Yttrium silicate formation on silicon: Effect of silicon preoxidation and nitridation on interface reaction kinetics

The effects of oxygen and nitrogen pretreatments on interface reaction kine tics during yttrium silicate formation on silicon are described. X-ray phot oelectron spectroscopy (XPS) and medium energy ion scattering (MEIS) are us ed to determine chemical bonding and composition of films formed by oxidati on of yttrium deposited on silicon. Capacitance-voltage testing is used to determine the quality of the dielectric and the electrical thickness. The e ffect of ultrathin silicon oxide, nitrided oxide, and nitrided silicon inte rfaces on metal oxidation kinetics is also described. When yttrium is depos ited on clean silicon and oxidized, XPS and MEIS indicate significant mixin g of the metal and the silicon, resulting in a film with Y-O-Si bonding and composition close to yttrium orthosilicate (Y2O3. SiO2). A thin (similar t o 10 Angstrom) in situ preoxidation step is not sufficient to impede the me tal/silicon reaction, whereas a nitrided silicon interface significantly re duces the silicon consumption rate, and the resulting film is close to Y2O3 . The mechanisms described for yttrium are expected to occur in a variety o f oxide and silicate deposition processes of interest for high-k dielectric s. Therefore, in addition to thermodynamic stability, understanding the rel ative rates of elementary reaction steps in film formation is critical to c ontrol composition and structure at the dielectric/Si interface. (C) 2000 A merican Institute of Physics. [S0003-6951(00)01741-1].