Porosity in thin Ni/Au metallization layers

Thin films of Ni covered with Au and supported on oxidized silicon wafers were deposited by thermal evaporation or electron beam evaporation. After heating in oxidizing environments from 250 to 400 °C, porosity was observed in the Au films. The pores were typically 2000 A in diameter and ∼2 μm apart after heating for 1 h at 400 °C in oxygen. By considering models of grain boundary grooving, it has been shown that a porous, discontinuous thin Au film is thermodynamically stable.