JPH02259511A - Interference measuring instrument - Google Patents

Abstract

PURPOSE:To improve the measurement accuracy and remeasurement performance of the instrument by making luminous flux incident on an interference part from a light source part in the best state. CONSTITUTION:A light source part which includes a light source 1 such as a laser and the interference part having a means such as a condenser lens 3 which receives the luminous flux from the light source 1 and forms a measurement wave front at least on a body 13 to be measured are arranged separately. Then a luminous flux optimizing means has a half-mirror 6 provided in the optical path of the interference part, a photosensor 7 which receives split light from the half-mirror 6, a total reflecting mirror 2 which receives the signal from the photosensor 7 and controls the state of incidence of the incidence luminous flux on the interference part from the light source part into the best state so that the detection light of the sensor 7 has a peak value, and a control means constituted of a driving mechanism which drives them as to at least two degrees of freedom, etc. Consequently, the state of the luminous flux which is incident on the interference part from the light source part is optimized automatically to measure the shape of the body to be measured with high accuracy.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is provided with means for optimizing the incident state of the incident light beam from the light source section to the interference section, in which the light source section and the interference section are arranged separately. The present invention relates to an interference measurement device.

[Prior Art] Conventionally, there have been known interference measuring devices that accurately measure the shape of the surface of an object using the interference effect of light.
In the Twyma-Green interferometer, the light beam from the light source is divided into two light beams by a splitting means such as an eight-point mirror in the interference section.
The shape of the surface to be measured can be measured by forming a reference beam from one side and light from the surface to be measured from the other side, interfering with both beams, and analyzing the interference fringes formed thereby.

[Problem to be Solved by the Invention] However, in conventional interference measurement devices, the light source and the interference part are usually placed on the same board, taking into consideration the influence of vibrations, etc. there were. However, in order to achieve high-precision measurements, if a heat generating element such as a light source is located near the interference part, the reference mirror and the optical elements that form the measurement wavefront will thermally expand due to the influence of the heat, causing the position of these parts to expand. There were problems with measurement accuracy and repeatability.

For this reason, a complete interference measuring device has been proposed that uses a length measuring device or the like to separate the light source and the interference part to enable highly accurate measurement. However, in an interferometric measurement device that measures the shape of a test surface with high precision, for example, in a method that requires the interference part to be moved according to the shape of the test object, the deviation of the interference part with respect to the incident light beam from the light source It is impossible to move the interference part using a drive mechanism without causing interference, and each time the interference part is moved, the alignment between the incident light beam and the interference part must be manually performed by visual inspection, which causes the problem of deterioration of measurement accuracy. be.

Therefore, in view of the above-mentioned problems, an object of the present invention is to provide a configuration in which the light source section and the interference section are separately disposed, and the incident light flux from the light source section to the interference section is always maintained in an optimal state. The object of the present invention is to provide an interference measurement device that can be used to measure interference.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a light source unit including a light source such as a laser, and a light source unit that receives a light beam from the light source to form at least a measurement wavefront to a test object. The light source and the interference section having means such as a condensing lens are arranged separately, and the relative positional relationship between the light source section and the interference section is changed so that an appropriate measurement wavefront is incident on the test object. A beam optimizing means is provided so that the beam is optimally incident on the interference portion from the interference portion.

Specifically, the beam optimization means includes a beam splitting means such as a half mirror provided in the optical path of the interference section, a light detection means that receives the divided light from the beam splitting means, and a signal from the detection means. The total reflection mirror is configured to control the incident state of the incident light beam from the light source section to the interference section so that the detection light of the detection means reaches a peak value, and a drive mechanism that drives the mirror in at least two degrees of freedom. and control means.

The light flux optimization means may include means for detecting the relative positional relationship between the light source section and the interference section, and a total reflection mirror that is controlled based on the detection by this means.
It may also include means for detecting the angle and a total reflection mirror that is controlled based on the detection by the means.

[Function] The present invention having the above configuration includes the above-mentioned light flux optimization means, so even if the light source section and the interference section are separated and the relative positions of the two sections change, the light source section does not reach the interference section. The incident state of the luminous flux is automatically optimized.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which the present invention is applied to a Twyman-Green interferometer for measuring the shape of a concave surface.

In the figure, 1 is a light source such as H, -N, laser, etc., and 2 is a total reflection mirror that reflects the light beam from the light source and guides it to the interference part.This mirror 2 is equipped with a drive mechanism with two degrees of freedom. The position of the reflected light beam can be controlled. 3 is a condensing lens that receives this reflected light flux; 4 is a pinhole plate provided near the spot formed by the condensing lens 3; 5 is a collimator lens with this spot position as its focal position; 6
is a half mirror, and one of the split lights is guided to a photosensor 7, and the other light is guided to a polarizing beam splitter 8. The signal obtained by the photosensor 7 is used to control the drive mechanism of the total reflection mirror 2, and the drive mechanism is controlled by the control system so that this signal always has a peak value.

9 is the % wave plate, lO is the reference mirror, 11 is the diagram wave plate, 1
2 is a condenser lens, 13 is a test object, and the light guided to the polarizing beam splitter 8 is split into two directions according to the polarization direction, and one of the lights is made into circularly polarized light by an electric wave plate 9. It is reflected by the reference mirror 10, passes through the residual liquid elongated plate again, returns to the polarizing beam splitter 8 with the polarization direction rotated by 90 degrees compared to the initial state, and is transmitted through there this time. The other light is circularly polarized by the residual liquid long plate 11, passes through the condenser lens 12, is reflected by the object 13, passes through the condenser lens 12 and the residual liquid long plate 11 again, and is sent to the polarizing beam splitter. 8, the polarization direction of the returned light beam is now rotated by 90 degrees compared to the initial direction, so this light is now reflected by the polarizing beam splitter 8 and directed downward.

In this way, the reference light and the light wave from the object 13 are combined, pass through the polarizing plate 14 and the mirror 15, and are then observed by the focusing mirror 16 as interference fringes on the imaging device 17, such as a CCD.

As shown in FIG. 1, elements serving as a heat source such as the light source 1 and the image sensor 17 are arranged as a light source section separated from an interference section including the polarizing beam splitter 8 and the condensing lens 12.

In the above configuration, if the measurement wavefront from the condensing lens 12 substantially matches the shape of the surface to be measured of the object 13 and the interference fringes on the image sensor 17 are rough enough to be measurable (i.e., the image sensor (If the difference between the shape of the adjacent portion of the test surface imaged on the 17 adjacent pixels from the measurement wavefront exceeds half of the wavelength used), the relative positional relationship between the interference part and the test object 13 is moved. It may be done without it, but if the interference fringes are too fine, it is necessary to move it. In this case, if the test object 13 is not moved, it is necessary to move the interference part to enable measurement. In this case, simply moving the interference part will ensure that the positional relationship between the interference part and the light source is in the appropriate state. There is a risk that deviation measurement may become impossible.

Therefore, as described above, the reflection mirror 2 is driven and controlled so that the signal from the photosensor 7 is always at its peak, and the interference section and the light source section are placed in a proper positional relationship to enable correct measurement.

Although the above embodiment was an example of a Twyman-Green interferometer, the present invention can be applied to other types of interferometers such as a Fizeau interferometer and a Shearing interferometer.

Furthermore, in the above embodiment, in order to ensure that the light flux from the light source of the light source always enters the interference part correctly, a detection means of the type that inserts a photosensor into the optical path is provided. An optical system may be set up in a separate system in between, and the relative position between the light source section and the interference section may be known to control the mirror 2 and the like.

Furthermore, a reference mirror may be attached to the stage stand of the interference section, and the position and angle of the interference section may be measured with a length measuring device to control the drive mechanism of the mirror 2.

It is also possible to move the light source section, and in this case as well, it is sufficient to correct the light beam so that it correctly enters the interference section.

[Effects of the Invention] As explained above, in the interference measurement device of the present invention in which the light source section and the interference section are separated and installed separately, adjustments are made so that an appropriate measurement wavefront is incident on the object to be measured. Even later, the state of the light beam entering the interference part from the light source section is automatically optimized, and the shape of the object to be inspected can be measured with high precision, without requiring any correction operations such as visual inspection.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of one embodiment of the present invention. l...Light source, 2...Total reflection mirror, 3...
...Condensing lens, 4...Pinhole treatment, 5...
・・Collimation lens 6・・・・Half mirror 7・
...Photo sensor, 8...Polarizing beam splitter-19, 11...Electronic wave plate 10...
・ ・ ・ Reference゛Mirror l 2 ・ ・ ・ ・
・Condensing lens, 13... Test object, 14...
W light i, 15...Cef-16...Imaging lens, 17...Image sensor

Claims (1)

[Scope of Claims] 1. An interference device in which a light source section including a light source and an interference section having means for receiving a light beam from the light source and forming at least a measurement wavefront toward a test object are separated and arranged. In the measuring device,
When the relative positional relationship between the light source section and the interference section is changed so that an appropriate measurement wavefront is incident on the test object, the light flux is optimized so that the light beam is optimally incident on the interference section from the light source section. An interference measuring device characterized by being provided with a converting means. 2. The light flux optimization means includes a light flux splitting means provided in the optical path of the interference section, a light detection means for receiving the split light from the light flux splitting means, and a light flux optimizing means receiving a signal from the light detection means and processing the light. 2. The interference measurement apparatus according to claim 1, further comprising a control means for controlling an incident state of the incident light beam from the light source section to the interference section so that the detection light of the detection section reaches a peak value. 3. The interference measurement according to claim 1, wherein the control means includes a total reflection mirror that reflects the light beam from the light source and makes it incident in the direction of the interference section, and a drive mechanism that drives the total reflection mirror in at least two degrees of freedom. Device. 4. The interference measuring device according to claim 1, wherein the light flux optimization means includes means for detecting a relative positional relationship between the light source section and the interference section. 5. The interference measuring device according to claim 1, wherein the light flux optimization means includes means for detecting the position and angle of the interference part.