Surface observation and modification of Si substrate in NH4F and H2SO4 solutions

Atomic force microscopy (AFM) images of a chemically oxidized p-type Si(111) substrate in a 0.3 M NH4F solution have been investigated to study the topographical change occurring during surface etching. During etching of the oxide layers, elongated structures along the (1 (1) over bar 0) direction were observed. After the oxide layers R-ere completely etched, anisotropic surface etching occurred, as it does in dilute alkaline solutions. We have also demonstrated surface modification of an H-terminated p-type Si(111) substrate oil a nanometer scale using electrochemical scanning tunneling microscopy (ESTM) in a 0.2 M H2SO4 solution. A fine line of width as small as 12 nm was obtained. The dependence of the size of modified surface features on the conditions of the modification is studied.