Native Oxide Growth and Hydrogen Bonding Features on Chemically Cleaned Silicon Surfaces

Abstract

The most advanced MOS devices now utilize the gate oxide as thin as 140 A Future giga-bit memory with a minimum feature size of 0.14 µm will need 50 A thick gate oxide with sufficient reliability and precise thickness uniformity. This implies that a few-angstrom-thick native oxide formed on a silicon wafer must be completely removed or otherwise the native oxide thickness must be exactly controlled and the surface should be kept clean until the wafer is loaded to the furnace. Also, the microroughness on the wafer must be minimized to get the flat Si02/Si interface. Native oxide on the silicon surface has currently been removed by diluted HF treatment. The surface is chemically stable compared to the atomically clean surface because the Si dangling bond is terminated with hydrogen1. Also, Si-F bonds remaining on the silicon surface after the HF treatment appears to passivate chemically reactive sites2. The pH modified BHF treatment of Si(111) surfaces and further boiling or room temperature rinse in ultra pure water have led to the formation of atomically-flat hydrogen-terminated surfaces as demonstrated by surface sensitive infrared spectroscopy3~6. The atomically flat surface is hardly oxidized for more than 300min, while the rough surface with many atomic steps or microfacets is easily oxidized5. It is difficult to prepare an atomically flat Si(100) surface by employing the HF or BHF treatment. The oxidation kinetics of hydrogen terminated Si(111) and (100) surfaces and the SiO2/Si interface structure will provide further insight on the nature of chemically treated silicon surfaces.