JP4066629B2 - 3D shape measurement optical system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a three-dimensional shape measurement optical system, for example, a confocal detection type three-dimensional shape measurement optical system characteristic of a slit illumination optical system.
[0002]
[Prior art]
A confocal detection method is known as one of methods used for measuring a three-dimensional shape. The confocal detection method includes a pinhole method, a slit method, etc. However, the slit method can obtain multi-point height information with a single scanning operation. The method is more advantageous. However, since the amount of light per unit area decreases because the point light source is expanded in a slit shape, high measurement accuracy can be obtained if the reflectivity of the measurement object is low or the angle of the measured surface with respect to the optical axis is large. It is difficult. Therefore, there is a demand for a compact slit illumination optical system that can obtain illumination light having a uniform and high light quantity in the longitudinal direction of the slit and having a full length. As a method of extending the illumination light in the longitudinal direction of the slit, use of an expander optical system for laser is common. For example, a slit illumination optical system for a defect inspection apparatus that includes an expander optical system including a lens group is described in Japanese Patent Application Laid-Open No. 2000-105203.
[0003]
[Problems to be solved by the invention]
However, as described in Japanese Patent Application Laid-Open No. 2000-105203, when the expander optical system is configured by a lens group, the light flux density decreases at both ends in the slit longitudinal direction, and the light amount in the slit longitudinal direction decreases unevenly. Will do. Further, as the enlargement magnification increases, the entire length of the expander optical system becomes longer. Further, the laser beam collimated by the collimator lens is expanded not only in the longitudinal direction of the slit but also in the lateral direction of the slit by the expander optical system including the lens group. For this reason, when a desired NA (Numerical Aperture) is to be obtained in a slit imaging optical system that forms an image of expanded collimated light in a slit shape, the focal length of the slit imaging optical system becomes long, and slit illumination optics The total length of the system becomes longer.
[0004]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a three-dimensional shape measurement optical system including a compact slit illumination optical system capable of obtaining uniform and high amount of illumination light. .
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a three-dimensional shape measuring optical system according to a first aspect of the invention forms a point light source that emits illumination light spreading in an elliptical cone shape, and forms an image of the illumination light from the point light source in a slit shape. A slit illumination optical system, a collimator optical system for converting the illumination light emitted by the slit illumination optical system into parallel light, and the elliptical long axis of the illumination light. An anamorphic prism system that expands only in the direction, a cylindrical optical system that focuses the illumination light only in the elliptical minor axis direction, and transmission when the illumination light is incident on the prism surface of the anamorphic prism system And a polarization direction conversion element that converts the polarization direction of the illumination light so as to maximize the rate.
[0006]
A three-dimensional shape measurement optical system according to a second aspect of the present invention is the configuration of the first aspect, wherein an imaging position of the illumination light is set to a desired position in the optical path of the illumination light converted into parallel light by the collimator optical system. An optical axis direction deflecting means for fine adjustment is arranged.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a three-dimensional shape measurement optical system embodying the present invention will be described with reference to the drawings. FIG. 1 shows a configuration example of a slit illumination optical system (9) that forms part of the three-dimensional shape measurement optical system. FIG. 2 shows a slit confocal detection type three-dimensional shape measurement optical system including the slit illumination optical system (9) of FIG.
[0008]
1 and 2, 1 is a laser diode, 2 is a collimator lens, 3 is a rectangular aperture plate, 4 is a wedge prism pair, 5 is a half-wave plate, 6 is a variable ND (Neutral Density) filter, and 7 is an analog. Morphic prism pair, 8 is a cylindrical lens, 9 is a slit illumination optical system, 10 is a slit mask, 11 is a polarizing beam splitter, 12 is an objective optical system, 13 is an XY stage, 14 is a line sensor, 15 is an object to be measured, Reference numeral 16 denotes a light shielding mask. L1 is a laser beam (illumination light), L2 is reflected light, AX1 is an optical axis of the slit illumination optical system (9), and AX2 is an optical axis of the objective optical system (12). In the drawings, X, Y, and Z indicate directions orthogonal to each other in the optical path development state, FIG. 1A corresponds to the YZ section, and FIG. 1B corresponds to the XZ section.
[0009]
The laser diode (1) is a point light source that emits a laser beam (L1) as illumination light. The laser beam (L1) emitted from the laser diode (1) is a Gaussian beam emitted in an elliptical cone shape. Laser beam (L1) emitted from laser diode (1) is collimator lens (2), rectangular aperture plate (3), wedge prism pair (4), half wavelength plate (5), variable ND filter (6 ), The slit illumination optical system (9) comprising the anamorphic prism pair (7) and the cylindrical lens (8), as described below, the aperture position of the slit mask (10) {ie, the position of the slit (10h)} The image is formed in a slit shape.
[0010]
The laser beam (L1) emitted from the laser diode (1) is first converted from emitted light into collimated light (ie, parallel light) by a collimator lens (2) which is a rotationally symmetric collimator optical system. Then, the laser beam (L1) passes through the rectangular opening (3h) of the rectangular opening plate (3), thereby being limited to a necessary light beam range. Fig. 3 shows the beam shape of the laser beam (L1), the cross-sectional light intensity distribution (i: light intensity, r: beam diameter position) of the elliptical cone-shaped Gaussian beam corresponding to the rectangular aperture (3h), and the slit direction. The relationship with (dL, dS) is shown. As shown in FIG. 3, the laser diode (1) is arranged so that the major axis direction of the ellipse of the laser beam (L1) coincides with the slit longitudinal direction (dL) of the slit (10h). Thereby, it is possible to increase the light amount utilization efficiency while keeping the light amount distribution in the slit longitudinal direction (dL) substantially uniform.
[0011]
The laser beam (L1) that has passed through the rectangular opening (3h) is incident on the wedge prism pair (4). The wedge prism pair (4) is optical axis direction deflection means for finely adjusting the imaging position of the laser beam (L1) to a desired position. By rotating the lens barrel of the wedge prism pair (4) about the optical axis (AX1), it is possible to slightly shift the slit-like light source image in parallel. Therefore, the position of the slit mask (10) at the time of optical adjustment and the slit imaging position can be aligned by fine adjustment of the position of the laser beam (L1).
[0012]
The laser beam (L1) emitted from the wedge prism pair (4) passes through the half-wave plate (5), the variable ND filter (6), the anamorphic prism pair (7), and the cylindrical lens (8) in this order. Then, a slit-like light source image is formed at the slit (10h) position. The half-wave plate (5) is a polarization direction conversion element that rotates the polarization direction of the laser beam (L1) by 90 ° as shown in FIGS. 1 (A) and 1 (B). The anamorphic prism pair (7) composed of the first and second prisms (7a, 7b) is an expander that expands the laser beam (L1) only in the elliptical long axis direction {that is, the slit longitudinal direction (dL)}. It is an optical system. Like a general laser diode, the laser diode (1) emits a laser beam (L1) polarized in a direction parallel to the joint surface (that is, the minor axis direction of the elliptical cone-shaped beam). As described above, the major axis direction of the ellipse of the laser beam (L1) is arranged so as to coincide with the slit longitudinal direction (dL) (FIG. 3). Therefore, the laser beam (L1) is incident on the anamorphic prism pair (7) in a state converted from S-polarized light to P-polarized light by the half-wave plate (5).
[0013]
By changing the polarization direction at the half-wave plate (5), the laser beam (L1) is applied to the prism surfaces of the anamorphic prism pair (7) (especially the first surfaces of the first and second prisms (7a, 7b)). ) Can be maximized. For this reason, the light quantity loss in the anamorphic prism pair (7) is reduced, and high efficiency of light quantity utilization can be achieved. Furthermore, by making the incident angle close to the Brewster angle, an antireflection film on the prism incident surface can be made unnecessary. Moreover, since the polarization direction coincides with the slit direction, the laser beam (L1) can efficiently pass through the slit. Although not shown in FIG. 1, a polarizing plate may be disposed immediately after the half-wave plate (5) so that the polarization direction of the laser beam (L1) is more accurately aligned.
[0014]
The anamorphic prism pair (7) can expand the laser beam (L1) only in the slit longitudinal direction (dL). While obtaining the desired slit length, the beam width in the slit short direction (dS) does not change, so the desired NA (Numerical Aperture) can be achieved without increasing the focal length of the cylindrical lens (8), which is a slit imaging optical system. And the overall length of the slit illumination optical system (9) can be made short and compact. As shown in FIG. 5A, the light beam can be expanded in one direction also by using a lens group including a negative cylindrical lens (G1) and a positive cylindrical lens (G2) as an expander optical system. However, when the anamorphic prism pair (7) is used, the decrease in the light flux density at both ends in the magnification direction is reduced as shown in FIG. 5 (B), compared with the case where the lens group (G1, G2) is used. . That is, when a lens group is used, it is not easy to configure an optical system with small aberration. Therefore, the use of the anamorphic prism pair (7) is also effective for keeping the light quantity in the slit longitudinal direction (dL), which is the enlargement direction, substantially uniform.
[0015]
As shown in FIG. 4, the variable ND filter (6) includes an ND vapor deposition part (6a) in which an ND vapor deposition film is formed on a glass substrate and an ND non-vapor deposition part in which the ND vapor deposition film is not formed on the glass substrate. (6b). Then, the ND vapor deposition section (6a) or the optical path of the laser beam (L1) is set so that the laser beam (L1) passes only one of the ND vapor deposition section (6a) and the ND non-vapor deposition section (6b). The ND non-deposition part (6b) can be switched and inserted.
[0016]
When the height position (Z direction) of the measurement object (15) is measured, the scanning is performed twice for the forward path and the backward path. In the forward scanning {scanning in the Z direction from the low position to the high position of the measurement object (15)}, the laser beam (L1) passes through the ND non-deposition part (6b) and the scanning of the return path {measurement object ( In the scanning in the Z direction from the high position to the low position in 15), the laser beam (L1) passes through the ND vapor deposition section (6a). In this way, if the light intensity of the laser beam (L1) is switched using the variable ND filter (6), the dynamic range of measurement by the line sensor (14) can be expanded, and therefore the measurement object (15) The measurable reflectance range can be expanded.
[0017]
The laser beam (L1) expanded in the slit longitudinal direction (dL) by the anamorphic prism pair (7) is converted by the cylindrical lens (8), which is a slit imaging optical system, into the short axis direction { That is, the image is formed only in the slit short direction (dS), FIG. 1B, and the collimated state is maintained in the long axis direction {that is, the slit long direction (dL), FIG. 1A}. The imaging position of the laser beam (L1) is the slit (10h) position of the slit mask (10). By using so-called critical illumination that forms an image in a slit shape and passes through the slit mask (10) in this way, light loss can be reduced. Instead of forming a light source image at the slit (10h) position by the slit illumination optical system (9), a slit light source that emits divergent light similar to the light source image may be arranged at the slit (10h) position.
[0018]
As shown in FIG. 2, the slit illumination optical system (9) is disposed at an angle with respect to the optical axis (AX2) of the objective optical system (12). That is, the optical axis (AX1) of the slit illumination optical system (9) is inclined with respect to the optical axis (AX2) of the objective optical system (12). Therefore, the laser beam (L1) that has passed through the slit (10h) of the slit mask (10) enters the objective optical system (12) as obliquely incident illumination light. However, the laser beam (L1) enters the polarization beam splitter (11) before entering the objective optical system (12). The polarization beam splitter (11) is a polarization separation element that performs optical path separation between the illumination light (L1) incident on the objective optical system (12) and the reflected light (L2) emitted from the objective optical system (12). Since the laser beam (L1) as the illumination light is polarized in the Y direction, it is incident on the polarization beam splitter (11) as S-polarized light. Therefore, the laser beam (L1) is deflected in the optical path toward the objective optical system (12).
[0019]
The objective optical system (12) is a double-sided telecentric optical system that forms an image of the illumination light (L1) in a slit shape toward the measurement object (15) and reflects light from the measurement object (15) (L2) Toward the line sensor (14). In the objective optical system (12), a quarter wavelength plate (12q) is disposed as a polarization direction conversion element. Illumination light (L1) obliquely incident on the objective optical system (12) passes through the quarter-wave plate (12q) in one region divided into two with the optical axis (AX2) as the center, and the object to be measured The reflected light (L2) from the measured surface (15s) of (15) passes through the quarter wavelength plate (12q) in the other region divided into two with the optical axis (AX2) as the center.
[0020]
As described above, the polarization direction of the reflected light (L2) is rotated by 90 ° with respect to the polarization direction of the illumination light (L1) by reciprocating the optical path through the quarter-wave plate (12q). As a result, the reflected light (L2) emitted from the objective optical system (12) enters the polarization beam splitter (11) as P-polarized light. Therefore, the reflected light (L2) can pass through the polarizing beam splitter (11), and the reflected light (L2) that has passed through the polarizing beam splitter (11) enters the light receiving surface (14s) of the line sensor (14). . Instead of performing polarization direction conversion on the illumination light (L1) and the reflected light (L2) using the quarter-wave plate (12q), the illumination light (L1) or the reflected light ( It may be configured to perform polarization direction conversion with respect to L2).
[0021]
The line sensor (14) consists of a one-dimensional array type CCD (Charge Coupled Device), and has a light receiving surface (14s) composed of a plurality of light receiving elements at the confocal position of the slit (10h) and receives the light. The measurement object (15) is fixedly arranged so as to project an image on the surface (14s). In other words, the slit (10h) and the light receiving surface (14s) are both arranged in a positional relationship conjugate to the measurement object (15) {that is, a confocal position optically equivalent to the objective optical system (12)}. It is. Therefore, when the surface to be measured (15s) of the measurement object (15) is in focus, the reflected light (L2) on the light receiving surface (14s) of the line sensor (14) at the conjugate position. Is formed, and the amount of reflected light (L2) is detected for each pixel.
[0022]
The objective optical system (12) moves only the image-side conjugate position {that is, the conjugate position on the measurement object (15) side} by moving the focus lens group (12f) disposed therein, and thereby the measurement object. Scan in the height direction (Z direction) of (15). Since the scanning in the Z direction is performed with a simple configuration by moving the focus lens group (12f), the scanning mechanism can be downsized and the scanning speed can be increased. The XY stage (13) moves in the X and Y directions together with the placed measurement object (15), so that the relative position of the measurement object (15) and the illumination light (L1) in the X and Y directions. To measure the entire measurement region for the measurement object (15).
[0023]
In the measurement of the three-dimensional shape of the measurement object (15), the size in the X direction is obtained by moving and scanning the measurement object (15) by the XY stage (13), and the size in the Y direction is determined by the objective optical system (12 ) From the size of the image projected on the light receiving surface (14s). However, when the projected image exceeds the Y direction range of the light receiving surface (14s), control for moving the XY stage (13) in the Y direction is performed. On the other hand, the size (that is, the height position) in the Z direction {direction parallel to the optical axis (AX2)} is determined by moving the focus lens group (12f) along the optical axis (AX2) while moving the line sensor (14 ) When the measurement target (15) is focused on the light receiving surface (14s) (that is, the conjugate relationship between the measured surface (15s) and the light receiving surface (14s) is established) Is obtained by detecting the position of the focus lens group (12f) when the output reaches a peak. Therefore, when the focus lens group (12f) is moved while moving the measurement object (15) on the XY stage (13), the cross-sectional shape of the measurement object (15) is sequentially detected and calculated. The three-dimensional shape of the measurement object (15) is measured.
[0024]
For example, when detecting the height position of an object to be measured such that a mirror surface and a diffusing surface are mixed on the surface by a general confocal optical system, even if the objective optical system is not focused on the surface to be measured, Diffuse reflected light from the diffusing surface may enter the sensor through an optical path similar to the irradiation optical path to the measurement object, and may affect the measurement accuracy. This will be described with reference to FIG. FIG. 6A shows the case of full aperture illumination, and FIG. 6B shows the case of oblique incidence illumination. In either case, the measured surface (15s) is out of the image side conjugate position (P2), but the pinhole (19h) of the pinhole plate (19) placed at the object side conjugate position (P1) is diffusely reflected. A part (R1) of light (R1, R2) passes through. Even when the pinhole plate (19) is arranged as a spatial filter in this way, the diffuse reflected light (R1) passes through the pinhole (19h), so when scanning the measuring object (15) in the height direction. When the height position at which the sensor output reaches a peak is detected, the diffuse reflected light (R1) affects the measurement accuracy as noise, and the height measurement data is shifted between the mirror surface and the diffusion surface.
[0025]
As a method of shielding the diffuse reflected light (R1), an illumination optical system arranged with the optical axis inclined with respect to the normal direction of the stage surface on which the measurement object is set, and the optical axis of the illumination optical system are aligned. There is known a method in which the diffusely reflected light (R1) is not incident on a sensor by optically configuring with a condensing optical system arranged with the optical axis aligned in the reflection direction. However, the configuration requires a mechanism for moving the entire optical system or the stage in the vertical direction when scanning in the height direction. Therefore, the apparatus configuration becomes large and is not effective for increasing the scanning speed.
[0026]
In the three-dimensional shape measurement optical system shown in FIG. 2, the illumination light (L1) at each image height is obliquely incident on the bilateral telecentric objective optical system (12) as shown in FIGS. 7 (A) and (B). (ST: Aperture), as shown in FIG. 7 (C), one side area of the pupil (EP) of the objective optical system (12) divided into two around the optical axis (AX2) of the objective optical system (12) ( The surface to be measured (15s) is illuminated through only A1). Then, the reflected light (L2) from the surface to be measured (15s) passes through the other side area (A2) and exits from the objective optical system (12). The diffuse reflected light (R1) in question follows the same optical path as that of the illumination light (L1) and passes through one side region (A1). However, as shown in FIG. 2 and FIG. ) And the line sensor (14) are shielded from light by a light shielding mask (16). Thus, the diffused reflected light (R1) that has passed through the one side region (A1) of the reflected light (L2) from the measurement object (15) is shielded by the light shielding mask (16) as a spatial filter. Even when the measurement surface (15s) is deviated from the image side conjugate position (P2), measurement noise due to the diffusely reflected light (R1) is reduced, and the height position detection accuracy is improved. This configuration is not limited to the slit confocal detection method, but is effective even when the pinhole confocal detection method is adopted.
[0027]
9A to 9C show the change in the defocus optical path with respect to the light receiving surface 14s of the line sensor 14 in the case of full aperture illumination and FIGS. 9D to 9F show the case of oblique incidence illumination. (A, D), changes in the light intensity distribution (B, E; i: light intensity) and changes in the detected light quantity (C, F; q: light quantity) are shown. As can be seen by comparing FIGS. 9 (A) to 9 (C) and FIGS. 9 (D) to 9 (F), by using obliquely incident illumination light (L1), incidence on the defocus on the light receiving surface (14s). The contrast of the light quantity change is improved, and the height position detection accuracy is improved. Also, if the illumination light (L1) passes through the position away from the optical axis (AX2) of the objective optical system (12) as much as possible, the light shielding effect against the diffuse reflected light (R1) is improved, and further the detected light quantity The change contrast is also improved.
[0028]
In the three-dimensional shape measurement optical system shown in FIG. 2, the light receiving surface (14s) of the line sensor (14) is located at the confocal position of the light source image formed at the slit (10h) position. The confocal position of the light source image related to the objective optical system (12) is not limited to the confocal position of the light source related to the objective optical system (12) (for example, when the slit light source is used). The confocal position related to 12) may be a conjugate position related to the relay optical system. FIGS. 10A and 10B show a three-dimensional shape measuring optical system provided with a relay optical system 18 on the line sensor 14 side. The three-dimensional shape measurement optical system is characterized by a slit mask (17) placed at the confocal position of the slit mask (10), and a relay optical system (18) between the slit mask (17) and the line sensor (14). ) Is placed. Other than that, the configuration is the same as that of the three-dimensional shape measurement optical system shown in FIG. In this case, the slit (17h) is positioned at the confocal position of the slit (10h) related to the objective optical system (12), and the line sensor (14) is positioned at the conjugate position of the slit (17h) related to the relay optical system (18). The light receiving surface (14s) is located. If a relay optical system is used, the position of the sensor can be made flexible, and an observation optical system (not shown) for observing the part to be measured through the objective optical system (12) for three-dimensional shape measurement can be provided.
[0029]
【The invention's effect】
As described above, according to the present invention, the illumination light is expanded by the anamorphic prism system, so that the slit illumination optical system can be reduced in size and an optical system with small aberration can be easily achieved. Further, since the polarization direction conversion of the illumination light is performed by the polarization direction conversion element, it is possible to reduce the light amount loss in the anamorphic prism system. Accordingly, a three-dimensional shape measurement optical system including a compact slit illumination optical system capable of obtaining uniform and high illumination light can be realized, and the dynamic range is constant over the entire measurement region.
[Brief description of the drawings]
FIG. 1 is an optical configuration diagram schematically showing a configuration example of a slit illumination optical system according to the present invention.
2 is a schematic configuration diagram schematically showing a three-dimensional shape measurement optical system including the slit illumination optical system of FIG. 1. FIG.
FIG. 3 is a diagram for explaining the relationship between the beam shape of a laser beam, its cross-sectional light amount distribution, and the slit direction.
FIG. 4 is a diagram for explaining the operation of a variable ND filter for expanding the dynamic range of a measurement system.
FIG. 5 is an optical path diagram for explaining beam shaping of a laser beam by an expander optical system.
FIG. 6 is a diagram for explaining an optical path of diffusely reflected light that affects measurement accuracy.
FIG. 7 is a diagram for explaining a relationship between a reflected light passage region and a reflected light shielding region on a pupil plane.
8 is a perspective view showing the arrangement of light shielding masks in the three-dimensional shape measurement optical system of FIG. 2. FIG.
FIG. 9 is a diagram for explaining a change in a defocus optical path with respect to a light receiving surface of a line sensor, a change in its light intensity distribution, and a change in a detected light amount.
FIG. 10 is an optical configuration diagram schematically showing a three-dimensional shape measurement optical system including a relay optical system on the line sensor side.
[Explanation of symbols]
1 ... Laser diode (point light source)
2 ... Collimator lens (collimator optical system)
3 ... Rectangular aperture plate
3h… Rectangular opening
4 ... Wedge prism pair (optical axis deflection means)
5… 1/2 wavelength plate (polarization direction conversion element)
6 ... Variable ND filter
7… Anamorphic prism pair (anamorphic prism system)
8… Cylindrical lens (cylindrical optics)
9… Slit illumination optical system
10… Slit mask
10h… slit
11… Polarizing beam splitter
12 Objective optical system
14… Line sensor
14s… Light receiving surface
15… Measurement object
15s… surface to be measured
16 ... Shading mask
L1 ... Illumination light (laser beam)
L2 ... Reflected light
AX1 ... Optical axis of slit illumination optical system
AX2 ... Optical axis of objective optical system

Claims (2)

A three-dimensional shape measurement optical system comprising: a point light source that emits illumination light spreading in an elliptical cone shape; and a slit illumination optical system that forms an illumination light from the point light source in a slit shape,
The slit illumination optical system includes a collimator optical system that converts radiated illumination light into parallel light, an anamorphic prism system that expands illumination light only in the major axis direction of the ellipse, and illumination light that is elliptical. A cylindrical optical system that forms an image only in the minor axis direction, and a polarization direction conversion element that converts the polarization direction of the illumination light so that the transmittance when the illumination light enters the prism surface of the anamorphic prism system is maximized And a three-dimensional shape measuring optical system. The optical axis direction deflecting means for finely adjusting the imaging position of the illumination light to a desired position is disposed in the optical path of the illumination light converted into parallel light by the collimator optical system. Item 3. The three-dimensional shape measurement optical system according to Item 1.

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