Cleaning and Oxidation of Heavily Doped Si Surfaces

Abstract

HF-treated Si surfaces and the oxidation kinetics in pure water or in clean room air have systematically been studied by x-ray photoelectron spectroscopy (XPS). The oxidation of heavily-doped n-type Si appears to proceed parallel to the surface, resulting in the layer-by-layer oxidation. The oxide growth rate in pure water for heavily-doped n-type Si is significantly higher than that of heavily-doped ptype Si. This is explained by the electron tunneling from the Si conduction band to adsorbed O2 molecules to form the O2 state. O2 ions easily decompose and induce a surface electric field, enhancing the oxidation rate. The growth rate of native oxide on heavily-doped n-type Si is less sensitive to the crystallographic orientations than the case of lightly doped Si where the steric hindrance against oxygen molecules significantly lowers the oxidation rate of the (110) and (111) surfaces. We suggest that the decomposed oxygen can penetrate into Si without steric hindrance. It is also found that the oxidation of heavily-doped n-type Si in pure water is effectively suppressed by adding a small amount (10 ∼ 3600 ppm) of HCI.

Nature of germanium nanowire heteroepitaxy on silicon substrates

“…20 Though rinsing hydrogen terminated silicon surfaces with water is expected to destroy the hydrogen passivation, we observed that a quick water rinse after oxide removal followed by immediate transfer into the vacuum system of the evaporator did not impact the epitaxial growth of the nanowires. 21 Samples without any native oxide removal or samples left in air for 1-2 h between oxide removal and gold deposition showed random directions of nanowire growth indicating the reduction or absence of epitaxial growth due to the formation of native oxide on the silicon surface. It should be noted that the nanowire growth on these samples though not epitaxial, were still single crystalline and has been reported to predominantly grow with a ͗110͘ crystal orientation.…”

Initial stage of native oxide growth on hydrogen terminated silicon (111) surfaces

“…[1][2][3][4] As a result, it has been found that native oxide growth at room temperature needs both oxygen and water. 1 Secondly, native oxide grows on every monolayer ͑layer-by-layer oxidation͒ as determined by the change in native oxide thickness.…”

“…1 Secondly, native oxide grows on every monolayer ͑layer-by-layer oxidation͒ as determined by the change in native oxide thickness. 1,4 This suggests lateral oxidation from step edges on the silicon surface. 4 Thirdly, since the binding energy of the silicon-hydrogen ͑Si-H͒ bond is higher than that of the Si-Si bond, the initial stage of native oxide growth does not arise at the Si-H bonds at the top of the silicon surface but at the Si-Si back bonds.…”

“…1,4 This suggests lateral oxidation from step edges on the silicon surface. 4 Thirdly, since the binding energy of the silicon-hydrogen ͑Si-H͒ bond is higher than that of the Si-Si bond, the initial stage of native oxide growth does not arise at the Si-H bonds at the top of the silicon surface but at the Si-Si back bonds. 2,5 Finally, the native oxide growth rate depends on the Fermi level position and on the crystallographic orientation of the silicon substrate.…”

“…2,5 Finally, the native oxide growth rate depends on the Fermi level position and on the crystallographic orientation of the silicon substrate. 4 Most of these results, however, were obtained from atomically rough H-terminated silicon surfaces. 6 It has been shown recently that atomically flat H-terminated Si͑111͒ surfaces can be obtained by wet chemical treatments at one atmosphere.…”