JP2006105835A - Shape measuring method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape measuring method capable of performing three-dimensional shape measurement accurately at high speed by using a two-dimensional array type confocal optical system, and performing easily manufacture or aligning of each part. <P>SOLUTION: Light emitted from a light source 1 is branched plurally, and a measuring object 9 is irradiated therewith through an objective lens 5. The measuring object 9 is moved relatively in the optical axis direction, and reflected light at each time of movement is detected by a photodetector array 8. Data processing is performed relative to a pair formed by the position data at each time in the optical axis direction of the measuring object 9 and a detection signal of the photodetector array 8 at that time. Hereby, the surface shape of the measuring object 9 is measured three-dimensionally, and the light emitted from the light source 1 is branched plurally through a diffraction grating 3. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a shape measuring method and a shape measuring apparatus for measuring a three-dimensional shape by applying a confocal optical system.

  An optical system that obtains an image using a confocal optical system is called a confocal imaging system, and an image obtained by the confocal imaging system is called a confocal image. Common confocal imaging systems include laser scanning microscopes and Nipkow disk scanning microscopes. In addition, as a high-speed confocal imaging system without a scanning mechanism, a confocal optical system, a two-dimensional array type confocal imaging system that simultaneously exposes each pixel of the confocal image by arranging the confocal pinholes in two dimensions (See, for example, Patent Document 1).

FIG. 4 shows a schematic configuration of a shape measuring apparatus of a two-dimensional array type confocal imaging system.
In this shape measuring apparatus, the light from the light source 1 is converted into parallel light by the collimator lens 2, and the light passing through the pinholes 7a arranged in a matrix in the pinhole array 7 is an optical path branching optical element such as a half mirror. 4, collected by the objective lens 5, and projected onto the object 9 to be measured placed on the moving stage 10.

  Then, the light reflected by the object to be measured 9 is collected again by the objective lens 5, branched by the optical path branching optical element 4, and imaged at a position conjugate with the pinhole array 7 by the imaging lens 6. Is passed through a pinhole 7a of another pinhole array 7 arranged at, detected by each photodetector of the photodetector array 8, photoelectrically converted and output as an electrical signal.

At this time, the object 9 to be measured is gradually displaced in the height direction (Z direction) by the moving stage 10, scanned in the height direction of the object 9 to be measured, and a photodetector based on the object 9 to be measured at each position. The individual outputs of the array 8 are sampled separately, and the position in the Z direction when the output of each photodetector is maximized is detected as the surface position of the object 9 to be measured. By processing the data in pairs with the position data, the surface shape in the height direction (Z direction) of the measured object 9 can be measured three-dimensionally.
JP-A-4-265918

However, the conventional method has the following problems.
(1) In order to obtain a highly accurate confocal effect, the two pinhole arrays 7 are precisely created with submicron accuracy, for example, so that the pitches of the pinholes 7a match each other, and they are divided into optical paths. It is necessary to precisely position and fix the optical element 4 at a conjugate position with the accuracy. However, it is technically difficult to produce the pinhole array 7 having hundreds of thousands of pinholes 7a with the above-mentioned accuracy, and its positioning and fixing are not easy.
(2) Since the light incident on the pinhole array 7 does not pass through portions other than the pinhole 7a, the light use efficiency is poor and only a few percent of the light from the light source 1 is used. Therefore, it takes time to obtain a sufficient amount of detected light, and it takes a long time to measure the shape of the object 9 to be measured.
(3) It is necessary to take measures to prevent the light reflected by the light-shielding portion of the pinhole array 7 from reaching the photodetector array 8 (two-dimensional detector).
(4) In a two-dimensional array type confocal imaging system, illumination light is required to be light with as low coherence as possible. This is to obtain an image with as little granular noise (hereinafter referred to as speckle) generated by local light interference.

  In this respect, in the above-described scanning confocal imaging system, the spot projected on the object to be measured 9 is moving even during exposure of the two-dimensional detector. While the speckle state changes and is averaged, in the two-dimensional array confocal imaging system, the spot does not move at all during the exposure of the two-dimensional detector, so the speckle occurs in the spot. If it does, it will affect the image as it is. Such an influence on an image is particularly remarkable when a rough surface is observed with a large spot size using an objective lens having a low magnification and a low numerical aperture. For this reason, in a two-dimensional array type confocal imaging system, an incoherent light source is used, or coherent light is made incoherent with a phase randomizer, but when using an incoherent light source, By passing through the pinholes of the hole array, the coherence becomes high after all, and the speckle that affects the image is generated.

  The present invention has been made in view of such circumstances, and a shape measuring method capable of performing three-dimensional shape measurement at high speed with high accuracy while using a two-dimensional array type confocal optical system, and manufacturing and positioning of each part are easy. An object is to provide a shape measuring apparatus.

  In the shape measuring method of the present invention, the object to be measured is irradiated with the light emitted from the light source via the objective lens, the object to be measured is relatively moved in the optical axis direction, and the reflected light or the projected light at the time of the movement is used. The amount of fluorescence emitted from the object to be measured itself is detected by the photodetector array, and data processing is performed by pairing the position data of the object to be measured in the optical axis direction with the detection signal of the photodetector array at that time. When measuring the surface shape of the object to be measured three-dimensionally, the light emitted from the light source is branched into the plurality through the diffraction grating and irradiated to the object to be measured through the objective lens, and the surface shape is tertiary. It is characterized by original measurement.

  Further, the shape measuring apparatus of the present invention includes a diffraction grating that branches light emitted from a light source into a plurality of point light sources, an objective lens that projects the point light source branched by the diffraction grating onto an object to be measured, and the objective lens An optical path that is disposed in an optical path between the diffraction grating and transmits the light from the diffraction grating toward the objective lens, reflects the reflected light from the object to be measured, and branches the reflected light that has passed through the objective lens again from the optical path A branching optical element, an imaging lens that forms an image of the reflected light branched by the optical path branching optical element, and a plurality of pinholes that are two-dimensionally arranged, are disposed at a focal point on the rear side of the imaging lens. A pinhole array, and a plurality of photodetectors corresponding to each of the plurality of pinholes of the pinhole array, and an image formed on each of the photodetectors by the imaging lens is photoelectrically converted. An optical detector array to be replaced, a moving stage for moving the object to be measured in the direction of the optical axis of the objective lens, scanning, position data of the object to be measured in the direction of the optical axis by the moving stage, and data at that time And a three-dimensional measuring unit configured to three-dimensionally measure the surface shape of the object to be measured by processing data in pairs with the detection signals of the photodetector array.

Further, a polarizing beam splitter is provided as an optical path branching optical element, and a quarter wavelength plate is provided between the polarizing beam splitter and the objective lens.
In addition, a diffraction grating moving stage for in-plane displacing the diffraction grating is provided.

  In addition, the shape measuring method of the present invention includes a bandpass filter that transmits a fluorescence wavelength in a path in which a photodetector array detects the amount of fluorescence emitted by the object to be measured by the projected light, and other than the fluorescence. The light is blocked.

  In the shape measuring method of the present invention, the light emitted from the light source is branched into a plurality through the diffraction grating, irradiated onto the object to be measured through the objective lens, and the surface shape of the object to be measured is measured three-dimensionally. It is possible to perform three-dimensional shape measurement at high speed by using light with high utilization efficiency of light source light.

  In order to obtain a non-scanning type (two-dimensional array type) confocal image, the shape measuring apparatus of the present invention is provided with a diffraction grating in place of a pinhole conventionally used in an illumination system. There are the following advantages compared with the pinhole illumination system.

a) The utilization efficiency of light source light can be remarkably improved, and three-dimensional shape measurement can be performed at high speed and with high accuracy.
b) Since the structure is simple, it is easy to manufacture, and the positioning of each part is also easy.

c) Since it is not necessary to align the pinhole array of the illumination system and the pinhole array for receiving light, it is possible to reduce the size and weight of the apparatus.
d) It is possible to reduce the conventional problem that the light source light incident on the pinhole array of the illumination system is reflected and observed by a portion other than the pinhole (light shielding film).

Furthermore, noise light can be cut by providing a polarizing beam splitter and a quarter-wave plate.
Further, by providing the diffraction grating moving stage, it is possible to suppress the generation of speckle even when using an objective lens having a low magnification and a low numerical aperture. The speckle suppression effect is very effective because the rough surface observation with a low-magnification objective lens is often required for 3D measurement on an automatic inspection line of factory automation.

Hereinafter, the shape measuring method of the present invention will be described with reference to FIGS. 1 to 3 showing specific embodiments.
(Embodiment 1)
FIG. 1 shows a shape measuring apparatus according to Embodiment 1 of the shape measuring method of the present invention.

  In the figure, 1 is a light source, 2 is a collimator lens, 3 is a transmissive diffraction grating, 4 is an optical path branching optical element such as a half mirror, and 5 is an objective lens, which are arranged in this order. The diffraction grating 3 is used as a means for generating a point light source array. When light is incident from the light source 1, the light is generated as if it is emitted from an array in which the light sources are arranged in a matrix. 6 is an imaging lens, 7 is a pinhole array in which a plurality of pinholes 7a are arranged in a matrix, and 8 is a photodetector in which a plurality of photodetectors are arranged in a matrix corresponding to the pinholes 7a. An array, which is arranged in this order along the direction in which the optical axis intersects with the objective lens 5 and the like. These members 1 to 8 constitute a confocal optical device.

  Reference numeral 9 denotes an object to be measured, and 10 a moving stage on which the object to be measured 9 is mounted and can be moved below the objective lens 5 in the height direction of the object to be measured 9 (in the Z direction and along the optical axis). . A movement control unit 12 performs movement control of the movement stage 10. Reference numeral 11 denotes a three-dimensional measurement unit, which is obtained from the position data in the optical axis direction of the object 9 to be measured by the moving stage 10 obtained from the movement control unit 12 and the detection signal of the photodetector array 8 at that time. Data processing is performed in pairs, and the surface shape of the object 9 to be measured is measured three-dimensionally.

The operation in the above configuration will be described.
The light emitted from the light source 1 is made into substantially parallel light by the collimator lens 2, and is branched as if it is a point light source array by the transmission type diffraction grating 3, then passes through the optical path branching optical element 4, and the objective lens 5 And is collected toward the object 9 to be measured. Here, only a part of the branched light (diffracted light) is shown for the sake of simplicity, but in reality, a point image generated from each of the branched lights is formed on the inspection surface of the object 9 to be measured.

  The reflected light reflected by the object to be measured 9 is incident again on the objective lens 5, condensed, deflected by the optical path branching optical element 4, and then incident on the image forming lens 6 to enter each pinhole 7 a of the pinhole array 7. The image is formed at the position. The light that has passed through each pinhole 7a is detected by each photodetector in the photodetector array 8, is photoelectrically converted, and is output as an electric signal corresponding to the received light intensity. Here, a confocal image is obtained on the photodetector array 8.

  At this time, the object 9 to be measured is displaced in the Z direction under the control of the movement control unit 12 while being placed on the moving stage 10, and each photodetector in the photodetector array 8 based on the reflected light at each position. Are sequentially sampled by the three-dimensional measuring unit 11 and obtained from the movement control unit 12, the position data of the object 9 to be measured in the optical axis direction by the moving stage 10, and the photodetector array 8 at that time The surface shape of the object 9 to be measured is three-dimensionally measured by pairing the detected signal with the data. Note that the position in the Z direction when the output of each photodetector in the photodetector array 8 is maximized is detected as the surface position of the object 9 to be measured.

  As described above, in the apparatus according to the first embodiment, in a two-dimensional array type confocal imaging system in which an image of a point light source is projected onto an object by an objective lens, it has been conventionally used in an illumination system to produce a point light source. The diffraction grating 3 is used in place of the pinhole (pinhole array) to obtain a non-scanning (two-dimensional array) confocal image.

  According to this method, when the diffraction efficiency of the diffraction grating 3 is set to 50%, for example, 50% of the illumination light is irradiated onto the object 9 to be measured and the reflected light is incident on the photodetector array 8. The light utilization efficiency can be significantly improved as compared with the prior art.

  Further, since no pinhole (pinhole array) is used in the illumination system, there is no light shielding film, and reflection on the light shielding film, which has been a problem with conventional devices, need not be considered. In general, a three-layered film of chromium oxide / chromium / chromium oxide is used as the light shielding film, but reflection of about 5 percent occurs even with chromium oxide. On the other hand, when there is no light-shielding film, a multilayer AR coat (Anti-Reflection Coat: antireflection film) is applied to the surface of each optical element in the system, thereby preventing the generation of stray light. The reflection can be reduced to about 0.2 percent.

  As the light source 1, a laser having high spatial and temporal coherence is suitable, and a light source having a necessary space, temporal coherence, and wavelength may be selected in accordance with the diffraction grating characteristics. As the photodetector array 8, a MOS type or CCD type area sensor is suitable.

  In the first embodiment, the light reflected by the measured object 9 is detected, but the amount of fluorescence emitted by the measured object 9 itself may be detected by the projection light. In that case, in order to block light other than the fluorescence to be detected, a band-pass filter that transmits the fluorescence wavelength is provided between the pinhole array 7 and the photodetector array 8 or between the imaging lens 6 and the pinhole array 7. It may be arranged between them.

  Further, in order to perform moving scanning in the Z direction, the moving stage 10 is provided to move the object 9 to be measured in the Z direction. However, the entire confocal optical device may be configured to be movable in the Z direction. Then, the object to be measured 9 may be relatively moved in the optical axis direction, and reflected light at the time of the movement may be detected by the photodetector array 8.

(Embodiment 2)
FIG. 2 shows a shape measuring apparatus according to Embodiment 2 of the shape measuring method of the present invention.
The shape measuring apparatus according to the second embodiment is provided with a polarizing beam splitter 13 as an optical path branching optical element, and a quarter wavelength plate 14 is provided between the polarizing beam splitter 13 and the objective lens 5. This is different from the first embodiment.

  According to this configuration, the illumination light emitted from the light source 1 is made into substantially parallel light by the collimator lens 2, branched by the transmission diffraction grating 3, passes through the polarization beam splitter 13, and becomes linearly polarized light. Then, the light is converted into circularly polarized light by the quarter-wave plate 14, enters the objective lens 5, and is condensed on the object 9 to be measured.

  Then, the light reflected on the object to be measured 9 is incident again on the objective lens 5 and condensed, and becomes linearly polarized light orthogonal to the illumination light by the quarter wavelength plate, deflected by the polarization beam splitter 13, and image forming lens. 6 is imaged at each pinhole 7a position of the pinhole array 7.

  Thus, by providing the polarizing beam splitter 13 and the quarter wavelength plate 14, the light reflected on the object 9 to be measured is prevented from returning to the illumination optical system side from the polarizing beam splitter 13 again. Generation of noise due to stray light can be prevented.

(Embodiment 3)
FIG. 3 shows a shape measuring apparatus according to Embodiment 3 of the shape measuring method of the present invention.
The shape measuring apparatus according to the third embodiment is different from the first embodiment only in that a diffraction grating moving stage 15 for moving the diffraction grating along the plane direction is provided.

  When the diffraction grating 3 is displaced in the plane perpendicular to the groove, the phase of the wave front of the diffracted light changes, and the black and white contrast of the interference fringes between the transmitted light and the diffracted light changes. In this shape measuring apparatus, the diffraction grating 3 is displaced in the plane at high speed by the diffraction grating moving stage 15, thereby canceling out the contrast of noise (speckle) generated by the interference and reducing the speckle. it can.

  On the other hand, in the conventional apparatus, even if the light source is a white incoherent light source such as a halogen lamp, the light emitted from the pinhole of the illumination system becomes highly coherent. When a rough surface is observed with a confocal imaging system having a numerical aperture, speckles are generated, leading to deterioration of image quality and deterioration of three-dimensional measurement accuracy.

  The shape measuring method of the present invention is useful for three-dimensional measurement in an automatic inspection line of factory automation.

Configuration diagram of a shape measuring apparatus according to Embodiment 1 of the present invention The block diagram of the shape measuring apparatus in Embodiment 2 of this invention The block diagram of the shape measuring apparatus in Embodiment 3 of this invention Configuration diagram of a conventional shape measuring device

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Diffraction grating 4 Optical path branching optical element 5 Objective lens 6 Imaging lens 7 Pinhole array 7a Pinhole 8 Photodetector array 9 Object to be measured 10 Moving stage 11 Three-dimensional measuring part 12 Movement control part 13 Polarizing beam splitter 14 1/4 wavelength plate 15 Diffraction grating moving stage

Claims (5)

Light emitted from the light source is irradiated onto the object to be measured through the objective lens, the object to be measured is relatively moved in the optical axis direction, and the amount of fluorescence emitted by the object to be measured by reflected light or projection light at the time of the movement Is detected by a photodetector array, and data processing is performed by pairing the position data of the object to be measured in the optical axis direction with the detection signal of the photodetector array at that time, and the surface shape of the object to be measured When measuring three-dimensional
A shape measuring method in which light emitted from the light source is branched into a plurality of light via a diffraction grating and irradiated onto an object to be measured via the objective lens to measure a surface shape three-dimensionally. A diffraction grating that divides the light emitted from the light source into a plurality of point light sources;
An objective lens that projects the point light source branched by the diffraction grating onto the object to be measured;
The light that is disposed in the optical path between the objective lens and the diffraction grating, transmits light that travels from the diffraction grating to the objective lens, reflects off the object to be measured, and passes through the objective lens again from the optical path. Optical path branching optical element for branching;
An imaging lens for imaging the reflected light branched by the optical path branching optical element;
A pinhole array having a plurality of pinholes arranged two-dimensionally and arranged at a rear focal position of the imaging lens;
A plurality of photodetectors corresponding to each of the plurality of pinholes of the pinhole array, and a photodetector array that photoelectrically converts an image formed on each of the photodetectors by the imaging lens;
A moving stage that moves and scans the object to be measured in the direction of the optical axis of the objective lens;
The surface shape of the object to be measured is measured three-dimensionally by pairing the position data of the object to be measured in the optical axis direction by the moving stage with the detection signal of the photodetector array at that time. A shape measuring device including a three-dimensional measuring unit.   3. The shape measuring apparatus according to claim 2, further comprising a polarizing beam splitter as the optical path branching optical element, and a quarter wavelength plate between the polarizing beam splitter and the objective lens.   The shape measuring apparatus according to claim 2, further comprising a diffraction grating moving stage that displaces the diffraction grating in a plane.   The shape according to claim 1, wherein light other than the fluorescence is blocked through a band-pass filter that transmits a fluorescence wavelength in a path in which a light amount of the fluorescence emitted by the measurement object itself is detected by the projected light. Measuring method.

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