JPH07159136A - Periodic pattern measuring device - Google Patents

Abstract

PURPOSE:To set the threshold value which is used for detecting the edge of the periodic pattern with the high precision, in a simple and correct manner, by arranging the second pin hole at the position got out of position by a prescribed quantity in the vertical direction to the optical axis and setting the optimum threshold value in an edge detecting means on the basis of the difference between two signals. CONSTITUTION:After the optical image of a sample 1 is converted into the parallel luminous flux by an objective lens 2, the optical image is branched into the transmitted light and the reflected light by a prism 6 arranged on the outgoing end side of an image formation lens 3. The transmitted light is inputted into a photoelectric transfer element 10 through a pin hole 9. When the sample 1 having a periodic pattern and the objective lens are shifted in the periodic pattern formation direction in the plane vertical to the optical axis, the periodic wave shape is formed according to the brightness and darkness of the periodic pattern, and since the pin hole 9 gets out of position in the plane vertical to the optical axis, the periodic output wave shape having the deflected phase is generated. A threshold value setting circuit 11 sets the intermediate value of the voltage value Va and Vb at the point where the difference between two output wave shapes becomes zero, as threshold value, in a comparator 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a periodic pattern measuring device capable of measuring a periodic pattern on a glass scale or the like.

[0002]

2. Description of the Related Art An optical image obtained by transmitting and illuminating a periodic pattern such as a glass scale with a microscope is projected onto a photoelectric conversion element through an imaging optical system, and an output signal of the photoelectric conversion element is preset. There are measuring devices that detect the edges of a periodic pattern by comparing it to a threshold that is present.

FIG. 11 shows an example of the configuration of an optical system of such a measuring device. This measuring device transmits and illuminates a sample 1 having a periodic pattern with illumination light from a light source (not shown), converts the illuminated object light from the sample 1 into a parallel light flux by an objective lens 2, and then forms the parallel light flux into an imaging lens 3. Incident. The pinhole 4 is arranged at the focal position of the imaging lens 3, and the light passing through the pinhole 4 is converted into an electric signal by the photodetector 5.

Since the transmitted illumination light incident on the sample 1 is partially blocked by the periodic pattern formed on the sample 1, the sample 1 is moved in the X direction shown in the drawing perpendicular to the pattern forming direction in the plane perpendicular to the optical axis. When moved, the photo detector 5
The output signal output from is a periodic signal as shown in FIG. Therefore, each edge of the periodic pattern can be detected by comparing the threshold value set to (V1 + V2) / 2 with the output signal of the photodetector 5.

[0005]

However, in the above-described measuring apparatus, there is a possibility that the edge detection position may include an error due to, for example, fluctuations in the light amount of the light source and fluctuations in the contrast of the sample, which is a problem in terms of reliability. It was

For example, assuming that the profile of the output voltage of the photodetector 5 when the threshold value is set is the profile 50 of FIG. 13, the profile of the output voltage is the profile 51 when the light quantity of the light source changes thereafter.
Changes to. A change in contrast also appears as a change in the output voltage profile.

As a result, with respect to the actual edge positions 50a to 50d detected before there is a change in the light quantity, 51a to 51d are detected as the edge positions after the change in the light quantity or contrast, and the actual edge positions 50a to 50d. In the meantime, a detection error will occur.

If the threshold value is set again for each measurement, the threshold value can be set for more realistic light amount and contrast. However, usually
Since the output voltage is observed with an oscilloscope and the threshold value is set by the trimmer resistance of the edge position detection circuit, the actually set threshold value is not always exactly (V1 + V2) / 2. As shown in, the actual edge positions 53a to 53d and the actual threshold value setting are exactly 50.
Edge positions 54a to 5 when the percentage is not set
4d, there is a problem that an error similar to that in the case of light amount variation occurs and the operation becomes complicated.

The present invention has been made in view of the above circumstances, and a threshold value used for edge detection of a periodic pattern can be set easily and accurately, and a highly reliable synchronous pattern can be obtained. An object is to provide a measuring device.

[0010]

In order to achieve the above object, the present invention has taken the following means. A periodic pattern measuring device according to claim 1, comprising: an optical system for guiding a subject image having a periodic pattern to form an image at a predetermined position; and a first pinhole arranged at the image forming position of the subject image. A first light receiving means for converting light passing through the first pinhole into an electric signal; and a first light receiving means for forming a subject image guided by the optical system in a plane perpendicular to the optical axis. A second pinhole arranged at a position displaced from the pinhole of
The second light receiving means for converting the light passing through the second pinhole into an electric signal is compared with the output signal of at least one of the first light receiving means and the second light receiving means and a threshold value. The edge detection means for detecting the edge of the periodic pattern, and the optimum threshold value is set in the edge detection means based on the difference between the output signals of the first light receiving means and the second light receiving means. It is configured to include a threshold value setting means.

According to a second aspect of the present invention, there is provided a periodic pattern measuring device, which comprises an optical system for guiding a subject image having a periodic pattern to form an image at a predetermined position, and a pinhole arranged at the image forming position of the subject image. A light receiving means for converting the light passing through the pinhole into an electric signal; an edge detecting means for detecting an edge of the periodic pattern by comparing an output signal of the light receiving means with a threshold value; And a threshold value setting means for setting an optimum threshold value to the edge detection means based on the maximum value and the minimum value of the output signal of the subject image output from.

[0012]

In the periodic pattern measuring device according to the first aspect, the first pinhole is arranged at the position where the subject image guided by the optical system is formed, and the position where the subject image is formed. Then, the second pinhole is arranged at a position that is deviated from the first pinhole by a predetermined amount in the direction perpendicular to the optical axis. Therefore, the output signal of the first light receiving element on which the light passing through the first pinhole is incident and the output signal of the second light receiving element on which the light passing through the second pinhole is incident have a periodic pattern. When moved in the pattern formation direction in a plane perpendicular to the optical axis, the profile has a phase shift. Based on such a difference between the two output signals, an optimum threshold value is set from the threshold value setting means to the edge detecting means. Then, the edge detecting means compares the output signal of one of the first light receiving means or the second light receiving means with the threshold value and detects the edge of the periodic pattern.

Since the difference between the output signals output from the first and second light receiving means does not change before and after the fluctuation of the light quantity or the fluctuation of the contrast, the threshold value is set based on the difference of the signals to thereby cause the fluctuation of the light quantity. The error can be removed.

In the periodic pattern measuring device according to the second aspect, the pinhole is arranged at the position where the image of the object is formed by the image forming optical system, and the light passing through the pinhole is electrically received by the light receiving element. It is converted into a signal and given to the edge detecting means and the threshold setting means. The threshold value setting means determines an optimum threshold value based on the maximum value and the minimum value of the output signal of the subject image and sets it to the edge detecting means. Then, the edge detecting means detects the edges of the periodic pattern by comparing the output signal of the light receiving means with the threshold value.

[0015]

EXAMPLES Examples of the present invention will be described below. FIG. 1 shows the overall configuration of a synchronous pattern measuring apparatus according to the first embodiment of the present invention. The synchronous pattern measuring apparatus according to the present embodiment transmits and illuminates a sample 1 having a periodic pattern with irradiation light emitted from a light source (not shown), and converts an optical image of the illuminated sample 1 into a parallel light flux by an objective lens 2. Then, the light enters the imaging lens 3. The prism 6 arranged on the exit end side of the imaging lens 3 splits the light flux into transmitted light and reflected light,
A first pinhole 7 is arranged at a position where the transmitted light is imaged by the imaging lens 3, and the light passing through the first pinhole 7 is received by the first photoelectric conversion element 8. on the other hand,
A second pinhole 9 is arranged on the optical path of the reflected light reflected by the reflecting surface 6a of the prism 6. The second pinhole 9 is arranged at the image forming position of the image forming lens 3 such that the center of the opening is located at a position displaced from the optical axis by a predetermined distance in the plane perpendicular to the optical axis. This second pinhole 9
The light that has passed through is received by the second photoelectric conversion element 10.

The first and second photoelectric conversion elements 8 and 10 are connected to a threshold value setting circuit 11, and the threshold value setting circuit 11 is connected.
Output terminal of the comparator 12 as an edge detecting means
It is connected to the positive input terminal of. In addition, the comparator 12
The output terminal of the first photoelectric conversion element 8 is connected to the negative side input terminal of.

FIG. 2 shows the configuration of the threshold value setting circuit 11. The threshold setting circuit 11 connects the output terminal of the first photoelectric conversion element 8 to the positive input terminal of the comparator 13 and connects the output terminal of the second photoelectric conversion element 10 to the negative input terminal of the comparator 13. is doing. Further, the output signal 8a of the first photoelectric conversion element 8 is input in parallel to the first sample hold circuit 14 and the second sample hold circuit 15. The first sample-hold circuit 14 holds the output signal 8a at the rise of the comparison output 13a of the comparator 13, and the second sample-hold circuit 15
Holds the output signal 8a at the fall of the comparison output 13a of the comparator 13. The output terminals of the first sample hold circuit 14 and the second sample hold circuit 15 are connected via a series circuit of resistors R1 and R2. Then, a voltage signal indicating a threshold value is input to the positive side input terminal of the comparator 12 through the intermediate tap between the resistors R1 and R2.

Next, the operation of this embodiment configured as described above will be described. Illumination light by transmitted illumination is sample 1
When it is irradiated with, the illumination light is partly blocked by the sample 1 and further enters the objective lens 2 to be a parallel light flux. The light flux that has passed through the objective lens 2 enters the prism 6 through the imaging lens 3. The light flux that has passed through the reflecting surface 6 a of the prism 6 enters the first photoelectric conversion element 8 through the first pinhole 7. On the other hand, the light flux reflected by the reflecting surface 6 a of the prism 6 enters the second photoelectric conversion element 10 via the second pinhole 9.

Here, when the sample 1 having a periodic pattern and the objective lens 2 are relatively moved in the direction in which the periodic pattern is formed in a plane perpendicular to the optical axis, a bright and dark periodic waveform of the periodic pattern is obtained. In addition, since the second pinhole 9 is displaced from the optical axis in the plane perpendicular to the optical axis with respect to the first pinhole 7, the periodic output waveforms are out of phase with each other as shown in FIG. . The output waveform of the first photoelectric conversion element 8 corresponding to the light passing through the first pinhole 7 is 80a, and the output waveform of the second photoelectric conversion element 10 corresponding to the light passing through the second pinhole 9. The waveform is 80b.

The threshold value setting circuit 11 sets the voltages at A and B where the difference between the two output waveforms 80a and 80b becomes 0 to Va and Vb, and sets the intermediate value (Va + V) between Va and Vb.
b) / 2 is set in the comparator 12 as a threshold value.

The operation of the threshold value setting circuit 11 will be described with reference to FIGS. The comparator 13 compares the output of the first photoelectric conversion element with the output of the second photoelectric conversion element,
When the point A at which the output of the first photoelectric conversion element and the output of the second photoelectric conversion element match is detected, the comparison output is activated. First
The sample hold circuit 14 holds the first photoelectric conversion element output Va in response to the rising of the comparison output. Then, when the voltage value changes according to the relative movement of the sample 1 and the objective lens 2 and the point B is detected by the comparator 13, the comparison output is lowered. The second sample hold circuit 15 holds the second photoelectric conversion element output Vb in response to the fall of the comparison output. The voltages Va and V held by the first and second sample and hold circuits 14 and 15, respectively.
b is applied across the series circuit composed of the resistors R1 and R2. The voltage (Va divided by the resistors R1 and R2 is
+ Vb) / 2 is applied to the positive terminal of the comparator 12 via the intermediate tap.

The threshold value (Va
The output signal from the first photoelectric conversion element 8 is input to the comparator 12 in which + Vb) / 2 is set. Then, the threshold value (Va + Vb) / 2 is compared with the output signal 8a to make an edge decision.

As described above, according to this embodiment, the voltages Va and Vb at the point where the difference between the outputs of the two photoelectric conversion elements becomes 0 are detected, and the intermediate value (Va +) between the voltages Va and Vb is detected.
Since Vb) / 2 is set in the comparator 12 as a threshold value, the threshold value for edge detection can be set accurately and easily, and even if there is a light amount fluctuation or contrast fluctuation, there is little error in the periodicity. The pattern can be measured.

In the above embodiment, the same optical system is used as the optical system for guiding the subject image to the first and second pinholes 7 and 9, but different optical systems may be used to guide the object images. You can

Next, a second embodiment of the present invention will be described. FIG. 5 shows the overall configuration of the second embodiment. It is to be noted that, except for the pinhole and the photoelectric conversion element portion, it is the same as the above-described first embodiment, so that the same portions are denoted by the same reference numerals.

In the present embodiment, the prism is removed from the optical system, and two pinholes 21a,
The pinhole plate 21 having 21b is arranged, and the two-division photoelectric conversion element 22 is arranged on the optical path of light transmitted through the pinhole plate 21.

The pinhole plate 21 and the two-division photoelectric conversion element 2
FIG. 6 shows a plan view of 2 viewed from the optical axis direction. The relationship between the two is that the light passing through one pinhole 21a is received by one photoelectric conversion element 22a and the other pinhole 21a is received.
The other photoelectric conversion element 22b receives light that has passed through b. The pinhole plate 21 is provided so that one pinhole 21 a is arranged at the image forming position of the image forming lens 3. The output signal of the photoelectric conversion element 22a that photoelectrically converts the light that has passed through the pinhole 21a arranged at the image formation position of the imaging lens 3 is input to the comparator 12 and the threshold value setting circuit 11, and the pinhole 21b.
The output signal of the photoelectric conversion element 22b for photoelectrically converting the light passing through is input to the threshold setting circuit 11.

In this embodiment having such a configuration, when the sample 1 and the objective lens 2 are relatively moved in the pattern forming direction in the plane perpendicular to the optical axis, an output waveform similar to that shown in FIG. 3 is obtained. To be Therefore, the threshold value setting circuit 11 detects the voltages Va and Vb at the point where the difference between the outputs of the two photoelectric conversion elements becomes 0, and the intermediate value (Va + Vb) / 2 of the voltages Va and Vb is set to the comparator 12. It is set as a threshold.

According to the present embodiment as described above, it is possible to measure a periodic pattern with a small error even if there is a light amount change, a contrast change, etc., as in the first embodiment.
Further, it is possible to save space because the prism can be removed.

Next, a third embodiment of the present invention will be described. FIG. 8 shows the overall configuration of the third embodiment. The same components as those in the first embodiment described above are designated by the same reference numerals.

In this embodiment, the prism is removed from the optical system and the pinhole 31 is arranged at the image forming position of the image forming lens 3. The light passing through the pinhole 31 is photoelectric conversion element 3
Light is received at 2, and an output signal having a voltage value corresponding to the amount of received light is input to the comparator 2 and the threshold setting circuit 33.

The structure of the threshold value setting circuit 33 is shown in FIG. In the threshold value setting circuit 33, the output signal of the photoelectric conversion element 32 is given to the comparator 34, the maximum value circuit 35, and the minimum value circuit 36, respectively. The comparator 34 has a reference voltage set at one of its input terminals, supplies the comparison output to the maximum value circuit 35 and the minimum value circuit 36 as a reset signal, and also holds sample and hold circuits 37, 38.
To each sample signal. The comparison output of the comparator 34 is input to the minimum value circuit 36 and the sample hold circuit 38 via an inverter 39. A series circuit of resistors R1 and R2 is connected between the output terminals of the sample and hold circuits 37 and 38,
The voltage between the resistors R1 and R2 is applied to the comparator 12 via the intermediate tap.

Next, the operation of this embodiment configured as described above will be described with reference to FIGS. 7 and 10. Sample 1 and objective lens 2 with sample 1 being transmitted and illuminated
When and are relatively moved in the pattern forming direction in the plane perpendicular to the optical axis, the output signal from the photoelectric conversion element 32 has a periodic output waveform as shown in FIG. Let Vmax be the maximum value and Vmin be the minimum value of the output waveform shown in FIG.
And the minimum value Vmin (Vmax + Vmin) / 2 are set as threshold values.

In the threshold value setting circuit 33, the maximum value Vmax
A voltage value between the minimum value Vmin and the minimum value Vmin is set in the comparator 34 as a reference value. Next, the sample 1 and the objective lens 2 are relatively moved in the plane perpendicular to the optical axis in the pattern forming direction, whereby an output signal having a periodic waveform is input from the photoelectric conversion element 32 to the comparator 34. Comparator 34
In, the output voltage of the photoelectric conversion element 32 is compared with the reference value, the comparison output rises when the output voltage falls below the reference value, and the comparison output falls when the output voltage exceeds the reference value.

The minimum value circuit 36 is reset at the rising edge of the comparison output, and outputs the minimum value Vmin of the output signal inputted thereafter to the sample hold circuit 38. Then, the sample hold circuit 38 holds the minimum value Vmin at the falling edge of the comparison output.

Further, the maximum value circuit 35 is reset at the falling edge of the comparison output and outputs the maximum value Vmax of the output signal inputted thereafter to the sample hold circuit 37. Then, at the rising edge of the comparison output, the sample hold circuit 37 holds the maximum value Vmax.

In this way, both sample and hold circuits 3
Maximum value Vmax and minimum value Vmin held at 7,38
Is applied across the series circuit of resistors R1 and R2, and the intermediate value (Vmax + Vmin) that appears at the intermediate tap
) / 2 is applied to the input terminal of the comparator 12.

The comparator 12 compares the output value of the photoelectric conversion element 32 with the intermediate value (Vmax + Vmin) / 2 determined as described above as a threshold value, and executes edge determination.

According to the present embodiment as described above, the threshold value for edge detection can be set accurately and easily, and a periodic pattern with a small error can be measured even if there is a change in the light amount or a change in the contrast. You can Further, since the prism can be removed as in the second embodiment, it is possible to save space.

In each of the above-mentioned embodiments, the case of transmission illumination has been described as an example, but the present invention can be applied to other illumination such as epi-illumination. The present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

[0041]

As described in detail above, according to the present invention, it is possible to easily and accurately set the threshold value used for edge detection of a periodic pattern, and to provide a highly reliable synchronous pattern measuring apparatus. Can be provided.

[Brief description of drawings]

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

FIG. 2 is a configuration diagram of a threshold value setting circuit provided in the first embodiment.

FIG. 3 is an output waveform diagram of the first and second photoelectric conversion elements provided in the first embodiment.

FIG. 4 is a time chart showing the operation of the threshold value setting circuit in the first embodiment.

FIG. 5 is a diagram showing an overall configuration of a second embodiment of the present invention.

FIG. 6 is a plan view of a pinhole plate and a two-division photoelectric conversion element provided in a second embodiment.

FIG. 7 is an output waveform diagram of the photoelectric conversion element according to the third embodiment of the present invention.

FIG. 8 is a diagram showing an overall configuration of a third embodiment of the present invention.

FIG. 9 is a configuration diagram of a threshold value setting circuit provided in a third embodiment.

FIG. 10 is a time chart showing the operation of the threshold value setting circuit in the third embodiment.

FIG. 11 is a configuration diagram of a conventional periodic pattern measuring device.

FIG. 12 is a diagram showing a relationship between a periodic pattern and an output signal waveform.

FIG. 13 is a diagram showing an edge detection error corresponding to a light amount variation and the like.

FIG. 14 is a diagram showing other edge detection errors.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sample, 2 ... Objective lens, 3 ... Imaging lens, 6 ... Prism, 7 ... 1st pinhole, 8 ... 1st photoelectric conversion element, 9 ... 2nd pinhole, 10 ... 2nd photoelectric Conversion element, 11, 33 ... Threshold setting circuit, 12 ... Comparator.

Claims (2)

[Claims] 1. An optical system for guiding a subject image of a periodic pattern to form an image at a predetermined position, a first pinhole arranged at the image formation position of the subject image, and the first pinhole. First light receiving means for converting the light passing therethrough into an electric signal, and a position where the object image formed by the optical system is formed and which is displaced from the first pinhole in a plane perpendicular to the optical axis. A second pinhole arranged, a second light receiving means for converting light passing through the second pinhole into an electric signal, and at least one of the first light receiving means or the second light receiving means. Edge detection means for detecting the edge of the periodic pattern by comparing the output signal of the
A cycle comprising threshold value setting means for setting an optimum threshold value to the edge detecting means based on a difference between output signals of the first light receiving means and the second light receiving means. Pattern measuring device. 2. An optical system for guiding a subject image having a periodic pattern to form an image at a predetermined position, a pinhole arranged at the image forming position of the subject image, and an electric light for passing through the pinhole. Of the light receiving means for converting into a signal, the edge detecting means for comparing the output signal of the light receiving means with a threshold value to detect the edge of the periodic pattern, and the output signal of the subject image output from the light receiving means. And a threshold setting means for setting an optimum threshold to the edge detecting means based on the maximum value and the minimum value of the periodic pattern measuring device.