JPS62197706A - Interferometer for surface-shape measurement - Google Patents

Abstract

PURPOSE:To enable high-accuracy measurements constantly of various specimen surfaces with the optimum shear value, by constructing a means of dividing a reflecting wave front from a specimen into wave fronts in the polarization direction intersecting each other through a right angle with a plurality of optical elements available for change of relative position. CONSTITUTION:Wollaston prisms 21, 22 are so located that a distance 'alpha'between them may be changed between 1/4-wave-length board 6 and polarized- beam splitter 8. The prisms 21, 22 are formed by contacting 2 right-angle prisms crystal-angles of them being intersected through a right angle and the prism 22 is so installed that is rotated relative to the prism 21 around the axis perpen dicular to the surface of this sheet through an angle of 180 deg.. And, when a reflected light flux from a specimen surface 5 is eradiated into the prism 21, it is divided into 2 fluxes provided with a constant divergent angle and conse quently, the optimum shear-value can be obtained by changing the distance (alpha) through relative displacement of the prism 21, 22 corresponding to the shape of the surface of the specimen surface 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an interferometer for surface shape measurement used to measure the surface shape of an aspherical lens or the like.

[Conventional technology]

As a conventional interferometer for surface shape measurement, JP-A-59-154
There is a fringe scanning jarring interferometer disclosed in Japanese Patent No. 309. FIG. 9 shows the configuration of this fringe scanning type Jarring interferometer, in which polarized light from polarized light 'rA1 passes through a polarized beam splinter 2, passes through a 174-wave plate 3, and is directed onto a surface to be measured 5 by a condenser lens 4. irradiated. The reflected light from the test surface 5 passes through the 174-wavelength plate 3 again so that its polarization direction is rotated by 90 degrees with respect to the incident light, and is reflected by the polarizing beam splinter 2.

This reflected light passes through a 174-wavelength plate 6, becomes circularly polarized light, and then enters a sharp prism 7.

For example, as shown in FIG. 10, the shaprism 7 includes two crystals 7a such as quartz crystals having different crystal axes indicated by double-headed arrows,
7b is used, and this separates the incident light into two polarized lights with mutually orthogonal polarization directions, which are parallel to each other by a distance determined by the thickness L of the first crystal 7a. .

The two polarized lights shattered by the polarizing prism 7 enter the polarizing beam splitter 8, and one of the polarized lights is reflected by the polarizing beam splitter 8, passes through the 174-wave plate 9, and is totally reflected iJ.
'! 10, where it is totally reflected and then transmitted again through the 174-wavelength plate 9, the polarization direction of which is rotated by 90 degrees with respect to the incident light, and transmitted through the polarization beam splitter 8.

In addition, the other polarized light passes through the polarizing beam splitter 8,
After passing through the 174-wavelength plate 11, the light is reflected by the total reflection mirror 12, and each time it passes through the 174-wavelength plate 11, the polarization direction is rotated by 90 degrees relative to the incident light, reflected by the polarization beam splitter 8, and from the total reflection mirror 10. is superimposed with the reflected light of This superimposed light beam is made into circularly polarized light by the 174-wavelength Fi, 13, and then forms interference fringes on the image sensor 14.

Further, the total reflection 8112 is driven by a control device (not shown) via the piezo element 15, so that the total reflection mirror 10
Then, an optical path difference is given to the wavefront reflected by the total reflection mirror 12 to perform fringe scanning.

This interferometer for surface shape measurement has the advantage that the reference beam and the object beam share almost the same optical path, so the system is stable, and a prototype serving as a reference is not required.

Furthermore, since polarized light is used, it has the advantage of having a degree of freedom in design, such as being able to place the stripe scanning section immediately after the polarized light source.

[Problems to be Solved by the Invention] However, in the interferometer for surface shape measurement shown in FIG. 9, since the shear amount by the Japrism 7 is fixed, it is difficult to measure surfaces of various shapes. Another problem is that the range of the optimum amount of interference is exceeded and the number of interference fringes on the image sensor 14 is too large, leading to a decrease in accuracy, which limits the range of the surface to be measured that can be measured. There is.

The present invention was made by focusing on these conventional problems, and provides an interferometer for surface shape measurement that is appropriately configured so that various test surfaces can always be measured with an optimal shear amount and with high precision. The purpose is to

Means and operation for solving problem C] In order to achieve the above object, in the present invention, in a surface shape measuring interferometer consisting of a fringe scanning jarring interferometer, the reflected or transmitted wavefronts from the test surface are mutually The means for separating the wavefront into two wavefronts having orthogonal polarization directions is constituted by a plurality of optical elements whose relative positions are variable so that an arbitrary amount of shear can be obtained.

〔Example〕

FIG. 1 shows a first embodiment of the invention. In this embodiment, in the interferometer for surface shape measurement shown in FIG. 9, the wavefront separation means for separating the reflected wavefront from the test surface 5 into wavefronts with polarization directions orthogonal to each other is implemented using two Wollaston prisms 21 and 22. The other configuration is the same as that shown in FIG. 9. The Wollaston prisms 21 and 22 are arranged between the 1/4 wavelength plate 6 and the polarizing beam splinter 8 so that the distance d between them can be varied. These Wollaston prisms 21 and 22 have crystal axes (
Wollaston prism 2
2 is arranged so as to be rotated by 180' around the optical axis with respect to the Wollaston prism 21.

In this way, if the two Wollaston prisms 21 and 22 are used, the light beam incident on the Wollaston prism 21 will be separated into two light beams with different polarization and a constant divergence angle, so that the An optimum shear amount can be obtained by relatively moving the Wollaston prisms 21 and 22 and changing the distance d between them depending on the surface shape.

FIGS. 3A, B and C show the main parts of a second embodiment of the invention. In this embodiment, four Wollaston prisms 25, 26, 27, and 28 are used to make the shear amount variable. Wollaston Prism 25, 2
The Wollaston prisms 27 and 28 are arranged in the same manner as in the first embodiment, and the Wollaston prisms 25 and 28 are arranged so that they function in the opposite way to the Wollaston prisms 25 and 26.
6 and rotated by 180'' around the optical axis.

In this embodiment, the Wollaston prisms 26 and 27 are movable together in the optical axis direction, and the distance d1 between the Wollaston prisms 25 and 26 and the distance d between the Wollaston prisms 27 and 28 are made variable.

In this way, as shown in FIG. 3A, dl・d2
When , the incident light flux is Wollaston prism 1.25°26
A predetermined amount of shear is given by this, and the state is returned to the amount of shear of 0 by the Wollaston prisms 27 and 28.

Further, as shown in FIG. 3B, if d2<dl, a difference occurs between the amount of shear provided by the Wollaston prisms 25 and 26 and the amount of return provided by the Wollaston prisms 27 and 28. Therefore, the optimum shear amount can be obtained by appropriately setting d, , d, depending on the surface to be inspected so that d2<d. Furthermore, as shown in Figure 3C,
If dl<dz, it is also possible to provide a shear amount in the opposite direction.

FIG. 4 shows the main part of a third embodiment of the invention. In this embodiment, Wollaston prisms 26 and 27 are joined together in the second embodiment. therefore,
In this embodiment, as in the second embodiment, a desired amount of shear can be obtained by moving the Wollaston prisms 26 and 27 in the optical axis direction.

As described above, according to the second and third embodiments, the amount of shear can be changed from 0 to any value by simply moving the Wollaston prisms 26 and 27 together in the optical axis direction, and thereby the amount of shear can be changed from 0 to any value. The optimum amount of shear can be obtained according to the inspection surface.

For example, the actual amount of shear in aspheric surface measurement is 10μ.
m ~ 1 dragon size, and Wollaston prism 21
, 22, and 25 to 28 are approximately 1 to 21, respectively, but in the first to third embodiments, these are exaggerated.

FIGS. 5A and 5B show essential parts of a fourth embodiment of the invention. In this embodiment, the amount of shear is made variable using four wedge-shaped Savard plates 31 to 34, and the double-headed arrow in the crystal constituting each Savard plate indicates the direction of the crystal axis. These Savard plates 31 to 34 are 1/1 in FIG.
disposed between the four-wavelength plate 6 and the polarizing beam splitter 8,
The Savard plate 32 is rotated 1806 degrees around the optical axis with respect to the Savard plate 31, and the Savard plate 33 is
34, the Savart plates 31 and 32 are arranged 180 degrees around the optical axis.
°Arrange as if rotated.

In this embodiment, the Savart plates 32 and 33 are movable in opposite directions in a direction orthogonal to the optical axis. In this way, as shown in FIG. 5A, the Savard plate 3
1, the amount given by 32 to the Savard plate 33
, 34 can be returned to zero, or as shown in FIG. 5B, the Savard plates 32, 33
A desired amount of shear can be obtained by moving the two in opposite directions.

According to this embodiment, each optical path between the Savard plates of the two polarized lights becomes parallel to the optical axis, so the movement of each Savard plate in the optical axis direction becomes irrelevant to the amount of shear. therefore,
When moving the Savart plates 32 and 33, restrictions on the degree of perpendicularity to the optical axis and the amount of movement in the optical axis direction can be significantly relaxed.

In each of the above-mentioned embodiments, the means for driving the Wollaston prism and the Savart plate include a linear motor,
Known driving means using piezoelectric elements, voice coils, etc. can be used.

FIG. 6 shows the main part of a fifth embodiment of the present invention. This embodiment consists of four parallel flat plates 41 that do not exhibit birefringence.
.about.44 and one π/2[1-take 45 to make the depth variable. Parallel plates 42 and 44
are fixedly arranged so as to be parallel to each other, and the parallel plates 41 and 43 are rotatable together on the back side of the parallel plate 42 and on the front side of the parallel plate 44 while maintaining parallel to each other with an axis perpendicular to the plane of the paper. A π/20-theta 45 is fixedly placed between the parallel plates 42 and 43. Further, the back surfaces of the parallel plates 42 and 43 are coated with polarizing films 46 and 47 that transmit P-polarized light and reflect S-polarized light, and their surfaces and π/20-take 4
The front and back surfaces of the parallel plates 41 and 44 are each coated with an antireflection film, and the surfaces of the parallel plates 41 and 44 are coated with a reflective film.

In the above configuration, when the four parallel plates 41 to 44 are parallel to each other and the light beam 48 from 174 wavelengths i6 shown in FIG. is reflected by the polarizing film 46, and the P-polarized component is transmitted. The reflected S-polarized light is converted to P-polarized light by the π/20-theta 45, passes through the polarizing film 47 of the parallel plate 43, is reflected on the surface of the parallel plate 44, and then returns to the parallel plate 4.
The light beam passes through the polarizing film 47 of No. 3 and becomes an output light beam 49. Similarly, P polarized light transmitted through the polarizing film 46 of the parallel flat plate 42 is reflected on the surface of the parallel flat plate 41, passes through the polarizing film 46 of the parallel flat plate 42 again, and is converted into S polarized light by π/20-theta 45. After that, it is reflected by the polarizing film 47 of the parallel plate 43 and becomes an output light beam 50.

Here, if the parallel plates 41 and 43 are integrally rotated minutely in the plane of the paper while keeping parallel plates 41 and 43 parallel to each other, the output beam 49 of P-polarized light reflected by the parallel plate 44 will hardly be affected, but P-polarized light transmitted through the polarizing film 46 of the parallel flat plate 42 and reflected by the parallel flat plate 41, that is, the polarizing film 47 of the parallel flat plate 43
The S-polarized outgoing light beam 50 reflected by the S-polarized light beam 50 becomes a light beam that is laterally shifted in parallel to the P-polarized outgoing light beam 49. Therefore, by adjusting the rotation angles of the parallel plates 41 and 43, an arbitrary shear amount can be obtained.

In the fifth embodiment shown in FIG. 6, a pair of parallel flats +f
By rotating the f141 and 43 within the plane of the paper, a light beam shifted laterally within the plane of the paper was obtained. However, in the sixth embodiment of the present invention, as shown in FIG. 7, the parallel plates 41 and 43 are By tilting from within the vertical plane perpendicular to the plane of the paper, a luminous flux that is shunted in the vertical direction is obtained. In addition, FIG. 7 is a drawing of the arrangement of FIG. 6 viewed from diagonally above the plane of the paper.

In this way, if the parallel plates 41 and 43 are tilted from the vertical line, the light will be reflected by the parallel plate 41, and the parallel plate 43 will be reflected.
The light beam reflected by the polarizing film 47 changes from a light beam 51 shown by a two-dot chain line to a light beam 52 that is shunted in the vertical direction as shown by a one-dot chain line. Therefore, by adjusting the inclination angles of the parallel plates 41 and 43, an arbitrary shear amount can be obtained in the vertical direction.

FIG. 8 shows the main part of a seventh embodiment of the present invention. In this embodiment, the light beam 61 from the 174-wavelength plate 6 shown in FIG.
and S-polarized components. The S-polarized component reflected by this polarizing beam splitter 62 is π/20−theta 6
After converting the light into P-polarized light in step 3, the light is incident on a polarizing beam splitter 66 through a reflecting mirror 64 and a variable focus lens 65, transmitted through the polarizing beam splitter 66, and incident on a polarizing beam splitter 8 shown in FIG. Furthermore, the P polarized light component transmitted through the polarizing beam splitter 62 is π72
After converting into S-polarized light at 0-te 67, reflection mirror 68
The light is then incident on a polarizing beam splitter 66 through a variable focus lens 69, reflected by the polarizing beam splitter 66, and incident on a polarizing beam splitter 8 shown in FIG.

In this embodiment, the focal points of the variable focus lenses 65 and 69 are slightly changed from one another. In this way, two wavefronts with different radii of curvature, so-called radial waves, are obtained. Therefore, by appropriately adjusting the focus of the variable focus lenses 65 and 69, an arbitrary amount of radial force can be obtained. Note that a zoom lens, a liquid crystal lens, or the like can be used as the variable focus lenses 65 and 69.

According to the 5.6 and 7th embodiments, since no expensive birefringent element is used, they are advantageous in that they can be made cheaper than in the 1st to 4th embodiments, and also can be easily constructed with a large diameter.

Note that this invention is not limited only to the embodiments described above, and numerous modifications and changes are possible. For example, in the second embodiment, the Wollaston prism 26
, 27 are moved together in the optical axis direction without changing the distance between them, but it is possible to move only one of them,
Alternatively, the same effect can be obtained by moving only the Wollaston prism 25 or 28 in the optical axis direction.

Further, in the fourth embodiment, the Savard plates 32 and 33
However, the four Savard plates 31-3
Similarly, a variable shear amount can be obtained by moving only one of the four Savart plates or by moving any plurality of Savart plates. Furthermore, it is also possible to omit the Savart plates 31, 32, or 33, 34, and to change the relative positions of the two Nahar plates with respect to the optical axis, thereby obtaining a variable shear amount. Furthermore, in the fifth and sixth embodiments, the parallel plate 41
, 43 are turned and tilted, but even if one or both of the parallel plates 41 and 43 are moved in parallel to change the mutual spacing, the In figure 7, parallel plate /11.

Similarly, a variable shear amount can be obtained by moving one or both of them so as to change the interval while maintaining mutual parallelism while tilting the shafts 43. Also, the fifth
In the sixth embodiment, the parallel plates 42 and 44 were fixed and the parallel plates 41 and 43 were displaced.
Conversely, the parallel plates 41 and 43 are fixed, and the parallel plate 42
, 44 may be displaced. Furthermore, the shear amount can be configured to be set manually to a desired shear amount, or it can be configured to automatically set the optimal shear amount by inputting the design value of the surface to be inspected. You can also do it. Further, in each of the above-described embodiments, fringe scanning jarring interference measurements are performed on the reflected wavefront from the test surface, but exactly the same measurement can be performed on the transmitted wavefront of the test optical system.

〔Effect of the invention〕

According to this invention, an arbitrary shear amount can be obtained in an interferometer that measures surface shapes by performing fringe scanning jarring interference measurement, so that the shapes of various test surfaces can always be accurately measured with the optimum shear amount. It can be measured by

[Brief explanation of drawings]

FIG. 1 is a diagram showing a first embodiment of this invention, FIG. 2 is a partially enlarged view thereof, FIG. 3 A, B, and C are diagrams showing main parts of a second embodiment of this invention, FIG. 4 is a diagram similarly showing the main part of the third embodiment, FIGS. 5A and 5B are diagrams similarly showing the main part of the fourth embodiment, FIG. This figure is a perspective view showing the main part of the sixth embodiment, FIG. 8 is a perspective view showing the main part of the seventh embodiment, and FIGS. 9 and 10 are diagrams showing the conventional technology. 1...Polarized light source 2.8...Polarized beam brick 3, 6.9.11.13...174 wavelength plate 4...Condensing lens 5...Test surface 10, 12... Total reflection mirror 14...Imaging element 15...Piezo element 21, 22.25-28...Wollaston prism 3
1-34...Savart plate 41-44...Parallel plate 45...π/20-theta 46.47...Polarizing film 62, 66...Polarizing beam splinter 63, 67
...π/20-theta 64, 68...Reflecting mirror 65.69...Variable focus lens Patent Applicant: Olympus Optical Industry Co., Ltd. Representative Patent Attorney Akatsuki Sugimura 6th Patent Attorney: Ko Mura Figure 4 Figure 5 Figure 6 Leap Figure 7 Figure 9 Figure 1O Figure tL Ding Continued Sleeve iL tjF 198616
March 24th, Director General of the Japan Patent Office, Michibe Uga, 1, Indication of the case, Patent Application No. 39001 of 1988, 2, Name of the invention, Interferometer for surface shape measurement 3, Person making the amendment, Relationship with the case, Patent applicant (OA7 ) Olympus Optical Industry Co., Ltd. 4, Agent 5, Subject of amendment [Detailed Description of the Invention 4]
', 'r j-, t, -': N-之-1-f゛. Poppy... 6. Contents of the amendment (attached paper introduction), 1: Yu 75. . , 1. "Around the optical axis" on page 5, line 16 of the specification.
Correct it to "around an axis perpendicular to the plane of the paper." 2. On page 7, line 15, "-" is corrected to "integrated." 3. Correct “S-polarized” to “S-polarized” on page 11, line 8.

Claims (1)

[Claims] 1. Separating the reflected or transmitted wavefront from the test surface into two wavefronts with polarization directions perpendicular to each other by a wavefront separation means,
In a surface shape measuring interferometer that measures the shape of a surface to be measured by interfering these wavefronts while giving an optical path difference and scanning the interference fringes, the wavefront separation means includes:
1. An interferometer for surface shape measurement, characterized in that it is constructed with a plurality of optical elements whose relative positions are variable so that an arbitrary shear amount can be obtained.