Paper TF-ThP21
Enhancement of Crystal Growth in μc-Si:H Thin Film Deposition by H Radical-Assisted Magnetron Sputtering and the Plasma Diagnostics

Thursday, October 23, 2008, 6:00 pm, Room Hall D

Silicon thin films are promising materials for TFTs and solar cells. It is desirable to deposit Si thin films with good electrical characteristics onto various substrates such as a glass at a low temperature. Magnetron sputtering deposition is useful to prepare silicon thin films because of the advantage in not using explosive gases and consequently, a low equipment cost. We measured the Si atom density in rf magnetron sputtering plasmas with a Si target and Ar/H₂ mixture gas by laser-induced fluorescence (LIF) spectroscopy. As a result, we found that the sputtering yield in the Ar/H₂ mixture discharge was higher than that in the pure Ar discharge. This suggests that sputtering in the Ar/H₂ mixture discharge is not simple physical sputtering but a process similar to reactive ion etching (RIE). Since the products of RIE are not Si atoms but molecular species SiH_x (typically SiH₄), the deposition mechanism similar to PECVD would be expected in magnetron sputtering of a Si target with the assist of chemical reactivity of H atoms. The objective of this work is to develop a new Si sputtering deposition system employing an H radical source. We expect the enhancement of the RIE effect by injecting additional H radicals produced in an ICP radical source. We prepared Si thin films by using simple sputtering with Ar/H₂ mixture gas and H radical-assisted sputtering. In the case of the simple sputtering, an amorphous film was deposited at a low gas pressure of 5 mTorr. The crystalline volume fraction (X_c) increased with the gas pressure from 10 to 200 mTorr, and was saturated at gas pressures above 200 mTorr. In the case of the H radical-assisted sputtering, the X_c increased steeply with the gas pressure from 3 to 5 mTorr, and was saturated at gas pressures from 5 to 500 mTorr. It should be noted that the films deposited by the H radical-assisted sputtering crystallized even at gas pressures below 3 mTorr, where the film deposited by the simple sputtering did not crystallize. This result may be attributed to both or one of the following two effects. One is the supply of H radicals produced in the radical source to the growing film surface. The other effect is the enhancement of the production of molecule species SiH_x by the RIE effect. The increases in the densities of molecular species SiH_x may result in the enhancement of the H coverage on the growing film surface.