DIRECT OBSERVATION OF CRYSTALLIZATION IN SILICON BY IN-SITU HIGH-RESOLUTION ELECTRON-MICROSCOPY

We have studied the nucleation and growth of crystalline silicon by in situ high-resolution electron microscopy. Amorphous silicon thin films, deposited onto oxidized silicon wafers by low-pressure chemical vapor deposition, were heated in the microscope in the nominal temperature range of 700-775-degrees-C. Many sub-critical crystal embryos exist at the a-Si/SiO2 interface, very few of which develop into viable nuclei. One nucleation event was recorded successfully at lattice resolution, allowing an estimate of the critical radius as 2.5 +/- 1.0 nm and the a-Si/c-Si interfacial energy as 600 +/- 200 mJ m-2. The crystal growth was followed for extended periods of time. It appeared to be characterized by sporadic growth bursts rather than a continuous advance of the crystal-amorphous phase interface. We specifically sought evidence for a ledge growth mechanism but did not find such behavior.