JP3359316B2 - Thickness measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact type thickness measuring device for measuring the thickness of a sample by detecting a back pressure at that time while spraying a compressed fluid on the sample.

[0002]

2. Description of the Related Art FIG. 6 shows the principle of a non-contact type thickness measuring device. In this thickness measuring apparatus, compressed air is blown from upper and lower surfaces of a sample 1 by spray nozzles 2 and 2. Thus, when the compressed air is blown, a back pressure is generated. This back pressure is applied to the tip of the injection nozzle 2 and the sample 1
It depends on the distance from the surface. That is, the closer the injection nozzle 2 is to the surface of the sample 1, the higher the back pressure is. Conversely, the tip position of the injection nozzle 2 is kept constant,
When compressed air is blown on the sample 2, the back pressure changes depending on the thickness of the sample 2. The non-contact type thickness measuring device uses this principle.

When using this measuring apparatus, the relationship between the distance between the tip of the injection nozzle and the sample surface and the back pressure is measured using a reference sample whose thickness is known in advance.
The distance x1 from the upper ejection nozzle 2 to the front surface of the sample 1 and the distance x2 from the lower ejection nozzle 2 to the back surface of the sample 1 are used as reference distances, and these reference distances x
The back pressure at 1, x2 is stored as reference back pressure values p1, p2. Next, the measuring object 1 is set, and while the compressed air is being injected, the injection nozzle 2 is moved up and down, and the injection nozzles 2 and 2 are stopped at the points of the reference back pressure values p1 and p2. And
The injection nozzle position there is detected by a linear gauge.

The same operation is performed from both the upper and lower sides of the measurement object 1. When the back pressure becomes the reference back pressure values p1 and p2, that is, when the distance from the sample surface becomes x1 and x2, the injection nozzle 2 , 2 are stopped and the position is measured. If the positions of the two injection nozzles 2 and 2 are known, the distance L between the two injection nozzles can be obtained from the position. Further, the distances x1, x between the surface of each injection nozzle 2 and the sample 1
2 is determined from the beginning. From these data, the thickness T of the object to be measured is T = L− (x1 + x2).
It can be calculated by (1). That is, the reference distance x
By setting the reference back pressures p1 and p2 corresponding to 1, x2, each time the measurement target 1 is set, the reference back pressures p1 and p2 are set.
It is only necessary to measure the position of the injection nozzle set to 2 using a linear gauge. The distance L between the injection nozzles is obtained from the positions of the upper and lower injection nozzles 2 and 2, and the thickness T of the measurement target 1 can be obtained from the above equation (1).

[0005]

In order to accurately determine the thickness of a sample by the above method, the value of L in the above equation (1) must be determined accurately. This distance L
Is a value determined by the position of the injection nozzle 2 detected by the linear gauge as described above. In order to increase the accuracy of L, the measurement accuracy of the linear gauge must be sufficient, and the injection nozzle 2 must be stopped accurately at the time of the reference back pressure values p1 and p2. Therefore, it is necessary to use moving means having high positioning accuracy. But,
For example, a moving means having a high positioning accuracy, such as a linear motor, is very expensive. for that reason,
The thickness measuring device using this has become very expensive. Also, as described above, in the case of the measurement method in which the compressed fluid is injected and the back pressure is used, the fluid pressure changes due to the fluctuation of the supply source of the compressed fluid and the temperature fluctuation.
As a result, the measurement results may be skewed.

An object of the present invention is to provide a thickness measuring device capable of performing accurate measurement without using expensive moving means. Another object of the present invention is to provide a thickness measuring device which is hardly affected by the pressure of the compressed fluid supplied to the injection nozzle or the temperature change.

[0007]

According to the first and second aspects of the present invention, there is provided a holding portion for setting a plate-shaped object to be measured, and a pair of holders which are located on both sides of the object to be measured and eject fluid to both sides of the object to be measured. Injection nozzle, nozzle moving means for moving the injection nozzle, nozzle position detection means for detecting the position of the injection nozzle, back pressure detection means for the injection nozzle, and nozzle position detection means for controlling the nozzle movement means And a data processing unit for performing calculations based on the detection data from the back pressure detecting means. The data processing unit includes a reference position of the injection nozzle set in advance using a reference sample and a reference back pressure corresponding to the position. The reference distance to the reference sample surface corresponding to the reference back pressure value is specified, and the injection nozzle position corresponding to the reference back pressure value with respect to the measurement target is detected. And position data, assuming the thickness measuring device in the configuration for calculating the thickness of the measurement target on the basis of the above reference distance.

On the premise of the above apparatus, the data processing unit detects the injection nozzle position a plurality of times based on the reference back pressure value, and obtains a plurality of coordinate points relating to the back pressure and the injection nozzle position. It is characterized in that an approximate curve is obtained based on these coordinate points, and the injection nozzle position corresponding to the reference back pressure value on the approximate curve is calculated.

In a second aspect of the present invention, the back pressure detecting means includes a first circuit comprising a fixed resistor and a variable resistor between the supply source of the compressed fluid and the injection nozzle, and a fixed resistor and a nozzle back pressure resistor. And a back pressure when the pneumatic bridge circuit is in an equilibrium state is set as a reference back pressure value.
The third invention is based on the premise of the second invention, and in the relationship between the distance from the tip of the nozzle to the object to be measured and the back pressure, a point at which the rate of change of the back pressure with respect to the distance becomes the maximum is a reference back pressure value. Is set.

According to a fourth aspect of the present invention, there is provided a holding section for setting a plate-shaped object to be measured, and a pair of ejection nozzles located on both sides of the object to be measured, and the ejection nozzles eject fluid to both sides of the object to be measured. A data processing unit that calculates the thickness of the measurement object based on the back pressure value at that time and the position of the injection nozzle at that time, wherein the holding unit comprises a plate having a penetrating measurement window. A feature of this plate surface is that a plurality of air suction holes are provided at least along the periphery of the measurement window.

[0011]

1 to 5 show an embodiment of the present invention. FIG. 1 is a schematic view of a measuring apparatus according to this embodiment. A main body base 3 having injection nozzles 2 is opposed to both sides of a measuring object 1 such as a wafer. Since the upper and lower sides of the measurement object 1 have the same configuration, only the upper side configuration will be described here. A stepping motor 4 and a linear gauge 6 are fixed to the main body base 3. A ball screw 5 is linked to the stepping motor 4, and the injection nozzle 2 is attached to the ball screw 5 via an injection nozzle base 7.

When the stepping motor 4 is rotated, the injection nozzle 2 moves up and down together with the injection nozzle base 7 by the ball screw 5. At this time, the movement amount of the injection nozzle base 7, that is, the movement amount of the injection nozzle 2, is detected by the linear gauge 6, and the data is input to the data processing unit 8. The data processing unit 8 performs calculations based on the input data, and controls the stepping motor 4. The stepping motor 4 and the ball screw 5 constitute the nozzle moving means of the present invention, and the linear gauge 6 is the nozzle position detecting means of the present invention.

On the other hand, a passage 9 for supplying compressed air is connected to the injection nozzle 2, and a back pressure detecting means 10 for detecting a back pressure is provided in the passage 9; To be entered. The back pressure detecting means 10 includes a pneumatic bridge circuit 11 and a semiconductor slight differential pressure sensor 12. The pneumatic bridge circuit 11 is a circuit as shown in FIG. In the drawing, R is the fluid resistance of the fixed throttle, and Ra is the fluid resistance of the variable throttle for adjustment. Rb indicates a fluid resistance created by the measurement object 1 and the gap x. That is, the pneumatic bridge circuit 11 includes a first circuit provided with the fixed resistor R and the variable resistor Ra, a second circuit provided with the fixed resistor R and the fluid resistor Rb, and a bridge. In such a circuit,
When the pressure Ps is supplied, the pressure Pa at both ends of the bridge
And Pb is determined by the fluid resistances Ra and Rb.

For example, when Ra = Rb, the pressure Pa
= Pb, and the differential pressure Pc is 0, but both the resistances Ra, Rb
Is lost, the differential pressure Pc is generated. This differential pressure Pc is measured by the semiconductor slight differential pressure sensor 12.
The semiconductor small differential pressure sensor 12 can detect a very small differential pressure as a voltage value. In this embodiment, when a reference sample is set, the fluid resistance Ra is set so that the differential pressure Pc between Pa and Pb becomes 0 when the distance x1 from the surface to the tip of the injection nozzle 2 is set. deep. That is, at the time of measurement, the back pressure is measured not by directly measuring the back pressure value of the injection nozzle 2 but by measuring the differential pressure Pc.

The back pressure when the differential pressure Pc = 0 is the reference back pressure value of the present invention, and the distance x1 between the measurement object and the injection nozzle at that time is the reference distance. And the differential pressure Pc
, It is possible to detect a minute change in the distance between the measurement object and the injection nozzle. Since the basic measurement principle is the same as that described in the conventional example, the details are omitted, but the injection nozzle position (linear position) when the distance between the injection nozzle 2 and the measurement target 1 is equal to the reference distance x1. The thickness of the measurement target 1 can be calculated by knowing the gauge reading value) and the position of the injection nozzle when the distance between the other injection nozzle 2 and the measurement target 1 is the reference distance x2.

Hereinafter, a method of measuring the thickness of a wafer or the like using this apparatus will be described. First, a reference sample with a known thickness is set and the origin is adjusted. Here, the upper injection nozzle 2 will be described first. First, while injecting compressed air to the reference sample,
The injection nozzle 2 is moved up and down. From the linear gauge reading at the appropriate ejection nozzle position and the thickness of the reference sample, the distance from the tip of the ejection nozzle to the sample surface is calculated and set as the reference distance x1. In the pneumatic bridge circuit 11, the fluid resistance Ra is adjusted so that the pressure difference Pc between the pressures Pa and Pb becomes zero. That is, the fluid resistance R due to the back pressure
When b is equal to the fluid resistance Ra and the differential pressure Pc = 0, the distance between the injection nozzle and the sample surface is the reference distance x1. When the differential pressure Pc = 0, that is, when the pneumatic bridge circuit 11 is in equilibrium, the back pressure is the reference back pressure.

Next, the measuring object 1 is set. next,
The injection nozzle 2 is stopped by blowing compressed air while bringing the injection nozzle 2 close to the surface of the measuring object 1 and detecting that the differential pressure Pc has become 0 from the output of the semiconductor fine differential pressure sensor 12. To The control of the stepping motor 4 as the nozzle moving means is performed using the differential pressure Pc = 0, which is the reference back pressure value, as the target stop position. The differential pressure P
Even if the injection nozzle 2 is controlled to stop at the point of time when c = 0 is detected, the stepping motor 4 does not have so good positioning accuracy. Therefore, at the position where the injection nozzle 2 actually stops, the differential pressure Pc = 0, but strictly speaking, the differential pressure Pc
= 0 is often not the case.

As described above, the injection nozzle 2 is supplied with the differential pressure Pc =
Although it cannot be stopped accurately at the position of 0, the differential pressure Pc =
In order to stop at 0, move the injection nozzle 2
Repeat stop. FIG. 3 shows the relationship between the actual output of the semiconductor differential pressure sensor 12 and the linear gauge reading at that time when the injection nozzle 2 is moved and stopped three times. However, when the differential pressure Pc = 0, the output voltage of the semiconductor fine differential pressure sensor 12 is V0.

The sensor voltage and the linear gauge reading at the time when the injection nozzle 2 actually stops are points a, b, and c in FIG. As described above, three points where the sensor voltage is not V0 are measured, and these three points a,
An approximate straight line 16 is obtained from b and c, and a linear gauge reading value A corresponding to the sensor voltage V0 is specified on the approximate straight line 16. That is, the injection nozzle 2 is set to the sensor voltage V
Even if it cannot be stopped exactly at the point 0, the position of the injection nozzle corresponding to the sensor voltage V0 can be specified by calculation from the data of the three points a, b, and c that stop close to it.

Note that the number of measurement points is not limited to three, but the more the number, the more accurate approximation can be made. In some cases, curve approximation is more preferable. However, the reference distances x1 and x2 are
If you set it appropriately, you can select a sufficient range by linear approximation,
In that case, sufficient accuracy can be obtained even with three points. Also, in FIG. 3, although each point a, b, and c seem to be apart from the approximate straight line, actually, since the measurement is performed in a very narrow range of the curve, the linear approximation is sufficient in most cases. It is.

Injection nozzle 2 located below measurement object 1
In the same manner as above, the injection nozzle position at which the reference distance is x2 is calculated, and the thickness of the measurement target 1 is calculated from the linear gauge reading values of both the injection nozzles 2 and 2. As described above, in this embodiment, based on data of a plurality of points,
Since the positions of the injection nozzles 2 and 2 that maintain the reference distances x1 and x2 from the surface to be measured are obtained by calculation,
Actually, even if the injection nozzle 2 cannot be stopped at the positions of the reference distances x1 and x2, accurate thickness measurement can be performed. Therefore, for example, accurate measurement can be performed without using an expensive motor with high positioning accuracy such as a linear motor. If an inexpensive motor whose positioning accuracy is not so high like the stepping motor 4 of the above embodiment is used, the cost of the entire apparatus can be reduced accordingly.

In this embodiment, the differential pressure Pc is zero.
The measurement is performed with the reference point as a reference point, but the differential pressure Pc is not limited to 0, and another value may be set. In short, it suffices to know the linear gauge reading at the time when the set value is reached. In addition, although the pneumatic bridge circuit 11 and the semiconductor fine differential pressure sensor 12 are used as the back pressure detecting means, if the back pressure can be measured directly, a reference value may be set using the back pressure value instead of the differential pressure. , And calculations.

However, if the back pressure corresponding to the differential pressure Pc = 0 between the bridges is set as the reference back pressure value using the pneumatic bridge circuit 11 as in the above embodiment, more stable measurement can be performed. . This is because, in the pneumatic bridge circuit shown in FIG. 2, when the supply pressure Ps or temperature of the compressed air fluctuates, the pressures Pa and Pb at both ends of the bridge change, but when the back pressure Pc = 0 is used as a reference, This is because the fluctuation affects the measurement result. The pressure Pa,
Pb is determined by the ratio between the fluid resistance Rb and Pa. However, even if the ratio between the fluid resistances Ra and Rb is constant, if the pressures Pa and Pb fluctuate due to fluctuations in the supply pressure Ps and the temperature, the differential pressure also changes. On the other hand, even if the pressure difference is determined as a reference, Pa,
The ratio of Pb is different, and the ratio of fluid resistances Ra and Rb is also different.

Therefore, even if the same differential pressure value is detected, the same back pressure value may not be detected. That is, if there is a change in the supply pressure Ps or the temperature, the thickness measurement accuracy also decreases. On the other hand, when the back pressure at the time of the differential pressure Pc = 0 is set as the reference back pressure as in the above-described embodiment, the supply pressure Ps and the temperature fluctuate, and the absolute values of the pressures Pa and Pb are changed. Even if both fluctuate, if Pa = Pb, the differential pressure P
Since c = 0 does not change, the stability of the measurement is increased on the basis of c = 0.

The reference distance x1 and the reference back pressure value p1
It is preferable to use a point at which the rate of change of the back pressure p with respect to the distance x from the nozzle tip to the surface to be measured is maximum. Thus, if the reference distance x1 and the reference back pressure value p1 are set, a slight change in the distance x can be detected as a large change in the back pressure value. The detection accuracy of the distance x increases accordingly.

The point at which the rate of change of the back pressure p becomes maximum will be described below. In the bridge circuit of FIG. 2, if the opening of the fixed fluid resistance R is s1 and the back pressure is p, p
And x are approximately p = Ps / ｛1+ (πdx / s
1) ² ｝ (2) Here, d is the diameter of the fluid passage. From the above equation (2), the distance x and the back pressure p
FIG. 4 is a graph showing the relationship with. This graph has an inflection point Q whose inclination is maximum. Therefore, x corresponding to the inflection point Q is set as a reference distance, and p is set as a reference back pressure.

When actually setting a reference point, first, a reference distance x1 is appropriately selected, and then a fixed point is set such that a point corresponding to the reference distance x1 is the inflection point Q. Set the aperture R. By changing the opening area s1 of the fixed stop R, the position of the inflection point Q in the graph changes. As described above, the reference distance x1 and the inflection point Q
Then, the variable resistance R of the pneumatic bridge circuit 11 is set so that the differential pressure Pc at the distance x1 becomes zero.
Adjust the processing area of a. As a result, the back pressure at the time when the differential pressure is 0 becomes the reference back pressure value, and the vicinity of this reference back pressure value becomes a range where the rate of change with respect to the distance x is the highest. Therefore, it is less susceptible to fluctuations in supply pressure and temperature,
Further, the measurement accuracy of the distance x is improved, and more accurate thickness measurement can be performed.

The holding unit for setting the measurement object 1 is:
This is a plate 13 as shown in FIG. This plate 1
3 has a measurement window 14, and a number of air suction holes 15 are formed along the periphery thereof. These air suction holes 15
Is connected to a vacuum pump via an air passage (not shown) formed on the back surface of the plate 13. Therefore, the measurement target 1 placed on the plate 13 can be attracted to the plate 13. In particular, since the air suction hole 15 is formed around the measurement window 14, a very thin measurement target 1 is tightened in the measurement window 14 by sucking the portion.

Then, the injection nozzle 2 is positioned above and below the measurement window 14 to measure the thickness. In this embodiment, since the measurement window 14 is formed in the diameter direction of the plate 13, the thickness can be measured at a plurality of points on the measurement target 1 while moving the injection nozzle 2 or the plate 13 in the diameter direction. For example, if the measurement portion of the measurement target 1 is bent or wavy, accurate measurement cannot be performed. However, if the plate 13 is used, accurate thickness measurement can be performed. Since only the periphery of the measurement window 14 is adsorbed by the plate 13, even when the measurement object is warped as a whole, only the measurement portion can be held flat.

Such a plate 13 can be applied to a device for measuring the thickness of a thin measuring object other than the device of this embodiment. In particular, when measuring by ejecting a compressed fluid to a thin object, the measurement target 1 may be vibrated by the ejected fluid. However, if the measurement target 1 is attracted to the plate 13 by the air suction holes 15, it is possible to prevent the measurement portion from vibrating and causing a measurement error. Further, the measurement window 14 is not limited to the one shown in FIG. 5, and may be formed at a position where measurement is desired. For example, a plurality of small windows may be provided, or the measurement window may be opened radially.

However, the air suction holes 15 provided around the
In order to sufficiently pull the measurement target 1 in the measurement window 14 by the suction force, it is better that the entire measurement window 14 is not too far from the suction hole 15. For example, a window opened in a linear shape is more preferable than a large circle or a square. Further, various positions can be measured by shifting the measurement target 1 on the plate 13.

[0032]

According to the first aspect of the invention, accurate thickness measurement can be performed even if the positioning accuracy of the nozzle moving means is not so high. Therefore, adopting inexpensive nozzle moving means,
The cost of the measuring device can be reduced. According to the second invention, the back pressure of the injection nozzle is measured using the pneumatic bridge circuit, and the back pressure at which the bridge circuit of the circuit is balanced is set as the reference back pressure, so that the supply pressure of the compressed fluid, It is less susceptible to temperature fluctuations.

According to the third aspect of the invention, the accuracy of distance measurement is improved, and more accurate measurement can be performed. According to the fourth aspect of the invention, even in the case of a thin and easily bent measurement target, the measurement portion of the measurement target can be held flat during measurement,
Accurate thickness measurement can be performed. Also, in the case of various measurements using a compressed fluid, an accurate measurement can be performed without the measurement object being vibrated by the ejected fluid.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram of a measuring device of this embodiment.

FIG. 2 is a circuit diagram of a back pressure detecting means of this embodiment.

FIG. 3 is a diagram for explaining a method of calculating a nozzle position in measurement using the apparatus according to the embodiment.

FIG. 4 is a graph showing a relationship between a distance between a nozzle and a surface to be measured and a back pressure in the apparatus according to the embodiment.

FIG. 5 is a plan view of a plate holding an object to be measured in the example.

FIG. 6 is a diagram illustrating a measurement principle in a conventional thickness measuring apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Measurement object 2 Injection nozzle 4 Stepping motor 5 Ball screw 6 Linear gauge 8 Data processing part 10 Back pressure detecting means 11 Pneumatic bridge circuit 12 Semiconductor micro differential pressure sensor 13 Plate 14 Measurement window 15 Air suction hole First circuit Second circuit Bridge p Back pressure x distance

Claims (4)

(57) [Claims] A holding unit for setting a plate-shaped measurement target;
A pair of ejection nozzles located on both sides of the measurement object and ejecting fluid to both sides of the measurement object, nozzle moving means for moving the ejection nozzle, nozzle position detection means for detecting the position of the ejection nozzle, and ejection nozzle Back pressure detecting means, and a data processing unit that controls the nozzle moving means and performs an operation based on detection data from the nozzle position detecting means and the back pressure detecting means, and the data processing unit includes:
The reference position of the injection nozzle set in advance using the reference sample and the reference back pressure value corresponding to the position are stored, and the reference distance to the reference sample surface corresponding to the reference back pressure value is specified, and In the thickness measurement device configured to detect the injection nozzle position corresponding to the reference back pressure value and calculate the thickness of the measurement target based on the injection nozzle position data and the reference distance, the data processing unit Detects the injection nozzle position a plurality of times based on the reference back pressure value, obtains a plurality of coordinate points relating to the back pressure and the injection nozzle position, obtains an approximate curve based on these coordinate points, A thickness measuring device for calculating an injection nozzle position corresponding to a reference back pressure value on a curve. 2. A holding unit for setting a plate-like measurement object,
A pair of ejection nozzles located on both sides of the measurement object and ejecting fluid to both sides of the measurement object, nozzle moving means for moving the ejection nozzle, nozzle position detection means for detecting the position of the ejection nozzle, and ejection nozzle Back pressure detecting means, and a data processing unit that controls the nozzle moving means and performs an operation based on detection data from the nozzle position detecting means and the back pressure detecting means, and the data processing unit includes:
The reference position of the injection nozzle set in advance using the reference sample and the reference back pressure value corresponding to the position are stored, and the reference distance to the reference sample surface corresponding to the reference back pressure value is specified, and In contrast, in the thickness measuring device configured to detect the injection nozzle position corresponding to the reference back pressure value and calculate the thickness of the measurement target based on the injection nozzle position data and the reference distance, As a means,
A pneumatic bridge circuit including a first circuit including a fixed resistor and a variable resistor and a second circuit including a fixed resistor and a nozzle back-pressure resistor is provided between the supply nozzle of the compressed fluid and the injection nozzle. A thickness measuring device, wherein a back pressure when the pneumatic bridge circuit is in an equilibrium state is set as a reference back pressure value. 3. A reference back pressure value is set at a point where a rate of change of the back pressure with respect to the distance becomes maximum in a relationship between a distance from a nozzle tip to a measurement target and a back pressure. Item 3. A thickness measuring device according to item 2. 4. A holding unit for setting a plate-like measurement object,
A pair of ejection nozzles located on both sides of the measurement target, the thickness of the measurement target based on the back pressure value when the ejection nozzle ejects fluid to both sides of the measurement target and the ejection nozzle position at that time In the thickness measuring device provided with a data processing unit for calculating, the holding unit comprises a plate having a penetrating measuring window, and a plurality of air suctions are provided along at least the periphery of the measuring window on the plate surface. A thickness measuring device comprising holes.