| AVS 58th Annual International Symposium and Exhibition | |
| Advanced Surface Engineering Division | Wednesday Sessions |
| Session SE+PS-WeA |
| Session: | Atmospheric Pressure Plasmas |
| Presenter: | Thomas S. Williams, University of California Los Angeles |
| Authors: | T.S. Williams, University of California Los Angeles R.F. Hicks, University of California Los Angeles |
| Correspondent: | Click to Email |
The wetting behavior of surfaces is important in many applications, such as for example, microfluidic devices that are fabricated on silicon wafers. In this study, silicon native oxide surfaces were cleaned with a radio frequency, atmospheric pressure helium and oxygen plasma and with ammonium hydroxide, hydrogen peroxide, and deionized water in a 1:1:5 ratio (RCA SC-1). Both processes created a hydrophilic state with water contact angles of <5° and 16.2±1.7°, respectively. During subsequent storage in a chamber purged with boil off from a liquid nitrogen tank, the water contact angle increased over several days at a rate dependant on the cleaning method used. Internal reflection infrared spectroscopy revealed that the change in water contact angle was due to the adsorption of organic molecules with an average hydrocarbon chain length of 10±2. The rate of the adsorption process decreased with the fraction of hydrogen-bonded hydroxyl groups on the surface relative to those groups that were isolated. On Si (100) surfaces that were cleaned by RCA SC-1 and the plasma, 96% of the silanol groups were hydrogen bonded. The first-order rate constant for adsorption of the organic contaminant on this surface was 0.182±0.008 hr-1. Several methods have been explored for keeping the silicon dioxide surface in a hydrophilic state for extended periods of time, and these will be presented at the meeting.