High energy, low energy density, radiation-resistant optics used with micro-electromechanical devices

• US 6,891,655 B2
• Filed: 01/02/2003
• Issued: 05/10/2005
• Est. Priority Date: 01/02/2003
• Status: Active Grant

• Current Assignee: Micronic Laser Systems AB (Mycronic AB)
• Original Assignee: Micronic Laser Systems AB (Mycronic AB)
• Inventors: Kurth, Eberhard, Dauderstadt, Ulrike A., Ljungblad, Ulric B., Sandström, Torbjörn, Kunath, Christian, Grebinski, Thomas J.
• Primary Examiner(s): THOMPSON, TIMOTHY J
• Application Number:
  US10/335,981
• Publication Number:
  US 20040130775A1
• Time in Patent Office: 859 Days
• Field of Search: 359/291, 359/290, 359/292, 359/295, 359/297, 359/298, 359/238, 359/237, 359/872, 359/873, 359/874, 359/871
• US Class Current: 359/291
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81B 7/0012 Protection against reverse engineering, unauthorised use, use in unintended manner, wrong insertion or pin assignment
• CPC Class Codes: G02B 1/105 Protective coatings
• CPC Class Codes: G02B 1/14 Protective coatings, e.g. hard coatings
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G03F 7/70291 Addressable masks, e.g. spatial light modulators [SLMs], digital micro-mirror devices [DMDs] or liquid crystal display [LCD] patterning devices
• CPC Class Codes: G03F 7/70983 Optical system protection, e.g. pellicles or removable covers for protection of mask

Abstract

The present invention includes methods and devices that improve the radiation-resistance of a movable micromechanical optical element. In particular, a radiation-resistant layer is added to a movable micro-mechanical optical element, suitable to reduce the surface and bulk material changes to the element that result from exposure to pulsed laser energy densities less than 100 micro-joules per square centimeter and at wavelengths less than or equal to about 248 nm.

Claims

1. A method to improve the resistance to radiation-induced damage in an optical micro-electromechanical system (MEMS) comprising at least one movable modulating element, said damage resulting from cumulative pulses of low-fluence, short wavelength electromagnetic radiation, comprising the action of:

forming at least one radiation-resistant layer on a front side of at least one movable modulating element.

2. The method according to claim 1, wherein said radiation-resistant layer is substantially reflective at an operating wavelength of about 248 nm or less.

3. The method according to claim 1, wherein said radiation-resistant layer includes at least one of oxide of hafnium (HfaOb), fluoride of magnesium (MgeFx), fluoride of lanthanum (LapFx), oxide of aluminum (AlsOt) oxide of silicon (SiyOx) or fluoride of lithium (LikFz).

4. A method according to claim 1, wherein said radiation-resistant layer includes an oxide of hafnium, an oxide of aluminum or an oxide of silicon.

5. A method according to claim 1, wherein said radiation-resistant layer includes a fluoride of magnesium, a fluoride of calcium or a fluoride of lithium.

6. A method according to claim 1, wherein said radiation-resistant layer is an implanted layer at the front side of the movable modulating element.

7. A method according to claim 6, wherein said implanted radiation-resistant layer is activated.

8. A method according to claim 7, wherein said implanted radiation-resistant layer consists of the implanted elements boron and carbon.

9. A method according to claim 1, further including forming a plurality of radiation-resistant layers, said radiation-resistant layers including at least one of an oxide of hafnium, an oxide of aluminum, an oxide of silicon, a fluoride of magnesium, a fluoride of calcium, a fluoride of lithium, or an activated implanted layer of boron and carbon.

10. A method according to claim 1, wherein the radiation-resistant layer has a thickness of about 30 nm to 70 nm.

11. A method according to claim 1, wherein the radiation-resistant layer has a thickness of about 2 nm to 50 nm.

12. A method according to claim 1, wherein the radiation-resistant layer has a thickness of about 50 nm to 100 nm.

13. The method according to claim 1, wherein the movable modulating element comprises aluminum.

14. The method according to claim 1, wherein the movable modulating element comprises one or more materials silicon nitride, silicon, titanium, tantalum or tungsten.

15. A method according to claim 1, wherein said material composition for the radiation-resistant layer is an averaged bulk composition from an upper portion of the layer to a lower portion of the layer.

16. A method according to claim 3, wherein said material composition for any one of the plurality of radiation-resistant layer is an averaged bulk composition from an upper portion of the layer to a lower portion of the layer.

17. A method according to claim 1, further including, prior to forming the radiation-resistant layer, forming a reflective layer including one or more of aluminum, silver and gold.

18. A method according to claim 1, wherein said movable modulating element has a back side, further including forming on said back side at least one anti-reflective layer.

19. A method according to claim 18, wherein said anti-reflective layer comprises CaF2 or MgF2.

20. A method according to claim 18, wherein said anti-reflective layer comprises a fluoride of Magnesium or Calcium.

21. A method according to claim 18, wherein said anti-reflective layer has a thickness of about 15 nm to 80 nm.

22. A method according to claim 18, wherein said anti-reflective layer has a thickness of about 40 nm to 60 nm.

23. A method according to claim 18, wherein said anti-reflective layer has a thickness of about 60 nm to 80 nm.

24. A method according to claim 1, wherein said movable modulating element transmits electromagnetic radiation.

25. A method according to claim 24, wherein said movable modulating element is substantially transparent to wavelengths less than or equal to 248 nm.

26. A method according to claim 24, wherein said movable modulating element comprises an oxide of silicon.

27. A method according to claim 24, wherein said radiation-resistant layer comprises one layer.

28. A method according to claim 24, wherein radiation-resistant layer comprises a plurality of layers.

29. A method according to claim 24, wherein said radiation-resistant layer comprises a fluoride of magnesium or calcium.

30. A method according to claim 24, wherein said radiation-resistant element is two or more oxides of aluminum or silicon.

31. A method according to claim 1, further including, prior to forming the radiation-resistant layer, planarizing the front side.

32. The method of claim 31, wherein the front side, after the planarizing, has an RMS flatness of better than 2 nm.

33. The method of claim 31, wherein the front side, after the planarizing, has an RMS flatness of better than 1 nm.

34. The method of claim 31, wherein the front side, after the planarizing, has an RMS flatness of better than 0.5 nm.

35. The method of claim 31, wherein the planarizing includes CPM with an abrasive particle size of less than 300 nm.

36. The method of claim 31, wherein the planarizing includes CPM with an abrasive particle size of about 70 nm.

37. The method of claim 31, wherein the planarizing includes CPM with an abrasive particle size of about 50 nm.

38. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, wherein said radiation-resistant layer is substantially reflective of radiation at an operating wavelength of about 248 nm or less.

39. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, wherein the movable modulating element and the radiation-resistant layer are substantially transmissive at an operating wavelength of about 248 nm or less.

40. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, wherein said radiation-resistant layer includes at least one of hafnium oxide (HfO2), magnesium fluoride (MgF2), aluminum oxide (Al2O3), silicon dioxide (SiO2) or lithium fluoride (LiF2).

41. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, wherein said radiation-resistant layer includes an oxide of hafnium, an oxide of aluminum or an oxide of silicon.

42. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, wherein said radiation-resistant layer includes a fluoride of magnesium, a fluoride of calcium or a fluoride of lithium.

43. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, wherein said radiation-resistant layer is an implanted layer at the front side of the movable modulating element.

44. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, wherein the front side is flat, having an RMS of 2 nm or better.

45. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, further including;

a back side of the movable modulating element; and

at least one anti-reflective layer formed on the back side.

46. At least one movable modulating element of an optical micro-electromechanical system (MEMS), comprising:

a front side; and

at least one radiation-resistant layer over the front side, further including;

a non-movable substrate below the movable modulating element, to which the movable element is movably coupled; and

at least one anti-reflective layer formed on a part of the non-movable substrate.