JPH10103915A - Apparatus for detecting position of face - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate highly accurate inspections even when a light quantity distribution of a light point image is irregular, by obtaining a distance in accordance with electric signals from first and second photoelectric conversion elements projecting the light point image through first and second photodetecting routes. SOLUTION: A light point image 16 from a face to be inspected is projected to photoelectric conversion elements PD1 , PD2 located in front of photodetecting optical systems 20, 22 through a first and a second photodetecting routes 24, 26 formed symmetrically to each other with respect to a projection route 14. The light point image 16 is projected with a center of gravity of the light amount shifted in opposite directions at both sensors of the elements PD1 , PD2 . Therefore, light point images 161 , 162 when the face to be inspected is at a position K0 are projected between sensors A1 and B1 , A2 and B2 . If the light point image 16 has an ideal light amount distribution, a position where a different of electric signals (A1 -B1 ) to the light amount from the sensors A1 , B1 is zero is detected as the position K0 . The same applies to the sensors A2 , B2 . Even when the light amount distribution of the light point image 16 is not uniform, the center of gravity of the light amount is shifted in opposite directions between the photoelectric conversion elements PD1 and PD2 , and therefore the shift is offset by utilizing signals from both elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for inspecting the position of a surface to be inspected, and more particularly to a non-contact type surface position detection used for autofocusing of optical equipment such as a microscope and measuring the height and level difference of the surface of an inspected object. Related to the device.

[0002]

2. Description of the Related Art For example, an autofocus device for positioning a microscope lens barrel at a focus position with respect to the surface of an object to be inspected, and moving and positioning the lens barrel with respect to a plurality of surfaces at respective focus positions. As a surface position inspection device such as a measuring device for obtaining a step or a shape of a surface from a driving amount thereof, a device using a triangulation method or a knife edge method is known.

FIG. 7 shows a surface position inspection apparatus using a triangulation method. For example, light from a light source LD such as a laser diode is projected as a light spot image on a test surface K0 to K2 via a projection lens L1, and the light spot image is photoelectrically converted through a light receiving lens L2 into a photoelectric conversion element PD such as a photodiode Projected onto The electric signal from the photoelectric conversion element is processed by utilizing the fact that the projection position of the light spot image on the light receiving surface of the photoelectric conversion element is displaced in accordance with the position of the inspection surface K0 to K2, and Is detected as a relative position, for example.

That is, as shown in FIG. 7, a case where the surface to be inspected is, for example, K0 at the focal position, and the upper and lower K1,
The position on the photoelectric conversion element PD is different from that at the position of K2.

[0005] As the photoelectric conversion element PD, a two-division sensor, a line sensor, or the like is used. FIG. 7 shows an example of a two-divided sensor. In this example of the two-divided sensor, a difference signal AB between signals from photodiodes arranged through a narrow gap in the two regions A and B is taken, and the position of the inspection surface when this signal becomes 0 is determined. It is detected that it is K0. Therefore, for example, the projection lens L1 is located at the position K0.
Is adjusted, the position of the surface to be inspected is moved so that the difference signal between the two photodiodes A and B becomes 0, and the position K at which the surface to be inspected is automatically focused is obtained.
It can be positioned at zero.

The photoelectric conversion element PD is a PSD.
(Position Sensitive Detector)
And the use of CCD line sensors, it is possible to detect the position of the light spot image itself on the light receiving surface of those sensors, and to detect the height displacement within a certain range up and down around the position K0. Can be.

FIG. 8 shows an example of a surface position inspection apparatus using the knife edge method. In this case, the lens L1 is
Has a function of both a projection lens for projecting the light onto the inspection surfaces K0 to K2 and a light receiving lens for projecting the light onto the photoelectric conversion element PD. Therefore, the optical system is simplified. M1 is a mirror, which is also provided with a two-divided sensor PD in this example. Therefore, as the surface to be inspected moves up and down to K0, K1, and K2, the position of the light spot image on the sensor PD is displaced to the center of the A and B regions, the A region, and the B region.

[0008]

The principle described above is based on the premise that the light spot reflected on the surface to be inspected is projected onto the photoelectric conversion element PD with an ideal light quantity distribution. FIG. 9A is a graph of the light intensity of a light spot image having such an ideal light amount distribution.

However, the actual surface of the object to be inspected is
It is often an optically non-uniform surface such as a scratch, a stain, a pattern, a metal machined surface, a mixed metal and plastic surface, or a step surface. Therefore, the light amount distribution of the light spot image projected on the photoelectric conversion element becomes non-uniform. FIG. 9B shows an example of such a non-uniform case. In this example, since the right side of the light spot image is missing, the center of gravity of the light amount is shifted by e from the original center position.

In the above method for detecting the position of the surface to be inspected,
Since the displacement of the surface to be inspected in the height direction is detected as a lateral displacement of the light spot image, the displacement of the center of gravity of the light amount as shown in FIG.
The apparent height is detected as if displaced, which causes a problem that a measurement error occurs.

Considering this point with a simple model shown in FIG. 10, when the light is projected onto the surface position K0, the height error he for the light receiving angle θ with respect to the shift e of the light quantity center of gravity is given by: e / tan θ. Therefore, the surface position K2 ', which is deviated from the surface position K0 by he, is detected, and the height error he increases as the deviation e of the light amount centroid increases. In order to reduce the height error and increase the detection accuracy, the light receiving angle θ may be increased. However, in such a method, the light receiving optical path is interrupted when the object to be inspected has a step. Not appropriate to respond.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a surface position inspection apparatus which is not easily affected by the unevenness of the surface of an object to be inspected and can detect the surface position with high accuracy.

[0013]

According to the present invention, a light source image is projected onto a surface to be inspected via a projection optical system, and a light spot image on the surface to be inspected is transmitted to a light receiving optical system. And the distance is detected from the position of the light spot image displaced on the light receiving surface of the photoelectric conversion element according to the distance between the projection and / or light receiving optical system and the surface to be inspected. In the surface position inspection device, a first light receiving path and a second light receiving path provided at substantially symmetrical positions on both sides of a projection path of the light source image, and the light spot image via the first light receiving path. Is projected, the second photoelectric conversion element on which the light spot image is projected via the second light receiving path, and the first and second photoelectric conversion elements A signal processing unit for obtaining the distance in accordance with an electric signal. Ri is achieved.

By symmetrically arranging the photoelectric conversion elements on both sides of the projection path, it is possible to extract a signal for canceling the detection position shift due to the nonuniformity of the light spot image.

According to the present invention, in the above-described surface position inspection apparatus, the first and second photoelectric conversion elements each include two elements arranged in a moving direction of the light spot image, and The processing unit detects a zero-cross point of a sum signal of a difference signal between the electric signals from the two elements of the first photoelectric conversion element and a difference signal between the electric signals from the two elements of the second photoelectric conversion element. It is characterized by doing.

Alternatively, according to the present invention, in the above-described surface position inspection apparatus, each of the first and second photoelectric conversion elements has two elements arranged in a moving direction of the light spot image, The signal processing unit includes: a first light amount ratio of a difference signal and a sum signal of electric signals from two elements of the first photoelectric conversion element; and an electric signal from two elements of the second photoelectric conversion element. A zero-cross point of a sum signal of the difference signal of the sum and the second light amount ratio of the sum signal is detected.

Alternatively, according to the present invention, in the above-described surface position inspecting apparatus, each of the first and second photoelectric conversion elements has light receiving position detecting means for detecting a position of a light spot image in the displacement direction. The signal processing unit calculates an average value of the first and second position data output from the light receiving position detecting unit.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. However, the technical scope of the present invention is not limited to the embodiment.

FIG. 1 is a block diagram of an example of a surface position detecting device when the present invention is applied to a triangulation method. The surface position detecting device 1 is provided with a predetermined driving device such that an object to be inspected is placed on a stage (not shown) and a relative distance between the optical system and the surface of the object to be inspected is displaced. Although the surfaces K0 to K2 are shown as being displaced for simplicity in FIG. 1, the optical system may be moved up and down.

In the example of FIG. 1, the surface of the object to be inspected is positioned at a focus position K0, for example, using a surface inspection device or a microscope, and the surface observed at that time is used for inspection for a desired purpose. is there. In order to detect the surface position, a light source LD such as a laser diode is used as an auxiliary light source, such as a lens L10, a mirror 12 such as a dichroic mirror,
The light is projected on the surface via the objective lens L12. As a result,
A light spot image as shown in FIG. 16 is projected on the surface to be inspected. This example is an example of an uneven light amount distribution as shown in FIG.

In the surface position inspection apparatus shown in FIG. 1, a first light receiving path 24 and a second light receiving path 26 are formed at substantially symmetric positions on both sides of the projection path 14. That is, the first and second light receiving optical systems 2 are provided on both sides of the objective lens L12.
0 and 22 are formed, and light receiving lenses L14 and L16 are provided in the respective optical systems. Then, the light spot image 16 from the surface to be inspected is projected onto the photoelectric conversion elements PD1 and PD2 provided before the light receiving optical systems 20 and 22 via the respective light receiving paths 24 and 26.

As described in the conventional example, the photoelectric conversion elements PD1 and PD2 can use a line sensor such as a sensor composed of two divided photodiodes or a PSD or CCD line sensor. Regardless of which sensor is used, the light spot image 16 projected on the light receiving surface of each of the photoelectric conversion elements is projected so that the center of the light amount shifts in the opposite direction in the sensors on both sides. FIG. 1 shows an example of a two-split sensor, but when the surface to be inspected is at the position K0,
The light spot images 161 and 162 are composed of two sensors A1 and B1, A
2 shows a state where projection is performed between B2 and B2.

When the light spot image 16 has an ideal light amount distribution as shown in FIG. 9A, the difference (A1-B1) between the electric signals corresponding to the light amounts from the sensors A1 and B1 in FIG. The position K0 can be detected by detecting the position where the value becomes zero. The same detection can be performed by using the sensors A2 and B2. Further, even when the light spot image 16 has a non-uniform light amount distribution as shown in FIG.
Since the light amount center of gravity is displaced in the opposite direction to 1 and PD2, it is possible to cancel out such shift of the light amount center of gravity by using signals from both elements.

FIG. 2 is a configuration diagram of an example of a signal processing unit when a two-divided sensor is used for a photoelectric conversion element. FIG.
FIG. 4 is a diagram showing changes in signals when the surface to be inspected is displaced in the height direction. The signal processing unit 2 shown in FIG. 2 includes amplifiers 30 to 3 which convert a current of a level corresponding to the amount of light from each of the photodiodes A1, B1, A2, and B2 into a voltage and amplify the voltage.
3, addition circuits 34, 37, 39, subtraction circuits 35, 36,
It has comparison circuits 38, 40, 46 and the like. Then, the difference signal S1 (= A1-B1) between the sensors A1 and B1 and the sensor A
An adder 39 generates a sum signal of the difference signal S2 (= A2−B2) between 2 and B2, and the comparison circuit 40 detects that the sum signal S (S1 + S2) becomes 0.

With reference to FIG. 3, the point that the position K0 of the inspection surface can be detected even when the light spot image has non-uniformity will be described. In FIG. 3, the horizontal axis direction is the height direction of the surface to be inspected,
A higher position K3 and a lower position K4 are added in addition to the surface positions K0 to K3 shown in FIG. Now, temporarily, Figure 1
It is assumed that the surface to be inspected moves from the upper side to the lower side. In that case, the light spot image is the sensor B of the photoelectric conversion elements PD1 and PD2.
Displaced from above the sensors A1 and A2 from above the sensors 1 and B2. Then, when the surface to be inspected is at K0, the light spot image is located between the two-divided sensors.

FIG. 3 shows how a light spot image having a non-uniform light amount distribution moves. First, at the position K3, a light spot image starts to be projected on the sensors B1 and B2. Therefore,
Although the signals A1 and A2 are both at the level 0, the signals B1 and A2
B2 has a corresponding level. However, since the nonuniformity of the light spot images is opposite in the elements PD1 and PD2, the signal of the sensor B1 is smaller than the signal of the sensor B2 at the position K3.
Level is higher than the signal of Therefore, after that, the peak of the signal B1 occurs at a higher position (left side in the figure), and the signal B1
In No. 2, a peak occurs on the lower side (right side in the figure).

Eventually, when moving from position K1 to K0,
The level of the signal A1 rises due to the nonuniformity of the light spot image,
The level of the signal B1 falls. Further, from position K0 to K
Moving to 2, the rise of the signal A2 and the fall of the signal B2 appear with a delay.

As a result, a difference signal S1 between the signals A1 and B1 is obtained.
Is generated with its zero-crossing point shifted above the position K0 (left side in the figure) by h1. The difference signal S2 between the signals A2 and B2 is that the zero-crossing point is below the position K0 (right side in the figure). At h2. Therefore, the difference signal S1
When the sum signal S of S2 and S2 is monitored, the zero cross point exactly matches the position K0. That is, a signal that cancels out the deviation due to the nonuniformity (deletion) of the light spot image is obtained as the sum signal S.

In FIG. 2, the AND circuit 41 calculates the logical sum of the comparison circuits 38 and 40, so that the optical system or stage is moved up and down by the driving device 45 to detect when it reaches the position K0. , The count value from the position reading device 44 can be triggered. That is, as shown in (8) of FIG. 3, when the light spot image is projected on the light receiving area of the photoelectric conversion element, the sum of the signals A1 and B1 exceeds a certain threshold T. At that time, the time when the signal S becomes 0 is the zero cross point.
Therefore, when the sum signal A1 + B1 is equal to or larger than the threshold value T, the output of the comparison circuit 38 that outputs the H level, and when the signal S is 0, the output level of the H
By applying a trigger to the counter that changes when the driving device 45 moves by the logical sum with the output of the comparison circuit 40 that becomes the level, the counter value at the position K0 can be latched. The sum signal A1 + B1 may be A2 + B2.

The signal S is given by S = (A1-B1) +
(A2-B2), on the premise that the photoelectric conversion elements PD1 and PD2 receive the same amount of light. However, the difference in the amount of received light between the photoelectric conversion elements PD1 and PD2 is
If it becomes large due to the optical directionality of the surface to be inspected or the variation of the optical system or signal processing system in the inspection device itself,
As indicated by the alternate long and short dash line in (6) and (7) of FIG. 3, the zero cross point of the signal S is shifted like d. That is, in this example, the amount of light received by the photoelectric conversion element PD2 is small.

Therefore, in the signal processing unit 2, as shown by the dotted line in FIG. 2, the sum circuit 39 calculates: S1 = (A1-B1) / (A1 + B1) S2 = (A2-B2) / (A2 + B2) Generate S = S1 + S2. The signals S1 and S2 are ratios of the difference signal and the sum signal, and are normalized in the range of +1 to −1, so that the influence of the difference in the amount of received light between the respective elements PD1 and PD2 can be eliminated. . Then, by taking the sum of the normalized signals S1 and S2, the zero-cross point coincides with the surface position K0.

FIG. 4 shows the photoelectric conversion elements PD1, PD of FIG.
2 is an example in which the light receiving position of the light spot image is detected as position data by light receiving position detecting means. As the light receiving position detecting means, for example, a CCD line sensor, a PSD (Position Sensitive Detector) element or the like can be used. In each element, the light receiving surface has a shape extending in the direction of displacement of the light spot image.
Is output. Therefore, the data of the position of the surface to be detected can be output as it is within a certain range without performing the signal processing as shown in FIG.

However, as shown in FIG. 4, when the light spot images 161 and 162 are chipped and lose uniformity, the center of gravity of the light quantity is shifted, and the output position data N1 and N2 are also shifted. Value. Therefore, when such a light receiving position detecting means is used, the position data N1 and N2 detected by the left and right optical systems may be averaged by the signal processing unit 2 to cancel the error. it can.

FIG. 5 is a structural diagram of a surface position inspection apparatus according to an embodiment when the present invention is realized by the knife edge method. As described above, in the case of the knife edge method, the structure can be made compact by using a part of the projection optical system for the light receiving optical system. In the apparatus shown in FIG. 5, an optical image from a light source such as a laser diode LD is used as an auxiliary light source in a lens barrel having an objective lens L12 formed on the optical axis of the observation system 10, and a lens L12 and a reflecting mirror 12 are provided. To project the light image 16 on the surfaces K0 to K2 to be measured. Then, the light spot image 16 is projected onto the two photodiodes PD1 and PD2 via light receiving optical paths 24 and 26 formed in a lens barrel having a projection optical system on both sides of the projection optical path 14.

In this example, both light receiving optical paths are taken out in the same direction by the dichroic mirror 12, and are vertically separated by the lens L15 and the prism L17. Further, the light spot images 161 and 16 projected by the two-split sensor
2 is detected. However, the position data may be detected by the light receiving position detecting means as shown in FIG.

FIG. 6 is a structural diagram of another example of the surface position inspection apparatus when the present invention is applied to the knife edge method.
In this example, as in the case of FIG. 5, the projection optical path 14 and the light receiving optical paths 24 and 26 on both sides thereof pass through a common lens barrel.
Therefore, light from the light source passes through the objective lens L12, and light reflected on the surface to be inspected also passes through the lens. Then, the light is split right and left by reflection mirrors 18 and 19 provided above the objective lens L12, and the light spot images 161 and 161 are formed on the respective photoelectric conversion elements PD1 and PD2 via the light receiving lenses L18 and L19.
162 is projected.

In this example, an example of a two-divided sensor is also shown, but the position data may be similarly detected by the light receiving position detecting means. The signal processing in both the two-divided sensor and the light receiving position detecting means is the same as described above.

[0038]

As described above, according to the present invention, in the apparatus for detecting the surface position of the object to be inspected, even if the light quantity distribution of the projected light spot image is not uniform, the displacement of the light quantity centroid caused by the unevenness is caused. Can be removed, and a more accurate surface position inspection can be performed. Therefore,
The surface of various inspection objects can be measured regardless of the state of the inspection surface.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an example of a surface position detection device when the present invention is applied to a triangulation method.

FIG. 2 is a configuration diagram of an example of a signal processing unit.

FIG. 3 is a diagram illustrating a change in each signal when a surface to be inspected is displaced in a height direction.

FIG. 4 is a diagram showing an example in which the photoelectric conversion elements PD1 and PD2 of FIG. 1 are configured by a light receiving position detecting means capable of detecting a light receiving position of a light spot image as position data.

FIG. 5 is a structural diagram of a surface position inspection apparatus according to an embodiment when the present invention is realized by the knife edge method.

FIG. 6 is a structural diagram of another example of the surface position inspection apparatus when the present invention is applied to the knife edge method.

FIG. 7 shows a surface position inspection apparatus using a triangulation method.

FIG. 8 shows a surface position inspection apparatus using a knife edge method.

FIG. 9 is a graph of light intensity of a light spot image of a light amount distribution.

FIG. 10 is a simple model diagram showing a height error he with respect to a shift e of a light quantity center of gravity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Surface position inspection apparatus 2 Signal processing part 14 Projection optical path 16 Light spot image 20, 22 Light receiving optical system 24, 26 Light receiving optical path L12 Objective lens LD Light source PD1, PD2 Photoelectric conversion element

Claims (8)

[Claims] An image of a light source is projected onto a surface to be inspected via a projection optical system, and a light spot image on the surface to be inspected is projected onto a photoelectric conversion element via a light receiving optical system. In a surface position inspection device that detects the distance from the position of the light spot image displaced on the light receiving surface of the photoelectric conversion element according to the distance between the optical system and the surface to be inspected, A first light receiving path and a second light receiving path provided at substantially symmetric positions; a first photoelectric conversion element onto which the light spot image is projected via the first light receiving path; A second photoelectric conversion element onto which the light point image is projected via the light receiving path, and a signal processing unit for obtaining the distance in accordance with an electric signal from the first and second photoelectric conversion elements. Characteristic surface position inspection device. 2. The first optical system according to claim 1, wherein the projection optical system has an objective lens located on the surface to be inspected, and the light receiving optical system is provided in the first light receiving path. A surface position inspection apparatus comprising: a light receiving optical system; and a second light receiving optical system provided in the second light receiving path. 3. The projection optical system according to claim 1, wherein the projection optical system has an objective lens located on the surface to be inspected, and wherein the first and second light receiving paths are formed via the objective lens. A surface position inspection apparatus characterized in that: 4. The apparatus according to claim 3, wherein the first and second light receiving paths are separated from the projection optical system by a reflection means disposed on a side of the objective lens opposite to the surface to be inspected. Characteristic surface position inspection device. 5. The signal processing unit according to claim 1, wherein the first and second photoelectric conversion elements each include two elements arranged in a moving direction of the light spot image. Detecting a zero-cross point of a sum signal of a difference signal between electric signals from two elements of the first photoelectric conversion element and a difference signal between electric signals from two elements of the second photoelectric conversion element. Surface position inspection device characterized by the above-mentioned. 6. The signal processing unit according to claim 1, wherein the first and second photoelectric conversion elements each include two elements arranged in a moving direction of the light spot image. Is a first light amount ratio of a difference signal and a sum signal of an electric signal from two elements of the first photoelectric conversion element, and a difference signal of an electric signal from two elements of the second photoelectric conversion element. A surface position inspection apparatus for detecting a zero cross point of a sum signal with a second light amount ratio of the sum signal. 7. The device according to claim 1, wherein each of the first and second photoelectric conversion elements has a light receiving position detecting unit for detecting a position of a light spot image in the displacement direction. The surface position inspection apparatus, wherein the processing unit obtains an average value of the first and second position data output from the light receiving position detection unit. 8. The device according to claim 7, wherein the light receiving position detecting means is a CCD line sensor or a P-line sensor.
A surface position inspection device comprising SD.