5. Concluding remarks

We can conclude that PECVD a-5iC is a very attractive and promising material. Its PECVD deposition enable low temperature processing and thus ensures compatibility with CMOS processing, which is essential when (bio) MEMS/NEMS structures need to be combined to gether with signal processing and data conditioning circuits, a sine qua non condition of realizing "smart sensors". Additionally, PECVD deposition enables the user to modify various deposition parameters (temperature, pressure, precursors gas flow ratios) which can allow the user to optimize -at least in principle- the desired film properties: chemical composition internal average stress and refractive index. However, in practice such multi-dimensional optimization may prove difficult to achieve, and the presence of some extra degrees of freedom is welcome. An example to the point is -in our case- the presence of dual LF and HF modes for the STS Multiplex Pro-CVD PECVD reactor, which provided valuable flexibility in usage and in varying independently various characteristics of the film (e.g. minimizing the stress) without compromising the others (e.g. the refractive index). In some cases, when such a machine is not available, some more maneuvering room is given by adding an anneal process, which always reduces (sometimes significantly) the film's stress.

Application-wise, the long list of extremely desirable properties exhibited by a-SiC (large hardness, high fracture strength, high modulus, excellent wear resistance, superb chemical inertness and excellent stability even at high temperatures and/or under corrosive conditions) ensure it can be used in a very large area of applications, particularly in harsh environments, where Si devices cannot be used. Moreover, the same properties recommend PECVD a-SiC as the material of choice for a large range of MEMS postprocessing fabrication techniques. Thus, it can be used as mold material (or mold-coating protective layer), masking material or active structural material in surface micromachining.

Finally, we should also highlight that a-SiC can has also been employed in bio-related applications. Our own tests have shown that PECVD a-SiC membranes fabricated by bulk micro machining can be used successfully in cell cultures. Here the intrinsic properties of a-SiC ensure very good chemical stability, possibility to easily functionalize the surface for, e.g., increased cell adhesion, and improved mechanical resistance and easy handling.
