CONTRIBUTION OF FREE-ELECTRONS TO AL CVD ON A SI SURFACE BY PHOTOEXCITATION

The contribution of surface free electrons to the selective Al CVD usi ng dimethylaluminum hydride (DMAH) and hydrogen has been investigated. As a selective growth mechanism of Al on a Si surface, we have propos ed a surface electrochemical reaction model. The most significant poin ts of this model are (1) contribution of free electron to surface reac tion, (2) surface terminated-hydrogen, (3) selective reaction between the terminated-H and CH3-radical of DMAH. The nucleation density at th e initial growth stage has been found to depend on the carrier density of the Si wafer: The nucleation density dramatically increases when t he electron density is larger than 1 X 10(15) cm-3. Since the intrinsi c carrier density of the Si wafer at a deposition temperature of 270-d egrees-C is 1 X 10(15) cm-3, the increase in the nucleation density me ans that the free electrons of the Si surface contribute to the surfac e reaction. Furthermore, with the photo-irradiation of a halogen lamp of a 380-840 nm broad band spectrum and 40 MW/cm2 power, the nucleatio n density increases and becomes independent of the carrier density of the Si wafer. The dependency of the nucleation density on the carrier density is considered to disappear because of free electrons excited b y photo-irradiation. It has been found that the free electrons on the Si surface contribute to the surface reaction. The reaction between te rminated-H and CH3-radical have been also confirmed by Al deposition o n the Si surface under various hydrogen termination conditions. Theref ore, the surface electrochemical reaction model has been experimentall y confirmed for the selective Al growth.