Chapter 5: Surface Micromachining

Introduction

Historical Note

Mechanical Properties of Thin Films

Introduction

Adhesion

Stress in Thin Films

Stress in Thin Films—Qualitative Description

Stress in Thin Films on Thick Substrates—Quantitative Analysis

Thermal Stress

Intrinsic Stress

Stress-Measuring Techniques

Introduction

Disk Method

Uniaxial Measurements of Mechanical Properties of Thin Films

Biaxial Measurements of Mechanical Properties of Thin Films: Suspended Membrane Methods

Poisson Ratio for Thin Films

Other Surface Micromachined Structures to Gauge Intrinsic Stress

Clamped-Clamped Beams

Ring Crossbar Structures

Vernier Gauges

Lateral Resonators

Stress Nonuniformity Measurement by Cantilever Beams and Cantilever Spirals

Cantilever Beams

Cantilever Spirals

Strength of Thin Films

Surface Micromachining Processes

Basic Process Sequence

Fabrication Step Details

Pattern Transfer to SiO₂ Buffer/Isolation Layer

Base Layer (also Spacer or Sacrificial Layer) Deposition and Etching

Deposition of Structural Material

Selective Etching of Spacer Layer

Selective Etching

Etchant-Spacer-Microstructure Combinations

Stiction

Stiction during Release

In-Use Stiction

Control of Film Stress

Dimensional Uncertainties

Sealing Processes in Surface Micromachining

IC Compatibility

Poly-Si Surface Micromachining Modifications

Porous Poly-Si

Hinged Polysilicon

Thick Polysilicon

Milli-Scale Molded Polysilicon Structures

Surface Micromachining Modifications not Involving Polysilicon

SOI Surface Micromachining

Introduction

SOI Wafer Fabrication Techniques

SOI Use in MEMS

Overview

Creating Buried Cavities in Silicon by Silicon Fusion Bonded Micromachining

Fabricating Pressure Sensors in SIMOX Surface Micromachining

Selective Epitaxy Surface Micromachining

SOI versus Poly-Si Surface Micromachining

Resists as Structural Elements and Molds in Surface Micromachining

Introduction

UV Depth Lithography

Polyimide Surface Structures

Other Resists Used for UV Depth Lithography Surface Micromachining

Comparison of Bulk Micromachining with Surface Micromachining

Materials Case Studies

Introduction

Polysilicon Deposition and Material Structure

Introduction

Undoped Poly-Si

Doped Poly-Si

PECVD and Sputtered Polysilicon

Amorphous and Hydrogenated Amorphous Silicon

Undoped

Silicon Nitride

Introduction

PECVD Nitride

LPCVD Nitride

CVD Silicon Dioxides

Introduction

CVD Undoped SiO₂

CVD Phosphosilicate Glass Films

Metals in Surface Micromachining

Polycrystalline Diamond and SiC Films

Diamond

SiC

GaAs

Examples

5.1 Analog Devices Accelerometer

5.2 TI Micromirrors

5.3 Design of SOI Based High-Sensitivity Piezoresistive Cantilevers for Label-Less Sensing

Problems