Low temperature amorphous silicon sacrificial layer for controlled adhesion in MEMS devices

• US 8,358,458 B2
• Filed: 11/04/2010
• Issued: 01/22/2013
• Est. Priority Date: 06/05/2008
• Status: Expired due to Fees

• Current Assignee: Snaptrack Incorporated (Qualcomm, Inc.)
• Original Assignee: Qualcomm MEMS Technologies Incorporated (Qualcomm, Inc.)
• Inventors: Webster, James Randolph, Tu, Thanh Nghia, Yan, Xiaoming, Chung, Wonsuk
• Primary Examiner(s): PERT, EVAN T
• Application Number:
  US12/939,909
• Publication Number:
  US 20110051224A1
• Time in Patent Office: 810 Days
• Field of Search: 359/290, 359/291, 359/295
• US Class Current: 359/290
• CPC Class Codes: B81B 2201/042 Micromirrors, not used as optical switches
• CPC Class Codes: B81B 3/0008 Structures for avoiding electrostatic attraction, e.g. avoiding charge accumulation
• CPC Class Codes: B81C 2201/0107 Sacrificial metal
• CPC Class Codes: B81C 2201/0109 Sacrificial layers not provided for in B81C2201/0107 - B81C2201/0108
• CPC Class Codes: B81C 2201/115 Roughening a surface
• 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
• CPC Class Codes: Y10T 428/24917 including metal layer

Abstract

Methods of fabricating an electromechanical systems device that mitigate permanent adhesion, or stiction, of the moveable components of the device are provided. The methods provide an amorphous silicon sacrificial layer with improved and reproducible surface roughness. The amorphous silicon sacrificial layers further exhibit excellent adhesion to common materials used in electromechanical systems devices.

Claims

1. An unreleased MEMS substrate comprising:

an optical stack;

a sacrificial layer comprising amorphous silicon, wherein a thickness of the sacrificial layer is selected to provide a cavity suitable for interferometric modulation of light, after removal of the sacrificial layer; and

a metal layer overlaying and forming an interface with the sacrificial layer;

wherein the interface of the sacrificial layer and the metal layer comprises a surface roughness greater than about 1.0 nm RMS.

2. The unreleased MEMS substrate according to claim 1, wherein the interface has a roughness that is greater than about 1.5 nm RMS.

3. The unreleased MEMS substrate according to claim 1, wherein the interface has a roughness that is greater than about 1.8 nm RMS.

4. The unreleased MEMS substrate according to claim 1, wherein the sacrificial layer comprises a lower region and an upper region, the lower region being compositionally distinct from the upper region.

5. The unreleased MEMS substrate according to claim 4, wherein the lower region has enhanced adhesion to the optical stack, as compared to the upper region.

6. The unreleased MEMS substrate according to claim 5, wherein the lower region comprises one or more of a silicon oxide, a silicon nitride, a silicon oxynitride, and amorphous silicon.

7. The unreleased MEMS substrate according to claim 1, wherein the metal layer comprises aluminum.

8. The unreleased MEMS substrate according to claim 1, wherein the optical stack comprises a dielectric layer.

9. The unreleased MEMS substrate according to claim 8, wherein the dielectric layer comprises a dielectric material selected from a silicon oxide and an aluminum oxide.

10. The unreleased MEMS substrate according to claim 1, wherein the optical stack comprises an electrode layer and a partially reflective layer.