Evaluation of Plasma Deposited Silicon Nitride Thin Flims for Microsystems Technology

Plasma deposited silicon nitride thin films were deposited at temperatures between 150 degrees C and 300 degrees C. Diagnostic microstructures were fabricated from the thin films using bulk micromachining, and the strain was calculated from optical measurement of postbuckling deflection. The results indicate that the residual strain of the thin films is dominated by film-substrate thermal mismatch, with the coefficient of thermal expansion monotonically increasing with decreasing deposition temperature. Metal-insulator-metal devices of variable area were also fabricated to measure the dielectric constant, which was shown to be independent of deposition temperature. The importance of these results to microsystems technology (MST) was briefly discussed.