%0 Journal Article
%T Synthesis and Characterization of LPCVD Polysilicon and Silicon Nitride Thin Films for MEMS Applications
%A N. Sharma
%A M. Hooda
%A S. K. Sharma
%J Journal of Materials
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/954618
%X Inherent residual stresses during material deposition can have profound effects on the functionality and reliability of fabricated MEMS devices. Residual stress often causes device failure due to curling, buckling, or fracture. Typically, the material properties of thin films used in surface micromachining are not very well controlled during deposition. The residual stress, for example, tends to vary significantly for different deposition conditions; experiments were carried out to study the polysilicon and silicon nitride deposited by Low Pressure Chemical Vapor Deposition (LPCVD) method at wide range of process conditions. High temperature annealing effects on stress in case polysilicon are also reported. The reduced residual stress levels can significantly improve device performance, reliability, and yield as MEMS devices become smaller. 1. Introduction The deposition of thin films is an important field of Micro Electro Mechanical Systems (MEMS) or micro system technology. Most of the thin films exhibit stress after deposition. This stress has many different causes. Most films are deposited at elevated temperature. If the thermal expansions of the film and substrate are not identical there will be stress between them after cooling. Other sources are lattice mismatch, crystallization, atomic peening, incorporation of foreign atoms, microscopic voids, variation of interatomic spacing with crystal size, crystallite coalescence at grain boundaries, phase transformations, and texture effect. Sometimes this stress is called internal stress or residual stress. This stress may cause problem for thin film technology. It changes the behavior of the thin films often in an uncontrolled manner (Figure 1 shows the one of the structure under stress), reducing the yields and long term durability and sometimes causing fracture. Many researchers had investigated the mechanical response of thin films, for example. Frequently, each particular investigation involving MEMS tends to be device dependent; type of film used and deposition methods adopted, and introduces new fundamental questions. Progress in this field has leaned towards providing more specific technological solutions rather than generating a basic understanding of mechanical behavior. Figure 1: Effect of residual stress on free standing structure. In the recently developed technology of microsystem, more and more standing thin film structures are used, for example, resonator, movable parts in surface micromachining, thin film membranes, and cantilever beams in transduction [1, 2]. For these applications, the
%U http://www.hindawi.com/journals/jma/2014/954618/