STRUCTURE AND COMPOSITION OF INTERFACIAL SILICON-OXIDE LAYER IN CHEMICAL-VAPOR-DEPOSITED Y2O3-SIO2 BILAYER DIELECTRICS FOR METAL-INSULATOR-SEMICONDUCTOR DEVICES

A silicon oxide layer is formed at the interface of low pressure chemical vapor deposited Y2O3 film on Si after an annealing in O2 at 580-degrees-C for 45 min. It shows a graded composition varying from SiO2 to SiO(x) (x approximately 1) which depends on the thickness of Y2O3 film as revealed by infrared and Auger electron spectroscopic studies. With 52-nm-thick Y2O3 film, a more ordered coesite-like (c-) SiO2 forms at the interface whose structure changes gradually to an amorphous (a-) SiO2, SiO2-x near the Si interface. With thicker Y2O3 film (approximately 110 nm) the formation of a-SiO2 is characterized by SiO4 linkage having short range order with larger size rings. The composition of silicon oxide changes gradually to SiO(x) with 1<x<2 near the Si interface. In thinner Y2O3 film (approximately 30 nm), in addition to c-SiO2 and a-SiO2, quasi-SiO2 with unlinked SiO4 tetrahedra are also observed. The interfacial growth of silicon oxide is due to the oxidation of Si by quasi atomic oxygen which migrates from its entrapped position in the Y2O3 film towards the Si-silicon oxide interface. This silicon oxide shows high intrinsic positive charges approximately 4 x 10(12) cm-2 and large density approximately 1.0 x 10(12) cm-2 eV-1 of interface states in comparison to thermally grown SiO2 on bare Si. According to this investigation, to use Y2O3/SiO2 bilayer dielectric as a metal-insulator-semiconductor capacitor in high density memory storage devices, the structure and composition optimization of SiO2 layer is very important.