Optical 3D measurement system

Abstract

The present invention discloses an optical 3D measurement system, which is specially used for high-speed online automatic inspection of semiconductor wafers and wafer packaging connection lines. The 3D measurement system of this system only needs to collect one picture to obtain the 3D topography of the entire object surface. Therefore, the measurement speed is extremely fast, and it is particularly suitable for online high-speed 3D inspection. The measurement system is also suitable for detecting the 3D surface topography of various other precision parts of objects, especially discontinuous surfaces that cannot be detected by other 3D measurement systems.

Description

Technical Field

[0001] The present invention relates to the field of three-dimensional measurement, and in particular to an optical three-dimensional measurement system. Background Art

[0002] Optical confocal 3D profilers are being used more and more widely in industrial 3D profile measurement. However, since optical confocal measurement technology is a point measurement technology, only one point can be measured at a time. If a surface is to be measured, it needs to be scanned vertically and horizontally to measure the 3D profile of an area. At present, most industrial optical confocal 3D profilers at home and abroad are completed by optical confocal point sensors plus mechanical scanning mechanisms. Manufacturers of optical confocal sensors include STIL SA, Fogale Nanotech, Micro Epsilon, FRT, Precitec, etc. Optical confocal sensors can measure the surface height of a point at high speed, but to obtain the surface profile of an area, it needs to scan point by point, so the measurement speed is very slow.

[0003] The optical focal displacement sensor of Keyence Commercial in Japan uses a vibration displacement sensor to measure the distance to an object. Due to mechanical movement, the speed is slow. The optical chromatic aberration confocal point sensor has more advantages because there is no mechanical movement, such as US Patents 5610734, 7561273B2, 7626705B2, 8134691B2, 821299B1, etc. The measurement principle of the optical chromatic aberration confocal point sensor is based on the chromatic aberration of the optical lens.

[0004] like Figure 4 As shown, when a white light beam passes through an objective lens, light of different wavelengths is focused at different focal lengths by the objective lens due to the influence of chromatic aberration. The out-of-focus light reflected by the sample surface will be filtered out by the pinhole, and only the spectrum in which the beam is focused is detected by the spectrometer. With the knowledge of the focal distance related to the wavelength, the height of a point on the specimen surface can be decoded by analyzing the reflected light with a spectrophotometer. Thus, the point height can be measured at high speed. However, in order to obtain a three-dimensional profile of an area, the specimen needs to be scanned laterally point by point by means of an XY motion stage.

[0005] Zeiss Axiotron 2CSM VIS-UV, such as Figure 5Shown is a scanning optical confocal microscope that uses chromatic aberration confocal and Nipkow technology with a high-speed scanning mechanism to produce a scanning optical confocal microscope. There are many pinholes on the Nipkow disk. When the Nipkow disk rotates, the light beam passes through the pinholes on the Nipkow disk and scans the entire surface of the specimen. The light beam is focused at different distances depending on the wavelength due to the chromatic aberration of the lens inserted between the tube lens and the objective lens named Chromat-C U.S. Patent 6038066. The light beam is sharply focused on the specimen surface and will be reflected back through the specimen surface and then follow the same path back to the same pinhole. The light beam that passes through the pinhole and then the reflected beam splitter is imaged onto a color camera. However, the confocal microscope is used for visualization only rather than three-dimensional profile measurement, it can provide color-coded images, but it cannot measure the surface height.

[0006] Ruprecht, et al (2004) described a 3D profilometer for chromatic aberration confocal microscopy. Figure 6 , a white light beam is collimated and illuminates a rotating Nipkow disk of microlenses. The focal points of the microlenses are imaged onto the object at different distances depending on the wavelength. The microlenses work in parallel as laterally distributed point sensors. Each microlens re-collimates the light reflected by the object. The CCD color camera images the field of view of the microlenses. The depth recognition aperture in this setting is a pinhole at the focus of the imaging optics.

[0007] There are two commercial confocal microscopes on the market that can be used as confocal 3D profilers, Bruker's VCMTM and Carl Zeiss's Axio CSM 700. This optical profiler uses the confocal microscopy technology of a rotating Nipkow disk and uses a large number of vertical scanning images to measure the surface profile morphology. Its measurement speed is slow and is only suitable for measurement laboratories.

[0008] The Carl Zeiss Axio CSM 700 is based on the optical confocal principle of chromatic aberration plus slit scanning using a slit and a chromatic aberration detector. A similar system was described by Lin et al. in 1998. Figure 7As shown, the slit confocal scanning principle uses a slit instead of a pinhole for the conjugate plane in front of the light source and the detector. Because the slit cannot filter out the out-of-focus light parallel to the direction of the slit, the confocal effect along the slit opening direction is greatly impaired. When a white light beam passes through the slit and is imaged on the sample surface by the objective lens chromatically, the different colors of light are focused at different distances from the objective lens. The light reflected by the surface will then pass through the slit to filter out the out-of-focus light in the direction perpendicular to the slit. The light passing through the slit is then dispersed by a grating or prism and imaged on a CCD camera. Light with different wavelengths will be imaged on the CCD at different positions depending on the height of the surface of the object. The image has two dimensions, where the first dimension represents the X-axis of the sample surface, and the second dimension represents the height information. The height information can be determined based on the image of the brightest pixel in the second dimension. To obtain a topographic map, the specimen needs to be scanned in the Y direction.

[0009] Ang KT et al. reported a high-speed confocal 3D profiler that can measure microfluidic biochips at high speed. It is a surface area measurement system and is suitable for measuring three-dimensional surfaces, but its measurement field of view is relatively small, the illumination light intensity is low, the uniformity is poor, and the stray light interference is large. These problems greatly limit its application in three-dimensional measurement in semiconductor production. Summary of the invention

[0010] The technical problem solved by the present invention is to provide an optical three-dimensional measurement system, which can realize high-speed online measurement of the three-dimensional morphology of the surface of an object.

[0011] The technical solution adopted by the present invention to solve its technical problems is: an optical three-dimensional measurement system, including a light source system, a first beam splitter is obliquely arranged on one side of the light source system, a Nipkow disk is arranged on one side of the first beam splitter, so that the parallel light emitted by the light source system is deflected 90 degrees after passing through the first beam splitter and is emitted to the Nipkow disk, a first projection objective lens, a chromatic aberration lens and a microscope objective lens are arranged in sequence on the side of the Nipkow disk away from the first beam splitter, and a placement table for placing the object to be measured is also arranged on the side of the microscope objective lens away from the chromatic aberration lens, so that the light beam passing through the Nipkow disk is imaged on the surface of the object to be measured via the first projection objective lens, the chromatic aberration lens and the microscope objective lens, and a second projection objective lens and a CCD color camera are arranged in sequence on the side of the first beam splitter away from the Nipkow disk, so that the light reflected from the surface of the measured product enters the CCD color camera via the microscope objective lens, the chromatic aberration lens, the first projection objective lens, the Nipkow disk, the first beam splitter and the second projection objective lens.

[0012] Furthermore, the light source system includes an integrating sphere coated with a high reflectivity material inside, the integrating sphere includes at least one light inlet and a light outlet, and a broadband white light source is disposed at the light inlet.

[0013] Furthermore, a bandpass filter for removing harmful infrared light energy is arranged at the light-emitting port of the broadband white light source.

[0014] Furthermore, a Kohler illumination system is arranged at the light outlet of the integrating sphere.

[0015] Furthermore, a first beam splitter is obliquely arranged between the microscope objective lens and the chromatic aberration lens, and an eyepiece is arranged on one side of the first beam splitter, so that the light reflected by the object to be measured reaches the eyepiece after passing through the microscope objective lens and the first beam splitter.

[0016] Furthermore, a second beam splitter is obliquely arranged between the first beam splitter and the eyepiece, and an imaging lens and a CCD camera are sequentially arranged on one side of the second beam splitter, so that the light reflected by the object to be measured reaches the CCD camera after passing through the microscope objective lens through the first beam splitter, the second beam splitter and the imaging lens.

[0017] Furthermore, the first beam splitter, the second beam splitter, the eyepiece, the imaging lens and the CCD camera are all installed on a movable frame, which also includes a movable guide rail for driving the movable frame to move horizontally.

[0018] Furthermore, it also includes a mechanical scanning device, the microscope objective lens is installed on the mechanical scanning device, the microscope objective lens and the mechanical scanning device include two sets, the two sets of microscope objective lenses are respectively a high-magnification microscope objective lens and a low-magnification microscope objective lens, and it also includes a switching device, the two sets of microscope objective lenses and the mechanical scanning device are both installed on the switching device.

[0019] Furthermore, the storage platform is a five-dimensional displacement platform.

[0020] Furthermore, the broadband white light source is a tungsten halogen lamp, and the CCD color camera (18) is a Foveon color camera.

[0021] The beneficial effects of the present invention are as follows: the system is based on the principles of optical confocality and optical chromatic aberration. Areas at different heights on the surface of an object present different colors on the image plane. The color of the surface of the object represents its height. The color of light is used as a ruler to perform three-dimensional height measurement. Therefore, there is no need for vertical height scanning for height measurement. One picture can measure the three-dimensional height of the entire surface, and the system has the characteristics of fast measurement speed and high measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the structure diagram of the optical three-dimensional measurement system.

[0023] Figure 2 This is the corresponding curve of the CCD color camera's photosensitive spectrum.

[0024] Figure 3 This is the spectrum of the bandpass filter.

[0025] Figure 4 This is the schematic diagram of the optical chromatic aberration confocal point sensor.

[0026] Figure 5 Schematic diagram of the Carl Zeiss Axiotron2 CSM VIS-UV optical confocal microscope.

[0027] Figure 6 Schematic diagram of optical confocal microscope.

[0028] Figure 7 It is the principle of slit confocal scanning.

[0029] Marked in the figure are: light source system 1, light outlet 2, Köhler illumination system 3, first beam splitter 4, Nipkow disk 5, first projection objective 6, chromatic aberration lens 7, microscope objective 9, mechanical scanning device 10, storage table 11, first beam splitter 12, second beam splitter 13, eyepiece 14, imaging lens 15, CCD camera 16, second projection objective 17, CCD color camera 18. DETAILED DESCRIPTION

[0030] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0031] like Figure 1 and Figure 2The optical three-dimensional measurement system shown in the figure includes a light source system 1, a first beam splitter 4 is obliquely arranged on one side of the light source system 1, a Nipkow disk 5 is arranged on one side of the first beam splitter 4, and the Nipkow disk 5 has many tiny pinholes and is in a high-speed operation process, so that the parallel light emitted by the light source system 1 is deflected 90 degrees after passing through the first beam splitter 4 and emitted to the Nipkow disk 5, and a first projection lens 6, a chromatic aberration lens 7 and a microscope lens 9 are sequentially arranged on the side of the Nipkow disk 5 away from the first beam splitter 4, and a lens for projection is also arranged on the side of the microscope lens 9 away from the chromatic aberration lens 7. The object to be tested is placed on a stand 11, so that the light beam passing through the Nipkow disk 5 is imaged on the surface of the object to be tested via the first projection lens 6, the chromatic aberration lens 7 and the microscope lens 9. The first beam splitter 4 is sequentially provided with a second projection lens 17 and a CCD color camera 18 on the side away from the Nipkow disk 5, so that the light reflected from the surface of the tested product enters the CCD color camera 18 via the microscope lens 9, the chromatic aberration lens 7, the first projection lens 6, the Nipkow disk 5, the first beam splitter 4 and the second projection lens 17. The CCD color camera used in this embodiment is of the model Foveon X3, and its three color chips (red, green and blue, RGB) are precisely overlapped pixel by pixel, and the color spectrum information of each point of the object to be tested is simultaneously recorded on the three color chips. This CCD color camera can work in two states: A. As a color camera, it can work in the visible light spectrum range. B. The infrared filter of this color camera is removed. The spectral range of this color camera includes visible light and near infrared, electromagnetic wave 380-1000nm. Other color cameras with equivalent functions can also be selected.

[0032] During the specific measurement, the object to be measured is placed on the object stand 11, and the light emitted by the light source system 1 is deflected 90 degrees by the first beam splitter 4 and emitted onto the Nipkow disk 5. The light beam passing through the tiny pinhole on the Nipkow disk 5 is imaged by the first projection lens 6, the chromatic aberration lens 7 and the microscope lens 9 and then formed on the surface of the object to be measured. Due to the longitudinal chromatic aberration produced by the chromatic aberration lens 7, light of different wavelengths is focused on different heights on the surface of the object, that is, the blue light is the highest, the red light is the lowest, and the green light is in the middle. Then, the light reflected from the surface of the object to be measured is imaged by the microscope lens 9, the chromatic aberration lens 7 and the first projection lens 6 on a conjugate surface of the Nipkow disk 5, which is clearly focused on the object to be measured. The light on the surface of the object to be measured will pass through the pinhole of the Nipkow disk, and all the out-of-focus light will be filtered out. Then the focused light will pass through the second projection lens and be imaged on the wide-spectrum CCD color camera 18. The color camera is composed of three layers of photosensitive devices stacked and integrated together. Its working spectrum range includes visible light and near-infrared electromagnetic waves in the range of 380-1000nm. This system is based on the principles of optical confocality and optical chromatic aberration. Areas at different heights on the surface of the object present different spectral colors on the image plane. Therefore, the color of the surface of the object represents its height. The spectral color is used as a ruler to perform three-dimensional height measurement, such as Figure 2 The figure shows the sensitive spectrum curve of the CCD color camera. Therefore, there is no need for vertical height scanning to measure the height. A color photo can accurately measure the three-dimensional height of the entire surface. The measurement speed is extremely fast and the diffraction grating design on the Nipkow surface minimizes the reflection on the surface. At the same time, the design of the optical device of the wedge and prism minimizes the reflection of the Nipkow disk.

[0033] On the basis of the above, the light source system 1 includes an integrating sphere coated with a high-reflectivity material inside, and the integrating sphere includes at least one light inlet and a light outlet 2. The light inlet is provided with a broadband white light source, and the light is projected into the integrating sphere, so that the light in the integrating sphere can be fully mixed to reduce the loss. In this embodiment, 5 broadband white light sources are provided, and are arranged in 5 different directions of the integrating sphere. This setting can form a high-power and high-intensity lighting system. Since each light source is not very large, there is no need to install a fan or cooling system, there is no vibration, and it is suitable for high-speed measurement.

[0034] On the basis of the above, a bandpass filter is provided at the light-emitting port of the broadband white light source for removing harmful infrared light energy with a wavelength greater than 1 micron. The spectrum of the bandpass filter is as follows: Figure 3 As shown, the heat of the infrared light energy is excluded from the measuring system. A heat sink may also be provided on the broadband white light source to exclude the heat generated by the broadband white light source from the measuring system.

[0035] On the basis of the above, if Figure 1As shown, a Kohler illumination system 3 is arranged at the light outlet 2 of the integrating sphere, so that the illumination system has high uniformity and high power.

[0036] On the basis of the above, if Figure 1 As shown, a first beam splitter 12 is obliquely arranged between the microscope objective lens 9 and the chromatic aberration lens 7, and an eyepiece 14 is arranged on one side of the first beam splitter 12, so that the light reflected by the object to be measured reaches the eyepiece 14 after passing through the microscope objective lens 9 and the first beam splitter 12. The operator can adjust the measurement position and focus the microscope objective lens 9 by observing the objective lens to ensure the accuracy of the measurement.

[0037] On the basis of the above, if Figure 1 As shown, a second beam splitter 13 is obliquely arranged between the first beam splitter 12 and the eyepiece 14, and an imaging lens 15 and a CCD camera 16 are sequentially arranged on one side of the second beam splitter 13, so that the light reflected by the object to be measured reaches the CCD camera 16 after passing through the first beam splitter 12, the second beam splitter 13 and the imaging lens 15. The person to be measured can adjust the measurement position and focus the microscope 9 by observing on the screen of the CCD camera 16, thereby ensuring the accuracy of the measurement.

[0038] On the basis of the above, if Figure 1 As shown, the first beam splitter 12, the second beam splitter 13, the eyepiece 14, the imaging lens 15 and the CCD camera 16 are all installed on a movable frame, which also includes a movable guide rail for driving the movable frame to move horizontally. The setting of the movable guide rail can adjust the positions of the first beam splitter 12, the second beam splitter 13, the eyepiece 14, the imaging lens 15 and the CCD camera 16. Moving them in can be used for observation adjustment, and moving them out can be used to maximize the utilization of light energy, shorten the exposure time required for imaging, and achieve high-speed measurement.

[0039] On the basis of the above, it also includes a mechanical scanning device 10, the microscope objective lens 9 is installed on the mechanical scanning device 10, the microscope objective lens 9 and the mechanical scanning device 10 include two sets, the two sets of microscope objective lenses 9 are respectively a high-magnification microscope objective lens 9 and a low-magnification microscope objective lens 9, and also includes a switching device, the two sets of microscope objective lenses 9 and the mechanical scanning device 10 are both installed on the switching device, the above mechanical scanning device 10 can be a PZT micro-motion scanning device, the placement table 11 is a five-dimensional displacement table, including XYZ three axes and angle αβ adjustment, the mechanical movement of the scanning mechanism is composed of a five-dimensional displacement table or a PZT micro-motion scanning device, so that it can be used to measure large-scale integrated circuit chips and other surfaces for continuous scanning measurements, such as line scanning or area scanning.

[0040] On the basis of the above, the broadband white light source is a halogen tungsten lamp, each of which is low-power, only 50W, so there is no need to install a fan or cooling system, which can reduce mechanical vibration and power consumption.

[0041] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. Optical three-dimensional measurement system, characterized by: The invention comprises a light source system (1), wherein a first beam splitter (4) is obliquely arranged on one side of the light source system (1), and a Nipkow disk (5) is arranged on one side of the first beam splitter (4), so that parallel light emitted by the light source system (1) is deflected by 90 degrees after passing through the first beam splitter (4) and emitted toward the Nipkow disk (5), and a first projection lens (6), a chromatic aberration lens (7) and a microscope lens (9) are arranged in sequence on a side of the Nipkow disk (5) away from the first beam splitter (4), and a placement table (6) for placing an object to be measured is also arranged on a side of the microscope lens (9) away from the chromatic aberration lens (7). 11), so that the light beam passing through the Nipkow disk (5) is imaged on the surface of the object to be tested via the first projection objective lens (6), the chromatic aberration lens (7) and the microscope objective lens (9), and the first beam splitter (4) is sequentially provided with a second projection objective lens (17) and a CCD color camera (18) on the side away from the Nipkow disk (5), so that the light reflected from the surface of the product to be tested enters the CCD color camera (18) via the microscope objective lens (9), the chromatic aberration lens (7), the first projection objective lens (6), the Nipkow disk (5), the first beam splitter (4) and the second projection objective lens (17); The light source system (1) comprises an integrating sphere coated with a high reflectivity material inside, the integrating sphere comprising at least one light inlet and a light outlet (2), the light inlet being provided with a broadband white light source; A first beam splitter (12) is also obliquely arranged between the microscope objective lens (9) and the chromatic aberration lens (7), and an eyepiece (14) is arranged on one side of the first beam splitter (12), so that light reflected from the object to be measured passes through the microscope objective lens (9) and then through the first beam splitter (12) to reach the eyepiece (14); A second beam splitter (13) is obliquely arranged between the first beam splitter (12) and the eyepiece (14), and an imaging lens (15) and a CCD camera (16) are sequentially arranged on one side of the second beam splitter (13), so that light reflected by the object to be measured passes through the microscope objective lens (9) and reaches the CCD camera (16) via the first beam splitter (12), the second beam splitter (13) and the imaging lens (15); The first beam splitter (12), the second beam splitter (13), the eyepiece (14), the imaging lens (15) and the CCD camera (16) are all mounted on a movable frame, and also include a movable guide rail for driving the movable frame to move horizontally; The invention also comprises a mechanical scanning device (10), the microscope objective lens (9) being mounted on the mechanical scanning device (10), the microscope objective lens (9) and the mechanical scanning device (10) comprising two sets, the two sets of microscope objective lenses (9) being respectively a high-magnification microscope objective lens (9) and a low-magnification microscope objective lens (9), and a switching device being also comprised, the two sets of microscope objective lenses (9) and the mechanical scanning device (10) being mounted on the switching device.

2. The optical three-dimensional measurement system according to claim 1, characterized in that: A bandpass filter for removing harmful infrared light energy is arranged at the light-emitting port of the broadband white light source.

3. The optical three-dimensional measurement system according to claim 1, wherein: A Kohler illumination system (3) is provided at the light outlet (2) of the integrating sphere.

4. The optical three-dimensional measurement system according to claim 1, wherein: The object placement platform (11) is a five-dimensional displacement platform.

5. The optical three-dimensional measurement system according to claim 1, wherein: The broadband white light source is a tungsten halogen lamp, and the CCD color camera (18) is a Foveon color camera.

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