Digital micromirror device having a window transparent to ultraviolet (UV) light

• US 20040190111A1
• Filed: 03/24/2003
• Published: 09/30/2004
• Est. Priority Date: 03/24/2003
• Status: Active Grant

• Current Assignee: Memphis Eye & Cataract Associates Ambulatory Surgery Center
• Original Assignee: Memphis Eye & Cataract Associates Ambulatory Surgery Center
• Inventors: Williams, Roy E., Callies, Brian M.
• Granted Patent: US 7,161,727 B2
• Time in Patent Office: Days
• US Class Current: 359/291
• 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

Abstract

A UV-transmissable window assembly for a DMD device includes a UV-transmissable glass window provided in a frame. The window and frame are bonded together to preferably effect a hermetic seal therebetween. Optical coatings specific to the intended wavelength of light transmission are applied to the inner and outer surfaces of the glass window to reduce reflection and increase -light transmission therethrough. The window assembly, and DMD provided with the same, is adapted for excellent transmission of ultraviolet light, even at the deep ultraviolet portion of the spectrum. The DMD window assembly has application in the medical arts, both surgery and device manufacture, in the production of integrated circuits (IC), and in other optical lithography applications, among other fields.

Claims

1. A window assembly for a digital micromirror device (DMD) having an array of individually addressable mirrors, comprising:

a) a frame adapted in size to be coupled to the DMD and having an aperture at least the size of the mirror array, said frame about said aperture having a first chamfered edge;

b) a UV light transmissable window coupled within said aperture, said window including a periphery provided with a second chamfered edge, said first and second chamfered edges together defining a channel; and

c) a brazing material provided in said channel that provides a seal between said window to said frame.

2. A window assembly according to claim 1, wherein:

said seal is a hermetic seal.

3. A window assembly according to claim 1, wherein:

said window is chosen to provide at least 50% transmission of light waves at and above 130-nm.

4. A window assembly according to claim 1, wherein:

said window is chosen to provide at least 65% transmission of light waves at and above 120-nm.

5. A window assembly according to claim 1, wherein:

said window is chosen to provide at least 80% transmission of light waves at and above 185-nm.

6. A window assembly according to claim 1, wherein:

said window is a fused silica glass window.

7. A window assembly according to claim 1, wherein:

said window is an argon fluoride (ArF) grade silica glass window.

8. A window assembly according to claim 1, wherein:

said window conforms to Corning code 7980.

9. A window assembly according to claim 1, wherein:

said window is made from a material selected from the group comprising calcium fluoride, barium fluoride, strontium fluoride, lithium fluoride, magnesium fluoride and sodium fluoride.

10. A window assembly according to claim 1, further comprising:

a dielectric coating on said window.

11. A window assembly according to claim 1, wherein:

said frame comprises a metal alloy.

12. A window assembly according to claim 11, wherein:

said metal alloy is a nickel-cobalt-iron alloy.

13. A window assembly according to claim 12, wherein:

said metal alloy is Kovar®

.

14. A window assembly according to claim 12, wherein:

said metal alloy is comprised of approximately 29% nickel, 17% cobalt, 0.30% manganese, 0.20% silicon, 0.02% carbon, and a balance of iron.

15. A window assembly according to claim 1, wherein:

said brazing material is a lead/silver alloy brazing material.

16. A window assembly according to claim 15, wherein:

said lead/silver alloy comprises approximately 97.5% lead and 2.5% silver.

17. A window assembly according to claim 1, wherein:

said window includes an inside and outside, and at least one of said inside and said outside is provided with one or more optical coatings.

18. A window assembly according to claim 17, wherein:

at least one of said optical coatings is a narrowband antireflection (AR) coating.

19. A window assembly according to claim 17, wherein:

at least one said optical coatings is a multilayer stack coating.

20. A window assembly according to claim 19, wherein:

said stack coating is optimized for an angle of incidence between 0° and

12°

.

21. A window assembly according to claim 17, wherein:

at least one of said optical coatings is optimized for a dual angle-of-incidence.

22. A digital micromirror device (DMD), comprising:

a) a base element provided with a two dimensional array of individually addressable mirrors;

b) a frame coupled to the base element and having an aperture at least the size of the mirror array; and

c) a window coupled within said aperture and bonded to said frame, said window comprising a material adapted to permit high transmission of UV wavelength light therethrough.

23. A DMD according to claim 22, wherein:

said frame has a first chamfered edge about said aperture, said window has a periphery with a second chamfered edge, and said first and second chamfered edges define a channel, and

wherein said window is bonded to said frame with a brazing material provided in said channel.

24. A DMD according to claim 22, wherein:

a bond between said window and said frame forms a hermetic seal.

25. A DMD according to claim 22, wherein:

said window is a fused silica glass window.

26. A DMD according to claim 22, wherein:

said window is an argon fluoride (ArF) grade silica glass.

27. A DMD according to claim 22, wherein:

said window material is selected from the group comprising calcium fluoride, barium fluoride, strontium fluoride, lithium fluoride, magnesium fluoride and sodium fluoride.

28. A DMD according to claim 27, further comprising:

a dielectric coating on said window.

29. A DMD according to claim 22, wherein:

said frame comprises a nickel-cobalt-iron alloy.

30. A DMD according to claim 22, wherein:

said window includes an inside and outside, and at least one of said inside and said outside is provided with one or more optical coatings.

31. A DMD according to claim 30, wherein:

at least one of said optical coatings is a narrowband antireflection (AR) coating.

32. A DMD according to claim 30, wherein:

at least one of said optical coatings is a multilayer stack coating.

33. A DMD according to claim 32, wherein:

said stack coating is optimized for an angle of incidence between 0° and

12°

.

34. A DMD according to claim 22, wherein:

said mirrors are provided with a coating to increase reflectance.

35. A DMD according to claim 34, wherein:

said coating is optimized for an angle of incidence between 10°

to 36°

angle of incidence.

36. A DMD according to claim 34, wherein:

said mirrors are manufactured from aluminum, and said coating is a dielectric material.

37. A digital micromirror device (DMD), comprising:

a) a base element provided with a two dimensional array of individually addressable mirrors;

b) a frame coupled to the base element and having an aperture at least the size of the mirror array, said frame comprised of a material having a first coefficient of thermal expansion;

c) a window coupled within said aperture of said frame, said window comprising a material adapted to permit high transmission of UV wavelength light therethrough and having a second coefficient of thermal expansion significantly different than said first coefficient of thermal expansion; and

d) a seal between said window and said frame.

38. A DMD according to claim 37, wherein:

said first and second coefficients of thermal expansions are different by approximately an order of magnitude.

39. A DMD according to claim 37, wherein:

said seal is a hermetic seal.

40. A digital micromirror device (DMD), comprising:

a) a base element having a first side and a second side, said first side provided with a two dimensional array of individually addressable mirrors;

b) a Kovar®

alloy frame having an aperture at least the size of the mirror array;

c) an argon fluoride grade fused silica window between said frame and said base element; and

d) a hermetic seal between said window and said base element.

41. A digital micromirror device (DMD), comprising:

a) a base element having a first side and a second side, said first side provided with a two dimensional array of individually addressable mirrors;

b) a frame having an aperture at least the size of the mirror array; and

c) a window between said frame and said base element, said window comprising a material adapted to permit at least 90% transmissibility of UV wavelengths at 185-nm and above, wherein said window and said base element are coupled in a manner which defines a hermetic seal about said array of mirrors.

42. A method of assembling a window unit for a digital micromirror device (DMD), comprising:

a) providing a frame having an aperture;

b) providing a fused silica glass window;

c) bonding said window in said aperture of said frame to form a window unit; and

d) optimizing said window for transmission of light at one or more particular wavelengths.

43. A method according to claim 42, wherein:

said window and said frame define a channel at the junction therebetween, and said bonding includes providing a brazing alloy in said channel and heating said window, said frame and said brazing alloy to effect a hermetic seal between said window and said frame.

44. A method according to claim 42, wherein:

said window includes an inside and an outside, and said optimizing includes applying to at least one of said inside and said outside of said window at least one coating adapted to increase UV light transmission through said window.

45. A method according to claim 44, wherein:

prior to applying said coating, masking portions of said window unit.

46. A method according to claim 44, wherein:

said applying utilizes a low temperature process.

47. A method according to claim 44, wherein:

said applying comprises sputtering.

48. A method according to claim 42, wherein:

said optimizing includes optimizing said window for a particular angle of incidence.

49. A method according to claim 42, wherein:

said optimizing includes optimizing said window for a range of angles-of-incidence.

50. A method according to claim 42, further comprising:

e) installing said window unit to a base element of a DMD, said DMD having a plurality of individually addressable mirrors.

51. A method according to claim 50, further comprising:

f) coating said mirrors with a relatively higher reflectance coating.