Silicon atomic-layer etching (ALET) was carried out by the adsorption of Cl-2 to form silicon chlorides followed by the desorption of the silicon chlorides formed on the surface by irradiating an Ar neutral beam of a low energy. The silicon surface during the silicon ALET was investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscopy, and its etch mechanism was studied. XPS data showed that during the Cl-2 adsorption stage, silicon chloride bonding peaks related to SiCl and SiCl3 were formed. The peak intensity related to SiCl bonding is slowly decreased during the desorption of silicon chlorides, and when the SiCl bondings are removed completely by irradiating enough Ar neutral-beam dose to the surface, the saturated silicon etch rate of 1.36 angstrom/cycle which is related to one Si monolayer per cycle could be obtained. Also, at this condition, the surface roughness is close to the roughness of the silicon substrate itself. The SiCl bondings formed on the silicon surface during the adsorption stage are related to the desorption species during the ALET, while the SiCl3 bondings are related to the species formed with the surface silicon damaged during the desorption stage. (c) 2007 The Electrochemical Society.