ELECTRON-CYCLOTRON-RESONANCE PLASMA CHEMICAL-VAPOR-DEPOSITED SILICON-NITRIDE FOR MICROMECHANICAL APPLICATIONS

We have studied the electron cyclotron resonance plasma chemical vapor deposition (ECR PCVD) of silicon nitride films onto unheated substrat es to evaluate their potential for use in micromechanical devices. We demonstrate that this low temperature process (<120 degrees C) is comp atible with lift-off patterning of both thin and thick films. We measu red the deposition rate, stress and buffered HF (BHF) etch rate for di fferent gas flows of silane, nitrogen and argon. The deposition rate i s rate controlled by the silane flow and we obtained rates sufficientl y high (0.7-1.4 mu m/h) to obtain films for practical use in micromech anics (0.5-2 mu m) in about 1 h. We measured stresses ranging from 100 0 MPa compressive to 60 MPa tensile, and we can repeatedly obtain film s with stress of less than 10 MPa. These films are ideal for both low- stress and stress-compensated device designs. We observed BHF (NH4F:HF 6:1 at 20 degrees C) etch rates from 5 nm/min to 150 nm/min, which ar e five times faster than those for films deposited by CVD. ECR films a re ideal for fast etched sacrificial layers at 150 nm/min or as slowly etched masking layers at 5 nm/min. We found that stress and the BHF e tch rate were strongly correlated: low etch rates are observed for hig hly compressively stressed films and high etch rates for lower stress. This correlation has a major impact on the design of micromechanical devices and on their fabrication processes using ECR PCVD. (C) 1998 Am erican Vacuum Society. [S0734-2101(98)08502-9].