JPH01259208A - Optical surface shape measuring instrument - Google Patents

Abstract

PURPOSE:To measure the fine displacement of the surface of a body to be measured at plural measurement positions at the same time by passing laser luminous flux through a unidirectional optical element and an objective, reflecting it by a body to be measured, and guiding the luminous flux to a divided photodetector through an optical means for defocusing detection. CONSTITUTION:The luminous flux emitted by a laser light source 10 is passed through the unidirectional optical element 11 and objective 12 and then converged on the surface of the body 13 to be measured. Return light which is reflected by the body 13 to be measured is passed through the optical means 14 for defocusing detection and then reaches the divided photodetector 16. Here, when the return light which is reflected at a point A is considered as to image formation 17 on the body 13 to be measured, the return light from the point A reaches a photodetection part 16A'. The fine displacement or surface roughness at the point A of the body 13 to be measured can be measured from the output signal of the detection part 16A through the operation of the optical means 14 for defocusing detection. Similarly, the surface shapes at points B, C - are measured by detection parts 16B', 16C' - corresponding to other points B, C - of the body 13 to be measured.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface shape measuring device that optically measures minute displacements and surface roughness of an object to be measured.

[Conventional technology]

An example of an optical surface shape measuring device using a laser beam is disclosed in Japanese Patent Application Laid-open No. 7246/1983.

FIG. 5 is a diagram showing the configuration of a conventional optical surface profile measuring device using such a method. In the figure, 1 is a laser light source, 2 is a collimator lens, and 3 is a polarizing prism. It is arranged in a direction such that the incident light from 1 becomes P-polarized light. Further, 4 is a 174 wavelength plate, 5 is an objective lens, 6 is a reflective object to be measured, and 7 is a critical angle prism. Incidentally, the reflecting surface 7C of the critical angle prism 7 is set to form a nearly critical angle with respect to the optical axis C of the reflected light from the reflecting object 6. 8 is a split light receiving sensor, and as shown in FIG. 6, a light receiving surface 8A is divided into two by a dividing line 8C.

It consists of 8B. This dividing line 8C is perpendicular to the plane of incidence including the normal to the reflecting surface 7C of the critical angle prism 7 and the optical axis C of the reflected light, and intersects with the optical axis C.

In the above-described configuration, the laser light emitted from the laser light source 1 is converted into a parallel light beam by the collimator lens 2, and enters the polarizing prism 3 as P-polarized light. The laser light incident on the polarizing prism 3 passes through the polarizing prism 3 and is guided to the next 174-wavelength plate 4. The laser light incident on the 174-wavelength plate 4 is converted into a circularly polarized light beam, and then focused on the surface of the reflective object 6 via the objective lens 5 . The laser beam reflected by the reflective object 6 becomes reflected light, passes through the objective lens 5 and 1/4 wavelength plate 4 again through the same optical path, becomes S-polarized light, and enters the polarizing prism 3. The reflected light from the reflective object 6 that is incident on the polarizing prism 3 is reflected and guided to the critical angle prism 7, reflected by the reflective surface 7C, and incident on the divided light receiving sensor 8, where the amount of light is detected.

Next, the principle of surface shape measurement using the above device will be explained. Consider the case where the surface of the reflective object 6 is located at the focal point of the objective lens (indicated by the solid line in FIG. 5). At this time, the reflected light reflected by the object to be measured 6 (hereinafter referred to as reflected light) is converted into parallel light by the objective lens 5, so that the incident angles of the reflected light at the reflective surface 7C of the critical angle prism 7 are all equal.

As a result, the amount of reflected light received by the split light receiving sensor 8 becomes uniform over the entire surface. Next, the surface of the reflective object 6 was displaced from the focal point position of the objective lens 5 in the direction of arrow X (broken line 6 in Figure 5).
Consider the case (denoted by ′). At this time, the reflected light becomes diverging light M after passing through the objective lens 5. As a result, if we focus on the light beam incident on the reflective surface 7C of the critical angle prism 7 in FIG. As the angle of incidence becomes smaller, the reflectance decreases. On the other hand, when focusing on the right half of the light beam R with respect to the optical axis C, each ray of this light beam has a large incident angle, so the reflectance increases. Due to this effect, the amount of reflected light incident on the divided light receiving sensor 8 becomes non-uniform. That is, the amount of light received by the light receiving surface 8A decreases.

Next, consider a case where the surface of the offending object 6 is displaced in the direction opposite to the direction of the arrow X (indicated by the broken line 6'' in FIG.
The relationship of the incident angle to the reflective surface 7C of the critical angle prism 7 is opposite to that for the diverging light, and the amount of light received by the light receiving surface 8B decreases this time. Therefore, by detecting the output difference between the light-receiving surfaces 8A and 8B of the split light-receiving sensor 8 using a differential amplifier (not shown), the relative positional relationship between the reflective object surface and the objective lens focus is determined. It measured minute displacements and surface roughness.

[Problems to be Solved by the Invention] The above-mentioned surface shape measuring device has the following drawbacks when two-dimensionally measuring the surface of an object. In other words, two-dimensional measurement using the above-mentioned conventional device requires repeating scanning by moving a minute circular spot linearly on the object surface many times while changing its position, which takes time. This has the drawback that the driving device is complicated and the cost is high.

An object of the present invention is to provide a surface profile measuring device that eliminates the above-mentioned drawbacks.

[Means and operations for solving the problems] FIG. 1 is a conceptual diagram for explaining the present invention. In FIG. 1(a), 10 is a light source, 11 is a unidirectional optical element such as a concave cylindrical lens, 12 is an objective lens, and 13 is an object whose surface shape is to be measured. Part 1) is a surface measurement diagram of FIG. 1(a) 6 14 in FIG. 1(C) is an optical means for detecting defocus that changes according to the change in shape of the object surface; 16
is a split photodetector.

Next, the effect will be explained. The laser beam emitted from the laser beam 'a10 passes through a unidirectional optical element 11 and an objective lens 12, and then is focused on the surface of the object to be measured 13. Here, the laser beam produces astigmatism due to the action of the unidirectional optical element 11, and forms a line image 17 on the object to be measured 13 as shown in FIG. 1(d). The direction of this line image is the y-axis, and the direction perpendicular to this is the y-axis.

The returned light reflected by the object to be measured 13 passes through the defocus detection optical means 14 and then reaches the split photodetector 16 .

The state of light condensation on the split photodetector 16 is shown in the enlarged view of FIG. 1(e). The divided photodetector 16 forms detecting sections 16A', 16B'- in which one unit is a collection of elements divided into at least two parts in the y-axis direction. These detection units 16A', 16B'- are composed of at least two pieces and are arranged along the X-axis direction which is the line segment direction of the line image 17.

Here, if we focus on the return light reflected at the position of point A in the line image 17 on the object to be measured 13 in FIG. 1(d), the return light at point A is The part 16A' is reached.

Therefore, by the action of the defocus detection optical means 14, the minute displacement or surface roughness of the point A on the object to be measured 13 can be measured from the output signal of the detection section 16A'.

Similarly, the detection unit 1 corresponding to other points B, C-.
6B', 16C'- allows the surface shape at points B and C- to be measured.

As described above, the present invention is capable of simultaneously measuring the surface shape of a plurality of positions on the object to be measured in the line image direction.

The surface profile measuring device of the present invention includes a light source, an objective lens that focuses a light beam from the light source onto the object to be measured, and an object lens disposed between the light source and the object to be measured. a unidirectional optical element that forms a line image thereon; a defocus detection optical means that detects the distance between the objective lens and the object to be measured as a defocus by light reflected from the object to be measured; The present invention is characterized by comprising a divided light detection means having at least two detection sections each of which detects the light that has passed through the defocus detection optical means.

(Example〕 An embodiment of the present invention will be described below based on the drawings.

FIG. 2 shows a first embodiment of the present invention. 2 in Figure 2(a)
0 is a laser light source, 21 is a collimator lens, 22 is a concave cylindrical lens which is a unidirectional optical element, 23 is a polarizing prism, 24 is a 174 wavelength plate, 25 is an objective lens, 26 is an object to be measured, and 27 is a critical angle prism , 28 is a cylindrical condenser lens, and 29 is a split photodetector.

Next, the operation of the first embodiment will be explained.

A laser beam emitted from a laser light source 20 is converted into a parallel beam by a collimator lens 21 and enters a concave cylindrical lens 22 . The cylindrical lens 22 has a lens effect in only one direction, and the light diverges in a direction perpendicular to the plane of the paper, but emits as a parallel beam in a direction parallel to the plane of the paper. Cylindrical lens 2
2 enters the polarizing prism 23 as P-polarized light, and after passing through the polarizing prism 23, it passes through the 174-wavelength plate 24 and becomes circularly polarized light.
The light is focused on 6.

At this time, the object to be measured 26 is placed near the focal position of the objective lens 25, so the light beam that has been subjected to astigmatism by the cylindrical lens 22 forms an image on the object to be measured 26 in a direction parallel to the plane of the paper. No image is formed on a plane perpendicular to the plane of the paper. As a result, measured II! The laser beam is focused on 126 in a linear state along the direction perpendicular to the plane of the paper. FIG. 2(b) shows a line image 30 on the object 26 to be measured. The longitudinal direction of this line image 30 is defined as the X-axis direction, and the direction orthogonal thereto is defined as the y-axis direction.

The return light reflected on the object to be measured 26 is returned to the objective lens 25.
The light passes through the 174 wavelength plate 24 and enters the polarizing prism 23. Since the light beam emitted from the 174-wave plate 24 is S-polarized, the light beam incident on the polarizing prism 23 is reflected by the polarizing prism 23 and enters the critical angle prism 27. The reflective surface 27G of the critical angle prism 27 is set at approximately a critical angle with respect to the optical axis C of the return light reflected by the object to be measured 26. The plane of incidence including the normal line of the reflective surface 27C and the optical axis C is the direction in which the cylindrical lens 22 does not have any lens action. The returned light reflected by the reflective surface 27C of the critical angle prism 270 is focused by the cylindrical condenser lens 28 only in the same direction as the lens action of the cylindrical lens 22, and is detected by the split photodetector 29.

The split photodetector 29 has a configuration similar to that shown in FIG. 1(e).

As shown in FIG. 2(C), the photodetecting elements 29AI' and 29At' divided into two in the y-axis direction constitute 11Jl and constitute one unit of the detecting section 29A'. Detection units 29B', 29C'-...- similarly have the same configuration.
are arranged along the y-axis direction.

Here, attention is paid to the reflected light reflected at the point 30A of the line image 30 on the object to be measured 26 in FIG. 2(b). This reflected light is imaged by the cylindrical condensing lens 28 in the X-axis direction and condensed onto the detection section 29A'.

This cylindrical lens 28 has the following functions.

Even if the reflection at point 30A is diffuse reflection, at least in the X-axis direction, it is imaged onto the split photodetector 29 on the object to be measured by the condenser lens 28 which has a condensing effect in the - direction. Therefore, the return light reflected at the point 30A is always incident on the detection section 29A'.

Here, consider a case where the surface of the object to be measured 26 is located at the focal plane of the objective lens 25. At this time, the reflected light from the object to be measured 26 becomes a parallel beam of light in the X-axis direction after passing through the objective lens 25, but becomes diverging light in the X-axis direction. Now considering the reflected light at point 30A of line image 30 on object to be measured 26, point 30
When A is within the mole plane of the objective lens 25, the objective lens 2
All of the output rays of No. 5 are parallel in the y-axis direction. Therefore, due to the action of the critical angle prism 27 explained in FIG. 5, the output values of the photodetecting elements 29A+' and 29A2' of the detecting section 298' to which the reflected light of the point 30A is irradiated are equal, and the output signal difference becomes zero. .

Next, consider a case where the surface of the object to be measured 26 approaches the objective lens 26 (indicated by a broken line 26' in FIG. 2(a)). At this time, the reflected light emitted from the objective lens 25 becomes diverging light in the y-axis direction. Therefore, the critical angle prism 27 mentioned above
Due to this effect, the amount of light at the photodetecting element 29AI' becomes small.

Next, when the surface of the object to be measured 26 moves away from the objective lens 26 (indicated by the broken line 26'' in FIG. 2(a)), the light emitted from the objective lens 25 becomes convergent light in the y-axis direction, and this time the light is detected. The amount of light at the element 29A2' becomes small.

By comparing the output values of the photodetecting elements 29AI' and 29A2' in this manner, minute displacement and surface roughness at the point 30A on the object to be measured 26 can be measured.

Points 30B, 30C- other than point 30A of line image 30
Likewise, the corresponding detection units 29B'.

The same measurements as above are carried out with 29C=-1.

In the above embodiment, the linear direction (X-axis direction) in the line image 30
The surface shape of each point can be measured simultaneously.

FIG. 3 shows a second embodiment of the invention.

The difference from the configuration of the first embodiment shown in FIG. 2 is that a light shielding plate 41 is provided instead of the critical angle prism 27.

In comparison with FIG. 2, the same reference numerals indicate the same configurations.

The reflected light of the line image 30 on the object to be measured 26 is made into a parallel light beam by the objective lens 25 and then focused onto the split photodetector 29 by the condenser lens 40 . The structure of this split photodetector 29 is almost the same as that explained in FIG. 2(C) of the first embodiment. The light shielding plate 41 is arranged in the optical path between the condenser lens 40 and the split photodetector 29 so that one side of the light shielding plate is in contact with the optical axis C.

Next, the operation of the second embodiment will be explained. Now, consider a case where the upper surface of the object to be measured 26 is within the mole plane of the objective lens 25. At this time, the line image 30 on the object to be measured 26 is focused by the condenser lens 40 onto the divided photodetector 29 as shown in FIG. 3(C). At this time, one point 30A of the line image 30 is connected to the photodetecting element 2 of the divided photodetector 29, as described in the first embodiment.
The image is formed so that the sight is equally incident on each of 9AI' and 29A2'. Photodetector element 29A+ at this time
FIG. 4(a) shows the incident state of the reflected light from the point 30A which is incident on ', 29At'. Therefore, when the difference between the output signals of the photodetecting elements 29A+' and 29A2' is detected, it becomes zero.

Next, the upper surface of the object to be measured 26 is located at the objective lens 2 from the focal plane position.
Let us consider the case where the position approaches 5 and is displaced to the position 26'.

At this time, the luminous flux emitted from the condenser lens 40 is shown in FIG.
) is in a divergent state compared to Therefore, point 30 of line image 30
Focusing on the reflected light A, due to the effect of the light shielding plate 41, the amount of light incident on the photodetecting elements 29A,' is larger than the amount of light incident on the photodetecting element 29A2', as shown in FIG. 4(b).

Conversely, when the upper surface of the object to be measured 26 is displaced to a position away from the objective lens 25 (indicated by the broken line 26'' in FIG. 3(a))
think of. Similar to the above, when focusing on the reflected light from the point 30A, the light flux emitted from the condenser lens 40 is in a convergent state compared to the case shown in FIG. 4(a). Therefore, due to the action of the light shielding plate 41, the amount of reflected light at the point 30A reaches the photodetecting element 29Az', as shown in FIG. 4(C).

By comparing the output values of the photodetecting elements 29AI' and 29tt' as described above, minute displacement or surface roughness at the point 30A of the line image 30 can be detected.

Similarly, for other points 30B, 30C, . . . - of the line image 30, the surface shape of each point is the detection portion (29B+').

2982'), (29CI', 29Cz')
-1--- simultaneously detected.

As described above, by disposing the light shielding plate 41 in place of the critical angle prism 27 of the first embodiment, the surface shape of each point of the line image 30 can be measured simultaneously as in the first embodiment.

In the case of this second embodiment, the light shielding plate 41 is the critical angle prism 2.
It has the advantage of being lower in price than 7.

In addition, in Embodiment 1.2, examples were shown using the critical angle method and the Naifezi method using a critical angle prism and a light shielding plate, respectively, as optical means for detecting defocus, but the present invention is limited to these two methods. It's not a thing. For example, the Foucault method
Auxiliary beam method etc. can also be used.

Further, in the above two embodiments, a concave cylindrical lens was used to form a line image on the object to be measured, but the present invention is not limited to such a lens; for example, a convex cylindrical lens may also be used. good.

〔Effect of the invention〕

The present invention has the advantage that minute displacements and surface roughness on the surface of an object to be measured can be simultaneously measured at a plurality of measurement positions distributed one-dimensionally in a certain arbitrary direction, and the measurement time is quick.

Furthermore, even when measuring the surface of a workpiece two-dimensionally, it is only necessary to scan the workpiece and the measuring device one-dimensionally by about 6 times relative to each other (compared to conventional two-dimensional scanning systems). This has the advantage that the drive device is extremely simple and can be realized at low cost.

[Brief explanation of the drawing]

Fig. 1 is a conceptual diagram for explaining the present invention, Fig. 2 is a diagram showing the first embodiment of the invention, Fig. 3.4 is a diagram showing the second embodiment of the invention, Fig. 5.6 The figure is a diagram showing a conventional technique. 10------1・--・--1------------
Light source 1, 20----------1.-Laser light source 11-----------------
--Unidirectional element 22--・--------------
...Concave cylindrical lens 3, 23----1--
・・Polarizing prism 4, 24−−−−−−−−−−・
1/4 wavelength plate 5, 12.25-Objective lens 6, 13.26-Object to be measured 14--------------Optical means for detecting defocus 7, 27 −−・−１−−−−−・・−・
Critical angle prism 28--
−−−−−−−・Cylindrical condensing lens 16, 29−・・
−・−111−−−・Divided photodetector 41−・・−・−−
−−−−−1−−−−・・・−Shading plate 171^ 2− Name of the optical surface profile measuring device 3. Person making the correction (voluntary) 5. Correct the width of the column in the "Detailed Description of the Invention" in the specification subject to amendment. (2) Page 11, lines 4-5 “Regarding the X-axis direction...
...because it is imaged" should be corrected as follows. "The line image 30 on the object to be measured is formed on two divided photodetectors in the X-axis direction." ” is corrected.

Claims (1)

[Claims] A light source, an objective lens that focuses a light beam from the light source onto the object to be measured, and an objective lens that is disposed between the light source and the object to be measured and forms a line image on the object to be measured. a directional optical element; a defocus detection optical means for detecting a distance between the objective lens and the object as a defocus using reflected light from the object; and light passing through the defocus detection optical means. 1. An optical surface shape measuring device comprising: divided light detection means having at least two divided detection sections for detecting at least two parts.