AVS 46th International Symposium
    The Science of Micro-Electro-Mechanical Systems Topical Conference Thursday Sessions
       Session MM+MI-ThM

Paper MM+MI-ThM9
Residual Stress Characterization of Thick PECVD Oxide Films for MEMS Applications

Thursday, October 28, 1999, 11:00 am, Room 620

Session: Processing and Integration Technology
Presenter: R. Ghodssi, Massachusetts Institute of Technology
Authors: R. Ghodssi, Massachusetts Institute of Technology
X. Zhang, Massachusetts Institute of Technology
K.-S. Chen, Massachusetts Institute of Technology
K.A. Lohner, Massachusetts Institute of Technology
M. Spearing, Massachusetts Institute of Technology
M.A. Schmidt, Massachusetts Institute of Technology
Correspondent: Click to Email
Vapor deposited films are of vital importance in many sensors and actuators where they are used to form electrical or mechanical elements. In order to achieve higher electrical and mechanical power levels, thicker films are often desired. However, the deleterious effects of residual stress tend to increase with film thickness. In particular, excessive wafer bow and even cracking may prohibit integration within a micro-device. This paper presents residual stress characterization for PECVD Novellus@super TM@ oxide films with thicknesses in the range of 10 - 40 µm. These films are deposited at 400°C and densified at 1100°C in a nitrogen environment. Wafer curvature measurements were performed to investigate the residual stress in the thick PECVD oxide films as a function of temperature. These results show that the residual stress in thick PECVD oxide films is a combination of both thermal expansion mismatch stress and an intrinsic stress due to the deposition process and resulting microstructure. Furthermore, the densification step plays an important role in determining the residual stress state. For instance, a 10 µm thick PECVD oxide film exhibits a wafer bow of 50 µm and 250 µm before and after densification, respectively. Additional high temperature experiments indicated that cracks formed at temperatures between deposition and densification. The tendency to form cracks is a strong function of film thickness. For films thicker than 15 µm, cracks formed in the film at temperature below 1100°C. Laminated plate theory has been applied to extract residual stress data for the curvature measurements. This data is then correlated with the deposition and densification conditions to guide process development so as to reduce wafer curvature and to eliminate cracking.