High speed, laser-based marking method and system for producing machine readable marks on workpieces and semiconductor devices with reduced subsurface damage produced thereby

• US 20060180580A1
• Filed: 04/18/2006
• Published: 08/17/2006
• Est. Priority Date: 05/17/2002
• Status: Abandoned Application

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: GSI Lumonics Corporation (Novanta Inc.)
• Inventors: Schramm, Rainer
• Application Number:
  US11/406,191
• Publication Number:
  US 20060180580A1
• Time in Patent Office: Days
• US Class Current: 219/121.690
• 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

An improved method of laser marking semiconductor wafers is provided wherein undesirable subsurface damage to a silicon semiconductor wafer is avoided while providing a relative improvement in marking speed for a predetermined spot diameter. A laser pulse of a laser beam has a predetermined wavelength, pulse width, repetition rate, and energy. The method further includes irradiating a semiconductor wafer with the pulsed laser beam over a spot diameter to produce a machine readable mark on the semiconductor wafer. The mark has a mark depth. The pulse width is less than about 50 ns, and the step of irradiating irradiates over the spot diameter to produce a mark having a mark depth substantially less than about 10 microns.

Claims

1-14. -14. (canceled)

15. A semiconductor device including a semiconductor substrate, circuitry formed on a first side of the substrate, and a machine readable mark formed on a second side of the substrate with a laser output, the mark having an average mark depth no greater than about 3.5 microns.

16. A semiconductor device including a substrate and a machine readable mark formed on the substrate with a laser output, the mark having an average mark depth no greater than about 4 microns, wherein the mark is produced during at least one step of a process for manufacturing the device by generating a laser output for wafer marking, the output comprising at least one pulse having a pulse width less than about 50 nanoseconds, a wavelength, and at least one energy characteristic;

and irradiating the wafer with the output over at least one spot having a diameter to produce a machine readable mark on the wafer, the mark having an average mark height, an average mark depth substantially less than about 10 microns, and wherein undesirable subsurface damage to the wafer is avoided.

17. A laser marking system, including a laser for marking a semiconductor wafer, the system comprising:

a laser means for generating a laser output for wafer marking, the output comprising at least one pulse having a pulse width less than about 50 nanoseconds, a wavelength, and at least one energy characteristic; and

means, including an optical system, for irradiating the semiconductor wafer with the output over at least one spot having a diameter to produce a machine readable mark on the wafer, the mark having an average mark height, an average mark depth substantially less than about 10 microns, and wherein undesirable subsurface damage to the semiconductor wafer is avoided.

18. The system of claim 17 wherein the means for irradiating includes a beam positioning subsystem that includes a beam deflector, the beam deflector being operable to deflect the at least one pulse over a marking field and to position a beam corresponding to the at least one pulse of the output relative to the wafer so as to mark the wafer during motion of the wafer relative to the output at a marking speed over the marking field.

19. The system of claim 18 wherein the positioning subsystem includes at least one translator for translating the wafer and wherein the deflector is a galvanometer-based X-Y mirror system for deflecting the at least one pulse.

20. The system of claim 17 wherein the average mark depth is in the range of about 3-4.5 microns

21. The system of claim 17 wherein the average mark depth does not exceed 4 microns.

22. The system of claim 17 wherein the semiconductor wafer comprises a silicon wafer, and wherein the laser means includes a frequency doubled Nd:

YVO₄ laser having a green output wavelength.

23. The system of claim 17 wherein the undesirable subsurface damage includes microcracking.

24. The system of claim 17 wherein the at least one pulse irradiates the wafer at about 10⁹ watts/cm² or greater over the at least one spot diameter.

25. The system of claim 24 wherein the pulse width is about 10-15 ns, a pulse energy is in the range of about 230-250 microjoules, and wherein the at least one spot diameter is about 25-40 microns.

26. The system of claim 17 wherein the output includes a plurality of pulses, and wherein at least one pulse energy incident on a surface of the wafer is in a range of about 230-250 microjoules, a pulse width is in a range of about 10-15 nanoseconds, and wherein temporal pulse spacing of at least some consecutive pulses of the output corresponds to a repetition rate in a range of about 15-30 KHz.

27. The system of claim 17 wherein a plurality of pulses irradiate the wafer over a corresponding plurality of spots, at least one spot having a spot diameter in a range of about 25-40 microns, marking is carried out at a linear marking speed of at least 150 mm/sec, whereby the marks are substantially continuous and a dimension of the mark is substantially greater than the spot diameter.

28. The system of claim 27 wherein the spot diameter is in a range of about 30-35 microns, and the marking speed is at least 150 mm/sec.

29. The system of claim 17 wherein the diameter is in a range of about 25-40 microns

30. The system of claim 17 wherein a plurality of pulses irradiate the wafer over a corresponding plurality of spots and wherein at least one of the laser means and the means for irradiating includes means for avoiding substantial separation of the spots on a surface of the wafer.

31. The system of claim 17 wherein the wherein the output includes a plurality of pulses, and wherein temporal pulse spacing of at least some consecutive pulses corresponds to a repetition rate of at least 10 KHz.

32. The system of claim 17 wherein the wherein the output includes a plurality of pulses, and wherein the temporal pulse spacing of at least some consecutive pulses corresponds to a repetition rate of at least 15 KHz.

33. A laser marking system for marking a semiconductor wafer, the system comprising:

a diode pumped solid state laser means for generating a laser output for wafer marking, the output comprising at least one pulse having a pulse width less than about 50 nanoseconds, a wavelength, and at least one energy characteristic; and

means, including an optical system, for irradiating the semiconductor wafer with the output over at least one spot having a diameter to produce a relatively shallow mark having sufficient contrast for machine readability, the mark having an average mark height, an average mark depth no greater than about 4 microns, and wherein undesirable subsurface damage to the semiconductor wafer is avoided.

34. The system of claim 33 wherein the semiconductor wafer comprises a silicon wafer, and wherein the laser includes a frequency doubled Nd:

YVO₄ laser having a green output wavelength.

35. The system of claim 33 wherein the at least one pulse irradiates the wafer at about 10⁹ watts/cm² or greater over the diameter of the at least one spot.

36. The system of claim 33 wherein the pulse width is about 10-15 ns, a pulse energy is in the range of about 230-250 microjoules, and wherein the diameter of the at least one spot is the range of about 25-40 microns.

37. The system of claim 33 wherein the output includes a plurality of pulses, and wherein a temporal pulse spacing of at least some consecutive pulses corresponds to a repetition rate of at least 10 KHz.

38. The system of claim 33 wherein the laser means includes a fiber optic amplifier in a MOPA configuration.

39. A system of laser marking a semiconductor wafer during at least one step of a semiconductor manufacturing process, the wafer having a first side with circuit features, and a second side having a rough wafer surface portion to be marked, the system comprising:

a q-switched diode pumped, solid state laser for generating a laser output for wafer marking, the output comprising an output wavelength less than an absorption edge of the semiconductor wafer material, laser output power of at least about 3 W at the wavelength, a plurality of pulses, each pulse having a pulse width less than about 50 ns, at least one pulse having a pulse width in the range of about 10-15 ns, the temporal spacing between at least some consecutive pulses of the plurality of pulses corresponding to a repetition rate of at least 15 Khz; and

means for irradiating the semiconductor wafer with the output over at least one spot having a diameter in the range of less than about 60 microns to produce a shallow mark having sufficient contrast for machine readability, whereby the at least one pulse irradiates at least about 10⁸ W/cm² over the diameter while avoiding undesirable subsurface damage to the semiconductor wafer.

40. The system of claim 39 wherein the diameter is in the range of about 25-40 microns.

41. The system of claim 39 wherein the energy of the at least one pulse is in the range of about 230-250 microjoules, whereby the at least one pulse irradiates at least 10⁹ W/cm² over the at least one spot diameter.

42. The system of claim 39 wherein the available output power is at least about 5 W at the wavelength.

43. The system of claim 39 wherein the output wavelength is a green wavelength.

44. The system of claim 39 wherein the semiconductor wafer comprises a silicon wafer and wherein the laser is a frequency doubled Nd:

YVO4 laser having a green output wavelength.

45. A semiconductor device including a substrate and a shallow, machine-readable mark formed on the substrate with a laser output, wherein the mark is produced during at least one step of a process for manufacturing the device by generating a q-switched laser output for wafer marking, the output comprising an output wavelength less than an absorption edge of the wafer material, a laser output power of at least about 3 W at the wavelength, a plurality of pulses, each pulse having a pulse width less than about 50 ns, at least one pulse having a pulse width in the range of about 10-15 ns, the temporal spacing between at least some consecutive pulses of the plurality of pulses corresponding to a repetition rate of at least 15 Khz:

and irradiating the wafer with the output at least one spot having a diameter in the range of less than about 60 microns to produce a shallow mark having sufficient contrast for machine readability, whereby the at least one pulse irradiates at least about 10⁸ W/cm² over the diameter while avoiding undesirable subsurface damage to the wafer.