Native Silicon Oxide Properties Determined by Doping

ABSTRACT: The physico-chemical properties of native oxidelayers, spontaneously forming on crystalline Si wafers in air, can bestrictly correlated to the dopant type and doping level. Inparticular, our investigations focused on oxide layers formedupon air exposure in a clean room after Si wafer production, withdopant concentration levels from ?1013 to ?1019 cm-3. In order todetermine these correlations, we studied the surface, the oxidebulk, and its interface with Si. The surface was investigated usingthe contact angle, thermal desorption, and atomic forcemicroscopy measurements which provided information on surfaceenergy, cleanliness, and morphology, respectively. Thickness wasmeasured with ellipsometry and chemical composition with X-rayphotoemission spectroscopy. Electrostatic charges within the oxidelayer and at the Si interface were studied with Kelvin probe microscopy. Some properties such as thickness, showed an abruptchange, while others, including silanol concentration and Si intermediate-oxidation states, presented maxima at a critical dopingconcentration of ?2.1 × 1015 cm-3. Additionally, two electrostatic contributions were found to originate from silanols present on thesurface and the net charge distributed within the oxide layer. Lastly, surface roughness was also found to depend upon dopantconcentration, showing a minimum at the same critical dopant concentration. These findings were reproduced for oxide layersregrown in a clean room after chemical etching of the native ones.