Reducing MEMS stiction by introduction of a carbon barrier

• US 9,463,973 B2
• Filed: 10/31/2014
• Issued: 10/11/2016
• Est. Priority Date: 12/18/2012
• Status: Expired due to Fees

• Current Assignee: NXP USA, Inc. (NXP Semiconductors NV)
• Original Assignee: Freescale Semiconductor, Inc. (NXP Semiconductors NV)
• Inventors: Montez, Ruben B., Steimle, Robert F.
• Primary Examiner(s): ZHU, SHENG-BAI
• Application Number:
  US14/529,824
• Publication Number:
  US 20150054096A1
• Time in Patent Office: 711 Days
• Field of Search: 257/415, 735/143.2, 333/186, 333/197, 438/77
• US Class Current: 1/1
• CPC Class Codes: B81B 2201/0221 Variable capacitors
• CPC Class Codes: B81B 2201/0235 Accelerometers
• CPC Class Codes: B81B 2203/0181 See-saws
• CPC Class Codes: B81B 2203/06 Devices comprising elements which are movable in relation to each other, e.g. slidable or rotatable
• CPC Class Codes: B81B 3/0005 Anti-stiction coatings
• CPC Class Codes: B81C 1/0038 Processes for creating layers of materials not provided for in groups B81C1/00357 - B81C1/00373
• CPC Class Codes: B81C 1/00952 Treatments or methods for avoiding stiction during the manufacturing process not provided for in groups B81C1/00928 - B81C1/00944
• CPC Class Codes: B81C 2201/0169 by post-annealing
• CPC Class Codes: B81C 2201/112 Depositing an anti-stiction or passivation coating, e.g. on the elastic or moving parts
• CPC Class Codes: G01P 15/0802 Details
• CPC Class Codes: G01P 2015/0871 using stopper structures for limiting the travel of the seismic mass
• CPC Class Codes: G01P 2015/0874 using means for preventing stiction of the seismic mass to the substrate

Abstract

A mechanism for reducing stiction in a MEMS device by decreasing an amount of carbon from TEOS-based silicon oxide films that can accumulate on polysilicon surfaces during fabrication is provided. A carbon barrier material film is deposited between one or more polysilicon layer in a MEMS device and the TEOS-based silicon oxide layer. This barrier material blocks diffusion of carbon into the polysilicon, thereby reducing accumulation of carbon on the polysilicon surfaces. By reducing the accumulation of carbon, the opportunity for stiction due to the presence of the carbon is similarly reduced.

Claims

1. A microelectromechanical systems (MEMS) device comprising:

a fixed surface comprising a first polysilicon layer formed over a substrate and a first insulating layer formed over at least a portion of the first polysilicon layer;

a moveable body comprising a second polysilicon layer providing a major surface facing the fixed surface; and

a carbon barrier layer formed on the major surface of the second polysilicon layer, wherein the carbon barrier layer comprises silicon-germanium-carbon.

2. The MEMS device of claim 1 wherein the carbon barrier layer comprises:

a thickness sufficient to prevent diffusion of carbon into the adjacent polysilicon layer from a TEOS sacrificial layer used during manufacture of the MEMS device.

3. The MEMS device of claim 2 wherein the thickness of the carbon barrier layer is at least about 45 nm.

4. The MEMS device of claim 1 wherein the MEMS device is an accelerometer.

5. An electronic device comprising the MEMS device of claim 1.

6. The MEMS device of claim 4 wherein the moveable body is a pivoting proof mass of the accelerometer.

7. The MEMS device of claim 6 wherein the pivoting proof mass comprises a travel stop configured to impact the fixed surface in event of extreme acceleration.

8. The MEMS device of claim 7 wherein the major surface of the second polysilicon layer comprises the travel stop region.