Microstructure, heat treatment, and oxidation study of porous silicon formed on moderately doped p-type silicon

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Abstract
A porous Si (PS) layer with a spongy microstructure on top of a dendritic microstructure was fabricated on a moderately doped p-type Si wafer using a two-step anodization process. This illustrates that in addition to substrate doping, anodization current density also has an effect on the porous Si microstructure. A preoxidation heat treatment of the spongy-type porous Si was found to change the porous structure significantly, making it more difficult to fully oxidize the layer at low temperatures. However, dendritic porous Si can better withstand the heat treatment without suffering noticeable changes in structure. X-ray photoelectron spectroscopy, infrared spectroscopy, and electrical breakdown tests were used to analyze the oxidized porous Si samples. The oxidation process and the resultant oxide were found to depend on several factors, including the porosity, the microstructure itself (e.g., spongy or dendritic-type), and the heat treatment history prior to oxidation. With similar porosity, dendritic PS is easier to oxidize compared to spongy PS.