ON THE GROWTH OF A METALLIC CE FILM ON SIO2

We present a new method to study the formation of a metallic film on an insulator. During the deposition of a metal on an insulator we measure the capacitance C(t) of the forming metal insulator structure and monitor the metal deposition rate with a quartz-crystal microbalance. Ce was deposited with rates of around 4 ML min-1 on a thermally, dry-grown, SiO2 layer on a Si substrate. From the C(t) curve of the forming metal-insulator-semiconductor (MIS) structure we can distinguish three stages of the Ce film growth. Up to 3 ML of Ce no capacitance change is observed. In the second stage, between 3 and 5 ML, a steep increase of the capacitance occurs. From 5 to 10 ML the capacitance saturates gradually to the maximum value. At coverages which correspond to the first stage, Ce diffusion into SiO2 was observed with X-ray photoelectron spectroscopy (XPS). The analysis of the Si(2s), O(1s) and Ce(3d) core levels suggest a Ce diffusion into oxygen vacancy positions of SiO2-δ at room temperature. © 1990.