Reaction Mechanism of Monomolecular Self-Assembled Films Modified by Free Radical Dominant Downstream Microwave Plasma

• Main Authors: Chih-Chiang Weng, 翁志強
• Other Authors: Jiunn-Der Liao
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/87067792756544672300

博士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 96 === In this work, we applied custom-made downstream microwave plasma (DMP) upon self-assembled monolayers (SAMs) chemically adsorbed on Au or Ag (Metal). The pristine and plasma-modified SAMs/Metal substrates were then characterized by synchrotron-based in-situ high resolution X-ray photoelectron spectroscopy. Their reaction mechanisms at the plasma/SAMs/Metal interfaces were studied. The diagnosis of the DMP system was performed by custom-made Langmuir probe. Plasma density of the DMP system was estimated as 106 particles/cm3 or correlated with an electron temperature of around 0.5 eV. Plasma state of current DMP system was thus considered as low content of energetic species, whereas only long-lives free radicals were possible to survive in the course of traveling a distance. A free radical-dominant DMP system was then provided for the subsequent studies. This defined plasma system was employed to react with various SAMs/Metal. The SAM molecules and head-group S-Metal bonds were sensitive to plasma composition, in particular, the oxygen-derivative species. The primary plasma-induced processes were dehydrogenation, desorption of hydrocarbon and sulfur-containing species, and the oxidation of the alkyl matrix and S-Metal interface. The reaction rates of all major plasma-induced processes were found to be directly proportional to the oxygen content in the plasma, which can be correlated with the measurement of plasma reactivity. In the study of minor oxygen content in non-oxygen plasma, it was found that oxygen/nitrogen plasma was much reactive in comparison with oxygen/argon plasma. The minor content of oxygen-derivative species played an important role in plasma reactivity, while nitrogen-derived species were relatively efficient in energy transfer. In addition, SAM molecules with long alkyl chains and S-Ag bonds, compared with S-Au bonds, were much resistant to an analogous plasma treatment owing to the characteristic of low-density plasma. Based upon these fundamental studies, we applied this technique to make a defined pattern on SAMs/Au using the analogous free radical-dominant DMP system and a particular synchrotron-based scanning photoelectron microscopy. By controlling the plasma exposure time, the modified SAMs/Au exhibited as a respective negative or positive resist, which was mostly related to plasma reaction with SAM molecules. After etching on the modified SAMs/Au, a clear pattern was exactly developed. From this frequently-used example, it is therefore very promising to apply this patterning method for the making of micro/nano devices such as micro-fluid channels, very small scale bio-chip, micro-discharges for novel micro-plasma system.