Hermetically sealed micro-device package with window

• US 6,627,814 B1
• Filed: 03/22/2002
• Issued: 09/30/2003
• Est. Priority Date: 03/22/2002
• Status: Expired due to Fees

• Current Assignee: Astravac Glass, Inc.
• Original Assignee: David H. Stark
• Inventors: Stark, David H.
• Primary Examiner(s): Ngo, Hung V.
• Application Number:
  US10/104,315
• Time in Patent Office: 557 Days
• Field of Search: 174/52.3, 174/52.4, 257/434, 257/680, 295/921
• US Class Current: 174/539
• CPC Class Codes: B81B 2201/047 Optical MEMS not provided for in B81B2201/042 - B81B2201/045
• CPC Class Codes: B81B 7/0067 for controlling the passage of optical signals through the package
• CPC Class Codes: B81C 1/00269 Bonding of solid lids or wafers to the substrate
• CPC Class Codes: B81C 1/00293 maintaining a controlled atmosphere with processes not provided for in B81C1/00285
• CPC Class Codes: H01L 21/50 Assembly of semiconductor devices using processes or apparatus not provided for in a single one of the subgroups H01L21/06 - H01L21/326, e.g. sealing of a cap to a base of a container
• CPC Class Codes: H01L 23/10 characterised by the material or arrangement of seals between parts, e.g. between cap and base of the container or between leads and walls of the container
• CPC Class Codes: H01L 27/14618 Containers
• CPC Class Codes: H01L 27/14625 Optical elements or arrangements associated with the device
• CPC Class Codes: H01L 27/14683 Processes or apparatus peculiar to the manufacture or treatment of these devices or parts thereof not peculiar thereto H01L21/00
• CPC Class Codes: H01L 27/14685 Process for coatings or optical elements
• 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
• CPC Class Codes: H01L 2924/09701 Low temperature co-fired ceramic [LTCC]
• CPC Class Codes: H01L 31/0203 Containers; Encapsulations , e.g. encapsulation of photodiodesfor photovoltaic devices H01L31/048; for organic photosensitive devices H10K30/80
• CPC Class Codes: H01L 31/02325 the optical elements not being integrated nor being directly associated with the device
• CPC Class Codes: Y02P 80/30 Reducing waste in manufacturing processes; Calculations of released waste quantities
• CPC Class Codes: Y10T 29/49002 Electrical device making

Abstract

A method for manufacturing a cover assembly including a transparent window portion and a frame that can be joined to a micro-device package base to form a hermetically sealed micro-device package. First, a frame is provided having a continuous sidewall defining a frame aperture therethrough. The sidewall includes a frame seal-ring area circumscribing the frame aperture. The frame seal-ring area has a metallic surface. A sheet of a transparent material is provided having a window portion defined thereupon. The window portion has finished top and bottom surfaces. Next, a sheet seal-ring area on the sheet is prepared, the sheet seal-ring area circumscribing the window portion. Next, the prepared sheet seal-ring area of the sheet is metallized. Next, the frame is positioned against the sheet such that at least a portion of the frame seal-ring area and at least a portion of the sheet seal-ring area contact one another along a continuous junction region that circumscribes the window portion. Next, the junction region is heated until a metal-to-metal joint is formed between the frame and sheet all along the junction region, whereby a hermetic seal circumscribing the window portion is formed.

Claims

1. A method for manufacturing a cover assembly that can be welded to a micro-device package base to form a hermetically sealed micro-device package, the cover assembly including a transparent window portion and a weldable frame, the method comprising the following steps:

providing a weldable frame having a continuous sidewall defining a frame aperture therethrough, the sidewall including a frame seal-ring area circumscribing the frame aperture, the frame seal-ring area having a metallic surface;

providing a sheet of a transparent material having a window portion defined thereupon, the window portion having finished top and bottom surfaces;

preparing a sheet seal-ring area on the sheet, the sheet seal-ring area circumscribing the window portion;

metallizing the prepared sheet seal-ring area of the sheet;

positioning the frame against the sheet such that at least a portion of the frame seal-ring area and at least a portion of the sheet seal-ring area contact one another along a continuous junction region that circumscribes the window portion; and

heating the junction region until a metal-to-metal joint is formed between the frame and sheet all along the junction region, whereby a hermetic seal circumscribing the window portion is formed.

2. A method in accordance with claim 1, wherein the transparent material of the sheet is a glass.

3. A method in accordance with claim 2, wherein the glass is selected from a group consisting of Abrisa soda-lime glass, Schott 8245 and Ohara S-LAM60.

4. A method in accordance with claim 3, wherein the soft glass is a soda-lime glass.

5. A method in accordance with claim 2, wherein the glass of the sheet is a hard glass.

6. A method in accordance with claim 5, wherein the hard glass is a borosilicate glass.

7. A method in accordance with claim 5, wherein the hard glass is selected from a group consisting of Corning 7050, Corning 7052, Corning 7055, Corning 7056, Corning 7058, Corning 7062, Kimble EN-1, Kimble K650 and Kimble K704.

8. A method in accordance with claim 6, wherein the weldable frame is primarily formed of an alloy having a nominal chemical composition of 54% iron (Fe), 29% nickel (Ni) and 17% cobalt (Co).

9. A method in accordance with claim 8, wherein the alloy is ASTM F-15 alloy.

10. A method in accordance with claim 8, wherein the alloy is Kovar alloy.

11. A method in accordance with claim 8, wherein the metallic surface of the frame seal-ring area is a surface layer of gold (Au) overlying a layer of nickel (Ni).

12. A method in accordance with claim 6, wherein the weldable frame is primarily formed of a material having a coefficient of thermal expansion (CTE) for the temperature range 30°

C. to 300°

C. that is within the range from about 5.0×

10<sup>−

6</sup>/°

K. to about 5.6×

10<sup>−

6</sup>/°

K.

13. A method in accordance with claim 1, wherein:

the frame seal-ring area of the frame has an exposed metallic layer of gold (Au) overlying a layer of nickel (Ni);

the step of positioning the frame against the sheet further comprises pressing the frame against the sheet with sufficient force to produce a predetermined contact pressure between the exposed metallic layer of the frame seal-ring area and the exposed metallic layer of the sheet seal-ring area along the junction region; and

the step of heating the junction region further comprises heating the junction region to a predetermined temperature while maintaining the predetermined contact pressure until plastic deformation occurs in the metallic layers of the frame seal-ring area and the sheet seal-ring area along the junction region, thereby causing a thermal compression bond therebetween to be formed.

14. A method in accordance with claim 13, wherein the predetermined contact pressure is about 95,500 psi and the predetermined temperature is about 380°

C.

15. A method in accordance with claim 13, wherein the step of metallizing the sheet seal-ring area further comprises depositing a first layer of aluminum (Al) onto the prepared sheet seal-ring area of the sheet using one of physical vapor deposition and chemical vapor deposition, the first layer having a thickness within the range from about 0.7 microns to about 25 microns.

16. A method in accordance with claim 15, wherein the step of metallizing the sheet seal-ring area further comprises:

depositing a second layer of copper (Cu) over the previous layer using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the second layer having a thickness within the range from about 0.002 microns to about 6.35 microns,

depositing a third layer of nickel (Ni) over the previous layers using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the third layer having a thickness within the range from about 0.002 microns to about 6.35 microns; and

depositing a fourth layer of one of tin (Sn) and tin-bismuth alloy (Sn—

Bi) over the previous layers using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the fourth layer having a thickness within the range from about 0.7 microns to about 63.5 microns.

17. A method in accordance with claim 15, wherein the step of metallizing the sheet seal-ring area further comprises:

depositing a second layer of zinc (Zn) over the previous layer using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the second layer having a thickness within the range from about 0.002 microns to about 6.35 microns, and

depositing a final layer of one of tin (Sn) and tin-bismuth alloy (Sn—

Bi) over the previous layers using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the final layer having a thickness within the range from about 0.7 microns to about 63.5 microns.

18. A method in accordance with claim 17, wherein the step of metallizing the sheet seal-ring area further comprises depositing a third layer of nickel (Ni) after the second layer and before the final layer using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the third layer having a thickness within the range from about 0.002 microns to about 6.35 microns.

19. A method in accordance with claim 13, wherein the step of metallizing the sheet seal-ring area further comprises:

depositing a first layer of tin (Sn) onto the prepared sheet seal-ring area of the sheet using one of physical vapor deposition and chemical vapor deposition, the first layer having a thickness within the range from about 0.002 microns to about 25 microns; and

de-stressing the tin layer by reflowing it in a 460°

F. oil bath.

20. A method in accordance with claim 13, wherein the step of metallizing the sheet seal-ring area further comprises depositing a first layer of tin-bismuth alloy (Sn—

Bi) onto the prepared sheet seal-ring area of the sheet using one of physical vapor deposition and chemical vapor deposition, the first layer having a thickness within the range from about 0.7 microns to about 63.5 microns.

21. A method in accordance with claim 13, wherein the step of metallizing the sheet seal-ring area further comprises depositing a first layer of chromium (Cr) onto the prepared sheet seal-ring area of the sheet using one of physical vapor deposition and chemical vapor deposition, the first layer having a thickness within the range from about 0.002 microns to about 0.15 microns.

22. A method in accordance with claim 21, wherein the step of metallizing the sheet seal-ring area further comprises:

depositing a second layer of nickel (Ni) over the previous layer using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the second layer having a thickness within the range from about 0.002 microns to about 6.35 microns; and

depositing a third layer of one of tin (Sn) and tin-bismuth alloy (Sn—

Bi) over the previous layer using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the third layer having a thickness within the range from about 0.7 microns to about 63.5 microns.

23. A method in accordance with claim 21, wherein the step of metallizing the sheet seal-ring area further comprises:

depositing a second layer of nickel (Ni) over the previous layer using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the second layer having a thickness within the range from about 0.002 microns to about 6.35 microns; and

depositing a final layer of aluminum (Al) over the previous layers using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the final layer having a thickness within the range from about 0.7 microns to about 63.5 microns.

24. A method in accordance with claim 23, wherein the step of metallizing the sheet seal-ring area further comprises:

depositing a third layer of zinc (Zn) after the second layer and before the final layer using one of physical vapor deposition, chemical vapor deposition and solution bath plating, the third layer having a thickness within the range from about 0.002 microns to about 6.35 microns.

25. A method in accordance with claim 1, wherein during the step of heating the junction region, the temperature of the window portion of the sheet remains below the glass transition temperature (T_G) of the transparent material.

26. A method in accordance with claim 1, wherein the transparent material of the sheet is a crystalline material.

27. A method in accordance with claim 26, wherein the crystalline material is quartz.

28. A method in accordance with claim 26, wherein the crystalline material is sapphire.

29. A method in accordance with claim 1, wherein the transparent material of the sheet is a polymeric material.

30. A method in accordance with claim 29, wherein the polymeric material is a polycarbonate plastic.

31. A method in accordance with claim 1, wherein the step of providing a sheet of transparent material further includes applying a surface treatment to the sheet.

32. A method in accordance with claim 31, wherein the surface treatment is a layer of siliconoxynitride (SiON) applied to the top surface of the sheet.

33. A method in accordance with claim 31, wherein the surface treatment is a layer of transparent scratch/abrasion-resistant material applied to the top surface of the sheet.

34. A method in accordance with claim 33, wherein the transparent scratch/abrasion-resistant material is an amorphous diamond-like carbon (DLC).

35. A method in accordance with claim 31, wherein the surface treatment is a refractive coating.

36. A method in accordance with claim 31, wherein the surface treatment is an achromatic coating.

37. A method in accordance with claim 31, wherein the surface treatment is an anti-reflective coating.

38. A method in accordance with claim 31, wherein the surface treatment is an optical filter.

39. A method in accordance with claim 31, wherein the surface treatment is an electromagnetic interference (EMI) filter.

40. A method in accordance with claim 31, wherein the surface treatment layer is a radio frequency (RF) filter.

41. A method in accordance with claim 1, wherein the finished surfaces of the window portion are flat.

42. A method in accordance with claim 41, wherein the finished surfaces of the window portion are ground and polished.

43. A method in accordance with claim 1, wherein at least one of the finished surfaces of the window portion is contoured.

44. A method in accordance with claim 43, wherein the finished surfaces of the window portion have the configuration of a refractive lens.

45. A method in accordance with claim 44, wherein the finished surfaces have the configuration of a plano-convex lens.

46. A method in accordance with claim 44, wherein the finished surfaces have the configuration of a double-convex lens.

47. A method in accordance with claim 44, wherein the finished surfaces have the configuration of a plano-concave lens.

48. A method in accordance with claim 44, wherein the finished surfaces have the configuration of a double-concave lens.

49. A method in accordance with claim 43, wherein the finished surfaces of the window portion have the configuration of a Fresnel lens.

50. A method in accordance with claim 43, wherein the finished surfaces of the window portion have the configuration of a diffractive lens.

51. A method in accordance with claim 1, wherein the step of preparing a sheet seal-ring area further comprises cleaning the top and bottom surfaces of the sheet to remove organic contaminants.

52. A method in accordance with claim 1, wherein the step of preparing a sheet seal-ring area further comprises roughening the surface of the sheet seal-ring area.

53. A method in accordance with claim 52, wherein the substep of roughening the surface of the sheet seal-ring area is performed by one of chemical etching, mechanical grinding, sandblasting and laser ablation.

54. A method in accordance with claim 53, wherein the sheet seal-ring area is roughened by removing material from the surface of the sheet to a depth within the range from about 0 inches to about 0.09 inches.

55. A cover assembly for a micro-device package manufactured in accordance with the method of claim 1.

56. A micro-device module including a micro-device encapsulated within a package having a cover assembly manufactured in accordance with the method of claim 1.

57. A cover assembly that can be welded to a micro-device package base to form a hermetically sealed micro-device package, the cover assembly including:

a weldable frame having a continuous sidewall defining a frame aperture therethrough, the sidewall including a frame seal-ring area circumscribing the frame aperture, the frame seal-ring area having a metallic surface;

a sheet of a transparent material having a window portion defined thereupon, the window portion having finished top and bottom surfaces, the sheet being hermetically bonded to the frame by preparing a sheet seal-ring area on the sheet, the sheet seal-ring area circumscribing the window portion, metallizing the prepared sheet seal-ring area of the sheet, positioning the frame against the sheet such that at least a portion of the frame seal-ring area and at least a portion of the sheet seal-ring area contact one another along a continuous junction region that circumscribes the window portion, and heating the junction region until a metal-to-metal joint is formed between the frame and sheet all along the junction region, whereby a hermetic seal circumscribing the window portion is formed.

58. A cover assembly in accordance with claim 57, wherein during the heating of the junction region, the temperature of the window portion of the sheet remains below the glass transition temperature (T_G) of the transparent material.

59. A micro-device module including:

a package base;

a micro-device mounted on the package base; and

a cover assembly welded to the package base so as to encapsulate the micro-device in a hermetically sealed cavity formed therebetween, the cover assembly including

a weldable frame having a continuous sidewall defining a frame aperture therethrough, the sidewall including a frame seal-ring area circumscribing the frame aperture, the frame seal-ring area having a metallic surface;

a sheet of a transparent material having a window portion defined thereupon, the window portion having finished top and bottom surfaces, the sheet being hermetically bonded to the frame by preparing a sheet seal-ring area on the sheet, the sheet seal-ring area circumscribing the window portion, metallizing the prepared sheet seal-ring area of the sheet, positioning the frame against the sheet such that at least a portion of the frame seal-ring area and at least a portion of the sheet seal-ring area contact one another along a continuous junction region that circumscribes the window portion, and heating the junction region until a metal-to-metal joint is formed between the frame and sheet all along the junction region, whereby a hermetic seal circumscribing the window portion is formed.

60. A micro-device module in accordance with claim 59, wherein during the heating of the junction region, the temperature of the window portion of the sheet remains below the glass transition temperature (T_G) of the transparent material.

61. A micro-device module in accordance with claim 60, wherein the coefficient of thermal expansion (CTE) of the package base, the CTE of the weldable frame, and the CTE of the transparent sheet are all within the range from about 5.0×

10<sup>−

6</sup>/°

K. to about 5.6×

10<sup>−

6</sup>/°

K. for the temperature range 30°

C. to 300°

C.