JPH09113794A - Automatic focusing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device capable of efficiently making focusing operation without being affected by the surface condition of a part to be measured. SOLUTION: The reflected light from the surface 21 to be measured is condensed by an optical system 22 and the reflected light condensed in such a manner is split by a beam splitting means 23. First and second photodetecting means 33, 32 are respectively disposed on the front side and rear side with respect to the positions where the split reflected light rays are condensed. A third photodetecting means 31 is disposed in the position where the reflected light split by the beam splitting means 23 is condensed. A driver 39 of a pulse motor 40 is controlled by the speed patterns based on the results of the calculation of (A+B)/c when the output signal of the first photodetecting means 33 is defined as A, the output signal of the second photodetecting means 32 as B and the output signal of the third photodetecting means 31 as C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic focusing device for optically focusing on a processed surface such as an IC substrate or a material.

[0002]

2. Description of the Related Art Recently, there is a product inspection method for an IC substrate or the like, which uses a result of image processing of an observation image by a microscope. Is provided with an automatic focusing device for automatically performing optical focusing.

However, conventionally, as this type of automatic focusing device, for example, one disclosed in Japanese Patent Laid-Open No. 5-346533 is known. That is, as shown in FIG. 4, such an automatic focusing device includes a light receiving element Pa,
The focus error signal from the position sensor 1 which detects the difference between the outputs of Pb is amplified by the amplifier 2, converted into a digital signal by the A / D converter 3, and the focus error signal converted into this digital signal is parallelized. It is taken into the computer 5 via the interface circuit 4.

Then, the computer 5 outputs a far focus control signal for generating a large number of pulses for performing the focusing of the microscope at high speed when it is far from the focusing point, and slows down the focusing of the microscope near the focusing point. Outputs a near focus control signal that generates fewer pulses for execution at.

When the far focus control signal is output from the computer 5, this far focus control signal value is converted into an analog signal by the D / A converter 7 via the parallel interface circuit 6, and the voltage is further converted into frequency. Is converted into pulses by the V-F converter 8 that converts the pulse motor into a pulse motor, and is given to a driver 9 as a power source for driving the pulse motor to rotate the pulse motor 10 at high speed.

On the other hand, when the near focus control signal is output from the computer 5, this near focus control signal is given to the parallel interface circuit 11, where it is directly turned on.
The pulse motor 10 is turned off and given to the driver 9 as pulses smaller than the pulses from the VF converter 8 to rotate the pulse motor 10 at a low speed.

The parallel interface circuit 11
And the VF converter 8 are connected to the gate 12, respectively, and output a pulse from one of them in response to a command from the computer 5.

By the way, the output voltage characteristic from the position sensor 1 is, as shown in FIG. 5, a so-called S-shaped curve which is the difference between the outputs A and B of the light receiving elements Pa and Pb. The output voltage becomes zero at the in-focus point, changes to the plus direction when it is far away, and changes to the minus direction when it approaches.
At a further distance or a near distance, it exhibits a characteristic of approaching zero again. Therefore, in order to autofocus under such a condition, it is necessary to move the focus of the microscope so that the output voltage from the position sensor 1 is always zero. In order to improve the focusing speed at this time, It is effective to switch the servo speed at some point.

Therefore, when it is far from the in-focus point, a large number of pulses are generated from the VF converter 8 to the vicinity of the in-focus point and the pulse motor 10 is rotated at a high speed to feed the microscope toward the in-focus point at a high speed. , When it approaches the in-focus point, the pulse is directly generated by changing the servo constant and the pulse motor 1
By rotating 0 at low speed, the microscope is directed toward the focal point at low speed.

[0010]

However, in such a conventional apparatus, since the far focus control signal and the near focus control signal are switched by the instruction from the computer 5, the servo system has a complicated structure and is expensive. In addition, each output A of the light receiving elements Pa and Pb,
The difference A-B of B is taken as the S-shaped curve of the focus error signal, but this S-shaped curve may change depending on the surface condition (reflectance or surface shape) of the measured portion, so it is always stable. However, there was a problem that it was difficult to secure the focusing speed.

As a means for solving such a problem,
As disclosed in Japanese Patent Laid-Open No. 25711/1992, assuming that the outputs of the two light receiving elements 32A and 32B are A and B, the calculation of (A−B) / (A + B) is performed. It is considered that an S-shaped curve of a normalized focus error signal can be obtained as shown in FIG. 6A that is not affected by the surface condition of the measurement unit.

Then, such (AB) / (A +
When the pulse speed to the pulse motor is determined based on the S-shaped curve of B), the measured position, for example, measurement positions F1 and F
2, the signal V1 of the same level is output, and as a result, the velocity pattern shown in FIG. However, according to the speed pattern at this time, the measurement position F2 is low until the measurement position F2 of the measured portion away from the in-focus position.
From 2 to F1, the speed becomes high, and the measurement position F
Since the operation becomes slow again at 1, there is a problem that it is difficult to efficiently move the microscope to the focal position.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an automatic focusing device capable of efficiently performing a focusing operation without being affected by the surface condition of a measured portion. And

[0014]

According to the first aspect of the present invention,
An optical system that irradiates the surface to be measured with the measurement light and collects the reflected light from the surface to be measured, a light splitting unit that splits the reflected light that is collected by the optical system, and a splitting unit that splits the light. First and second light detecting means respectively arranged on the front side and the rear side with respect to the collected light collecting position of the reflected light, and a third light collecting means arranged at the light collecting position of the reflected light divided by the light dividing means. And a focusing drive source for performing a focusing operation on the surface to be measured, the output signal of the first light detecting means is A, and the output signal of the second light detecting means is A. When the signal is B and the output signal of the third photodetector is C, the focusing drive source is controlled by a control pattern based on the calculation result of (A + B) / C.

According to a second aspect of the present invention, in addition to the first aspect, the sign of the control pattern is determined based on the calculation result based on the output signals A and B, and the focus is determined based on the control pattern with the sign. The matching drive source is controlled.

As a result, according to the first aspect of the present invention,
Based on the calculation result of (A + B) / C, the position of the surface to be measured with respect to the focus position can be uniquely determined without being affected by the surface state of the surface to be measured. In the vicinity of the focal point position, a control pattern with low speed can be obtained.

According to the second aspect of the present invention, a control pattern with a sign can be obtained according to the calculation result based on the output signals A and B, and an efficient focusing operation can be realized.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic configuration of an automatic focusing device to which the present invention is applied. In this case, an optical system 22 that irradiates the measurement target surface 21 with measurement light and collects the reflected light from the measurement target surface 21, and the reflected light that is collected by the optical system 22 is divided into three directions. The light splitting means 23 is arranged.

In the optical system 22, the laser beam as the measurement light emitted from the semiconductor laser 24 is reflected by the polarization bevel splitter 25 and is measured via the quarter-wave plate 26, the imaging lens 27 and the objective lens 28. The light reflected by the surface 21 to be measured is reflected on the surface 21, and the reflected light is given to the light splitting means 23 through the objective lens 28, the imaging lens 27, the quarter wave plate 26 and the polarization beam splitter 25. .

The light splitting means 23 has a first beam splitter 29 and a second beam splitter 30, and the reflected light from the surface 21 to be measured which has passed through the polarization beam splitter 25 of the optical system 22. Is split into two directions by the first beam splitter 29, and the reflected light transmitted through the first beam splitter 29 is split into two directions by the second beam splitter 30. That is, the first beam splitter 29 further reflects the reflected light that has passed through the polarization beam splitter 25 of the optical system 22 and irradiates the light receiving means 31 whose light receiving surface is located at the converging point Q, and at the same time, The reflected light transmitted through the beam splitter 29 is given to the second beam splitter 30, and in the second beam splitter 30, the reflected light transmitted through the first beam splitter 29 is further reflected to collect light. The light receiving means 32 whose light receiving surface is positioned behind Q is irradiated, and the reflected light transmitted through the second beam splitter 30 is irradiated to the light receiving means 33 whose light receiving surface is positioned in front of the converging point Q. I am trying.

Here, the light receiving means 31 has a light receiving element 311 whose light receiving surface is positioned at the light condensing point Q, and
The reflected light reflected from the beam splitter 29 is directly irradiated to the light receiving element 311. Further, the light detecting means 32 has a diaphragm 321 and a light receiving element 322 whose light receiving surface is positioned behind the converging point Q, and the reflected light reflected from the second beam splitter 30 is at the converging point Q. The light receiving element 322 is irradiated through the aperture 321. Further, the light detecting means 33 includes a diaphragm 33.
1 and a light receiving element 332 having a light receiving surface positioned in front of the condensing point Q, and light transmitted through the second beam splitter 30 is applied to the light receiving element 332 via the diaphragm 331. ing.

These light receiving elements 311, 322, 332
Outputs an electric signal corresponding to the amount of received light. The electric signal C from the light receiving element 311 is input to one input terminal of the divider 37, and the electric signal B from the light receiving element 322 is added to the subtractor 34 and the addition. The electric signal A from the light receiving element 332 is input to one input terminal of the device 35 and the other input terminal of the subtractor 34 and the adder 35, respectively.

Further, the subtraction output of the subtractor 34 is divided by the divider 36
The addition output of the adder 35 is connected to one of the input terminals of the divider 3
6 and the other input terminal of the divider 37, respectively.

Here, the subtractor 34 outputs a subtraction signal of (AB) by the electric signal A from the light receiving element 332 and the electric signal B of the light receiving element 322, and the adder 35 outputs from the light receiving element 332. The addition signal of (A + B) is output by the electric signal A and the electric signal B of the light receiving element 322, and the divider 36
Is a subtraction signal (AB) from the subtractor 34 and an adder 35.
Addition signal (A + B) from (A−B) / (A +
The division signal of (B) is generated, and the divider 37 outputs the division signal of (A + B) / C by the addition signal (A + B) from the adder 35 and the electric signal C from the light receiving element 311. .

Then, the division signals of the dividers 36 and 37 are given to the pulse controller 38. This pulse control unit 38
Generates a speed pattern from the outputs of the divider 36 and the divider 37 and outputs a pulse velocity signal. Then, by outputting this pulse speed signal to the motor driver 39 and rotating the pulse motor 40,
I try to send the microscope to the focal point.

Next, the operation of the embodiment thus configured will be described. Now, when a laser beam is emitted as the measurement light from the semiconductor laser 24 of the optical system 22, this laser beam is reflected by the polarization bevel splitter 25, and the quarter wave plate 26, the imaging lens 27 and the objective lens 28 are reflected. The light is condensed on the surface to be measured 21 via the measuring surface 21, and the reflected light from the surface to be measured 21 is an objective lens 28, an imaging lens 27, a quarter-wave plate 26, and a polarization beam splitter 2.
After passing through 5, the light is given to the light splitting means 23.

Then, in the light splitting means 23, the optical system 22
Of the surface to be measured 21 transmitted through the polarization beam splitter 25 of
The reflected light from the first beam splitter 29 is reflected by the first beam splitter 29, is irradiated to the light receiving means 31 whose light receiving surface is located at the condensing point Q, and the reflected light transmitted through the first beam splitter 29 is second light. The reflected light reflected by the beam splitter 30, irradiated onto the light receiving means 32 whose light receiving surface is positioned behind the converging point Q, and further transmitted through the second beam splitter 30 has a light receiving surface in front of the converging point Q. The positioned light receiving means 33 is irradiated.

As a result, the light receiving element 33 from the subtractor 34 is received.
The subtraction signal of (A−B) from the electric signal A from 2 and the electric signal B from the light receiving element 322 is output from the adder 35 to the light receiving element 3
An addition signal of (A + B) is obtained by the electric signal A from 32 and the electric signal B from the light receiving element 322, and the addition signal from the divider 36 to the subtractor 3
The subtraction signal (A−B) from the adder 4 and the addition signal (A + B) from the adder 35 give a division signal of (A−B) / (A + B), and the addition signal (A +) from the adder 35 from the divider 37.
B) and the electric signal C from the light receiving element 311 (A +
B) / C division signals are respectively output, and among them, the division signal (AB) / (A + B) of the divider 36 and the divider 37 are output.
The division signal (A + B) / C is given to the pulse controller 38.

Here, if the surface state of the surface to be measured 21 is rough, the adder 35 outputs the addition signal (A + B) shown in FIG. 2A corresponding to the displacement of the surface to be measured 21. If the light receiving element 311 outputs the electric signal C as shown in FIG.
Although the signal level of the addition output (A + B) decreases near the in-focus position, the signal level of the electric signal C also decreases, and as a result, the division signal (A + B) / C of the divider 37 results.
Indicates that the fluctuation of the signal level in the vicinity of the in-focus position is corrected, and there is no fluctuation in the signal level in the vicinity of the in-focus position as shown in FIG. , The signal level will be monotonically attenuated. Such characteristics are the same even when the reflectance of the surface to be measured 21 is low.

As a result, the pulse control section 38 generates a pulse speed pattern as shown in FIG. 7D by the division signal (A + B) / C of the divider 37. Here, such a pulse velocity pattern is simple by obtaining the difference between the signal levels of the characteristic shown in FIG. 2C from the signal level slightly larger than the maximum value of the signal level of the characteristic shown in FIG. Can be obtained.

Further, in the pulse control unit 38, the divider 36
Division signal (A−B) / (A +) shown in FIG.
From (B), it is determined that the displacement of the surface to be measured 21 inverts the signs (+) and (-) across the in-focus position, and in consideration of this sign, based on the pulse velocity pattern shown in FIG. The pulse motor 40 is rotated by generating a pulse speed pattern with a sign as shown in FIG. 3B, converting this speed pattern into a pulse signal and outputting it to the driver 39.

By the way, the division signal (A−B) / (A +
B) is an equation for obtaining the focus error signal as described above, but here, the subtraction signal (A
It is only necessary to be able to determine that the sign of −B) is inverted between (+) and (−). That is, if it is only necessary to determine the inversion of the sign, it is sufficient to perform the calculation by replacing the division signal (AB) / (A + B) with the subtraction signal (AB).

Therefore, according to such an embodiment,
The signal level for the measured surface 21 is uniquely determined by the division signal (A + B) / C of the divider 37.
Since the distance between the focal position and the surface to be measured 21 can also be uniquely obtained, the surface state of the surface to be measured 21 is unaffected, and the distance is high at a position distant from the focal position and close to the focal position. It is possible to generate a speed pattern that makes the speed low, and further, a division signal (AB) from the divider 36.
/ (A + B) or a sign obtained from the subtraction signal (A-B) is added to obtain a signed pulse velocity pattern for automatic focusing, and the pulse motor 40 is rotated based on this to obtain a signed pulse velocity pattern. An efficient focusing operation can be realized.

[0034]

As described above, according to the present invention, (A
The position of the measured surface relative to the focal position can be uniquely determined based on the calculation result of + B) / C without being affected by the surface state of the measured surface. In the vicinity of the position, it is possible to obtain a control pattern that is performed at low speed, and further to obtain a control pattern with a sign according to the calculation result based on the output signals A and B, so that an efficient focusing operation can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of one embodiment.
Is a diagram showing output signal characteristics of the adder 35, (b) is a diagram showing electric signal characteristics output from the light receiving element 311,
(C) is a figure which shows the division signal characteristic output from the divider 37, (d) is a figure which shows the speed pattern produced based on the division signal characteristic of (c).

FIG. 3 is a view for explaining the operation of one embodiment, and (a)
Is a diagram showing characteristics of a division signal output from the divider 36,
2B is a pulse velocity pattern of FIG. 2D and FIG.
The figure which shows the signed velocity pattern produced from the sign of the division signal characteristic of.

FIG. 4 is a diagram showing a schematic configuration of an example of a conventional automatic focusing device.

FIG. 5 is a diagram for explaining the operation of a conventional automatic focusing device.

FIG. 6 is a view for explaining the operation of a conventional automatic focusing device.

[Explanation of symbols]

 Reference numeral 21 ... Surface to be measured, 22 ... Optical system, 23 ... Light splitting means, 24 ... Semiconductor laser, 25 ... Polarization bevel splitter, 26 ... Quarter wave plate, 27 ... Imaging lens, 28 ... Objective lens, 29 ... 1 beam splitter, 30 ... Second beam splitter, 31 ... Light receiving means, 311 ... Light receiving element, 32 ... Photo detecting means, 321 ... Aperture, 322 ... Photo receiving element, 33 ... Photo detecting means, 331 ... Aperture, 332 ... Light receiving element, 34 ... Subtractor, 35 ... Adder, 36, 37 ... Divider, 38 ... Pulse control unit, 39 ... Driver, 40 ... Pulse motor.

Claims (2)

[Claims] 1. An optical system for irradiating the surface to be measured with the measurement light and condensing the reflected light from the surface to be measured, and a light splitting means for splitting the reflected light condensed by the optical system. The first and second light detection means are respectively arranged on the front side and the rear side with respect to the converging position of the reflected light divided by the light dividing means, and the converging position of the reflected light divided by the light dividing means. It is provided with the 3rd photon detection means arrange | positioned, and the focusing drive source which performs a focusing operation with respect to the said to-be-measured surface, The output signal of the said 1st photon detection means is A, and the said 2nd. When the output signal of the light detecting means is B and the output signal of the third light detecting means is C, the focusing drive source is controlled by a control pattern based on the calculation result of (A + B) / C. And an automatic focusing device. 2. The code of the control pattern is determined based on a calculation result based on the output signals A and B, and the focusing drive source is controlled by the control pattern with the code. Item 1. The automatic focusing device according to item 1.