JP2001208518A - Analytic shape correction method in measurement of relative shape of surface to be inspected - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a higher accuracy of a correction shape of a surface to be inspected regardless of possible positional deviation of both of an absolute shape of a reference surface and a relative shape therepf on a screen and any difference in photographing magnification and measuring instrument by carrying out a coordination conversion of a function according to the absolute shape based on a difference in measuring conditions pertaining to a coordinate in the measurement of the relative shape and the absolute shape at a state prior to the computation made to subtract the absolute shape from 'a surface to be inspected-the relative shape of the reference surface' obtained using an interferometer. SOLUTION: Prior to the computation made to subtract an absolute shape of a reference surface from 'a surface to be inspected-a relative shape of the reference surface' obtained using an interferometer, measuring conditions pertaining to a coordinate in the main measurement made for the relative shape are compared with measuring conditions pertaining to a coordinate in the preliminary measurement made for the shape of the reference surface and based on the results of the comparison, a function a (x, y) corresponding to the shape of the reference surface 2a obtained by the preliminary measurement is converted to a function a' (x, y) on the coordinate in the main measurement so that both the shapes are set to correspond to each other on the same coordinate in a screen.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an analytical shape correction method for measuring a relative shape of a surface to be inspected by an interferometer, and more particularly, to a method of measuring a relative shape between a shape of a surface to be inspected and a reference shape using an interferometer. The present invention relates to a method for measuring the shape of a surface to be inspected on the basis of the above, and to an analytical shape correction method for obtaining the relative shape.

[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 its reflected light (or transmitted light) object light, and converts the other light beam. The reflected light (or transmitted light) is incident on the reference surface of the reference plate, and the reflected light (or transmitted light) is used as the reference light. The shape is measured as the shape of the surface to be measured.

[0003] Therefore, since the shape of the reference surface directly causes an error in the shape of the surface to be inspected, it is important to ensure sufficient flatness and surface accuracy of the reference surface.

However, in recent surface measurements, accuracy on the order of sub-microns has been required, and it is difficult to prepare a reference surface corresponding to the accuracy. A method of measuring a shape in advance, measuring the relative shape, and then analytically subtracting a reference surface shape measured in advance from the relative shape has attracted attention (for example, Japanese Patent Application Laid-Open No. Three
No. 7742).

[0005]

By the way, in the above-described method, the relative shape and the reference surface shape are different from each other by CC.
Since these are obtained based on the fringe image captured by the D camera or the like, when performing the subtraction calculation of both shapes, both captured images must be set to correspond to each other on the same coordinates. Is a necessary condition.

However, there is a time lag between the above two measurement states, so that the measurement environment changes between them, and a physical displacement occurs when setting the reference plate or the subject. Inevitably, misalignment occurs between these captured stripe images in the screen.

[0007] In addition, the imaging magnification may be different between the two measurements, or the interferometer to be measured itself may be different. Therefore, it is difficult to obtain the shape of the surface to be measured with high accuracy in the actual measurement using the theoretically superior method using the subtraction operation.

The present invention has been made in view of such circumstances, and a method for measuring a shape of a test surface by subtracting an absolute shape of a reference from a relative shape of the test surface and a reference obtained by using an interferometer. In the measurement of the relative shape and the absolute shape, even if there is a displacement on the screen or the imaging magnification or the measurement device is different, the test result obtained by the subtraction calculation is It is an object of the present invention to provide an analytical shape correction method for measuring a relative shape of a test surface, which can make the surface shape highly accurate.

[0009]

According to the present invention, there is provided an analytical shape correcting method for measuring a relative shape of a surface to be inspected, which uses an interferometer to detect the relative shape of the surface to be inspected and a reference shape. In the test surface relative shape measurement for measuring the shape of the surface, perform preliminary measurement to measure the reference shape, obtain a function a according to the measured shape, and store the function a in a memory, On the other hand, the main measurement for measuring the relative shape between the shape of the test surface and the reference shape is performed using an interferometer, a function b corresponding to the measured shape is obtained, and the function b is stored in the memory. The function a stored in the memory is converted into a function a ′ on the coordinates in the main measurement based on a difference between the measurement conditions related to the coordinates in the main measurement and the measurement conditions related to the coordinates in the preliminary measurement. The function stored in the memory Wherein by calculating the difference between b and The function a'it is characterized in that for correcting the measured shape of the surface.

Further, the coordinates relating to the preliminary measurement and the coordinates relating to the main measurement are, for example, rectangular coordinates.
The measurement condition relating to the coordinates is, for example, the image center position and / or the magnification of the image and / or the amount of rotation from the reference position of the image. Further, the preliminary measurement may include:
For example, a three-plane alignment measurement method using three reference plates.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 2 is an overall configuration diagram showing an interferometer device for performing an analytical shape correction method in measurement of a relative shape of a test surface according to an embodiment of the present invention.

As shown, the interferometer device 10
Comprises a Fizeau-type vertical interferometer 12, a reference plate 2 disposed above the subject 16 so as to face the subject 16, a computer 18, and a monitor 20. I have.

The vertical interferometer 12 causes the coherent light from a light source (not shown) to enter the reference surface 2a of the reference plate 2 by the interferometer main body 22, and converts the transmitted light beam and the reflected light beam on the reference surface 2a. The light is divided into two parts, the reflected light on the reference surface 2a is used as reference light, and the transmitted light beam is made incident on the test surface 16a of the subject 16 and the reflected light is used as object light. The interference fringes generated by the above are captured by a CCD camera (not shown).

The vertical interferometer 12 has a fringe scan analysis function. That is, the reference plate 2 is moved in the direction of the optical axis Ax together with the reference plate support frame 14 (or the subject 16 is moved in the direction of the optical axis Ax). The data is output to the computer 18. Then, the computer 18 automatically analyzes the interference fringes by the fringe scanning method based on the input image data of the interference fringes, and performs the relative shape measurement (the unevenness determination and the three-dimensional shape measurement) between the test surface 16a and the reference surface 2a. At the same time, interference fringes or three-dimensional image data is displayed on the monitor 20. In the fringe scanning method, the interference fringe intensity corresponding to each point on the test surface 16a is obtained from the interference fringe image data captured at each predetermined fringe scan step while changing the relative distance between the test surface 16a and the reference surface 2a. Is measured, and interference fringe analysis such as phase calculation for each point is performed using the measurement result.

In recent years, surface measurements have been required to have an accuracy on the order of submicrons, and the shape of the reference surface 2a can be determined by, for example, a well-known three-plane alignment method (for example, disclosed by the present applicant. JP 11-377
No. 42) is measured in advance using the test surface 1
A method is known in which after measuring the relative shape of the reference surface 2a and the reference surface 2a, the previously measured shape of the reference surface 2a is analytically subtracted from the relative shape.

However, in the above-described method, since the relative shape and the shape of the reference surface 2a are obtained based on a fringe image captured by a CCD camera or the like, a subtraction operation of both shapes is performed. In this case, it is necessary that both shapes are set to correspond to each other on the same coordinates on the screen.

Therefore, in the present embodiment, before subtracting the absolute shape of the reference surface from the relative shape of the test surface and the reference surface obtained by using the interferometer, the relative shape is measured before the actual measurement. Are compared with the measurement conditions relating to the coordinates at the time of the preliminary measurement of the shape of the reference surface 2a, and based on the comparison result, the measurement conditions according to the shape of the reference surface 2a obtained by the preliminary measurement are obtained. Function a
(X, y) is converted to a function a ′ (x,
y) so that the two shapes are set to correspond to each other on the same coordinates on the screen. Therefore, after this, the function a ′ (x, y) is subtracted from the function b (x, y) corresponding to the relative shape obtained by the main measurement, thereby calculating the measured shape of the surface to be measured. Correction can be made accurately and easily.

Hereinafter, an analytical shape correction method in the relative shape measurement of the surface to be inspected in the present embodiment will be specifically described with reference to a flowchart shown in FIG. That is, in the method of the present embodiment, first, as described above, the absolute shape of the reference plate surface is measured (preliminary measurement) using a well-known method such as the three-plane alignment method, and a function on the rectangular coordinates according to the shape is measured. a (x,
y) is obtained (S1).

Next, the first coordinate conditions (orthogonal coordinates) such as the center position, magnification, and the amount of rotation from the reference position of the reference surface 2a on the screen during the preliminary measurement are measured (S2). The function a (x, y) and the first coordinate condition obtained in the above steps 1 and 2 (S1, S2) are
8 (S3). Thereafter, the relative shape of the test surface 16a and the reference surface 2a is measured (main measurement) using the interferometer device 10, and a function b (x, y) on the orthogonal coordinates corresponding to the shape is obtained (S4). ).

Next, second coordinate conditions (orthogonal coordinates) such as the center position, magnification, and rotation amount from the reference position of the reference surface 2a on the screen at the time of the main measurement are measured (S5). Function b obtained in steps 4 and 5 (S4, S5)
(X, y) and the second coordinate condition are stored in the computer 18
(S6).

Next, the first coordinate condition and the second coordinate condition stored in the memory are compared (S7). If they match, the process directly proceeds to step 10 (S10). Before proceeding to step 10 (S10), the processes of step 8 (S8) and step 9 (S9) are performed.
That is, if they do not match, the function a (x, y) related to the absolute shape of the reference plate surface obtained in the preliminary measurement and stored in the memory is subjected to coordinate conversion based on the second coordinate condition. To obtain a new function a ′ (x, y) (S
8), and store this function a ′ (x, y) in the memory (S
9).

Finally, a function b corresponding to the relative shape obtained in the above main measurement and stored in the memory
The function a '(x, y) is subtracted from (x, y) to perform an arithmetic operation (S10). When the process directly proceeds from step 7 (S7) to step 10 (S10), this step 1
0 (S10), a function b corresponding to the relative shape
The above function a (x, y) is subtracted from (x, y) to calculate.

This will be conceptually described with reference to FIG. In this case, for convenience of explanation, it is assumed that the difference between the above two coordinate conditions is due to only a parallel positional displacement (center positional displacement) on the coordinates.

That is, FIG. 3A is an interference fringe image (actually not obtained as an image) representing the absolute shape of the reference plane 2a obtained by preliminary measurement, and the corresponding function is a (X, y). On the other hand, FIG.
This is an interference fringe image showing the relative shape between the test surface 16a and the reference surface 2a obtained by the main measurement, and the corresponding function is b
(X, y).

[0025] when obtaining the two interference fringe image, when comparing the measurement condition relating to the coordinates, to the position O'a point on the image of interest from the position O, only x ₁ on the x-coordinate and y-coordinate and it had been shifted by y ₁ above.

In this case, the function a (x, y) is converted to the x coordinate
X on the mark₁Only, and y on the y coordinate ₁Function shifted
a ′ (x, y). This function a '(x, y)
Conceptually represented so as to correspond to the function b (x, y)
Is shown in FIG. At this time, the function b (x, y) and the function
The number a '(x, y) corresponds on the same coordinates on the screen
Will be set to a state where

Thereafter, by performing a subtraction operation between the function b (x, y) and the function a '(x, y), the corrected shape of the test surface 16a as shown in FIG. It can be obtained with high accuracy.

In the above description, the difference between the measurement conditions (coordinate conditions) for the two coordinates is based only on the parallel positional shift (center position shift) on the coordinates. However, the measurement may be performed instead or together with this. Even in the case where there is a difference in magnification or the case where the coordinates are rotated on the screen, it is possible to obtain an accurate corrected shape of the test surface 16a in the same manner.

Various methods can be used for measuring the measurement conditions (coordinate conditions) relating to the coordinates. For example, as disclosed in Japanese Patent Application Laid-Open No. 9-203619, the yarn is cross-shaped. The image may be stretched and marked to determine the amount of rotation of the image from the reference position, the image center position, and the like. Also, for example, a scale functioning as a scale may be arranged in the visual field, and the magnification of the image may be determined based on the ratio of the scale size observed during the two measurements.

In the above embodiment, the measurement conditions (coordinate conditions) for the two coordinates are temporarily stored in the memory, and the comparison process is performed by the computer 18. In the above, the operator may input a predetermined comparison result to the computer 18 by input means such as a keyboard.

In the above embodiment, the two coordinates are both orthogonal coordinates. However, the method of the present invention is not limited to this. Is also applicable, and is also applicable to a case where two coordinates are different coordinate systems.

Further, in the above embodiment, the case where the interferometer 12 is a Fizeau type interferometer has been described. The same operation and effect as in the present embodiment can be obtained by adopting.

Further, the present invention is applicable not only to fringe analysis of interference fringe images but also to fringe analysis in general, and can be applied to fringe analysis of moire fringe images, for example.

[0034]

According to the analytical shape correcting method for measuring the relative shape of the test surface according to the present invention, the method for subtracting the absolute shape of the reference from the relative shape of the test surface and the reference obtained by using the interferometer is performed. In the step, a function corresponding to the absolute shape is coordinate-transformed based on a difference in measurement conditions relating to coordinates when measuring the relative shape and the absolute shape, and the two shapes correspond on the same coordinate on the screen. , So that even if both shapes are displaced on the screen or if the imaging magnification or the measurement device is different,
The shape of the test surface obtained as a result of the subtraction operation can be made highly accurate.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating an analytical shape correction method in measurement of a relative shape of a test surface according to an embodiment of the present invention.

FIG. 2 is an overall configuration diagram showing an interferometer apparatus for performing an analytical shape correction method in relative shape measurement of a test surface according to an embodiment of the present invention.

FIG. 3 is a diagram conceptually illustrating an analytical shape correction method in measuring a relative shape of a test surface according to an embodiment of the present invention.

[Explanation of symbols]

 2 Reference Plate 2a Reference Surface 10 Interferometer Device 12 Interferometer 14 Reference Plate Supporting Frame 16 Subject 16a Test Surface 18 Computer 22 Interferometer Body Ax Optical Axis

Claims (4)

[Claims] 1. A relative surface shape measurement for measuring a shape of a test surface based on a relative shape between the shape of the test surface and a reference shape using an interferometer, wherein the reference shape is measured. Preliminary measurement is performed, a function a corresponding to the measured shape is obtained, and the function a is stored in a memory. On the other hand, a relative shape between the shape of the test surface and the reference shape is measured. The main measurement is performed using an interferometer, a function b corresponding to the measured shape is obtained, and the function b is stored in a memory. The measurement conditions related to the coordinates in the main measurement and the measurements related to the coordinates in the preliminary measurement Based on the difference from the condition, the function a stored in the memory is converted into a function a ′ on the coordinates in the main measurement, and the difference between the function b stored in the memory and the function a ′ is calculated. To correct the measured shape of the test surface, Analytical shape correction method in the test surface relative shape measurement, characterized and. 2. The method according to claim 1, wherein the coordinates relating to the preliminary measurement and the coordinates relating to the preliminary measurement are orthogonal coordinates. 3. The relative shape of a surface to be inspected according to claim 1, wherein the measurement condition relating to the coordinates is an image center position and / or an image magnification and / or a rotation amount from a reference position of the image. Analytical shape correction method in measurement. 4. The preliminary measurement is performed using three reference plates.
4. The method according to claim 1, wherein the method is a surface alignment measurement method.