Surface preparation of Si(001) substrate using low- p H HF solution

We prepared atomically flat Si(001) surfaces that have well-ordered step-and-terrace structures using a low- p H ( p H < 1 ) HF solution (LPH) and subsequent low-temperature ( 750 ° ⁢ C ) annealing in H 2 . The flattening was attributed to the enhanced migration of Si atoms on the LPH-treated surface because anisotropic etching is suppressed by the low concentration of OH ions. The reduction in the H 2 annealing temperature to below the decomposition temperature of Si oxide enabled us to form an atomically flat Si(001) surface in a window area surrounded by a thick device isolation oxide.