JPS62215808A - Interferometer for measuring surface shape - Google Patents

Abstract

PURPOSE:To make it possible to measure the shape of a surface to be inspected of every kind with high accuracy, by providing a lens for equivalently increasing the number of apertures between a condensing lens and the surface to be inspected in a freely detachable manner and also providing a mechanism for centering said lens to the condensing lens. CONSTITUTION:The centering of a lens holder 32 is performed using a reference spherical surface 60 before the lens holder is mounted prior to measuring a surface to be inspected. In this centering, the output of an image pickup element 14 obtained by applying streak scanning to the wave front reflected from the reference spherical surface 60 is analyzed by a streak analytical part 61 and the centering to the condensing lens 4 of the reference spherical surface 60 is automatically performed on the basis of the output information of said analytical part 61 through a drive part 62. Next, the lens holder 32 is mounted on a condensing lens holder 31 and error information showing the shift of centering is obtained with respect to the wave front obtained by the combination with the reference spherical surface 6 in the streak analytical part 61 and, on the basis of this information, required voltage is applied to the height controller 37 of the condensing lens holder 31 and the lateral shift controller 47 of the lens holder 32 through the drive part 62 to automatically perform the centering of the lens 21 with respect to the condensing lens 4.

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. 7 shows the configuration of this fringe-scanning jarring interferometer, in which polarized light from a polarized light source 1 passes through a polarized beam splitter 2, passes through a quarter-wave plate 3, and then passes through a condensing lens 4 onto the surface to be inspected. 5. The reflected light from the test surface 5 passes through the quarter-wave plate 3 again, so that the polarization direction is rotated by 90 degrees with respect to the incident light, and is reflected by the polarizing beam splitter 2. This reflected light is made into circularly polarized light through a quarter-wave plate 6, and then enters a Japrism 7 consisting of a compound refraction element, where it is shunted in parallel into two polarized lights whose polarization directions are orthogonal to each other.

The two polarized lights shunted by the Schille 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 guided to the total reflection mirror 10, where the total polarization is reflected. After being reflected, the light passes through the 1/4 wavelength plate 9 again, so that the polarization direction becomes 90 degrees with respect to the incident light.
The other polarized light is rotated and transmitted through the polarizing beam splitter 8.The other polarized light is transmitted through the polarizing beam splitter 8 and is
It passes through the 4-wavelength plate 11, is reflected by the total reflection mirror 12, and is again 1/
By passing through the four-wavelength plate 11, the polarization direction of the incident light is rotated by 90'', reflected by the polarizing beam splitter 8, and superimposed with the reflected light from the total reflection!!10.

This superimposed light beam is made into circularly polarized light by the quarter-wave plate 13, and then forms interference fringes on the image sensor 14. Further, the total reflection mirror 12 is driven by a control device (not shown) via a 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.

According to this interferometer for surface shape measurement, the optical path of the reference beam and the object beam is almost the same, so the system is stable and there is no need for a prototype as a reference. In addition, since polarized light is used, the design allows the fringe scanning section including the polarized beam splitter 8, quarter wavelength plates 9 and 11, total reflection mirror 10 and piezo element 15 to be placed right in front of the polarized light source. It has the advantage of having a degree of freedom.

[Problem that the invention seeks to solve]

However, with the interferometer for surface shape measurement shown in FIG. 7, there is no problem when the surface to be measured 5 is spherical or has a small amount of aspherical surface, but when the amount of spherical or aspherical surface is large, that is, If the slope of the normal to the surface is large, as shown in FIG. 8, part of the reflected light from the surface to be measured 5 is not focused by the condenser lens 4, resulting in eclipse of the light beam, which reduces measurement accuracy. There is a problem that the amount decreases.

This invention was made with attention to these problems, and it provides an interference method for surface shape measurement that is appropriately configured so that various test surfaces can be measured with high accuracy at all times without causing any vignetting of the light beam. The purpose is to provide a

(Means for Solving the Problems) In order to achieve the above object, the present invention provides an interferometer for surface shape measurement consisting of a fringe scanning jarring interferometer, in which a surface to be measured is illuminated and the surface to be measured is illuminated. A lens that equivalently increases the numerical aperture of the condenser lens is removably provided between the condenser lens that condenses the reflected light flux of To enable centering against the object.

[Effect]

As shown in FIG. 1, a hemispherical lens 21, for example, is arranged between the condenser lens 4 and the surface to be inspected 5 so that its plane side is perpendicular to the optical axis at the focal point F of the condenser lens 4. Then, the incident light beam 22 passes through the focal point F and becomes a fast planar diverging wave that illuminates the surface to be inspected 5 . Here, if the test surface 5 is a spherical surface and is arranged so that its center of curvature coincides with the focal point F, the reflected light beam is again converged at the focal point F, and is guided to the jarring interference part via the condenser lens 4. However, in the case of a surface to be inspected 5 where the slope of the normal to the surface with respect to the incident light beam is large, without the lens 21, the reflected light beam would exceed the numerical aperture of the condenser lens 4 and be eclipsed, as shown by the broken line, resulting in high accuracy. measurement becomes impossible.

In this invention, in order to solve such a problem, the lens 21 is arranged between the condenser lens 4 and the surface to be inspected 5 so as to be centered with respect to the condenser lens 4 using a centering mechanism.
With this configuration, even if the reflected light flux exceeds the numerical aperture of the condenser lens 4, this light flux is refracted by the lens 21 and falls within the range of the numerical aperture of the condenser lens 4, so that the equivalent This means that the numerical aperture of the condenser lens 4 is increased.

The reason why the lens 21 is made detachable is that there are convex and concave surfaces to be tested, and there are cases where it is desired to directly measure a convex surface even if the measurable numerical aperture is low and limited to ajJ.

(Example) FIG. 2 shows an embodiment of the present invention.

In this embodiment, in the interferometer for surface shape measurement shown in FIG.
A hemispherical lens 21 that equivalently increases the numerical aperture of the lens 21 is detachably arranged, and the centering of this lens 21 with respect to the condensing lens 4 is automatically performed. It is similar to the figure.

Therefore, in this embodiment, as shown in FIG. 3, a lens holder 32 that holds the lens 21 is detachably attached to a condensing lens holder 31 that holds the condensing lens 4. , while this lens holder 32 is attached, the lens holder 32 is three-dimensionally displaced with respect to the condensing lens holder 31, and the shift of the lens 21 in the optical axis direction with respect to the condensing lens 4, the inclination with respect to the optical axis, and Corrects lateral deviation and automatically aligns.

As shown in FIG. 4A, a ring-shaped magnet 34 centered on the optical axis is embedded in the lens holder mounting end surface 33 of the condensing lens holder 31, and a ring-shaped magnet 34 centered on the optical axis is also embedded inside the lens holder mounting end surface 33. The reference ring 35 is provided protrudingly divided into three parts in an arc shape along the circumference. A portion of the outer periphery of this reference ring 35 is provided with a protrusion 36 that engages with the fixing ring of the lens holder 32, which will be described later, and is used to attach the °C lens holder 32 in a bayonet manner. Furthermore, as shown in FIG. 4B, a height adjuster 37 made of a piezoelectric element is provided on the mounting end surface 32 of each divided portion of the reference ring 35, and a height adjuster 37 made of a piezoelectric element is provided on each height adjuster 31. A plate 38 is provided.

In this embodiment, the voltage applied to each height adjuster 31 causes the plate 38 to be displaced in the optical axis direction shown by the arrow in an area where it protrudes beyond the reference ring 35 by six or more, thereby causing the lens to move toward the condenser lens 4. 21 in the optical axis direction and inclination.

On the other hand, the lens holder 32 has a condensing lens holder 3
1, as shown in FIG.
The magnet 42 is provided protrudingly divided into three parts in an arc shape centered on the optical axis, and the fixing ring 43 is similarly provided in a protruding manner divided into three parts in an arc shape along the circumference centered on the optical axis inside the magnet 42. . The polarity of the magnet 42 is selected so that it is mutually attracted to the magnet 34 provided on the condenser lens holder 31. In addition, the fixing ring 43 is positioned outside the reference ring 35 with a clearance when the lens holder 32 is attached to the condensing lens holder 31, and a part of the fixing ring 43 has a portion shown in FIG. 5B. Thus, a cutout groove 44 is formed for engaging the projection 36 provided on the reference ring 35 and attaching the lens holder 32 to the condensing lens holder 31 in a bayonet manner.

To attach each divided portion of the fixed ring 43, an arc-shaped variable ring 45 is protruded from the end surface 41 so as to contact the outer periphery of the reference ring 35 with the lens holder 32 attached to the condensing lens holder 31. shall be established. One of these variable rings 45 is biased inward in a direction perpendicular to the optical axis by a coil spring 46, and the other two are biased inward in a direction perpendicular to the optical axis by lateral displacement adjusters 47 each made of a piezoelectric element. Let it be displaced.

The coil spring 46 is inserted between a lid 49 provided on the stator 48 and a movable element 50 slidably provided on the stator 48, and biases the variable ring 45 inwardly via the movable element 50. let The stator 50 is attached to the end face 41 via a holding jig 51, and the movable element 50 has a hole formed in the end face to rotatably hold the steel ball 52.
2 to the outer peripheral surface of the variable ring 45.

Further, the 8 lateral shift adjuster 47 is attached to a holding plate 54 provided on a holding jig 53 fixed to the end face 41, and a plate 55 is attached to the tip of the holding plate 54 as shown in FIG. 5C. A V-hole 56 is formed in the hole 56 to rotatably hold the steel ball 51, and the steel ball 51 is brought into contact with the outer peripheral surface of the variable ring 45 via the plate 55 and the steel ball 57.

Note that the magnet 42, fixed ring 43, and variable ring 45
In this case, when the lens holder 32 is attached to the condensing lens holder 31, the plate 38 at the tip of each height adjuster 37 provided on the condensing lens holder 31 is always in contact with the end surface 41 when the lens holder 32 is attached. make it stand out.

In this embodiment, the lateral deviation of the optical axis of the lens 21 with respect to the condenser lens 4 is adjusted by displacing the eight lateral deviation adjusters 47 in a direction perpendicular to the optical axis by applying a voltage thereto.

Next, a mechanism for automatically centering the lens 21 with the lens holder 32 attached to the condensing lens holder 31 will be described with reference to the block diagram shown in FIG.

First, prior to measuring the surface to be measured and before mounting the lens holder 32, centering is performed using the reference spherical surface 60. This centering is performed by scanning the wavefront reflected from the reference spherical surface 60 and using the output of the imaging probe 14 as a fringe analyzer 61.
Based on the output information, the reference spherical surface 60 is automatically centered with respect to the condenser lens 4 via the drive unit 62.

Next, the lens holder 32 is attached to the condensing lens holder 31, and the fringe analysis unit 61 obtains error information representing misalignment with respect to the wavefront obtained in combination with the reference spherical surface 60.
Based on this, the condenser lens holder 31 is
By applying a required voltage to the height adjuster 37 of the lens holder 37 and the lateral shift adjuster 47 of the lens holder 32, the centering of the lens 21 with respect to the condenser lens 4 is automatically performed.

That is, the lens holder 32 has the protrusion 36 and the notch groove 4.
4 and the attraction action of the magnets 34 and 42, the lens is attached to the condenser lens holder 31. Here, if equal voltage is applied to the three height adjusters 31, the lens holder 32
resists the attractive force of the magnets 34 and 42, and the protrusion 36 is guided by the notch groove 44 and rotates while being displaced in parallel to the optical axis direction. Furthermore, if the voltages applied to the three height adjusters 37 are different, the heights, that is, the amount of protrusion in the optical axis direction will differ, so the lens holder 32 will not tilt with respect to the optical axis of the condenser lens 4. become. Therefore, the height of the three:
By controlling the voltage applied to each of the A nodes 37 based on the error information from the fringe analysis unit 61, it is possible to correct the deviation of the lens 21 in the optical axis direction with respect to the condenser lens 4 and the inclination with respect to the optical axis. .

Furthermore, if the voltages applied to the two lateral shift adjusters 47 are different, the amount of displacement in the direction orthogonal to the optical axis will be different, so the lens holder 32 will be displaced in the direction orthogonal to the optical axis of the condenser lens 4. do. Therefore, by controlling the voltages applied to these two lateral shift adjusters 41 based on the error information from the fringe scanning section 61, the lateral shift of the lens 21 with respect to the optical axis of the condenser lens 4 can be corrected.

In this way, the voltages applied to the height adjuster 37 and the lateral shift adjuster 47 are controlled based on the error information from the fringe analysis unit 61, and the lens holder 32 is three-dimensionally moved relative to the condenser lens holder 31. By displacing the lens 21, the centering of the lens 21 with respect to the condenser lens 4 is automatically performed.

After the centering of the lens 21 is completed as described above, the reference spherical surface 60 is removed, the surface to be measured is set, and its shape is measured.

According to the embodiment described above, since the lens holder 32 is attached to the condensing lens holder 31 using a bayonet method, it can be attached and detached extremely easily. In addition, since the centering of the lens 21 is automatically performed, the operation during installation is simplified, and the centering is controlled by the height adjuster 37 and the lateral shift adjuster 4 made of piezoelectric elements.
7, it becomes possible to control the displacement on the order of 10 nm, and it is possible to perform highly accurate centering, thereby making it possible to measure the surface shape with high accuracy.

Note that this invention is not limited to the above-described embodiments, and can be modified or changed in many ways. For example, in the embodiment described above, one of the variable rings 45 of the lens holder 32 is biased by the coil spring 46, but like the other variable rings 45, it may be displaced by a lateral shift adjuster made of a piezoelectric element. It's okay. Furthermore, although the adjustment of the deviation and inclination in the optical axis direction is performed by the three height adjusters 37 at the three divided positions, it may be performed at the four divided positions in two orthogonal directions. The same applies to the lateral shift adjustment of the optical axis. Further, the height adjuster 37 and the lateral shift adjuster 41 are not limited to piezoelectric elements, but may be configured using coils and magnets so as to be displaced by electromagnetic force or the like. Further, in the above-described embodiment, the hemispherical lens 21 is made detachable, but other lenses, such as an abranatic lens, can also be detachably provided. Such a configuration is effective for measuring the surface shape of a convex lens having a large numerical aperture and a small radius of curvature as the surface to be measured. Also, in Figure 3,
The condensing lens 4 may be configured with three lenses with the outermost lens on the surface to be inspected removed, and the removed outermost lens may be detachably attached instead of the lens 21.

Such a configuration is effective for measuring the surface shape of a convex lens having a small numerical aperture and a large radius of curvature as the surface to be measured. Furthermore, in the above-described embodiment, the lens 21, which is detachably attached, is automatically centered with respect to the condenser lens 4, but it is also possible to configure the centering to be done manually, or by simply attaching the lens 21. If the centering accuracy can be compensated mechanically, it is not necessarily necessary to provide an automatic centering mechanism.

〔Effect of the invention〕

According to this invention, in an interferometer that measures the shape of a surface to be measured by performing fringe scanning jarring interferometry on a reflected wavefront from a surface to be measured, a condenser lens is provided between the condenser lens and the surface to be measured. In addition to providing a removable lens that equivalently increases the numerical aperture, this lens is centered with respect to the condenser lens horizontally on the centering axis. It is possible to always measure with high accuracy without causing any problems.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the invention in detail, FIG. 2 is a diagram showing an embodiment of the invention, FIG. 3 is a sectional view showing the specific structure of the main part, and FIGS. 4A and B is a side view and a partial plan view showing the configuration of the condensing lens holder shown in FIG. 3; FIGS. The figure is a block diagram showing the configuration of an automatic centering mechanism, and FIGS. 7 and 8 are diagrams showing conventional technology. 1...Polarized light source 2.8...Polarized beam splitter 3, 6. 9.11.13...1/4 wavelength plate 4...
・Condensing lens 5...Test surface 7...Shaprism 10.12...Total reflection mirror 14...Image carrier element 15...Piezo element 21...Lens
22...Incoming light flux 31...Condensing lens holder 32...Lens holder 33...Mounting end surface
34...Magnet 35...Reference ring 36
...Protrusion 37...Height adjuster 38...Plate 41...Mounting end surface 42...Magnet 43...
・Fixing ring 44... Notch groove 45... Variable ring 46... Coil spring 47... Lateral shift adjuster 48... Stator 49... Lid
50... Mover 51... Presser jig
52... Steel ball 53... Holding jig 54.
...Press plate 55...Plate 56...V
Hole 57...Steel ball 60...Reference spherical surface 6
1... Fringe analysis section 62... Drive unit Patent applicant Olympus Optical Industry Co., Ltd. Figure 1 Figure 2 Figure 3 Figure 4 Figure 7 Figure 8

Claims (1)

[Claims] 1. The reflected wavefront on the test surface that is illuminated through a condenser lens and focused by the condenser lens is separated into two wavefronts with polarization directions orthogonal to each other, and these wavefronts are interfered while giving an optical path difference. In the surface shape measuring interferometer, the surface shape measuring interferometer measures the shape of the surface to be measured by scanning the interference fringes. An interferometer for surface shape measurement, comprising a lens that equivalently increases the numerical aperture of an optical lens, and a mechanism that centers this lens with respect to the condensing lens.