BONDING PARTNER CHANGE REACTION IN OXIDATION OF GE ON SI(001) - OBSERVATION OF 2-STEP FORMATION OF SIO2

Oxidation of 5 angstrom Ge deposited at room temperature on Si(001) and the dependence of temperature on the oxidation behavior are investigated by employing synchrotron radiation photoelectron spectroscopy. The sample on exposure to air forms a mixture of Ge oxides and a small amount of Si oxides. Upon annealing, oxygen changes its bonding partner from Ge to Si forming SiO2 as the predominant final product. Two distinct steps have been observed in such a reaction. First step is the cleavage of all the Ge-O bonds and formation of Si-O bonds to form mainly Si suboxide. The second step is the rearrangement of Si-O bonds to form SiO2. The former one takes place in the temperature range 200-300-degrees-C whereas the latter one in the range 300-600-degrees-C.