CHEMICAL VAPOR-DEPOSITION OF TUNGSTEN IN A UHV SYSTEM - EFFECT OF SUBSTRATE CONDITIONS ON THE INITIAL-STAGES OF GROWTH

The initial stages of growth in chemical vapour deposition of W from WF6 have been studied in a UHV system using three different substrate conditions: HF-etched Si(100), partially oxidized Si(100) and an Si(100) substrate with a native oxide. A more detailed study of the initial growth process was possible using very low total pressures of WF6 (10(-6)-10(-5) Torr). It was found that the interaction between WF6 and the HF-etched substrate was affected strongly by a passivating layer of chemisorbed H-atoms on the Si surface. The hydrogenated surface reduced the nucleation rate and played an important role in keeping the W-Si interface clean. The native oxide and the partially oxidized substrate were more reactive than the HF-etched substrate towards WF6 over a broad temperature range.This effect was attributed to the presence of hydroxyl groups on the substrate surface.