Micromirror array having reduced gap between adjacent micromirrors of the micromirror array

• US 6,985,277 B2
• Filed: 01/11/2005
• Issued: 01/10/2006
• Est. Priority Date: 07/03/2003
• Status: Expired due to Term

• Current Assignee: Texas Instruments, Inc.
• Original Assignee: Reflectivity, Inc. (Texas Instruments, Inc.)
• Inventors: Huibers, Andrew, Patel, Satyadev
• Primary Examiner(s): Mack, Ricky L.
• Assistant Examiner(s): THOMAS, BRANDI N
• Application Number:
  US11/034,318
• Publication Number:
  US 20050122561A1
• Time in Patent Office: 364 Days
• Field of Search: 359/290, 359/291, 359/292, 359/293, 359/294, 359/295, 359/298
• US Class Current: 359/290
• CPC Class Codes: B82Y 30/00 Nanotechnology for materials or surface science, e.g. nanocomposites
• CPC Class Codes: G02B 26/0841 the reflecting element being moved or deformed by electrostatic means
• CPC Class Codes: H04N 5/7458 the modulator being an array of deformable mirrors, e.g. digital micromirror device [DMD]

Abstract

A spatial light modulator is disclosed, along with a method for making such a modulator that comprises an array of micromirror devices. The center-to-center distance and the gap between adjacent micromirror devices are determined corresponding to the light source being used so as to optimize optical efficiency and performance quality. The micromirror device comprises a hinge support formed on a substrate and a hinge that is held by the hinge support. A mirror plate is connected to the hinge via a contact, and the distance between the mirror plate and the hinge is determined according to desired maximum rotation angle of the mirror plate, the optimum gap and pitch between the adjacent micromirrors.

In a method of fabricating such spatial light modulator, one sacrificial layer is deposited on a substrate followed by forming the mirror plates, and another sacrificial layer is deposited on the mirror plates followed by forming the hinge supports. The two sacrificial layers are removed via the small gap between adjacent mirror devices with spontaneous vapor phase chemical etchant. Also disclosed is a projection system that comprises such a spatial light modulator, as well as a light source, condensing optics, wherein light from the light source is focused onto the array of micromirrors, projection optics for projecting light selectively reflected from the array of micromirrors onto a target, and a controller for selectively actuating the micromirrors in the array.

Claims

1. A method, comprising:

forming first and second sacrificial layers with a plurality of hinges formed in a hinge layer on one of the first and second sacrificial layers and with an array of mirror plates formed in a mirror plate layer on the other of the first and second sacrificial layers;

wherein the mirror plates are formed with a gap between adjacent mirror plates of from 0.15 to 0.5 micrometers;

wherein one of the first and second sacrificial layers is between the mirror plate layer and hinge layer and has a thickness of from 0.15 to 1.5 micrometers;

forming a hinge support on the second sacrificial layer for each mirror plate for supporting the mirror plate; and

removing at least a portion of one or both of the first and the second sacrificial layers using a spontaneous vapor phase chemical etchant.

2. The method of claim 1, wherein a center-to-center distance between adjacent mirror plates is from 4.38 to 10.16 micrometers.

3. The method of claim 1, wherein the array of mirror plates comprises at least 1280 mirror plates along a length of the array.

4. The method of claim 1, wherein the array of mirror plates comprises at least 1400 mirror plates along a length of the array.

5. The method of claim 1, wherein the array of mirror plates comprises at least 1600 mirror plates along a length of the array.

6. The method of claim 1, wherein the array of mirror plates comprises at least 1920 mirror plates along a length of the array.

7. The method of claim 1, wherein the step of removing the first and second sacrificial layers further comprises:

removing the first sacrificial layer using the spontaneous vapor phase chemical etchant via the gap between adjacent mirror plates.

8. The method of claim 1, wherein the gap is from 0.15 to 0.25 micrometers.

9. The method of claim 1, wherein the gap is from 0.25 to 0.5 micrometers.

10. The method of claim 1, wherein the gap is 0.5 micrometers or less.

11. The method of claim 1, wherein the thickness of the second sacrificial layer is from 0.5 to 1.5 micrometers.

12. The method of claim 1, wherein the thickness of the second sacrificial layer is from 0.8 to 1.25 micrometers.

13. The method of claim 1, wherein the thickness of the second sacrificial layer is from 0.95 to 1.15 micrometers.

14. The method of claim 1, wherein a center-to-center distance between adjacent mirror plates is from 8.07 to 10.16 micrometers.

15. The method of claim 1, wherein a center-to-center distance between adjacent mirror plates is from 6.23 to 9.34 micrometers.

16. The method of claim 1, wherein a center-to-center distance between adjacent mirror plates is from 4.38 to 6.57 micrometers.

17. The method of claim 1, wherein a center-to-center distance between adjacent mirror plates is from 4.38 to 9.34 micrometers.

18. The method of claim 1, further comprising:

forming the hinge for the mirror plates such that, after removing the first and second sacrificial layer, a) the mirror plate can rotate relative to the substrate along a rotation axis that is parallel to but offset from a diagonal of the mirror plate when viewed from the top of the mirror plate; and

b) the mirror plate can rotate to an angle at least 14 degrees relative to the substrate; and

wherein the step of forming the array of mirror plates on the first sacrificial layer further comprises;

forming the array of mirror plates on the first sacrificial layer such that adjacent mirror plates have a gap from 0.15 to 0.5 micrometers therebetween.

19. The method of claim 1, wherein the step of forming a hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate above the substrate to a rotation angle at least 14°

degrees relative to the substrate.

20. The method of claim 1, further comprising:

forming an electrode for each mirror plate; and

disposing the electrode proximate to the mirror plate for electrostatically deflecting the mirror plate.

21. The method of claim 1, wherein the substrate is glass or quartz that is visible light transmissive.

22. The method of claim 20, further comprising:

depositing an anti-reflection film on a surface of the substrate.

23. The method of claim 20, further comprising:

depositing a light absorbing frame around an edge of the substrate.

24. The method of claim 1, wherein the step of removing the first and second sacrificial layer further comprises:

monitoring an endpoint of the sacrificial layer being removed using a residual gas analyzer.

25. The method of claim 1, wherein the first sacrificial layer or the second sacrificial layer comprises amorphous silicon.

26. The method of claim 1, wherein the spontaneous vapor phase etchant is an interhalogen.

27. The method of claim 1, wherein the spontaneous vapor phase etchant is HF.

28. The method of claim 1, wherein the spontaneous vapor phase etchant is a noble gas halide.

29. The method of claim 28, wherein the noble gas halide comprises xenon difluoride.

30. The method of claim 26, wherein the interhalogen comprises bromine trichloride or bromine trifluoride.

31. The method of claim 1, wherein a diluent is mixed with the vapor phase etchant during removing the first and second sacrificial layer.

32. The method of claim 31, wherein the diluent is selected from N₂, He, Ar, Kr and Xe.

33. The method of claim 31, wherein the diluent is selected from N₂ and He.

34. The method of claim 1, wherein each mirror plate has an area;

and wherein a ratio of a summation of the areas of all mirror plates of the mirror plate array to an area of the substrate is 90 percent or more.

35. The method of claim 1, wherein each mirror plate rotates relative to the substrate in response to an electrostatic force.

36. The method of claim 1, further comprising:

disposing a first electrode proximate to each mirror plate for electrostatically driving the mirror plate to rotate in a first direction relative to the substrate; and

disposing a second electrode proximate to the mirror plate for electrostatically driving the mirror plate to rotate in a second direction opposite to the first direction relative to the substrate.

37. The method of claim 36, wherein the first electrode and the second electrode are disposed on the same side relative to a rotation axis of the mirror plate.

38. The method of claim 36, wherein the first electrode and the second electrode are disposed on the opposite sides relative to a rotation axis of the mirror plate.

39. The method of claim 1, wherein the substrate is semiconductor.

40. The method of claim 1, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a first direction to an angle from 15°

degrees to 27°

degrees relative to the substrate.

41. The method of claim 40, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a second direction opposite to the first direction to an angle from 2°

degrees to 9°

degrees relative to the substrate.

42. The method of claim 1, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a first direction to an angle from 17.5°

degrees to 22.5°

degrees relative to the substrate.

43. The method of claim 42, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a second direction opposite to the first direction to an angle from 2°

degrees to 9°

degrees relative to the substrate.

44. The method of claim 1, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a first direction to an angle around 20°

degrees relative to the substrate.

45. The method of claim 44, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a second direction opposite to the first direction to an angle from 2°

degrees to 9°

degrees relative to the substrate.

46. The method of claim 1, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a first direction to an angle around 30°

degrees relative to the substrate.

47. The method of claim 46, wherein the step of forming the hinge support on the second sacrificial layer for each mirror plate further comprises:

forming a hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a second direction opposite to the first direction to an angle from 2°

degrees to 9°

degrees relative to the substrate.

48. The method of claim 11, further comprising:

forming the hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a first rotation direction to an angle from 12°

degrees to 20°

degrees relative to the substrate.

49. The method of claim 48, further comprising:

forming the hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a second rotation direction opposite to the first rotation direction to an angle from 2°

degrees to 9°

degrees relative to the substrate.

50. The method of claim 2, further comprising:

forming the hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a first rotation direction to an angle from 12°

degrees to 20°

degrees relative to the substrate.

51. The method of claim 50, further comprising:

forming the hinge for the mirror plate such that, after removing the first and second sacrificial layer, the mirror plate can rotate in a second rotation direction opposite to the first rotation direction to an angle from 2°

degrees to 9°

degrees relative to the substrate.