Removal of Poly(Dimethylsiloxane) Contamination from Silicon Surfaces with UV/Ozone Treatment

Abstract

ABSTRACTUV/ozone cleaning is known to be effective for removing thin organic contaminants, but removal of silicon containing contaminants is questionable. Organo-silicon contaminants, e.g., silicones, can result from a variety of integrated circuit chip and electronic packaging fabrication processes. In this investigation, films of poly(dimethylsiloxane) (PDMS) on silicon substrates, with and without a gold coating, have been used to simulate such contamination up to a thickness of 50 nm. Although treatment consistently reduced the advancing DI water contact angle, in some cases from a value greater than 100° to a value less than 5°, the hydrophilic nature of the treated surfaces was not due to complete contaminant removal, i.e., a significant amount of modified contaminant remained on the surface. High resolution x-ray photoelectron spectroscopy (XPS) in the Si 2p region suggest that O-Si-C bonds in the siloxane, observed prior to treatment, are converted to SiOx, where x is between 1.6 and 2. The time required to reduce the contact angle to a minimum value was greater for the thicker PDMS film samples. Deflection testing was used to evaluate the adhesion of an epoxybased adhesive to intentionally-contaminated silicon chips, before and after UV/ozone treatment. Although PDMS contamination induced loss of adhesion between the chip and the adhesive, complete conversion to silicon oxides by UV/ozone treatment of contaminants having a thickness of 5.0 nm has been demonstrated to restore adhesion to a value equivalent to that of uncontaminated silicon chip surfaces.