# US 9,434,602 B2 · Reducing MEMS stiction by deposition of nanoclusters

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- Number: US 9,434,602 B2
- Document ID: US9434602B2
- Status: Granted
- Kind: B2
- Application number: 14/446,910
- Filed: 2014-07-30
- Published: 2016-02-04
- Granted: 2016-09-06
- Earliest claimed: 2014-07-30
- Assignees: Freescale Semiconductor, Inc.
- Applicants: Robert F. Steimle; Ruben B. Montez
- Inventors: Robert F. Steimle; Ruben B. Montez
- Web page: https://patentgrep.com/patent/US9434602B2

## CPC

- B81B 3/001: {Structures having a reduced contact area, e.g. with bumps or with a textured surface}
- B81B 2201/0235: Accelerometers
- B81B 2203/0181: See-saws
- B81B: MICROSTRUCTURAL DEVICES OR SYSTEMS, e.g. MICROMECHANICAL DEVICES (piezoelectric, electrostrictive or magnetostrictive elements per se H10N30/00, H10N35/00)

## Abstract

Certain microelectromechanical systems (MEMS) devices, and methods of creating them, are disclosed. The method may include forming a structural layer over a substrate; forming a mask layer over the structural layer, wherein the mask layer is formed with a material selective to an etching process; forming a plurality of nanoclusters on the mask layer; and etching the structural layer using at least the etching process.

## Claims

### Claim 1

A method for manufacturing a microelectromechanical systems (MEMS) device, the method comprising:
forming a structural layer over a substrate;
forming a mask layer over the structural layer, wherein the mask layer is formed with a material selective to an etching process;
forming a plurality of nanoclusters on the mask layer;
using the nanoclusters as a mask for removing portions of the mask layer; and
etching the structural layer using remaining portions of the mask layer as a mask for the etching of the structural layer forming a plurality of surface roughness features on a travel stop of the MEMS device.

### Claim 2 (depends on 1)

The method of claim 1, wherein the etching process comprises:
a first etching process for the removing portions of the mask layer; and
a second etching process operable to etch the structural layer.

### Claim 3 (depends on 2)

The method of claim 2, wherein performing the second etching process further comprises removing the plurality of nanoclusters.

### Claim 4 (depends on 1)

The method of claim 1, wherein the etching process comprises an anisotropic etch.

### Claim 5 (depends on 1)

The method of claim 1, wherein the etching process comprises an isotropic etch.

### Claim 6 (depends on 1)

The method of claim 1, further comprises:
forming a sacrificial layer on the etched structural layer; and
forming a second structural layer over the sacrificial layer.

### Claim 7 (depends on 6)

The method of claim 6, further comprising planarizing a portion of the sacrificial layer prior to forming the second structural layer.

### Claim 8 (depends on 1)

The method of claim 1, wherein a nanocluster comprises one of silicon carbide, silicon germanium, polysilicon, silicon, or germanium, wherein the nanocluster is one of the plurality of nanoclusters.

### Claim 9 (depends on 1)

The method of claim 1, wherein the structural layer comprises a polysilicon layer.

### Claim 10 (depends on 1)

The method of claim 1, wherein the material selective to the etching process comprises a silicon oxide.

### Claim 11

A method for manufacturing a microelectromechanical systems (MEMS) device, the method comprising:
forming a structural layer over a substrate;
forming a mask layer over the structural layer;
forming a plurality of nanoclusters on the mask layer;
using the nanoclusters as a mask for removing portions of the mask layer; and
etching the structural layer using remaining portions of the mask layer as a mask for the etching of the structural layer forming a plurality of surface roughness features of a travel stop feature of the MEMS device; and
forming a movable body, wherein the structural layer forms a fixed surface having a portion facing a major surface of the movable body, and the fixed surface is operable to contact at least a portion of the plurality of surface roughness features.

### Claim 12 (depends on 11)

The method of claim 11, further comprising:
forming a sacrificial layer on the etched structural layer; and
forming a second structural layer over the sacrificial layer.

### Claim 13 (depends on 11)

The method of claim 11, wherein the movable body comprises:
a pivoting proof mass of a teeter-totter accelerometer;
the travel stop feature is configured to contact the structural layer to prevent over rotation of the pivoting proof mass, and comprises a portion of the major surface facing the fixed surface.

### Claim 14 (depends on 13)

The method of claim 13, wherein:
a portion of the travel stop feature is formed using a process comprising:
forming a sacrificial layer on the etched structural layer; and
forming a second structural layer over the sacrificial layer.

### Claim 15 (depends on 14)

The method of claim 14, wherein the portion of the travel stop feature is formed using a process further comprising planarizing a portion of the sacrificial layer prior to forming the second structural layer.

### Claim 16 (depends on 11)

The method of claim 11, wherein the plurality of nanoclusters are formed of one of silicon carbide, silicon germanium, polysilicon, silicon, or germanium.