Structural characterization of ultrathin nanocrystalline silicon films formed by annealing amorphous silicon

The fabrication and structural characteristics of ultrathin nanocrystallization silicon films is reported. Amorphous Si layers, with nominal thicknesses in the range of 3.5-11 nm, were deposited by low-pressure chemical vapor deposition onto amorphous SiO₂ and then crystallized using rapid thermal annealing at temperatures from 650 to 750 °C. High-resolution electron microscopy revealed that the resulting films were comprised almost entirely of Si nanocrystallites with a small fraction of remaining amorphous material. The grain size in the vertical growth direction was controlled by the thickness of the as-deposited amorphous Si film, whereas the lateral grain size was determined by appropriate choice of the annealing conditions.