The Origins of Fluorine in Dry Ultrathin Silicon Oxides

摘要

Ultrathin oxides (< 1 nm) were grown at room temperature by UV/O_2 in a cluster tool combining HF vapor pretreatment and oxide growth in a single chamber. The chemical composition and thickness of the layers were characterized by XPS. It is shown that incorporation of fluorine in these oxides originated mainly from the contamination of the tool and the fluorine left at the wafer surface by the in-situ HF process. When oxides were grown in a specially built non-contaminated cell no increase in fluorine concentration was observed. Hence no evidence was found for the incorporation of subsurface fluorine during the growth of these oxides and the existence of subsurface fluorine is questioned. From their continued growth upon air exposure, these ultrathin oxides do not seem to show sufficient diffusion barrier properties for high k applications, independent of their fluorine content.