Process control monitors for interferometric modulators

• US 7,403,323 B2
• Filed: 11/17/2005
• Issued: 07/22/2008
• Est. Priority Date: 09/27/2004
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: IDC, LLC
• Inventors: Cummings, William, Gally, Brian
• Primary Examiner(s): Ben; Loha
• Application Number:
  US11/281,176
• Publication Number:
  US 20060066872A1
• Time in Patent Office: 978 Days
• Field of Search: 359290-295, 359/298, 359/245, 359/247, 359/254, 359/577, 359/578, 359/585, 359/588, 359/237, 356/32, 356/519, 356/352, 356/45, 356/450, 356/237.6, 356/503, 356/504, 356/506, 430/321, 438/16, 438/21, 438/29, 438/48, 438/222, 345 84- 86, 345/88, 385/147, 216/11, 257/499
• US Class Current: 359/291
• 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 testing a process used to manufacture a polychromatic interferometric modulator display, wherein different color interferometric modulators in the display are manufactured by forming different depth gaps between a partial reflector and a reflective mechanical membrane, wherein the depth of at least one gap is determined by deposition of one or more sacrificial layers, the method comprising:

forming a process control monitor that comprises the one or more sacrificial layers, wherein at least one region of the process control monitor comprises a plurality of sacrificial layers deposited on top of each other;

measuring a profile of the process control monitor; and

determining a cumulative thickness of the one or more sacrificial layers from the profile.

2. The method of claim 1, wherein forming the process control monitor comprises:

sequentially depositing the plurality of sacrificial layers; and

patterning each sacrificial layer after its deposition and before depositing another sacrificial layer so that regions of the process control monitor are formed where less than all of the plurality of sacrificial layers are present.

3. The method of claim 1, wherein forming the process control monitor comprises depositing the mechanical membrane on top of the process control monitor so as to protect the sacrificial layers during an interferometric modulator release etch.

4. The method of claim 1, wherein measuring the profile of the process control monitor comprises:

measuring the thickness of the process control monitor in a region comprising a single sacrificial layer;

measuring the thickness of the process control monitor in a region comprising two sacrificial layers; and

measuring the thickness of the process control monitor in a region comprising three sacrificial layers.

5. The method of claim 1, wherein measuring the profile of the process control monitor comprises sweeping a profilometer across the process control monitor.

6. The method of claim 5, wherein the profilometer is swept once across the process control monitor.

7. The method of claim 1, comprising forming the different color interferometric modulators substantially simultaneously with the process control monitor.

8. The method of claim 7, wherein the different color interferometric modulators and the process control monitor are formed by applying an identical sequence of material deposition steps.

9. The method of claim 1, wherein the profile of the process control monitor comprises at least two steps.

10. The method of claim 9, comprising determining the heights of the steps.

11. The method of claim 9, wherein steps in the process control monitor monotonically increase and then monotonically decrease from one side of the profile to the other.

12. The method of claim 9, wherein at least one step in the process control monitor consists of one or more dielectric layers.

13. The method of claim 9, wherein at least one step in the process control monitor consists of a mechanical membrane structure.

14. The method of claim 9, wherein the height of at least one step in the process control monitor is substantially determined by the thickness of a sacrificial layer.

15. The method of claim 9, wherein the height of at least one step in the process control monitor is substantially determined by the thickness of planar material.

16. The method of claim 1, wherein the process control monitor is formed on a substrate.

17. The method of claim 16, wherein the different color interferometric modulators are also formed on the substrate.

18. The method of claim 16, comprising cutting the substrate to remove the process control monitor.

19. The method of claim 1, wherein the process control monitor comprises planar material between regions comprising sacrificial layers.

20. The method of claim 1, wherein the depth of the gap determined by one of the one or more sacrificial layers is such that an interferometric modulator having that depth reflects predominately red light.

21. The method of claim 1, wherein the depth of the gap determined by one of the one or more sacrificial layers is such that an interferometric modulator having that depth reflects predominately green light.

22. The method of claim 1, wherein the depth of the gap determined by one of the one or more sacrificial layers is such that an interferometric modulator having that depth reflects predominately blue light.

23. The method of claim 1, wherein one of the one or more sacrificial layers comprises one or more of polysilicon, amorphous silicon, or photoresist.

24. The method of claim 1, wherein one of the one or more sacrificial layers comprises molybdenum.