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 modi fications of the Si (100) surface induced by standard SC1/SC2 etching cycle s. SC1/SC2 etching (also known as RCA cleaning) submits silicon wafers to o xidation by NH3:H2O2:H2O mixtures, oxide removal in diluted HF, further oxi dation by HCl:H2O2:H2O mixtures, and final etching in diluted HF. Samples w ere 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 adopt ing a special cross-section geometry enhancing HRTEM sensitivity to surface species. Atomic-resolution HRTEM micrographs displayed a partial loss of t he crystalline order in a 4 nm layer at the Si surface only when samples ha d undergone SC1/SC3 cycles. No (2 x 1) reconstruction pattern could be obse rved by either HRTEM or LEED. PEELS analyses allowed one to rule out the pr esence of either oxygen, carbon or fluorine at the surface or within the di sordered layer, thereby leading to the conclusion that oxidation treatments yield to a modification of the crystalline structure at the Si (100) surfa ce. (C) 2000 Elsevier Science S.A. All rights reserved.