Evaluation of plasma process-induced damage to off-stoichiometric SiN<i>x</i> films

Various SiN films—stoichiometric (Si3N4) and off-stoichiometric (SiNx) films—have been implemented in electronic devices. These films are exposed to process plasmas leading to create defects referred to as plasma process-induced damage (PID), which should be clarified in detail. We investigated the effects of PID on the optical, mechanical, and electrical properties of various SiNx films. For optical analysis using spectroscopic ellipsometry, a damaged SiNx film was modeled with an optical structure of the SiO2/interfacial layer (IL)/bulk SiNx, where IL was assumed to be a mixture of SiO2 and SiNx. A thicker IL was formed in Si-rich SiNx films than in N-rich SiNx films. For the mechanical analysis using a cyclic nanoindentation, a larger increase in contact stiffness by PID was assigned for Si-rich SiNx films. For the electrical analysis, the current–voltage and capacitance–voltage characteristics were measured. A larger decrease in leakage current (Ileak) by PID was identified for Si-rich SiNx films than for N-rich SiNx films, while a slight increase in Ileak in the lower bias voltage region was observed only for the latter. The shift in capacitance–voltage curve, attributed to the creation of carrier trapping sites, was larger for Si-rich SiNx films. These results suggest that Si-rich SiNx films suffer from greater PID due to the creation of numerous defects, presumably because of the lower Si–Si bonding energy. The defects created in the form of broken bonds induced fatigue (such as elastic property change) and carrier trapping in the mechanical and electrical characterizations, respectively.