This paper reports on the results of an improved surface modification method called Molecular Vapor Deposition (MVD). MVD allows for the creation of molecular organic coatings which are denser and more durable than those obtained by current liquid or vapor-phase methods. This improvement has been achieved using a “sequential” or “layered” vapor deposition scheme of two different molecular films. The first molecular coating is a “seed” or adhesion promoter layer which is used to increase the binding sites for the subsequent functional molecular layer. The resulting surface coatings were observed to have improved stability to immersion applications, higher temperature stability and overall improved durability as a result of the increased surface coverage when compared to standard self-assembled monolayers (SAMs). These new film capabilities will have significant importance in improving the functionality and reliability of many micro- and nano-scale devices. The sequential approach with the seed layer has also been used to deposit molecular coatings on a variety of substrate materials (such as polymers, plastics and metals) which normally do not allow high quality surface coatings.
We have developed an improved vapor-phase deposition method and an apparatus for the wafer-scale coating of monolayer films typically used in anti-stiction applications. The method consists of a surface preparation step using an O2 plasma followed by the tunable deposition of a monolayer film in the same reactor. This process has been successfully applied to MEMS test structures and has demonstrated superior anti-stiction performance. The deposition process allows tuning of the film properties by the precise metering of the precursor and a catalyst as part of the process control scheme. The anti-stiction monolayer film deposited from dimethyldichlorosilane (DDMS), tridecafluoro-1,1,2,2-tetrahydrooctyltrichlorosilane (FOTS), and heptadecafluoro-1,1,2,2-tetrahydrodecyltrichlorosilane (FDTS) were characterized using contact angle analysis, atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The coefficient of static friction was measured using a sidewall test device and the work of adhesion using a cantilever beam array. The results showed that excellent quality, uniformity, and reproducibility could be achieved across a whole wafer using this method and equipment.