No abstract

Final capping insulation layer is a critical step in the microfabrication process that determines the lifetime of analytical microsensors in real fluids. Actual processes encounter considerable limitations as (i) organic passivation layers do not provide a satisfying long-term protection against liquids and (ii) inorganic passivation processes (dielectric materials deposition and patterning) are very aggressive for the underlying layers, imposing severe constraints on the integration of sensitive materials. We present here a low temperature deposition process of high quality silicon nitride Si3N4 using ICP-CVD technique combined with a lift-off based process to pattern conformal deposition, in order to avoid harsh treatments such as wet or dry etching.High-density SiNx films with low H content (5 x 10 20 at/cm 3 ) were synthesized at 100°C with controlled uniformity (5%), refractive index (2.025 at 830 nm), etch rate in buffered hydrofluoric acid (8 nm/min), residual stress (-500 MPa), breakdown field (3.9 MV/cm) and dielectric constant (6.0). In order to validate the compatibility of this passivation process with long-term fluids analysis, microelectrodes were fabricated and their lifetime in natural seawater was evaluated. Their active surfaces were defined by patterning the insulation layer. Special care was given to their accurate estimation through the modelling of chronoamperometric curves.Reproducible and stable electrochemical response was obtained for months (> 50 days), demonstrating a considerably extended lifetime in harsh liquid media.

A new imaging method is presented enabling the monitoring of the lateral wet thermal oxidation of a thin Al-containing layer embedded in a vertical cavity lasers (VCSEL) structure. This method is based on the measurement of the modification of the VCSEL reflectivity spectrum inherent to the aperture layer refractive index change, with an observation window restricted to the wavelength ranges for which this reflectivity variation is maximal. The main purpose is the accurate control of the buried confinement aperture, and, thereby, that of the electro-optical characteristics of the laser device. The kinetics of the lateral oxidation has been studied for small-size aperture VCSEL (3-10 μm) and for long-range oxidation depths. This straightforward method based on an optical imaging system will enable robust improvement of the production yield of this multifactor-dependent technological process.