JPH09257416A - Position detection apparatus for object face - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a position detection apparatus, for an object face, which reduces an increase in an error when a reflectance boundary is overlapped with a position in which the movement of a secondary light source is almost stopped in the position detection apparatus, for the object face, in which the secondary light source is scanned by a scanning means. SOLUTION: A dotlike or linear luminous flux from an illumination light source 12 is scanned via a scanning mirror 21, the scanned luminous flux is projected on an object face 8a, and the secondary light source image of the light source by the luminous flux is formed on the object face 8a. In addition, a suboptical system 11 is provided in such a way that a luminous flux from a secondary light source is guided to a light-receiving sensor 15 and that a detection signal used to detect the position of the object face 8a is output from the light-receiving sensor 15. Then, a computing and control circuit 30 is installed in such a way that it ignores a position detection result by the detection signal in a period of time in which the movement of the secondary light source by the scanning mirror 24 is almost stopped substantially.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an object surface position detecting device for detecting the position of an object surface with respect to a focal position of a main optical system.

[0002]

2. Description of the Related Art In a conventional optical device, the position of a surface (target surface) of an object is detected by a position detecting device (position detecting optical system), and the position of the main optical system with respect to the target surface is detected. There is something. As this optical device, for example, after a reticle (target object) used for constructing an electronic circuit on a wafer using a photographic technique is manufactured, the position of the surface (target surface) of the reticle is detected by a position detection device. There is one in which the surface of the reticle is detected and observed and measured while scanning it with the main optical system.

As a position detecting device used in this type of optical device, as shown in FIG. 7, an object is irradiated with a focus detecting device (focus detecting optical system) different from the main optical system, and the target surface is irradiated. There is considered a basic type for detecting the position of, or a so-called TTL type for improving the position to detect the position through the objective lens of the main optical system as shown in FIG.

First, in (1), the optical configurations of the basic type shown in FIG. 7 and the TTL type shown in FIG. 8 will be described. Next, the reason for performing scanning in (2) will be described, and in (3), a typical circuit configuration for processing a signal obtained in the TTL type will be described.

(1) Optical configuration (1-1). Optical Configuration of Focus Position Detection Device Separate from Main Optical System FIG. 7 shows a basic position in which a scanning type focus position detection device of an optical lever type, that is, a focus position detection optical system 2 is provided separately from the main optical system 1. This is a typical example. Reference numeral 1a is an objective lens of the main optical system 1.

The focus position detecting optical system 2 includes a light source 3, a scanning mirror 4, an illuminating lens 5, which emits a point-like or linear luminous flux.
A light receiving lens 6 and a light receiving sensor 7 such as a line sensor or a PSD are used.

The point-like or line-like illuminating light flux from the light source 3 is projected on the object 8 through the illumination lens 5 while being scanned by the scanning mirror 4, and an image is formed on the object surface 8a of the object 8. Then, a secondary light source image is formed on the target surface 8a.

On the other hand, this secondary light source image is enlarged by the light receiving lens 6 and projected on the light receiving sensor 7, and the light receiving sensor 7 outputs a detection signal. And this light receiving sensor 7
The position of each part of the target surface 8a can be known by calculating the barycentric position of the secondary light source or calculating the light amount distribution based on the signal from.

At this time, even if the height of the target surface 8a partially fluctuates up and down due to unevenness and the amount of reflected light of the secondary light source image formed at this fluctuating portion fluctuates, the position of the center of gravity of the secondary light source or By knowing the light quantity distribution, the position of the changing part can be known. Incidentally, there is also a type in which the scanning mirror 4 is not used and scanning is not performed.

(1-2). Optical Configuration of TTL Focus Position Detection Device The optical device shown in FIG. 8 has a main optical system 10 including an objective lens 10a, a beam splitter 10b, and other optical members (not shown).

Further, the optical device has a position optical system detection system (position detection device) 11 of a TTL type optical lever system. The position detecting optical system 11 is an optical member common to the main optical system 10, that is, the objective lens 10a and the beam splitter 10.
b.

In the position detecting optical system 11, the illumination light source 1
An auxiliary lens 13 for projecting a point-like or line-like light flux from 2
A scanning mirror 21 (scanning means), an optical system 22 including lenses 22a and 22b, a beam splitter 10b, and an objective lens 10a are used to project and form an image on a target surface 8a of an object 8, and a secondary light source image is formed on the target surface 8a. Is imaged. In this optical system 22, the position 31 where the light beam deflected by the scanning mirror 21 intersects with the light beam before being deflected is conjugate with the pupil position 23 of the objective lens 10a. Moreover, this secondary light source image is obtained by the objective lens 10a and the beam splitter 1.
0b, the optical system 22, the scanning mirror 21, and the PS as a light receiving sensor via the light receiving (image forming) auxiliary lens 14 of the light receiving system.
An image is formed on D15.

Then, by calculating the barycentric position of the secondary light source or the light amount distribution based on the output signal from the PSD 15, the position of each part of the target surface 8a can be known.

With this configuration, as compared with the external focus position detection optical system 2 shown in (1), the positional deviation between the focus position detection optical system and the main optical system due to temperature change and the change in the focal length are caused. Can be ignored, and the focus position can be detected more accurately. Further, since the objective lens 10a is usually telecentric on the side of the object 8, the scanning mirror 2 is configured by making the position 31 and the pupil position 23 of the objective lens 10a conjugate.
Even if the light beam from the light source 12 is scanned by 1, the incident angle α on the target surface 8a does not change, and 2Δβ tan α (Δ is the amount of vertical movement of the surface to be inspected, β is the optics of the objective lens 10a and the light receiving system). The magnification, α, does not change the relationship between the vertical variation of the target surface 8a represented by the incident angle shown in FIG. 6 and the movement amount of the secondary light source on the target surface 8a, so that the focus position detection accuracy is kept high. be able to.

(2) Scanning In each of the examples shown in (1), the structure is such that the position of the secondary light source on the target surface 8a is scanned. This is performed in order to reduce the following errors as much as possible.

If the surface to be inspected is one having a difference in reflectance, such as a reticle (usually a glass surface having a pattern made of chromium), and a step is present, the secondary light source Is overlapped with a reflectance boundary (hereinafter, simply referred to as a reflectance boundary), the light intensity distribution on the light receiving sensor changes due to the following reasons, and this cannot be separated from the movement of the target surface 8a. However, an error will occur in the focus position detection result.

A. Light intensity distribution occurs in the secondary light source Since the secondary light source has a certain size, a distribution occurs in the intensity of the light source when overlapping with the boundary of reflectance. For example, when a point light source is used as the primary light source and a sensor such as PSD that detects the center of gravity of light is used as the light receiving sensor, if the reflectance is uniform, the center of gravity of the light of the secondary light source matches the geometric center. However, if the reflectances are non-uniform, they will not match. That is, although the position of the secondary light source does not move, the position of the center of gravity of the light moves and the PSD output fluctuates.

B. There is always a step at the boundary between glass and chrome where diffuse reflection and diffraction occur at the boundary. Diffuse reflection and diffraction occurring at this portion are different depending on the shape of the step, and a part of the light is incident on the light receiving element, causing an error in the detection result.

C. Other sources of error Since photo-etching is performed during the reticle fabrication stage, there is a possibility that some changes may occur in the glass near the boundary, and there are disadvantageous elements at the boundary compared to other areas.

In this way, if the position of the secondary light source overlaps the boundary between the glass and the chrome, it is inevitable that an error will occur in the position detecting device using the optical lever method. Therefore, in the conventional device, the secondary light source is scanned to average the measurement result of the boundary portion (including the error) with the measurement result of the portion other than the boundary (not include the error) to measure the variance of the error. , I have been trying to reduce the absolute value of the error.

That is, if a range sufficiently wider than the size of the secondary light source is scanned, the secondary light source exists on the reflectance boundary for the time (a) required for one scan (error occurs). The time (b) is sufficiently short and the error is b
It should decrease to / a. However, the range where the error exists extends to the range where the reflectance boundary exists on the scan range. It should be noted that the above reduction rate is the 0th order approximation, and the intensity distribution and shape originally possessed by the secondary light source must be taken into consideration.

In the optical configurations shown in the two conventional examples,
The movement of the target surface is 2 in the direction of the paper surface on the light receiving sensor.
It appears as the movement of the next light source image. Therefore, the light receiving sensor is arranged so that the barycentric position of the secondary light source or the axis for obtaining the light amount distribution exists in this direction. According to the above theory, the reflectance boundary in the direction perpendicular to the detection axis (that is, perpendicular to the paper surface) on the light receiving sensor surface causes the largest measurement error. (A reflectance boundary in a direction perpendicular to this (that is, in the plane of the paper) causes almost no measurement error.) When a secondary light source image is scanned with respect to this reflectance boundary, it is perpendicular to the reflectance boundary on the light receiving sensor. It is most effective to scan in the direction. (For example, when scanning is performed in the same direction as the reflectance boundary line, the secondary light source image may always overlap with the reflectance boundary.) Further, in the movement of the secondary light source image on the light receiving sensor, Since only the one-dimensional in-plane direction has position information of the target surface, scanning other than reciprocating motion (for example,
Even if a circular scan or the like on the target surface is performed, it is only the one-dimensionally projected component in the in-plane direction of the paper that helps reduce the error.

(4) Control / Signal Processing Circuit FIGS. 8 and 9 show examples of circuit block configurations when PSD is used as a light receiving sensor in the TTL focus detection device of (1-2) described above.

In FIG. 8, the light source drive unit 101 drives the illumination light source 12 composed of a laser diode, and blinks it at a high frequency (a frequency that is two orders of magnitude higher than the band of the required position detection signal). Further, the oscillator 102 generates a reference signal for scanning the scanning mirror 21, and the scanning mirror driving circuit 103 controls the driving device 103a such as a galvanometer or a voice coil by the reference signal from the oscillator 102 to operate the scanning mirror 2.
1 is rockingly driven.

In FIG. 8, the signal processing circuit 104 processes the signal from the PSD 15 as the light receiving sensor to obtain the final focus detection output C. A concrete example of the signal processing circuit 104 is shown in FIG.

The PSD 15 has A and B as shown in FIG.
It outputs two signals. This signal contains position information as an AC signal modulated at the blinking frequency of the illumination light source. Then, the respective signals are sent to the head amplifier 10
Amplify at 5,106. Bandpass filter (BPF)
107 and 108 extract only the blinking frequency component of the illumination light source 12, and the detection circuits 109 and 110 and the low-pass filters (LPF) 111 and 112 separate the blinking component of the illumination light source and extract only the position information component. By using such a modulation technique, the DC error generated in the circuits up to this point is avoided.

The adder circuit 113, the subtractor circuit 114, and
(A'-B ') / (A' + B ') by the division circuit 115
Is calculated. This is the position signal C indicating the position of the target surface 8a.
become. The amplifier circuit 116 is a buffer amplifier for adjusting the signal amplitude.

In the optical system, there is a slight non-uniformity of the performance depending on the position. However, the light beam is affected by the non-uniformity due to the scanning, and the noise component of the same frequency as the scanning frequency or its harmonics is located. It may be included in signal C. If this causes a problem, a low-pass filter (LP) that transmits only frequency components lower than the scanning frequency of the scanning mirror 21 is transmitted.
F) 117 may be added to remove this frequency component.

[0029]

By the way, in the method described above, the position detection error at the reflectance boundary is reduced by averaging by scanning, but this method is as described above. The shorter the time that the secondary light source exists on the reflectance boundary (error occurs) is, the more effective the time required for one scan is. However, since the scanning mirror 21 reciprocates, there is a time to stop at both ends of the scanning, and if there is a reflectance boundary near the end of the scanning range of the secondary light source, the secondary light source takes a relatively long time. It will remain on the reflectance boundary, reducing its effectiveness.

For example, as shown in FIG. 10, the secondary light source S has a radius r
Let us consider a case of a circular shape and scanning with a sine wave for a length of 2R. When the reflectance boundary RB is inside the scan by r from the end of the scanning range, the secondary light source S will reach the reflectance boundary RB for the longest time (FIG. 10). The secondary light source S is separated from the reflectance boundary RB because the center of the secondary light source S is at the end of the scanning range at the positions E1 and E2 (the reflectance boundary R
This is the time when it is inside by 2r from B) (that is, inside by r minutes from the reflectance boundary RB). Since the sine wave scanning is performed, the ratio of the period T (t1 to t2) between the positions E1 and E2 and the time required for one scanning reciprocation (t0 to t4) is (2 (90-sin ^-1 ((R -2r) / R))) / 36
0 ° On the other hand, when the reflectance boundary RB is at the center of the fastest scanning (FIG. 11), the periods t1 to t2 and t3 to t5 overlap twice, so the time ratio is (2 × 2 ( sin ⁻¹ (r / R))) / 360 °. For example, considering R: r = 100: 1,
Approximately 6.4%: 0.64%, which means that the secondary light source S is in contact with the reflectance boundary RB for a maximum length of about 10 times that of the shortest case.

Since the influence of the light intensity distribution of the secondary light source S must be taken into consideration, it cannot be said that the error changes with this ratio, but when the reflectance boundary RB exists at the end of the scanning range,
There are certain disadvantages compared to being located near the center.

Further, even if scanning other than reciprocating motion is performed, it is useful to reduce the error in the same direction as the direction in which the position information is detected.
Since only the components are projected in a dimension, even if a circular scan is performed on the target surface, it is substantially equivalent to a sine wave scan. As long as the secondary light source image is always projected on the light receiving sensor, no matter what form of scanning is performed, the scanning always has an end in the one-dimensional direction. If the deflecting mirror is driven with a triangular wave instead of a sine wave, theoretically the secondary light source image always moves at a constant speed, but this is impossible in reality, and the speed always drops momentarily at both ends.

When a highly accurate target surface position detecting device is to be constructed, it may not be possible to allow the accuracy to deteriorate near the end of the scanning range.

In the present invention, the reflectance boundary overlaps with the position where the movement of the secondary light source is almost stopped in the position detecting device for the target surface where the scanning means scans the secondary light source as shown in the prior art. It is an object of the present invention to provide a position detection device for a target surface in which an increase in error in the case is reduced.

[0035]

In order to achieve this object, the invention of claim 1 scans a point or linear luminous flux from a light source through a scanning means and targets the scanned luminous flux. By projecting onto the surface, a secondary light source image of the light source is formed by the light flux on the target surface, and
In a position detection device for a target surface, which is provided with an optical system configured to guide a light beam from a next light source to a light receiving sensor and output a detection signal used for position detection of the target surface from the sensor,
The target surface position detecting device is provided with signal processing means for ignoring the position detection result by the detection signal during the period when the movement of the secondary light source by the scanning means is substantially stopped. .

More specifically, more specifically, the position detection signal in a period in which the secondary light source is almost stopped is forcibly fixed to a certain value (for example, the focus position of the main optical system and the position shift of the target surface are zero). By replacing the time value), the position can be detected without being affected by the signal in this period.

The signal processed in this way contains the position detection information only intermittently in time, but it is possible to restore the continuous information by taking the time average over a period of one or more scanning periods. You can The output in this case is an average of the certain value and the position detection information weighted by the replacement ratio.

The invention according to claim 2 is a main optical system for inspecting or measuring the target surface through an objective lens facing an object, and a point-like or linear light beam from the light source. Is projected onto the target surface via the objective lens to form a secondary light source image of the light source on the target surface by the light flux, and the light flux from the secondary light source is passed through the objective lens. A sub-optical system for guiding the light to the light-receiving sensor, the sub-optical system having a scanning means for scanning a point or linear luminous flux from the light source in the optical path, and a high-speed scanning position of the scanning means and the objective. In a position detecting device for a target surface having an optical member for conjugating the pupil position of a lens between the scanning means and the pupil position, the movement of the secondary light source by the scanning means is substantially The detection signal during the almost stopped period Signal processing means to ignore the position detection result by characterized in that the position detecting device of the target surface is provided.

[0039]

FIG. 1 is a block diagram showing an embodiment of the present invention.
This will be described with reference to FIG.

[First Embodiment] FIGS. 1 to 4 show a first embodiment of the present invention.

<Optical System> The optical device shown in FIG. 1 includes a main optical system 10 for observation and a sub optical system 11 as a position optical system detection system (position detection device) of the TTL type optical lever system. Have. The main optical system 10 includes common optical components,
That is, the objective lens 10a, the beam splitter 10b,
Other optical members (not shown) are provided. Further, the position detection optical system 11 is an optical member common to the main optical system 10,
That is, it has an objective lens 10a and a beam splitter 10b.

In the sub optical system 11, the point-like or line-like light beam from the illumination light source 12 is projected onto the auxiliary lens 13 and the scanning mirror 2.
1 (scanning means), an optical system 22 including lenses 22a and 22b (optical members), a beam splitter 10b, and an objective lens 10a to project and form an image on a target surface 8a of a target object 8 to form a secondary image on the target surface 8a. A light source image is formed. A laser diode or the like is used for the illumination light source 12. Moreover, the illumination light source 12 includes the light source driving unit 101.
It is driven and controlled by and is made to blink at high frequency.

The optical system 22 makes the position 31 where the light beam deflected by the scanning mirror 21 intersects with the light beam before being deflected, conjugate with the pupil position 23 of the objective lens 10a. The scanning mirror 21 is driven and controlled by the arithmetic control circuit 30. In addition, the secondary light source image is formed on the light receiving sensor 15 through the objective lens 10a, the beam splitter 10b, the optical system 22, the scanning mirror 21, and the light receiving (image forming) auxiliary lens 14 of the light receiving system. It has become. A PSD is used for the light receiving sensor 15 in this embodiment.

The output signal from the light receiving sensor 15 is input to the arithmetic control circuit 30. The arithmetic control circuit 30 calculates the barycentric position of the secondary light source or the light amount distribution based on the output signal from the light receiving sensor 15,
The position of each part of the target surface 8a can be known.

With this configuration, it becomes possible to ignore the positional deviation between the focal position detecting optical system and the main optical system and the change in the focal length due to temperature changes and the like, and the focal position can be detected more accurately. Further, the objective lens 10a is usually the object 8
Since it is telecentric on the side, the position 31 and the pupil position 23 of the objective lens 10a are made conjugate, so that the incident angle α to the target surface 8a does not change even when the scanning mirror 21 scans the light beam from the light source 12. The target surface 8a represented by 2Δβtanα (Δ is the amount of vertical movement of the surface to be inspected, β is the optical magnification of the objective lens 10a and the light receiving system, and α is the incident angle shown in FIG. 6).
Since the relationship between the amount of vertical movement of the secondary light source and the amount of movement of the secondary light source on the target surface 8a does not change, it is possible to maintain high accuracy in detecting the focal position.

<Operation Control Circuit 30> As described above, the operation control circuit (signal processing means) 30 includes the oscillator 102 for generating the reference signal 301 as shown in FIG. A drive circuit 103 such as a galvanometer or a voice coil whose operation is controlled based on a reference signal 301 from an oscillator 102, and a scan mirror drive device 103a for swinging the scan mirror 21 by the drive circuit 103.

As shown in FIG. 2, the arithmetic control circuit 30 has a signal processing circuit 104 for processing the signal from the light receiving sensor 15 to obtain the final focus detection output C. A concrete example of the signal processing circuit 104 is shown in FIG.

As shown in FIG.
It outputs two signals A and B. The signals A and B include position information as an AC signal modulated at the blinking frequency of the illumination light source. Then, the respective signals A and B are
It is amplified by the head amplifiers 105 and 106. Bandpass filters (BPF) 107, 108 extract only the blinking frequency component of the illumination light source 12, and the detection circuits 109, 110,
The low-pass filters (LPF) 111 and 112 separate the blinking component of the illumination light source and extract only the position information component. By using such a modulation technique, the DC error generated in the circuits up to this point is avoided.

The adder circuit 113, the subtractor circuit 114, and
(A'-B ') / (A' + B ') by the division circuit 115
Is calculated. This is the position signal C indicating the position of the target surface 8a.
become. The amplifier circuit 116 is a buffer amplifier for adjusting the signal amplitude.

In the optical system, there is a slight non-uniformity of the performance depending on the position, but the light beam is affected by the non-uniformity due to the scanning, and the noise component of the same frequency as the scanning frequency or its harmonics is located. It may be included in signal C. If this causes a problem, a low-pass filter (LP) that transmits only frequency components lower than the scanning frequency of the scanning mirror 21 is transmitted.
F) 117 may be added to remove this frequency component. Further, the arithmetic control circuit 30 includes a delay circuit 201,
It has a phase detection circuit 202, a gate circuit 203, and an averaging circuit 204.

The reference signal 301 output from the oscillator 102 described above is a sine wave in FIG. This reference signal 30
1 controls the operation of the scanning mirror 21 via the scanning mirror drive circuit 103 as described above, and is input to the delay circuit 201. Thus, the reference signal 301 from the oscillator 102
The scanning mirror 21 is operated by, but since the scanning mirror 21 is mechanically operated, the scanning mirror 21 operates slightly later than the reference signal 301 in FIG.

For this reason, the reference signal 301 is the delay circuit 2
It is input to 01, delayed by an operation delay, and output. That is, the delay circuit 201 outputs the reference signal 301 (sine wave) from the oscillator 102 for the time ta (t0 to t1) of the operation delay of the scanning mirror 21 with respect to the reference signal 301 as shown in FIG. Delay the reference signal 301
The signal 302 having the same phase as that of the operation of the scanning mirror 21 which is slightly delayed by the time ta. The delay circuit 201 may be set so as to output a position signal 302 ′ that is shifted by 90 degrees with respect to the signal 302, as shown in FIG.
The position signal 30 which is the output from the delay circuit 201
2 or 302 ′ is input to the phase circuit 202.

At this time, from the characteristics of the sine wave which is the reference signal 301, the signal 302 of the same phase is used when the period in which the position detection signal is ignored is long, and is shifted by 90 degrees when the period in which the position detection signal is ignored is short. When the phase position signal 302 'is used, it is possible to refer to a portion having a large sine wave change rate when the gate signal 303 shown below is generated by the phase circuit 202, and the adjustment can be simplified.

That is, the phase detection circuit 202 is based on the position signal 302 or 302 ', and the phase detection period (t2 to t3, t4) shown in FIG.
~ T5, t6 to t7) pulse gate signal 30
3 is generated and input to the gate circuit 203. At this time, the pulse width of the gate signal 303 is determined by referring to the ratio between the scanning range of the scanning mirror 21 and the size of the secondary light source while observing the actual error size. For example, in the case of sine wave drive, when there is a possibility that the secondary light source and the reflectance boundary overlap at the end of scanning for a phase angle of 30 degrees at the maximum, a desired amount is set based on 30 degrees. Set the phase angle so that the error can be reduced.

This gate circuit 203 is a phase circuit 202.
The position detection signal C is output according to the gate signal 303 from the constant value signal 30 from the constant value generation circuit 205.
4 is switched, and the mixed signal c ′ of the alternating position signal C and the constant value signal 304 is input to the signal averaging circuit 204 as shown in FIG.

As shown in FIG. 4 (f), the averaging circuit 204 time-averages the output signal c'of the gate circuit 203, obtains the average of the position detection signal and the constant value 304, and obtains the signal c '. Output as'. When using this output in a circuit with time-averaged characteristics such as a servo amplifier,
The averaging circuit can be omitted depending on the conditions.

With this configuration, it is not necessary to include in the average a portion having a large position detection error, so that the position detection error can be improved.

Further, the characteristic of the present invention that position detection is not performed at both ends of scanning can be utilized more positively for accuracy improvement. That is, in the conventional light receiving method using PSD, it is necessary that the image of the secondary light source is always formed on the light receiving sensor 15. Moreover, when the illumination light does not enter the light-receiving sensor 15, the light-receiving sensor 15 detects the center of gravity of the stray light in the surroundings as position data, causing a malfunction. Therefore, the light from the illumination light source 12 should not always go beyond the effective range of the optical system. However, in this embodiment, there is a period (range) in which the position detection signal may not be output at both ends of scanning. That is, during this period, there is no problem even if the light from the illumination light source 12 goes out of the effective range of the optical system. Therefore, the scanning range of the scanning mirror 21 can be expanded so that the portion actually using the position detection signal uses the effective range of the optical system to the full.

By adjusting in this way, even if a reflectance boundary is formed near the center of the scanning range, the averaging effect can be increased by expanding the scanning range.

[Second Embodiment] FIG. 5 shows a second embodiment of the present invention. The same functions as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, the oscillator 102 and the delay circuit 2
01, the phase detection circuit 202, the digital synthesizer 2
Replaced with 05. That is, the scanning mirror drive circuit 103 is driven and controlled by the output from the digital synthesizer 205, and the operation of the gate circuit 203 is controlled. By using this digital signal synthesizing technique, a necessary signal can be obtained without using a complicated analog circuit.

Moreover, the gate processing of the signal by the gate circuit 203 is also devised. That is, the gate circuit 203 includes the A / D conversion circuit 206 to which the position signal C from the signal processing circuit 104 is input, and the A / D conversion circuit 2
Memory 20 for temporarily storing the signal A / D converted in 06
7 and a D / A conversion circuit 208 for D / A converting the data from the memory 207. This D / A conversion circuit 2
In 08, the data excluding both end portions of the scan is D / A converted at a cycle slower than the A / D conversion, and apparently,
The position detection signal is not interrupted so that the signal can be used easily.

[0063]

As described above, according to the present invention, the point or linear luminous flux from the light source is scanned through the scanning means, and the scanned luminous flux is projected onto the target surface to thereby obtain the target object. A secondary light source image of the light source is formed on the surface by the light flux, the light flux from the secondary light source is guided to a light receiving sensor, and a detection signal used for position detection of the target surface is output from the sensor. In the position detecting apparatus for a target surface including the optical system described above, signal processing means for ignoring the position detection result by the detection signal is provided during a period in which the movement of the secondary light source by the scanning means is substantially stopped. Since it is configured as described above, that is, 2 by the scanning means.
Since the position detection result during the period when the movement of the next light source is substantially stopped is ignored, it is possible to reduce the error generated at the reflectance boundary and provide a position detection device with higher accuracy.

Moreover, according to this configuration, the present invention can be implemented by adding a function to the conventional signal processing circuit without changing the optical system, so that it is easy to improve the performance of the existing device. Is.

Further, the signal processed in this way contains the position detection information only intermittently in time, but by taking a time average over a period of one cycle or more of scanning, it becomes continuous information. Can be returned. The output in this case is an average of the certain value and the position detection information weighted by the replacement ratio.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an optical system showing a first embodiment of a position detecting device for a target surface according to the present invention.

FIG. 2 is an explanatory diagram showing functional blocks of a signal processing system shown in FIG.

FIG. 3 is a detailed block diagram of the signal processing circuit shown in FIG.

FIG. 4 is an explanatory diagram showing signals of respective parts in FIG. 2 and schematic timing relationships thereof.

FIG. 5 shows a second position detecting device for a target surface according to the present invention.
It is an explanatory view showing a functional block of a signal processing system of an example.

FIG. 6 is an explanatory diagram showing signals of respective parts in FIG. 5 and schematic timing relationships thereof.

FIG. 7 is an explanatory diagram showing an example of an optical system of a conventional target surface position detection device.

FIG. 8 is an explanatory diagram showing another example of the optical system of the conventional target surface position detection device.

FIG. 9 is an explanatory diagram showing an example of functional blocks of a signal processing system of a conventional target surface position detection device.

FIG. 10 is an explanatory diagram illustrating an example of a relationship between a boundary of change in reflectance of the target surface and scanning.

FIG. 11 is an explanatory diagram illustrating another example of the relationship between the boundary of the change in the reflectance of the target surface and the scanning.

[Explanation of symbols]

 8 ... Object 8a ... Object surface 10 ... Main optical system 10a ... Objective lens 11 ... Sub optical system (positional optical system detection system) 12 ... Illumination light source 12 21 ... Scanning mirror 21 (scanning means) 22 ... Optical system 22 22a, 22b ... Lens (optical member) 31 ... Position 23 ... Pupil position of the objective lens 10a 15 ... Light receiving sensor 30 ... Arithmetic control circuit (signal processing means)

Claims (2)

[Claims] 1. A point or linear light beam from a light source is scanned by a scanning means, and the scanned light beam is projected onto a target surface, whereby the light source 2 of the light source is projected onto the target surface. Position of the target surface including an optical system for forming a secondary light source image, guiding the light flux from the secondary light source to the light receiving sensor, and outputting a detection signal used for position detection of the target surface from the sensor The detection device is provided with signal processing means for ignoring the position detection result by the detection signal during the period when the movement of the secondary light source by the scanning means is substantially stopped. Position detection device. 2. A main optical system for inspecting or measuring the target surface via an objective lens facing an object, and a point-like or linear light beam from the light source via the objective lens. A sub that projects onto the target surface to form a secondary light source image of the light source on the target surface by the light flux, and guides the light flux from the secondary light source to the light receiving sensor via the objective lens. An optical system is provided, and the sub-optical system has a scanning means for scanning a point or linear luminous flux from the light source in the optical path, and a high-speed scanning position of the scanning means and a pupil position of the objective lens are conjugated. In a position detecting device for a target surface having an optical member for controlling the movement of the secondary light source between the scanning means and the pupil position, the detection is performed during a period when movement of the secondary light source by the scanning means is substantially stopped. No position detection result by signal Position detecting device of the target surface, characterized in that is provided with signal processing means for.