The formation of ordered, ultrathin SiO2/Si(100) interfaces grown on (1 x 1) Si(100)

Ordering is observed at SiO2/Si(100) interfaces when 2-40 nm thick SiO2 films are grown on passivated, ordered (1 x 1) Si(100) surfaces produced by a novel wet chemical cleaning, A mechanism is proposed for the occurrence of this ordering. The thin oxides are grown by a variety of conventional oxidation techniques or by rapid thermal oxidation between 750 and 1100 degreesC. The evolution of oxygen, carbon, hydrogen and silicon coverages are detected by ion beam analysis (IBA) using a combination of ion channeling, nuclear resonance, elastic recoil detection and time-of-flight secondary ion mass spectrometry. IBA detects Si surface peak areal densities lower than that of a disorder-free, bulk-terminated (1 x 1) Si(100) crystal calculated by Monte-Carlo methods. This result indicates that Si substrate atoms are shadowed by Si atoms located in a 2 mn ordered region on the oxide side of the interface. Beyond 2 nm, the oxide becomes amorphous. Reflection high-energy electron diffraction (RHEED) at 10 keV confirms the presence of order: a (1 x 1) streaky pattern commensurate with Si(100) is observed instead of an amorphous surface. Infrared (IR) spectroscopy shows that the ordered SiO2/Si(100) interfaces exhibit a constant, well-defined frequency of optical absorption across a 1 nm thickness in the interfacial oxide region near Si. This is in contrast to a rapidly changing frequency found for conventional oxides in the same region. Thus, IR supports the presence of a well-defined bond-length and stoichiometry as detected by IBA and RHEED. (C) 2001 Published by Elsevier Science B.V.