Stress stability of PECVD silicon nitride films during device fabrication

Conventional, dense dielectrics serve as structural elements in Cu/low-k interconnect structures, and a full understanding of their thermo-mechanical properties is desired to help optimize device fabrication and avoid mechanical failure. Wafer curvature measurements were made on plasma-enhanced chemical vapor deposited (PECVD) silicon nitride films during thermal cycling to explore the large, irreversible, tensile stress developed. Spectroscopic techniques were used to probe the composition and structure of the films after annealing steps and indicate that reaction of hydrogen-containing defects provides the mechanism for stress change. A simple kinetic model, modified by the inclusion of an equilibrium function of hydrogen defects, is proposed and is found to adequately describe stress development.