AVS 52nd International Symposium
    Applied Surface Science Thursday Sessions
       Session AS+TF-ThM

Paper AS+TF-ThM6
Microbridge Testing of Plasma Enhanced Chemical Vapor Deposited Silicon Oxide Films on Silicon Wafers

Thursday, November 3, 2005, 10:00 am, Room 206

Session: Thin Film Characterization
Presenter: Z. Cao, Boston University
Authors: Z. Cao, Boston University
T.-Y. Zhang, Hong Kong University of Science and Technology
X. Zhang, Boston University
Correspondent: Click to Email
Plasma-enhanced chemical vapor deposited (PECVD) silane-based oxides (SiOx) have been widely used in both microelectronics and MEMS (MicroElectroMechanical Systems) to form electrical and/or mechanical components. During fabrication of such microelectronic and MEMS devices, PECVD SiOx undergo many thermal cycles, which often causes unwanted changes in thermal-mechanical properties of the material, and consequent degradation of device performance and reliability. In this paper, a novel nanoindentation-based microbridge testing method for thin films is proposed to measure both the residual stresses and Young's modulus of PECVD SiOx thin films. In this method, freestanding microbridges are fabricated from the thin films using the micromachining techniques. The tests are performed at the center of the microbridges with an instrumented nanoindentation system and the load-deflection curves are recorded. Our theoretical model used a closed formula of deflection vs. load, considering both substrate deformation and residual stress in the thin film. To simulate real thermal processing in device fabrication, some microbridges underwent various rapid thermal annealing (RTA) at temperatures up to 800ºC. An interferometric microscope was also used to measure the curvature profiles of the bridges. Together with nanoindentation test results on the microbridges, we were able to decide the changes in residual stresses and Youngâ?Ts modulus of the PECVD SiOx thin films under different thermal annealing. Two factors, density change and plastic deformation, were identified as controlling mechanisms of stress changes in the films. A microstructure based mechanism elucidates "seams" as source of density change and "voids" as source of plastic deformation, accompanied by viscous flow. This mechanism was applied to explain our experimental results of thermal annealing of PECVD SiOx films.