JPH0560558A - Optical micro displacement measuring apparatus - Google Patents

Abstract

(57) [Summary] [Purpose] To prevent displacement errors due to non-uniformity of the intensity distribution of the luminous flux. [Structure] Light emitted from the semiconductor laser 1 is converted into a half-wave plate 10
After passing, it is made incident on the polarization beam splitter 3.
Therefore, when the semiconductor laser 1 emits P-polarized light, the P-polarized light is incident on the two-divided detectors 9A and 9B, and the direction in which the intensity distribution is non-uniform in the direction orthogonal to the active layer of the semiconductor laser 1 is detected by two-divided detection. It coincides with the dividing line direction of the containers 9A and 9B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical micro-displacement measuring device for measuring micro-displacement and surface roughness of an object to be measured by optical means.

[0002]

2. Description of the Related Art Conventionally, as an optical micro-displacement measuring apparatus for detecting a micro-displacement and a surface roughness of an object to be measured by detecting a defocus, for example, one using a critical angle method (optical technology contact Vol. 26, No. 11, 1988, p.7.
48-755), using the astigmatism method (Optical Technology Contact Vol. 26, No. 11, 1988, p. 75).
6-762), using the Foucault method (Optical Technology Contact Vol. 26, No 11, 1988, p. 773-
784) and so on.

Here, the critical angle method utilizes the property that the intensity of the light beam incident near the inherent critical angle of the prism exhibits a rapid change with respect to a minute angle change. FIG. 4 shows an example of the configuration of a conventional optical micro-displacement measuring device according to the above. In the figure, 101 is a semiconductor laser which is a laser light source, 102 is a collimating lens,
Reference numeral 103 is a polarization beam splitter, 104 is a quarter wavelength plate, 105 is an objective lens, 106 is an object to be measured, 107 is a beam splitter, 108A and 108B are critical angle prisms, 109A and 109B are two-divided light receiving elements, and a semiconductor. The laser light from the laser 101 is collimated lens 10
It is converted into a parallel light flux by 2 and is guided to the quarter-wave plate 104 as S-polarized light through the polarization beam splitter 103.
The laser light guided to the quarter-wave plate 104 is converted into a circularly polarized light beam, and then is condensed on the surface of the DUT 106 via the objective lens 105. The laser light reflected by the DUT 106 is P-polarized by the quarter-wave plate 104, then passes through the polarization beam splitter 103, is guided to the beam splitter 107, and is dispersed. The separated lights are reflected by the critical angle prisms 108A and 108B whose reflection surfaces are set to the critical angles, respectively, and are incident on the two-divided light receiving elements 109A and 109B, respectively, and the amount of light is detected.

As described above, when the object to be measured 106 is located at the focal point of the objective lens 105, the reflected light becomes parallel, the reflectance at the critical angle prisms 108A and 108B is constant for all luminous fluxes, and is divided into two. Light receiving element 109A, 1
The amount of light received by 09B becomes equal. However, when the DUT 106 is located farther than the focal point of the objective lens 105, the reflected light becomes a convergent light, so that the incident angle of the light flux entering the critical angle prisms 108A and 108B is critical with respect to the optical axis. The angle prism 108A has a right side in the figure, and the critical angle prism 108b has an upper side in the figure smaller than the critical angle, and the reflectance decreases, which causes a difference in the amount of light received by the two-divided light receiving elements 109A and 109B. Similarly, when the DUT 106 is located closer to the focal point of the objective lens 105, the reflected light becomes divergent light, which is the opposite of the above case,
A difference occurs in the amount of light received by the two-divided light receiving elements 109A and 109B. From such a difference in the amount of light, the DUT 106
Of the displacement of the objective lens 105 from the focus position,
It is possible to measure the minute displacement and the surface roughness of the DUT 106.

On the other hand, in the astigmatism method, astigmatism is applied to a detected image by using a cylindrical lens, and the displacement amount of the position of the object to be measured is converted into image deformation. In the device, when the object to be measured is the focus position of the objective lens, the received light beam has a circular shape, but when the image forming position is close, it has an elongated elliptical shape, and when it is far, it has a horizontal shape. Since it has an elliptical shape, it is photoelectrically converted by a 4-division photodiode, the sum of each of the vertical and horizontal directions is calculated, and the output signal of the difference between them is calculated, and the output proportional to the displacement amount of the measured object is output. Is what you get.

Further, the Foucault micro-displacement measuring apparatus uses a splitting prism having an optical knife edge effect to split a light beam reflected from an object to be measured into two light beams and make them enter a two-divided photodiode. When the distance between the objective lens and the surface to be measured changes, the angle of divergence of the reflected light beam from the object to be measured changes, which causes a difference in the amount of light received by the two-divided photodiodes. It is what you want.

[0007]

When the object to be measured is tilted in the above-described conventional optical micro displacement measuring device,
The reflected light beam axis moves in parallel to the incident light beam axis.
For example, in the device shown in FIG. 4, when the DUT 106 is tilted by θ, as shown in FIG.
The reflected light beam axis 111 is translated by ΔX.
Then, in this case, assuming that the focal length of the objective lens 105 of the DUT 106 is f, the relationship of ΔX = f · tan2θ holds.

By the way, in the apparatus shown in FIG. 4, the reflected light is separated into two split light receiving elements 109A and 109B.
The light is received by each of the light receiving elements A, B,
Letting C and D be, [(A−B) + (C−D)] / (A + B + C + D) is the displacement output. Then, the above-mentioned deviation ΔX of the optical axis occurs in mutually opposite directions in the two-divided light receiving elements 109A and 109B, that is, when A is large in the two-divided light receiving element 109A, D is large in the two-divided light receiving element 109B. Therefore, the difference in the amount of received light due to ΔX is offset.

However, since the intensity distribution of the reflected light flux is non-uniform in the ΔX direction, there is a problem that the difference in the amount of received light due to ΔX is not canceled and a measurement error occurs. That is, as shown in FIG. 6, the light flux from the semiconductor laser 101 becomes an ellipse elongated in the direction perpendicular to the active layer 101a, and the direction parallel to the active layer 101a and the polarization direction coincide with each other. On the other hand, since the detection sensitivity in the critical angle method or the like is better for P-polarized light (polarized light whose polarization direction is parallel to the paper surface in FIG. 4), S-polarized light (polarization direction is orthogonal to P-polarized light) is input to the polarization beam splitter 102. ), The beam shape becomes a horizontally long ellipse as shown in FIG. However, the intensity distribution in the vertical direction in FIG. 6 does not become a Gaussian distribution due to the influence of diffraction etc., but becomes non-uniform as shown in FIGS. 7 (A) and 7 (A). Therefore, when such a light flux is deviated in the ΔX direction, it becomes as shown in FIGS. 8B and 8B, and there is a problem that the error is not corrected.

In view of such circumstances, it is an object of the present invention to provide an optical micro-displacement measuring device which does not cause a displacement error due to the non-uniformity of the intensity distribution of the reflected light flux.

[0011]

A micro-displacement measuring apparatus according to the present invention that achieves the above object comprises an irradiation optical system for irradiating an object to be measured with a light beam from a semiconductor laser, and a reflected light beam from the object to be measured. An optical micro-displacement measuring device having a focus error detecting optical system for detecting a focus error, the device having an element for rotating a polarization direction of a light beam by 90 degrees, the reflection entering a split detector of the focus error detecting optical system. It is characterized in that the polarization direction of the light beam and the beam diameter in the direction parallel to the active layer of the semiconductor laser are the same and these directions are orthogonal to the division line of the division detector.

[0012]

[Operation] The irradiation optical system is usually a polarization beam splitter and 1 /
The light flux emitted from the semiconductor laser having the four-wavelength plate and the reflected light flux entering the split detector of the focus error detection optical system are deviated in polarization direction by 90 degrees. However, in the above-mentioned configuration, since there is an element that rotates the polarization direction by 90 degrees, the light flux emitted from the semiconductor laser and the reflected light flux have the same polarization direction. On the other hand, in view of the sensitivity of the split detector, the deflection direction of the reflected light beam is preferably orthogonal to the split line, and the light beam emitted from the semiconductor laser is polarized in the direction parallel to the active layer. Therefore, in the device having the above configuration, the direction parallel to the active layer of the semiconductor laser and the dividing line of the split detector are orthogonal to each other, and the beam intensity distribution in the direction parallel to the active layer is a Gaussian distribution. Is improved.

[0013]

EXAMPLES The present invention will be described below based on examples.

FIG. 1 shows the configuration of an optical micro-displacement measuring device according to an embodiment. In the figure, 1 is a semiconductor laser which is a laser light source, 2 is a collimating lens, 3 is a polarization beam splitter, 4 is a quarter wavelength plate, 5 is an objective lens, 6 is an object to be measured, 7 is a beam splitter, 8A, 8B is a critical angle prism, 9A and 9B are two-divided light receiving elements, and 10 is 1
It is a half wave plate. In the device of this embodiment, the laser light from the semiconductor laser 1 is emitted in the P-polarized state. Then, after being converted into a parallel light flux by the collimator lens 2, it is converted into S-polarized light by the ½ wavelength plate 10. This S-polarized light is transmitted through the polarization beam splitter 3 to the quarter-wave plate 1
You are led to 04. The laser light guided to the quarter-wave plate 4 is converted into a circularly polarized light beam, and then is condensed on the surface of the DUT 6 via the objective lens 5. The laser light reflected by the DUT 6 is P-polarized by the quarter-wave plate 4, then passes through the polarization beam splitter 3, is guided to the beam splitter 7, and is dispersed. The separated lights are reflected by the critical angle prisms 8A and 8B whose reflecting surfaces are set to the critical angles, respectively, and are incident on the two-divided light receiving elements 9A and 9B, and the light amounts are detected.

In this embodiment, the light beam emitted from the semiconductor laser 1 is a vertically elongated elliptical P-polarized light, which also becomes a vertically elongated elliptical S-polarized light after passing through the half-wave plate 10. After being reflected by the polarization beam splitter 3, passing back and forth through the quarter-wave plate 4 and passing through the polarization beam splitter 3, it becomes P-polarized light again and a highly sensitive state is secured, but the beam shape is a vertically long elliptical shape. There is. Therefore, 2
The reflected light entering the split light receiving elements 9A and 9B is also a vertically elongated elliptical beam, and as shown in FIGS. 2 and 3, has a non-uniform intensity distribution in the split line direction of the two split light receiving elements 9A and 9B. Become. However, as shown in the figure, the intensity distribution in the direction orthogonal to the dividing line is a Gaussian distribution. Therefore, even if the beams incident on the two-divided light receiving sections 9A and 9B deviate in the direction orthogonal to the dividing line due to the inclination of the DUT 6, as described above, the beams shift in the opposite directions in 9A and 9B. It is completely corrected by taking the sum with the output difference of 9A.

[0016]

As described above, according to the present invention,
Since the device for rotating the polarization direction by 90 degrees is provided, the deflection direction of the reflected light beam entering the split detector of the focus error detection optical system is orthogonal to the division line, and this deflection direction is parallel to the active layer of the semiconductor laser. Match the direction. Therefore, it is possible to prevent the occurrence of the displacement error due to the nonuniformity of the intensity distribution of the light flux.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an optical micro-displacement measuring device according to an embodiment.

FIG. 2 is an explanatory diagram showing a reflected light beam on the split detector of FIG.

FIG. 3 is an explanatory view showing a reflected light flux on the split detector of FIG.

FIG. 4 is a configuration diagram showing an example of an optical micro-displacement measuring device according to a conventional technique.

FIG. 5 is an explanatory diagram showing a light beam deviation when an object to be measured is tilted.

FIG. 6 is an explanatory diagram showing an emission beam of a semiconductor laser.

FIG. 7 is an explanatory diagram showing a beam intensity distribution of a semiconductor laser.

FIG. 8 is an explanatory diagram showing a beam intensity distribution of a semiconductor laser.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 2 Collimating lens 3 Polarization beam splitter 4 1/4 wavelength plate 5 Objective lens 6 DUT 7 Beam splitter 8A, 8B Critical angle prism 9A, 9B Divided light receiving element 10 1/2 wavelength plate

Claims (1)

[Claims] 1. An optical micro-displacement measuring device having an irradiation optical system for irradiating an object to be measured with a light beam from a semiconductor laser, and a focus error detection optical system for detecting a focus error by a reflected light beam from the object to be measured. And having a device for rotating the polarization direction of the light beam by 90 degrees, the polarization direction of the reflected light beam entering the split detector of the focus error detection optical system and the beam diameter in the direction parallel to the active layer of the semiconductor laser are An optical micro-displacement measuring device characterized in that they coincide with each other and these directions are orthogonal to a division line of a division detector.