Microstructure evolutions upon Ni(Pt) silicidation and the different responses to the metal etch

Abstract

Ni(Pt) films were silicided at nominally 400 °C. Electrostatic discharging (ESD) failure of devices occurred, which prompted root cause investigation. The silicide stack on the wafer was Ni(Pt)/Ni2Si(/Si). Flakes of SiO2 emerged on the wafer after the metal etch. With a higher silicidation temperature of 570 °C, the extent of the silicidation was greater. The stack on the wafer became Ni-oxide/Si-oxide/(NiPtx)Si/NiSi(/Si). The flaking issue was resolved and the desired etch selectivity achieved. It is the decomposition of Ni2Si that led to the bi-layer structure of NiSi, and the minimization of free energy that drove the out-diffusion of Ni and Si from the NiSi to form the surface oxides. Ni-oxide formed on Si-oxide because Si-oxide is thermodynamically more stable than Ni-oxide. The two layers of oxides and the density of bond energy of (NiPtx)Si being higher than that of Ni2Si made the stack more resistant to the metal etch and resulted in the desired etch selectivity. No reliability failure was observed after the flaking issue was addressed.