The low-temperature anodization of silicon in a gaseous plasma

A comprehensive investigation of the low-temperature anodization of silicon in RF and microwave oxygen plasmas is discussed. A comparison of the growth results and ion signals observed, using quadropole mass spectrometry, indicates a strong correlation between the growth rate and the presence of O^- ions in the plasma. Characterization of parameters such as pressure, electrode spacing, and current density has allowed wafers up to 4-in. diameter to be anodized with good growth rates (0.3 μm/h) and excellent oxide uniformity, using low temperatures (⩽600°C), low input power densities (~59 W-cm^-2), and low current densities (~7 mA-cm^-2). Oxide properties such as etch rate and refractive index were found to be indistinguishable from thermally grown oxides. Optimization of anneals and the use of a halogen gas enables plasma oxides with high breakdown fields (10-11 MV/cm), an interface trap density of ~5×10¹⁰ cm^-2-eV^-1 at midgap, and a fixed oxide charge of 6×10¹⁰ cm^-2 to be fabricated without resorting to high-temperature (⩾600°C) processing