JPS5842908A - Interference device for plane measurement - Google Patents

Abstract

PURPOSE:To perform interference measurement with high precision by providing a means of allowing measuring luminous flux to strike the air gap between a surface to be inspected and a reference surface while the air gap is fixed. CONSTITUTION:A plane measuring interference device is equipped with a mounting table 16 which is rotatable including the optical axis of the measuring device while the conditions between a reflective surface 14 to be inspected and a reference reflective surface 15 are fixed. In accordance with the rotation of the mounting table 16, an optical recording material 18 is rotated in the same plane with the rotation of the mounting table 16 and in a different direction from the mounting table 16 by using a turntable 19. This operation imprints distortion- free images from the reflective surfaces 14 and 15 on the optical recording materials 18 so that they overlap to each other. Namely, this invented interference device varies the angle of incidence of measuring luminous flux striking the reflecting mirror of the interferometer to record interference fringes on the same member, thus performing interference measurement with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a planar accuracy measurement interference device,! An interference device that changes the sensitivity of interference fringes and generates new interference fringes between the interference fringes by controlling the angle of the light beam incident on the test surface and the reference surface. It is.

Conventionally, a repeating reflection interferometer as shown in FIG. 1 has been used to measure the surface accuracy of a surface to be inspected. A beam from a monochromatic laser light source passes through an aperture 2 such as a pinhole, becomes a collimated beam by a collimator lens 3, is repeatedly reflected between a reference reflector 4 and a test reflector 5, and then becomes a condensed light beam. It reaches the recording surface 7 via the image lens '6. By increasing the reflectance of the reference reflective surface and the test reflective surface, the finesse of the dyed soil pattern is increased. In this type of device, the interference fringes represent an air spacing between the two planes (of the same wavelength). In order to read interference fringes with high accuracy, it is necessary to detect minute displacements from the straight line of the interference fringes. However, as shown in Figure 2, it is necessary to widen the distance between adjacent interference fringes.

However, in this case, the area between the interference fringes (second
The problem was that the shape (within the wavy line) could not be measured, and even though the accuracy was high, the accuracy of the field was low.

SUMMARY OF THE INVENTION An object of the present invention is to provide a plane measurement interferometry device that improves the above-mentioned conventional drawbacks and enables highly accurate interferometry with a high measurement density.

In the plane measurement interference device according to the present invention, there is provided a means for making the beam of light incident on the air gap at different angles 1 into the air gap with the air gap between the transverse surface and the reference plane fixed, and a beam projected onto the ψ plane. The above object is achieved by providing means for making the image forming surface and the test surface optically conjugate while maintaining the imaging magnification of the test surface constant. Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 3 is a diagram showing an example of a disaster in the planar measurement interference device according to the present invention, in which 11 is a monochromatic feW such as a laser, etc. %12 is a light beam from a light source 11 that is narrowed down by a lens pinhole. A collimator lens system 14 and 15 converts the light beam from the point source 12 into a parallel light beam, one of which is a test reflecting surface (test surface) and the other is a reference reflecting surface (reference surface). ) 16 is the test reflective surface and reference reflective surface (14, 15)
A stage that can be rotated by a predetermined amount with respect to the optical axis of the measuring device while keeping the state of the surface fixed; 17 imaging lenses; This is a rotary table capable of rotating an optical recording material sheet 19 for recording the intensity at each location within the rotating plane of the stage 16.

The luminous flux emitted from the light 1111 is formed into a point light source 12, and is further converted into a parallel luminous flux by a premeter lens system 13, and is fixed to a parallel luminous flux 11 with a parallel surface and is directed to a cover provided so as to face each other. Examination reflector and reference reflector (14, 15
) into the pair.

The reflective surfaces of these two reflective mirrors (14, 15) can reflect light and at the same time allow some of it to be transmitted. These two reflections 1ii, (14, 15) interfere with each other, and the optical recording material 18 is caused by the imaging lens system 17.
recorded as an interference pattern on the top. 17 manufacturers of imaging lens systems, and the above two reflective surfaces (14
, 15) is provided at a position to focus on the optical recording material 1B.

Here, the five conditions in which the transmitted light interferes and strengthens from the two reflecting surfaces (14, 15) K are expressed as follows.

0 represents the order (integer) of the angle of 1 m at which the light beam enters the reflective surface 15 within the medium between the reflective surfaces (bright fringes because interference a is constructive), and λ represents the wavelength. In other words, when the angle of incidence is changed, the interference pattern appears as if the distance between the two reflecting surfaces is llI! It shows behavior as if the id has changed or the wavelength has changed.

Therefore, in the present invention, the angle of incidence θ is controlled by using a rotatable stage 16. First, the above-mentioned measurement is performed at a certain incident angle #l to record an interference pattern on the optical recording material 18. Then the interferometric method &I[rn is recorded as d t
-dt, the following relationship holds true.

ds-mλ/2acos#l Further, when the stage 16 is rotated and the angle of incidence on the reflecting mirror is set to one angle, the relationship between the interference fringe order and d, which is the same as described above, is as follows.

da -ml/2ncos#m In other words, as the incident angle changes, interference fringes are formed at different distances 111d even if the interference fringe order is the same.The angle of the test surface is set to almost 0, and interference fringes with a wide width are formed. Suppose that it occurs as shown in FIG. If this continues, the measured density will be low. Therefore, the stage 16 is rotated so that the angle of incidence of the light beam incident on the reflecting mirror is made into the # island, and the light beam is recorded on the optical recording material 18 by multiple exposure so as to be superimposed on the #l interference pattern. 6s #4s...Φ...#n are recorded in a similar manner. Fifth
This figure represents an interference pattern that has been subjected to multiple exposures as described above.

In other words, interference fringes having almost the same shape as the interference pattern at the incident angle of -1 are recorded in such a way as to fill in the space between the interference fringes at the -1 angle. In the conventional example shown in Fig. 1, the interference fringes were at the same height every 1 interval λ4, but with the method of the present invention, the recorded interference fringes were measured by varying the incident angle up to -n. case Ktj
One interval of interference fringes is λ/2111.

In other words, if the accuracy (reading of interference fringes) is the same, then the measurement accuracy in Figures 4 and 5 will be the same, or the measurement density will be 1 times higher.

Furthermore, since the stage 16 rotates when the incident angle is 1i#l and when the incident angle is sudden, the image formed by the imaging lens 17 also rotates, causing distortion on the surface of the optical recording material. In order to eliminate this drawback, it rotates in accordance with the rotation of the stage 16. By this operation, the optical recording material 18 is constantly exposed to the reflective surfaces (14, 15).
It is possible to accurately overlay images without any design.

The imaging lens system 17ti includes two lens groups 7a and 7b having positive power. For this reason, as mentioned above, it is possible to record a positionless image on the optical recording material. The optical recording material 18 may be a photographic material, or an image pickup device such as a TV camera, an arithmetic circuit such as a computer, etc. Use. When using photographic light-sensitive materials, a so-called multiple achromatic method is used, and when using an image sensor, the output at the incident angle of the company name is added to the memory for each location.

FIG. 61 is a diagram showing another embodiment of the present invention. The light emitted from the light source 21 is focused by a lens system or a pinhole, etc. to form a point light source 22, and then to a collimator lens system 23.
Parallel Te, -? bundled.

This parallel light flux becomes a large number of point light sources 25 by a lens array 24 provided to shape the large number of point light sources. By means of a collimator lens system 26 whose surface is located at the location where the point light sources 25 are formed, the light beams from these multiple point light sources 25 are converted into parallel light beams at multiple angles. That is, there are two reference, test, and reflective surfaces (27,
28), parallel light beams will be incident at various angles of incidence.

The image height of a point light source with respect to the collimator lens system 26 by one lens Lm in the lens array 24 is bn.

If the focal length of the collimator lens system 26 is fc, then the angle of incidence on the reflecting surface is -nil #n-1an C
VrV7C). That is, in the above-described embodiment, the angle of incidence per person was changed by rotating the rotary stage 6, but in this embodiment, the angle of incidence can be controlled by the image height of the point light source with respect to the collimator lens using the lens array. In addition, in the above embodiment, a large number of interference fringes were superimposed by the multi-grain beam method, but
In this embodiment, it is possible to simultaneously record interference fringes at multiple incident angles. The image of the reflective surface (27, 28) is formed onto the recording surface 30 by the imaging lens system 29.

The same effect can be obtained by replacing the lens array 24 with an array of zone plates 31 as shown in FIG.

FIG. 8 is an embodiment of an optical system for miniaturizing a collimator lens for sending a parallel beam of light to a lens array or zone plate array. In FIG. 8, a light beam from a laser light source 41 is condensed by a lens system or a pinhole (not shown) to form a point light source 42, and after being made into a parallel light beam by a collimator lens 43, it is passed through a semi-transparent mirror array 44.
incident on . Each parallel light beam separated into a plurality of beams by this semi-transparent mirror array enters the lens array 45,
A number of point light sources 46 are formed. Since this arrangement is the same as the configuration shown in FIG. 6, a description thereof will be omitted.

As described above, in the interference device according to the present invention, by changing the incident angle of the measurement light image incident on the reflecting mirror of the interferometer and recording the interference fringes on the same member, the flatness of the interference fringes can be determined with high precision. , which embodies a jealousy density measurement.

[Brief explanation of drawings]

Figures 1 to 2, which show fl in conventional planar measurement interference, were obtained by conventional measurement.2. A diagram showing the appearance of interference fringes,
FIG. 3 is a diagram showing an embodiment of the plane measurement interference device according to the present invention, and FIGS. 4 and 5 are diagrams showing the appearance of interference fringes obtained by the device of the present invention. Figures showing other embodiments of the plane measurement interference device according to the invention; FIG. 7 is a diagram showing a zone plate array that can be replaced with the lens array of the device shown in FIG. 6; FIG. 8 is a diagram showing the device shown in FIG. 6. The figure which shows the modification of a part of. 11・Φ...Laser light source, 15...Collimator lens, 14.15...9 Reference reflective surface and test reflective surface, 16...Product table s 17 m * Curvature ...Imaging lens system, 18...Optical recording material, 19...Axis...
Turntable.

Claims (1)

[Claims] (1) Plane n! In a multi-beam interference device that measures beams,
means for causing measurement light beams to be incident on the air gap at different angles with the air gap between the test surface and the reference surface being the same;
It is characterized by being equipped with a means for optically making the imaging surface and the surface to be examined optically conjugate while maintaining the imaging magnification of the object projected onto the imaging surface at a constant level. A planar measurement interferometer.