JPH1089917A - Edge detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an edge detector which can accurately detect the edge of a sample by a simple method even when the edge detecting direction is already known. SOLUTION: An edge detector is provided with a stage 34 on which a sample 32 can be placed, an edge detecting optical system 38 which can detect the edge of the sample 32 based on the intensity fluctuation of the light from the sample 32 irradiated with illumination light when the system 38 receives the light through a slit plate 36, a relatively moving means which relatively moves the stage 34 and optical system 38 so as to relatively move the sample 32 in the direction perpendicular to the optical axis A of the optical system 38. The optical system 38, in addition, is provided with a slit plate rotating mechanism 40 which rotates the slit plate 36 by a prescribed angle based on the moving direction of the sample 32 relatively to the optical axis A of the optical system 38.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge detector for detecting an edge of a sample by detecting, for example, the intensity of light from the sample.

[0002]

2. Description of the Related Art Conventionally, an edge detector as disclosed in, for example, Japanese Patent Application Laid-Open No. 5-99619 is generally known. FIG. 4A schematically shows the configuration of such an edge detector.

That is, in this edge detector, the light source 2
Is converted into a parallel light beam via the collimator lens 4 and then converged from the half mirror 6 via the objective lens 8 onto the sample 12 placed on the stage 10. At this time, the reflected light reflected from the sample 12 is guided to the half mirror 6 via the objective lens 8, a part of which is transmitted through the half mirror 6, and then transmitted through the imaging lens 14 and the pinhole 16. Detected by detector 18. The photodetector 18 is configured to output a current signal corresponding to the light intensity of the received reflected light.
Is converted into a predetermined voltage signal by the current-voltage conversion circuit 20, and then the current signal
2 is output. The comparator 22 is supplied with a preset threshold voltage from a voltage source 24.

In such a state, when the stage 10 is moved by the stage driving means 26, the sample 12
As the edge moves, the light intensity of the reflected light detected by the photodetector 18 via the pinhole 16 changes, and a voltage signal corresponding to the light intensity change of the reflected light is output to the comparator 22. You. The comparator 22 compares the input voltage signal with a preset threshold voltage, and outputs the comparison operation signal to the pulse generation circuit 28. At this time, the pulse generation circuit 28 outputs an edge detection signal based on the input comparison operation signal. Then, based on the edge detection signal, the edge of the sample 12 is detected.

[0005]

FIG. 4 (b)
As shown in FIG. 1, in the conventional edge detector, the bright portion L1 and the dark portion L2 of the reflected light received through the pinhole 16 are provided.
The edge is recognized based on the occupied area ratio. Specifically, it is a linear edge as shown in FIG.
The output voltage from the current-voltage conversion circuit 20 when the area L1 of the bright part and the area L2 of the dark part in the pinhole 16 projected on the surface of the sample 12 are equal to each other is set in the voltage source 24 in advance as a threshold voltage. Every other current-voltage conversion circuit 20
And the threshold voltage are compared by the comparator 22 to calculate the light portion L1 and the dark portion L2.
At the time when the boundary S crosses the center of the pinhole 16, that is, the edge can be recognized.

On the other hand, as shown in FIG.
For example, when the edge of the sample 12 has a curvature having substantially the same diameter as the pinhole 16, the following problem occurs. That is, also in this case, the boundary S between the light portion L1 and the dark portion L2 is the pinhole 1
Edge detection is performed at the time of coincidence with the center of No. 6, but at this time, the area ratio (L1> L2) of the light portion L1 and the dark portion L2 in the pinhole 16 is not equal to each other. In general, in the edge detection method using the pinhole 16, when the edge shape is not a straight line, the edge cannot be detected accurately even by using a preset threshold voltage. Therefore, it is necessary to perform correction after edge detection in order to perform accurate edge detection.

[0007] Such a problem is a problem (area ratio; L1> L2) that occurs even when, for example, a slit 30 other than the pinhole 16 is used, as shown in FIG. When the detection direction of the edge of the sample 12 (that is, the direction in which the pinhole 16 or the slit 30 projected on the surface of the sample 12 crosses the edge) is known in advance, for example, the length of the slit 30 is detected during the edge detection. If the control is performed so that the axial direction intersects the edge perpendicularly, the edge detection error as described above can be reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide an edge detector capable of accurately detecting an edge by a simple method when the edge detection direction is known in advance. It is in.

[0009]

An edge detector according to the present invention comprises a stage on which a sample can be mounted, and a light receiving means for receiving light from the sample illuminated by illumination light through a slit plate. An edge detection optical system capable of detecting an edge of the sample based on a change in intensity; and the stage and the edge detection optical system so as to relatively move the sample in a direction orthogonal to an optical axis of the edge detection optical system. Relative movement means for relatively moving the stage and the edge detection optical system when the stage and the edge detection optical system are relatively moved by the relative movement means. A slit plate rotating mechanism is provided for rotating the slit plate by a predetermined angle based on a relative movement direction of the sample with respect to the optical axis of the detection optical system.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An edge detector according to an embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, the edge detector according to the present embodiment is configured such that when the light from the sample 32 illuminated by the illumination light is received through the slit plate 36 and the stage 34 on which the sample 32 can be mounted, , The sample 32 based on the light intensity change.
An edge detection optical system 38 capable of detecting the edge of the sample 32 and a sample 32 in a direction orthogonal to the optical axis A of the edge detection optical system 38.
Relative movement means for relatively moving the stage 34 and the edge detection optical system 38 so as to relatively move the stage 34 and the edge detection optical system 38. A slit plate rotating mechanism 4 for rotating the slit plate 36 by a predetermined angle based on the relative movement direction of the sample 32 with respect to the optical axis A of the edge detection optical system 38 when the optical system 38 is relatively moved.
0 is provided. Note that the slit plate 36 is provided on the optical axis A.

The stage 34 applied to this embodiment is
It is configured to be movable in a direction orthogonal to the optical axis A of the edge detection optical system 38 by a relative moving means. The stage 34 is provided with an illumination optical path 34a so that a sample 32 mounted on the stage 34 can be irradiated with transmitted illumination light by an illumination system 42 described later.

The illumination system 42 includes a light source 44 and the light source 4.
The illumination light emitted from the sample 4 is transmitted through the illumination optical path 34a to the sample 3.
2 is provided. The relative moving means is based on X and Y motors 48 and 50 for moving the stage 34 in the X and Y directions in the figure and a control signal output from a controller 52 controlled by a control device (not shown). X-axis and Y-axis driver 5 for driving X and Y motors 48 and 50
4,56.

The edge detection optical system 38 includes a photodetector 58
And an objective lens 60 for receiving light from the sample 32 illuminated by the illumination light with the photodetector 58 through the slit plate 36, and a slit plate 36 based on a control signal output from the controller 52. A slit plate rotating mechanism 40 for rotating by an angle is provided.

The photodetector 58 is configured to be able to output a current signal S _I corresponding to the quantity of the received light through the slit plate 36, the current - voltage (I-
V) It is connected to a comparator 64 via a conversion circuit 62. In this case, the current signal output from the photodetector 58 S _I is current - converted into a predetermined voltage signal S _V by the voltage conversion circuit 62, so that the input to the comparator 64.

[0015] The comparator 64, the threshold voltage S _T which is preset by a control device (not shown), D / A
It is input via a converter 66. Such comparator 64 compares calculating the voltage signal S _V and the threshold voltage S _T, is controlled so as to output to the comparison operation signal S _C a pulse generating circuit (not shown).

The slit plate rotating mechanism 40 includes the slit plate 3
6 for rotating the motor 6 and the controller 52
And a driver 70 for driving a motor 68 based on a control signal output from the controller 70. The motor 68
The slit plate 36 is connected to the slit plate 36 through a general gear mechanism 72, for example, and the driving force of the motor 68 is transmitted to the slit plate 36 via the gear mechanism 72 to move the slit plate 36 in a predetermined direction. It is configured to be able to rotate by the rotation angle.

Next, the operation of this embodiment will be described with reference to FIG.
This will be described with reference to FIG. When the stage 34 is moved by the relative moving means, the light intensity of the reflected light received by the photodetector 58 via the slit plate 36 changes with the movement of the edge of the sample 32, and the reflected light voltage signal S _V corresponding to the light intensity change is output to the comparator 64. The comparator 64 receives the input voltage signal S _V
And a predetermined threshold voltage _ST, and outputs a comparison operation signal S _C to a pulse generation circuit (not shown). In this case, the pulse generating circuit, based on a comparison calculation signal S _C input, and outputs an edge detection signal. Then, based on the edge detection signal, the edge of the sample 32 is detected.

In such an edge detection operation, the edge detector according to the present embodiment uses the edge detection direction D that is known in advance, that is, the edge of the sample 32 with respect to the optical axis A of the edge detection optical system 38. Is controlled so that the rotation angle of the slit plate 36 is appropriately changed by the slit plate rotation mechanism 40 when the movement of the stage 34 is controlled so as to cross substantially vertically.

For example, a sample 32 having a circular edge
In the case of performing edge detection (see FIG. 2B), when moving the stage 34, the controller 52 uses the slit plate rotating mechanism 40 to control the slit 36 of the slit plate 36.
a is made parallel to the edge detection direction D, and the X and Y motors 4 are driven through the X and Y axis drivers 54 and 56.
The stage 34 is moved such that the edge of the sample 32 crosses the optical axis A of the edge detection optical system 38 perpendicularly by controlling the positions 8 and 50.

At this time, the area ratio between the light portion L1 and the dark portion L2 of the slit 36a projected on the surface of the sample 32 relatively changes, and the light detector 58 passes through the slit plate 36 to the comparator 64 via the slit plate 36. A voltage signal S _V (see FIG. 2A) corresponding to the amount of received light is output.

[0021] Then, the voltage signal S _V, which is input to the comparator 64, the comparison operation between the threshold voltage S _T is performed. In this case, the threshold voltage S _T, the area ratio of bright portions L1 and dark L2 of the slit 36a is set to the voltage V ₁ of the time became 50%.

[0022] Therefore, as shown in FIG. 2 (a), (b) , the comparator when the voltage signal S _V, which is input to the comparator 64 is coincident with the threshold voltage _{S T (S V = S T} = V 1) If the comparison operation signal S _C output from 64 is taken in through the pulse generation circuit, the edge of the sample 32 can be detected with high accuracy.

As described above, according to the present embodiment, the edge detection direction D and the long axis direction of the slit 36a are made parallel to each other, so that even a circular edge, the light portion L1 and the dark portion L2 in the slit 36a are formed. It is possible to accurately detect a position corresponding to a light intensity of 50% as an edge.

For example, when detecting the edge of the sample 32 (see FIG. 2C) having a linear but fine uneven edge, the slit 36a is set in a direction substantially perpendicular to the edge detection direction D. The rotation of the slit plate 36 may be controlled by the slit plate rotation mechanism 40 so that the long axes coincide. By such control, similarly to the above, the bright portion L1 and the dark portion L in the slit 36a are independent of the edge shape.
The position where the area ratio of 2 corresponds to the light intensity of 50% can be accurately detected as an edge.

In the above-described embodiment, the edge detection of the sample 32 by the transmission illumination method has been described.
For example, as shown in FIG. 3, even if an epi-illumination method is adopted, the same operation and effect as described above can be achieved.

That is, in the epi-illumination type edge detector, the stage 34 is fixed, and the edge detecting optical system 38 is moved by the relative moving means. In this case, an epi-illumination type illumination system 42 is arranged in the edge detection optical system 38, and illumination light emitted from the illumination system 42 is reflected by a half mirror 74 arranged on the optical axis A.
After being reflected in the direction of the objective lens 60 through the lens, the light is condensed on the sample 32 by the objective lens 60. At this time, the reflected light reflected from the sample 32 is guided from the objective lens 60 to the imaging lens 76 disposed on the optical axis A via the half mirror 74, and then the slit plate 36 is formed by the imaging lens 76. The light is received by the photodetector 58 via the. In this case as well, the sample 3 with respect to the optical axis A of the edge detection optical
By rotating the slit plate 36 by a predetermined angle on the basis of the relative movement direction of the slits 2, the area ratio between the light portion L 1 and the dark portion L 2 in the slit 36 a is 50% regardless of the edge shape.
(See FIGS. 2 (b) and 2 (c)) can be accurately detected as an edge.

As described above, according to the edge detector of the present embodiment, for example, the edges of a plurality of products (samples 32) formed according to the same standard are continuously detected, and the edge accuracy of the products is inspected. At this time, the preset edge detection direction D
The edge can be easily and accurately detected by appropriately changing the rotation angle of the slit plate 36 based on the above.

[0028]

According to the present invention, when the edge detection direction is known in advance, the edge is easily and accurately detected by appropriately changing the rotation angle of the slit plate based on the preset edge detection direction. A possible edge detector can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of an edge detector according to an embodiment of the present invention.

2A is a diagram illustrating characteristics of a voltage signal input from a photodetector to a comparator, and FIG. 2B is a diagram illustrating a case where edge detection of a sample having a circular edge is performed. FIG. 4C shows a state in which the major axis direction is made parallel to the edge detection direction. FIG. 6C shows the major axis direction of the slit of the slit plate when performing edge detection of a sample having a linear but fine uneven edge. The figure which shows the state matched with the direction substantially orthogonal to the edge detection direction.

FIG. 3 is a diagram schematically showing a configuration of an edge detector according to another modification of the present invention.

FIG. 4A is a diagram showing a configuration of a conventional edge detector. FIG. 4B is a diagram illustrating a case where a sample has a straight edge, and a half of the area of a pinhole is a bright portion during edge detection. FIG. 4C shows a state in which the other half is a dark part. FIG. 4C shows that, when the edge of the sample is circular, the area ratio between the bright part and the dark part in the pinhole is not equal to each other at the time of edge detection. FIG. 3D is a diagram illustrating a state in which, when a slit is used in place of a pinhole, the area ratio between a bright portion and a dark portion in the slit is not equal to each other when a circular edge is detected.

[Explanation of symbols]

 32 sample 34 stage 36 slit plate 38 edge detection optical system 40 slit plate rotation mechanism A optical axis

Claims (3)

[Claims] 1. A stage on which a sample can be placed, and when light from the sample illuminated by illumination light is received through a slit plate, an edge of the sample can be detected based on a change in light intensity thereof. An edge detection optical system, and relative moving means for relatively moving the stage and the edge detection optical system so as to relatively move the sample in a direction orthogonal to the optical axis of the edge detection optical system. The edge detection optical system, when the stage and the edge detection optical system are relatively moved by the relative movement means, relative to the optical axis of the edge detection optical system of the sample An edge detector provided with a slit plate rotating mechanism for rotating the slit plate by a predetermined angle based on a moving direction. 2. The slit plate rotating mechanism according to claim 1, wherein, when the edge of the sample is not linear, the long axis direction of the slit of the slit plate is moved relative to the optical axis of the edge detection optical system. 2. The edge detector according to claim 1, wherein the rotation angle of the slit plate is controlled so as to be parallel to the edge detector. 3. The slit plate rotating mechanism according to claim 1, wherein the edge of the sample has a linear shape but a fine uneven shape.
The rotation angle of the slit plate is controlled so that a major axis direction of the slit of the slit plate is substantially perpendicular to a moving direction of the sample relative to an optical axis of the edge detection optical system. 2. The edge detector according to 1.