Chemically induced disordering of Si (100) surfaces upon SC1/SC2 etching analysed by high-resolution transmission electron microscopy

In this article, evidence will be put forward for the first time about modifications of the Si (100) surface induced by standard SC1/SC2 etching cycles. SC1/SC2 etching (also known as RCA cleaning) submits silicon wafers to oxidation by NH3:H2O2:H2O mixtures, oxide removal in diluted HF, further oxidation by HCl:H2O2:H2O mixtures, and final etching in diluted HF. Samples were analysed using high-resolution transmission electron microscopy (HRTEM)-parallel electron energy loss spectroscopy (PEELS) and Low-energy electron diffraction (LEED) techniques. HRTEM-PEELS analyses were carried out adopting a special cross-section geometry enhancing HRTEM sensitivity to surface species. Atomic-resolution HRTEM micrographs displayed a partial loss of the crystalline order in a 4 nm layer at the Si surface only when samples had undergone SC1/SC2 cycles. No (2×1) reconstruction pattern could be observed by either HRTEM or LEED. PEELS analyses allowed one to rule out the presence of either oxygen, carbon or fluorine at the surface or within the disordered layer, thereby leading to the conclusion that oxidation treatments yield to a modification of the crystalline structure at the Si (100) surface.