KR20120084738A - High speed, high resolution, three dimensional solar cell inspection system - Google Patents

Abstract

Optical inspection systems and methods are provided. The workpiece transporter moves the workpiece 12 in a non-stop manner. Illuminator 40 includes a light pipe and is configured to provide first and second strobe illumination field shapes. The first (3) and second (5) camera arrays 2 are arranged to provide a stereoscopic image of the material 12. The first camera array 3 is configured to produce a plurality of first images of the workpiece 12 in a first illumination field of view and a plurality of second images of the workpiece 12 in a second illumination field of view. The second camera array 5 is configured to produce a plurality of third images of the work piece 12 in a first illumination field of view and a plurality of fourth images of the work piece 12 in a second illumination field of view. The processing device stores at least some of the first, second, third, and fourth plurality of images and provides the images to other devices.

Description

High speed, high resolution, 3D solar cell inspection system {HIGH SPEED, HIGH RESOLUTION, THREE DIMENSIONAL SOLAR CELL INSPECTION SYSTEM}

The present invention relates to a high speed, high resolution, three dimensional solar cell inspection system.

Advances in automated solar cell manufacturing technology enable high throughput, yield and cell conversion efficiency. For example, commercially available automated equipment for applying conductive layers to crystalline silicon solar cells screen prints metallization consistently at a rate of one cell per second. Improve cell conversion efficiencies such as selective emitter processes, metal-wrap-through and print-on-print, which require accurate registration of the metallization layer Newer technologies are being adopted to do this.

In addition, cell efficiency is affected by the height-to-width ratio of the metallized collector fingers that collect the current generated by the solar cell. This finger should be printed narrow in order to avoid unnecessary shading of the cell active area, but should be printed high in height to improve conductivity. In addition, the fragility of thin silicon solar cells and the tendency to warp during manufacturing also provide a challenge for automated handling facilities to avoid chips and cracks. The wafer may crack, for example, when it is vacuumed during one of a number of manufacturing process steps, or when pressure is applied to the wafer during the screen printing process. Given this industrial demand, there is a need for an automated optical inspection system that is distributed throughout the solar cell manufacturing process to ensure high process yields. As the demand for precise positioning, narrower and higher characteristics and detection of wafer bowing increases, it is faster than the prior art and can provide two-dimensional and three-dimensional inspection of high resolution solar cells. It would be beneficial to provide an automated optical inspection system.

In the present invention, an optical inspection system and method are provided.

In the optical inspection system of the present invention, the workpiece transporter is configured to transport the workpiece in a non-stop manner. The illuminator is configured to provide a form of a first strobe illumination field and a form of a second strobe illumination field. The illuminator includes a light pipe having a first end proximate the workpiece and a second end opposite the first end and spaced apart from the first end. The light pipe also has at least one reflective sidewall. The first end has an outlet aperture, the second end has at least one second end opening, and provides a view of the workpiece through the opening.

The first camera array is configured to digitally image the workpiece. The first camera array is configured to generate the plurality of first images of the workpiece into the first illumination field and the plurality of second images of the workpiece into the second illumination field. The second camera array is configured to digitally image the workpiece. The second camera array is configured to generate the plurality of third images of the workpiece into the first illumination field and the plurality of fourth images of the workpiece into the second illumination field. The first and second camera arrays are configured to provide stereoscopic imaging of the workpiece.

The processing device is operably connected to the illuminator and the first and second camera arrays. The processing apparatus is configured to store at least some of the first, second, third and fourth plurality of images and provide the first, second, third and fourth plurality of images to another apparatus.

1 is a cross-sectional front view of an automated high speed optical inspection system having a camera array and a compact integrated illuminator in accordance with an embodiment of the present invention.
2 is a schematic front view of a plurality of cameras having an overlapping field of view according to an embodiment of the present invention.
3 is a system block diagram of an inspection system according to an embodiment of the present invention.
4 is a top plan view of a camera array field of view acquired in the form of a transport conveyor, a solar cell and a first illumination field.
5 is a top plan view of the camera array field of view acquired in the form of a transport conveyor, a solar cell and a second illumination field.
6A-6D illustrate the workpiece and camera array field of view acquired at different locations and under alternating first and second illumination field shapes in accordance with embodiments of the present invention.
7 is a coordinate system for defining the direction of illumination.
8 is a perspective view of a known linear line source illuminating the camera array field of view.
FIG. 9 is a polar coordinate diagram of the illumination direction of the illuminator shown in FIG. 8.
10 is a perspective view of an exemplary hollow light pipe illuminator in accordance with an embodiment of the present invention.
FIG. 11 is a polar coordinate diagram of the input illumination direction of the illuminator shown in FIG. 10.
12 is a polar coordinate diagram of the output illumination direction of the illuminator shown in FIG. 10.
13 is a perspective view of a reflecting surface of a light pipe wall according to an embodiment of the present invention.
14A-14B are cross-sectional views of the reflective surface shown in FIG. 13.
15A is a perspective view of a light pipe illuminator and camera array in accordance with an embodiment of the present invention.
15B is a cut away perspective view of a light pipe illuminator and camera array in accordance with an embodiment of the present invention.
16 is a cutaway perspective view of a camera array and illuminator with multiple light sources according to an embodiment of the invention.
17A is a cut away perspective view of an illuminator and a camera array in accordance with an embodiment of the present invention.
17B is a cross-sectional view of a chevron shaped mirror used in accordance with an embodiment of the present invention.
18 is a cutaway perspective view of an illuminator and a camera array according to an embodiment of the present invention.
19 is a second cutaway perspective view of the illuminator and camera array shown in FIG. 18.
20 is a polar coordinate diagram of the illumination direction of the illuminator shown in FIGS. 18 and 19.
21 is a cross-sectional perspective view of an inspection sensor according to an embodiment of the present invention.
FIG. 22 is a polar coordinate diagram of the illumination direction of the illuminator shown in FIG. 21.
23 is a perspective view of two camera arrays arranged in a three-dimensional configuration according to an embodiment of the present invention.
24 is a cutaway perspective view of two camera arrays arranged in a stereoscopic configuration incorporating an illuminator according to an embodiment of the present invention.
25 is a perspective view of two camera arrays and configured light projectors disposed in accordance with an embodiment of the invention.
Figure 26 is a perspective view of two camera arrays and configured light projectors disposed in accordance with an embodiment of the present invention.
27 is a perspective view of a camera array and configured light projector according to an embodiment of the present invention.

Embodiments of the present invention generally provide a compact inspection system and method that does not require expensive and complex motion control hardware and has a high speed acquisition of multiple illuminated two-dimensional and three-dimensional images. Processing of images acquired in other illumination forms can significantly increase inspection capabilities and results.

1 illustrates a cross-sectional front view of a system for producing a high contrast, high speed digital image of a material suitable for automated inspection in accordance with an embodiment of the present invention.

The camera array 4 is composed of cameras 2A to 2H, which are preferably arranged at regular intervals. Each camera 2A to 2H simultaneously digitizes and digitizes a rectangular region of a material or substrate, such as silicon solar cell 12, while the material performs relative movement relative to the cameras 2A to 2H.

Illuminator 45 provides a series of pulsed short duration illumination fields called strobe illumination. The short duration of each illumination field effectively "freezes" the image of the solar cell 12 in order to suppress motion blurring. Two or more sets of images for each position of the solar cell 12 are generated by the camera array 4 having a different illumination field shape for each exposure. Depending on the particular features of the solar cell 12 that need to be inspected, the inspection results can be significantly increased by the co-processing of the reflected images generated in the form of other illumination fields. Other details of the illuminator 45 are provided in the description of FIGS. 21 and 22.

The material transport conveyor 26 moves the solar cell 12 in the non-stop mode in the X direction to provide a high speed image of the solar cell 12 by the camera array 4. The conveyor 26 includes a belt 14 driven by a motor 18. Since the selectable encoder 20 measures the position of the shaft of the motor 18, the approximate distance traveled by the solar cell 12 can be calculated. Other methods of measuring and encoding the traveled distance of the solar cell 12 include time-based, acoustical or vision-based encoding methods. By using strobe illumination and not stopping the solar cell 12, the time consuming transportation steps of accelerating, decelerating and fixing before imaging by the camera array 4 are eliminated. It is contemplated that the time required to fully acquire two complete 80 megapixel images of solar cell 12 with an area of 156 mm by 156 mm in the form of two illumination fields can be achieved in less than approximately one second.

2 shows the Y-dimensional position of each field 30A-30H of the solar cell 12 imaged by the cameras 2A-2H, respectively. There is some overlap between adjacent fields to fully image all positions of the solar cell 12.

During the inspection process, the images of the individual fields 30A-30H are digitally merged or stitched into one continuous image in the overlap area. An exemplary camera array 4 is shown in FIGS. 1 and 2 arranged in a single dimensional array of individual cameras. As shown, the cameras 2A-2H are configured to be imaged in a non-telecentric manner. This has the advantage that the fields 30A to 30H can overlap. However, the magnification, or effective resolution, of the non-telecentric imaging system will change as the solar cell 12 thickness changes, as well as the amount of warpage. The effects of warpage, thickness change and other camera alignment errors of the solar cell 12 can be compensated for by image stitching.

In other embodiments, the camera array may be arranged in a two dimensional array. For example, individual cameras may be arranged in a two-column camera array of four cameras in which adjacent views overlap. Other arrangements of camera arrays may be advantageous, depending on the cost, speed, and performance goals of the inspection system including arrays that do not overlap the field of view. For example, a staggered array of cameras with a telecentric imaging system can be used.

3 is a block diagram of inspection system 92. The inspection application 71 is preferably executed on the system computer 76. Inputs to the inspection program 71 include, for example, solar cell 12 geometry, metallization printing contours for printing defects, color defects, edge chipping, micro crack sizes and saw marks. Includes test tolerances. In addition, lighting and camera calibration data may be input to the inspection program 71.

The inspection program 71 constitutes a logic controller 22 that is programmable at the conveying direction and speed of the solar cell 12 via the conveyor interface 72. The inspection program 71 also configures the main electronic board 80 through the PCI high speed interface with the number of encoder 20 counts between each subsequent image acquisition of the camera array 4. Optionally, time-based image acquisition sequences can be performed based on the known speed of the solar cell 12. In addition, the inspection program 71 programs or sets appropriate configuration parameters in the cameras 2A-2H before inspection as well as the strobe board 84 having the individual flash lamp output levels.

Panel sensor 24 is loaded into inspection system 92 to sense the edge of solar cell 12, and this signal is sent to main board 80 to initiate the image acquisition sequence. The main board 80 generates an appropriate signal to initiate exposure of each image by the camera array 4 and commands the strobe board 84 to activate the appropriate flash lamps 87 and 88 at the appropriate times. The strobe monitor 86 senses some of the light emitted by the flash lamps 87 and 88, which data can be used by the main electronic board 80 to compensate for image data for slight flash lamp output variations. have. The image memory 82 is provided for storing all the images generated for the at least one solar cell 12 and preferably includes sufficient capacity.

For example, in one embodiment, each camera in the array of cameras has a resolution of about 5 megapixels, and memory 82 has a capacity of about 2.0 gigabytes. Image data from cameras 2A-2H can be sent at high speed to image memory buffer 82 so that each camera is quickly ready for subsequent exposure. This allows the solar cell 12 to be transported through the inspection system 92 in a non-stop manner and to produce an image of each position of the solar cell 12 in the form of at least two different illumination fields. The image data may begin to be read from the image memory 82 into the PC memory via a high speed electrical interface, such as a PCI component interconnect express (PCIe), as the first image is transferred to the memory 82. Similarly, inspection program 71 may begin to calculate inspection results as soon as image data becomes available in PC memory.

The image acquisition process is described in more detail by FIGS. 4-6.

4 shows a top plan view of the transport conveyor 26 and the solar cell 12. The cameras 2A-2H image (image) the overlapping fields of view 30A-30H, respectively, to generate an effective field of view 32 of the camera array 4. The field of view 32 is acquired in the form of a first strobe illumination field. The solar cell 12 is transported by the conveyor 26 in a non-stop manner in the X direction. The solar cell 12 may be provided with large velocity variations and accelerations, but it is desirable to move at a rate that varies to a less than 5% during the image acquisition process.

In one preferred embodiment, each field of view 30A-30H has nearly 5 million pixels with a pixel resolution of 17 microns and a range of 34 mm in the X direction and 45 mm in the Y direction. Each field of view 30A-30H overlaps an adjacent field of view up to nearly 3 mm in the Y direction such that the center-to-center spacing for each camera 2A-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 of approximately 5: 1 in the Y direction compared to the X direction.

FIG. 5 shows the solar cell 12 at a position displaced in the positive X direction from the position in FIG. 4. For example, solar cell 12 may be advanced almost 15 mm from the position in FIG. 4. The effective field of view 33 is composed of an overlapping field of view 30A-30D and is obtained in the form of a second illumination field.

6A-6D show time sequences of camera array views 31, 33, 34, and 35 acquired in the form of alternating first and second illumination fields. The solar cell 12 is moved in the X direction in a non-stop manner. FIG. 6A shows the solar cell 12 in one X position during image acquisition for the entire solar cell 12. The field of view 31 is acquired in the form of a first strobe illumination field as discussed with respect to FIG. 4. FIG. 6B shows the view 33 acquired in the form of a solar cell 12 and a second strobe illumination field further displaced in the X direction as discussed with respect to FIG. 5. FIG. 6C shows the solar cell 12 further displaced in the X direction and the field of view 34 acquired in the form of the first illumination field, and FIG. 6D shows the solar cell 12 and the second illumination field further displaced in the X direction. The visual field 35 acquired in the form is shown.

There is a small overlap in the X dimension between the field of view 31 and the field of view 34 so as to have sufficient overlapping image information to record and digitally merge the images acquired in the form of the first illumination field or suture one another. In addition, there is a small overlap in the X dimension between the field of view 33 and the field of view 35 so as to have sufficient overlapping image information to record and digitally merge the acquired image in the form of a second illumination field. In an embodiment with a field of view 30A-30H having a range of 33 mm in the X direction, about 5 mm overlap in the X direction was found to be effective between fields of view acquired in the form of the same illumination field. Also preferred is a displacement of about 15 mm in the X direction between the fields of view acquired in other illumination forms.

Images of each feature of the solar cell 12 can be recorded by two or more by increasing the number of fields collected and ensuring sufficient image overlap to record and digitally merge the images generated in the form of similar illumination fields, or stitch them together. It can be obtained in the form of an illumination field. Finally, the sealed image generated for each type of illumination can be registered for each. In the preferred embodiment, the material transport conveyor 26 has a positional accuracy lower than the inspection requirements in order to reduce system cost. For example, the encoder 20 may have a resolution of 100 microns and the conveyor 26 may have a position accuracy of 0.5 mm or more. Image closure of the field of view in the X direction compensates for the positional error of the solar cell 12.

It is desirable for each illumination field of view to be illuminated from a spatially uniform and consistent angle. In addition, it is desirable that the lighting system be compact and have high efficiency. The limitations of the two prior art lighting systems, the linear light source and the annular light source, are discussed with reference to FIGS. 7-9. The linear light source has high efficiency, but inferior uniformity at the azimuth angle of the projected light. The annular light source has good uniformity at the azimuth angle of the projected light, but it is not compact and inferior in efficiency when used with a large aspect ratio camera array.

7 defines a coordinate system for illumination. Direction Z is perpendicular to solar cell 12 and directions X and Y define a horizontal position on solar cell 12 or other material. Angle β defines the elevation angle of the illumination. The angle γ overlaps the illumination ray angle with respect to the vertical. Angle α is the azimuth angle of the light beam. Illumination from almost all azimuth and elevation angles is called cloud day illumination. The illumination from the low level β, which is almost horizontal, is called dark field illumination. Illumination from a nearly vertical high elevation β is called bright field illumination. The best general purpose illumination system will produce a light field with uniform emission (spatial uniformity) over the entire field of view, and will be illuminated from a matched angle (angle uniformity) over the entire field of view.

8 shows a known linear light source 48 that illuminates the camera array field of view 32. Linear light source 48 may use an array of LEDs 46 to efficiently concentrate light on narrow rectangular field of view 32. The disadvantage of using the linear light source 48 is that no light can be received from the direction toward the long axis of the FOV, even if the object receives symmetrical illumination from two directions towards the light source.

9 is a two-axis polar coordinate plot showing the direction of illumination for the two linear light sources 48. The polar plot shows that strong illumination is received by the camera array field of view 32 from the direction closest to the light source 48 (at 0 degrees and 180 degrees azimuth) and no illumination is received from 90 degrees and 270 degrees azimuth. do. Since the azimuth angle varies between 0 and 90 degrees, the light source elevation angle drops, and the light source makes a smaller angle and less light is received. Camera array field of view 32 receives light that varies with azimuth at both intensity and elevation. The linear light source 48 illuminates the field of view 32 efficiently, but the uniformity is inferior in azimuth. In contrast, known annular light sources have good uniformity in azimuth, but must be large to provide acceptable spatial uniformity for large aspect ratio camera field of view 32.

Although an annular light source can be used to provide acceptable uniformity in the azimuth angle, the annular light source will need to be very large to provide acceptable spatial uniformity for the camera field of view 32 of nearly 170 mm in the Y direction. In typical inspection applications, it is contemplated that the annular light source needs to be at least 500 mm diameter to provide sufficient spatial uniformity. This huge annular light source does not meet market demand in several respects: large size consumes very useful space on the assembly line, large light source is expensive to build, illumination angle is not consistent across the workplace, it is very inefficient The light output will be scattered over a substantial portion of the 500 mm circle while only a small rectangle of solar cells is actually imaged.

Optical devices, referred to as light pipes, can be used to create a very uniform light field for illumination. For example, US Pat. No. 1,577,388 describes a light pipe used to back illuminate 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 in connection with FIGS. 10-12. Embodiments of the present invention are described with respect to FIGS. 13-17 and significantly reduce the length of the light pipe required for uniform illumination. In one embodiment, the inner wall of the light pipe is made of a reflective material that scatters light in only one direction. In another embodiment of the present invention, the light pipe is comprised of input and output ports that allow simple integration of the camera array to obtain an image of a uniformly and efficiently illuminated material.

10 shows an illuminator 65 composed of a light source 60 and a light pipe 64. The hollow box light pipe 64, when used as described, will produce a uniform dark field illumination pattern. The camera 2 sees the workpiece 11 below the length of the light pipe 64 through the openings 67 and 69 at the end of the light pipe. A light source 60, for example an arc of the parabola reflector, is arranged such that the light is projected by the internal reflecting surface into the inlet opening 67 of the light pipe 64 so that the light is lowered at the desired elevation angle. Optionally, a lens LED or other light source can be used as long as the range of the light source elevation angles matches the desired range of elevation angles in the workpiece 11. The light source can be strobe or continuous. The light fan from the light source 60 goes down until it hits one of the side walls across the pipe. The radial fan extends apart at an azimuth at the corner of the pipe but maintains the elevation. This expanded ray fan is further expanded to impinge on a number of other sidewall portions, where the azimuth angle is more diffused, not constant, and the elevation angle is not significantly changed. After a number of reflections all azimuth angles are present in the exit opening 68 and the workpiece 11. Thus, every point on the object is illuminated by light from all azimuth angles, but only the elevation angle is present in the original light source. In addition, the illumination field in the material 11 is spatially uniform. It should be noted that the lateral extent of the light pipe 64 is only slightly larger than the field of view, in contrast to the required size of the annular light source for conditions of spatially uniform illumination.

FIG. 11 shows the polarization diagram of an illumination direction at a light source and a nearly focused bundle of rays from a small range of elevation and azimuth angles.

12 is a polar coordinate diagram of the light rays in the material 11, and the angular spread of the light source is included for comparison. All azimuth angles are present in the material 11, and the elevation angle of the light source is maintained.

Since the elevation angle of the light exit illuminator 65 is the same as that present in the light source 60, it is relatively easy to adjust the elevation angle for a particular application. If a low illumination elevation is desired, the light source may be close to horizontal. The lower limit of the illumination angle is set by the standoff of the light pipe bottom edge since the light cannot reach the target from an angle below the bottom edge of the light pipe. The upper limit of the illumination elevation angle is set by the length of the light pipe 66 because several reflections are required to make the illumination azimuth angle not constant or uniform. As the elevation angle increases, there will be less bounces against the length of light pipe 64 before reaching the workpiece 11.

Polygonal lightpipe homogenizers only form new azimuths at the corners, so multiple reflections are necessary to obtain a uniform output. If all parts of the light pipe sidewall can extend or become inconsistent in the light pattern in the azimuth direction, less reflection is required and the length of the light pipe in the Z direction can be reduced, so that the illuminator is shortened in the Y direction or Make it wider.

13 and 14 illustrate an embodiment of the present invention having light pipe sidewalls that diffuse or scatter light only on one axis. In this embodiment, the azimuth angle of the bundle of rays is preferably extended for each reflection while maintaining the elevation. This is accomplished by adding a curved or faceted reflective surface 70 to the inner surface of the light pipe sidewall 66, as shown in FIG. Cross-sectional views of sidewall 66 are shown in FIGS. 14A and 14B. 14A illustrates whether the focused bundle of rays 62 extends perpendicular to the axis of cylindrical curvature on the reflective surface 70. In FIG. 14B, the angle of reflection for ray bundle 62 is maintained along the axis of cylindrical curvature of reflective surface 70. Therefore, the elevation angle of the light source is maintained since the plane perpendicular to all points of the reflection surface 70 does not have a Z component. The curved or angled surface of the reflective surface 70 creates a new range of azimuth angles for all reflections over the entire surface of the light pipe wall 66, so that the azimuth angle of the light source is not quickly constant. Embodiments of the present invention may be practiced using any combination of refractive, diffractive, and reflective surfaces for the inner surface of the light pipe sidewall 66.

In one aspect of the invention, the reflecting surface 70 is curved at the portion of the cylinder. This extends the incident light uniformly on one axis, approaching a one-dimensional Lambertian surface, but not extending it on another axis. In addition, this shape is easily formed from sheet metal. In another aspect, the reflecting surface 70 has a sinusoidal waveform. However, since the sinusoidal waveform has more curvature at peaks and valleys and less curvature at the side, the angular spread of ray bundle 62 is stronger at the peak and valley than at the side.

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 illuminator includes a side wall 66 and a light source 87. The one-dimensional diffuse reflecting surface 70 makes the azimuth angle not to be constant faster than a light pipe consisting of a planar reflective inner surface. This enables more compact light pipes to bring the camera array 4 close to the material. FIG. 15B shows whether the light beam is not constant at azimuth after a small number of reflections.

The light pipe illuminator 42 may be shortened in the Z direction compared to the illuminator 41 when a plurality of light sources are used. Rows of multiple light sources, for example focused LEDs, reduce the total number of reflections required to achieve a spatially uniform light source, thus reducing the required light pipe length. Illuminator 42 is illustrated as light sources 87A-87E, which may be a strobe arc lamp light source.

In another aspect of the present invention shown in FIGS. 17A-17B, illuminator 43 includes a mirror 67 that reflects a portion of the input beam from light source 87 at a desired light source elevation. As with many light source embodiments, this also makes the light field spatially uniform in short light pipes. Mirrors 67 are positioned between cameras and at different heights to avoid blocking of the object field of view, such that each mirror interferes with some of the light incident from light source 67. The mirror 67 is formed to reflect light toward the light pipe sidewall 66 at the desired elevation angle, where the curved reflecting surface 70 quickly causes the light source azimuthal direction not to be constant. A cross-sectional view of the mirror 67 is shown in FIG. 17B. The mirror 67 may be, for example, a planar mirror formed of a series of sebrons.

In another embodiment of the invention, FIGS. 18 and 19 illustrate an illuminator 44 integrated with the camera array 4. Light is introduced by light source 88 into light mixing chamber 57 defined by mirrors 54 and 55, top opening plate 58 and diffuser plate 52. The inner surfaces of the mirrors 54, 55 and the top opening plate 58 are reflective, while the diffuser plate 52 is preferably comprised of a translucent light diffusing material. An opening 56 is provided on the top plate 58 and an opening 50 is provided on the diffuser plate 52 so that the camera 2 has an unobstructed view of the material. To make the diffuser plate 52 and opening 50 more visible, the mirror 55 was removed in FIG. 19 compared to FIG.

Light projected by the light source 88 is reflected by the mirrors 54 and 55 and the opening plate 58. Since light is reflected in the mixing chamber 57, the diffuser plate 52 also reflects some of this light and introduces it back into the mixing chamber 57. After multiple light reflections in the mixing chamber 57, the diffuser plate 52 is uniformly illuminated. Light transmitted through the diffuser plate 52 is emitted to the bottom of the illuminator 44, which consists of a reflecting surface 70 as discussed with reference to FIGS. 13 and 14. Reflective surface 70 maintains the illumination elevation emitted by diffuser plate 52. The result is a spatially uniform illumination field in the workpiece 12.

20 is a polar coordinate diagram showing an output illumination direction of the illuminator 44. Illuminator 44 produces an output light field, called a cloudy day, as the illumination is about the same from almost all elevations and azimuths, as shown in FIG. 20. However, the range of the output elevation angle can be controlled by the diffusion property of the diffuser plate 52.

21 illustrates another embodiment of an optical inspection sensor 94. The optical inspection sensor 94 includes a camera array 4 and an integrated illuminator 45. Illuminator 45 facilitates independently controlled cloudy day and dark field illumination. The dark field illumination field is created on the solar cell 12 by activating the light source 87. The cloudy day illumination field is projected onto the solar cell 12 by activating the light source 88. 22 shows polar plots and lighting directions for cloudy day and dark field illumination. In one aspect, the light sources 87 and 88 are strobe in order to suppress the operational unsharpening effect due to the transport of the solar cell 12 in a non-stop manner.

It is understood by those skilled in the art that the image contrast of various object features varies depending on several factors, including the feature appearance, color, reflectivity, and angular spectrum of illumination accompanying each feature. Since each camera array field of view may include various features along with different lighting requirements, embodiments of the present invention provide for each feature and location of material 12, with each image being acquired under a different lighting condition and then stored in digital memory. This challenge is addressed by imaging at least twice. In general, inspection performance can be improved by using object feature data from two or more images acquired in the form of different illumination fields.

Embodiments of the present invention are not limited to two types of illumination, such as dark field and cloudy day light fields, nor are they limited to specific illuminator configurations. The light source can be projected directly onto the material 12. In addition, the light sources may have different wavelengths or colors and may be positioned at different angles relative to the workpiece 12. The light source can be located at various azimuth angles around the workpiece 12 to provide illumination from other quadrants. The light source may be a number of high power LEDs that "stop" the operation of the work piece 12 and emit light pulses with sufficient energy to suppress operational opacity in the image. Many other lighting configurations, including light sources that transmit through the substrate of workpiece 12 to create a bright field illumination field or to back-illuminate the feature to be inspected, are within the scope of the present invention. For example, since silicon is translucent at near infrared wavelengths, it is particularly effective to back-illuminate solar cell 12 with strobe near infrared light to inspect micro cracks and holes in the substrate.

Several solar cell inspection requirements call for the acquisition of three-dimensional image data at full production rates. This requirement includes measuring metallization print height and wafer warpage. Three-dimensional information, such as the profile of the collector finger, can be measured using, for example, well-known laser triangulation, phase shape measurements, or moire methods. U. S. Patent No. 6,577, 405 (Kranz et al.) Assigned to the assignee of the present invention describes a representative three-dimensional imaging system. In addition, the stereo vision based system can generate high speed 3D image data.

Stereo vision systems are well known. Commercial stereo systems begin with the 19th century stereoscope. More recently, many work has been done by pairing two camera stereo images ("A Taxonomy and Evaluation of Dense Two-Frame Stereo Correspondence Algorithms" by Scharstein and Szeliski) or multiple cameras ("A Space-Sweep Approach to True"). Multi-Image Matching "by Robert T. Collins). This last reference includes a description of a single camera moved to a target for aerial reconnaissance.

Alternative stereo vision systems project structured light patterns onto a target, or material, to produce a clear texture in the reflected light pattern ("A Multibaseline Stereo System with Active Illumination and Real-time Image Acquisition" by Sing Bing Kang, Jon A. Webb, C. Lawrence Zitnick, and Takeo Kanade).

In order to obtain high speed two-dimensional and three-dimensional image data that meets solar cell inspection requirements, multiple camera arrays can be placed in a stereo configuration overlapping the camera array field of view. The solar cell can be moved non-stop relative to the camera array. Multiple strobe illumination fields effectively "freeze" the image of the solar cell to suppress operational opacity.

23 shows camera arrays 6 and 7 arranged in a stereo configuration. The camera arrays 6 and 7 image the solar cell 12 in superimposition with the camera array field of view 37. The lighting system has been removed for clarity.

24 is a cutaway perspective view of an integrated illuminator 40 and an optical inspection sensor 98 for high speed acquisition of stereo image data. Camera arrays 3 and 5 overlap the field of view 36 on solar cell 12 and are arranged in a stereo configuration. The solar cell 12 is moved non-stop relative to the inspection sensor 98. The upper opening plate 59 includes an opening 56, and the translucent diffuser plate 53 includes an opening 50 to allow an unobstructed view 36 for the camera arrays 3 and 5. Activation of the light source 88 will produce a cloudy day illumination field shape on the solar cell 12, and activation of the light source 87 will produce a dark field illumination field shape. Other illumination field shapes, such as backlights, can be achieved by proper placement of the strobe illuminator so that light transmitted by or past the edge of solar cell 12 is acquired by camera arrays 3 and 5. The image acquisition sequence may be, for example, a series of superimposed images acquired simultaneously by both camera arrays 3 and 5 alternately in the form of strobe cloudy days, dark field and backlight illumination fields.

Block Diagram Referring again to FIG. 3, the functional block diagram of the optical inspection sensor 98 is very similar to the block diagram of the optical inspection sensor 94. However, in the optical inspection sensor 98, the camera array 4 is removed and replaced by the camera arrays 3 and 5 alternately interfaced to the main electronic 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 image memory 82 and transmitted to system computer 76 via a high speed electrical interface, such as PCI High Speed (PCIe).

The application inspection program 71 calculates the three-dimensional image data by a known stereo method using the disparity or offset of the image features between the image data from the camera arrays 3 and 5. Inspection results are calculated by the application 71 for solar wafer 12 properties and defects such as wafer geometry, chip edges, holes, cracks, microcracks, surface inspection, warpage, cut marks and colors. Print inspection results for position, thickness, width, length and obstruction can also be calculated by the application 71. In addition, the positioning of metallized printing can be augmented by measuring fiducials such as laser etched on the surface of the solar cell 12. This reference point often exhibits good contrast in dark field illuminated images and can be used to set up a coordinate system for measuring positioning. Combinations of two-dimensional and / or three-dimensional image data can be used for either of these inspection calculations.

FIG. 25 shows another embodiment in which camera arrays 6 and 7 are arranged in a stereo configuration overlapping with camera array field of view 37 on solar cell 12. Integrated cloudy days and dark field illuminators have been removed for clarity. Stereo vision systems sometimes do not work when there is no observable structure on the object. A way to overcome this is to add an artificial structure or "texture" to the surface with the patterned light source, which can be seen by a camera placed in a stereo configuration. The structured light projector 8 projects a strobe light pattern on the solar cell 12 through 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 inconsistency of the projected patterns seen by the camera arrays 6 and 7 can be used by the application 71 to calculate three-dimensional image data. The image acquisition sequence may be a series of superimposed images acquired simultaneously by both camera arrays 6 and 7 alternately in the form of strobe cloudy days, dark field and structured pattern illumination fields.

FIG. 26 shows another embodiment with camera arrays 6 and 7 and structured light projector 8 arranged in a stereo configuration. Integrated cloudy days and dark field illuminators have been removed for clarity. The camera array 6 is arranged to look at the solar cell 12 from the vertical direction to exclude the perspective, as in FIG. 25, to improve the two-dimensional measurement of the solar cell 12 feature.

FIG. 27 shows another embodiment with camera array 6 arranged to view camera array field of view 38 on solar cell 12. The structured light projector 8 projects the strobe light pattern through the camera array field of view 38 on the solar cell 12. The light pattern can be, for example, a laser stripe, a series of laser stripes, a sinusoidal pattern, or a random dope pattern. The range and features of the solar cell 12 are calculated by known methods by measuring the position of the projected light pattern observed by the camera array 6. Optional cloudy days, dark fields, bright fields, backlights, or other light sources are not shown for clarity.

Although the present invention has been described with reference to preferred embodiments, those 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)

Material transport configured to transport material non-stop,
Configured to provide a first strobe illumination field shape and a second strobe illumination field shape and having a first end proximate to the workpiece and a second end opposite the first end and spaced from the first end and at least one reflective sidewall. An illuminator having a light pipe, said first end having an outlet opening and said second end having at least one second end opening to provide a field of view of the workpiece,
A first camera array configured to digitally image the workpiece, the first camera array configured to generate a plurality of first images of the workpiece into a first illumination field and a plurality of second images of the workpiece into a second illumination field;
A second camera array configured to digitally image the workpiece, the second camera array configured to generate a plurality of third images of the workpiece into a first illumination field and a plurality of fourth images of the workpiece into a second illumination field, wherein the first and first 2 the camera array is configured to provide a stereoscopic image of the material, and
And a processing device operatively connected to the illuminator and the first and second camera arrays and configured to provide at least some of the first, second, third and fourth plurality of images to another device. The method of claim 1, wherein the first camera array comprises non-telecentric optics, wherein the cameras of the first camera array are aligned with each other along an axis perpendicular to the direction of material movement, The camera has an optical inspection system having a field of view that overlaps each other. The method of claim 1, wherein the first camera array comprises non-telecentric optics, the cameras of the second camera array being aligned with each other along an axis perpendicular to the direction of workpiece movement, and wherein the first plurality of cameras in the workpiece movement direction. Optical inspection system spaced from the camera. The method of claim 1, wherein the first camera array has a telecentric optics, the cameras of the first camera array are aligned with each other along an axis perpendicular to the direction of material movement, and have a field of view that does not overlap each other,
And a third camera array having telecentric optics, wherein the cameras of the third camera array are aligned with each other along an axis perpendicular to the direction of material movement and have a field of view that does not overlap each other, and wherein the first and first Three camera arrays have staggered fields of view,
The second camera array has telecentric optics, the cameras of the second camera array are aligned with each other along an axis perpendicular to the direction of workpiece motion and have a field of view that does not overlap one another,
And a fourth camera array having telecentric optics, wherein the cameras of the fourth camera array are aligned with each other along an axis perpendicular to the direction of material movement, have a field of view that does not overlap each other, and wherein the second and second 4 The camera array is an optical inspection system having a staggered field of view. The optical inspection system of claim 1, further comprising an encoder operably connected to a workpiece transporter to provide an indication of workpiece motion to the processing device. The optical inspection system of claim 5, wherein the indication has a resolution of 100 microns. The optical inspection system of claim 1, wherein the illuminator comprises at least one arc lamp. The optical inspection system of claim 1, wherein the illuminator comprises at least one light emitting diode (LED). The optical inspection system of claim 1, wherein the light pipe comprises a plurality of reflective sidewalls. The optical inspection system of claim 1, wherein the at least one reflective sidewall comprises a curved reflective surface that maintains the illumination elevation while mixing the illumination at an azimuth angle. The optical inspection system of claim 1, wherein the illuminator includes at least one mirror disposed to reflect at least a portion of the illumination at a desired light source elevation. The optical inspection system of claim 11, wherein the at least one mirror is inclined to reflect a portion of the illumination at a desired elevation angle towards the at least one reflective sidewall. 2. The illuminator of claim 1, wherein the illuminator comprises an illumination mixing chamber proximate a second end, wherein the mixing chamber and the light pipe are each made by a translucent diffuser having at least one diffuser opening aligned with at least one second end opening. Separate optical inspection system. The optical inspection system of claim 13, wherein a first light source is configured to introduce strobe illumination into the mixing chamber. 15. The optical inspection system of claim 14, wherein a first light source is configured to introduce strobe illumination with light pipes between the diffuser and the first end. 16. 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 comprises a high speed data transfer bus to provide the first, second, third and fourth plurality of images to another device. 18. The optical inspection system of claim 17, wherein the processing device is configured to simultaneously acquire and store an image from the first and second camera arrays and to provide the image to another device. 19. The optical inspection system of claim 18, wherein the high speed data transfer bus operates in accordance with a peripheral component interconnect high speed (PCIe) bus. The optical inspection system of claim 1, wherein the other apparatus is configured to at least partially provide inspection results for a feature based on a workpiece with respect to the first, second, third, and fourth plurality of images. The optical inspection system of claim 1, further comprising a structured light projector configured to project structured light onto a workpiece. The optical inspection system of claim 21 wherein the structured light projector is configured to project a random dot pattern. The optical inspection system of claim 21 wherein the structured light projector is configured to project at least one laser stripe. 22. The optical inspection system of claim 21, wherein the structured light projector is configured to project at least one sinusoidal fringe onto the workpiece. The optical inspection system of claim 1, wherein the first and second camera arrays are inclined with respect to a surface 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 the surface of the workpiece. Generating relative motion between the article of manufacture and a pair of camera arrays,
Simultaneously strobing a first illumination field shape into the article of manufacture, simultaneously acquiring a first set of images from a pair of camera arrays of first camera array through a light pipe during relative operation;
Generating at least a first stitched image from the acquired first image set,
Obtaining a second set of images from a second camera array through a light pipe, while strobing the first illumination field shape into the article of manufacture,
Generating at least a second sealed image from a second set of images acquired from a second camera array, and
Determining an inspection result for the article of manufacture based at least in part on the first and second sealed images. 28. The method of claim 27, wherein strobing a second illumination field shape into the article of manufacture while simultaneously acquiring a third set of images from the first camera array of the camera array pair through a light pipe during relative operation;
Generating at least a third sealed image from the acquired third image set,
Obtaining a fourth set of images from a second camera array through a light pipe, while strobing a second illumination field shape into the article of manufacture,
Generating at least a fourth sealed image from a fourth set of images acquired from a second camera array, and
Determining an inspection result for the article of manufacture based at least in part on the first, second, third, and fourth sealed images. 29. The method of claim 28 wherein the first illumination field shape is a dark field. 30. The method of claim 29 wherein the second illumination field shape is a cloudy day. 30. The method of claim 29 wherein the second illumination field shape is bright field. 29. The method of claim 28 wherein the first illumination field shape is structured illumination. 29. The method of claim 28 wherein the first illumination field shape is a backlight. 34. The method of claim 33 wherein the backlight has a near infrared wavelength. 29. The method of claim 28 wherein the first and second illumination field shapes are alternately activated. The method of claim 27, wherein the image closure is used to correct a positional error of the article of manufacture. The method of claim 27, wherein the suture is used to correct material 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. 28. The article of manufacture of claim 27, wherein the pair of camera arrays are arranged to stereoscopically view the article, and further comprising calculating three-dimensional surface information based on at least one of the first and second image sets. Way. 40. The method of claim 39, wherein the inspection result is based on two-dimensional and three-dimensional image data. The method of claim 27 wherein the article of manufacture is a solar cell. 42. The method of claim 41 wherein the article of manufacture is a solar cell and further comprising setting a coordinate frame using a solar cell reference point 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 positioning. 42. The method of claim 41 wherein the inspection results indicate solar cell warpage. 42. The method of claim 41 wherein the inspection results indicate a solar cell wafer appearance. 42. The method of claim 41 wherein the test result indicates the presence of a chip in the solar cell. 42. The method of claim 41 wherein the inspection results indicate the presence of cracks in the solar cell.

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