Method and system for marking a workpiece such as a semiconductor wafer and laser marker for use therein

• US 20040144760A1
• Filed: 05/15/2003
• Published: 07/29/2004
• Est. Priority Date: 05/17/2002
• Status: Abandoned Application

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Inventors: Gillespie, John R. Jr., Leslie, Walter J., Pelsue, Kurt, Ehrmann, Jonathan S., Woelki, Michael, Nemets, Chris, Cahill, Steven P., Sullivan, Kevin E., Schramm, Rainer, Li, You C.
• Application Number:
  US10/438,500
• Publication Number:
  US 20040144760A1
• Time in Patent Office: Days
• US Class Current: 219/121.68
• CPC Class Codes: B23K 2101/007 Marks, e.g. trade marks
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/04 Automatically aligning, aiming or focusing the laser beam, e.g. using the back-scattered light
• CPC Class Codes: B23K 26/042 Automatically aligning the laser beam
• CPC Class Codes: B23K 26/043 along the beam path, i.e. alignment of laser beam axis relative to laser beam apparatus
• CPC Class Codes: B23K 26/0853 Devices involving movement of the workpiece in at least in two axial directions, e.g. in a plane
• CPC Class Codes: B23K 26/361 for deburring or mechanical trimming B23K26/351 takes precedence
• CPC Class Codes: B23K 26/40 taking account of the properties of the material involved
• CPC Class Codes: B23K 26/705 Beam measuring device
• CPC Class Codes: G06K 1/126 by photographic or thermographic registration recording apparatus for measuring instruments G01D15/00
• CPC Class Codes: H01C 17/242 by laser trimming by laser in general B23K26/351
• CPC Class Codes: H01L 21/67282 Marking devices
• CPC Class Codes: H01L 21/681 using optical controlling means
• CPC Class Codes: H01L 2223/5442 comprising non digital, non alphanumeric information, e.g. symbols
• CPC Class Codes: H01L 2223/54453 for use prior to dicing
• CPC Class Codes: H01L 2223/54473 for use after dicing
• CPC Class Codes: H01L 2223/5448 Located on chip prior to dicing and remaining on chip after dicing
• CPC Class Codes: H01L 23/544 Marks applied to semiconductor devices or parts, e.g. registration marks, alignment structures, wafer maps test patterns for characterising or monitoring manufacturing processes H01L22/00
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 : Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00

Abstract

A system for semiconductor wafer marking is provided. The system includes: (a) a first positioning subsystem for positioning a laser marking field relative to a wafer, the positioning along a first direction; (b) an alignment vision subsystem; (c) a laser marker including a laser for marking a location within the marking field with a laser marking beam; (d) a calibration program for calibrating at least one subsystem of the system; and (e) a controller. The marking field is substantially smaller than the wafer, and the laser marker includes a scan lens for optically maintaining a spot formed by the beam on the wafer within an acceptable range about the location within the marking field so as to avoid undesirable mark variations associated with wafer sag or other variations in depth within the field.

Claims

1. A system for semiconductor wafer marking comprising:

(a) a first positioning subsystem for positioning a laser marking field relative to a wafer, the positioning being along a first direction;

(b) an alignment vision subsystem;

(c) a laser marker including a laser for marking a location within the marking field with a laser marking beam;

(d) a calibration program for calibrating at least one subsystem of the system; and

(e) a controller, wherein the marking field is substantially smaller than the wafer, and wherein the laser marker comprises means including a scan lens for optically maintaining a spot formed by the beam on the wafer within an acceptable range about the location within the marking field so as to avoid undesirable mark variations associated with wafer sag or other variations in depth within the field.

2. The system of claim 1 wherein spot placement accuracy is within about one spot diameter over the marking field.

3. The system of claim 1 wherein the scan lens is a three element lens.

4. The system of claim 1 wherein the alignment vision subsystem also comprises a substantially telecentric imaging lens.

5. The system of claim 1 wherein the laser marker comprises a moveable optical element for focusing the laser marking beam onto the wafer using computer control.

6. The system of claim 1 wherein the laser marker includes a computer-controlled beam expander for adjusting the spot size.

7. The system of claim 1 wherein the spot size at a focus position of the marking beam is in the range of about 25-40 microns and the marking field size is in a range of about 75-100 mm.

8. The system of claim 1 further comprising a second positioning subsystem for automatically positioning the wafer relative to the laser marker along a direction substantially perpendicular to a plane of the wafer.

9. The system of claim 8 wherein the second positioning subsystem comprises means for supporting wafers having predetermined sizes and for providing at least two degrees of freedom for relative positioning of the wafers.

10. The system of claim 1 wherein the calibration program includes a three-dimensional calibration algorithm for calibrating the marker at a plurality of three-dimensional locations.

11. The system of claim 1 wherein the first positioning subsystem comprises an X-Y stage and the calibration program includes means for calibrating the alignment vision system, the X-Y stage, and the laser marker.

12. The system of claim 1 further comprising a vision inspection subsystem including a camera for inspecting the marks.

13. The system of claim 12 wherein the inspection subsystem comprises an inspection positioning subsystem for positioning the wafer relative to the camera, the inspection positioning subsystem being separate from the first positioning subsystem.

14. The system of claim 1 further comprising a first imaging subsystem for imaging a first side of the wafer, a second imaging subsystem for imaging a second side of the wafer, the imaging subsystems being used to superimpose an image of a mark on the second side of the wafer with an image of a corresponding portion of the first side.

15. The system of claim 1 further comprising a calibration target and an algorithm for substantially matching first and second target images obtained with first and second imaging subsystems so that the superimposed target images correspond.

16. The system of claim 1 wherein the laser is a frequency doubled Vanadate laser having a green output wavelength and a pulse width less than about 50 ns.

41. The system of claim 1 wherein at least one of the alignment vision system and the laser marker comprises a focus or height sensor.

43. The system as claimed in claim 1 wherein the scan lens is a telecentric lens.

17. A method for marking a semiconductor wafer, wherein a marking field is substantially smaller than the wafer, the method comprising:

positioning a laser marking field relative to the wafer along a first direction;

optically maintaining spot placement accuracy within the marking field so as to avoid undesirable mark variation associated with wafer sag or other variations in depth within the field; and

marking the wafer.

18. The method of claim 17 wherein the step of maintaining is based on a predetermined relationship between spot placement accuracy at a marker field location and wafer placement along the axis, and wherein the step of positioning the wafer location relative to the marking field is based on the relationship, whereby the spot placement accuracy is improved.

23. The method of claim 17 further comprising automatically positioning a marking beam relative to the wafer along an axis substantially perpendicular to a plane of the wafer so that the marking beam is incident at the marking location on the wafer whereby the wafer is marked at the location notwithstanding variations in depth of the wafer relative to a focus position of the marking beam.

24. The method of claim 17 wherein the step of positioning is repeated for a plurality of positions.

25. The method of claim 23 wherein the positioning includes relatively positioning the wafer and focus position of the marking beam.

26. The method of claim 23 wherein at least one of the steps of relatively positioning along the first direction and along the axis is based on a predetermined estimate of wafer sag.

27. The method of claim 23 wherein at least one of the steps of relatively positioning along the direction and along the axis is based on a measurement of a wafer location with a depth sensor.

28. The method of claim 23 wherein at least one of the steps of relatively positioning along the direction and along the axis is based on a plane fit to the wafer.

29. The method of claim 23 wherein the wafer is translated along the axis.

30. The method of claim 25 wherein positioning is carried out using a movable lens element.

31. The method of claim 23 wherein the steps of relatively positioning in the first direction and along the axis are carried out concurrently.

32. The method of claim 17 further comprising calibrating a system for carrying out the method.

33. The method of claim 24 wherein a portion of the wafer within the marking field is also within the marking field at the plurality of positions.

19. The method of 17 wherein the step of maintaining includes the step of selecting a portion of the marking field and wherein the step of positioning the wafer relative to the marking field positions the wafer location to be marked within the selected portion of the marking field whereby the spot placement accuracy is improved.

20. The method of 19 wherein the selected portion of the marking field has a preferred axis with reduced telecentricity error.

21. The method of 19 wherein the selected portion of the marking field is a rectangular field aligned with the preferred axis.

22. The method of 19 wherein the selected portion of the marking field is a substantial part of a quadrant with a reduced thermal drift characteristic.

34. A laser marker for marking workpieces, the marker including a substantially telecentric scan lens for correcting spot placement to within about one spot diameter over a marking field substantially smaller than the workpiece so as to avoid undesirable mark variations associated with workpiece sag or other variations in depth.

35. The laser marker of claim 34 wherein the telecentricity error is further reduced using pupil correction.

36. The laser marker of claim 34 wherein the telecentricity error is further reduced using additional scan lens elements.

37. The laser marker of claim 34 wherein the scan lens is a color corrected telecentric scan lens.

38. The laser marker of claim 34 wherein the marking field is a selected sub-field selected to further improve beam-positioning accuracy.

39. The marker of claim 34 wherein the selected subfield is a rectangular field aligned with the preferred axis.

40. The marker of claim 34 wherein characteristics of marks are determined by detecting radiation collected through the scan lens.

42. The marker of claim 34 wherein an undesirable mark variation includes at least one of mark position, mark line width, and mark contrast variation with depth.