Strengthening ultrathin Si3N4 membranes by compressive surface stress

[Display omitted] •Fracture strength of Si3N4 thin film membranes is studied using bulge test.•Compressive surface stress is created by Ar-ion bombardment or coating with an adlayer.•Two failure modes of membranes under applied pressure identified: extrinsic and intrinsic.•Compressive stress at the surface reduces max stress under load and increases fracture strength.•As a result, burst pressure is increased by 50 %. 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.