JPH02284014A - Strain inspection device for semiconductor wafer cassette - Google Patents

Abstract

PURPOSE:To accurately measure the strain of a cassette in a short time without contacting by providing the cassette to be inspected, which is located on the stage of a main body, with a means which measures the distance to the reverse surface of the inserted cassette photoelectrically. CONSTITUTION:The values of respective measurement points X1 and X2, and Y1 and Y2 which are measured by photosensors 31 and 34 are read in an arithmetic part to correct respective measured values on a data display part to zero by using the read values as reference points of sensors 31 to 34, and then the cassette 5' is detached from the stage 2. Then the measurement points X1 and Y1, and X2 and Y2 and the permissible quantities of the inclinations DELTAX and DELTAY of X and Y are inputted by key operation. Then a cassette 5 is placed on the stage 2 and a wafer 7 is inserted into a groove 6 of the same height with the cassette 5' to a specific position. Then, when a measurement start key is pressed, the sensors 31 to 34 measure the distance L to the wafer reverse surface 8 and the measured value is compared with respective origins of the cassette 5 to operate their deviations, which are compared with the permissible values, thereby deciding that the wafer is normal when the measured values are within the permissible range.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to reducing distortion of wafer cassettes (hereinafter referred to as cassettes) used when storing and transporting semiconductor wafers (hereinafter referred to as wafers). Regarding the equipment to be inspected.

[Conventional technology]

As is well known, during repeated use, cassettes are subject to various influences during use, such as being heated, being dropped, and being strained due to internal stress, causing deformation. and,
When this deformation becomes large, accidents occur in which devices that automatically take out and transport wafers from cassettes are unable to take out the wafers, or the hand that picks up and takes the wafers hits them, damaging the expensive wafers. In particular, recent wafer transport mechanisms have changed from belt transport to hand transport in order to reduce dust generation.As a result, even slight deformation of the cassette can cause transport troubles, which is a big problem. It has become.

For this reason, a method has been adopted in which cassette distortion, which is the cause of this trouble, is measured, and cassettes that are likely to cause trouble are inspected in advance and removed.

Therefore, the conventional method for measuring cassette distortion was to use a caliper, hide gauge, etc. by one person. Measure the dimensions of each part with a 111 fixture, insert metal pseudo wafers into the cassette as a jig, press the wafers against the cassette with constant pressure, pull them out, and measure the A method was used to indirectly measure cassette distortion using the applied force.

[Problem that the invention seeks to solve]

However, with the conventional manual measurement method, each measurement value had to be compared with a value within an acceptable range and a human had to make a judgment, so it took nearly 10 minutes to measure one cassette. However, detailed measurements, such as measuring the pitch of the groove into which the wafer is inserted, take several hours. For this reason, only a few cassettes can be inspected per day, and dozens of cassettes are used in large semiconductor W manufacturing factories, making it virtually impossible to manually inspect all of them. There is also a manual process.

Problems such as measurement errors were also unavoidable.

In addition, since the method of measuring by pulling force uses frictional force, the error in the measurement value is large and only rough measurements can be made, and cassettes that are still usable are judged to be unusable.
There are problems such as wasteful disposal of cassettes, or conversely, cassettes that cannot be used are determined to be usable, causing transport problems such as damage to the wafers.Furthermore, when pulling out wafers by hand, the wafers may be damaged. It comes into contact with the wafer groove of the cassette and rubs, contaminating the cassette.
When handling at home, not only must the wafer be cleaned, but it also causes damage to the wafer, generates burr cracks, and lowers the yield of wafer processing.
Furthermore, since it is not possible to numerically express how the cassette is distorted, there are many other problems, such as the inability to isolate the cause of the distortion.

The present invention was made in view of the problems of the conventional technology, and its purpose is to accurately measure the distortion of a cassette without contact, in a short time, and to determine whether the cassette is a good product. An object of the present invention is to provide a strain inspection device for a semiconductor wafer cassette that can automatically determine whether it is a defective product.

[Means for solving problems]

For this purpose, the present invention provides means for photoelectrically measuring the distance to the lower surface of a wafer inserted into a cassette to be inspected placed on a stage of one main body, and a measurement value measured by the means and a set value set by the means. The present invention is characterized by a configuration comprising means for comparing and calculating the inspection reference values obtained and determining the presence or absence of distortion in the cassette to be inspected.

〔Example〕

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

FIG. 1 is a schematic plan view of an example of the device according to the present invention, and FIG.
The figures are explanatory diagrams of the main parts. In these figures, 1 is the main body, 2
is a stage provided on the main body 1 on which the object to be measured is placed;
3. - 34 are four photoelectronic position sensors (hereinafter referred to as optical sensors) arranged two by two opposite each other, and the optical sensors include those using red LEDs (light emitting diodes) and laser light. Sensor 3□~3
．． are attached to the main body 1 via each lifting mechanism 41 to 44 so that their respective optical axes are perpendicular to the stage 2, and the groove 6 of the cassette 5 to be inspected is placed on the stage 2.
The distance to the bottom surface 8 of the wafer 7 is measured photoelectrically as a measuring element inserted into the sensor, and when the distance to the bottom surface 8 of the wafer 7 is out of the measurable range of each optical sensor 3□ to 34, , each lifting mechanism section 4. -44, each optical sensor -31-34 is raised and lowered from each opening 9°-94 of main body 1 and stage 2, and the distance is IN! l
! IL is designed to be measurable.

Note that there is no limit to the number of optical sensors, and it goes without saying that the number of optical sensors may be one.

In FIG. 1, reference numeral 10 denotes a calculation unit built into the main body 1, and the measured values of measurement points X1, X2, Yo, and Y2 on the lower surface 8 of the wafer 7 measured by each of the optical sensors 31 to 34 shown in FIG. The calculation unit 1o is a well-known microcomputer, and basically consists of a CPU, RAM, and ROM.

11 is a data display section for displaying processed data from the calculation section 10; 12 is a keyboard section for setting and inputting allowable values of each measurement value of each of the optical sensors 31 to 34 to the calculation section 10; and 13 is a This is the power switch section. Further, in FIG. 1, reference numeral 14 denotes a positioning member for positioning the cassette 5 on the stage 2.

Next, a method for inspecting cassette distortion using the apparatus of the present invention having the above configuration will be described.

First, insert the wafer 7 into the groove 6' of the cassette 5', which is the same type as the cassette to be inspected and has no distortion (it is preferable that the lower surface 8 of the wafer 7 is slightly cloudy), and place it in a predetermined position on the stage 2. The wafer is placed in place via the positioning member 14, and then, by operating a predetermined key on the keyboard section 12, each of the optical sensors 31 to 34 measures the distance ML to the lower surface 8 of the inserted wafer 7.

In addition, instead of the cassette 5', as shown in FIG. 4, calculate the height of the lower surface of the wafer from the drawing 14 of the cassette to be inspected. A gauge 15 is made using this height H as a reference, and the gauge 15 is placed on the stage 2. In the same manner as described above, each optical sensor 31 to 34 is connected to the lower surface 16 of the gauge 15.
Alternatively, the distance L' may be measured.

Each measurement point X2 measured by each optical sensor -31 to 34
, Y, X2, and Y2 are read into the calculation unit 10, and using this as a reference point for each optical sensor 31 to 34, each measured value on the data display unit 11 is corrected to zero (origin), and the rear cassette 5
'or remove the gauge 15 from above the stage 2.

Next, each measurement point X1. Input the allowable values of Y, Xt, Y, and the slopes ΔX and ΔY of X and Y.

Next, the cassette 5 to be inspected is placed at a predetermined position on the stage 2, and the wafer 7 is inserted into the groove 6 at the same height as the reference cassette 5' (or gauge 15) up to a predetermined position.

Next, when the measurement start key on the keyboard section 12 is pressed, each optical sensor 3, to 34 measures the distance to the wafer lower surface 8, reads the measured value into the calculation section 10, and selects the cassette 5 (or Compare with each origin of gauge 15),
Calculate the amount of deviation and compare this with the tolerance value entered earlier.

If each measurement value is within the allowable range, it is judged as a good product (OK)
If it is off, the product is determined to be defective (NG). This result is displayed on the data display section 11 as roKJ or rNGJ.

Note that the result of judgment 1 can be printed out.

The elements for determining the distortion of the cassette 5 are the respective optical sensors 3 to 3. Depending on the distance to the bottom surface of the wafer and the inclination in the X and Y directions, the absolute values of the inclination △X and ΔY are Δx = 1x1-x,
l Δy= 1y1-y, l, which makes X
and the inclination in the Y direction.

For example, the examples shown in FIGS. 5A, 5B, and 6 show that the wafer 7 is tilted in the direction of X knee X2 from the reference plane. In other words, cassette 5 is X, -X
It is thick in two directions (indicating that it is deformed).

Conversely, this deformation is the cause of the positional deviation of the wafer 7 from the reference plane, and if this positional deviation is large, when the hand for carrying the wafer goes to pick up the wafer from the cassette, it may hit the wafer and damage the wafer. This may cause problems such as damage, scratches, or failure to remove the wafer.

Note that the inclinations of X and Y can be determined not only by absolute values but also by inclination angles calculated by the calculation unit.

〔Effect of the invention〕

According to the present invention, by using a reference cassette or a gauge, setting the - degree reference height as the origin, and manually setting the tolerance value, the wafer can be inserted into the cassette to be inspected and placed on the stage. Just by placing the product in a predetermined position and operating the 4111 fixed start key, you can instantly determine whether it is a good product or a defective product. Due to this.

It has become possible to inspect all cassettes in a short time, and it has become possible to reliably remove defective cassettes in advance, preventing wafer transport accidents that previously occurred in the automatic wafer transport section, and preventing wafer processing. It becomes possible to improve the yield of the process.

Furthermore, since the object to be measured is measured without contact, the wafer groove is not contaminated and there is no need to clean the cassette every time it is inspected. Furthermore, since frictional force or the like is not used, there is little measurement error and accurate 1l11 determination can be performed.

In addition, when pulling out wafers by hand, the wafers do not rub against the wafers in the cassette, so there is no chance of damaging the wafers or causing burr cracks, which improves the yield of wafer processing. .

Furthermore, since the device of the present invention has a simple structure, it is easy to automatically inspect a large number of cassettes in combination with an automatic cassette transport device.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view of an example of the device according to the present invention, and FIG.
The figure is an explanatory diagram of the main parts, Figure 3 is a layout diagram of the photoelectronic position sensor, Figure 4 is an explanatory diagram showing an example of correction of the reference height of the cassette to be inspected, and Figures 5 (A), (B) and FIG. 6 is an explanatory diagram of an example of wafer tilt, which is one of the factors for determination. 1...Main body 2...Stage 3, ~3. ...Photoelectric distance measuring means (photoelectronic position sensor) 5...Cassette to be inspected 7...Wafer 10...Calculating section

Claims (1)

[Claims] 1. A means for photoelectrically measuring the distance to the lower surface of the wafer inserted into the cassette to be inspected placed on the stage of the main body, and comparing the measurement value measured by the means with the inspection reference value set by the means. A distortion testing device for semiconductor wafer cassettes, comprising means for calculating and determining the presence or absence of distortion in the cassette to be tested.