Pulsed Laser Recrystallization of Polysilicon: Analysis Via A Novel Sem Technique

ABSTRACTLarge crystals of silicon were obtained via pulsed laser annealing of thinfilms of fine grain CVD polycrystalline silicon. These films were analyzed using a novel technique that provides rapid feedback of crystallographic and defect information. The technique uses very shallow angle metallurgical sections in conjunction with chemical decoration and scanning electron microscopy and results in excellent depth resolution (<10 nm) across large spatial distances (>100 μm). The technique was used to reveal conversion of very large areas (≈ 1 mm 2) of polysilicon films deposited on silicon into single crystal film, albeit with point defects, without requiring the melt depth to reach the polysilicon/silicon interface. A gradual transition from single crystal to increasingly polycrystalline material was observed going from top to bottom of the initially uniform polycrystalline film depending on the pulse energy used. Polysilicon on top of an oxide layer, on the other hand, transforms into large (≈ 10 μm) single crystals with grain boundaries penetrating the entire polysilicon film thickness. These experimental results shed new light on two very important questions: (1) Is laser annealing entirely an epitaxial process or is it strongly influenced by the thermal properties of the underlying substrate, and (2) Whether substantial regrowth of polysilicon requires equilibrium thermodynamics.