Strengthening ultrathin Si3N4 membranes by compressive surface stress

Abstract In this work, the effect of compressive surface stress on thin film membrane fracture was studied by bulge test. In order to create membranes with compressive residual stress at the surface, low-pressure chemical vapor deposition (LPCVD) Si3N4 membranes were coated with a 1-8 nm compressive SiNx adlayer or subjected to Ar-ion bombardment. Fracture strength analysis, done using finite element method and Weibull distribution, and microscope inspection of failed membranes showed that the pressure limit of the membranes is determined by the intrinsic fracture mode, caused by high stress induced at the membrane edge near the top surface. By creating compressive residual stress at the membrane surface, the maximum stress induced by the applied pressure was reduced and the fracture strength of the Si3N4 was increased from 17.3 GPa to 18.3 GPa. As a result, membranes with a compressive surface showed a 50% increase in pressure limit, from 5 kPa/nm to 7.5 kPa/nm.