The Deposition of Contaminants from Deionized Water onto Hydrophobic Silicon Wafers

Abstract

The liquid-based deposition of particles onto hydrophobic silicon surfaces was investigated by exposing hydrophobic silicon wafers to sample contaminants in a stirred deionized water bath. Wafers were rendered hydrophobic by exposure to dilute hydrofluoric acid, and a goniometer was employed to monitor wafer contact angles. As has been observed in the past for hydrophilic wafers, the zeta potential recorded for the test particle had a significant impact on the deposition resulting on the hydrophobic silicon surfaces. This suggests that, despite treatment with HF and an overall hydrophobic surface behavior, regions remain on the wafer surface which are ionizable in aqueous solutions. The behavior of the silicon test wafers used in these studies is consistent with the presence of a negative zeta potential at the hydrophobic silicon surface. In contrast to the deposition seen on hydrophilic wafers, however, deposition onto hydrophobic silicon is frequently nonuniform. Additionally, Auger analysis indicates that hydrophobic surfaces show a marked tendency to attract hydrocarbon contaminants from the deionized (DI) water. The rinsing technique employed when rendering wafers hydrophobic was found to have a significant effect on baseline particulate levels, and test results indicate that contamination differences between hydrophobic and hydrophilic wafers may be more strongly related to exposure to gas/liquid interfaces than to differences in the rates of particle deposition in bulk solution.