PECVD SILICON OXYNITRIDE - A NEW INSULATOR FOR ISFETS WITH INSULATOR SURFACE MODIFIED BY CHEMICAL GRAFTING

The aim of this work is to deposit thin layers of silicon oxynitride, prepared by PECVD (plasma-enhanced chemical vapour deposition) onto the silica of a SiO2/c-Si structure and use them as pH-sensitive membranes for ISFETs. One of the advantages offered by PECVD oxynitride compared to silica is the possibility to control the surface site number by varying the sample composition. Hydroxyalkylsilane has been used in order to check the feasibility of the dense grafting. For this study the single surface sites required were SiNH/NH2 with a surface density of 4.4-mu-mol m-2. The pH response, determined through C(V) measurements on electrolyte/insulator/semiconductor structures, is Nernstian and becomes 15 mV/pH after grafting with C18 alkylhydroxysilane. The effect of aging in water has been observed. In parallel the alkylation of the surface of silicon nitride powders by alkylhydroxysilane has been monitored by IR spectroscopy. The intensity and the shift of OH and NH2 bands and the kinetics of isotopic exchange with deuterium have been followed before and after the chemical grafting.