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.
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