Wafer transfer system

• US 4,836,733 A
• Filed: 12/21/1987
• Issued: 06/06/1989
• Est. Priority Date: 04/28/1986
• Status: Expired due to Term

• Current Assignee: Varian Semiconductor Equipment Associates Incorporated (Applied Materials Incorporated)
• Original Assignee: Varian Associates, Inc. (Siemens AG)
• Inventors: Jennings, Robert E., MacIntosh, Edward D., Bhargava, Akhil, Delforge, Adrian C., Hertel, Richard J., Mears, Eric L.
• Primary Examiner(s): Spar, Robert J.
• Assistant Examiner(s): Underwood, Donald W.
• Application Number:
  US07/135,568
• Time in Patent Office: 533 Days
• Field of Search: 414/222, 414/225, 414/217, 414/331, 414/416, 414/417, 414/786, 29/703, 29/705, 29/712, 29/714, 29/720, 198/341, 198/464.1, 198/464.2, 294/102
• US Class Current: 414/744.5
• CPC Class Codes: H01L 21/67259 Position monitoring, e.g. misposition detection or presence detection
• CPC Class Codes: H01L 21/67766 Mechanical parts of transfer devices robots in general in B25J
• CPC Class Codes: H01L 21/681 using optical controlling means
• CPC Class Codes: Y10S 414/136 including wafer orienting means
• CPC Class Codes: Y10S 414/137 including means for charging or discharging wafer cassette
• CPC Class Codes: Y10S 414/139 including wafer charging or discharging means for vacuum chamber
• CPC Class Codes: Y10T 29/53087 with signal, scale, illuminator, or optical viewer

Abstract

Wafer transfer apparatus for horizontal transfer of a wafer between a cassette and an input station of a vacuum processing system includes a wafer transfer arm with a primary section linked to a secondary section so as to move a wafer in a straight line to a location and orientation station and then to the input station. The actual location of the wafer center and the angular orientation of the wafer flat are determined, and the wafer is rotated to a desired angular orientation at the location and orientation station. A solar cell is used to sense actual wafer position by sensing the wafer edge as it is rotated. The required correction and rotation are calculated from the solar cell output. As the wafer is transferred to the input station, correcting displacements are added to the movement so that the wafer is accurately positioned at the input station. A strain gauge is used to reliably sense wafer presence or absence on the transfer arm.

Claims

1. Apparatus for transferring a wafer from a cassette holder to an input station of a processing system, comprising:

a single wafer transfer arm for removing a waver from the cassette holder and for transferring the waver between the cassette holder and the input station, said waver transfer arm including elongated primary and secondary section coupled together for rotation about a pivot axis, said primary section having a primary axis of rotation spaced apart from and parallel to said pivot axis, said secondary section having a wafer support pick at the opposite end from said pivot axis, said transfer arm further including linkage means for causing said secondary section to rotate about the pivot axis at a predetermined rate greater than said primary section rotates about the primary axis;

an intermediate station for sensing undesired displacement of said wafer relative to said wafer pick;

means for holding the cassette holder and for indexing said wafer into engagement with said wafer pick; and

means for extending and retracting said waver transfer arm to and between the cassette holder, the intermediate station and the input station, including means for causing said wafer transfer arm to transfer said waver from said cassette holder to said intermediate station for sensing undesired displacement of said wafer relative to said wafer pick and means for causing said waver transfer arm to place said wafer in said input station in a corrected position which compensates for said undesired displacement by a correction factor equal in magnitude and opposite in direction to said undesired displacement, said correction factor being introduced as said wafer is moved by said wafer transfer arm from said intermediate station to said input station.

2. Wafer transfer apparatus as defined in claim 1 further including means for moving said wafer transfer arm and said means for extending and retracting said wafer transfer arm, for access to a plurality of cassette holders.

3. Wafer transfer apparatus as defined in claim 2 wherein the distance between said primary axis and said pivot axis is equal to the distance between said pivot axis and a nominal wafer center of said wafer pick, and wherein said linkage means causes said secondary section to rotate about said pivot axis at twice the rate at which said primary section rotates about said primary axis, whereby said wafer transfer arm moves a wafer in a straight line.

4. Wafer transfer apparatus as defined in claim 3 wherein said linkage means includes a primary pulley in a fixed position on the primary axis, a secondary pulley coupled to the secondary section on the pivot axis and a belt drive coupled between the primary pulley and the secondary pulley.

5. Wafer transfer apparatus as defined in claim 1 wherein said intermediate station includes means for rotating said wafer and noncontact means for sensing the edge position of said wafer during rotation and means for converting edge information to a displacement relative to a reference point.

6. Wafer transfer apparatus as defined in claim 1 wherein said means for causing said wafer transfer arm to place the wafer in a corrected position includes means for correcting the travel of said wafer transfer arm and means for translating said wafer transfer arm laterally so as to obtain said correction factor.

7. Wafer transfer apparatus as defined in claim 1 wherein said intermediate station is located on said primary axis and further including orientation sensing means on said primary axis comprising an orientation chuck, means for lifting said chuck above said wafer pick, means for rotating said orientation chuck and said wafer, and means for sensing the edge position of said wafer as the wafer is rotated.

8. Wafer transfer apparatus as defined in claim 7 wherein said orientation chuck is lifted on said primary axis through a hole through said wafer pick.

9. Apparatus for transferring a wafer to an input station comprising:

a wafer location station at a predetermined distance from said input station, including means for determining an actual wafer center location in x and y directions relative to a desired wafer center location at a point x_o, y_o and determining a correction based on the difference between the actual wafer center location and the desired wafer center location; and

means for transferring said wafer from said wafer location station to said input station, said transfer means including means for translating said wafer by said correction as it is transferred from said wafer is positioned at the desired location at said input station.

10. Wafer transfer apparatus as defined in claim 9 wherein said transfer means includes a robot-like transfer arm having a wafer pick movable between said wafer location station and said input station.

11. Wafer transfer apparatus as defined in claim 10 wherein said wafer location sensing means includes means for rotating said wafer and means for sensing the wafer edge position as said wafer is rotated.

12. Wafer transfer apparatus as defined in claim 11 wherein said wafer edge sensing means includes a light source and a light sensor positioned on opposite sides of said wafer edge.

13. Wafer transfer apparatus as defined in claim 10 wherein the correction in one of said x and y directions is obtained by varying the extension of said wafer transfer arm from the normal extension thereof.

14. Wafer transfer apparatus as defined in claim 13 wherein said transfer means further includes means for translating said wafer transfer arm laterally with respect to the axis between said wafer location station and said input station and the correction in the other of said x and y directions is obtained by lateral translation of said wafer transfer arm.

15. Wafer transfer apparatus as defined in claim 9 wherein said wafer location station further includes means for sensing the angular orientation of said wafer and correcting said angular orientation to a desired orientation.

16. Wafer transfer apparatus as defined in claim 15 wherein said means for correcting said angular orientation includes means for rotating said wafer at said wafer location station.

17. Wafer transfer apparatus as defined in claim 9 wherein said transfer means includes a wafer transfer arm for transferring a wafer between the wafer location station and the input station, said wafer transfer arm including elongated primary and secondary sections coupled together for rotation about a pivot axis, said primary section having a primary axis of rotation spaced apart and parallel to said pivot axis, said secondary section having a wafer support pick at the opposite end from said pivot axis, said transfer arm further including linkage means for causing said secondary section to rotate about the pivot axis at a predetermined rate greater than said primary section rotates about the primary axis.

18. Wafer transfer apparatus as defined in claim 17 wherein said wafer location sensing means is located on said primary axis and comprises an orientation chuck, means for lifting said chuck above said wafer pick and means for rotating said orientation chuck and said wafer and means for sensing the position of the wafer edge as the wafer is rotated.

19. Apparatus for transferring a semiconductor wafer form a cassette holder to an input station of a processing system comprising;

a wafer location station intermediate said cassette holder and said input station at a predetermined distance from said input station including means for sensing an actual wafer location relative to a desired wafer location and for determining a correction based on the difference between the actual wafer location and the desired wafer location; and

means for transferring said wafer from said cassette holder to said wafer location station for wafer location sensing and for transferring said wafer from said wafer location station to said input station, said transfer means including means for translating said wafer by said correction as it is transferring from said wafer location station to said input station so that said wafer is positioned at the desired location at said input station.

20. Wafer transfer apparatus as defined in claim 19 wherein said transfer means includes a robot-like transfer arm having a wafer pick movable between said wafer location station and said input station.

21. Wafer transfer apparatus as defined in claim 20 wherein said wafer location sensing means includes means for rotating said wafer and means for sensing the wafer edge position as said wafer is rotated.

22. Wafer transfer apparatus as defined in claim 21 wherein said wafer edge sensing means includes a light source and a light sensor positioned on opposite sides of said wafer edge.

23. Wafer transfer apparatus as defined in claim 20 wherein the correction in one direction is obtained by varying the extension of said wafer transfer arm from the normal extension thereof.

24. Wafer transfer apparatus as defined in claim 23 wherein said transfer means further includes means for translating said wafer transfer arm laterally with respect to the axis between said wafer location station and said input station and the correction normal to the direction of arm extension is obtained by lateral translation of said wafer transfer arm.

25. Wafer transfer apparatus as defined in claim 19 wherein said wafer location station further includes means for sensing the angular orientation of said wafer and correcting said angular orientation to a desired orientation.

26. Wafer transfer apparatus as defined in claim 25 wherein said means for correcting said angular orientation includes means for rotating said wafer at said wafer location station.

27. Wafer transfer apparatus as defined in claim 19 wherein said transfer means includes a wafer transfer arm for transferring a wafer between the wafer location station and the input station, said wafer transfer arm including elongated primary and secondary sections coupled together for rotation about a pivot axis, said primary section having a primary axis of rotation spaced apart and parallel to said pivot axis, said secondary section having a wafer support pick at the opposite end from said pivot axis, said transfer arm further including linkage means for causing said secondary section to rotate about the pivot axis at a predetermined rate greater than said primary section rotates about the primary axis.

28. Wafer transfer apparatus as defined in claim 27 wherein said wafer location sensing means is located on said primary axis and comprises an orientation chuck, means for lifting said chuck above said wafer pick and means for rotating said orientation chuck and said wafer and means for sensing the position of the wafer edge as the wafer is rotated.

29. Wafer transfer apparatus as defined in claim 28 wherein said input station is an end station disk of an ion implantation system.

30. Wafer transfer apparatus as defined in claim 28 wherein said cassette holder, said wafer location station and said transfer means are located in an evacuated chamber communicating with a vacuum treatment chamber for said wafer.

31. Apparatus for transferring a wafer from a cassette holder to an input station of a processing system, comprising:

a single wafer transfer arm for removing a wafer form the cassette holder and for transferring the wafer between the cassette holder and the input station, said wafer transfer arm including elongated primary and secondary sections coupled together for rotation about a pivot axis, said primary section having a primary axis of rotation spaced apart form and parallel to said pivot axis, said secondary section having a wafer support pick at the opposite end from said pivot axis, said transfer arm further including linkage means for a causing said secondary section to rotate about the pivot axis at a predetermined rate greater than said primary section rotates about the primary axis;

means for holding the cassette holder and for indexing said wafer into engagement with said wafer pick, said cassette holder being held in a vaccuum lock and said holding means including a sealed bellows mounted to expand when the vacuum lock is evacuated and to hold said cassette holder firmly in place; and

means for extending and retracting said wafer transfer arm to and between the cassette holder and the input station.

32. A method for transferring a semiconductor wafer from a cassette holder to an input station of a processing system comprising the steps of:

transferring the wafer from the cassette holder to a wafer location station;

sensing an actual wafer location relative to a desired wafer location;

determining a correction based on the difference between the actual wafer location and the desired wafer location;

transferring said wafer from said wafer location station to said input station; and

translating said wafer during the step of transferring the wafer to the input station by said correction so that said wafer is positioned at the desired location at said input station.

33. A method for transferring a semiconductor wafer as defined in claim 32 wherein the step of sensing the actual wafer location includes the steps of rotating the wafer about the desired wafer location and sensing the position of the wafer edge during the step of rotation.

34. A method for transferring a semiconductor wafer as defined in claim 33 further including the step of sensing the angular orientation of said wafer by determining the location of a wafer flat and rotating the wafer to a desired angular orientation at said wafer location station.

35. A method for transferring a semiconductor wafer as defined in claim 34 wherein the step of determining the correction includes the steps of

determining the actual angular orientation of the wafer flat by convolving the wafer edge data and identifying zero crossings in the convolved data, and

determining the position of the actual wafer center relative to the center of rotation by calculating the difference mean between wafer edge data 180 degrees apart for at least two sets of points not in the wafer flat.

36. A method for transferring a semiconductor wafer as defined in claim 35 further including the step of rotating the wafer from the actual angular orientation to a desired angular orientation at said wafer location station.

37. A method for transferring a semiconductor wafer as defined in claim 36 wherein the step of rotating the wafer to a desired angular orietantion includes the step of compensating for rotation occurring during the step of transferring the wafer to said input station so that the wafer is accurately placed at the input station.

38. Apparatus for transferring a wafer from a cassette holder to an input station of a vacuum processing system, comprising:

means for transferring the wafer to and between the cassette holder and the input station;

a vacuum lock containing said cassette holder; and

means for holding the cassette holder and for indexing said wafer into engagement with said transfer means, said holding means including a sealed bellows mounted to expand when the vacuum lock is evacuated and to retain said cassette holder firmly in place in said vacuum lock.