Effects of surface pretreatments on interface structure during formation of ultra-thin yttrium silicate dielectric films on silicon

X-ray photoelectron spectroscopy (XPS) and medium energy ion scattering (ME IS) are used to determine chemical bonding and composition of ultra-thin fi lms of mixed yttrium, silicon, and oxygen, formed by oxidation of metal on clean and pretreated silicon. XPS and MEIS analyses indicate that oxidation of yttrium on bare silicon results in a fully oxidized film with a signifi cant fraction of Y-O-Si bonding. The mixed Y-O-Si structure results from th e relatively rapid reaction between Y and the Si substrate to form yttrium silicide, followed by oxidation. The effect of various silicon pretreatment s, including in situ oxidation and nitridation, on bulk and interface film composition are also examined. Transmission electron microscopy (TEM) of 40 Angstrom thick films indicates that the yttrium silicate films are amorpho us with uniform contrast throughout the layer. MEIS shows evidence for a gr aded metal concentration in the dielectric near the silicon interface, with uniform oxygen concentration (consistent with full oxidation) throughout t he film. Angle resolved XPS (ARXPS) shows no significant signal related to Si+4, as would be expected from a substantial SiO2 interface layer. Capacit ance-voltage analysis demonstrates that a similar to 10 Angstrom equivalent oxide thickness can be achieved. The effects of ultra-thin silicon oxide, nitrided-oxide and nitrided silicon interfaces on silicon consumption durin g the oxidation of yttrium are investigated. When yttrium is deposited on a thin (similar to 10 Angstrom) SiO2 film and oxidized, a yttrium silicate f ilm is formed with bonding and composition similar to films formed on bare silicon. However, when the interface is a thin nitride, the silicon consump tion rate is significantly reduced, and the resulting film composition is c loser to Y2O3. The consumption of the silicon substrate by metal is shown t o occur during oxidation and during vacuum annealing of yttrium on silicon. The relatively rapid formation of metal-silicon bonds suggests that metal- silicon structures may also be important reactive intermediates in silicon/ dielectric interface formation reactions during chemical vapor deposition. In addition to thermodynamic stability, understanding the relative rates of elementary reaction steps in film formation is critical to control composi tion and structure at the dielectric/Si interface. (C) 2001 Elsevier Scienc e B.V. All rights reserved.