Nickel-affected silicon crystallization and silicidation on polyimide by multipulse excimer laser annealing

Abstract

Nickel enhanced amorphous Si crystallization and silicidation on polyimide were studied during multipulse excimer laser annealing (ELA) from submelting to melting conditions. A ∼8 nm thick Ni film was deposited on a 100 nm thick α-Si layer at ∼70 °C in order to promote partial nickel diffusion into silicon. In the submelting regime, Ni atoms distributed during deposition in α-Si and the thermal gradient due to the presence of the plastic substrate were crucial to induce low fluence (≥0.08 J/cm2) Si crystallization to a depth which is strictly related to the starting Ni profile. Αmorphous-Si crystallization is not expected on pure Si at those low fluences. Additional pulses at higher fluences do not modify the double poly-Si/α-Si structure until melting conditions are reached. At a threshold of ∼0.2 J/cm2, melting was induced simultaneously in the polycrystalline layer as well as in the residual α-Si due to a thermal gradient of ∼200 °C. Further increasing the laser fluence causes the poly-Si layer to be progressively melted to a depth which is proportional to the energy density used. As a consequence of the complete Si melting, columnar poly-Si grains are formed above 0.3 J/cm2. For all fluences, a continuous NiSi2 layer is formed at the surface which fills the large Si grain boundaries, with the beneficial effect of flattening the poly-Si surface. The results would open the perspective of integrating Ni-silicide layers as metallic contacts on Si during α-Si-crystallization by ELA on plastic substrate.