Atomic layer deposited Al2O3 capping layer effect on environmentally assisted cracking in SiNx barrier films

Abstract

We investigated the effect of an atomic-layer-deposited alumina (Al2O3) capping layer (2 or 10 nm thick) on the environmentally assisted cracking (EAC) properties of 250-nm-thick, plasma-enhanced-chemical-vapor-deposited silicon nitride (SiNx) barrier films on polyethylene terephthalate polymer substrates, using in situ optical microscopy tensile tests and numerical modeling. The 10-nm-thick capping layer resulted in a 5% decrease in crack onset strain, corresponding to the cracking of the Al2O3/SiNx bi-layer. Even though the Al2O3 layer itself is immune to EAC, its use as a capping layer did not significantly improve the mechanical reliability of the Al2O3/SiNx bi-layer under strain in ambient conditions, except for a minor 30%-50% increase in the driving force threshold required to induce crack growth. An effective capping layer should remain un-cracked during the cracking of the underlying SiNx, and a parametric study showed that it was not possible with alumina. A high fracture energy, low elastic modulus (e.g., organic material) layer is required such that cracking only occurs in the SiNx layer, presumably expected to protect SiNx from EAC degradation.