Behavior of Polyethylene Oxide Based Nonionic Surfactants in Silicon Processing Using Alkaline Solutions

The adsorption of polyethylene oxide (PEO) based nonionic surfactants onto hydrophobic silicon from an alkaline solution was investigated using an in situ attenuated total reflection Fourier transform infrared spectroscopy technique. The adsorption/desorption profiles of surfactants were affected by the type and length of the hydrophobic group and the lengths of hydrophilic PEO chains. Complete wetting of hydrophobic silicon was measured at surfactant concentrations in the range of 50 to 200 ppm. Surfactant adsorption was controlled by hydrophobic attractions between the hydrophobic moiety of surfactant and the silicon surface. The addition of surfactant to alkaline solutions dramatically reduced the etch rate of silicon and resulted in a smoother silicon surface. Oxidizing treatments followed by buffered oxide etching (BOE) were effective in the complete removal of adsorbed surfactant.