Preparation of polycrystalline silicon thin films by pulsed ion-beam evaporation

Polycrystalline silicon (poly-Si) thin films are widely used in various electronic devices, such as a semiconductor in thin film transistors (TFTs), solar cells, peripheral circuits of liquid-crystal displays, and electrodes in Si integrated circuits because of its considerably higher carrier mobility compared to that of hydrogenated amorphous silicon thin films. Plasma-enhanced chemical vapor deposition (PECVD) is one of methods to deposit poly-Si films. However, the PECVD has disadvantages because the substrate should be annealed to high temperature (typically, 400 - 1,000 0C). The purpose of this study is to prepare poly-Si thin films without heating the substrate by intense, pulsed, ion-beam evaporation (IBE). Using IBE technique, we have succeeded in the preparation of polycrystalline silicon thin films on the substrate of silicon or quartz. High crystallinity has been achieved without annealing. Since the life time of the ablation plasma obtained by the pulsed ion beam with 50 ns pulse width is on the order of 20 μs, the instantaneous deposition rate will be ∼1 cm/s. The crystallinity of poly-Si film has been improved with increasing the density of the ablation plasma, while the grain size of the film has been found to be smaller. Here, we will report the characteristics of poly-Si films using X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy and scanning electron microscope measurements.