Abstract:
Methods and apparatus for use in analyzing probe cards are provided. For some embodiments, chucks with particular materials selected to achieve desired properties, such as improved conductivity, robust viewing windows, and the like, are provided. For other embodiments, useful features, such as force measurements for probe pins may be provided. For still other embodiments, improved flipping tables or features thereof may be provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims benefit of U.S. Provisional Patent Application Ser. Nos. 60/746,117 filed May 1, 2006 and 60/889,125 filed Feb. 9, 2007, both of which are herein incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     Embodiments of the present invention generally relate to integrated circuit testing, and more particularly, to a method and apparatus for testing probe cards used to test integrated circuits on a wafer.  
         [0004]     2. Description of the Related Art  
         [0005]     Probe card test and verification systems are commonly used as production tools for the characterization of probe cards (used in testing integrated circuit devices/substrates) before and after use and to facilitate rework of probe cards which do not conform to predefined standards. Such systems typically consist of a computer, a precision measurement system, a software based vision system, and precision motion control and measurement system. Such equipped systems allow for the measurement and adjustment of probe card planarization, visual X/Y location and adjustment, Probe contact resistance, leakage and component measurements.  
         [0006]     Electrical parameters including contact resistance and leakage may also measured against reference values and an indication may be provides as to whether a probe card assembly under test has passed or failed. If a failure is determined, a full report may be printed to accompany the card for rework. Quick verification provided by such systems may validate that a probe card assembly is ready for test or is in need of rework.  
         [0007]     There is a continuing need to improve such systems, for example, by adding new features, increasing performance and robustness.  
       SUMMARY OF THE INVENTION  
       [0008]     Embodiments of the present invention provide methods and apparatus for use in analyzing probe cards.  
         [0009]     For some embodiments, chucks with particular materials selected to achieve desired properties, such as improved conductivity, robust viewing windows, and the like, are provided.  
         [0010]     For some embodiments, useful features, such as force measurements for probe pins may be provided.  
         [0011]     For some embodiments, improved flipping tables or features thereof may be provided. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0013]      FIG. 1  is a picture of a portion of a probe card analyzer, zoomed in to show the chuck and the camera window, according to embodiments of the invention;  
         [0014]     FIGS.  1 A-B are pictures of the chuck illustrating areas uncoated and coated with a conductive ceramic material, according to embodiments of the invention;  
         [0015]      FIG. 2A  is a computer-aided design model of a portion of a probe card analyzer, detailing the chuck, the optical window, and the probe friction force measurement system, according to embodiments of the invention;  
         [0016]      FIG. 2B  is a computer-aided design model of the probe friction force measurement system showing two separated sections, according to embodiments of the invention;  
         [0017]      FIG. 2C  is a computer-aided design model of the probe friction force measurement system, zoomed into to show the pin insert and the two force sensors, according to embodiments of the invention;  
         [0018]     FIGS.  3 A-B are pictures of a portion of a probe card analyzer, zoomed in to show a block containing the light source with and without the chuck disposed above the light source, according to embodiments of the invention;  
         [0019]      FIG. 4  is a mechanical schematic of the components of the flipping table, according to one embodiment of the invention;  
         [0020]      FIG. 5  is a mechanical schematic with dimensions of one carbon fiber sheet composing the flipping table sandwich, according to one embodiment of the invention;  
         [0021]     FIGS.  6 A-D are computer-aided design models of the flipping table and automatic balancing counter weight in a 180° rotation sequence, according to embodiments of the invention;  
         [0022]      FIG. 7  is a prior art image of a camera window comprising sapphire, portraying scratches in the window;  
         [0023]     FIGS.  8 A-D are design drawings of a probe repair tool, according to embodiments of the invention; and  
         [0024]     FIGS.  9 A-C are pictures of a z stage and a line scanner mounted on an x stage of a probe card analyzer, according to embodiments of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0025]     Embodiments of the invention provide for a probe card analyzer used for testing integrated circuit probe cards.  
       An Exemplary Probe Card Analyzer Chuck  
       [0026]      FIG. 1  is a picture of a portion of a probe card analyzer, zoomed in to show a chuck  10 , which may hold the probe card under test (not shown). For some embodiments, the chuck  10  may comprise a special conductive ceramic coating, such as TiN. Being a hardened material, this ceramic coating may provide extended life for the chuck  10 . For some embodiments, the grain size of the ceramic coating can be manufactured to be 1 micron, thereby achieving a roughness to replicate real silicon wafer bonding pads. The base of the chuck  10  may comprise nickel, and the ceramic coating may be sputtered on. The upper surface of the chuck  10  may have a polished area for testing other aspects of the probe card. Different sizes of the chuck  10  may be available for testing different sized wafers, and some versions of the chuck  10  may allow for verifying probe cards at extended temperatures, such as 125° C.  
         [0027]     A transparent camera window  15  may be used to view the probe pins. Images of probe pin locations at first (e.g., zero force) and second (predefined pressure to simulate actual use in testing) contact forces may be captured to determine “scrub marks” indicating where a probe pin will contact a device during test. Such scrub marks may be analyzed to determine of adjustment or rework is necessary to ensure the corresponding probe pins will contact a desired pad during testing.  
         [0028]     As illustrated in  FIG. 1A , for some embodiments, the chuck  10  may comprise a section  19  with a conductive ceramic material coated thereon (e.g., sputtered on), while portions  17  may be left uncoated. For some embodiments, the uncoated portions  17  may include the transparent camera window  15  as depicted in  FIG. 1A . A larger chuck is shown in  FIG. 1B , where corner portions  17  may be left uncoated. For some embodiments, the base of the chuck may be ceramic that is specially treated to allow for sputtering. The uncoated areas may accommodate mounting of the window for the camera function to take the air and scrub images used in the probe card analysis. The larger chuck may accommodate multiple cameras (e.g., four) and may have a larger number of isolated dots (e.g., sixteen).  
         [0029]     Multiple isolated dots that are sufficiently close to each other may allow for rapid identification of probe pin electrical characterization. For example, the electrical characterization may include which channel and from which coordinate a probe should be referenced to from a reference list. This may reduce an amount of motion stepping conventionally needed for such characterizing and, therefore, speeding tests.  
         [0030]     For some embodiments, air and scrub image(s) may be used for finding the X/Y location concerning the related scrub marks. For example, when a scrub mark direction does not relate to the probe position, it may indicate that there is a malfunction of a probe card and/or motherboard (e.g., the test fixture of the probe card). To detect such instances, the system may be able to measure the difference between the air and scrub position in relation to a predetermined probe angle, for example, loaded from a reference file. This solution may lead to faster testing and also less wearing for the probe card.  
         [0031]     Referring back to  FIG. 1 , for some embodiments, the camera window  15  may be part of the chuck  10 , as illustrated in  FIG. 1 . The camera window  15  may comprise diamond or diamond-like carbon because of their scratch-resistant properties in an effort to secure a long life. In fact, a camera window comprising either of these two materials may never need to be replaced, thereby avoiding maintenance costs. Diamond and diamond-like carbon may also provide a clearer view over conventional camera windows comprising sapphire.  
       An Exemplary Probe Friction Force Sensor  
       [0032]     For some embodiments, a probe friction force measurement system  20  may be attached to the chuck  10 , as shown in the computer-aided design model of  FIG. 2   a.  The probe friction force measurement system  20  may be used to measure the resistance a probe pin experiences when pushed into a planar surface to make a scrub mark. This measurement may be used to measure the life expectancy of an individual probe or the entire probe card as the forces tend to get weaker with age. The details of this system  20  may be seen more clearly in  FIGS. 2   b  and  2   c,  which show a pin insert  22  and two force sensors  24  placed perpendicularly to measure the force in two different axes, according to some embodiments. Because the pin insert  22  can be replaced with inserts comprising any suitable material, the probe friction force measurement system  20  may be used to measure the differences between sliding over materials used in the camera window, such as glass, sapphire, diamond, and diamond-like carbon, and materials used on the actual semiconductor wafer bonding pads, such as aluminum. With these different measurements, the system  20  may be used to measure the resistance force on real aluminum pads and subsequently set the corresponding test limits for measurements on the camera window  15  of the probe card analyzer.  
       An Exemplary Light Source  
       [0033]     To view the probe card pins through the camera window  15  of the probe card analyzer, a constant light source with high contrast may be used.  FIG. 3A  illustrates a portion of a probe card analyzer, zoomed in to show a block  31  containing a light source  30  disposed therein. For some embodiments, the light source  30  may comprise a light source designed to provide high contrast. For example, the light source  30  may comprise a monochromatic blue-green light-emitting diode (LED) possessing a wavelength between 498 nm and 513 nm. This wavelength range may provide a high contrast light for viewing probe card pins. In addition, since this blue-green LED may be very stable, the illuminating wavelength should change little over time. As a result, there should not be a need for frequent recalibration of the probe card analyzer. The light source  30  may also comprise a lens, mirrors  32  and a beam splitter cube  33 . The beam splitter cube  33  may possess a certain wave reflection in an effort to minimize polarization.  FIG. 3B  illustrates the chuck  10  overlying the block  31  and covering the light source  30 , which may illuminate the probe card pins through the window  15 .  
       An Exemplary Flipping Table  
       [0034]     An automatic flipping table  35  may support the probe card while it is being imaged and tested, and then it may rotate 180°, or flip over, in a controlled manner (e.g., using pneumatics upon an operator request) so that the probe pins or other aspects of the probe card may be reworked. After a rework, the flipping table  35  may easily be reverted back to its original position to continue testing without ever having to realign the probe card.  
         [0035]     In an effort to assist in this function, the flipping table  35  may be composed of a lightweight, yet strong and stable material. As such, the flipping table  35  may comprise a sandwich of two carbon fiber sheets  40  interposed by an aluminum frame  45  as shown in the mechanical schematic of  FIG. 4 . An exemplary carbon fiber sheet for some embodiments is shown in  FIG. 5  and may have general dimensions of 732 mm×600 mm×31.4 mm.  
       An Automatic Flipping Table Counterbalance  
       [0036]     In an effort to counterbalance the weight of the flipping table  35  as it rotates (thereby assisting in an even and controlled motion with little interaction from a user), a counter weight  60  may be utilized as shown in  FIG. 6   a.  The counter weight  60  may be automatically adjusted via software to counterbalance the weight of the flipping table  35  and the probe card.  FIGS. 6   a - d  are computer-aided design models of the flipping table  35  and automatic balancing counter weight  60  in a 180° rotation sequence, according to some embodiments.  
       An Exemplary Camera Window  
       [0037]     As described above, the camera window made from a diamond material. This material may provide a more clear view than a standard sapphire window. As shown in  FIG. 7 , sapphire windows may be prone to scratches  72 . In addition, a window made from diamond material may have an increased life time. In some cases, the window may not need to be replaced for the life of the system, thereby reducing maintenance costs. For some embodiments, the diamond material may be a synthetic type A1 material, which would result in one of the hardest windows in the world.  
         [0038]     For some embodiments, a 3-D camera system for fast detection may be utilized. For example, such a system may be configured to measure planarity and alignment in one movement. For non-contact, optical planarization (Z measurement), it may be possible to incorporate multiple cameras. For example, there may be two or more cameras measuring a 3-D view and a shadow (identified by the processor via image analysis) may be valid for the Z position (height) after calibrating the shadow length.  
       An Exemplary Probe Repair Tool  
       [0039]     Once a damage probe is detected by the probe card analyzer, a misaligned or bent probe may be repaired by a probe repair tool  80  as illustrated in  FIG. 8A . The upper portion of the probe repair tool  80  may be shaped like a small, hollow cylinder cut in half along the longitudinal axis. The bottom portion of the probe repair tool  80  may be a solid rod for robustness. Mounted on the z stage of the probe card analyzer for vertical movement, the probe repair tool  80  may also have a small motor (not shown) coupled to it so that the tool  80  can rotate 360° as illustrated in  FIG. 8B .  
         [0040]     Because the probe card analyzer knows the direction of the integrated circuit test card probes after recording the air and scrub images, an individual probe  82  may be determined to have a positional error due to a bent probe tip or misaligned probe that should be adjusted to the ideal position. For some embodiments, the ideal position of the probe  82  may be known by the probe card analyzer from a spreadsheet. If a probe  82  is out of position, the probe repair tool  80  may be moved in the X and Y directions using the motors in the X stage and moved vertically using the z stage motor to the present, incorrect location of the misaligned probe  82 . Upon reaching the probe  82 , the probe repair tool  80  may be rotated such that the receiving position in the upper half of the probe repair tool  80  is facing a desired direction. For instances where the probe  82  should be corrected laterally, the receiving position of the probe repair tool  80  may be rotated to face the corrective lateral direction as illustrated in the side and top views of  FIG. 8C . For instances where the probe  82  should be corrected vertically, the receiving position of the probe repair tool  80  may face the arm of the probe  82  as shown in  FIG. 8D .  
         [0041]     Once the probe repair tool  80  has been positioned under the probe  82  and rotated so that the receiving position is facing the desired direction, the probe repair tool  80  may be moved laterally via the X stage ( FIG. 8C ), vertically via the Z stage ( FIG. 8D ), or both either simultaneously or sequentially in an effort to push the probe  82  or probe tip  84  back into the known ideal position. Afterwards, the camera under the diamond window  15  in the chuck  10  may measure the new position of the probe  82 , and if the analyzer determines that the probe  82  should be adjusted further, the repair process may be repeated using the probe repair tool  80 .  
         [0042]     For some embodiments, the probe repair tool  80  may be used as an individual probe cleaner by employing a relatively abrasive cleaning pad adhering to the inner surface of the hollow half cylinder of the upper portion of the tool  80 .  
       An Exemplary Line Scanner Image Sensor  
       [0043]     Referring now to FIGS.  9 A-C, the probe card analyzer may employ a line scanner image sensor  90  in an effort to quickly image and determine probe positions on high probe count test cards. The image sensor  90  may be mounted on an X stage  92  above a Z stage  94  for vertical movement. Providing images of several probes at one time, the image sensor  90  may comprise a rectangular window composed of glass with a diamond-like carbon (DLC) coating in an effort to prevent scratches on the window. With the Z stage  94 , the image sensor  90  can move up and down to determine the air and scrub image(s) position measurements. The X stage  92  provides for lateral movement of the image sensor  90 , and the combination may allow the images to be taken from left to right, from right to left, from top to bottom, or from bottom to top.