JPH05322516A - Apparatus for measuring displacement of sample - Google Patents

Abstract

PURPOSE:To correctly measure the absolute value of the shift of a minute sample or the rough surface of the sample by combining an out-of-focus detecting device and a detecting system detecting the intensity change of interference fringes to be compact with the use of the minimum optical element. CONSTITUTION:A light generating means comprised of a semiconductor laser 2 and a collimator lens 4 generates a parallel light which is substantially a linearly polarized light. The light emitted from the laser 2 is not a perfect linearly polarized light, and therefore divided into a necessary perpendicular component or first polarized component and a parallel component or second polarized light which crosses the necessary component and is not naturally required. The required perpendicular component (first polarized component) of the imperfect linearly polarized light from the light source is utilized for a de-focus detecting system, and the parallel component (second polarized component) is used as an interference fringe generating/detecting system. Accordingly, a detecting system for detecting the intensity change of interference fringes so as to evaluate measuring values of a focus error detecting device 20 is incorporated the detecting device 20, making it possible to measure the absolute value of the shift of a very small sample 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical device for measuring a sample displacement which can be used in the field of measuring a very small displacement of a sample of about several microns or unevenness of the sample surface.

[0002]

2. Description of the Related Art Such extremely slight displacement of a sample has been measured by using a conventional focus error detector. In this focus error detection device, the sample surface is irradiated with convergent light, the reflected light from the sample surface is detected, and the displacement of the sample is measured as the displacement of the sample from the focus position. However, this measurement cannot measure the absolute value of the displacement of the sample. In order to measure the absolute value of the displacement of the sample by the focus error detection device, the sample is given a displacement of a known size, this is measured, and the measured value is evaluated with reference to this to obtain the absolute value of the displacement. However, this requires complicated steps and cannot obtain sufficient accuracy. As another method, interference fringes are formed, and the absolute value of the displacement is obtained by evaluating the measured value of the displacement of the sample with reference to the change in the intensity of light having a constant relationship with the wavelength of light. This also requires complicated procedures, and is susceptible to mechanical vibration and external changes, making accurate measurement difficult.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical device for measuring sample displacement, which accurately measures an extremely small amount of sample displacement or the absolute value of the unevenness of the sample surface.

[0004]

The present invention utilizes a required vertical component of incomplete linearly polarized light (hereinafter referred to as "first polarized light component") from a light source such as a semiconductor laser in a defocus measurement system, and originally, Parallel components not required (hereinafter referred to as "second
The above-mentioned object is achieved by incorporating the interference fringe intensity change measurement system for evaluating the measurement value into the focus error detection device by utilizing the "polarization component") in the interference fringe generation / detection system. ..

The sample displacement measuring optical device of the present invention reflects the first polarized light component of the parallel light and the light generating means for generating parallel light which is substantially linearly polarized light, and outputs the second polarized light component of the parallel light. A polarizing beam splitter that transmits light, a first, a second, and a third beam splitter, a quarter-wave plate that converts the first polarized component into a second polarized component (when it passes back and forth), and sample An objective lens for observation, a focus shift detection device that detects displacement of the sample as a focus shift, and an interference fringe detection device that includes a photodetection element that detects a change in the intensity of the interference fringes are provided. The optical path of the system is as follows. That is, the first polarized component of the parallel light from the light generating means is reflected by the polarization beam splitter in the first direction that intersects the traveling direction of the parallel light, and the second polarized component that intersects the first direction.
Is reflected by the first beam splitter, then passes through the quarter-wave plate and the objective lens to converge on the sample surface, and then is reflected from the sample surface to move the objective lens and the quarter-wave plate. The reflected light that passes through the polarization beam splitter, is reflected by the first beam splitter, passes through the wave plate back and forth, and becomes the light of the second polarization component, and is detected by the defocus detector. .. The optical path of the interference fringe intensity change measurement system is as follows. That is, the second polarized component of the parallel light from the light generating means passes through the polarizing beam splitter and is reflected by the third beam splitter. On the other hand, the first polarization component of the parallel light from the light generating means is reflected by the polarization beam splitter in the first direction and by the first beam splitter in the second direction, and then from the quarter wavelength plate and the objective. It converges on the sample surface through the lens, and is reflected from the sample surface, and passes through the objective lens and the quarter-wave plate (the light of the second polarization component is obtained by passing back and forth through the wave plate). The reflected light passes through the first beam splitter, is reflected by the second beam splitter, and passes through the third beam splitter. The transmitted reflected light and the second polarized component of the parallel light transmitted from the polarization beam splitter from the light generating means interfere with each other to form interference fringes. The change in the intensity of the interference fringes is measured to determine the absolute value of the displacement of the sample, which is expressed as the defocus.

[0006]

Embodiments of the apparatus of the present invention will be described with reference to the accompanying drawings. The light generating means consisting of the semiconductor laser 2 and the collimator lens 4 generates parallel light which is substantially linearly polarized light. The light emitted by the semiconductor laser 2 is not perfectly linearly polarized, so that the light is divided into a required vertical component or first polarized component and an originally undesired parallel component or second polarized component which intersects this component. Will be divided. The polarization beam splitter 10 reflects the first polarized component of parallel light and transmits the second polarized component of parallel light.

First, the optical path of the defocus measurement system will be described.
The polarized light of the semiconductor laser 2 is collimated by the collimator lens 4, and the first polarized component is reflected by the polarization beam splitter 10 in the first direction (horizontal direction in the drawing) intersecting the traveling direction of the parallel light. This first polarization component is
The first beam splitter 12-1 arranged so as to intersect with the first direction reflects the light toward the sample 5 in the second direction (the vertical direction in the drawing) intersecting with the first direction.
Then, the first polarized component passes through the quarter-wave plate 8 and the objective lens 6 and is converged on the sample surface, and the reflected light reflected from the sample surface is again the objective lens 6 and the quarter.
It passes through the wave plate 8 and is reflected by the first beam splitter 12-1 toward the polarization beam splitter 10 in the first direction. At this time, the first polarization component has reciprocated through the quarter-wave plate 8 and thus has changed to the second polarization component. The second polarization component of this reflected light is not reflected by the polarization beam splitter 10 and passes through the polarization beam splitter 10. The defocus detection device 20 produces a signal that changes in proportion to the magnitude of defocus due to the second polarization component of the reflected light.

Next, the optical path of the interference fringe intensity change measuring system will be described. As described above, since the light from the semiconductor laser 2 is not perfectly linearly polarized light, the light from the semiconductor laser 2 which is collimated by the collimator lens 4 contains the second polarization component. This second polarization component is not reflected by the polarization beam splitter 10 and passes through the polarization beam splitter 10. On the other hand, the first polarization component of the parallel light from the semiconductor laser 2 is reflected by the polarization beam splitter in the first direction, and then the first beam splitter 1
2-1 is reflected in the second direction, passes through the quarter-wave plate 8 and the objective lens 6 and is converged on the sample surface, and after reflecting the sample surface, the objective lens 6 and the quarter-wave plate 8 are reflected.
Through the first beam splitter 12-1. The reflected light at this time is the second polarization component as described above. After passing through the first beam splitter 12-1, the second polarized component is reflected to the third beam splitter 12-3 by the second beam splitter 12-2 arranged at a position intersecting the traveling direction. It The third beam splitter 12-3 transmits the second polarized component of the reflected light to the interference fringe detection device 30 including a photodetector. At this time, the second polarized component of the reflected light and the semiconductor laser are transmitted. 2 is projected from the polarization beam splitter 10
Interference fringes are formed between the second polarized light component which is transmitted through the second beam splitter 12-3 and is reflected by the third beam splitter 12-3. This interference fringe is detected by the interference fringe detection device 30 through the pinhole 28, and a signal corresponding to the intensity of this interference fringe is produced. This signal changes sinusoidally when the sample surface is displaced, but the magnitude of defocus is evaluated with reference to the period from the peak of the sinusoidal wave to the absolute value. Therefore, the data processing is performed by a data processing device (not shown) connected to the defocus detection device 20 and the interference fringe detection device 30.

The above is the main configuration of the apparatus of the present invention.
After being reflected by the sample 5, the first beam splitter 12-1
It is also possible to observe the sample by causing the reflected light that has passed through the second beam splitter 12-2 to enter the eyepiece lens 40. There are a critical angle method, an astigmatism method, a Foucault method, and a knife edge method as defocus detection methods that can be used in the sample displacement measuring apparatus of the present invention, and these will be described below.

FIG. 1 shows an apparatus for detecting defocus by the critical angle method. The defocusing detection device 20 includes a beam splitter 22, critical angle prisms 24-1 and 24-2 arranged to totally reflect parallel light, and a light detection element 26-1 for detecting light intensity. ~ 26-4
Equipped with. To measure the sample surface displacement, the critical angle prism 2
It suffices to provide 4-1 and the photodetection elements 26-1 and 26-2, but when the sample surface is not horizontal and there is a slight inclination, another set of another critical angle is provided in order to eliminate measurement errors due to it. A prism 24-2 and light detecting elements 26-3 and 26-4 are provided.

The second polarized light component, which is the reflected light from the surface of the sample, is transmitted through the polarization beam splitter 10 and then split into two directions by the beam splitter 22.
It is incident on 4-1 and 24-2, respectively. When the sample surface is displaced from the focal position of the objective lens 6 due to the displacement of the sample, the second polarization component incident on the critical angle prism 24-1 is not parallel light. For example, when the light is displaced away from the objective lens 6, the incident angle of the light above the central axis becomes smaller than the critical angle in the drawing, part of the light passes through the critical angle prism 24-1, and the rest of the light is converted into light. Light incident on the detecting element 26-1 and downward in the drawing from the central axis has an incident angle larger than the critical angle, and thus is totally reflected and is detected by the light detecting element 26-2.
Incident on. A signal proportional to the displacement of the sample surface can be obtained from the difference between the outputs of the photodetection elements 26-1 and 26-2.

If the sample surface is not horizontal and has a slight inclination, the sum of the signal difference between the photodetection elements 26-1 and 26-2 and the signal difference between the photodetection elements 26-3 and 26-4 is obtained. By obtaining the above, it is possible to cancel the error due to the inclination and obtain a signal that is accurately proportional to the displacement of the sample surface. FIG. 2 shows a defocus detection device based on the astigmatism method. This defocus detection device includes a beam splitter 42, four-division photodetection elements 46-1, 46-2,
Then, each is provided with curvature anisotropic lenses 44-1 and 44-2 each having two convergent lines. Anisotropic lens 44-1 and four-division photodetector 46-
1 is sufficient, but curvature anisotropy lenses 44-2 and 4
The measurement error can be eliminated by using the divided photodetector element 46-2. When the incident light is parallel light, the curvature anisotropy lens 44-1 linearly converges the light at points A and B. That is, this light is a line (4
It converges as a finite line on a line extending from 1 to 3 of the split photodetector and is a line (2 to 4 of the 4-split photodetector) orthogonal to the central axis (dotted line) in the plane of the paper at point B. Converges as a finite line on the line extending in the direction of. The shape of this converged light in a cross section perpendicular to the plane of the paper changes from an ellipse extending in the directions 1 to 3 of the four-division photodetection element to a circle from the point A toward the midpoint of points A and B. Changes to an ellipse extending from 2 to 4 from point B to point B.

Now, the four-division detector element 46-1 is connected to points A and B.
Place it at the midpoint of the point. The second polarized component is reflected from the surface of the sample and transmitted through the polarized beam splitter 10, then is split into two directions by the beam splitter 42 and enters the curvature anisotropic lenses 44-1 and 44-2. When there is no displacement in the sample and the sample surface is at the focal position of the objective lens, this incident light is parallel light, so the light transmitted through the curvature anisotropy lens 44-1 is on the 4-division photodetection element. It is projected as a circle on. When the sample has a displacement and the surface of the sample is displaced from the focal position of the objective lens, the incident light is not parallel light, so that the convergent position of the light deviates before and after the points A and B. As a result, the cross-sectional shape of the light appearing on the four-division photodetection element is an ellipse extending from 1 to 3 or 2
It becomes an ellipse extending from 4 to 4. Therefore, these 4
The intensity of light detected by each element of the divided photodetection element is different, and a signal proportional to the displacement of the sample surface is obtained.

FIG. 3 shows a defocus detecting device based on the Foucault method. This defocus detecting device includes a beam splitter 52, lenses 54-1 and 54-2, and split prisms 56-1 and 5-5 for diverging incident light in two directions.
6-2 and 4-division photodetector elements 58-1 and 58-2 are provided. To measure the sample surface displacement, a lens 54-1, a split prism 56-1 and a four-division photodetector element 58-
1 is sufficient, but the measurement error can be offset by taking the sum of the output signals of both photodetection elements by using the lens 54-2, the split prism 56-2, and the 4-division photodetection element 58-2. .. The split prism 56-1 diverges incident light in two directions, a and b. This light appears as a circular or semicircular cross-sectional shape in the four-division photodetector element 58-1. When the converging point of the incident light is at the apex of the split prism 56-1, the incident light diverges and transmits as shown in FIG. 4A, so that the sectional shape of the four-division photodetection element 58-1 is 4 1 and 2 of split photodetector
Two complete circles whose center axis is the dividing line dividing the area of 1 or the dividing line dividing the areas of 3 and 4. When the converging point of the incident light is on the upstream side of the split prism 56-1, its cross-sectional shape is as shown in FIG. A semi-circle with the dividing line as the central axis appears in the region 2 and a semi-circle with the dividing lines in the regions 3 and 4 as the semi-circle in the region 3, and the convergence point of the incident light is downstream of the split prism 56-1. When it is on the side, as shown in FIG. 4C, its cross-sectional shape is such that regions 1 and 2 of the four-division photodetection element 58-1.
Appears in region 1 as a semicircle with the dividing line as the central axis, and in region 4 as a semicircle with the dividing lines in regions 3 and 4 as the central axis. The size of these semicircles changes depending on the convergence position with respect to the apex of the split prism 56-1.

Now, the converging point of the parallel light by the lens 54-1 is arranged so as to be exactly at the apex of the split prism 56-1. The second polarized component, which is the reflected light from the sample surface, passes through the polarization beam splitter 10, is split into two directions by the beam splitter 52, passes through the lens 54-1 and then enters the split prism 56-1. When there is no displacement in the sample and the sample surface is at the focal position of the objective lens, the light incident on the lens 54-1 is parallel light and therefore converges on the apex of the split prism 56-1. Therefore, the cross-sectional shape that appears in the four-division photodetector element 58-1 is a perfect circle (FIG. 4A). When the sample is displaced and the sample surface is displaced from the focal position of the objective lens, the light incident on the lens 54-1 is not parallel light. Therefore, the convergence point of the light converged by the lens 54-1 is deviated from the apex of the split prism 56-1 and the cross-sectional shape appearing in the four-division photodetection element 58-1 is 2 and 3 or 1 and 4 regions. It becomes a half circle in. Since the size of this semicircle changes in proportion to the displacement of the sample surface, the displacement of the sample surface can be determined by measuring the intensity of light detected by each element of the 4-split photodetector. A proportional signal is obtained.

FIG. 5 shows a defocus detecting device by the knife edge method. This defocus detection device includes a beam splitter 62 and a knife edge 6 that blocks half of the light.
6-1 and 66-2, lenses 64-1 and 64-2, and two-divided photo detection elements 68-1 and 68-2. To measure the sample surface displacement, a general lens 64-1 and knife edge 6 are used.
It suffices to provide 6-1 and the photodetection element 68-1, and another set of the lens 64-2, the knife edge 66-2, and the photodetection element 68-2 are for canceling and eliminating the parasitic error. ..

The second polarized light component, which is the reflected light from the surface of the sample, is transmitted through the polarizing beam splitter 10 and is then split into two directions by the beam splitter 62, so that the knife edge 6
After half of the second polarized component is blocked by 6-1 and 66-2, it is converged on the two-divided photodetection elements 68-1 and 68-2 by lenses 64-1 and 64-2. When there is no displacement in the sample and the sample surface is at the focal position of the objective lens, the light converged by the lens 64-1 is divided into regions 1 and 2 on the two-division photodetection element 68-1. If the sample surface is displaced from the focus position of the objective lens although it converges on the line, the lens 6
The convergence point of the light converged by 4-1 shifts to either the front or the rear of the photodetection element, and as a result, a difference occurs in the intensity of the detected light in each of the regions 1 and 2. A signal proportional to the displacement of the sample surface can be obtained by measuring the intensity of light detected by each of these two-division photodetection elements.

[0018]

The defocus detecting device and the interference fringe intensity change measuring system are combined in a compact manner by using the smallest optical element,
It is possible to accurately measure the absolute value of extremely small sample displacement of a few microns.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a sample displacement measuring device of the present invention.

FIG. 2 is a schematic diagram showing a defocus detection device using an astigmatism method that can be used in the sample displacement measuring device of the present invention.

FIG. 3 is a schematic diagram showing a defocus detection device using the Foucault method that can be used in the sample displacement measuring device of the present invention.

FIG. 4 is an explanatory diagram showing a mode of defocus detection of the Foucault method.

FIG. 5 is a schematic view showing a defocus detection device using a knife edge method that can be used in the sample displacement measuring device of the present invention.

[Explanation of symbols]

 2 Semiconductor laser LD 4 Collimator lens 5 Sample 6 Objective lens 8 Quarter wave plate 10 Polarization beam splitter 12-1 Beam splitter 12-2 Beam splitter 12-3 Beam splitter 20 Focus error detection device 22 Beam splitter 24-1 Critical angle prism 24-2 Critical angle prism 26-1 Photodetector 26-2 Photodetector 26-3 Photodetector 26-4 Photodetector 28 Pinhole 30 Interference fringe detector 40 Eyepiece 42 Beam splitter 44-1 Curvature anisotropy lens 44-2 Curvature anisotropy lens 46-1 4-division photo detection element 46-2 4-division photo detection element 52 beam splitter 54-1 lens 54-2 lens 56-1 split prism 56-2 Split prism 58-1 4-split photodetector 58 2 four divided light detection element 62 beam splitter 64-1 lens 64-2 lens 66-1 knife edge 66-2 knife edge 68-1 2 divided photodetection element 68-2 2 divided light detecting elements

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ichiro Yamaguchi 2-1, Hirosawa, Wako-shi, Saitama RIKEN

Claims (4)

[Claims] 1. A light generating means for generating parallel light that is substantially linearly polarized light, and a polarization beam splitter that reflects a first polarization component of the parallel light and transmits a second polarization component of the parallel light.
The first, second, and third beam splitters, the quarter-wave plate, the objective lens for observing the sample, the defocus detection device that detects the displacement of the sample as the defocus, and the intensity change of the interference fringes. An interference fringe detection device for detecting, wherein the polarization beam splitter reflects the first polarized component of the parallel light from the light generating means in a first direction intersecting the traveling direction of the parallel light, and The second polarized light component of the polarized light beam splitter is arranged to transmit the parallel polarized light in the traveling direction of the parallel light, and the first beam splitter is configured to transmit the first polarized light from the polarized light beam splitter in a second direction intersecting the first direction. The first polarized component is arranged so as to reflect light, and the first polarized component passes through the quarter wavelength plate and the objective lens to converge on the sample surface.
A wavelength plate and an objective lens are arranged, and the defocus detection device reflects from the sample surface, passes through the objective lens and the quarter wavelength plate, and is reflected by the first beam splitter. Is arranged to receive the second polarization component of the reflected light that has passed through the polarization beam splitter, and the second beam splitter reflects the second polarization component of the reflected light that has passed through the first beam splitter. And the third beam splitter reflects the second polarization component of the parallel light transmitted through the polarization beam splitter and the second polarization of the reflected light reflected from the second beam splitter. Is arranged to transmit the component, and the interference fringe detection device transmits the second polarization component of the reflected light from the second beam splitter and the polarization beam splitter. Sample displacement measuring optical apparatus characterized by being arranged to detect the interference fringes of the second polarized light component of the parallel light. 2. An eyepiece for observing a sample is further provided, and the eyepiece transmits the second polarized component of the reflected light which is transmitted through the first beam splitter and is transmitted through the second beam splitter. The sample displacement measuring optical device according to claim 1, wherein the optical device is arranged so as to pass therethrough. 3. Light generating means for generating parallel light that is substantially linearly polarized light, and a polarizing beam splitter that reflects the first polarized light component of the parallel light and transmits the second polarized light component of the parallel light.
First, second, and third beam splitters, a quarter-wave plate that converts the first polarized component into a second polarized component, an objective lens for observing the sample, and displacement of the sample is detected as defocus. The polarization beam splitter includes a defocus detection device, an interference fringe detection device that detects a change in the intensity of interference fringes, and a data processing device, and the polarization beam splitter converts the first polarization component of the parallel light from the light generation means into parallel light. Is arranged so as to reflect in a first direction intersecting the traveling direction of the parallel light and transmit the second polarized component of the parallel light in the traveling direction of the parallel light, and the first beam splitter is arranged in the first direction. It is arranged so as to reflect the first polarization component from the polarization beam splitter in the second direction intersecting, and the first polarization component is converged on the sample surface through the quarter wavelength plate and the objective lens. As described above, the quarter-wave plate and the objective Lens is disposed, the defocus detection device reflects from the sample surface, passes through the objective lens and the quarter-wave plate, and is reflected by the first beam splitter. Is arranged to receive a second polarization component of the reflected light transmitted through the second beam splitter, and the second beam splitter is arranged to reflect a second polarization component of the reflected light transmitted through the first beam splitter. The third beam splitter reflects the second polarization component of the parallel light transmitted through the polarization beam splitter and transmits the second polarization component of the reflected light reflected from the second beam splitter. The interference fringe detection device is provided with a second polarization component of the reflected light from the second beam splitter and a second polarization component of the parallel light transmitted through the polarization beam splitter. Interference fringes are arranged to detect, and the data processing apparatus is connected to said focus deviation detecting system and the interference fringe detector,
A sample displacement measuring device, characterized in that the focus shift is evaluated by the intensity change to obtain an absolute value of the shift of the sample surface. 4. An eyepiece lens for observing a sample is further provided, wherein the eyepiece lens transmits a second polarization component of the reflected light which is transmitted through the first beam splitter and is transmitted through the second beam splitter. The sample displacement measuring optical device according to claim 3, wherein the optical device is arranged so as to pass therethrough.