Wafer center finding with a kalman filter

{
  "publication_number": "US2010324732A1",
  "country": "US",
  "kind": "A1",
  "title": "Wafer center finding with a kalman filter",
  "abstract": "A device is provided having a robotic arm for handling a wafer, the robotic arm including one or more encoders that provide encoder data identifying a position of one or more components of the robotic arm. The device also having a processor adapted to apply an extended Kalman Filter to the encoder data to estimate a position of the wafer.",
  "claims": [
    "1. A device comprising: a robotic arm for handling a wafer, the robotic arm including one or more encoders that provide encoder data identifying a position of one or more components of the robotic arm; and a processor adapted to apply an extended Kalman Filter to the encoder data to estimate a position of the wafer. 2. The device of claim 1 wherein the position includes a wafer center. 3. The device of claim 1 wherein the position includes a wafer radius. 4. The device of claim 1 wherein the position is determined with reference to an end effector of the robotic arm. 5. The device of claim 1 wherein the position is determined with reference to a center axis of the robotic arm. 6. The device of claim 1 wherein the processor recalculates the position each time new encoder data is received. 7. The device of claim 6 wherein new encoder data is received at substantially 2 kHz. 8. A method comprising: disposing a plurality of sensors within an interior of a wafer handling device, each one of the plurality of sensors capable of detecting a transition between presence and absence of a wafer at a predetermined location within the interior; handling a wafer with a robotic arm, the robotic arm including one or more encoders that provide encoder data identifying a position of one or more components of the robotic arm; and applying the encoder data to an extended Kalman Filter to provide an estimated position of the wafer. 9. The method of claim 8 wherein applying the encoder data includes calculating a wafer position every 0.5 milliseconds. 10. The method of claim 8 wherein the estimated position of the wafer includes a center of the wafer. 11. The method of claim 8 wherein the estimated position of the wafer includes a radius of the wafer. 12. The method of claim 8 wherein the estimated position of the wafer is determined with reference to an end effector of the robotic arm. 13. The method of claim 8 wherein the estimated position is determined with reference to a center axis of the robotic arm. 14. The method of claim 8 wherein the plurality of sensors includes four sensors. 15. The method of claim 8 wherein applying encoder data includes recalculating the estimated position each time encoder data is received. 16. The method of claim 8 wherein handling a wafer includes moving the wafer between two openings to the wafer handling device. 17. The method of claim 8 wherein handling a wafer includes moving the wafer between a load lock and a process module. 18. The method of claim 8 wherein handling a wafer includes moving the wafer between a first process module and a second process module. 19. A device comprising: a robotic arm for handling a wafer, the robotic arm including one or more encoders that provide encoder data identifying a position of one or more components of the robotic arm; and a processor adapted to apply an extended Kalman Filter to the encoder data to estimate a position of the wafer, wherein the processor is adapted to update one or more equations of the Kalman Filter using transition data from one or more sensors that detect the presence of a wafer at one or more predetermined locations within a robotic wafer handler. 20. A method comprising: disposing a plurality of sensors within an interior of a wafer handling device, each one of the plurality of sensors capable of detecting a transition between presence and absence of a wafer at a predetermined location within the interior; handling a wafer with a robotic arm, the robotic arm including one or more encoders that provide encoder data identifying a position of one or more components of the robotic arm; applying the encoder data to an extended Kalman Filter to provide an estimated position of the wafer; detecting a transition at one of the plurality of sensor to provide an actual position of the wafer; determining an error between the actual position and the estimated position; and updating one or more variables for the extended Kalman Filter based upon the error."
  ],
  "description_excerpt": "In semiconductor manufacturing, wafers and other substrates are transferred among various process chambers using robotic handlers. One of the enduring challenges of wafer handling is the need to locate wafers or wafer centers with sufficient precision to permit accurate placement and processing within the process chambers. In general, semiconductor manufacturing systems employ various beam-breaking sensor arrangements to “stripe” passing wafers and detect the wafer edges. This data can be used, in turn to locate a wafer center relative to a robotic handler so that subsequent movement and placement can be more accurately controlled. Center finding is sufficiently important to fabrication that this process is routinely calibrated and repeated throughout the processing of each wafer. While numerous physical sensors and processing algorithms have been devised for centering wafers in a semiconductor manufacturing process, there remains a need for improved wafer center finding techniques that reduce the number of sensors required or improve the simplicity and/or accuracy of center finding calculations.\n\nA number of wafer center finding methods and systems are disclosed herein that improve upon existing techniques used in semiconductor manufacturing.",
  "cpc": [
    "H10P 72/0608",
    "B65G 25/02",
    "B65G 37/00",
    "H10P 72/0452",
    "H10P 72/0464",
    "H10P 72/3302",
    "H10P 72/3304",
    "H10P 72/3306",
    "H10P 72/7626",
    "Y10S 414/129",
    "Y10S 414/136"
  ],
  "ipc": [
    "G06F 19/00",
    "H01L 21/68",
    "H04N 23/40"
  ],
  "assignees": [
    "BROOKS AUTOMATION INC"
  ],
  "inventors": [
    "KILEY CHRISTOPHER C",
    "MEULEN PETER VAN DER",
    "BUZAN FORREST T",
    "FOGEL PAUL E"
  ],
  "filing_date": "2010-09-03",
  "publication_date": "2010-12-23",
  "priority_date": "2003-11-10",
  "application_number": "US-87546210-A",
  "family_id": "39527450",
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}