JP2008032951A - Optical device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical device capable of acquiring a high-quality color confocal image. <P>SOLUTION: The optical device 1 is equipped with: an illuminating light source 2 emitting illuminating light; a confocal optical system 3 radiating light emitted from the illuminating light source to an object to be inspected 8 through a confocal minute aperture 34a and obtaining passing light reflected by the object to be inspected 8 and passing through the confocal minute aperture; a photodetector part 4 detecting the passing light obtained in the confocal optical system 3; and a processing part 50 reading and processing the detection data of the passing light from the photodetector part 4. The illuminating light source 2 is constituted to emit monochrome light of three colors, and the photodetector part 4 has monochrome configuration. The processing part 50 is configured to obtain the color image of the object to be inspected 8 by synthesizing the detection data read from the photodetector part 4 by every monochrome light of three colors emitted by the illuminating light source. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical apparatus that includes a confocal optical system and observes the surface shape of a test object.

  As an optical device that has a confocal optical system and observes the surface shape of an object to be examined, for example, a confocal microscope for inspecting fine patterns such as a semiconductor wafer substrate, an integrated device (IC), and a liquid crystal display panel, and area height measurement There is an inspection device such as a machine. The confocal optical system used in these inspection apparatuses irradiates the object with illumination light through the confocal microscopic aperture, and reflects the reflected light (point image) from the test object again through the confocal microscopic aperture. Pass through and observe. When the focal position of the confocal optical system is set in the vicinity of the surface of the test object and the focus position is relatively displaced in the optical axis direction, the reflected light that passes through the confocal micro-aperture out of the reflected light from the test object ( The light intensity of the passing light is maximized when the light intensity of the passing light increases or decreases and the focal position coincides with the surface of the test object.

  For this reason, an inspection apparatus equipped with a confocal optical system obtains a sharp two-dimensional image (confocal image) that displays only the in-focus area that matches the focal position of the confocal optical system within the visual field range. Can do. In addition, by acquiring confocal images at a plurality of height positions and synthesizing them, an image in which the entire field of view is in focus (an all-focus image) is displayed, or the obtained two-dimensional image and height are displayed. Data can be processed to display a three-dimensional stereoscopic image.

  Here, as an inspection apparatus as described above, a color confocal inspection apparatus using a white light source and a color image sensor (three-color CCD) has been known. However, color image sensors generally have lower sensitivity and S / N ratio than monochrome image sensors, and are easily affected by the reflectance of the test object. Further, it is difficult to obtain a high-quality confocal image due to the presence of chromatic aberration, and it is necessary to take measures such as making the diameter larger than the ideal confocal minute aperture. For this reason, among the inspection apparatuses using the confocal optical system, those that measure the height with high accuracy are configured to pick up an image with a monochrome imaging device using monochromatic light as illumination light. A scanning confocal microscope that measures the height by scanning a laser beam is also known, but the same is true in that the light source is monochromatic light. On the other hand, even in a high-precision inspection apparatus, when observing the surface state of a test object, a color image that is visually easier to recognize than a monochrome image is often desired. For this reason, various methods for pseudo-color display of confocal images obtained in a single color have been devised (see, for example, Patent Document 1).

JP 2001-56438 A

  However, a conventional inspection apparatus that measures the height of an object to be measured with a monochrome confocal optical system and displays a confocal image in color has the following problems. For example, in a display method in which a high area of a omnifocal image is displayed in red and blue in a low area, and is displayed in multiple colors of red to blue according to the height, each part of the test object is actually Are displayed in completely different colors. For this reason, it is difficult to understand when the shape of the test object becomes a complicated pattern, and the area at the same height is displayed in the same color regardless of the difference in the actual material and color. There was a problem that it was not easy.

  Further, in an inspection apparatus that displays a color image by combining color information captured by a general bright field optical system with a confocal image obtained by a confocal optical system, for example, when there is a step in the region, There is a problem that the color information at the in-focus position and the color information at the out-of-focus position are mixed and synthesized, resulting in lack of accuracy. That is, the color image obtained by such a method is merely a colored confocal image to which a pseudo color is added, and is not a strict color confocal image.

  The present invention has been made in view of the above problems, and an object thereof is to provide an optical device capable of acquiring a high-quality color confocal image.

  In order to achieve the above object, an invention according to claim 1 is directed to an illumination light source that emits illumination light and irradiating the object with illumination light emitted from the illumination light source through a confocal minute aperture, The confocal optical system that obtains the passing light reflected by the confocal micro aperture, the light detection unit that detects the passing light obtained in the confocal optical system, and the detection data of the passing light is read from the light detection unit The processing unit is configured to emit monochromatic light of three colors, and the processing unit synthesizes the detection data read from the light detection unit for each of the monochromatic light emitted by the illumination light source. The optical device is configured to obtain a color image of the test object.

  According to a second aspect of the present invention, in the optical device of the first aspect, the optical device according to the first aspect further includes a displacement unit that displaces the focal position of the confocal optical system with respect to the test object in the optical axis direction. For each of the monochromatic lights, the three-color monochromatic light obtained by reading the detection data from the light detection unit at a plurality of positions where the focal position of the confocal optical system is displaced by the displacement unit, and obtained at each of the plurality of positions. These detection data are combined to obtain a color image.

  According to a third aspect of the present invention, there is provided the optical device according to the first aspect, further comprising a displacement unit that displaces the focal position of the confocal optical system with respect to the test object in the optical axis direction. The time-division monochromatic light detection data is synchronized by synchronizing the emission operation of sequentially emitting three colors of monochromatic light from the illumination light source and the acquisition operation of reading and acquiring the detection data from the light detection unit while shifting the focal position of It is configured to obtain and synthesize the obtained monochromatic light detection data to obtain a color image.

  According to a fourth aspect of the present invention, in the optical device according to any one of the first to third aspects, the processing unit has a difference in position in the optical axis direction of detection data generated based on a difference in wavelength of three colors of monochromatic light. Is configured to be corrected based on a preset setting value.

  According to a fifth aspect of the present invention, in the optical device according to any one of the first to third aspects, the confocal optical system includes a disk that is provided with a large number of confocal micro-apertures on a disk and is driven to rotate. And a light source for illuminating the test object.

  ADVANTAGE OF THE INVENTION According to this invention, the optical apparatus which can acquire a high-definition color confocal image using a monochrome light detection part can be provided.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. As an example of an optical apparatus to which the present invention is applied, FIG. 1 shows a schematic configuration of an inspection apparatus 1 that observes the fine shape of the surface of an object. First, the configuration of the inspection apparatus 1 will be described.

  The inspection apparatus 1 irradiates the test object 8 with the illumination optical system 2 and the illumination light emitted from the illumination light source via the confocal pinhole (confocal micro-aperture) 34a, and is reflected by the test object 8. The confocal optical system 3 that obtains the passing light that has passed through the confocal pinhole, the imaging device (light detection unit) 4 that detects the passing light obtained in the confocal optical system 3, and the detection data read from the imaging device 4 It includes a processing device (processing unit) 50 for processing and a control device 5 that controls the operation of each unit.

  The illumination optical system 2 is located on the side of the confocal optical system 3 and includes a condenser lens 22 and an illumination light source 21 on an optical axis extending laterally from the polarization beam splitter 23. The confocal optical system 3 is arranged on the optical axis extending upward from the test object 8, and includes a 1 / 4λ plate 31, a first objective lens 32, a second objective lens 33, a pinhole disk 34, a polarization beam splitter 23, The imaging device 4 is configured to include an imaging camera 41 provided at an imaging position of the relay lens 35. The test object 8 is placed on the stage 7 and disposed below the confocal optical system 3. The illumination light source 21 and the imaging camera 41 will be described in detail later.

  The light beam emitted from the illumination light source 21 is converted into parallel light by the condenser lens 22 and enters the polarization beam splitter 23. The polarization beam splitter 23 has a function of transmitting the P-polarized component of the incident light and reflecting the S-polarized component, and the reflected S-polarized illumination light is applied to the upper surface of the pinhole disk 34.

  The pinhole disk 34 has a thin disk shape, and is formed by arranging a number of confocal pinholes 34a that transmit light in a spiral shape on a light-shielding thin film that has been subjected to antireflection treatment (such as this). A pinhole disk with a simple structure is also referred to as a Nippon disk). The pinhole disk 34 is disposed orthogonal to the optical axis of the confocal optical system 3 so as to block the illumination light reflected by the polarization beam splitter 23. The pinhole disk 34 is rotated at a predetermined rotational speed by a motor 34m, and the illumination light that has passed through the confocal pinhole 24a is placed on the stage 7 via the second objective lens 33 and the first objective lens 32. The test object 8 is condensed and irradiated as an image (point image) of the confocal pinhole 34a. In FIG. 1, two confocal pinholes 34a are illustrated.

  The image of the confocal pinhole 34a focused and irradiated on the test object 8 is reflected by the surface of the test object 8 (hereinafter referred to as “object plane O”) and is incident on the first objective lens 32 again. The light is condensed by the first objective lens 32 and the second objective lens 33 to form an image of the surface of the test object 8 on the lower surface of the pinhole disk 34, and passes through the confocal pinhole 34a. Here, the reflected light that has passed through the confocal pinhole 34a (referred to as “passed light” in the same manner as described above) passes through the quarter-λ plate 21 twice by the illumination light that has been changed to S-polarized light by the polarization beam splitter 23. It has been converted to P-polarized light, passes through the polarization beam splitter 23, is collected by the relay lens 35, and forms an image as a reflection image of the confocal pinhole 34 a on the imaging surface of the imaging camera 41.

  In addition, by providing the 1 / 4λ plate 21 and the polarization beam splitter 23 so that the imaging camera 41 captures the polarization component of the reflected light (P-polarized light), the entire amount of reflected light with weak light intensity is obtained. While transmitting, it is possible to block the flare light caused by the surface reflection of the optical member located closer to the test object than the polarizing beam splitter 23, thereby obtaining a clear confocal image.

  Then, the pinhole disc 34 on which a large number of confocal pinholes 34a are formed is rotated at a high speed by a motor 34m at a predetermined speed, so that the illumination light passing through each confocal pinhole 34a becomes spot light as the test object 8 The object plane O is scanned, and a reflected image (confocal image) of the test object 8 that has passed through the confocal pinhole 34 a is captured by the imaging camera 41 and processed by the processing device 50 in the control device 5. Thus, a confocal image including the height information of each part of the test object 8 can be obtained.

  That is, in the confocal optical system 3, when the object plane O (the surface of the test object) is at the height position of the focal plane of the objective lenses 32 and 33, the reflected light is incident on the pinhole forming surface of the pinhole disk 34. An image is formed, and almost all of the reflected light passes through the confocal pinhole 34a. However, when the object plane O slightly deviates from the height position of the focal plane of the objective lenses 32 and 33, the reflected light enters the pinhole forming surface. No image is formed and only a part can pass through the confocal pinhole 34a. Therefore, by capturing a confocal image at a predetermined height position with the imaging camera 41, it is possible to acquire a sharp confocal image in which the brightness of the in-focus portion where the focal plane coincides with the object plane O is high and the others are dark. it can.

  Further, at least one of the test object 8 and the confocal optical system 3 (for example, the first objective lens 32) is displaced in the optical axis direction (height direction), and the height of the focal plane relative to the object plane O is relative. The height position at which the intensity of the passing light reaching the imaging camera 41 reaches a peak is obtained for each pixel of the imaging camera 41, and the height position of each part of the test object corresponding to each pixel is increased. It can be detected with accuracy. Then, by synthesizing an image obtained by integrating the luminance corresponding to each pixel from the image data of the confocal image captured by the imaging camera 41 at a plurality of heights, a confocal image in which the entire imaging range is in focus (all Focus image). It is desirable to appropriately perform black level offset or the like.

  In the inspection apparatus 1 of the present embodiment, the stage 7 is moved up and down in the optical axis direction by the stage drive unit 37, and the control device 5 controls the operation of the stage drive unit 37 to place the test object 8. The placed stage 7 is displaced, and the imaging camera 41 is caused to take a confocal image at a plurality of heights, and the luminance is integrated for each pixel from the obtained image data of the plurality of confocal images, thereby obtaining an imaging range. It is configured to obtain a confocal image (omnifocal image) that is entirely in focus.

  In the inspection apparatus 1 of this configuration, since a plurality of spot lights scan the object 8 by rotating the pinhole disk 34 formed with a large number of confocal pinholes at a predetermined speed, the inspection object 8 is scanned. A plurality of points on the specimen 8 can be measured simultaneously. In addition, a height detection optical system with high long-term reliability can be configured with a simple configuration that does not use a complicated mechanism configuration such as a galvanometer mirror in the X and Y directions.

  In the inspection apparatus 1 configured as described above, the illumination light source 21 is configured to be able to emit three colors of monochromatic light, and the imaging camera 41 has a monochrome configuration.

  The illumination light source 21 shown in the figure selectively transmits R (red), G (green), and B (blue) wavelengths to a light source 210 that emits white light and each region obtained by dividing the disk into three angular directions. The filter 212 includes a band-pass filter, a motor 213 that rotates the filter 212, a filter sensor 214 that detects the color position of the monochromatic light emitted by detecting the angular position of the filter, and the like. By rotating and positioning one of the R, G, and B bandpass filters on the optical axis of the illumination light, it is configured to emit red, green, and blue monochromatic light. Instead of such a configuration, light emitting diodes of R, G, and B colors may be used to control the light emission.

  The imaging camera 41 can be configured using, for example, a monochrome imaging camera using a monochrome CCD (individual imaging device), and thereby has a higher sensitivity and a higher S / N ratio characteristic than a color imaging camera. Can be used for high-precision measurement. Note that the imaging camera is not limited to a camera using an individual imaging element, and may be an imaging tube.

  Next, FIG. 2 shows a block diagram of a processing device 50 that performs image capturing processing in the inspection device 1, and the configuration of the processing device and the operation of the inspection device 1 will be described below with reference to both drawings. Will be described.

  The processing device 50 includes a CPU 51, a drive control unit 52 that controls the operation of the stage drive unit 37, an image data storage unit 53 that stores image data input from the imaging camera 41, and image data stored in the image data storage unit 53. The image data extraction unit 54 extracts the data of the in-focus portion from the image, the image synthesis unit 55 generates the color confocal image by synthesizing the extracted single color image data, and the like.

  Image data is input from the imaging camera 41 to the processing device 50, and position data in the optical axis direction of the stage 7, that is, height data of the focal plane with respect to the test object 8 is input from the stage driving unit 37. Further, the processing device 50 is provided with an output unit 56 that outputs a confocal image synthesized by the image synthesis unit, and the output is output to an image display device 61 such as a liquid crystal display panel or CRT, a printer 62, and the like.

  When the confocal image acquisition process is started, the processing device 50 first sets the filter 212 in the illumination light source 21 to the angular position of the first monochromatic light, for example, an R (red) bandpass filter on the optical axis of the illumination light. The filter 212 is fixed by being controlled so that the light source 21 emits red monochromatic light. Then, a command signal is output from the drive control unit 52 to the stage drive unit 37 to start the movement of the stage 7, and confocal from the imaging camera 41 every predetermined height interval sequentially set from the image data acquisition start position. The image data of the image is read, and the image data with red illumination at each height position is stored in the image data storage unit 53.

  When the acquisition of the image data by the first monochromatic light illumination is completed for a predetermined height range (or a predetermined number), the processing device 50 sets the angular position of the filter 212 to the angle of the second monochromatic light. A position, for example, a G (green) bandpass filter is positioned and fixed on the optical axis of the illumination light, and is set so that green monochromatic light is emitted from the illumination light source 21. Then, similarly to the first monochromatic light illumination, the stage 7 is moved, the image data is read from the imaging camera 41 at the same position and at the same interval, and the image data of the green illumination at each height position is stored in the image data storage unit 53. Let Similar processing is performed for the third monochromatic light G (blue), and the image data of the blue illumination at each height position is stored in the image data storage unit 53. Thus, when the acquisition of the image data in the monochromatic illumination of the three colors is completed by the three scans, the processing device 50 performs the synthesis process of the omnifocal color image from each image data stored in the image data storage unit 53. .

  Here, the image data read from the imaging camera 41 and stored in the image data storage unit 53 is a signal obtained by interlaced scanning a large number of pixels constituting the imaging device of the imaging camera 41, and the reflection detected for each pixel. It is a collection of luminance signals proportional to the light intensity. Therefore, for the same pixel, by obtaining an integrated image obtained by integrating the luminance from a plurality of pieces of image data stored in the image data storage unit, the focused image data of the minute portion of the test object captured by the pixel is extracted. be able to.

  Therefore, in the processing device 50, the image data extraction unit 54 obtains an integrated image from a plurality of image data stored in the image data storage unit 53. This extraction process is performed for each color of illumination light. Thereby, the image data of the confocal image in which the entire photographing range is in focus for each color of each illumination light is generated.

  Then, the single color confocal image data is synthesized by the image synthesis unit 55 to generate a color confocal image. Here, the confocal image data of each color shifts in the height direction under the influence of axial chromatic aberration due to the difference in wavelength of illumination light. This shift amount differs depending on the material and combination of the lenses constituting the confocal optical system 3. In the inspection apparatus 1, height information of all pixels is acquired in advance by capturing a reflected image using a reference mirror surface that is neutral with respect to color and has sufficiently high flatness. Then, for each color, the correction amount of the field curvature component within the imaging range, the relative height position shift amount for each color, and the correction amount of the light reception sensitivity of each color in the image sensor are obtained, and these are processed as correction values. Parameters are set in the memory in the device.

  For this reason, when combining the three colors of confocal image data, the image combining unit 55 corrects the image data using the set correction values, removes these influences, and combines the entire imaging range. A color confocal image (omnifocal image) in a focused state is generated. In addition, when color images are combined, so-called white balance can be adjusted, and gain can be set when G (green) image data is mixed with B (blue) and R (red). Yes. The white balance may be automatically adjusted using a known appropriate algorithm.

  The generated color omnifocal image is output from the output unit 56 and displayed on an image display device 61 such as a CRT or a liquid crystal display panel. The color omnifocal image generated in this way is a color image displayed in the actual color of the test object 8, and all the image data is acquired using the confocal optical system 3. It is a high-definition color confocal image.

  Next, an inspection apparatus 1 ′ according to the second embodiment will be described. As shown in FIG. 3, the inspection apparatus 1 ′ is different from the inspection apparatus 1 described above only in the processing by the illumination light source 21 ′ and the processing apparatus 50 as shown in FIG. Therefore, the same number is assigned to the same part, and the duplicate description is omitted, and the process by the processing device 50 will be described in detail.

  The illumination light source 21 'in the inspection apparatus 1' is composed of monochromatic light emitting diodes 215 (215R, 215G, 215B) that emit light of wavelengths of R (red), G (green), and B (blue), respectively. The blinking timing of the light emitting diode is controlled by the processing device 50.

  When the confocal image acquisition process is started, the processing device 50 outputs a command signal from the drive control unit 52 to the stage drive unit 37 to start the movement of the stage 7. Further, in synchronization with the interlace scanning timing of the imaging camera 41, the light emitting diodes 215R, 215G, and 215B of R (red), G (green), and B (blue) are sequentially turned on. Specifically, the red light emitting diode 215R, the green light emitting diode 215G, and the blue light emitting diode 215B are caused to emit light in order for each frame of the imaging camera 41.

  When the image data acquisition start position is reached, the image data input from the imaging camera 41 is read, and image data of a confocal image by R (red) monochromatic light illumination for each frame, G ( The image data storage unit 53 stores confocal image data of green (monochromatic light) and confocal image data of monochromatic light (B). That is, the image data of each color is image data of a single color confocal image that is time-divided at a predetermined height position.

  The processing device 50 sequentially repeats the above-mentioned image acquisition at predetermined height intervals while moving the stage 7, and the image data for each of the red, green, and blue monochromatic illuminations time-divided at each height position. The image data is stored in the image data storage unit 53. Thus, when the acquisition of the image data in the three-color monochromatic illumination is completed in one scan, the processing device 50 performs the synthesis process of the omnifocal color image from each image data stored in the image data storage unit 53. .

  Here, each image data stored in the image data storage unit 53 is stored, although there is a difference in whether the recording area on the data structure is a time series for each color or time division in which each color is repeated in order. The image data itself is the same. Therefore, by extracting the data with the maximum luminance signal for the same pixel from the image data for each color stored discretely, as in the above-described embodiment, the minute portion of the test object photographed by each pixel is obtained. In-focus image data can be extracted.

  In the processing device 50, the image data extraction unit 54 reads out image data for each color from the plurality of image data stored in the image data storage unit 53, and extracts data having the maximum luminance signal for each pixel. Thereby, the image data of the confocal image in which the entire photographing range is in focus for each color of each illumination light is generated. Then, the single color confocal image data is synthesized in the same manner as described above by the image synthesis unit 55 to generate a color confocal image.

  Therefore, the color omnifocal image obtained by the inspection apparatus 1 ′ of the present configuration also has the actual color of the test object 8 in the same manner as the color omnifocal image obtained by the inspection apparatus 1 of the above-described embodiment. This is a color image to be displayed, and is a strict high-definition color confocal image in which all image data is acquired using the confocal optical system 3. Furthermore, in the inspection apparatus 1 ′ having this configuration, the image data of the confocal image by the three-color monochromatic illumination is acquired by only scanning the observation range, so that the processing time can be shortened and the entire color can be obtained in a short time. A focus image can be acquired. An operation mode in which the movement of the stage is stopped and the three-color image data is sequentially acquired at every predetermined height position, and the three-color image data is sequentially acquired without stopping the movement of the stage and accompanying the movement of the stage. Any of the operation forms for correcting in the height direction may be used.

1 is a schematic configuration diagram of an optical device according to a first embodiment of the present invention. It is a block diagram of the processing apparatus in the said inspection apparatus. It is a schematic block diagram of the optical apparatus of 2nd Embodiment of this invention.

Explanation of symbols

1 Inspection device (optical device) 2 Illumination optical system (illumination light source)
3 Confocal optical system 4 Imaging device (light detector)
8 Object 34m Confocal Pinhole (Confocal Micro Aperture)
37 Stage drive unit (displacement unit) 50 Processing device (processing unit)

Claims (5)

An illumination light source that emits illumination light;
A confocal optical system that irradiates the object to be examined with the illumination light emitted from the illumination light source through the confocal microscopic aperture, and obtains the passing light reflected by the test object and passing through the confocal microscopic aperture. When,
A light detection unit for detecting the passing light obtained in the confocal optical system;
A processing unit that reads and processes the detection data of the passing light from the light detection unit,
The illumination light source is configured to be capable of emitting monochromatic light of three colors,
The processing unit is configured to synthesize the detection data read from the light detection unit for each of the three color monochromatic lights emitted from the illumination light source to obtain a color image of the test object. Optical device characterized. A displacement unit for displacing a focal position of the confocal optical system with respect to the test object in an optical axis direction;
The processing unit reads the detection data from the light detection unit at a plurality of positions where the focal position of the confocal optical system is displaced by the displacement unit for each of the three colors of monochromatic light emitted from the illumination light source. The optical apparatus according to claim 1, wherein the color image is obtained by combining the detection data of the three colors of monochromatic light acquired at the plurality of positions. A displacement unit for displacing a focal position of the confocal optical system with respect to the test object in an optical axis direction;
The processing unit reads and obtains detection data from the light detection unit and an emission operation for sequentially emitting the monochromatic light of the three colors from the illumination light source while displacing the focal position of the confocal optical system by the displacement unit. The detection operation of time-division monochromatic light is acquired in synchronization with the acquisition operation, and the color image is obtained by synthesizing the acquired detection data of the monochromatic light. 2. The optical device according to 1.   The processing unit is configured to correct a difference in position in the optical axis direction of the detection data generated based on a difference in wavelength of the monochromatic light of the three colors based on a preset setting value. The optical device according to any one of claims 1 to 3, wherein the optical device is characterized in that:   2. The confocal optical system includes a disk provided with a large number of confocal micro-apertures on a disk and driven to rotate, and a light source that illuminates the test object via the disk. The optical device according to any one of claims 1 to 4.

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