Novel optical sensors the most often require thin films or surface structures with strictly controlled properties, playing a critical role in them by initiating or modifying their sensorial responses. Selected results of research on atomic layer deposited (ALD) metallic oxides will be shown, regarding their applicability for thin functional coatings in lossy mode resonance (LMR) and long period grating (LPG) optical fiber sensors. Basically amorphous films of tantalum oxide (TaxOy), zirconium oxide (ZrxOy) and hafnium oxide (HfxOy) below 200 nm were deposited at relatively low temperature (LT) of 100°C. The optical, structural, topographical, tribological, hydrophilic and chemical stability properties of the films and their technological controllability were analysed. The TaxOy was selected and successfully applied as an oxide coating in LPG sensor. As chemically robust in alkali environment (pH over 9) it allowed to gain a potential for fabrication of regenerable/reusable biosensor. Additionally, ALD technique was tested as a tool for tailoring sensorial properties of LMR sensors. The double-layer coatings composed of two different materials were experimentally tested for the first time; the coatings were composed of plasma-enhanced chemical vapour deposited (PECVD) silicon nitride (SixNy) followed by much thinner ALD TaxOy. That approach yielded operating devices, ensuring fast overlay fabrication and easy tuning of the resonant wavelength at the same time. The LT ALD TaxOy films turned out to be slightly overstoichiometric (y/x approx. 2.75). Therefore, the issue of TaxOy chemical composition was studied by secondary ion mass spectroscopy, Rutherford backscattering spectrometry and x-ray photoelectron spectrometry.
This study described a novel and original method of ultra-shallow fluorine and nitrogen implantation from radio
frequency (RF = 13,56MHz) CF4 and NH3 plasmas, performed in classical RIE / PECVD reactors. The performed
experiments indicate that ultra-shallow implantation of high concentration of fluorine and nitrogen ions by using r.f.
plasma reactors (PECVD ad RIE) is feasible. It is also possible to control the implantation process parameters, ie
implantation depth and maximum concentration, by controlling the parameters of the plasma processes.
Electrical characterization of MOS structures with HfO2 layer as a gate dielectric, shows that samples implanted with
nitrogen, have the best insulating properties, better even the reference sample. Samples prepared by fluorine
implantation, exhibit much worse I-V behavior for low, medium and high electric fields, than all samples studied in this
article. This samples exhibit the highest leakage currents, too.