Laser processing

• US 5,998,759 A
• Filed: 12/24/1996
• Issued: 12/07/1999
• Est. Priority Date: 12/24/1996
• Status: Expired due to Term

• Current Assignee: Electro Scientific Industries Incorporated (MKS Instruments Incorporated)
• Original Assignee: General Scanning, Inc. (KOCH Industries Incorporated)
• Inventors: Smart, Donald V.
• Primary Examiner(s): MILLS, GREGORY L
• Application Number:
  US08/774,107
• Time in Patent Office: 1,078 Days
• Field of Search: 219/121.6, 219/121.61, 219/121.68, 219/121.69, 219/121.73, 219/121.75, 219/121.77, 219/121.85, 216/65, 438/601, 438/940, 29/847
• US Class Current: 219/121.69
• CPC Class Codes: B23K 2101/40 Semiconductor devices
• CPC Class Codes: B23K 2103/42 Plastics B23K2103/16 takes precedence
• CPC Class Codes: B23K 2103/50 Inorganic material, e.g. metals, not provided for in B23K2103/02 – B23K2103/26
• CPC Class Codes: B23K 26/0622 by shaping pulses
• CPC Class Codes: B23K 26/082 Scanning systems, i.e. devices involving movement of the laser beam relative to the laser head
• 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: H01L 21/76894 using a laser, e.g. laser cutting, laser direct writing, laser repair

Abstract

A controlled, switched laser system for vaporizing a target structure on a substrate includes a diode-pumped, solid-state laser for producing a laser output, a controllable switch for controlling the on/off state and power level of the laser, and a wavelength shifter. The wavelength shifter shifts the wavelength of the laser output from a conventional wavelength to a wavelength beyond the absorption edge of the substrate but shorter than 1.2 μm in order to obtain a decrease in absorption of the laser output by the substrate due to the shift in the wavelength of the laser output. The wavelength shifter is removably insertable into the switched laser system so as to enable the switched laser system to operate at the conventional wavelength and at the wavelength beyond the absorption edge of the substrate. Heating of the substrate and hence damage to the substrate is limited due to the wavelength being beyond the absorption edge of the substrate. Good depth of focus of the laser beam output is maintained relative to spot size of the laser beam output due to the wavelength being less than about 1.2 μm.

Claims

1. A method of vaporizing and removing a target link structure on a silicon substrate, comprising the steps of:

providing a controlled, switched laser system comprising a diode-pumped, solid-state laser assembly and a controllable switch for controlling the on/off state and power level of the laser assembly;

producing a laser beam output having an output pulse width less than about 8 nanoseconds at an operating repetition rate of about 5 kilohertz or higher, and a wavelength beyond the absorption edge of the silicon substrate but shorter than 1.2 μ

m in order to obtain low absorption of the laser beam output by the silicon substrate; and

directing the laser beam output at the target link structure on the silicon substrate to vaporize and remove the target link structure;

whereby heating of the silicon substrate and hence damage to the silicon substrate is limited due to the output pulse width being less than about 8 nanoseconds and due to the wavelength remaining beyond the absorption edge of the silicon substrate.

2. The method of claim 1 wherein the output pulse width of the laser beam output is less than about 5 nanoseconds at an operating repetition rate of about 5 kilohertz or higher.

3. The method of claim 2 wherein the output pulse width of the laser beam output is less than about 4 nanoseconds at an operating repetition rate of about 5 kilohertz or higher.

4. The method of claim 3 wherein the output pulse width of the laser beam output is less than about 4 nanoseconds at an operating repetition rate of about 8 kilohertz or higher.

5. The method of claim 2 wherein the output pulse width of the laser beam output is less than about 5 nanoseconds at an operating repetition rate of about 10 kilohertz or higher.

6. The method of claim 1 wherein the output pulse has a peak beam power sufficiently high to evaporate a metal link in a high-density memory.

7. The method of claim 1 wherein the laser assembly comprises a neodymium vanadate laser.

8. The method of claim 1 wherein the laser assembly comprises a neodymium:

YLF laser.

9. The method of claim 1 wherein the laser assembly comprises a neodymium:

YAG laser.

10. The method of claim 1 wherein the laser assembly comprises a laser having a cavity length optimized for limiting the output pulse width.

11. The method of claim 1 wherein the target structure comprises a metal link in a high-density memory.

12. The method of claim 1 wherein the second target structure comprises a link formed of a material selected from the group of polysilicide and polysilicon.

13. The method of claim 1 wherein the substrate comprises silicon.

14. A method of vaporizing and removing a target link structure on a silicon substrate, comprising the steps of:

providing a controlled, switched laser system comprising a diode-pumped, solid-state laser and a controllable switch for controlling the on/off state and power level of the laser;

producing a laser output having an output pulse width less than about 8 nanoseconds at an operating repetition rate of about 5 kilohertz or higher;

shifting the wavelength of the laser output from a wavelength that is not beyond the absorption edge of the silicon substrate to a wavelength beyond the absorption edge of the silicon substrate but shorter than 1.2 μ

m in order to obtain a decrease in absorption of the laser output by the silicon substrate due to the shift in the wavelength of the laser output, whereby heating of the silicon substrate and hence damage to the silicon substrate is limited due to the wavelength remaining beyond the absorption edge of the silicon substrate; and

directing the laser output at the target link structure on the silicon substrate to vaporize and remove the target link structure.

15. The method of claim 14 wherein the laser is a tunable fosterite laser and the wavelength shifter is a tuner incorporated into the laser.

16. The laser-system of claim 14 wherein the wavelength shifter is not part of the laser.

17. The method of claim 14 further comprising the step of removably inserting the wavelength shifter into the controlled, switched laser system so as to enable the switched laser system to operate at the wavelength that is not beyond the absorption edge of the silicon substrate and at the wavelength beyond the absorption edge of the silicon substrate but shorter than 1.2 μ

m.

18. The method of claim 14 wherein the wavelength that is not beyond the absorption edge of the substrate is about 1.047 μ

m.

19. The method of claim 14 wherein the wavelength that is not beyond the absorption edge of the substrate is about 1.064 μ

m.

20. The method of claim 19 wherein the output pulse width of the laser output is less than about 4 nanoseconds at an operating repetition rate of about 8 kilohertz or higher.

21. The method of claim 19 wherein the output pulse width of the laser output is less than about 5 nanoseconds at an operating repetition rate of about 10 kilohertz or higher.

22. The method of claim 14 wherein the wavelength shifter is a Raman shifter.

23. The method of claim 14 wherein the output pulse has a peak beam power sufficiently high to evaporate a metal link in a high-density memory.

24. A method of vaporizing and removing a target link structure on a silicon substrate, comprising the steps of:

providing a controlled, switched laser system comprising a diode-pumped, solid-state laser assembly and a controllable switch for controlling the on/off state and power level of the laser assembly;

producing a laser beam output having an output pulse width less than about 8 nanoseconds at an operating repetition rate of about 5 kilohertz or higher, and a wavelength beyond the absorption edge of the silicon substrate but shorter than 1.2 μ

m in order to obtain low absorption of the laser beam output by the silicon substrate; and

directing the laser beam output at the target link structure on the silicon substrate to vaporize and removing the target link structure;

whereby heating of the silicon substrate and hence damage to the silicon substrate is limited due to the output pulse width being less than about 8 nanoseconds and due to the wavelength remaining beyond the absorption edge of the silicon substrate, and whereby good depth of focus of the laser beam output is maintained relative to spot size of the laser beam output due to the wavelength being less than 1.2 μ

m.

25. The method of claim 24 wherein the output pulse has a peak beam power sufficiently high to evaporate a metal link in a high-density memory.

26. The method of claim 24 wherein the laser beam output has a spot size and depth of field sufficient for processing of target structures on a substrate having a substantially non-flat surface.

27. The method of claim 26 wherein the laser beam output has a spot size and depth of field sufficient for processing of target structures on a wafer having approximately an 8-inch diameter, a thickness of less than about 300 μ

m, and a substantial variation in flatness over its surface.

28. The method of claim 24 wherein the target structure vaporized by the laser beam output is about 1 μ

m wide.

29. The method of claim 24 wherein the target structure vaporized by the laser beam output is about 1/3 μ

m thick.

30. The method of claim 24 wherein the target structure comprises a metal link in a high-density memory.

31. A method of vaporizing and removing target link structures on substrates, comprising the steps of:

providing a controlled, switched laser system comprising a diode-pumped, solid-state laser and a controllable switch for controlling the on/off state and power level of the laser;

producing a laser output having an output pulse width less than about 8 nanoseconds at an operating repetition rate of about 5 kilohertz or higher;

directing the laser output at a first target link structure on a first, silicon substrate to vaporize and remove the first target link structure, the laser output remaining at a wavelength beyond the absorption edge of the first, silicon substrate but shorter than 1.2 μ

m in order to obtain low absorption of the laser output by the first, silicon substrate, whereby heating of the first, silicon substrate and hence damage to the first, silicon substrate is limited due to the wavelength remaining beyond the absorption edge of the first, silicon substrate, the laser output being focused by optics of the laser;

shifting the wavelength of the laser output from the wavelength beyond the absorption edge of the first, silicon substrate to a wavelength that is not beyond the absorption edge of the first, silicon substrate; and

directing the laser output at a second target link structure on a second substrate to vaporize and remove the second target link structure, the laser output being at the wavelength that is not beyond the absorption edge of the first, silicon substrate, the laser output being focused by the optics previously used to focus the laser output onto the first, silicon substrate, without modification of the optics.

32. The method of claim 31 wherein the wavelength that is not beyond the absorption edge of the substrate is about 1.064 μ

m.

33. The method of claim 31 wherein the wavelength beyond the absorption edge of the substrate is shorter than 1.2 μ

m.

34. The method of claim 31 wherein the wavelength shifter is a Raman shifter.

35. The method of claim 31 wherein the output pulse has a peak beam power sufficiently high to evaporate a metal link in a high-density memory.

36. The method of claim 31 wherein the second target structure comprises a link formed of a material selected from the group of polysilicide and polysilicon.

37. The method of claim 31 wherein the first target structure comprises a metal link.

38. A method of vaporizing and removing target link structures on substrates, comprising the steps of:

providing a controlled, switched laser system comprising a diode-pumped, solid-state laser and a controllable switch for controlling the on/off state and power level of the laser;

producing a laser output having an output pulse width less than about 8 nanoseconds at an operating repetition rate of about 5 kilohertz or higher;

directing the laser output through a removably insertable wavelength shifter to a first target link structure on a first, silicon substrate to vaporize and remove the first target link structure, the laser output remaining at a wavelength beyond the absorption edge of the first, silicon substrate but shorter than 1.2 μ

m in order to obtain low absorption of the laser output by the first, silicon substrate while maintaining good depth of focus of the laser beam output relative to spot size of the laser beam output, the laser output at the wavelength beyond the absorption edge of the first, silicon substrate but shorter than 1.2 μ

m having an output pulse width less than about 8 nanoseconds at an operating repetition rate of about 5 kilohertz or higher, whereby heating of the first, silicon substrate and hence damage to the first, silicon substrate is limited due to the wavelength remaining beyond the absorption edge of the first, silicon substrate;

removing the removably insertable wavelength shifter from the switched laser system, in order to shift the wavelength of the laser output from the wavelength beyond the absorption edge of the first, silicon substrate to a wavelength that is not beyond the absorption edge of the first, silicon substrate; and

directing the laser output at a second target link structure on a second substrate to vaporize and remove the second target link structure, the laser output being at the conventional wavelength.

39. The method of claim 38 wherein the laser output has an output pulse width less than about 8 nanoseconds at an operating repetition rate of about 5 kilohertz or higher, whereby heating of the substrate and hence damage to the substrate is limited due to the output pulse width being less than about 8 nanoseconds.

40. The method of claim 38 wherein the laser is a neodymium vanadate laser.

41. The method of claim 38 wherein the laser is a neodymium:

YLF laser.

42. The method of claim 38 wherein the laser is a neodymium:

YAG laser.

43. The method of claim 38 wherein the laser has a cavity length optimized for limiting the output pulse width.

44. The method of claim 38 wherein the wavelength shifter is a Raman shifter.

45. The method of claim 38 wherein the output pulse has a peak beam power sufficiently high to evaporate a metal link in a high-density memory.