Thick porous silicon membranes for gas sensing applications

A technological process aiming to realise passivated porous silicon (PS) layers as thermo-insulating material for thin as well as thick film gas sensor applications, is reported and discussed. To passivate the PS layer, a nitridation process performed in a rapid thermal system (RTS) in ammonia is proposed. In this case the Si rods are covered by a thin oxy-nitride layer, which stabilises the PS structure without introducing a large stress. Nitrided PS membranes (25-30 ?m thick) coplanar with the surrounding bulk Si and with good mechanical stability have been obtained and complete substrate heater element having nitrided PS membrane as thermo-insulating layer have been realised.