Investigation of the Mechanical/Thermal Properties of Nano-Scale Silicon Nitride Membranes

In micro/nano electro-mechanical system, silicon nitride (SiNx) membrane has been widely used in sensors, energy harvesting and optical filters because of its mechanical/chemical stability. However, it is necessary to verify mechanical and thermal properties of nanoscale SiNx membranes to ensure the desirable reliability and durability of a device because the properties of nanoscale films vary with thickness which is severely depending on changes in density, grain size, and crystallinity. In this paper, SiNx membranes were fabricated by low pressure chemical vapor deposition followed by reactive ion etching and KOH wet etching. The composition, surface roughness, thickness uniformity and residual stress of the deposited SiNx films were measured to confirm the reliability of the deposition process. Plane-strain modulus, failure stress and emissivity were evaluated by bulge test and heat load test. As a result, the failure stress of the membrane was enhanced by decreasing SiNx thickness while the plane-strain modulus was insensitive to the thickness variation. Through the UV laser heat-load test, it was found that the thermal durability of the thinner membrane deteriorated due to decreased emissivity. To investigate the emissivity depending on membrane thickness, a finite element method simulation was performed based on the experimental results. The calculated emissivity of each membrane coincided with the reported values within 8% difference.