JPH01291105A - Measurement preparing method for surface shape measuring method - Google Patents

Abstract

PURPOSE:To exactly install an object to be inspected in a measuring position where the measuring range becomes maximum and to exactly set an analytic area by simulating one of optical paths extending from the measuring position of the object to be inspected to a photoelectric detecting device. CONSTITUTION:By simulating an optical path extending from a measuring position of an object O to be inspected to an area sensor 30 as shown in a figure (a), a program for tracking a light beam is stored in a controller (CPU). Subsequently, the setting surface OS is installed in a reference position (a point C in a figure b) of the optical path which has been simulated, plural reflected light beams L1-L7 by the setting surface OS are set, a number is given in order from an optical axis Ax, tracking of a light beam against each reflected light beam is executed by a simulation, vignetting, an omission and an intersection of the light beam are checked up by the number of light beams of the reflected light beams on the light receiving surface S of the sensor 30 which has been simulated, the incident position and the array rank order of the light beam, and a measurable range of the surface OS and an effective analytic area are derived. In this state, the surface OS is moved on an optical axis by a simulation, said process is repeated, the object O to be inspected is installed in the measuring position where the measurable range is maximum, and also, an effective analytic area to this position is set as an analytic area.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a measurement preparation method in a surface shape measurement method.

(Prior art) As a device that measures the surface shape of an object using an interferometry method,
Conventionally, a device as shown in FIG. 8 has been known (Japanese Unexamined Patent Publication No. 59-90009).

The beam diameter of the light emitted from the laser light source 10 is expanded by the beam expander 12, passes through the beam splitters 14 and 18 as a parallel beam, is converged by the objective lens 18, and then becomes a diverging beam to be focused on the object 0. The light is incident on the surface to be measured, that is, the surface to be inspected.

The light reflected by the test surface passes through the objective lens 18 and is separated into two beams by the beam splitter 16, one of which passes through the beam splitters 14 and 26 and the imaging lens 28 to the area of the photoelectric detection device. The light is incident on the light receiving surface of the sensor 30. The other side is a mirror 20 and a parallel plate 24
, beam splitter 26, and imaging lens 28 onto the light receiving surface. The preceding vehicle passing through the above plane g2D is
By passing through the parallel plate 24, the light beam is laterally shifted or sheared by a predetermined distance in a direction perpendicular to the optical axis. As a result, the two light beams incident on the light receiving surface of the area sensor 30 interfere with each other and generate interference fringes. The plane mirror 20 is displaced by small distances by the piezoelectric element 22. As a result, the difference in optical path length between the two light beams incident on the area sensor 30 changes, and the interference fringes on the light receiving surface change. Each pattern of interference fringes that changes in this way is read by an area sensor and predetermined analytical calculation processing is performed.

The shape of the surface to be inspected is obtained.

In this type of surface profile measurement method, the measurement range changes depending on the installation position of the surface of the test object, so it is extremely important to determine where the test object is positioned on the optical axis of the measuring device. Become.

Conventionally, in order to determine the position to install a test object in such a measurement device, the test object was actually set in the measurement device, moved in the optical axis direction of the measurement device, and placed at various positions. The output of the area sensor is observed on a monitor, the test object is fixed at the position where the image size of the test surface is maximized, and WJ determination is performed.

However, with this conventional installation method, simple vignetting of light rays can be detected, but missing or crossing light rays cannot be detected. Therefore, if there is a missing or crossing light ray during measurement,
Since erroneous data is analyzed during analytical calculations, large errors will be included in the measurements, making accurate measurements impossible.

Here, the vignetting, omission, and intersection of the light rays mentioned above will be briefly explained.

In FIG. 9, the symbol O indicates the object to be tested as in FIG. 8, the symbol A indicates the aperture of the optical system of the measuring device, and the symbol S indicates the light-receiving surface of the area sensor.

The test surface of the test object O is assumed to be symmetrical with respect to the optical axis AX, and seven reflected light rays L1 to L7 on one side of the optical axis AX are considered.

These reflected rays 1 to L7 are respectively rays L12°L22. L32. ,,,L72
Furthermore, on the light-receiving surface S, the light ray L13. L23. L
33. ．． ．． , L73.

In FIG. 9(I), among the reflected rays, only rays L12. L22. L32. L42, and on the light receiving surface S there is light fiL13. L23. L33. L
43 reached and tailed. That is, the reflected light Hs is 1 to L7 and L5. L6. L7Lt7 Perch Your A with ray L52. L
62. The light enters as L72, eclipses the aperture A, and does not reach the light receiving surface S. This is vignetting of the light rays.

Looking at FIG. 9 (II), in this example the reflected rays L1 to L
7, the reflected ray L7 enters the aperture A with light 11L72
However, it does not reach the light-receiving surface S due to eclipse
Other light rays appear on the light receiving surface S, such as light ray L13. L23. It has been reached as L33°,,L63. However, although the reflected rays are arranged in J order numbers L1 to L7 from the optical axis, the corresponding rays are out of order on the light receiving surface S.
The order of rays LS3 and L83 has been swapped. This means that, as shown in the figure, an intersection that should not exist between the light rays L53 and L63 occurs within the optical system.

In this way, a case where the original order of the reflected light rays and the arrangement order of the corresponding light rays on the light receiving surface do not match is called a ray intersection.

In FIG. 9 (III), light j9iL1 on the light receiving surface S
Although the arrangement order of L4.3 to L73 is from the smallest number to the first, one reflected light L4. These reflected rays, which the ray corresponding to L5 has not reached, enter the aperture A with ray L42. The light enters as L52 and vignettes the aperture A. Such a case is called ray omission.

In the case of the above-mentioned conventional installation method, no matter how much you monitor the output of the area sensor, it is impossible to establish a correspondence between the points on the test surface and the points on the image on the light receiving surface, resulting in light rays missing and Crossing cannot be detected, and in reality, if there is a missing beam or a crossing force of 1, the measurement error will increase. Further, even if it is found that there are omissions or intersections of light rays, it is not possible to determine how far the effective range of analysis can be made, that is, what is the effective analysis area.

Since the measurement range cannot be known, it is not possible to find the installation position where the measurement range is maximum and perform efficient measurement.

(Purpose) The present invention has been made in view of the above-mentioned circumstances, and its purpose is to measure the six objects to be measured to maximize the measurement range when measuring the surface shape by interferometric measurement. The purpose of the present invention is to provide a new measurement preparation method that allows accurate setting of values and locations, and allows accurate setting of analysis areas.

(composition) The present invention will be explained below.

The present invention provides a surface profile measurement method that uses an interferometry method to measure a target having a surface shape similar to a set surface with a known surface shape. This is a method for setting an analysis area, and has the following characteristics.

One of the optical paths from the target measurement position to the photoelectric detection device is simulated, and a setting surface is installed at the reference position of the simulated optical path. A plurality of reflected light rays by this set surface are set, and codes are assigned in order from the optical axis, and ray tracing for each reflected light ray is performed by simulation on the light receiving surface of the simulated photoelectric detection device. The measurable range and effective analysis area of the set surface are determined by checking the vignetting, missing, and crossing of the reflected rays based on the number of rays, the incident position, and the arrangement order of the rays. Then, by moving the above setting surface on the optical axis by simulation, the above measurable range,
Repeat the process of determining the effective analysis area, identify the position with the maximum measurable range as the measurement position, install the test object at the measurement position specified in this way, and set the effective analysis area corresponding to the measurement position as the analysis area. Set as .

The basic idea of the present invention is as follows. If we consider specifically the case where the surface shape of a test object is measured using an interferometric measurement method, the test object is often an aspherical lens or a mold for manufacturing an aspherical lens, for example.
In other words, the shape of the surface to be measured is rarely completely unknown; in many cases, the desired shape is known in advance, and measurement is performed by determining how the surface to be measured is shaped. This is often done for the purpose of determining whether the approximation is reasonably good. To explain specifically, 1. For example, if we consider the above-mentioned mold for manufacturing an aspherical lens as the test object, the test surface corresponds to the shape of the aspheric surface of the lens to be manufactured, and therefore, this shape has been determined in advance. It is a designed and known shape. Therefore, this known surface shape will be referred to as a setting surface. Then, the shape of the surface to be inspected of the mold to be inspected is machined so that it is -fi to the above-mentioned setting surface, but at the final finishing stage, the shape of the surface to be inspected that is actually machined is At this stage, where it is necessary to know how well the target surface matches the set surface, it can be said that the shape of the test surface approximates the shape of the set surface with considerable accuracy.

The present invention utilizes this fact.

(Example) Hereinafter, description will be given based on specific examples.

To implement the invention, one must first simulate one of the optical paths from the measured measurement position to the photoelectric detection device.

As a specific surface shape measuring device, one whose optical system is shown in FIG. 8 is assumed. As shown in FIG. 3, the measuring device 100 and drive system 200 can be controlled by a control device 300, and control conditions can be set by an operating section 400. The measuring device 100 is a device as shown in FIG.
This is the part that is moved above and controls the opening and closing of the shutter necessary for measurement. In addition, the control device is
It is a part that performs simulation for installing the test object, performs data calculation based on the output of the photoelectric detection device of the measurement device, or controls the drive of the drive system 200, and has no specific details. A computer is used.

Further, the operation unit is, for example, a keyboard.

In this embodiment, the part shown in FIG. 4 of the optical system shown in FIG. 8 is used for the simulation.
, 14, 2B, the optical path passing through the imaging lens 28 and reaching the area sensor 30, which is a photoelectric detection device, is simulated, and a ray tracing program is stored in the control device.

The cat's eye point C (FIG. 5), where the illumination light beam is converged by the action of the objective lens 18, is taken as a measurement reference.

The installation of the test object is performed according to the procedure shown in FIG.

First, the object to be tested is set in the disposal system and placed at a reference position. Here, the reference position is a position where the designed center of curvature of a portion on the optical axis of the test surface, that is, the center of curvature of the setting surface on the optical axis coincides with the cat's eye point C, as shown in FIG. This is the position shown in . The distance 1iR■ is the radius of curvature of the setting surface on the optical axis. This position is called the R match point.

Next, as shown in FIG. 1, correspondence is established between the actual machine and the simulation. This correspondence is performed as follows. That is, data related to the set surface, such as the radius of curvature and the aspheric coefficient, which are essential for ray tracing, are set in the control device 300 by operating the operating section.

Further, the position of the setting plane, that is, the position on the simulation is set at the R match point.

Subsequently, measurement is started as shown in FIG. The measurement referred to here is the measurement of the measurement range etc. by simulation.

The simulation can be performed as follows. First, as shown in Figure 6, the optical axis (optical axis in the simulation) A
The r-axis is taken in the direction perpendicular to X, and there are multiple points on this r-axis, seven points r1 to r7 in this example.

The erl to be set is a point on the optical axis, and as it leaves the optical axis, it is sequentially r2. r3. , , , , r6. r7 yells.

Next, correspond to these points R1 to R7. The reflected light rays from each point on the setting plane O5 are sequentially labeled from the optical axis side, and are sequentially labeled L1 to L7 as shown in FIG.

In addition, the rays of these reflected rays L1 to L7 at the position of the aperture A are as shown in the figure. L22. L32
．． L42°L52. L62. L72, and the light above the light receiving surface S of the area sensor is 11tL13. L23. L33. L
43. IJ3, L83. L73 Nisole (and corresponds to it. After all, in these codes, the number next to L (
Light rays having the same values (1 to 7) represent the same light ray, and this number represents the order of each reflected light, that is, the light ray number. The reflection origin and direction of each reflected ray are calculated according to the ray tracing simulation program according to the previously set data.Next, as shown in the flow diagram of Figure 1, the position on the optical axis of the setting surface ( (This is determined as a setting condition), the measurable range of the setting surface, and the effective size of the image on the area sensor are detected.

For this purpose, ray tracing is performed by simulation for each of the reflected lights L1 to L7, and the rays reaching the light-receiving surface S and their arrival positions are investigated. Based on the results, the presence or absence of vignetting, omissions, and intersections is determined. investigate. Then, based on the results, the measurable range of the measurement surface and the effective size of the image on the area sensor are laterally compared.

This simulation step is performed in accordance with the flowchart shown in FIG.

First, it is checked whether the number of light rays on the area sensor, that is, the number of light rays that have reached the light receiving surface of the area sensor, is equal to the maximum number of light rays, that is, 7 in the example being explained. It will be done. If they are equal, there will be no vignetting, and if they are not equal, there will be vignetting. This determines the presence or absence of vignetting.Next, it is checked whether the arrangement of the light beams on the light receiving surface is in numerical order. In this case, whether or not the arrangement is in numerical order does not matter whether the rays are missing or not, but whether the rays are arranged in descending order of the ray number from the optical axis side.

If the array starts with a small ray number, it can be seen that there is no intersection of rays. If it is found that there is no intersection, the first step is to check whether there are any missing ray numbers in the array of ray numbers on the light receiving surface. If there are no gaps, it is clear that there are no missing rays.

Now, according to the above investigation, if there are no missing or intersecting rays, then
Perform the procedure (■) in Figure 2. At this time, there is no omission or crossing of the light rays, and there is no or no vignetting, and the state of the light rays on the light-receiving surface S is as shown in (1) in Figure 7. (If there is no vignetting) Or, for example, the result will be as shown in (2) in the same figure (if there is vignetting, the two reflected rays L6 and L7 are vignetted). The area defined by the distance from the optical axis of the ray corresponding to the largest number of rays (7 when there is no vignetting, 5 when there is vignetting, for example 5 in Fig. 7 (2)) is the effective area. This is the analysis range of interference fringes, that is, the effective analysis area, and the test surface range defined by the reflected light beam having the above-mentioned ray number is the measurable range, so these are respectively defined as the effective analysis area and the measurable range.

As a specific example, the state of the light beam on the light receiving surface is shown in Figure 7 (2).
), the effective analysis area, which is the axis rotation of the effective image, is a circular area on the light-receiving surface S centered on the optical axis, with the radius being the distance between the optical axis and the ray L5 with the largest ray number. It becomes an area. Moreover, the measurable range at this time is the setting surface area surrounded by a circle with radius r5 centered on the optical axis in FIG.

Next, in FIG. 2, if there is a missing ray number on the area sensor, perform the procedure (2). In this state, the light rays may be missing, and there may or may not be vignetting.

(3) in Fig. 7 is a case where there is no vignetting but there is a missing light ray (reflected light @ L5 and L6 are missing), and Fig. 7 (4) is a case where there is vignetting and missing (reflected light ray L7). is vignetted, and the same rays L4 and L5 are missing)
In this case, in step (2), the rays Li2, etc. on the light-receiving surface are looked at in order from the optical axis side, that is, in order from the smallest ray number, and the rays with one ray number one younger than the missing ray are found. For example, if the state of the light beam is as shown in Fig. 7 (4) on the light receiving surface S, the distance between the light beam L33 and the optical axis is defined as the radius. The area around the optical axis is the effective analysis area, and the measurable range is the area with radius r3 around the optical axis.

Next, if the light rays on the area sensor are not in numerical order in Figure 2, perform the procedure (■) as shown in Figure 1.This state is when there is intersection of the light rays, specifically, there is only intersection. In some cases, there may be intersections and vignetting, and there may be intersections, vignetting, and omissions.

Specific examples are shown in FIG. 7 (5) to (8).

Figure 7 (5) is the case where there is only intersection of rays;
Figure (6) shows a state where there is intersection and vignetting, and Figure 7 (7) shows a state where there is intersection, vignetting, and omission.

In these cases, the distance from the optical axis of the ray with the highest ray number among the rays that reached the light receiving surface and other rays is compared, and if the distance from the optical axis of the ray with the highest ray number is exceeded, rays with the longest distance from the optical axis (Fig. 7 (5), (6)
), the range defined by the ray L23 (in the case of Fig. 7 (7), the ray L33) is the effective analysis area, and the area defined by the corresponding reflected ray (in the case of Fig. 7 (5) and (6)) is the effective analysis area. In both cases, the range within a radius of 12 from the optical axis (in FIG. 7, the range within a radius of 13 from the optical axis) is the measurable area. 7th
Figure (8) also shows a state in which there are crossings, omissions, and vignetting, but in this case, there is a omission of the light ray inside the state that was set as the effective area by the procedure in step ① above, so in this case, first, In other words, compare the distance from the optical axis of the ray with the highest ray number among the rays that reached the light receiving surface with the distance from the optical axis of the other rays, and make sure that the distance from the optical axis of the ray with the highest ray number is not exceeded. , the range defined by the ray having the longest distance from the optical axis is examined, and then, as shown in FIG. 2, the presence or absence of missing ray numbers within this range is examined. If the ray number is missing, that is, as shown in Figure 7 (8), follow the steps in ■. In this case, within the range investigated in (■), do the same procedure as in (■) above. , Check the effective analysis area and the measurable range in the same manner as in the procedure (2) above.

In this way, the measurable range for the test object is determined, so this measurable range is set as 51, the effective analysis area AN, and the upper optical axis 'tlx on the simulation surface of the setting surface.
It is taken into the control device 300 as data along with x.

Next, change the position axis of the setting surface by a predetermined distance on the optical axis, for example, llI■, and follow the above procedure to measure the measurable range S! for this new position x8. , effective analysis area AN! Then, change the position of the setting surface on the optical axis and repeat the same process. As shown in Figure 16, detect in the entire detection area. The above process is repeated a predetermined number of times, for example, 20 times, until the process is completed, and the data x1 to Xxo=St-5zo, ANx to A
Got Nzo and these 51~S! ! Find the largest SMAX among the 1s and the corresponding XMAX. XMAX obtained at this time is the position where the measurement range is maximum when the setting surface is placed at this position.

Therefore, this position is specified as the measurement position. Then, the test object already held in the drive system is moved so that its test surface is located at the measurement position. Then, actual surface shape measurement is performed. At this time, analysis is performed on the effective analysis area determined above, that is, the analysis area determined together with the measurement position.

As mentioned above, the actual test surface approximates the set surface, so the measurable range and effective analysis area determined as above are the measurable area and effective analysis area for the actual test surface. If the measurement is performed in the manner described above, it is possible to eliminate the effects of abnormalities such as vignetting, omission, and crossing of light beams, making it possible to perform extremely efficient measurements.

(Effects) As described above, according to the present invention, a measurement preparation method in a surface shape measurement method can be provided.

This method has the above configuration, so by preparing for measurement using this method, the test object can be placed at a position where the measurement range is maximum, and the effective range of the analysis area can also be determined. This eliminates the influence of abnormalities such as vignetting, omission, and intersection of light beams, making it possible to measure the surface shape with extremely high accuracy.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram for explaining the present invention. FIG. 2 is a flow diagram for explaining the characteristic parts of the present invention, FIG. 3 is a system diagram, FIGS. 4 to 7 are diagrams for explaining the present invention in connection with embodiments, and FIG. 8 and 9 are diagrams for explaining the solution section of one invention. OS, , Setting surface, O06, Test object, S01. Photoelectric detection device No.42 Atsushi e2? mouth (i) (2)
(3) ('7) (f3)

Claims (1)

[Claims of Claims] In a surface profile measurement method in which a test object having a surface shape similar to a set surface with a known surface shape is measured by an interferometric measurement method, the test object is placed at an optimal measurement position, In addition, there is a method for setting an analysis area, which includes simulating one of the optical paths from the measurement position of the object to the photoelectric detection device, installing a setting surface at the reference position of the simulated optical path, and
A plurality of reflected rays by this setting surface are set, codes are assigned in order from the optical axis, ray tracing for each reflected ray is performed by simulation, and the reflected rays on the light receiving surface of the simulated photoelectric detection device are The measurable range and effective analysis area of the set surface are determined by examining the number of light rays, the incident position, and the arrangement order of the light rays for vignetting, dropouts, and intersections, and the above set surface is moved on the optical axis through simulation, and the above Repeat the process of determining the measurable range and effective analysis area, identify the position with the maximum measurable range as the measurement position, install the object to be measured at the thus identified measurement position, and perform effective analysis for this measurement position. A test object setting method characterized by setting a region as an analysis region.