Formation and Properties of Porous Silicon and Its Application

Preparation, properties, and applications of porous silicon film were investigated. Silicon single crystal is converted into porous silicon film by anodization in concentrated hydrofluoric acid at currents below the critical current density. When an n‐type silicon was anodized, the silicon surface was illuminated to generate holes which were necessary for this anodic reaction. The growth rate of the film, from n‐type silicon, was larger than that from p‐type silicon in this experimental condition. The crystalline structure was the same as that of silicon single crystal. A new isolation technique for bipolar integrated circuits was proposed by making use of the properties of the film such that it can be formed several microns thick and oxidized easily to form an insulator. The main feature of the technique is that it provides a means to form thick insulating film inlaid through the n‐type epitaxial layer without prolonged heat‐treatment. A preliminary experiment was carried out to test the practical usage of the technique.