Porous silicon formation by HNO3/HF vapor etching

Abstract

The formation of porous silicon (PS) via a HNO3/HF vapor-etching (VE)-based technique is described. VE of silicon was found to lead to the growth of PS layers (PSLs) and/or a thick white layer identified as the (NH4)2SiF6 compound. Which phase dominates depends on the HNO3/HF volume ratio. High-resolution SEM observations show that p- and p+-type PSLs are composed of dot-like crystalline Si particles embedded in an amorphous phase, having sizes not exceeding 5 nm. Almost pure (NH4)2SiF6 may be obtained in a wide range of thicknesses for a HNO3/HF volume ratio exceeding 1/4. The (NH4)2SiF6 is highly soluble in water, enabling fabrication of grooves in Si wafers. Control over the growth of the (NH4)2SiF6 is demonstrated to realize groove patterns, which could be used in a variety of applications.