The formation of ordered, ultrathin SiO₂/Si(1 0 0) interfaces grown on (1 × 1) Si(1 0 0)

Ordering is observed at SiO₂/Si(1 0 0) interfaces when 2-40 nm thick SiO₂ films are grown on passivated, ordered (1 × 1) Si(1 0 0) 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°C. 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 (1×1) Si(100) crystal calculated by Monte-Carlo methods. This result indicates that Si substrate atoms are shadowed by Si atoms located in a 2 nm 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 × 1) streaky pattern commensurate with Si(1 0 0) 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.