Stain etching of micro-machined silicon structures

Grooved silicon structures with deep vertical trenches that can be considered as a reactor prototype for bio and chemical reactions have been subjected to stain etching in a HF + NaNO2 solution. The depth profile of photoluminescence (PL) properties of the micro-porous layer formed under the stain etching has been studied by local excitation. It has been found that different parts of the structures are stain etched differentially: the upper area of the groove side walls and their upper surface are etched with the highest etch rate and possess the most intensive PL. The lower part of the side walls has minimal porous film thickness and the weakest PL, while the light emission from the bottoms of the grooves is higher. The rugged surfaces demonstrate higher PL intensity than the smooth surfaces.