Nanoindentation fracture and fatigue characterization of PECVD silicon nitride films subjected to rapid thermal annealing

• Fracture and fatigue behaviors of PECVD silicon nitrides after RTA are investigated.
• We believe that the effect of RTA duration is first time to be investigated.
• Elastic properties vs. RTA temperature and duration are characterized and explained.
• Interfacial strength can be improved by RTA.
• A good correlation is observed between the nitride toughness and their fatigue crack growth rate.

In this work, the fracture and fatigue behaviors of PECVD silicon nitride films deposited on silicon substrates after rapid thermal annealing were characterized. Specimens were fabricated using different fabrication parameters and post-deposition annealing temperatures and duration. Indentation methods were primarily used for qualitatively examining the effect of process conditions on the resultant mechanical properties. The experimental results indicated that the residual stress, fracture toughness, interfacial strength, and fatigue crack propagation, strongly depend on the processing conditions, such as deposition temperatures, chamber pressures, temperature, and duration of annealing. Specifically, preliminary results indicated that the specimen deposited at a lower temperature and a lower pressure exhibited much less residual tensile stress and better interface strength. Meanwhile, the study of rapid thermal annealing duration on the film stress demonstrated that the evolution of the residual stress was mainly controlled by the intrinsic stress generation dynamics and stress relaxation. It was also found that rapid thermal annealing could enhance the interfacial strength but the high tensile stress generated could actually reduce the equivalent toughness and lead to structural reliability concerns. In sum, the characterization results should provide useful information for correlating mechanical reliability and processing parameters for future structural design optimization and for improving the structural integrity of PECVD silicon nitride films for MEMS and IC fabrication.