressure is measured by a vacuum gage so as to measure the height of the horizontal arm 24 at the time of the measured value of pressure becoming the specified reference value or lower. Since the difference between the height of the insert reference position and the height of the stage into which the semiconductor wafer 12 is inserted is predetermined, a computer computes the height of the insertion reference position of the cassette 10 from this difference and the measured height of the horizontal arm 24.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining an insertion reference position of a cassette in a semiconductor wafer transfer device.

[0002]

2. Description of the Related Art When a semiconductor wafer is inspected or processed, a cassette is first placed on a cassette table of a wafer transfer device, and the wafer transfer device takes out a semiconductor wafer from the cassette or inserts it into the cassette. The operation of housing the semiconductor wafer is performed.

By the way, the height of the reference position for inserting the semiconductor wafer in the cassette (usually the lowest stage of the cassette) is not standardized, but it actually varies depending on the type of the cassette. Therefore, when a certain type of cassette is handled for the first time by the wafer transfer device, it is necessary to set the height of the insertion reference position of the cassette in the wafer transfer device.

[0004]

When setting the insertion reference position of the cassette, the arm for holding the semiconductor wafer is manually moved so that the arm is attached to the lower surface of the wafer inserted at the insertion reference position. The operator adjusts the height of the arm while visually checking it so that the upper surface comes into contact, and the height of the arm is set as the insertion reference position.

As described above, since the reference position is conventionally determined by manual operation, it takes a considerable time for setting,
In addition, there is a high possibility that an operation error will occur.

The present invention has been made to solve the above-mentioned problems in the prior art, and an object thereof is to provide a method by which an operator can determine a reference position for inserting a cassette without visually confirming it. And

[0007]

A reference position determining method according to the present invention comprises a cassette table on which a cassette having a plurality of steps for accommodating semiconductor wafers is placed,
A horizontal arm having suction holes on the upper surface for vacuum-sucking and holding the semiconductor wafers housed in the cassette one by one, a drive mechanism for driving the horizontal arm in at least horizontal and vertical directions, and the horizontal arm In the semiconductor wafer transfer apparatus, which comprises: a conduit communicating with the suction hole, a vacuum pump connected to the conduit, a vacuum gauge connected to the conduit, and a computer for controlling. This is a method of determining the height of a reference position for inserting a semiconductor wafer in a cassette placed on a cassette table. This method includes (A) a step of mounting a cassette loaded with semiconductor wafers on a predetermined stage on the cassette table, and (B) operating the vacuum pump while moving the horizontal arm by the drive mechanism. Measuring the height of the horizontal arm at a time when the pressure measured by the vacuum gauge becomes equal to or lower than a predetermined value by raising the semiconductor wafer loaded on the predetermined stage from below. ) Based on a predetermined difference between the height of the predetermined step of the cassette and the height of the insertion reference position, and the height of the horizontal arm measured in the step (B), the computer inserts the cassette. And a step of calculating the height of the reference position.

In step (B), if the suction hole of the horizontal arm comes into contact with the lower surface of the semiconductor wafer, the pressure in the conduit decreases and falls below a predetermined value. Therefore, the height of the horizontal arm measured at the time when the pressure in the pipeline becomes a predetermined value or less indicates the height of a predetermined step. Since the difference between the height of the predetermined stage of the cassette and the height of the insertion reference position is known in advance, the height of the insertion reference position is calculated from this difference and the height of the horizontal arm measured in step (B). Can be calculated.

[0009]

1 is a perspective view showing a wafer transfer apparatus to which an embodiment of the present invention is applied. As shown in FIG. 1, this wafer transfer apparatus includes a cassette table 20 for mounting a cassette 10, a horizontal arm 24 for holding a semiconductor wafer, and a guide for guiding the horizontal movement of the horizontal arm 24. The rail 26 and a first stepping motor 30 for driving the horizontal arm 24 along the guide rail 26.
A second stepping motor 32 that drives the guide rail 26 in the vertical direction; a vacuum pump 40; a pipe 42 that connects the communication port provided at the rear end of the horizontal arm 24 to the vacuum pump 40; A vacuum gauge 44 connected in the middle of 42 and a personal computer 50 are provided.

The personal computer 50 controls the stepping motors 30 and 32 and the vacuum pump 40, and also has a function of receiving and processing data of pressure measured by the vacuum gauge 44.

A suction hole 22 for holding the semiconductor wafer 12 by vacuum suction is provided on the upper surface of the tip of the horizontal arm 24.
Is provided. This suction hole 22 has a horizontal arm 24.
It communicates with the above-mentioned communication port provided at the rear end, and a pipe 42 is connected to this communication port.

FIG. 2 is a sectional view of a front main part of the wafer transfer device. However, FIG. 2 is a diagram mainly illustrating a drive mechanism that drives the horizontal arm 24, and other portions are omitted. As shown in FIG. 2, two pulleys 34 each having a ring-shaped wire 33 hung on the side surface of the guide rail 26,
35 are provided. When the pulley 35 is driven by the first stepping motor 30, the wire 33 moves,
This causes the horizontal arm 24 to move horizontally along the guide rail 26.

The guide rail 26 is fixed to a vertical support 28, and the vertical support 28 has a ball screw mechanism 36.
Is engaged with. When the second stepping motor 32 rotates the screw 37 via the belt 38, the vertical support 28, the guide rail 26, and the horizontal arm 24 are thereby rotated.
Moves in the vertical direction together with the ball screw mechanism 36. A limit switch 3 for indicating the lower limit of the guide rail 26 is provided on the top plate 39 provided on the upper end of the screw 37.
1 is provided.

FIG. 3 is a front sectional view of the cassette 10. The cassette 10 is provided with a plurality of steps 14a, 14b ... For inserting wafers at a predetermined pitch P, but most of the steps are omitted in FIG. 3 for convenience. The reference position for inserting the cassette 10 is the lowermost stage 14c.

When the reference position for inserting the cassette 10 is determined, the semiconductor wafer 12 is placed in the central step 14 of the cassette 10.
inserted in a. As described above, since each stage of the cassette 10 is provided at the predetermined pitch P, if the height of any one stage is measured, the insertion reference position (the bottom stage 14
The height of c) can be determined. For example, center stage 1
If there are N stages from 4a to the bottom stage 14c, the height of the bottom stage 14c can be determined by subtracting N × P from the height of the center stage 14a. The cassettes that store the same size wafers (6 inch wafers or 8 inch wafers) are designed at the same pitch P even if the cassette manufacturers are different. When determining the insertion reference position (height of the lowest stage), the center stage 14a
Is measured in order to minimize the cumulative error of the pitch P due to the deformation of the cassette 10.

When measuring the height of the central step 14a, first, the horizontal arm 24 is placed below the semiconductor wafer 12 (see FIG. 2).
At the position indicated by the alternate long and short dash line). Then, as shown by the arrow, the horizontal arm 24 is raised at a constant speed. At this time, the vacuum pump 40 is operated to operate the pipe 42.
Is evacuated, and the pipe 42 is
Measure the pressure inside.

FIG. 4A is a graph showing the change in the pressure measurement value of the vacuum gauge 44 as the horizontal arm 24 moves up.
When the horizontal arm 24 is well below the semiconductor wafer 12, the pressure exhibits a substantially constant and relatively high value. On the other hand, when the upper surface of the horizontal arm 24 contacts the lower surface of the semiconductor wafer 12, the suction holes 22 on the upper surface of the horizontal arm 24
Since (FIG. 1) is closed, the pressure in the pipe 42 drops to a predetermined reference pressure RP or less as shown in FIG. 4 (A). Then, the pressure measurement value of the vacuum gauge 44 is the reference pressure RP.
The height Zb of the horizontal arm 24 when it becomes below and the height Za of the horizontal arm 24 at the time of pressure measurement immediately before becoming below the reference pressure RP are stored in the personal computer 50. The height of the horizontal arm 24 is equal to that of the horizontal arm 2.
The height is measured with 0 as a predetermined reference position of 4 (for example, the height defined by the limit switch 39), and is determined from the number of pulses of the stepping motor 44. However, a measuring device such as a linear encoder may be used to measure the height of the horizontal arm 24.

When the first measurement is completed in this way, as shown in FIG.
The second measurement shown in (B) is executed. In the second measurement, the two heights Za and Zb determined in the first measurement
The pressure is measured at each position that is divided more finely than the first measurement. Specifically, from the height Za to the horizontal arm 2
4 is moved upward, and its rising speed is set to be smaller (for example, 1/10) than the rising speed in the first measurement.

Also in the second measurement, the pressure change as shown in FIG. 4 (B) is measured as in the first measurement. The personal computer 50 determines the height Zc of the horizontal arm 24 when the measured pressure value becomes equal to or lower than the reference pressure RP.
Is determined as the height of the central stage 14a of the cassette 10.

The personal computer 50 has a pitch P of steps and a number N of steps from the center step 14a to the bottom step 14c.
Has been input in advance, and N × P is subtracted from the height Zc of the central step 14a obtained by the measurement of FIG. 4B to determine the height of the lowermost step 14c as the insertion reference position.

In the above-described operation for determining the insertion reference position, the operator only needs to place the cassette 10 containing the semiconductor wafer 12 on the cassette table 20 and give the personal computer 50 an instruction to start the operation. . When instructed, the personal computer 50
Automatically executes the above operation according to a software program stored in advance to determine the height of the insertion reference position. Therefore, in the above-mentioned embodiment, there is an advantage that the time required for determining the reference position is short and there is no possibility of damaging the wafer or the transfer device due to an operator's operation error.

In the above embodiment, the insertion reference position is determined by two measurements as shown in FIG. 4, but it may be determined by only one measurement. However, when the insertion reference position is determined by only one measurement, the accuracy of the insertion reference position deteriorates, or if it is attempted to determine the insertion reference position with good accuracy, a considerable measurement time is required. Become. On the other hand, as in the above-mentioned embodiment, the interval of the height for measuring the pressure is set roughly (the rising speed is small) in the first measurement, and the interval of the height for measuring the pressure is fine in the second measurement ( If the rising speed is set high), the measurement time is relatively short and the measurement accuracy is good.

In the above embodiment, the pressure measured by the vacuum gauge 44 is sampled by the personal computer 50 at regular intervals. However, the pressure is continuously monitored and the pressure falls below a predetermined reference value. The insertion reference position may be determined based on the height of the horizontal arm 24 at the time of lowering.

The present invention is not limited to the above embodiments, and can be implemented in various modes without departing from the scope of the invention.

[0025]

As described above, according to the method of the present invention, there is an advantage that the operator can determine the insertion reference position of the cassette without visually confirming it.

[Brief description of drawings]

FIG. 1 is a perspective view showing a wafer transfer device to which an embodiment of the present invention is applied.

FIG. 2 is a sectional view of a front main part of the wafer transfer device.

3 is a front sectional view of the cassette 10. FIG.

FIG. 4 is a graph showing changes in measured pressure with the rise of the horizontal arm 24.

[Explanation of symbols]

 10 ... Cassette 12 ... Semiconductor wafer 14a ... Center stage 14c ... Bottom stage 20 ... Cassette stand 22 ... Adsorption hole 24 ... Horizontal arm 26 ... Guide rail 28 ... Vertical support 30, 32 ... Stepping motor 31 ... Limit switch 33 ... Wire 34, 35 ... Pulley 36 ... Ball screw mechanism 37 ... Screw 38 ... Belt 39 ... Top plate 40 ... Vacuum pump 42 ... Pipe 44 ... Vacuum gauge 50 ... Personal computer N ... Number of stages P ... Pitch RP ... Reference pressure

Claims (1)

[Claims] 1. A cassette base on which a cassette having a plurality of steps for accommodating semiconductor wafers is placed, and adsorption holes for accommodating and holding the semiconductor wafers accommodated in the cassette one by one under vacuum. A horizontal arm, a drive mechanism for driving the horizontal arm at least in the horizontal and vertical directions, a pipe line communicating with the suction hole of the horizontal arm, a vacuum pump connected to the pipe line, and the pipe. A method for determining a height of a reference position for inserting a semiconductor wafer in a cassette placed on the cassette table, in a semiconductor wafer transfer apparatus including a vacuum gauge connected to a path and a computer for performing control. (A)
Placing a cassette loaded with semiconductor wafers on a predetermined stage on the cassette table; and (B) operating the vacuum pump while the horizontal mechanism is loaded on the predetermined stage by the drive mechanism. Rising from the lower side of the semiconductor wafer and measuring the height of the horizontal arm at the time when the pressure measured by the vacuum gauge becomes equal to or lower than a predetermined value, and (C) the predetermined stage of the cassette. The computer calculates the height of the insertion reference position of the cassette from the predetermined difference between the height and the height of the insertion reference position and the height of the horizontal arm measured in the step (B). A method for determining a reference position of a semiconductor wafer cassette, comprising: