Process control monitors for interferometric modulators

• US 20060077381A1
• Filed: 11/17/2005
• Published: 04/13/2006
• Est. Priority Date: 09/27/2004
• Status: Active Grant

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Cummings, William, Gally, Brian
• Granted Patent: US 7,618,831 B2
• Time in Patent Office: Days
• US Class Current: 356/237.600
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81C 99/004 during manufacturing
• CPC Class Codes: G01N 21/55 Specular reflectivity
• CPC Class Codes: G01N 21/9501 Semiconductor wafers manufacturing processes per se of semiconductor devices implementing a measuring step H01L22/10
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26

Abstract

Process control monitors are disclosed that are produced using at least some of the same process steps used to manufacture a MEMS device. Analysis of the process control monitors can provide information regarding properties of the MEMS device and components or sub-components in the device. This information can be used to identify errors in processing or to optimize the MEMS device. In some embodiments, analysis of the process control monitors may utilize optical measurements.

Claims

1. A method of monitoring the extent of etching of a first material positioned between and adjacent to two layers of other material during manufacturing of a micro-electro-mechanical system (MEMS), comprising:

manufacturing a process control monitor that comprises the two layers of other material and the first material disposed between and adjacent to the two layers, wherein one of the two layers comprises a hole;

exposing the hole to an etchant; and

optically detecting a distance from the center of the hole to where the etchant has etched away the first material, whereby the distance is indicative of the extent of etching of the first material.

2. The method of claim 1, wherein the optical detecting comprises detecting reflectance of light from a side of the process control monitor where the first material and the two layers of other material are deposited during manufacturing of the process control monitor.

3. The method of claim 1, wherein the optical detecting comprises detecting reflectance of light from a side of the process control monitor opposite the side where the first material and the two layers of other material are deposited during manufacturing of the process control monitor.

4. The method of claim 1, wherein the MEMS includes interferometric modulators and the first material is a sacrificial layer that determines positioning of a mechanical membrane relative to other layers in the interferometric modulators.

5. The method of claim 4, wherein the first material is molybdenum.

6. The method of claim 4, wherein the first material is silicon.

7. The method of claim 1, wherein the hole is photolithographically created.

8. The method of claim 1, wherein substantially different reflectivity in the visible spectrum is detected where the etchant has etched away the first material as compared to where the etchant has not etched away the first material.

9. The method of claim 1, wherein the optical detecting includes visually observing the process control monitor.

10. The method of claim 1, wherein the optical detecting includes detecting light reflected from the process control monitor with a camera.

11. The method of claim 1, wherein the optical detecting comprises visually observing the distance.

12. The method of claim 1, wherein the optical detecting is performed while exposing the hole to the etchant.

13. The method of claim 1, wherein the optical detecting is performed after exposing the hole to the etchant.

14. The method of claim 13, wherein the optical detecting is performed after removing the process control monitor from an etchant chamber.

15. The method of claim 1, wherein the manufacturing comprises forming a plurality of posts in the process control monitor that support the separation of the two layers of other material after removal of the first material.

16. The method of claim 15, wherein the posts are used as a vernier to determine said distance.

17. A wafer, comprising:

a plurality of structures comprising a sacrificial layer and at least one layer above and adjacent to the sacrificial layer, wherein the structures become interferometric modulators upon removal of the sacrificial layer, wherein the at least one layer above and adjacent to the sacrificial layer comprises a plurality of holes through which an etchant can reach the sacrificial layer; and

a process control monitor also comprising the sacrificial layer and the at least one layer above and adjacent to the sacrificial layer, wherein the at least one layer above and adjacent to the sacrificial layer in the process control monitor comprises multiple holes, wherein the distance between the holes in the process control monitor is greater than the distance between the plurality of holes in said plurality of structures.

18. The wafer of claim 17, wherein the distance between the holes in the interferometric modulators and the process control monitor are such that the etchant can substantially completely remove the sacrificial layer in the interferometric modulators before it can substantially completely remove the sacrificial layer in the process control monitor.

19. The wafer of claim 17, wherein the at least one layer above the sacrificial layer comprises a mechanical membrane that includes a mirror.

20. The wafer of claim 17, wherein the plurality of structures and the process control monitor are disposed on a substantially transparent substrate.

21. A wafer, comprising:

a plurality of structures comprising a sacrificial layer and at least one layer above and adjacent to the sacrificial layer, wherein the structures become interferometric modulators upon removal of the sacrificial layer, wherein the at least one layer above and adjacent to the sacrificial layer comprises a plurality of holes through which an etchant can reach the sacrificial layer; and

a process control monitor also comprising the sacrificial layer and the at least one layer above and adjacent to the sacrificial layer, wherein the at least one layer above and adjacent to the sacrificial layer in the process control monitor comprises a single hole.

22. The wafer of claim 21, wherein the single hole has a diameter substantially the same as the plurality of holes.

23. The wafer of claim 21, wherein the process control monitor is adapted so that the etchant can substantially completely remove the sacrificial layer in the interferometric modulators before it can substantially completely remove the sacrificial layer in the process control monitor.

24. The wafer of claim 21, wherein the distance between the single hole and the edges of the process control monitor is greater than the distance between the plurality of holes in said plurality of structures.

25. The wafer of claim 21, wherein the at least one layer above the sacrificial layer comprises a mechanical membrane that includes a mirror.

26. The wafer of claim 21, wherein the plurality of structures and the process control monitor are disposed on a substantially transparent substrate.

27. A method of manufacturing a wafer having a micro-electro-mechanical system (MEMS) and a process control monitor structure, the method comprising:

forming a plurality of structures, wherein forming the plurality of structures includes one or more material deposition and removal steps, wherein the structures comprise a sacrificial layer and at least one layer above and adjacent to the sacrificial layer, wherein the at least one layer above and adjacent to the sacrificial layer comprises a plurality of holes through which an etchant can reach the sacrificial layer;

simultaneously forming a process control monitor, wherein forming the process control monitor includes said one or more material deposition and removal steps, wherein the process control monitor also comprises the sacrificial layer and the at least one layer above and adjacent to the sacrificial layer, wherein the at least one layer above and adjacent to the sacrificial layer in the process control monitor comprises multiple holes, wherein the distance between the holes in the process control monitor is greater than the distance between the plurality of holes in said plurality of structures; and

exposing the plurality of structures and the process control monitor to an etchant.

28. The method of claim 27, wherein the process control monitor is formed with a structure different from the plurality of structures by applying at least one different patterning step.

29. The method of claim 28, wherein the different patterning step comprises defining a pattern for the multiple holes in the process control monitor.

30. A wafer, comprising:

a micro-electro-mechanical structure (MEMS); and

means for measuring extent of etching of a material removed during manufacturing of the MEMS.

31. The wafer of claim 30, wherein the means comprises a process control monitor.

32. The wafer of claim 30, wherein the MEMS comprises an interferometric modulator.

33. The wafer of claim 32, wherein the material comprises a sacrificial layer that determines the depth of a gap in the interferometric modulator.

34. A process control monitor produced by process comprising:

depositing at least three layers of material on top of each other; and

forming a hole in the top layer of material.