Poisson´s Ratio of Low-Temperature PECVD Silicon Nitride Thin Films

In this paper, the Poisson´s ratio of low-temperature plasma-enhanced chemical vapor deposited silicon nitride thin films has been determined by a modified double-membrane bulge test. This test method utilizes a square membrane and a large-aspect-ratio rectangular membrane that is fabricated alongside from the same thin film. The Poisson´s ratio is determined from the ratio of the bulge deflections of the two membranes under an applied pressure. The method is suitable for determining of either stress-free thin films or those containing low tensile residual stresses. Poisson´s ratio values of 0.23 0.02 and 0.25 0.01 were measured for films that were deposited at 125 and 205 , respectively.