• PDF / 1,300,399 Bytes
• 2 Pages / 612 x 792 pts (letter) Page_size
• 91 Downloads / 163 Views

DOWNLOAD

REPORT

Surface

Micromachining: A Brief Introduction

Mehran Mehregany and Christian A. Zorman The rapid expansion of microelectromechanical systems (MEMS) into new application areas is due in large part to the development of surface-micromachining techniques that allow the fabrication of a wide variety of MEMS devices with structural components that can execute motion in at least one direction. In general terms, surface micromachining involves the deposition, photolithographic patterning, and selective etching of multilayered thin films to form the device structures. Unlike bulk micromachining, where select regions of the substrate are etched to form the desired structure, the substrate in surface micromachining provides little more than mechanical support for the device. An essential part of surface micromachining is the use of sacrificial thin films that serve initially as a platform for the deposition and patterning of the structural layers; they are later dissolved to release the freestanding micromechanical components of the device. By using mulitlayered thin films in conjunction with selective etching, surface micromachining enables the fabrication of complex, micrometer-scale structures that would be difficult, if not impossible, to create with bulk micromachining techniques. Surface micromachining is arguably the most versatile micromachining technology for several key reasons. First, surface micromachining is an additive process that is accomplished by thin-film deposition techniques, enabling the fabrication of complex, multilevel structures. Second, the patterning of structural and sacrificial layers is typically accomplished by wet- and/or dryetching processes that are relatively insensitive to the microstructure of the film, thereby providing great flexibility for planar, free-form designs. Finally, there is no inherent restriction on the structural and sacrificial layers used in a particular process, so long as the compatibility between the two materials, in terms of such properties as etch selectivity, is maintained. MRS BULLETIN/APRIL 2001

Without question, the most widely used material system for surface micromachining to date uses polycrystalline silicon (polysilicon) as the structural material, silicon dioxide (SiO2) as the sacrificial material, silicon nitride as an electrical isolation layer, and single-crystal silicon as the substrate. Polysilicon is typically grown on the sacrificial silicon dioxide layers by low-pressure chemical vapor deposition (LPCVD) at temperatures between 580C and 650C in a silane atmosphere. Deposition pressures range from 100 mTorr to 400 mTorr. As with single-crystal silicon, the resistivity of polysilicon can be modified by doping, either from solid or gaseous sources during film growth. SiO2 is an excellent sacrificial material because polysilicon films adhere well to silicon dioxide surfaces, and hydrofluoric acid (HF), which does not etch silicon, can be used as a sacrificiallayer etchant. The simplest process for the growth of SiO2 layers is thermal oxidation of s

Recommend Documents

A Brief Introduction

167 34 3MB

A Brief Introduction

168 103 5MB

A Brief Introduction

207 6 6MB

A Brief Historical Introduction

196 44 5MB

Brief Introduction

158 28 23MB

Understanding Pendulums A Brief Introduction

177 108 492KB

Landscape Theories A Brief Introduction

163 34 5MB

High-Entropy Materials A Brief Introduction

205 63 11MB

A Brief Introduction to MEMS and NEMS

218 26 2MB

Malunions: Introduction and Brief Overview

211 35 24MB

News and views on meat: a brief introduction

175 110 95KB

Modern Poisons A Brief Introduction to Contemporary Toxicology

136 63 3MB