JP2000283733A - Method for measuring capability of deforming reference plate of reference plate holding frame for vertical interferometer, and method of selecting reference plate for vertical interferometer using this - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide method of measuring the capability of deforming a reference plate of a reference plate holding frame for a vertical interferometer, which can provide useful data for enhancing the measurement accuracy of an interference fringe of the vertical interferometer, by calculating the capability of deforming the reference plate of the reference plate holding frame according to a predetermined procedure using an interferometer device for inspecting the reference plate. SOLUTION: A reference plate 2, which is held by a reference plate holding frame 14, is horizontally placed as a sample reference plate, and a standard reference plate 16 is horizontally placed and opposed to the plate 2, where a first interference fringe measurement is done. Then, the sample plate 2, the standard plate 16 and the frame 14 are relatively rotated by a predetermined angle, where a second measurement is done. The capability of deforming the reference plate 2 of the frame 14 is calculated, by averaging the first and second interference fringe measurement data, removing the rotation asymmetric component of the sample reference plate 2, and removing the rotation symmetric component from the averaged data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vertical interferometer in which a reference plate is arranged horizontally, and more particularly to a method for measuring a reference plate deformability of a reference plate supporting frame for supporting the reference plate. The present invention relates to a method of selecting a reference plate for a vertical interferometer using the same.

[0002]

2. Description of the Related Art Conventionally, an interferometer has been known as a means for measuring the surface shape of an object such as an optical member. This interferometer divides coherent light from a light source into two, makes one light beam incident on a surface to be inspected of a subject, makes the reflected light into object light, and uses the other light beam as a reference surface of a reference plate. And the reflected light is used as reference light, and interference fringes caused by the optical interference of these object light and reference light are measured. To improve the measurement accuracy, the flatness of the reference surface must be sufficient. It is important to secure

Further, in a vertical interferometer in which a reference plate is disposed horizontally, even if the reference plate itself has a sufficient flatness of its reference surface, the reference plate is positioned with respect to the reference plate support frame. If the support is not provided evenly over the entire circumference, it is deformed by contact with the reference plate support frame, and there is a problem that the measurement accuracy of interference fringes cannot be sufficiently increased.

The present applicant has disclosed Japanese Patent Application No. 11-55113 as a method for solving this problem.

[0005]

However, in both the prior art described above and the technology described in the above specification, the basic idea is that the reference plane is not deformed with respect to the reference plate supporting frame. Because of the consideration of fixing, the measurement accuracy of the interference fringes could not be sufficiently improved for the reference plate whose flatness was not sufficiently ensured from the beginning.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and a vertical interferometer can be used in a vertical interferometer without paying special attention to a method of fixing a reference plate to a reference plate support frame. Provided is a method for measuring a reference plate deformability of a reference frame supporting frame for a vertical interferometer and a method for selecting a reference plate for a vertical interferometer using the same, which can obtain useful data for improving the measurement accuracy of interference fringes. It is intended to do so.

[0007]

According to the present invention, there is provided a method for measuring the deformability of a reference plate of a reference plate supporting frame for a vertical interferometer, comprising the steps of: A method for measuring a reference plate deformability of a plate support frame, wherein the reference plate is horizontally arranged as a sample reference plate while being supported by the reference plate support frame, and is opposed to the sample reference plate. The first interference fringe measurement is performed in a state where the original reference plate is horizontally arranged, and then, in a state where the reference plate support frame is relatively rotated by a predetermined angle with respect to the sample reference plate and the original reference plate. Performing a second interference fringe measurement, averaging the first and second interference fringe measurement data, and calculating a reference plate deformability of the reference plate support frame based on the averaged data. Is what you do.

[0008] Here, the "reference plate deformability" means that the reference plate support frame abuts on the reference plate in a state where the reference plate support frame is not uniform all around the reference plate while the reference plate support frame supports the reference plate. It refers to the ability to deform a board.

More specifically, the above method is, for example, a method for measuring the deformability of a reference plate supporting frame supporting a reference plate in a vertical interferometer in which the reference plate is horizontally arranged. The first reference plate is horizontally arranged as a sample reference plate while the reference plate is supported by the reference plate support frame, and the original reference plate is horizontally arranged so as to face the sample reference plate. An interference fringe measurement is performed, and then a second interference fringe measurement is performed with the reference plate supporting frame relatively rotated by a predetermined angle with respect to the sample reference plate and the prototype reference plate. Averaging the interference fringe measurement data to remove the rotationally asymmetric component of the sample reference plate, and removing the rotationally symmetric component from the averaged data to calculate the reference plate deformability of the reference plate support frame. One It is.

Further, the method of selecting a reference plate for a vertical interferometer according to the present invention comprises measuring the reference plate deformability of a plurality of reference plate supporting frames using the above-described reference plate deformability measuring method, and selecting a plurality of reference plates. The shape of the reference surface of the plate is measured in advance, and when the reference plate and the reference plate support frame are combined from the reference plate and the reference plate support frame, the reference plate shape and the reference plate support frame become the closest to the flat surface. Is selected.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an overall configuration diagram showing a reference plate inspection interferometer device 10 to which a method of measuring a reference plate deformability of a reference plate support frame for a vertical interferometer according to an embodiment of the present invention is applied. .

As shown in the figure, the reference plate inspection interferometer device 10 includes a Fizeau type vertical interferometer 12, a reference plate support frame 14 for horizontally supporting a sample reference plate 2 as an object, and A prototype reference plate 1 horizontally arranged below the sample reference plate 2 so as to face the sample reference plate 2
6, a computer 18, and a monitor 20.

The vertical interferometer 12 causes the coherent light from a light source (not shown) to be incident on the sample reference surface 2a of the sample reference plate 2 serving as a test surface by the interferometer main body 22, and transmitted through the sample reference surface 2a. 2 for ray bundle and reflected ray bundle
The light is divided, the reflected light on the sample reference surface 2a is used as object light, and the transmitted light beam is made incident on the original reference surface 16a of the original reference plate 16, and the reflected light is used as reference light. The interference fringes generated by the light interference are captured by a CCD camera (not shown).

The vertical interferometer 12 has a fringe scan analysis function. That is, the sample reference plate 2 is moved together with the reference plate support frame 14 in the direction of the optical axis Ax (or the reference plate 16 is moved in the direction of the optical axis Ax), and the image data of the interference fringe that changes due to this movement is interferometrically measured. The main body 22 outputs the data to the computer 18. Then, the computer 18 automatically analyzes the interference fringes based on the input interference fringe image data by the fringe scanning method to measure the shape of the sample reference surface 2a (determination of unevenness and measurement of the three-dimensional shape), Alternatively, three-dimensional image data is displayed on the monitor 20.
To be displayed. In the fringe scanning method, the interference fringe intensity at each point of the sample reference plane 2a is determined from the interference fringe image data captured at each predetermined fringe scan step while changing the relative distance between the sample reference plane 2a and the prototype reference plane 16a. This is a method of measuring and performing interference fringe analysis such as phase calculation of each point using the measurement result.

In the present embodiment, the reference plate support frame 14 is formed using the reference plate inspection interferometer device 10 in the following procedure.
The reference plate deformability is measured.

That is, first, as shown in FIG. 2A, which is a view taken along the line AA in FIG.
4, scales 14 a are formed at intervals of 10 ° about the optical axis Ax of the vertical interferometer 12, and marks 2 b and 16 b are formed on the outer peripheral surfaces of the sample reference plate 2 and the prototype reference plate 16. Then, the mark 2b of the sample reference plate 2 and the mark 16b of the prototype reference plate 16 are aligned at the same angular position with respect to the scale 14a of the reference plate support frame 14.

In this state, the sample reference surface 2a of the sample reference plate 2 and the prototype reference surface 16a of the prototype reference plate 16 are set.
Then, the interference fringes formed between the sample and a are measured.

Next, as shown in FIG. 2B, the sample reference plate 2 and the prototype reference plate 16 are rotated by 10 °. At this time, the reference plate support frame 14 is not rotated. Then, in this state, the interference fringe formed between the sample reference plane 2a and the prototype reference plane 16a is measured again.

Similarly, every time the sample reference plate 2 and the prototype reference plate 16 are rotated by 10 °, interference fringes formed between the sample reference surface 2a and the prototype reference surface 16a are measured. Interference fringe measurement is performed at 36 locations.

Next, the interference fringe data (light intensity data at each point of the interference fringe image) at each angular position thus measured is averaged, and the sample reference plane 2a and the prototype reference plane 1 are averaged.
A rotationally asymmetric component around the optical axis Ax due to the relative shape to 6a is removed.

Then, a rotationally symmetric component around the optical axis Ax is removed from the interference fringe data from which the rotationally asymmetric component has been removed by a known method.

Specifically, such an operation is performed by, for example, fitting the interference fringe data with a Zernike polynomial (power series polynomial) or the like and developing it into a functional expression consisting of a rotationally symmetrical term and a rotationally asymmetrical term. From the above, the rotationally asymmetric component around the optical axis Ax due to the relative shape between the sample reference plane 2a and the prototype reference plane 16a is removed, and then the rotationally symmetric component around the optical axis Ax is removed by a known method. By doing so, only the rotationally asymmetric component representing the reference plate deformability of the reference plate support frame 14 is calculated.

As described above, in the present embodiment, data relating to the deformability of the reference plate useful for improving the measurement accuracy of the interference fringes in the vertical interferometer can be obtained.

Specifically, the reference plate deformability can be utilized, for example, as follows.

That is, first, the reference plate deformability of a plurality of reference plate support frames 14 is measured using the above-described reference plate deformability measuring method. Next, as shown in FIG. 3, a plurality of reference plate support frames 14 (1) whose reference plate deformability has been clarified,
14 (2),..., 14 (n), a plurality of sample reference plates 2 whose reference surface shapes were measured during the measurement of the reference plate deformability.
(1), 2 (2),..., 2 (n) are sequentially combined, and the reference surface shape of the sample reference plate 2 in each combination is calculated. From the calculation data thus obtained, when the sample reference plate 2 and the reference plate support frame 14 are combined, an optimum combination in which the shape of the reference surface 2a is closest to a plane as shown in FIG. 4 is selected. If the set of the reference plate 2 and the reference plate support frame 14 thus selected is incorporated in a vertical interferometer that actually performs interference fringe measurement, the accuracy of interference fringe measurement can be improved. .

In this embodiment, a plurality of sample reference plates 2 (1), 2 (2),..., 2 (n) whose reference surface shapes are simultaneously measured when measuring the reference plate deformability. To a plurality of reference plate support frames 14 (1), 14 (2),.
4 (n) is sequentially combined, but instead of this, a plurality of sample reference plates whose reference surface shapes are measured by another method may be used.

In this embodiment, the sample reference plate 2 and the prototype reference plate 16 are rotated by 10 ° without rotating the reference plate support frame 14, but instead of this, the sample Reference plate 2 and prototype reference plate 1
The reference plate supporting frame 14 may be rotated by 10 ° without rotating the reference plate supporting frame 6. In this case, the sum of the rotationally asymmetric component around the optical axis Ax and the rotationally symmetric component around the optical axis Ax due to the relative shape between the sample reference plane 2a and the prototype reference plane 16a is determined. However, if the obtained result is subtracted from at least one interference fringe data obtained as described above, only a rotationally asymmetric component representing the reference plate deformability of the reference plate support frame 14 can be calculated. .

Further, in the present embodiment, the sample reference plate 2 and the prototype reference plate 16 are rotated by 10 ° each,
Although interference fringe measurement was performed at all 36 locations,
The method is not limited to this method. For example, the interference fringe measurement is performed at two positions of 0 ° and 90 ° as in the method disclosed in Japanese Patent Laid-Open No. 10-325710, which has already been disclosed by the present inventors. In this way, the reference plate deformability of the reference plate support frame 14 can also be calculated.

When the sample reference plate 2 and the reference plate support frame 14 are incorporated in the vertical interferometer, the sample reference plate 2 is suspended in a suspended state where the sample reference plate 2 is not directly supported by the reference plate support frame 14 (that is, the sample reference plate 2 Both may be incorporated into a vertical interferometer (while supported by the reference plate support frame 14 via an agent or the like).

In such a case, one set of sample reference plates 2 selected as the optimum combination as described above
When the reference plate support frame 14 is incorporated in the vertical interferometer, the sample reference plate 2 is not affected by the reference plate deformability of the reference plate support frame 14, so that the sample reference plate 2 cancels the reference plate deformability. It remains with a band having a deformed shape. Therefore, when performing interference fringe measurement using this vertical interferometer,
The accuracy of the interference fringe measurement data is reduced by the deformation of the sample reference plate 2.

In such a case, the interference fringe measurement data is corrected by subtracting the deformation of the sample reference plate 2 due to the reference plate deformability of the reference plate support frame 14 from the interference fringe measurement data. In addition, it is possible to prevent the accuracy of the interference fringe measurement data from being lowered.

In the present embodiment, the case where the vertical interferometer 12 is a Fizeau-type vertical interferometer has been described. However, even when the vertical interferometer 12 is a Michelson-type or Mach-Zehnder-type vertical interferometer, the present embodiment is also applicable. By adopting the same configuration as described above, the same operation and effect as in the present embodiment can be obtained.

[0034]

According to the method for measuring the deformability of a reference plate of a reference frame for a vertical interferometer according to the present invention, the reference plate is horizontally arranged as a sample reference plate while being supported by the reference plate support frame. In addition, the first interference fringe measurement is performed in a state where the prototype reference plate is horizontally arranged so as to face the sample reference plate, and then the reference plate support frame is fixed to the sample reference plate and the prototype reference plate. The second interference fringe measurement is performed in the state of being rotated relative to the angle, the first and second interference fringe measurement data are averaged, and the reference plate deformability of the reference plate support frame is calculated based on the averaged data. Therefore, it is possible to obtain useful data for improving the measurement accuracy of the interference fringes in the vertical interferometer.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram showing a reference plate inspection interferometer apparatus to which a method of measuring a reference plate deformability of a reference plate support frame for a vertical interferometer according to an embodiment of the present invention is applied.

FIG. 2 is a view taken along the line AA of FIG. 1;

FIG. 3 is a diagram for explaining an example of utilization of the above-described reference plate deformability measuring method.

FIG. 4 is a diagram showing an example of an optimal combination of a sample reference plate and a reference plate support frame selected in the above utilization example.

[Explanation of symbols]

2, 2 (1), 2 (2),..., 2 (n) Sample reference plate (reference plate) 2a Sample reference surface 2b Mark 10 Reference plate inspection interferometer device 12 Vertical interferometer 14, 14 ( 1), 14 (2), ..., 14 (n)
Reference plate support frame 14a Scale 16 Standard reference plate 16a Standard reference surface 16b Mark 18 Computer 22 Interferometer body Ax Optical axis

Claims (3)

[Claims] 1. A method for measuring the deformability of a reference plate supporting frame for supporting a reference plate in a vertical interferometer in which the reference plate is horizontally disposed, the method comprising: The first interference fringe measurement is performed in a state in which the sample reference plate is horizontally arranged in a state where the sample is supported and the prototype reference plate is horizontally arranged so as to face the sample reference plate. A second interference fringe measurement is performed in a state where the reference plate support frame is relatively rotated by a predetermined angle with respect to the reference plate and the prototype reference plate, and the first and second interference fringe measurement data are averaged. A method for measuring a reference plate deformability of a reference plate support frame for a vertical interferometer, comprising calculating a reference plate deformability of the reference plate support frame based on the averaged data. 2. A method for measuring a reference plate deformability of a reference plate supporting frame supporting a reference plate in a vertical interferometer in which the reference plate is horizontally disposed, wherein the reference plate is connected to the reference plate supporting frame. The first interference fringe measurement is performed in a state in which the sample reference plate is horizontally arranged in a state where the sample is supported and the prototype reference plate is horizontally arranged so as to face the sample reference plate. With the reference plate support frame rotated relative to the reference plate and the prototype reference plate by a predetermined angle, the second
By averaging the first and second interference fringe measurement data to remove the rotationally asymmetric component of the sample reference plate, and removing the rotationally symmetric component from the averaged data, A method for measuring a reference plate deformability of a reference plate support frame for a vertical interferometer, comprising calculating a reference plate deformability of the reference plate support frame. 3. The reference plate deformability of the plurality of reference plate supporting frames is measured using the reference plate deformability measuring method according to claim 1 and the shape of the reference plane of the plurality of reference plates is measured. A combination of a reference plate and a reference plate supporting frame whose reference surface shape is closest to a plane when both are combined from the reference plate and the reference plate supporting frame. Method for selecting the reference plate for the interferometer.