engleski

Electrical activation of phosphorus by rapid thermal annealing of doped amorphous silicon films

Heavily phosphorus doped amorphous and polycrystalline silicon samples were prepared by the LPVCD (low pressure chemical vapour deposition) method at different deposition temperatures. Thereafter, samples were subjected to RTA (rapid thermal annealing) at 950 °C in different time intervals (10, 20, 30 and 45 s). In this way the structure of amorphous samples changed to polycrystalline and in all annealed samples the phosphorus electrical activation was achieved and defect density was reduced. Sheet resistance, although clearly decreasing with the RTA duration, does not significantly change with the annealing time. This behaviour can be ascribed to the high quantity of dopant concentration when the resistivity of polycrystalline silicon approaches the one of monocrystalline silicon and finally its limiting value. By analyzing the Fano type resonance on the transversal optical TO(Γ ) phonon mode, Raman spectroscopy served as a tool for distinguishing between the accumulation of the activated phosphorus atoms at the grain boundaries and inside the grains. The spectrum of the amorphous sample which was subjected to the longest annealing time reveals a shift and asymmetry of the same peak characteristic to the Fano interaction.

LPCVD; amorphous silicon; polysilicon; phosphorus doping. rapid thermal annealing

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