JPH04319614A - Measuring apparatus for thickness of thin plate - Google Patents

Abstract

PURPOSE:To measure the thickness of a thin plate without being affected by the precision of a moving device such as an X-Y table which changes relative positions of a detector such as a displacement meter and a measuring stage, and to obtain a measuring apparatus of the thickness of the thin plate which is convenient and inexpensive and has high measuring precision. CONSTITUTION:A measuring stage 1 and a reference plate 2 are made opposite and parallel to each other and held by a holding metal fitting 7, and the holding metal fitting 7 is made to be movable by a moving device 8. A detector couple formed by putting a first detector 3 and a second detector 4 in one body is disposed between the measuring stage 1 and the reference plate 2. Distances to the flat surface 1A of the measuring stage 1 and to a thin plate 10 are measured by the first detector 3 and a distance to a reference plane 2A is measured by the second detector 4. The measured distance to the flat surface 1A of the measuring stage and the measured distance to the reference plane 2A at this time are added up. The measured distance to the thin plate 10 and the measured distance to the reference plane 2A at this time are added up. The thickness is determined from a difference between two addition values thus obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a technique for precisely measuring the thickness of a thin plate-shaped object, and in particular, the thickness of a thin plate suitable for measuring a flat plate such as a silicon wafer with submicron precision. This invention relates to a measuring device.

0002

2. Description of the Related Art Conventionally, many methods have been used to precisely measure the thickness of a flat plate such as a silicon wafer. The first method uses optical interference, and uses a Fizeau interferometer or a Michelson interferometer. The second method is to measure using a general distance meter.

One of the second methods is to utilize changes in capacitance. This is a non-contact capacitive sensor.
The distance from the capacitance sensor to the silicon wafer surface is measured by applying an alternating current between the two electrodes and measuring the capacitance while approaching the surface of the silicon wafer. This makes it possible to measure the irregularities on the surface of the silicon wafer. Furthermore, as a method for measuring distance non-tangentially, there is also a method using a laser displacement meter.

According to the first method, the entire plane of the silicon wafer can be measured simultaneously without the need to scan measurement points, resulting in high measurement accuracy and short measurement time. In particular, when a laser beam is used as a light source for a Michelson interferometer, stable and extremely accurate measurement is possible, and the method has an accuracy of 0.01 micron or more, making it an ideal method in terms of accuracy. However, such devices are expensive and bulky, and are not suitable for being incorporated into machines such as automatic inspections.

[0005] The second method can only measure one point on the surface of a silicon wafer, so the surface must be scanned to measure the entire plane, but it is extremely simple and inexpensive, and can be incorporated into a machine. Also suitable for Note that the precision of the detector itself, such as a laser displacement meter, is sufficient to measure an error of about 1 micron, such as in the case of a silicon wafer, and one with an error of about 0.03 micron is currently on the market.

However, it is difficult to process a mechanical part for scanning an entire plane, that is, a mechanical part for moving a detector or an object to be measured along a fixed plane, with an accuracy comparable to that of the detector. is extremely difficult. Furthermore, in order to maintain a constant plane, the mechanical elements must be made large to maintain rigidity, making the entire device bulky. That is, even if the detector is small and inexpensive, the entire device becomes large and expensive.

There are two types of factors related to the accuracy of mechanical parts that scan the entire plane: the first is the error between the scanning plane and the ideal plane, and the second is the repeatability. If an attempt is made to maintain both of these to a degree of about 0.1 micron, it will become large and expensive.

[0008] For this reason, various efforts have been made in the past. A commonly used method is to hold the detector 101 and the detector 102 in a C-shaped holder 10 as shown in FIG.
4, the distance from the detectors 101 and 102 to the plate 103 to be measured is measured, and this measured value is subtracted from a constant value to determine the thickness of the plate 103 to be measured. Note that this measurement value is the thickness of one point, and is the thickness of holder 1.
04 on a scanning means 105 such as an XY table and scans the entire plane.

According to this method, the repeatability error, that is, the detectors 101 and 102 due to backlash of the scanning means
Measurement errors due to variations in the distance between the object and the object to be measured are canceled out, and the accuracy of the detectors 101 and 102
This is a good method that is completely unaffected by errors in the scanning means 105.

However, when measuring the plane accuracy of the entire plane by scanning the plane, there is a drawback that the error between the movement of the scanning means 105 and the ideal plane directly becomes an error in the measured value.

[0011] If you want to use a simple device such as a commercially available XY table, the latest precision
Even on a table, the accuracy between the two is about 1 micron, which is sufficient accuracy for normal mechanical parts, but it is difficult to measure the thickness of silicon wafers by 0.1 microns.
If measurement accuracy of microns or higher is required, it cannot be used as is.

0012

[Problems to be Solved by the Invention] The present invention addresses not only the repeatability caused by the backlash of the scanning means that scans a detector such as a laser displacement meter, but also the errors from the ideal plane of its movement that affect the measured values. To provide a simple, inexpensive, and high-accuracy thin plate thickness measuring device that does not give a thin plate thickness and does not affect the measured value even if an inexpensive and low-accuracy scanning means is used. It is in.

[0013]

[Means for Solving the Problems] The thin plate thickness measuring device of the present invention, which has been made to solve the above problems, has a first plane that holds a thin plate as an object to be measured, and a plane that is substantially parallel to the first plane. a pair of planes constituted by a second plane facing the plane, a first detector that measures the distance to the first plane and the thin plate, and a second detector that measures the distance to the second plane, respectively;
a detector pair integrally configured with a detector; a moving means for changing the relative position of the plane pair and the detector pair in a direction substantially parallel to the plane of the plane pair; a calculation means for calculating the thickness of the thin plate based on the measured distance of the detector and the second detector;
The difference between the measured distance to the first surface by the first detector and the measured distance to the thin plate is the difference between the measured distance to the second plane by the second detector when measuring the first plane and when measuring the thin plate. The present invention is characterized in that the thickness of the thin plate is calculated by correcting the difference between each measured distance.

[0014]

[Operation] In the thin plate thickness measuring device of the present invention, the thickness of the thin plate as the object to be measured is determined by the distance measured by the first detector and the second detection when the thin plate is not held on the first plane of the pair of planes. ,
And, it is calculated by each distance measured by the first detector and the second detection when the thin plate is held on the first plane. here,
Even if the relative positions of the pair of planes and the pair of detectors are changed by the moving means, and a positional shift occurs between the pair of planes and the pair of detectors between when the thin plate is not held and when the thin plate is held as described above,
The amount of this positional shift is such that the measured distance on the first detector side and the measured distance on the second detector side cancel each other out. Therefore, the difference between the measured distance to the first surface by the first detector and the measured distance to the thin plate is calculated for each measurement to the second plane by the second detector when measuring the first plane and when measuring the thin plate. Calculating the thickness of the thin plate by correcting it based on the difference in distance, we get:
Errors caused by the moving means do not affect the calculated thickness.

[0015]

[Embodiment] FIG. 1 is a front view of a thin plate thickness measuring device according to an embodiment of the present invention, in which 1 is a measuring table whose first plane is a measuring table surface 1A finished as a flat surface, and 2 is a measuring table whose surface 1A is a flat surface as a second plane. A reference plate with a flat reference surface 2A, 3 a first detector with a detection part facing the measurement table surface 1A, and 4 a reference plate with a detection part facing the reference surface 2A.
A second detector facing towards the side.

A large number of pores are opened in the measurement table plane 1A of the measurement table 1, and a thin plate 10, which is an object to be measured, is held by negative pressure generated in the pores by a suction device (not shown). A laser distance meter is used as the first detector 3 and the second detector 4, and the first detector 3 measures the distance from a predetermined position of the first detector 3 to the measurement table surface 1A and the thin plate 10. measure. Further, the second detector 4 measures the distance from a predetermined position of the second detector 4 to the reference surface 2A. Note that this type of laser distance meter has recently made remarkable progress, has an accuracy of about 0.05 microns, can be applied to surface accuracy inspection of silicon wafers, and has become simple and inexpensive.

The measuring table 1 and the reference plate 2 are held by a U-shaped holding fitting 7 such that the measuring table surface 1A and the reference surface 2A face each other substantially parallel to each other. The relative position with 2A is kept constant. Also,
The holding fitting 7 is arranged on a moving device 8 such as an XY table, and the holding fitting 7 can be moved independently in the direction of arrow P in the figure and in the direction perpendicular to the drawing, and the holding fitting 7 can be moved with respect to the base 9. The relative position of 7 can be changed. On the other hand, the first detector 3 and the second detector 4 are fixed to the lower and upper ends of a vertical plate 5, respectively, and the vertical plate 5 is fixed to a base 9 by an arm 6.

When the holding fitting 7 is moved by the moving device 8, if the thin plate 10 is not placed on the measuring table 1, the first detector 3 outputs a change in the distance from the measuring table plane 1A. However, the second detector 4 outputs the change in distance to the reference surface 2A. Further, when the thin plate 10 is disposed on the measurement table 1, the first detector 3 outputs a change in the distance from the thin plate 10.

FIG. 2 is a block diagram of the arithmetic processing section of the thickness measuring device according to the embodiment. The switch 11 and the switch 12 are opened and closed simultaneously by the synchronization signal generator 15, and the switch 13 and the switch 14 are similarly opened and closed simultaneously by the synchronization signal generator 15.

First, a thin plate 10 is placed on the measurement table surface 1A of the measurement table 1.
When the switch is not placed, the switches 11 and 12 are closed and the switches 13 and 14 are opened. As a result, the output of the first detector 3 is guided to the first adder 16 via the switch 11, and the output of the second detector 4 is also guided to the first adder 16 via the switch 12. Guided to vessel 16.

The first adder 16 adds the two input signals and sends the added output to the first memory 18. Therefore, as shown in FIG. 3, the first memory 18 stores the sum (a+b ) to hold.

Next, when the thin plate 10 as the object to be measured is placed on the measuring table plane 1A and the switches 11 and 12 are opened and the switches 13 and 14 are closed, the output of the first detector 3 and The output of the second detector 4 is led to the second adder 17, which adds the two input signals and sends the added output to the second memory 19. Therefore, as shown in FIG. 4, the second memory 19 stores the sum (c+b ' ) is retained.

Next, the output (a+b) of the first memory 18
and the output (c+b') of the second memory 19 is subtracted by the subtracter 20.
The subtracter 20 subtracts the value of the second memory 19 from the value of the first memory 18, and the subtraction output x expressed by the following equation (1) is calculated as the measured value of the thickness of the thin plate 10. get as. x=(a+b)-(c+b')...(1)

[
That is, the value stored in the first memory 18 is obtained by subtracting the distance D between the first detector 3 and the second detector 4 from the distance A between the measuring table plane 1A and the reference plane 2A. , and the value stored in the second memory 19 is obtained by subtracting the distance D between the first detector 3 and the second detector 4 from the distance B between the thin plate 10 and the reference plane 2A. Therefore, the subtraction output x of the subtractor 20 indicates the thickness of the thin plate 10.

According to the above configuration, in FIG. 1, the holding fitting 7 moves away from the ideal plane due to the mechanical error of the moving device 8, and the measuring table plane 1A and the reference plane 2A,
Even if the detectors 3 and 4 are moved vertically with an error, the output of the subtractor 20 is not affected by this error at all, and the thickness of the thin plate 10 can be measured accurately.

For example, the distances a and a' between the measurement table surface 1A and the first detector 3 are different when the thin plate 10 is not placed on the measurement table surface 1A (FIG. 3) and when the thin plate 10 is placed on the measurement table surface 1A (FIG. 4). If they are equal, the thickness of the thin plate 10 is obtained by a-c, but
The measurement time points are different between the state in FIG. 3 and the state in FIG. 4. For example, from the time of measurement in FIG. 3 to the time of measurement in FIG. If it is removed from positions 3 and 4, each distance a between the first detector 3 and the measurement table plane 1A at the different times mentioned above.
, a' are not necessarily equal.

However, the distance A between the measuring table plane 1A and the reference plane 2A and the distance D between the first detector 3 and the second detector 4
are both constant values, so for example, if a'> a, this distance difference (a' - a) becomes the difference between the distances b and b' between the second detector 4 and the reference plane 2A. appeared,
Distance b' becomes smaller than distance b by (a' - a). That is, a'-a=b-b'=δ...(2). Further, in this state, the actual thickness X of the thin plate 10 is expressed by the following equation (3). X=a-(c-δ)...(3)

On the other hand, since the subtraction output x of the subtractor 20 is expressed by the forward tilt equation (1), the subtraction output x becomes equal to the actual thickness X.

That is, the positional deviation between the measurement of the distance a to the measuring table plane 1A and the measurement of the distance c to the thin plate 10 becomes the measurement distance b, b' by the second detector 4 to the reference plane 2A. Corrected based on

[0030]The current accuracy of silicon wafers is 1
It is within microns, and the equipment that measures it is 0.1
Precision within microns, preferably around 0.05 microns, is desired. The accuracy of recent laser detectors has improved dramatically, specifically the LD manufactured and sold by Keyence.
0.05 micron for a detector such as the 2510, and 0.0 micron for a detector such as the KL130A manufactured and sold by Anritsu.
It has an accuracy of 1 micron, which is sufficient for practical use.

[0031] On the other hand, with the current machining technology,
Even with the most accurate XY table, the repeatability due to backlash is approximately 1 micron, and an error of about 1 micron from the ideal plane of motion is unavoidable.

However, by applying the present invention as described above, it is possible to perform highly accurate thickness measurement by combining the detector as described above and the XY table.

[0033]

Effects of the Invention As explained above, according to the thin plate thickness measuring device of the present invention, the first plane and the second plane are substantially parallel to each other.
a first detector that measures the distance to the first plane and the thin plate held on the first plane, and a second detector that measures the distance to the second plane, respectively. They form a pair of detectors, and the difference between the distance measured by the first detector to the first surface and the measured distance to the thin plate is measured to the second plane when measuring the first plane and when measuring the thin plate. The thickness of the thin plate is calculated by correcting the difference between the measured distances of Even if there is an error from the ideal plane, the thickness of the thin plate can be measured without the influence of this error. Therefore, it is possible to obtain a simple, inexpensive, and highly accurate thin plate thickness measuring device in which the measured value is not affected even if an inexpensive and low-accuracy scanning means is used.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a thin plate thickness measuring device according to an embodiment of the present invention.

FIG. 2 is a block diagram of an arithmetic processing unit in an embodiment of the present invention.

FIG. 3 is a diagram showing a measurement state between a measurement table plane and a reference plane in an embodiment of the present invention.

FIG. 4 is a diagram showing a measurement state of a thin plate and a reference plane in an embodiment of the present invention.

FIG. 5 is a diagram showing an example of a conventional thickness measurement method.

[Explanation of symbols] 1A Measurement table plane (first plane) 2A Reference plane (second plane) 3 First detector 4 Second detector 8. Mobile device

Claims (2)

[Claims] 1. A pair of planes constituted by a first plane holding a thin plate as an object to be measured and a second plane facing substantially parallel to the first plane; a pair of detectors configured by integrating a first detector that measures the distance to the second plane and a second detector that measures the distance to the second plane; and a relative position between the pair of planes and the pair of detectors. a moving means for changing the thickness of the thin plate in a direction substantially parallel to the plane of the pair of planes; a calculating means for calculating the thickness of the thin plate based on the measured distances of the first detector and the second detector;
The calculation means calculates the difference between the distance measured by the first detector to the first surface and the distance measured to the thin plate by the second detector when measuring the first plane and when measuring the thin plate.
A thickness measuring device for a thin plate, characterized in that the thickness of the thin plate is calculated by correcting the difference in distance measured by a detector to a second plane. 2. first storage means for storing the sum of the distance to the first plane determined by the first detector and the distance to the second plane determined by the second detector when the thin plate is not held; a second storage means for storing the sum of the distance to the thin plate measured by the first detector and the distance to the second plane measured by the second detector when holding the thin plate; 2. The thin plate thickness measuring device according to claim 1, wherein the thickness of said thin plate is calculated based on the difference between the calculation result of said means and the calculation result of said second storage means.