Sodium passivation in HCl oxide films on Si

Abstract

Chlorine has been incorporated into SiO2 films by thermal oxidation of Si in a mixture of O2 and HCl gases. Mobile sodium ions adsorbed on the oxide surface were drifted to the Si-SiO2 interface (0.5 MV cm−1 bias at 200 °C). Passivation, defined as the fraction of mobile sodium charge neutralized, exhibited a pronounced threshold with HCl content in the growth ambient. This was partly due to a similar variation of oxide chlorine content (measured by α-particle backscattering). For fixed growth temperature, passivation was a monotonic function of oxide chlorine content, and was only weakly dependent on the level of sodium contamination over the range 5×1011 to 1×1013 Na/cm2.

On the Nature of Fixed Oxide Charge

“…A higher steadystate broken-bond density is obtained both within the oxide film and within the transition region. Intermediates such as St-C1, which have bond energies only 0.7 eV less than Si-O (4.7 eV), are detected within the first 200A of the oxide film (38). Oxidation kinetics are also enhanced at the SiO2-Si interface (37).…”

“…The second oxidation reaction step involving oxygen as oxidant is the thermally activated reaction in which siloxane groups are formed as is shown in [5] _=St-+ (St-O) + + e--> St-O-St [5] In reaction [5], (St-O)+ complexes react at typical oxidation temperatures with incompletely oxidized Si atoms such as --St., as shown above, or with St-St bonds. Restructuring, or the displacement of Si atoms from their original lattice sites during this thermal oxidation reaction, can occur at three levels: at the substrate surface, within the transition region, and within the oxide film where bond angles are modified to accommodate newly formed oxide film (38). This reaction is exothermic and leads to a stable siIoxane structure.…”

Thermal Oxidation Kinetics of Silicon in Pyrogenic H 2 O and 5% HCl / H 2 O Mixtures

“…Coincidentally increased oxidation rates have been observed with increasing chlorine concentration in the oxygen ambient (1)(2)(3)(4). The reported improvements in device properties are probably due in part to actual incorporation of a chlorine species in the silicon oxide and reaction of this species with impurities (8,9). It has been proposed that the increased oxidation rates are due either to the reaction products (such as I-t20 and C12 from 02 plus HC1) or the effect of the chlorine species itself on the oxide growth mechanism, or both (1)(2)(3)(4).…”

The neutralization of Na+ ions in HCl grown SiO2

“…Previous reports [1,2] have shown that partial or complete neutralization of the Na+ at the Si-Si02 interface can occur in these oxides. It is known [1,3] that the neutralized ions are trapped much more strongly at this interface than are charged ions in normal dry oxides.…”