JP2013505465A - High-speed, high-resolution 3D solar cell inspection system - Google Patents

Abstract

Optical inspection systems and methods are provided. The workpiece transport mechanism moves the workpiece (12) non-stop. The lighting device (40) includes a light pipe and is configured to provide first and second strobe lighting field types. First (3) and second (5) cameras (2) arrays are arranged to provide stereoscopic imaging of the workpiece (12). The first camera array (3) generates a first plurality of images of the processing object (12) using the first illumination field, and uses the second illumination field for the processing object (12). A second plurality of images is configured to be generated. The second camera array (5) generates a third plurality of images of the workpiece (12) using the first illumination field, and uses the second illumination field to A fourth plurality of images are configured to be generated. The processing device stores at least some of the first, second, third and fourth plurality of images and provides them to other devices.

Description

Background Advances in automated solar cell manufacturing have enabled higher throughput, yield and cell conversion efficiency. For example, commercially available automated equipment for applying conductive layers to crystalline silicon solar cells typically screen prints metallization at a rate of one cell per second. Relatively new techniques for improving cell conversion efficiency that require precise alignment of the metallization layer, such as selective emitter, metal wrap-through and print-on-print methods have been employed. Cell efficiency is also affected by the height: width ratio of the metallized collector finger that collects the current generated by the solar cell. These fingers must be printed narrowly to avoid unnecessary solar shielding of the cell working area, but they must be printed tall to increase conductivity. Also, the fragility of thin silicon solar cells and their tendency to warp during manufacture present challenges for automated handling equipment to avoid chipping and cracking. A warped wafer can crack, for example, when vacuumed during any of a number of manufacturing processes, or when pressure is applied during a screen printing process. In view of these industrial requirements, a need has arisen for automated optical inspection systems that are distributed throughout the solar cell manufacturing process to ensure high process yields. Given the increased need for precision alignment, narrower, higher feature and wafer warpage detection, it is not only faster than the prior art, but also better provides higher resolution 2D and 3D solar cell inspection. It would be beneficial to provide an automated optical inspection system that can.

SUMMARY Optical inspection systems and methods are provided. A workpiece transport mechanism is configured to transport the workpiece in a non-stop manner. The lighting device is configured to provide a first strobe illumination field type and a second strobe illumination field type. The lighting device includes a light pipe having a first end close to the workpiece and a side opposite to the first end and having a second end spaced from the first end. The light pipe also has at least one reflective sidewall. The first end has an exit aperture and the second end has at least one second end aperture to provide a view of the workpiece through them. The first camera array is configured to digitally image the workpiece. The first camera array generates a first plurality of images of the workpiece using the first illumination field, and generates a second plurality of images of the feature using the second illumination field. It is configured. A second camera array is configured to digitally image the workpiece. The second camera array generates a third plurality of images of the workpiece using the first illumination field, and a fourth plurality of images of the feature using the second illumination field. It is configured. The first and second camera arrays are configured to provide stereoscopic imaging of the workpiece. A processing device is operably coupled to the illumination device and the first and second camera arrays. The processing device stores at least some of the first, second, third and fourth images and provides the first, second, third and fourth images to other devices. It is configured.

1 is an elevational cross-sectional view of an automated high speed optical inspection system with a camera array and a compact built-in illuminator in an embodiment of the present invention. 2 is an elevational view of multiple cameras having overlapping fields of view of an embodiment of the present invention. FIG. It is a system block diagram of the inspection system of the embodiment of the present invention. FIG. 6 is a plan view of a camera array field of view acquired using a transport conveyor, a solar cell, and a first illumination field type. It is a top view of the camera array visual field acquired using the transport conveyor, the solar cell, and the second illumination field type. 6A-6D show workpiece and camera array fields of view acquired at various locations with alternating first and second illumination field types, in accordance with an embodiment of the present invention. It is a coordinate system for demarcating an illumination direction. It is a perspective view of the well-known line light source which illuminates a camera array visual field. It is a polar coordinate plot of the illumination direction of the illuminating device shown in FIG. 1 is a perspective view of an exemplary hollow light pipe lighting device according to an embodiment of the present invention. FIG. It is a polar coordinate plot of the input illumination direction of the illuminating device shown in FIG. It is a polar coordinate plot of the output illumination direction of the illuminating device shown in FIG. It is a perspective view of the reflective surface of the light pipe wall of the embodiment of this invention. 14A and 14B are cross-sectional views of the reflecting surface shown in FIG. It is a perspective view of the light pipe illuminating device and camera array of the embodiment of the present invention. It is a notch perspective view of the light pipe illuminating device and camera array of the embodiment of the present invention. It is a notch perspective view of the illuminating device provided with the camera array and multiple light sources of the embodiment of this invention. It is a notch perspective view of the illuminating device and camera array of the embodiment of this invention. 1 is a cross-sectional view of a chevron shaped mirror used in accordance with an embodiment of the present invention. It is a notch perspective view of the illuminating device and camera array of the embodiment of this invention. It is a 2nd notch perspective view of the illuminating device and camera array shown in FIG. 20 is a polar coordinate plot of the illumination direction of the illumination device shown in FIGS. 18 and 19. It is a section perspective view of the inspection sensor of the embodiment of the present invention. It is a polar coordinate plot of the illumination direction of the illuminating device shown in FIG. FIG. 4 is a perspective view of two camera arrays arranged in a three-dimensional configuration according to an embodiment of the present invention. FIG. 3 is a cutaway perspective view of two camera arrays arranged in a three-dimensional configuration with an embedded lighting device, according to an embodiment of the present invention. FIG. 3 is a perspective view of two camera arrays and structured projectors arranged in accordance with an embodiment of the present invention. FIG. 3 is a perspective view of two camera arrays and structured projectors arranged in accordance with an embodiment of the present invention. 1 is a perspective view of a camera array and a structured projector according to an embodiment of the present invention. FIG.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS Embodiments of the present invention generally provide a compact inspection system and method for fast acquisition of multi-illuminated 2D and 3D images without the need for expensive and sophisticated motion control hardware. . Processing of images acquired using different illumination types can significantly enhance inspection capabilities and results.

  FIG. 1 shows an elevational cross-sectional view of a system for generating a high-contrast, high-speed digital image of a workpiece suitable for automated inspection according to an embodiment of the present invention. The camera array 4 is preferably composed of cameras 2A to 2H arranged at equal intervals. Each camera 2A-2H simultaneously images and digitizes a rectangular area on the workpiece or substrate, eg, silicon solar cell 12, as the workpiece is moved relative to the cameras 2A-2H. The illuminator 45 provides a series of pulsed short term illumination fields called strobe illumination. The short period of each illumination field effectively “freezes” the image of the solar cell 12 to reduce motion blur. The camera array 4 generates two or more image sets for each position on the solar cell 12 using different illumination field types for each exposure. Depending on the particular features on the solar cell 12 that must be inspected, the inspection results can be significantly enhanced by the concatenation of reflection images generated using different illumination field types. Further details of the lighting device 45 are provided in the detailed description of FIGS.

  A workpiece transport conveyor 26 translates the solar cell 12 in the non-stop mode in the X direction to provide high-speed imaging of the solar cell 12 by the camera array 4. The conveyor 26 includes a belt 14 that is driven by a motor 18. The encoder 20 that is used in some cases measures the shaft position of the motor, so that the approximate distance traveled by the solar cell 12 can be calculated. Other methods for measuring and coding the distance traveled by the solar cell 12 include time-based, sound-based or visual-based coding methods. By using strobe lighting and not stopping the solar cells 12, the time-consuming transport steps of accelerating, decelerating and fixing before imaging by the camera array 4 are eliminated. It is believed that the time required to fully capture two complete 80 megapixel images of the solar cell 12 with dimensions of 156 mm × 156 mm in the two illumination field types can be achieved in about 1 second or less.

  FIG. 2 shows the Y-dimensional position of each field of view 30A-30H on the solar cell 12 imaged by the cameras 2A-2H, respectively. In order to fully image all positions on the solar cell 12, there is a slight overlap between adjacent fields of view. During the inspection process, the images of the separate fields of view 30A-30H are digitally merged or stitched together into one continuous image in the overlap region. An exemplary camera array 4 arranged as a one-dimensional array of separate cameras is shown in FIGS. As shown, the cameras 2A-2H are configured to image non-telecentrically. This has the advantage that the fields of view 30A-30H can be overlapped. However, the magnification, or effective resolution, of the non-telecentric imaging system changes as the thickness of the solar cell 12 and the amount of warpage change. The effects of warpage, thickness change and other camera alignment errors of the solar cell 12 can be corrected by image stitching. In another embodiment, the camera array can be arranged in a two-dimensional array. For example, separate cameras can be arranged in a two-row camera array with four rows in a row where adjacent fields of view overlap. Depending on the cost, speed and performance goals of the inspection system, other arrangements of camera arrays may be advantageous, including arrays where the fields of view do not overlap. For example, staggered camera arrays with telecentric imaging systems can be used.

  FIG. 3 is a block diagram of the inspection system 92. The inspection application program 71 preferably runs on the system computer 76. Inputs to the inspection program 71 include, for example, solar cell 12 geometry, metallization print geometry and inspection tolerances for print defects, color defects, edge defects, microcrack sizes and saw marks. Lighting and camera calibration data can also be input to the inspection program 71.

  The inspection program 71 configures the programmable logic controller 22 according to the transport direction and speed of the solar cell 12 via the conveyor interface 72. The inspection program 71 also configures the main electronics board 80 with the count number of the encode 20 during each subsequent image acquisition of the camera array 4 via the PCI Express interface. Alternatively, a time-based image acquisition sequence can be performed based on the known speed of the solar cell 12. The inspection program 71 also sets appropriate configuration parameters in the cameras 2A-2H prior to inspection, as well as the strobe board 84 having individual flash lamp power levels.

  The panel sensor 24 senses the edge of the solar cell 12 as it is loaded into the inspection system 92 and this signal is sent to the main board 80 to initiate the image acquisition sequence. The main board 80 generates appropriate signals to initiate each image exposure by the camera array 4 and commands the strobe board 84 to activate the appropriate flash lamps 87 and 88 at the correct timing. A strobe monitor 86 senses a portion of the light emitted by the flash lamps 87 and 88, and this data can also be used by the main electronics board 80 to correct the image data for slight flash lamp output variations. . An image memory 82 is provided and preferably includes sufficient capacity to store all the images generated for the at least one solar cell 12. For example, in one embodiment, each camera in the camera array has a resolution of about 5 megapixels and the memory 82 has a capacity of about 2.0 gigabytes. Image data from the cameras 2A-2H can be transferred to the image memory buffer 82 at high speed so that each camera can quickly prepare for subsequent exposure. This allows the solar cell 12 to be transported non-stop through the inspection system 92 and to generate an image of each position on the solar cell 12 using at least two different illumination field types. As soon as the first image is transferred to the memory 82, the image data can be read from the image memory 82 via a high speed electrical interface such as PCI Express (PCIe) and can be read into the PC memory. Similarly, the inspection program 71 can begin calculating inspection results as soon as image data is available in the PC memory.

  Hereinafter, the image acquisition process will be described in more detail with reference to FIGS.

  FIG. 4 shows a plan view of the transport conveyor 26 and the solar cell 12. The visual fields 30A to 30H overlapped by the cameras 2A to 2H are respectively imaged to generate an effective visual field 32 of the camera array 4. The field of view 32 is acquired using the first strobe illumination field type. The solar cell 12 is transported non-stop in the X direction by the conveyor 26. The solar cell 12 preferably moves at a speed that varies by less than 5% during the image acquisition process, but can accommodate larger speed fluctuations and accelerations.

  In one preferred embodiment, each field of view 30A-30H has about 5 million pixels, the pixel resolution is 17 microns, and the range is 34 mm in the X direction and 45 mm in the Y direction. Each field of view 30A to 30H overlaps the adjacent field of view by about 3 mm in the Y direction, and the center-to-center distance of each camera 2A to 2H is 42 mm in the Y direction. In another embodiment, the camera array 4 consists of only four cameras 2A-2D. In this embodiment, the camera array field of view 32 has a large aspect ratio in the Y direction compared to the X direction of about 5: 1.

  FIG. 5 shows the solar cell 12 in a position moved in the positive X direction from that position shown in FIG. For example, solar cell 12 may have advanced about 15 mm from its position in FIG. The effective visual field 33 includes overlapping visual fields 30A to 30D and is acquired using the second illumination field type.

  6A-6D show a time sequence of camera array fields 31, 33, 34 and 35 acquired using alternating first and second illumination field types. It will be appreciated that the solar cell 12 is moving non-stop in the X direction. FIG. 6A shows the solar cell 12 in one X position during image acquisition with respect to the entire solar cell 12. The field of view 31 is acquired using the first strobe field type as detailed with reference to FIG. FIG. 6B shows the solar cell 12 further moved in the X direction and the field of view 33 acquired using the second strobe illumination field type as detailed with reference to FIG. 6C shows the field of view 34 acquired using the solar cell 12 further moved in the X direction and the first illumination field type, and FIG. 6D shows the solar cell 12 further moved in the X direction and the second illumination field. The field of view 35 acquired using the type is shown.

  In order to align the images acquired using the first illumination field type and have enough overlap image information to digitally merge, i.e., stitch, X between the fields 31 and 34. There is a small overlap in the dimension. Also, in order to have sufficient overlapping image information to align and digitally merge images acquired using the second illumination field type, there is an X dimension between the fields 33 and 35. There is a small overlap. In the embodiment of fields 30A-30H having a range of 33 mm in the X direction, an overlap of about 5 mm in the X direction has been found to be effective between fields acquired using the same illumination field type. Furthermore, a displacement of about 15 mm in the X direction is preferred between fields of view acquired using different illumination types.

  On the solar cell 12 by increasing the number of fields collected and aligning images generated using the same illumination field type and ensuring sufficient image overlap to digitally merge or stitch together It is also possible to acquire an image of each feature of the above using two or more illumination field types. Finally, stitched images generated for each illumination type can be registered with respect to each other. In the preferred embodiment, to reduce system costs, the workpiece transport conveyor 26 has a lower positional accuracy than the inspection requirement criteria. For example, the encoder 20 can have a resolution of 100 microns and the conveyor 26 can have a positional accuracy of 0.5 mm or more. The image stitching of the visual field in the X direction corrects the position error of the solar cell 12.

  Each illumination field is spatially uniform and it is desirable to illuminate from a consistent angle. It is also desirable that the lighting system is compact and has high efficiency. With reference to FIGS. 7-9, the problems of two prior art illumination systems, a line light source and a ring light source, will be discussed. A linear light source has high efficiency but is inferior in uniformity in the azimuth angle of projection light. Ring light sources have good uniformity in the azimuth of the projected light, but are not compact and are less efficient when used with large aspect ratio camera arrays.

  FIG. 7 defines an illumination coordinate system. The direction Z is perpendicular to the solar cell 12, and the directions X and Y define a horizontal position on the solar cell 12 or other workpiece. The angle β defines the elevation angle of the illumination. The angle γ redundantly defines the illumination ray angle relative to the normal. The angle α is the azimuth angle of the light beam. Illumination from almost all azimuths and elevations is called cloudy illumination. Illumination from a low elevation angle β, which is mainly near horizontal, is called dark field illumination. Illumination from a high elevation angle β that is mainly near vertical is called bright field illumination. A good general lighting system creates a light field with uniform irradiance over the entire field of view (spatial uniformity) and illuminates from a consistent angle over the entire field of view (angle uniformity).

  FIG. 8 shows a known line light source 48 that illuminates the camera array field of view 32. The line light source 48 can use the LED array 46 to efficiently focus the light into the narrow rectangular field of view 32. The disadvantage of using a line light source 48 is that the target receives symmetrical illumination from two directions facing the light source, but does not receive light from the direction facing the long axis of the field of view.

  FIG. 9 is a biaxial polar coordinate plot showing the illumination directions of two line light sources. The polar plot shows that intense illumination is received by the camera array field of view 32 from directions closest to the light source 48 (0 ° and 180 ° azimuth), and no illumination is received from 90 ° and 270 ° azimuth. . When the azimuth angle changes between 0 ° and 90 °, the light source elevation angle decreases, the light source faces a smaller angle and receives less light. The camera array field of view 32 receives light whose intensity and elevation change with azimuth. The line light source 48 efficiently illuminates the field of view 32, but the uniformity in azimuth is poor. In contrast, known ring lights have good uniformity in azimuth, but must be made large to provide acceptable spatial uniformity for large aspect ratio camera fields 32.

  Ring light can be used to provide acceptable uniformity in azimuth, but for a camera field of view of approximately 170 mm in the Y direction, the ring light provides acceptable spatial uniformity. To be very big. For general inspection applications, the ring light would need to exceed 500 mm in diameter to provide sufficient spatial uniformity. This too large ring cannot meet market needs in several ways. The large size consumes valuable space on the assembly line, the large light source is expensive to build, the illumination angle is not consistent across the work field and is very inefficient. While the light output scatters in a significant part of the 500 mm circle, in practice only a thin rectangle of the solar cell is imaged.

  The use of an optical device called a light pipe can produce a very uniform light field for illumination. For example, U.S. Pat. No. 1,577,388 describes a light pipe used for backlighting a film gate. However, conventional light pipes need to be physically long to provide uniform illumination.

  A brief description of the light pipe principle is provided with reference to FIGS. Then, with reference to FIGS. 13-17, an embodiment of the present invention will be described that significantly reduces the length of the light pipe required for uniform illumination. In one embodiment, the inner wall of the light pipe is constructed of a reflective material that scatters light in only one direction. In another embodiment of the invention, the light pipe is comprised of input and output ports that allow simple integration of the camera array to acquire a uniformly and efficiently illuminated image of the workpiece. Yes.

  FIG. 10 shows an illuminating device 65 including a light source 60 and a light pipe 64. A hollow box light pipe 64, when used as described, produces a uniform dark field illumination pattern. The camera 2 looks down at the workpiece 11 in the longitudinal direction of the light pipe 64 through the apertures 67 and 69 at both ends of the light pipe. A light source 60, for example an arc lamp in a parabolic reflector, is arranged to project the light into an entrance aperture 67 of a light pipe 64 having an inner reflective surface so that the light falls at a desired elevation angle. . Or as long as the range of a light source elevation angle corresponds to the desired elevation angle range in the workpiece 11, LED with a lens or another light source can also be used. The light source may be either a strobe illumination type or a continuous type. Fan-shaped rays from light source 60 travel down across the pipe until they finally hit one of the side walls. Fan-shaped rays are split in the azimuth direction at the angle of the pipe and spread, but the elevation angle is preserved. This expanded fan-shaped beam then spreads and collides with many different sidewall portions where it further spreads in the azimuthal direction and is randomized, but with little change in elevation. After numerous reflections, all azimuth angles are present at the exit aperture 68 and the workpiece 11. Thus, all points on the target are illuminated by light from all azimuths, but only by light from elevation angles present in the original light source. In addition, the illumination field in the workpiece 11 is spatially uniform. Note that the lateral size of the light pipe 64 is only slightly larger than the field of view, in contrast to the size required for ring light in the case of spatially uniform illumination conditions.

  FIG. 11 shows a polar coordinate plot of the illumination direction in a light source that is a nearly parallel bundle of rays from a small range of elevation and azimuth angles.

  FIG. 12 is a polar coordinate plot of the light beam on the workpiece 11 and includes the angular spread of the light source for comparison. Although all azimuth angles exist in the workpiece 11, the elevation angle of the light source is preserved.

  Since the elevation angle of the light exiting the illumination device 65 is the same as that present in the light source 60, it is relatively easy to adjust this angle for a particular application. If a lower illumination elevation angle is desired, the light source may be aimed closer to the horizon. Since light cannot reach the target from an angle lower than the lower edge of the light pipe, the lower limit of the illumination angle is determined by the separation distance of the lower edge of the light pipe. In order to randomize the illumination azimuth, that is, to make the illumination uniform several times, the upper limit of the illumination elevation angle is determined by the length of the light pipe 66. In the case of a light pipe 64 of a given length, the number of rebounds until reaching the workpiece 11 decreases as the elevation angle increases.

  Polygonal light pipe homogenizers form a new azimuth only at that corner, and therefore require multiple reflections to obtain a uniform output. If all parts of the side wall of the light pipe can spread or randomize the light pattern in the azimuth direction, fewer light reflections are required, reducing the length of the light pipe in the Z direction, Could be shorter and / or wider in the Y direction.

  FIGS. 13 and 14 show an embodiment of the present invention having a light pipe sidewall that diffuses or scatters light in only one axis. In this embodiment, it is preferable that the azimuth angle of the light beam expands each time it is reflected while maintaining the elevation angle. This is accomplished by adding a curved faceted reflective surface 70 to the inner surface of the light pipe sidewall 66 as shown in FIG. A cross-sectional view of the sidewall 66 is shown in FIGS. 14A and 14B. FIG. 14A shows how the parallel light bundles 62 spread perpendicular to the axis of the cylindrical curve on the reflecting surface 70. In FIG. 14B, the angle of reflection of the light beam 62 is maintained along the axis of the cylindrical curvature on the reflecting surface 70. Therefore, since the surface normal at each point of the reflecting surface 70 does not have a Z component, the elevation angle of the light source is maintained. The curved or faceted surface of the reflective surface 70 creates a range of new azimuths for each reflection across the entire surface of the light pipe wall 66, and thus the azimuth of the light source is quickly randomized. Embodiments of the present invention can be realized using a combination of refractive, diffractive and reflective surfaces on the inner surface of the light pipe sidewall 66.

  In one embodiment, the reflective surface 70 is curved in a cylindrical section. This spreads the incident light evenly on one axis while approximating the one-dimensional Lambertian surface, but not on the other axis. This shape is also easy to form in sheet metal. In another embodiment, the reflective surface 70 has a sinusoidal shape. However, in the sine wave shape, the peaks and valleys have more curvature, and the curvature on the hypotenuse is small. Therefore, the spread of the angle of the light beam 62 is stronger in the peaks and valleys than the hypotenuse.

  15A and 15B show a curved reflective surface applied to the inner surface of the light pipe illuminator 41 for the camera array 4. The light pipe lighting device includes a side wall 66 and a light source 87. The one-dimensional diffuse reflection surface 70 randomizes the azimuth angle more quickly than a light pipe composed of a planar reflective inner surface. This makes it possible to use a more compact light pipe, which makes it possible to bring the camera array 4 closer to the workpiece. FIG. 15B shows how the light rays are randomized in azimuth after several reflections.

  If a large number of light sources are used, the light pipe illumination device 42 can be shortened in the Z direction compared to the illumination device 41. Multiple light sources, such as parallel LED arrays, reduce the total number of reflections required to achieve a spatially uniform light source and thus reduce the required light pipe length. The illumination device 42 is illuminated by light sources 87A-87E, which can also be strobe arc lamp light sources.

  In another embodiment of the invention shown in FIGS. 17A-17B, the illumination device 43 includes a mirror 67 that reflects a portion of the input beam from the light source 87 to a desired light source elevation angle. Similar to the multiple light source embodiment, this also produces a spatially uniform light field in a relatively short light pipe. The mirrors 67 are arranged between the cameras so as not to obstruct the visual recognition of the target, and each mirror is arranged at a different height so as to block a part of the light from the light source 67. The mirror 67 is shaped to reflect light toward the light pipe side wall 66 at a desired elevation angle, and the curved reflecting surface 70 quickly randomizes the light source azimuth direction on the light pipe side wall. A cross-sectional view of mirror 67 is shown in FIG. 17B. The mirror 67 can be, for example, a flat mirror formed in a series of chevrons.

  In another embodiment of the invention, FIGS. 18 and 19 show a lighting device 44 integrated with the camera array 4. Light is injected by light source 88 into light mixing chamber 57 defined by mirrors 54 and 55, upper aperture plate 58 and diffuser plate 52. Although the inner surfaces of 54, 55 and 58 are reflective, the diffuser plate 52 is preferably composed of a translucent light diffusing material. The upper plate 58 is provided with an aperture 56, and the diffusion plate 52 is provided with an aperture 50 so that the camera 2 can be seen without being blocked. In order to make the diffusion plate 52 and the aperture 50 easier to see, the mirror 55 is removed in FIG. 19 compared to FIG.

  The light projected by the light source 88 is reflected by the mirrors 54 and 55 and the aperture plate 58. As the light reflects in the mixing chamber 57, the diffuser 52 also reflects a portion of this light back into the mixing chamber 57. After multiple reflections in the mixing chamber 57, the diffuser plate 52 is illuminated uniformly. The light transmitted through the diffusing plate 52 is emitted into the lower section of the illuminating device 44, which is made up of the reflective surface 70, as described in detail with reference to FIGS. The reflective surface 70 preserves the illumination elevation angle emitted by the diffuser plate 52. The result is a spatially uniform illumination field on the workpiece 12. FIG. 20 is a polar coordinate plot showing the output illumination direction of the illumination device 44. The illuminator 44 produces an output light field, such as that shown in FIG. 20, because the illumination is approximately equal from almost all elevation and azimuth angles. However, the range of the output elevation angle can be controlled by the diffusibility of the diffusion plate 52.

  FIG. 21 shows another embodiment of the optical inspection sensor 94. The optical inspection sensor 94 includes a camera array 4 and an integrated illumination device 45. The illumination device 45 facilitates cloudy sky illumination and dark field illumination that are independently controlled. A dark field illumination field is generated on the solar cell 12 by energizing the light source 87. By turning on the light source 88, a cloudy illumination field is generated on the solar cell 12. FIG. 22 shows polar coordinate plots and illumination directions for cloudy and dark field illumination. In one embodiment, the light sources 87 and 88 are stroboscopically illuminated in order to reduce the motion blur effect due to non-stop transport of the solar cell 12.

  It will be appreciated by those skilled in the art that the image contrast of various object features will vary depending on several factors including feature geometry, color, reflectivity and the angular spectrum of illumination incident on each feature. Because the field of view of each camera array may include a wide variety of features with different lighting requirements, embodiments of the present invention may do this by imaging each feature and position on the workpiece 12 more than once. Addressing the challenges, each of these images is captured under different lighting conditions and then stored in digital memory. In general, inspection performance can be improved by using object feature data from two or more images acquired using different illumination field types.

  It will be appreciated that embodiments of the present invention are not limited to two illumination types, such as a dark field illumination field and a cloudy illumination field, and are not limited to a particular illumination device configuration. The light source can also be projected directly onto the workpiece 12. The light sources can also have different wavelengths, i.e. colors, and can be arranged at different angles with respect to the workpiece 12. Light sources can also be placed around the workpiece 12 at various azimuths to provide illumination from various quadrants. The light source can also be a number of high power LEDs that emit light pulses of sufficient energy to “freeze” the motion of the workpiece 12 and reduce motion blur in the image. Numerous other illumination configurations are within the scope of the present invention, including a light source that produces a bright field illumination field or that is transmitted through the substrate of the workpiece 12 to back-illuminate the feature to be inspected. For example, since silicon is translucent at near infrared wavelengths, it is particularly effective in backlighting solar cells 12 with strobe near infrared light to inspect microcracks and holes in the substrate.

  Several solar cell inspection requirements force the need to capture 3D image data at full production rates. These requirements include measuring metallization print height and wafer bow. Three-dimensional information such as the contour of the collector finger can also be measured using, for example, the well-known laser triangulation, phase profilometry or moire method. US Pat. No. 6,577,405 (Kranz et al.), Assigned to the assignee of the present invention, describes a representative three-dimensional imaging system. Stereovision-based systems can also generate high-speed 3D image data.

  Stereoscopic systems are well known. Commercially available 3D systems date back to 19th century stereoscopic mirrors. In recent years, two camera stereo image pairs ("A Taxonomy and Evaluation of Dense Two-Frame Stereo Correspondence Algorithms" by Scharstein and Szeliski) or many cameras ("A Space-Sweep Approach to True Multi-" by Robert T. Collins) A considerable amount of work has been done in the use of computers to evaluate "Image Matching"). This last reference refers to one camera that is moved relative to the target for air reconnaissance.

  An alternative stereo vision system projects a structured light pattern onto a target, i.e., a workpiece, to create a clear texture in the reflected light pattern (Sing Bing Kang, Jon A. Webb, C. Lawrence Zitnick and “Multibaseline Stereo System with Active Illumination and Real-time Image Acquisition” by Takeo Kanade).

  In order to acquire high speed 2D and 3D image data to meet solar cell inspection requirements, multiple camera arrays can be arranged in a 3D configuration with overlapping camera array fields of view. And a solar cell can be moved non-stop with respect to a camera array. Numerous strobe lighting fields effectively “freeze” the solar cell image to reduce motion blur.

  FIG. 23 shows the camera arrays 6 and 7 arranged in a three-dimensional arrangement. Camera arrays 6 and 7 image the solar cell 12 with overlapping camera array fields of view 37. The lighting system has been removed for clarity.

  FIG. 24 is a cutaway perspective view of an optical inspection sensor 98 incorporating the illumination device 40 for high-speed acquisition of stereoscopic image data. The camera arrays 3 and 5 are arranged in a three-dimensional arrangement with the fields of view of the solar cells 12 overlapping. The solar cell 12 moves non-stop with respect to the inspection sensor 98. The upper aperture plate 59 includes an aperture 56 and the translucent diffuser plate 53 includes an aperture 50 so that the field of view 36 of the camera arrays 3 and 5 is not obstructed. The activation of the light source 88 creates a cloudy illumination field type on the solar cell 12, and the activation of the light source 87 creates a dark field illumination field type. To achieve other illumination field types, such as backlighting, by appropriate arrangement of strobe lighting devices such that light passing through the solar cell 12 or passing through its edges is captured by the camera arrays 3 and 5 You can also. The image acquisition sequence can be, for example, a series of overlapping images that are captured simultaneously by both camera arrays 3 and 5 while alternating strobe cloudy, dark field and backlight field types.

  Referring again to block diagram 3, the functional block diagram of optical inspection sensor 98 is very similar to the block diagram of optical inspection sensor 94. However, in the case of the optical inspection sensor 98, the camera array 4 is omitted and replaced by the camera arrays 3 and 5, which are on the other hand interfaced to the main electronics board 80. Image memory 82 preferably includes sufficient capacity to store all images generated by camera arrays 3 and 5 for one solar cell 12. Image data is read from the image memory 82 and transferred to the system computer 76 via a high-speed electrical interface such as PCI Express (PCIe).

  An application inspection program 71 calculates the three-dimensional image data by a known stereo method using image feature mismatch or offset between the image data from the camera arrays 3 and 5. Inspection results are calculated by the application program 71 regarding the nature and defects of the solar cell wafer 12, such as wafer geometry, edge chipping, holes, cracks, microcracks, surface inspection, warpage, saw marks and colors. Print inspection results relating to position, thickness, width, length and breaks can also be calculated by the application program 71. It is also possible to enhance the alignment of the metallized print by measuring a reference point, for example, laser etched on the surface of the solar cell 12. These reference points often show good contrast in dark field illumination images and can be used to establish a coordinate system for measuring alignment. A combination of 2D and / or 3D image data can be used for any of these inspection calculations.

  FIG. 25 shows another embodiment in which the camera arrays 6 and 7 are arranged in a three-dimensional configuration with the camera array field of view 37 in the solar cell 12 overlapping. For ease of viewing, built-in cloudy and dark field illumination devices have been removed. Stereoscopic systems may not work if there is no observable structure on the object. A way to solve this is to add an artificial structure or “texture” to the surface by a patterned light source that can be viewed by a camera arranged in a configuration. The structured projector 8 projects a strobe light pattern onto the solar cell 12 above the camera array field of view 37. The light pattern can be, for example, a laser stripe, a series of laser stripes, or a random dot pattern. The projection pattern mismatch seen by the camera arrays 6 and 7 can be used by the application program 71 to calculate 3D image data. The image acquisition sequence can be a series of overlapping images captured simultaneously by the camera arrays 6 and 7 with alternating strobe cloudy, dark field and structured light pattern illumination field types.

  FIG. 26 shows another embodiment with camera arrays 6 and 7 and structured projector 8 arranged in a three-dimensional configuration. For ease of viewing, built-in cloudy and dark field illumination devices have been removed. In order to improve the two-dimensional measurement of the solar cell 12 shape, the camera array 6 is arranged so that the solar cell is viewed from the vertical direction and not obliquely as shown in FIG.

  FIG. 27 shows another embodiment having a camera array 6 arranged to view a camera array field of view 38 on the solar cell 12. A structured projector 8 projects a strobe light pattern onto the solar cell 12 above the camera array field of view 38. The light pattern can be, for example, a laser stripe, a series of laser stripes, a sinusoidal pattern, or a random dot pattern. The range to the solar cell 12 and its shape are calculated by measuring the position of the projected light pattern observed by the camera array 6 by a known method. For the sake of clarity, optional cloudy, dark field, bright field, backlighting or other light sources are not shown.

  Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Claims (47)

Workpiece transport mechanism configured to transport workpieces non-stop,
A lighting device configured to provide a first strobe lighting field type and a second strobe lighting field type, wherein the lighting device is opposite the first end and the first end close to the workpiece. And a light pipe having a second end spaced apart from the first end, the light pipe having at least one reflective sidewall, the first end having an exit aperture, and the second end. A lighting device having at least one second end aperture for providing a view of the workpiece through them,
A first camera array configured to digitally image the workpiece, the first camera array using a first illumination field and a first plurality of the workpieces. A first camera array configured to generate an image and generate a second plurality of images of the workpiece using a second illumination field;
A second camera array configured to digitally image the workpiece, wherein the second camera array uses the first illumination field to provide a third plurality of the workpieces. And generating a fourth plurality of images of the object to be processed using the second illumination field, wherein the first and second camera arrays are formed of the object to be processed. A second camera array configured to provide stereoscopic imaging; and a processing device operably coupled to the illumination device and the first and second camera arrays, the processing device comprising: An optical inspection system including a processing device configured to provide at least some of the first, second, third and fourth plurality of images to another device.   The first camera array includes non-telecentric optical elements, and the cameras of the first camera array are aligned with each other along an axis perpendicular to a moving direction of the workpiece; The optical inspection system of claim 1, wherein the cameras have overlapping fields of view.   The first camera array includes non-telecentric optical elements, and the cameras of the second camera array are aligned with each other along an axis perpendicular to the workpiece movement direction. The optical inspection system according to claim 1, wherein the optical inspection system is spaced apart from the first plurality of cameras. The first camera array has a telecentric optical element, and the cameras of the first camera array are aligned with each other along an axis perpendicular to the moving direction of the workpiece, and have fields of view that do not overlap each other. And
A third camera array having telecentric optical elements, wherein the cameras of the third camera array are aligned with each other along an axis perpendicular to the moving direction of the workpiece, and have non-overlapping fields of view. The first and third camera arrays have staggered fields of view;
The second camera array has a telecentric optical element, and the cameras of the second camera array are aligned with each other along an axis perpendicular to the moving direction of the workpiece, and have non-overlapping fields of view. And
A fourth camera array having telecentric optical elements, wherein the cameras of the fourth camera array are aligned with each other along an axis perpendicular to the moving direction of the workpiece, and have non-overlapping fields of view. The optical inspection system of claim 1, wherein the second and fourth camera arrays have staggered fields of view.   The optical inspection system of claim 1, further comprising an encoder operably coupled to the workpiece transport mechanism for providing an instruction to the workpiece to move the workpiece.   The optical inspection system of claim 5, wherein the indication has a resolution of about 100 microns.   The optical inspection system of claim 1, wherein the illumination device includes at least one arc lamp.   The optical inspection system of claim 1, wherein the illumination device comprises at least one light emitting diode.   The optical inspection system of claim 1, wherein the light pipe includes a plurality of reflective sidewalls.   The optical inspection system of claim 1, wherein the at least one reflective sidewall includes a curved reflective surface that preserves illumination elevation while mixing illumination in an azimuthal direction.   The optical inspection system of claim 1, wherein the illumination device includes at least one mirror arranged to reflect at least a portion of the illumination to a desired light source elevation angle.   The optical inspection system of claim 11, wherein the at least one mirror is tilted to reflect a portion of the illumination at a desired elevation angle toward the at least one reflective sidewall.   The lighting device includes an illumination mixing chamber disposed near the second end, the mixing chamber and the light pipe having at least one diffuser aperture aligned with each of at least one second end aperture. The optical inspection system according to claim 1, wherein the optical inspection system is divided by a transparent diffusion plate.   The optical inspection system of claim 13, wherein the first light source is configured to introduce strobe illumination into the mixing chamber.   The optical inspection system of claim 14, wherein the second light source is configured to introduce strobe illumination into the light pipe between the diffuser and the first end.   The optical inspection system of claim 15, further comprising a third light source configured to introduce additional illumination into the light pipe between the diffuser and the first end.   The optical inspection system of claim 1, wherein the processing device includes a high-speed data transfer bus for providing the first, second, third and fourth images to the other device.   The optical inspection system of claim 17, wherein the processing device is configured to acquire and store images from the first and second camera arrays simultaneously while providing images to the other devices.   The optical inspection system of claim 18, wherein the high speed data transfer bus operates according to a peripheral component interconnect express (PCIe) bus.   The other apparatus is configured to provide inspection results for a feature on the workpiece based at least in part on the first, second, third, and fourth images. Item 3. The optical inspection system according to Item 1.   The optical inspection system of claim 1, further comprising a structured light projector configured to project structured light onto the workpiece.   The optical inspection system of claim 21, wherein the structured projector is configured to project a random dot pattern.   The optical inspection system of claim 21, wherein the structured projector is configured to project at least one laser stripe.   The optical inspection system of claim 21, wherein the structured projector is configured to project at least one sinusoidal fringe onto the workpiece.   The optical inspection system according to claim 1, wherein the first and second camera arrays are inclined with respect to a plane perpendicular to the workpiece.   The optical inspection system of claim 1, wherein the first camera array is oriented to view the workpiece from an angle that is substantially perpendicular to a surface of the workpiece. A method for inspecting a product,
Creating a relative movement between the product and a pair of camera arrays;
Acquiring a first set of images from a first camera array of the pair of camera arrays via a light pipe while strobe illuminating a first illumination field type on the product during the relative movement. ,
Generating at least a first stitched image with the acquired first image set;
Acquiring a second set of images from the second camera array via the light pipe while strobe lighting the first illumination field type for the product;
Generating at least a second stitched image from the second set of images acquired from the second camera array, and an inspection result for the product based at least in part on the first and second stitched images A method comprising determining. During the relative movement, a third image set is acquired from the first camera array of the pair of camera arrays via a light pipe while simultaneously strobe illuminating a second illumination field type on the product. about,
Generating at least a third stitched image with the acquired third image set;
Acquiring a fourth set of images from the second camera array via the light pipe while strobe lighting the second illumination field type for the product;
Generating at least a fourth stitched image from the fourth set of images acquired from the second camera array, and based at least in part on the first, second, third and fourth stitched images 28. The method of claim 27, further comprising: determining test results for the product.   30. The method of claim 28, wherein the first illumination field type is dark field.   30. The method of claim 29, wherein the second illumination field type is cloudy.   30. The method of claim 29, wherein the first illumination field type is bright field.   30. The method of claim 28, wherein the first illumination field type is structured illumination.   30. The method of claim 28, wherein the first illumination field type is backlighting.   34. The method of claim 33, wherein the backlighting has a near infrared wavelength.   29. The method of claim 28, wherein the first and second illumination field types are alternately activated.   28. The method of claim 27, wherein image stitching is used to correct the position error of the product.   28. The method of claim 27, wherein stitching is used to correct workpiece warpage.   28. The method of claim 27, further comprising providing at least some images to another device while collecting images from the pair of camera arrays.   The pair of camera arrays are arranged to view the product in three dimensions, and the method calculates three-dimensional surface information based on at least one of the first and second image sets. 28. The method of claim 27, further comprising:   40. The method of claim 39, wherein the inspection results are based on 2D and 3D image data.   28. The method of claim 27, wherein the product is a solar cell.   42. The method of claim 41, wherein the product is a solar cell and the method further comprises establishing a coordinate frame using a solar cell recognition mark.   42. The method of claim 41, wherein the inspection result indicates at least one of collector finger height, collector finger width, and collector finger alignment.   42. The method of claim 41, wherein the test result indicates solar cell warpage.   42. The method of claim 41, wherein the inspection result indicates a solar cell wafer geometry.   42. The method of claim 41, wherein the inspection result indicates the presence of a chip in the solar cell.   42. The method of claim 41, wherein the inspection result indicates the presence of a crack in the solar cell.

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