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0904-BB04-21.1

Rate Sensitivity and Size Effects in Plasma-Enhanced Chemical Vapor Deposited Silicon Oxide Films Zhiqiang Cao and Xin Zhang Department of Manufacturing Engineering, Boston University, Boston, MA 02215, U.S.A. ABSTRACT Plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiOx) thin films have been widely used in MEMS to form electrical and mechanical components. In this paper, both the time-independent and the time-dependent plastic responses of the PECVD SiOx films were studied by the instrumented nanoindentation experiments. Our experiments found an enhanced rate-sensitivity and size-effect in the plastic responses of the PECVD SiOx thin films. In addition, the plastic flow behavior is more homogeneous compared with most inorganic glasses and many metallic glasses. The deformation mechanism in the PECVD SiOx thin films is depicted by the shear transformation zone (STZ) based amorphous plasticity theory. The physical origin of the STZ is elucidated and linked with the plastic deformation dynamics.

INTRODUCTION Plasma-enhanced chemical vapor deposited (PECVD) silicon oxide (SiOx) thin films have been widely used in Micro Electro Mechanical Systems (MEMS) to form both electrical and mechanical components [1, 2]. Specifically, in Power MEMS (micro energy-harvesting devices such as micro heat turbine engines and related components) [3], PECVD SiOx serves as the insulation layers, and endures a high level of stress even at low temperatures [4]. Severe plastic deformations in the PECVD SiOx thin films often occur, which cause device degradation or even prohibit process integration. So far, however, the plastic properties of the PECVD SiOx, especially at lower temperatures, are not well understood. Depth-sensing instrumentation, or nanoindentation is a popular technique widely used for the estimation of mechanical properties of materials down to nanoscale. It can reveal a wealth of detailed information about the mechanisms and mechanics of the studied thin film materials, including elastic modulus, hardness, surface adhesion, creep, and stress relaxation behaviors, etc [5, 6]. In this paper, two types of nanoindentation experiments, constant rate of loading (CRL) and indentation load relaxation (ILR), were conducted on the blank PECVD SiOx films. Both the time-independent and the time-dependent plastic responses were studied. In addition, the influence of nanoindentation size effects was investigated by employing two different nanoindenter tips, one with a sharp (~150 nm) and one with a blunt radius (~5 µm). Our results indicate that the plastic flow behavior in the PECVD SiOx thin films is more homogeneous, and qualitatively different from the typical inorganic glasses [7] and many metallic glasses [8, 9]. In addition, enhanced rate-sensitivity and size-effect were observed. The unique plastic deformation behavior is explained by the shear transformation zone (STZ) based amorphous plasticity theory [10-14]. The physical origin of the STZ is elucidated and linked with the plastic deformation dy