JP2018059733A - Three-dimentional shape measurement system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a three-dimensional topography measurement apparatus with high accuracy and measurable for a large sized object.SOLUTION: A three-dimensional shape measurement system comprises a first two-dimensional shape measurement mechanism which measures a two-dimensional shape of a surface of a measurement object in a first direction by scanning a first autocollimator 2 relatively in the first direction at plural positions of the measurement object 4, and a second two-dimensional shape measurement mechanism which measures a two-dimensional shape of a surface of the measurement object 4 in a second direction by scanning the first autocollimator 2 relatively at a specified position of the measurement object 4 in the second direction crossing to the first direction. By coupling the two-dimensional shape in the first direction which the first two-dimensional shape measurement mechanism measured and the two-dimensional shape in the second direction which the second two-dimensional shape measurement mechanism measured at intersections of both, a three-dimensional shape of the measurement object 4 is derived.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a three-dimensional shape measurement system.

In recent years, there has been a growing need for optical components with extremely high-precision surface shapes, such as cutting-edge physics and chemistry research fields and semiconductor industry, as well as optical communication, measurement, medical care, and astronomical telescopes.
The Fizeau interferometry is the most common method for measuring the surface shape with high accuracy. The shape measurement method using the Fizeau interferometer can obtain a 3D topography at a time, and the resolution can be achieved at the nanometer level. However, because it is basically a differential measurement with a standard prototype (reference plane, reference sphere, etc.), the absolute accuracy of the measurement is limited by the accuracy of the standard prototype, and it is not easy to achieve nanometer-level absolute accuracy. Absent.

Furthermore, since the range of difference measurement is limited to a range of about several μm, it is not suitable for measurement of a high dynamic range (for example, a free-form surface). Also, the Fizeau interferometer is very difficult to increase in size due to the configuration of the apparatus.
On the other hand, in recent years, as a highly accurate shape measurement method, a method using local inclination angle measurement of an object surface has attracted attention. This method is based on the simple principle of measuring the local angle change of the object surface sequentially and obtaining the shape by integrating the obtained angle change data, and requires a reference surface. In addition, it has a feature that a large aperture shape can be measured.
Globally, the German Institute for Physical Engineering (PTB) has been developing ahead, and nano-level measurement accuracy has already been achieved.

The inventors have developed an ultra-high-precision shape measuring device (SDP: Scanning Deflectometric Profiler), and since 2015, have started calibration services related to straightness shape measurement up to about 1 m.
In SDP, as shown in FIG. 1, the measurement light of the autocollimator (AC1) is reflected by a pentamirror held on an air slide type variable stage by an air slide just before a measurement target (SUT) not shown. Irradiate the surface of the object to be measured through the held aperture.
Next, the pentamirror is scanned (scanned) by a moving stage to obtain a local tilt angle distribution on the surface to be measured. At this time, the pitching error of the moving stage can be canceled by using the pentamirror. By integrating the obtained local inclination angle distribution, a two-dimensional shape (line shape) of the surface to be measured is obtained.

  Further, in Patent Document 1, a light beam is projected onto a measurement target surface from an autocollimator, the light beam reflected on the measurement target surface is received and a local inclination angle of the measurement target surface is specified. A shape measuring device is described that accumulates local inclination angles that are sequentially specified by the specifying unit with translation, and calculates a continuous shape of the measurement target surface.

JP 2011-179891 A

However, when the local inclination angle measurement of the object surface is used, there is a problem that the measurement target is limited to a two-dimensional shape (line shape).
Moreover, although it is described in the shape measuring apparatus described in Patent Document 1 that two-dimensional shape measurement can be performed by measuring a plurality of line shapes, a moving mechanism used to obtain different line shapes is described. The relative positional relationship between the line shapes cannot be specified due to the motion error, and it is difficult to obtain a three-dimensional shape by accurately connecting the line shapes.

  Therefore, in the present invention, the SDP is used to measure the local inclination angle of the surface in the first direction, such as the radial direction or the diameter direction, and the direction intersecting these or the circumferential direction, etc. The object is to realize highly accurate 3D topography measurement by measuring the local inclination angle of the surface in the second direction and connecting both measurement results as vector information.

  In order to solve the above problems, the three-dimensional shape measurement system of the present invention uses an already developed SDP as a base, and scans at least one of the autocollimator and the measurement object relative to the other at a plurality of positions of the measurement object. A first two-dimensional shape measuring mechanism for measuring a two-dimensional shape in a first direction on the surface of the measurement object, and at least one of the autocollimator and the measurement object at the specific position of the measurement object with respect to the other. A second two-dimensional shape measuring mechanism that scans in a second direction intersecting with the first direction and measures a two-dimensional shape in the second direction on the surface of the measurement object is provided. Then, the two-dimensional shape in the first direction measured by the first two-dimensional shape measurement mechanism is connected to the two-dimensional shape in the second direction measured by the second two-dimensional shape measurement mechanism at the intersection of both. By doing so, the three-dimensional shape of the measurement object was obtained.

According to the present invention, the first two-dimensional shape obtained by the first two-dimensional shape measurement mechanism and the second two-dimensional shape obtained by the second two-dimensional shape measurement mechanism are intersected with each other. By connecting the two, the vector components of both are specified, and the three-dimensional shape of the measurement target can be accurately measured.
However, in order to measure the three-dimensional shape with higher accuracy, it is necessary to correct the angular deviation that occurs when the measurement sample is scanned in the second direction. By adopting a connection algorithm that suppresses error propagation at the time of connection by measuring the circumferential shape of the surface, the surface shape (free-form surface) with a curvature of about several meters from the plane with a measurement range of φ800 mm in the end 3D topography measurement is possible with a measurement accuracy of ± 5 nm (the world's highest accuracy).

FIG. 1 is a schematic view of an already developed ultra-high accuracy shape measuring apparatus. FIG. 2 is a schematic diagram of a three-dimensional shape measurement system according to the present invention. FIG. 3 is a diagram illustrating an intersection when a three-dimensional shape is measured. FIG. 4 is a diagram illustrating an example in which the range of the angle measurement range is expanded by measuring the rotation angle of the rotating mirror.

  Hereinafter, examples will be described with reference to the drawings.

A schematic diagram of a three-dimensional shape measurement system according to the present invention is shown in FIG.
In this three-dimensional shape measurement system, the upper part of the sample base plate 1 that supports the measurement target (SUT) adopts the same structure as that of the aforementioned SDP.
That is, the measurement is performed by the first autocollimator (AC1) 2 through the aperture held by the air slide just before the measuring object 4 (not shown) through the reflection of the pentamirror 3 holding the measurement light by the air slide. Irradiate the surface of the object 4.
Next, the pentamirror 3 is scanned in the diameter direction (first direction) of the measurement object 4 by a moving stage (not shown) to obtain a local inclination angle distribution (first diameter direction inclination angle distribution) of the measurement object surface.
At this time, by using the pentamirror 3, it is possible to cancel the pitching error of the air slide type moving stage. Then, by integrating the obtained local inclination angle distribution, a two-dimensional shape (line shape) in the first direction is obtained on the surface of the measuring object 4.
The amount of movement of the pentamirror can be measured using a linear scale or a laser length measuring machine (not shown).

In this embodiment, the sample base plate 1 of this SDP is placed on the rotary table 6 via an inclination angle adjusting device 5 arranged at equal intervals in the circumferential direction, and is measured by the first autocollimator (AC1) 2. The light and the normal vector of the surface of the measuring object 4 can be adjusted to match.
The rotary table 6 is fixed to a hollow cylindrical body 7 and is integrally rotated and positioned by an electric motor connected to the rotary table 6 or the cylindrical body 7 through a transmission mechanism such as a belt and a gear. It has come to be. The rotation angle of the rotary table 6 is measured by a built-in rotary encoder (not shown).

The bottom surface of the cylindrical body 7 is rotatably supported on a support plate 8 having an opening in the center, and the lower surface of the support plate 8 is an inclination angle composed of piezo elements and the like arranged at equal intervals in the circumferential direction. It is fixed to the base 10 via the adjusting actuator 9.
A first mirror 11 is mounted on the back surface of the rotary table 6, and the light beam emitted from the second autocollimator (AC 2) 12 is reflected in the vertical direction by the second mirror 13, and the opening of the support plate 8 is opened. The tilt angle of the turntable 6 can be measured by reflecting the first mirror 11 through the hollow portion of the cylindrical body 7.

By rotating the turntable 6, angular shake occurs on the surfaces of the turntable 6 and the measurement object 4. As will be described later, when the circumferential angle is measured by the first autocollimator 2, the measurement object 4 is measured. The combined angle of the local inclination angle and the angular deflection on the surface of the surface is read. For this reason, in order to accurately calculate the shape in the circumferential direction, it is necessary to remove the angular shake.
Therefore, in this embodiment, the first mirror 11 is installed on the back surface of the rotary table 6, the angular shake of the rotary table 6 generated during the rotation is read by the second autocollimator 12, and the inclination is reduced to reduce the angular shake. The angle adjusting actuator 9 is controlled in real time.

  When a piezo actuator with high positioning accuracy is used as the tilt angle adjusting actuator 9, the coarse movement electric actuator and the fine movement piezo actuator are connected in two stages, and the steady fluctuation is changed by the coarse movement electric actuator. The stroke adjustment width, positioning accuracy, and responsiveness may be increased by sharing the fine movement piezo actuator.

  Further, since the measurement light reflected in the vertical direction by the second mirror 13 is aligned with the center of the rotary table 6, even if the rotary stage 6 rotates, the measurement position of the second mirror 13 does not change, and the second mirror 13 does not change. The angular shake can be corrected accurately without being affected by the shape accuracy of the two mirrors 13.

If the angular deflection of the rotating table 6 can be measured, instead of the second autocollimator 12, the first mirror 11, and the second mirror 13, two level levels arranged in the orthogonal two-axis directions are used. Also good. Since the rotation angle of the rotary table 6 is measured with high accuracy by a built-in rotary encoder, angular swing of the rotary stage at an arbitrary rotation angle can be detected by these two levels.
Further, the measurement result by the first autocollimator 2 and the measurement result by the second autocollimator 12 are synchronized, and the measurement result by the first autocollimator 2 is corrected based on the measurement result by the second autocollimator 12. Also good. In this case, the tilt angle adjusting actuator 9 is not necessarily provided.

Hereinafter, the procedure for actually measuring the three-dimensional shape of the surface of the measuring object 4 will be described using the present embodiment.
Here, it is assumed that the motion axis of the air slide type moving stage for scanning the pentamirror 3 is the X axis, the gravity direction (vertical direction) is the Z axis, and the axis orthogonal to XZ is the Y axis.
(1) Optical axis adjustment of the first autocollimator 2 The angles around the Y axis and the Z axis of the first autocollimator 2 are adjusted so that the measurement light vector of the first autocollimator 2 coincides with the X axis.

(2) Adjustment of roll angle around optical axis of first autocollimator 2 Next, a flat substrate for adjustment is installed on the sample base plate 1. At this time, the adjustment flat substrate is adjusted so that the normal direction of the adjustment flat substrate coincides with the gravity direction (Z-axis). Then, the inclination of the adjustment planar substrate is measured using the first autocollimator 2. At this time, two orthogonal measurement axes of the first autocollimator 2 are taken as an H axis and a V axis. The rotation around the optical axis of the first autocollimator 2 is adjusted so that the value of the V axis of the first autocollimator 2 does not change when the pentamirror 3 is rotated around the Z axis.
(See Ralf D Geckeler, Optimal use of pentaprisms in highly accurate deflectometric scanning, measurement science and technology, 18 (2007), 115-125)

(3) Alignment adjustment of the pentamirror 3 The inclination of the pentamirror 3 around the X axis and the Z axis is adjusted. (See above paper)

(4) the rotational center coordinates of the installation and adjustment turntable 6 of the rotary table 6 Or (Xo, Yo) and when the X-axis component X ₀ of the center of rotation, by scanning the first pentagonal mirror 3, the air slide type The point at which the position of the moving stage in the motion axis direction coincides with the X coordinate of the rotation center coordinate of the rotary table 6 is defined as the origin of the X axis coordinate.
Then, the Y-axis direction of the rotary table 6 is adjusted so that the optical axis of the first autocollimator 2 passes through the rotation center of the rotary table 6 at the position (Xo) of the pentamirror.
The Y coordinate at this time is set as the origin of the X axis coordinate. The X coordinate and Y coordinate may be adjusted by adjusting not only the rotary table 6 and the first pentamirror 2 but also the aperture.

(5) Adjustment of the first mirror 11 The first mirror 11 is mounted on the rear surface of the center portion of the rotary table 6 using a tilt stage that is rotatable around the X axis and the Y axis (not shown). The first mirror 11 is a parallel plane substrate in which the reflection surface and the mounting surface are parallel, the normal vector on the first autocollimator 2 side is N1, and the normal vector on the mirror surface on the second autocollimator 12 side is N2. . The first mirror 11 is adjusted so that N1 and the rotation axis of the turntable 6 coincide.

(6) Adjustment of the second autocollimator 12 The optical axis of the second autocollimator 12 is adjusted so that the optical axis of the irradiation light reflected by the second mirror 13 matches the normal vector N2 of the first mirror 11. Thereby, the optical axis parallelisms of the first autocollimator 2 and the second autocollimator 12 coincide with each other with the accuracy of the parallel plane substrate (parallelism between N1 and N2).
Here, two orthogonal measurement axes of the second autocollimator 12 are set to H2 and V2.
At this time, the tilt angle adjusting actuator 9 is used to rotate the first mirror 11 around the Y axis or the X axis, and the amount of change in the V component and H component of the first autocollimator 2 generated at this time The second autocollimator 12 is rotated and adjusted around the measurement optical axis so that the change amounts of the V component and H component of the second autocollimator 12 coincide with each other.

(7) Placement of measurement sample When the initial adjustment of the measurement device is completed by the above operation, the measurement object 4 is placed on the sample base plate 1.
Basically, it is installed so that the center of the preset evaluation range of the surface of the measurement object 4 coincides with the rotation center of the turntable 6 as follows. Note that the evaluation range can be freely set to be circular or rectangular.
(7-1) When the measurement object 4 is a circular sample The outer periphery of the measurement object 4 placed on the rotary table 6 is measured using a dial gauge, an electric micrometer, or the like, and the measurement object 4 is placed so that there is no eccentricity. Adjust the position.
(7-2) When the measurement target 4 is a rectangular sample The first autocollimator 2 is scanned in one direction in advance, the measurable left and right end coordinates are read, and the center coordinates coincide with the rotation center of the turntable 6. Adjust to Next, the rotary table 6 is rotated by 90 °, and this operation is repeated again. In place of the first autocollimator 2, a dial gauge or an electric micrometer may be used.
If the evaluation range of the surface of the measurement object 4 is deviated from the center, the evaluation range of the surface of the measurement object 4 may be shifted from the center of the turntable 6 accordingly.

As described above, when the preliminary adjustment and the preliminary preparation are completed, scanning of the surface of the measuring object 4 by the first autocollimator 2 is started.
Hereinafter, the case where the measuring object 4 is a circular sample will be described as an example.
First, the pentamirror 3 is moved by an air slide type moving stage, and the first autocollimator 2 is scanned in the diameter direction passing through the center of the circular sample, and is located inside the outer edge 14 of the measuring object 4 as shown in FIG. The line shape from one end 15a to the other end 15b of the evaluation range 15 is measured.
This corresponds to a first two-dimensional shape measurement mechanism that measures a two-dimensional shape in the first direction (diameter direction).
In this embodiment, eight line shapes are measured every 22.5 °, and when one diametrical scan is completed, the rotary table 6 is rotated 22.5 °, and eight lines are obtained for each rotation angle. The shape measurement is repeated and recorded in the storage device.

However, the line shape obtained by this is the deviation amount (straightness shape) from the least square line of the result obtained from the first autocollimator 2, and the relative angle between each line measurement due to the movement error of the rotary stage. The relationship is unknown.
Then, in order to connect each line shape, the shape measurement of the circumference direction is performed next.
That is, after moving the pentamirror 3 from the rotation center to a radial position corresponding to the other end 15 b of the evaluation range 15, the rotary table 6 is rotated, and the circumferential direction perpendicular to the diametrical scanning axis of the pentamirror 3 Next, the local inclination angle of the surface to be measured is measured. This is a specific position of the object to be measured, and is relatively scanned in a second direction (circumferential direction) intersecting the first direction (diameter direction), and the two-dimensional in the second direction on the surface of the object to be measured. This corresponds to a second two-dimensional shape measurement mechanism that measures the shape.
In the present embodiment, the shape of the outermost diameter of the evaluation range in the circumferential direction is measured, but the radius of the circumference measurement may be arbitrarily selected within a range that intersects the line shape.

  The rotation angle of the turntable 6 can be measured with high accuracy by incorporating a rotary encoder, and the surface shape in the circumferential direction can be obtained by integrating the obtained local inclination angle distribution.

Here, in the measurement in the circumferential direction, the angular shake of the turntable 6 becomes a measurement error of the circumferential shape.
Therefore, the second autocollimator 12 and the first mirror 11 installed on the back surface of the rotary table 6 are fed back by the tilt angle adjusting actuator 9 so that the first mirror 11 does not tilt even if the rotary stage is angularly shaken. By performing the control, it is possible to cancel the circumferential measurement error.

  Each line measurement data is connected from the line shape measured in the radial direction (diameter direction) obtained as described above and the intersection point data (black dot portion in FIG. 3) of the center point and the circumference shape of the measurement object 4. Thus, it is possible to calculate highly accurate 3D topography.

The target surface that can be measured by the system is limited to the angle measurement range by the autocollimator. If the target surface is flat, it is sufficient to use a commercially available high-precision autocollimator, but the measurement range is sufficient for measuring spherical surfaces or free-form surface mirrors with a curvature of several meters to several hundred meters. Not.
Therefore, as shown in FIG. 4, in the line shape measurement, the pentamirror cut out from the half mirror 16 while performing feedback control by the tilt angle adjusting actuator 9 so that the measurement angle of AC1 does not change in the line shape measurement as described above. The reflected light from 3 is incident on the position sensor 19 through the lens 18 as reflected by the rotating mirror 17.

The position sensor 19 is placed on the focal plane of the lens 18, and when the local tilt angle changes as the pentamirror 3 scans, the beam spot position on the position sensor 19 changes, but the local tilt angle changes. Also, feedback control is performed by changing the angle of the rotating mirror 17 so that the spot position does not change.
The rotation angle of the rotary mirror 17 is measured by a high-precision rotary encoder built in the rotary table 6, and thus, a wide measurement with a measurement range of ± 10 degrees, a resolution of 0.001 angular seconds, and an accuracy of ± 0.01 angular seconds. Angle measurement with a range (high dynamic range) can be realized, and even three-dimensional surface shapes can be measured with high accuracy, even for measurement objects with a curvature of several meters to several hundred meters, such as spherical surfaces and free-form surface mirrors. It becomes possible to measure.

In the above embodiment, the autocollimator is scanned in the diameter direction as the first direction and the circumferential direction is scanned as the second direction with respect to the measurement object. As long as the three-dimensional shape of the surface to be measured can be specified by intersecting these directions, various directions can be selected according to the form of the measurement object and the measurement range.
Further, when scanning is performed in the first direction and the second direction, any of the two may be moved as long as the rotation table 6 and the first autocollimator 2 can be relatively moved.

  Currently, development of a 3D topography measurement system by XY orthogonal scanning of the measurement sample is also in progress. However, in the case of the XY orthogonal scanning system, there is a system that corrects stage motion errors by installing a bar mirror on each orthogonal axis. Necessary. In this case, since the motion error includes the shape error of the bar mirror, it is necessary to apply a method for separating the motion error and the shape error. Complex error separation techniques are a major uncertainty factor in 3D topography construction. Further, when the sample is scanned XY, the sample feeding direction orthogonal to the line shape measurement requires an apparatus space more than twice the measurement range, which hinders the enlargement.

On the other hand, according to the present invention, it is possible to measure a large-diameter shape without requiring a reference surface, and the following effects can be achieved.
(1) Space saving Since it is based on radial line measurement, it can handle large-sized objects with the minimum necessary space.
(2) The measurement light of the second autocollimator 12 that is not affected by the shape error of the angular shake correction mirror does not change the irradiation position of the first mirror 11 that corrects the angular shake of the rotary table. The angular shake can be corrected without being affected by the shape error 11. In addition, by introducing a feedback control system that mechanically corrects angular shake, the second autocollimator 12 used for correction can only measure near the center, so the two-dimensional uniformity of the autocollimator. Non-linearity is not a problem.
(3) High-precision line shape connection based on circumference measurement is possible The measurement of the circumference shape by scanning in the second direction has a resolution sub-nm and accuracy on the order of ± 1 nm as in the case of the linear shape. Since the circumferential shape with a radius of several hundred mm can be measured with high accuracy (on the order of nanometers), the relative angular relationship between the line shapes can be determined with high accuracy.

  As described above, according to the present invention, a measurement object such as a large-sized substrate can be accommodated in a necessary minimum space, and a highly accurate 3D topography can be constructed. It can be expected to be widely adopted in various fields such as the semiconductor manufacturing field.

1: Sample base plate 2: First autocollimator 3: Penta mirror 4: Measurement object 5: Inclination angle adjustment device 6: Rotary table 7: Cylindrical body 8: Support plate 9: Inclination angle adjustment actuator 10: Base 11: First 1 mirror 12: second autocollimator 13: second mirror 14: outer edge 15 of the measurement object 4: evaluation range 16: half mirror
17: Rotating mirror 18: Lens 19: Position sensor

Claims (7)

At a plurality of specific positions of the measurement object, at least one of the autocollimator and the measurement object is scanned in the first direction with respect to the other, and a plurality of two-dimensional shapes in the first direction on the surface of the measurement object are obtained. A first two-dimensional shape measuring mechanism for measuring at a position;
The autocollimator is scanned at a specific position of the measurement object, and at least one of the autocollimator and the measurement object is scanned in a second direction crossing the first direction with respect to the other, A second two-dimensional shape measuring mechanism for measuring a two-dimensional shape in the second direction on the surface,
An intersection of the two-dimensional shape in the first direction measured by the first two-dimensional shape measurement mechanism and the two-dimensional shape in the second direction measured by the second two-dimensional shape measurement mechanism A three-dimensional shape measurement system characterized in that a three-dimensional shape of the measurement object is obtained by connecting with the two.   The second two-dimensional shape measuring mechanism uses a support table on which the measurement object is placed as a rotary table, and fixes the autocollimator and rotates the rotary table when scanning in the second direction. The three-dimensional shape measurement system according to claim 1, wherein:   The three-dimensional shape measurement system according to claim 2, further comprising an inclination angle measurement device that measures an inclination angle of the rotary table with respect to a horizontal plane.   The tilt angle measuring device includes a second autocollimator that measures the tilt angle of the rotary table using a mirror attached to the center of the back surface facing the measurement object mounting surface of the rotary table. The three-dimensional shape measurement system according to claim 3.   The said inclination angle measuring device consists of two level levels arrange | positioned in the orthogonal biaxial direction on the back surface which opposes the measurement object mounting surface of the said rotary table. 3D shape measurement system.   The rotary table is fixed to a base via an inclination angle adjustment actuator, and the inclination angle adjustment actuator is fed back based on the measurement value of the inclination angle measurement device so that the rotation table is kept horizontal. The three-dimensional shape measurement system according to claim 4, further comprising a control device for controlling.   The angular shake is measured based on the measured value of the tilt angle measuring device, and the two-dimensional shape in the second direction measured by the second two-dimensional shape measuring mechanism is corrected. 5 is a three-dimensional shape measurement system.

Images