THE ROLE OF CHEMICAL-SPECIES IN THE PASSIVATION OF [100] SILICON SURFACES BY HF IN WATER-ETHANOL SOLUTIONS

The role played by the chemical species present in HF/water-ethanol so lutions as last cleaning steps of the [100] silicon surface has been a nalyzed. The concentrations of these species as a function of the etha nol content have been calculated from measured equilibrium constants f or the dissociation and homoconjugation reactions of HF in water-ethan ol solutions. The correlation of these data with the measured etching rates of silicon oxide in these solutions suggests that etching in KF/ pure ethanol is controlled almost completely by the ion HF2-. The cont ribution of the H2F2 dimers to the etching process diminishes as ethan ol content increases. This indicates an increasing activation energy o f the dimer etching reaction when the ethanol content is raised. This characteristic behavior is associated with the slower and more homogen eous etching action of HF/ethanol solutions as well as with the absenc e of faceting and lower microroughness generation in [100] silicon Sur faces. The effects of overetching are not significant, and moreover, t he characteristic surfactant properties of alcohols contribute to the effects of these cleaning solutions.