Characterization of vapor deposited thin silane films on silicon substrates for biomedical microdevices

Uniform, conformal and ultrathin coatings for microfabricated silicon based devices are desirable to control the hydrophilicity of the surface and minimize unspecific protein adsorption. One method to achieve this is to solution coat the surface with alkyltricholorosilanes. However, when solution coated, these silanes tend to polymerize to form sub-micron level aggregates and multilayers on the silicon surface. Chemical vapor deposition reduces the risk of formation of multilayers since it involves coating at an ambient pressure in a nitrogen atmosphere. Using this method, uniform and controlled nanometer thick organo-silane films can be formed on silicon surfaces. Standard microfabrication techniques were used to make microchannels on silicon wafers, which were then coated in vapor phase along with plain wafers. These films were characterized using analytical techniques such as ellipsometry, contact angle measurements, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The protein adsorption was also studied under physiological conditions and protein interaction with the modified surface was investigated with AFM and XPS. The uniformity and stability of these organo-silane films was compared under varying conditions.