Patent Application
20110010122
The present invention relates generally to the field of integrated circuit manufacturing and testing. Specifically, the present invention is directed toward an apparatus and method for calibrating cameras for an IC device testing handler.
Semiconductor devices are commonly tested using specialized processing equipment. The processing equipment may be used to identify defective devices and other characteristics related to the performance of such devices. Processing equipment for device testing includes pick and place machines. Pick and place machines commonly implement vision systems with cameras to automatically view, orient, transport and recognize semiconductor devices. The accuracy and efficiency of these visions systems is driven by the ability of the vision system to correctly align and place devices. Accordingly, because of the small scale of semiconductor devices, vision systems with an extremely high degree of accuracy are needed for efficient and accurate testing.
In some instances, multiple cameras are used to send information to the vision system to accurately identify, pick up, and align a semiconductor device. The cameras are calibrated by viewing each other or focusing on the same object at the same time. However, these calibration techniques are lengthy and cumbersome.
Accordingly, there is a need for a system to that efficiently establishes a single coordinate system for multiple cameras. Further, such a camera coordinate calibration system should easily integrate into existing IC device testing handlers.
According to one embodiment, a camera coordinate calibration system is provided. The system includes a calibration contactor having at least two fiducials, and a double sided visible calibration target having a first side and a second side opposing the first side. The system further includes a pick and place handler comprised of a device holder having at least two fiducials, such that the device holder is configured to pickup the double sided visible calibration target and place the double sided visible calibration target onto the calibration contactor by a locking change between the device holder and the calibration contactor. A device view camera is provided to image the first side of the double sided visible calibration target inserted into the device holder, and a contactor view camera is provided to image the second side of the double sided visible calibration target inserted into the calibration contactor. A processor calculates a common coordinate system for the device view camera and the contactor view camera based on the images of the first and second sides of the double sided visible calibration target.
According to another embodiment, a double sided visible calibration target configured to be picked up by a pick and place handler is provided. The double sided visible calibration target is comprised of a transparent material and is configured to deflect along an axis perpendicular to a calibration contactor during a locking change between the device holder and the calibration contactor.
According to yet another embodiment, a method of defining common coordinates for a multiple camera system having a calibration contactor having at least two fiducials, and a device holder having at least two fiducials is provided. The method includes the steps of picking up a double sided visible calibration target comprised of a transparent material with the device holder, imaging a first side of the double sided visible calibration target inserted into the device holder, and placing the double sided visible calibration target onto the calibration contactor by a locking change between the device holder and the calibration contactor. The method also includes the steps of imaging a second side of the double sided visible calibration target inserted into the calibration contactor, and calculating a common coordinate system based on the images of the first and second sides of the double sided visible calibration target.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention as claimed. These and other features, aspects and advantages of the present invention will become apparent from the following description, appended claims, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.
Embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the following description is intended to describe exemplary embodiments of the invention, and not to limit the invention.
Applicant notes that additional pick and place handler alignment systems and methods are discussed in U.S. patent application Ser. No. 12/153,780, now U.S. Pat. No. 7,506,451, U.S. patent application Ser. No. 12/153,779, and U.S. patent application Ser. No. 12/219,106, which are incorporated herein by reference in their entirety for the pick and place handler alignment systems and methods disclosed therein.
The testing station 112 is designed to test a placed target for defects and other characteristics related to the performance of such devices. In this example, the testing station 112 has a calibration contactor 107. A guiding mechanism may be provided with the calibration contactor 107, such as guiding plate 113 to which actuators 108 are attached to allow for movement of the guiding plate 113. The calibration contactor 107 is used by the camera coordinate calibration system 111 to provide the common coordinate system. In order to provide the common coordinate system, a double sided visible calibration target 202, described below in reference to
The device view camera 103 is designed to image a first side of the double sided visible calibration target 202 when the double sided visible calibration target is picked up by the pick and place handler 101 and the device holder 102. Correspondingly, the contactor view camera 106 is designed to image a second side of the double sided visible calibration target 202 once the double sided visible calibration target 202 is placed onto the calibration contactor 107. In order to allow the system to generate images with good contrast, a lighting system may be provided. In the illustrated embodiment of
In some embodiments, a guiding mechanism such as guiding plate 113 is provided for the calibration contactor 107. In such an embodiment, the calibration contactor 107 is stationary. Actuators 108 are attached to the guiding plate 113 which allow the guiding plate 113 to be moved in the x and y directions relative to the calibration contactor 107. In some embodiments, the actuators 108 are moved into a nominal position such that when the device holder 102 is plunged while holding the double sided visible calibration target 202, the device holder's 102 position relative to the calibration contactor 107 is not changed in the x and y directions. In other embodiments, the actuators 108 may be moved to move the guiding plate 113 such that when the device holder 102 is plunged while holding the target 202, the device holder 102 contacts the guiding plate 113 and is moved in the x or y directions or both relative to the calibration contactor 107 to facilitate more accurate center placement of the target 202 onto the calibration contactor 107 following the locking change between the device holder 102 and the calibration contactor 107.
Accordingly, the position of the guiding plate 113 may be iteratively adjusted through movement of the actuators 108 to improve the accuracy of the calculated common coordinate system through increased center placement accuracy at the calibration contactor 107. Iterative adjustment of the guiding plate 113 may be necessary if the target 202 is placed into the calibration contactor 107 with insufficient center alignment. Insufficient center alignment of the target 202 is determined by analyzing the image taken by the contactor view camera 106 by the processor 110 to determine the double sided visible calibration target's 202 position within the calibration contactor 107 relative to the fiducials 301.
Iterative adjustment of the actuators 108 and the guiding plate 113 begins by first analyzing the image taken by the contactor view camera 106 by the processor 110 to determine the double sided visible calibration target's 202 position within the calibration contactor 107 relative to the fiducials 301. If the target 202 is acceptably aligned within the calibration contactor 107, no adjustment of the actuators 108 is necessary. If the target 202 is not acceptably aligned with the calibration contactor 107, the processor 110 calculates movement adjustments to be made to the actuators 108 such that the guiding plate 113 is moved. Before the actuators 108 are moved, the pick and place handler 101 picks the target 202 back up into the device holder 102. Then, the actuators 108 are moved to move the guiding plate 113 as specified by the processor 110 calculation. The pick and place handler 101 then moves back into the device placement position and the device holder 102 contacts and moves in the x or y direction or both relative to the calibration contactor 107 based on where the guiding plate 113 was moved during movement of the actuators 108, and the double sided visible calibration target 202 is placed onto the calibration contactor 107 by a locking change. The pick and place handler 101 then moves away from the device placement position. The contactor view camera 106 once again images the double sided visible calibration contactor 202 as placed in the calibration contactor 107. The newly taken image is transmitted to the processor 110 which then analyzes the image to determine the double sided visible calibration target's 202 position within the calibration contactor 107 relative to the fiducials 301.
Here again, if the target 202 is acceptably aligned within the calibration contactor 107, no additional movement of the actuators 108 is necessary, as the device holder 102 is contacting the guiding plate 113 and moving in the x or y or both directions relative to the calibration contactor 107 sufficiently to place the target 202 with acceptable center alignment onto the calibration contractor 107. If the target 202 is not acceptably aligned, additional actuator 108 movement is calculated and the process is repeated until an acceptable alignment of the double sided visible calibration target 202 as placed onto the calibration contactor 107 is achieved. If the actuators 108 are iteratively adjusted to correct insufficient alignment of the target 202 within the calibration contactor 107, any intermediate images taken by the contactor view camera 106 of the target 202 as placed onto the calibration contactor 107 are not used in the calculation of the common coordinate system between the device 103 and contactor view 106 cameras. Rather, only the final image take by the contactor view camera 106 of the target 202 as acceptably inserted into the calibration contactor 107 is used for the calculation of the common coordinate system between the device 103 and contactor view 106 cameras.
The device holder 102 and the calibration contactor 107 may be designed to pick up and place the double sided visible calibration target 202 with more accuracy. In some embodiments, the device holder 102 has a device vacuum mechanism which applies a vacuum against the double sided visible calibration target 202 during pickup of the double sided visible calibration target 202. By applying a vacuum during pickup, the double sided visible calibration target 202 remains in approximately the same alignment within the device holder 102 during the period the double sided visible target 202 is inserted into the device holder 102. In such an embodiment, the device vacuum mechanism of the device holder 102 is configured to release the vacuum applied to the double sided visible calibration target 202 during the locking change of the double sided visible calibration target 202 with the calibration contactor 107. Additionally, in some embodiments, the calibration contactor 107 also has a contactor vacuum mechanism which applies a vacuum against the double sided visible calibration target 202 during the locking change of the double sided visible calibration target 202 with the device holder 102. The application of a vacuum by the calibration contactor 107 prevents the double sided visible calibration target 202 from shifting in the x or y plane during the locking change of the target 202 between the device holder 102 and the calibration contactor 107. The locking change between the device holder 102 and the calibration contactor 107 would occur after any adjustment of the device holder 102 relative to the calibration contactor 107 by, for example, a guiding mechanism such as guiding plate 113 as shown in
Referring now to
Referring now to the device view 103 and contactor view 106 cameras, the device view camera 103 and the contactor view camera 106 may be any one of a number of different types of digital cameras. Accordingly, either of the device view camera 103 or the contactor view camera 106 may generate a variety of different digital images. Additionally, the device view camera 103 and the contactor view camera 106 need not be the same type of camera. In some embodiments, either of the cameras may be a digital camera, which generates black and white images. In other embodiments, either of the cameras may be a digital camera which generates color images. Further, either of the cameras may be configured to generate images of varying color depth as well as varying resolution.
Further, in some embodiments, the camera coordinate calibration system 111 has a lighting system. The lighting system provides light so that the device view 103 and contactor view 106 cameras capture high contrast images. In some embodiments, a single lighting system is provided. In other embodiments, the device view camera 103 has an attached device lighting system 105. In yet other embodiments, the contactor view camera 106 has an attached contactor lighting system 109. An attached lighting system may create light angles in the range of 0 to 90 degrees incident to the object being imaged. An attached lighting system may be a three-channel programmable LED. Further, an attached lighting system can adjust the intensity of light.
Referring now to the processor 110 of the system, the processor 110 is configured to calculate a common coordinate system for the device view camera 103 and the contactor view camera 106. The processor 110 receives an image of the first side of the double sided visible calibration target 202 from the device view camera 103, and an image of the second side of the double sided visible calibration target 202 from the contactor view camera 106. With respect to the image of the first side of the double sided visible calibration target 202 supplied by the device view camera 103, the processor 110 is configured to segregate the two fiducials 201 from the double sided visible calibration target 202. Accordingly, the processor 110 is configured to determine the orientation of the double sided visible calibration target 202 relative to the fiducials 201 in the supplied image. Similarly, with respect to the image of the second side of the double sided visible calibration target 202 supplied by the contactor view camera 106, the processor 110 is configured to segregate the four fiducials 301 from the double sided visible calibration target 202. Accordingly, the processor 110 is configured to determine the orientation of the double sided visible calibration target 202 relative to the fiducials 301 in the supplied image.
Recall, from the previous discussion of
In some embodiments, a device holder 102 may be larger than the field of view of the device view camera 103. In such an embodiment, a double sided visible calibration target 202 for which an entire image can be stitched together from multiple images is provided.
In other embodiments, a calibration contactor 107 may be larger than the field of view of the contactor view camera 106. In such an embodiment, a double sided visible calibration target 202 for which an entire image can be stitched together from multiple images is provided.
In one embodiment, a processor 110 might include a general purpose computing device in the form of a conventional computer, including a processing unit, a system memory, a system bus that couples various system components including the system memory to the processing unit, and software to perform the calculations necessary to generate the common coordinate system. The system memory may include read only memory (ROM) and random access memory (RAM). The computer may also include a magnetic hard disk drive for reading from and writing to a magnetic hard disk, a magnetic disk drive for reading from or writing to a removable magnetic disk, and an optical disk drive for reading from or writing to removable optical disk such as a CD-ROM or other optical media. The drives and their associated computer-readable media provide nonvolatile storage of computer-executable instructions, data structures, program modules and other data for the computer. In another embodiment, the processor 110 may be implemented with a special purpose computer or embedded device to calculate the common coordinate system. In other embodiments, the processor 110 may be implemented in a plurality of separate computers wherein each of the computers has separate software modules configured to calculate a portion of the common coordinate
Elements of embodiments of the processor 110 within the scope of the present invention include program products comprising computer-readable media for carrying or having computer-executable instructions or data structures stored thereon. Such computer-readable media can be any available media that can be accessed by a general purpose or special purpose computer. By way of example, such computer-readable media can comprise RAM, ROM, EPROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to carry or store desired program code in the form of computer-executable instructions or data structures and which can be accessed by a general purpose or special purpose computer. When information is transferred or provided over a network or another communications connection (either hardwired, wireless, or a combination of hardwired or wireless) to a computer, the computer properly views the connection as a computer-readable medium. Thus, any such connection is properly termed a computer-readable medium. Combinations of the above are also to be included within the scope of computer-readable media. Computer-executable instructions comprise, for example, instructions and data which cause a general purpose computer, special purpose computer, or special purpose processing device to perform a certain function or group of functions.
Elements of the processor 110 may be implemented in one embodiment by a program product including computer-executable instructions, such as program code, executed by computers in networked environments. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps.
Once a common coordinate system for the device view camera 103 and the contactor view camera 106 has been calculated by the processor 110, during testing runtime any offset of a device under test as held in a device holder 102 can be corrected using the actuators 108 as attached to a guiding mechanism such as a guiding plate 113 as shown in
The present system provides a user friendly solution to the problem of establishing a common coordinate system among separately located cameras. Vision systems of integrated circuit testing handlers are typically comprised of multiple cameras. In many situations, these cameras cannot view one another. In those instances where the cameras cannot view one another, a common coordinate system must be substituted such that the cameras can operate together in a single known space to identify, pick up, and align semiconductor devices. The present system provides a solution to the problem of establishing a common coordinate system through the use of fiducials on a device holder and a calibration contactor, in combination with a processor and a double sided visible calibration target.
The foregoing description of embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principals of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.
