JP2000088512A - Interference measuring apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the surface shape at a high precision for a short time by inserting a reference surface and test surface in a thermostatic chamber the apparatus has. SOLUTION: A Fizeau surface and sample surface are disposed in a thermostatic chamber 15. A light from an interferometer 11 is irradiated on a reference surface 12a and test surface 13a to produce an interference fringe. The interference fringe is measured and analyzed by an arithmetic unit 21 to measure the surface shape of a sample under test 13 wherein the required moving of the sample 13 in the optical axis direction and direction perpendicular thereto for this measurement and the correction of the inclination to the optical axis are all automatically made from outside the thermostatic chamber 15. A sample stand 17 chucks the sample to be measured through an axially movable chuck 101 having a rotary shaft and sets it at a measuring position. The outputs of sensors 41a-41n for measuring the temp. distribution in the chamber 15 are given to a temp. controller 42 to control so that the temp. in the chamber 15 is uniform and const. After ending the measurement, it is replaced with a sample housed in a next sample stand 18 by opening/closing a door 31.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer and an interferometer for performing high-accuracy shape measurement using an interferometer of a Fizeau interferometer.

[0002]

2. Description of the Related Art An interference state (typically observed as an interference fringe) is defined as a wavefront (a plane having the same phase) of two light beams which satisfies coherence (temporal and spatial coherency). Indicates phase difference information. The characteristic evaluation of the optical system can be performed in principle by measuring the shape of the equiphase wavefront, and interference fringes are used for measuring the shape of the equiphase wavefront. That is, if one of the two light beams is reflected by a reference surface serving as a reference (referred to as a reference light beam) and the other is reflected by a test surface (referred to as a test light beam), the reference surface is ideal. If the surface is an irregular surface, the surface shape error of the
Observed as interference fringes due to 1 Path Difference (OPD).

[0003] Typical interferometers include a Twyman-Green interferometer and a Fizeau interferometer. The Twyman-Gulin interferometer has an arrangement as shown in FIG. In this case, since the distance between the test surface 55 and the reference surface 51 to the beam splitter 53 can be made completely equal, light having a short coherence distance such as white light can also be used. If laser light is used as the light source, a Fizeau interferometer can be used instead. The λ / 4 plate and the polarizing plate are not shown in the figure.

[0004] The Fizeau interferometer has an arrangement as shown in FIG. In this case, since the distance between the reference surface 63 and the test surface 65 cannot be made completely zero, an optical path difference occurs between the test light beam and the reference light beam. For this purpose, attention must be paid to the coherence of the light used (monochromaticity of the light). However, considering the interference optical path length, the distance between the Fizeau surface 63, which is the reference surface, and the test surface 65 can be made shorter than the distance from the beam splitter in the Twyman interferometer to the reference surface or the test surface. For this reason, the Fizeau interferometer is characterized in that it is more resistant to fluctuations in the refractive index (n) of air that occur in the interference optical path. Accordingly, highly accurate surface shape measurement can be performed based on the observed interference fringes.

[0005]

SUMMARY OF THE INVENTION However,
Even if a Fizeau interferometer is used, for example, as shown in FIG. 3 (c), when the distance between the Fizeau surface 73 and the test surface 75 must be large and the measurement of the spherical test surface must be performed. Unlike the plane, the distance between the Fizeau surface 73 and the test surface 75 cannot be freely changed, so that the measurement error caused by the fluctuation of the refractive index of air and disturbance caused in the interference optical path is unavoidable. There was a point.

An object of the present invention is to solve the above-mentioned problems and to provide means for measuring a surface shape with high accuracy. Further, another object of the present invention is to provide means for performing this high-accuracy measurement in a shorter time.

[0007]

According to the present invention, the following means are used to achieve the above object. As a first means, an interferometer that obtains at least shape information of the test surface by applying coherent light to the reference surface and the test surface to cause reflected light from both surfaces to interfere with each other, The reference surface and the test surface were placed in the constant temperature chamber. This makes it possible to obtain an interference measurement device with high measurement accuracy that suppresses the influence of the change in the refractive index of air due to a temperature change.

[0008] As a second means, when the first means is used, a mechanism for holding an unmeasured test object in a constant temperature chamber and a mechanism for setting the test object at a predetermined position from outside the chamber are provided. I did it. This eliminates the need to open and close the constant temperature chamber, so that the temperature inside the chamber can be maintained at all times, and an interference measurement device with no waste in measurement time can be obtained.

As a third means, when the first or second means is used, a subchamber for exchanging an object adjacent to the constant temperature chamber, and a temperature controller for independently controlling the temperatures of the subchamber and the constant temperature chamber And. Thus, an interferometer capable of setting the temperature of the measured object to a predetermined value before putting the measured object into the measurement chamber is obtained. As a fourth means, when the third means is used, the temperature controller controls the temperature in the constant temperature chamber and the temperature distribution in the sub-chamber to be the same. As a result, an interference measurement device having no temperature change when the test object is replaced can be obtained.

As a fifth means, when using an interference measurement method for obtaining at least shape information of a test surface by applying coherent light to the reference surface and the test surface and causing reflected light from both surfaces to interfere with each other, The test surface was placed in a constant temperature chamber for measurement. As a result, it is possible to obtain an interference measurement method with high measurement accuracy in which the influence of a change in the refractive index of air due to a temperature change is suppressed.

As a sixth means, when the fifth means is used, an unmeasured object is held in a constant temperature chamber, and the measured object is set at a predetermined position from outside the chamber and measured. did. This eliminates the need to open and close the constant temperature chamber, so that the temperature inside the chamber can be maintained at all times, and measurement time is not wasted.

As a seventh means, when the fifth or sixth means is used, a subchamber for exchanging a test object is provided next to the constant temperature chamber, and the temperatures of the subchamber and the chamber are independently controlled. It was decided to measure. Thus, the temperature of the object to be measured can be set to a predetermined value before the object is placed in the measurement chamber.

As an eighth means, when the seventh means is implemented, the temperature in the constant temperature chamber and the temperature in the sub-chamber are controlled to be the same. As a result, a temperature change at the time of replacement of the test object can be eliminated.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a reference lens and a surface to be inspected are placed in a constant temperature chamber, and the temperature distribution in the chamber is kept uniform to reduce air disturbance, thereby enabling high-precision measurement. An interference measurement device and method are realized. However, even in such an apparatus, the temperature distribution in the constant temperature chamber changes when the specimen is replaced, and in order to perform high-precision measurement without disturbance, the temperature in the chamber that has changed is changed. In some cases, it takes time to adjust the temperature until the distribution becomes uniform again and the surface temperature of the test surface becomes uniform. In such a case,
In the present invention, this is achieved by adjoining a pre-chamber sub-chamber and controlling its temperature.

[0015]

FIG. 1 shows a first embodiment of the first, second, fifth and sixth means of the present invention. The Fizeau surface and the surface to be inspected shown in FIG. Are located. Light emitted from the interferometer 11 includes a reference surface 12a and a test surface 13a.
And reflected light interfere with each other to generate interference fringes. The surface shape of the test object 13 is measured by measuring the fringes and analyzing the fringes by the arithmetic unit 21. At this time, the movement of the test object necessary for the measurement, that is, the movement in the optical axis direction, the movement in the direction perpendicular to the optical axis, and the inclination correction with respect to the optical axis are all automatically performed from outside the constant temperature chamber. FIG.
Reference numeral 101 denotes a chuck having a rotating shaft, which is movable in the axial direction. The chuck 101 chucks an object to be measured from an object stand 17 that stores an unmeasured object and sets the object at a measurement position. Have a role to do. This enables the setting of the test object from outside the chamber. In addition, 41a ~
Reference numeral 41n denotes a temperature sensor for measuring the temperature in the chamber and its distribution, the output of which is given to the controller 42, which controls the temperature in the chamber to a uniform constant temperature. When the measurement of the test object on the test object stand is completed, the test object is replaced with the test object stored in the next test object stand 18 by opening and closing the door 31.

FIG. 2 shows a second embodiment for explaining the third, fourth, seventh and eighth means of the present invention. The description of the parts common to the first embodiment is omitted. In FIG. 2, reference numeral 16 denotes a subchamber for exchanging the test object, which is provided adjacent to the constant temperature chamber 15. Constant temperature chamber 15 and sub-chamber 16
Are partitioned by a door 31, and the sub-chamber is partitioned from the outside by a door 32. Each chamber has a temperature sensor 41 for measuring the temperature in the chamber and its distribution.
There are temperature controllers 42 and 44 for controlling the temperature in the chamber to a predetermined uniform temperature based on the values of the temperature sensors a to n and 43a to n. In particular, if the temperature of the sub-chamber is controlled to be the same as the temperature of the constant temperature chamber for measurement, the time required for measurement can be reduced. 1
Reference numerals 7 and 18 denote test object stands on which test objects are held.

According to the present invention, it is possible to reduce the disturbance of the air, which is one of the causes of the deterioration of the accuracy of the interference measurement, by the means as described above. That is, if the temperature distribution in the chamber 15 is uniform, there is no air disturbance and high-precision interference measurement is possible. As a result, in the case of measurement of one surface to be measured, high-precision measurement free from the influence of air disturbance can be performed if sufficient time is taken after the surface to be measured is set in the chamber and the temperature is sufficiently adjusted. However, when there are a plurality of test surfaces, such a method is very inefficient. For this reason, in the present invention, the specimen stands 17 and 18 are provided in the chamber 15 and the sub-chamber 16, and the specimen can be exchanged in a uniform temperature distribution. During the measurement, the temperature of another test object can be adjusted at the same time, so that efficient measurement can be performed.

A method of exchanging the test object will be described below with reference to FIG. In the initial state, the temperature distribution in the chamber 15 is assumed to be uniform, and the doors 31 and 32 are assumed to be closed. First, the temperature distribution in the sub-chamber 16 is controlled to match the temperature distribution in the chamber 15. When the temperatures match, the door 31 is opened, and the test object whose measurement has been completed is transported from the test object stand 17 to the test object stand 18 of the sub-chamber 16. Next, the sub-chamber 16
The new test object prepared in the test object stand 18 is transferred to the test object stand 17 in the chamber 15. Next, the door 31 is closed, the door 32 is opened, and the sub-chamber 16 is opened.
The test object in the test object stand 18 is carried out of the chamber. Then, a new DUT is placed in sub-chamber 1
6 is carried into the test object stand 18, the door 32 is closed, and control is performed so that the temperature distribution in the sub-chamber 16 matches the temperature distribution in the chamber 15.

The loading and unloading can be performed separately instead of simultaneously as described above. The Fizeau lens 12 can be replaced by preparing a Fizeau lens stand in the sub-chamber and adjusting the temperature in advance. As described above, the sub-chamber 16 is provided adjacent to the chamber 15, and the test object 13 can be replaced from outside the chamber 15 without changing the temperature distribution in the chamber 15.

[0020]

As described above, if the interferometer system according to the present invention is adopted, the "environmental disturbance" resistance is improved particularly when the surface accuracy of the test surface is measured using a Fizeau interferometer. Higher and more accurate measurement is possible. In addition, the provision of a specimen stand in the chamber facilitates replacement of the specimen, allowing another specimen to adapt to the temperature in parallel with the measurement, shortening the measurement time and improving efficiency. Good measurement is possible.

[Brief description of the drawings]

FIG. 1 is a first embodiment according to claims 1 and 2 of the present invention.

FIG. 2 is a second embodiment according to claims 3 and 4 of the present invention.

FIG. 3 is a diagram illustrating the principle of an interference measurement apparatus according to the related art.

[Explanation of symbols]

11: Interferometer body, 12: Fizeau lens, 12a: Reference surface, 13:
Test object, 13a ... Test surface, 15 ...
Constant temperature chamber, 16 ... sub-chamber, 1
7 ... test object stand, 18 ... test object stand,
21: arithmetic unit, 31: door,
32: Door, 41a-n: Temperature sensor 43a-n: Temperature sensor, 42: Temperature controller, 44: Temperature controller 51: Reference surface 53: Test surface 53: Beam splitter 61: Fizeau lens 63: Reference surface 65: Target surface 73: Reference surface 75: Target surface 101: Chuck

Claims (8)

[Claims] 1. An interferometer that obtains at least shape information of a test surface by applying coherent light to a reference surface and a test surface to cause reflected light from both surfaces to interfere with each other, comprising: a constant temperature chamber; An interferometer, wherein a surface and a surface to be inspected are placed in the constant temperature chamber. 2. The interference measurement apparatus according to claim 1, wherein
An interference measurement apparatus comprising: a mechanism for holding an unmeasured test object in the constant temperature chamber; and a mechanism for setting the test object at a predetermined position from outside the chamber. 3. The interference measurement apparatus according to claim 1, wherein a sub-chamber for exchanging a test object adjacent to the constant temperature chamber, and a temperature in the sub-chamber and the temperature in the chamber are independently controlled. An interferometer having a temperature controller. 4. The interference measurement apparatus according to claim 3, wherein
An interference measurement apparatus, wherein the temperature controller controls the temperature in the constant temperature chamber and the temperature in the sub-chamber to be the same. 5. An interference measurement method in which coherent light is applied to a reference surface and a test surface to cause reflected light from both surfaces to interfere with each other to obtain at least shape information of the test surface. An interference measurement method characterized in that the measurement is carried out in a constant temperature chamber. 6. The interference measurement method according to claim 5, wherein
An interference measurement method, comprising: holding an unmeasured test object in the constant temperature chamber; setting the measurement test object at a predetermined position from outside the chamber; 7. The interference measurement method according to claim 5, wherein a sub-chamber for exchanging a test object is provided next to the constant temperature chamber, and the temperature in the sub-chamber and the temperature in the chamber are independently controlled. Interferometric measurement method characterized in that the measurement is performed 8. The interference measurement method according to claim 7, wherein:
An interference measurement method, wherein the temperature in the constant temperature chamber and the temperature in the sub-chamber are controlled so as to be the same and measured.