Silicon Epoxide: Unexpected Intermediate during Silicon Oxide Formation

Abstract

Infrared absorption spectroscopy and density functional cluster calculations are used to identify the intermediate oxide structures formed by high temperature annealing of the water-exposed Si͑100͒-͑2 3 1͒ surface. We find that initially there is a strong tendency for oxygen to agglomerate on single dimer units at T ϳ 800 K. Upon dehydrogenation, a remarkable structural transition is observed, wherein the dangling bonds recombine to form silicon epoxides (three-membered Si-O-Si rings). We demonstrate that these epoxides are the thermodynamically favored product in such constrained systems and, consequently, should be preferentially formed at silica interfaces. [S0031-9007(98)07445-6] PACS numbers: 81.65. Mq, 31.15.Ar, 68.35.Ja, 78.55.Ap Understanding the formation and evolution of SiO (defect) structures at silica surfaces and Si͞SiO 2 interfaces is of prime importance due both to the utilization of ultrathin oxide ͑ϳ10 Å͒ films as the gate dielectric layer in state-of-the-art semiconductor devices [1] and to the production of ultralow loss silica-based fiber for long distance optical communications. The detailed structural understanding of such interfaces poses a formidable scientific challenge due to the lack of long-range order and critical dependence on a wide array of production parameters. Therefore, a comprehensive knowledge of the fundamental physical and chemical properties of such systems must commence with the characterization of related systems that are more reproducible and amenable to control. In accordance with this prescribed approach, a wide variety of experimental [2] and theoretical [3] studies of such model systems have been undertaken over the past decade, but have singularly failed to provide a definitive mechanistic picture. For example, previous theoretical studies have focused primarily on a few simple Si-O structures that may result from the insertion of a single oxygen into the Si͑100͒-͑2 3 1͒ surface, with little exploration of the wider group of multiply oxidized structures that are subsequently formed during oxidation.Similarly, experimental studies have typically employed techniques [e.g., ultraviolet photoemission spectroscopy (UPS), x-ray photoemission spectroscopy (XPS)] and conditions that do not permit identification of the relevant discrete (sub)oxide structures formed. Recently, a combined infrared and theoretical study of the initial water-induced oxidation of Si͑100͒-͑2 3 1͒ [4] has shown that oxygen is first inserted into the dimer bonds and then into the Si backbonds, although the formation of the "real" multiply oxidized Si structures (that are the constituent subunits of extended layer growth) could not be delineated, as the spectral signatures of these oxide species were below the accessible range ͑,1000 cm 21 ͒.In this work, we have implemented a novel spectroscopic configuration that allows access to a broad spectral range ͑550 4000 cm 21 ͒ with submonolayer sen-sitivity to all vibrational components. We have primarily focused on the H 2 O:Si͑100͒-͑2 3 1͒ system a...

Electrochemical Passivation and Modification of c-Si surfaces

“…4.15b). This behaviour points to higher amount of defects due to stress at the Si(111)/SiO 2 interface than for the Si(100)/SiO 2 and Si(311)/SiO 2 interfaces, which can be expected due to better Si-O-Si bond angle alignment at the interface for (100) and (311) orientation of Si as compared to the Si(111) [47][48][49][50][51]. Even during oxidation, is higher when current oscillations at +8 V occur at the Si(100) surface.…”

Assignment of surface IR absorption spectra observed in the oxidation reactions: 2H + H2O/Si(1 0 0) and H2O + H/Si(1 0 0)

“…The reaction of water with a Si(1 0 0) surface has been studied by an IR external transmission (ET) method and by ab initio quantum chemical cluster calculations, which clearly establish that there is not a barrier to dissociative chemisorption of H 2 O on a Si(1 0 0)-(2 · 1) surface and leads to the formation of stable Si-H and Si-OH bands on the same Si-Si dimer unit [2]. Further annealing induces the insertion of oxygen atoms into the Si back bonds or the formation of epoxides through dehydrogenation [3,4]. Recent STM studies concerning the C-defect on the Si(1 0 0) have shown that water dissociates on two adjacent dimers and/or the same dimer [9,10].…”

“…In the model systems, the dangling bonds of Si atoms other than the top silicon atoms were terminated by tritium atoms to avoid artifacts due to excess spin or charge. Unlike reported theoretical methods in which the third and forth layer silicon atoms were fixed at the ideal bulk crystalline positions [2][3][4][5]7], all the atoms of the clusters in this study were allowed to fully relax without constraints. Termination with tritium atoms was very effective in localizing all the surface vibrations, which eased the assignments of the calculated vibrational modes.…”

“…The reaction of water with a Si(1 0 0) surface has received considerable attention due to its importance in industrial oxidation processes and in studies on the initial oxidation mechanism at Si surfaces [1][2][3][4][5][6][7]. Vibrational spectroscopy combined with ab initio quantum chemical cluster calculations has emerged as a powerful tool for investigating the atomic level picture of the Si oxidation process, which is essential for understanding and controlling extremely thin gate oxide film ($15 Å ) for Si MOS transistors [3,4,7,8].…”

“…Vibrational spectroscopy combined with ab initio quantum chemical cluster calculations has emerged as a powerful tool for investigating the atomic level picture of the Si oxidation process, which is essential for understanding and controlling extremely thin gate oxide film ($15 Å ) for Si MOS transistors [3,4,7,8]. The reaction of water with a Si(1 0 0) surface has been studied by an IR external transmission (ET) method and by ab initio quantum chemical cluster calculations, which clearly establish that there is not a barrier to dissociative chemisorption of H 2 O on a Si(1 0 0)-(2 · 1) surface and leads to the formation of stable Si-H and Si-OH bands on the same Si-Si dimer unit [2].…”