Atomic-Scale Dynamics of the Formation and Dissolution of Carbon Clusters in SiO2

Abstract

Oxidation of SiC produces SiO2 while CO is released. A 'reoxidation' step at lower temperatures is, however, necessary to produce high-quality SiO2. This step is believed to cleanse the oxide of residual C without further oxidation of the SiC substrate. We report first-principles calculations that describe the nucleation and growth of O-deficient C clusters in SiO2 under oxidation conditions, fed by the production of CO at the advancing interface, and their gradual dissolution by the supply of O under reoxidation conditions. We predict that both CO and CO2 are released during both steps.PACS numbers: 68.55. Ln, 68.35.Dv The most significant property of semiconductors is their ability to sustain heterogeneous n-type and p-type doping. This property, however, is eroded by high temperatures and high voltages that cause intrinsic excitation of electron-hole pairs across the band gap. As a result, semiconductors with significantly larger band gaps than silicon have been investigated as candidates for electronic devices suitable for high temperatures and high voltages. Silicon carbide is a particularly attractive candidate because its native oxide is SiO 2 which works so well as a dielectric in Si-based microelectronics. The presence of a third element, however, namely C, results in a wide range of phenomena that do not occur in the Si-SiO 2 system. In particular, oxidation of SiC entails the production of CO which effuses through the oxide [1,2]. Afanas'ev et al. have suggested that carbon clusters at and near the interface form during oxidation [3,4], but the structure and dynamics of these clusters has not been established. Lipkin and Palmour found that, after oxidation, a 'reoxidation' step is necessary to produce high-quality oxides and SiC-SiO 2 interfaces [5,6]. During this step, oxygen is supplied as during oxidation, but the temperature is lowered so that no further oxidation takes place. In contrast, post-oxidation heat treatment without the supply of O leads to an increase of charged defects in the oxide [7]. It is believed that the 'reoxidation' step cleanses the interface and bulk SiO 2 of residual carbon [3]. Duscher et al. recently presented direct experimental evidence for the existence of carbon in as-grown samples and its removal after reoxidation [8].The nucleation and growth of impurity clusters in semiconductors is a generic problem for which totalenergy calculations are well suited to provide detailed information. In this Letter we present the results of extensive first-principles density-functional calculations that allow us to give a detailed account of the nucleation and growth of O-deficient carbon clusters in SiO 2 during oxidation conditions and their dissolution during reoxidation conditions. Basically, a CO molecule, generated at the advancing interface and diffusing through the oxide, can bind weakly to an O site in the SiO 2 network. A second CO molecule, however, can bind to the first and the new complex is very stable. Additional CO molecules can extend the cluster. The process is ...

Limiting Step Involved in the Thermal Growth of Silicon Oxide Films on Silicon Carbide

“…This interface cannot be wider than 15 nm, according to previous results [22]. In this near-interface reactive region [2,3,6,7,[11][12][13][14] carbon and/or excess silicon (from SiC not completely oxidized or from Si interstitials injected as a result of SiC oxidation) may also be present. The mobility of lattice oxygen could also be responsible for this phenomenon, but it has been ruled out [21] by previous analyses of samples oxidized in the 16 O 2 = 18 O 2 = 16 O 2 gas sequence.…”

“…On the other hand, the properties of the SiO 2 =SiC interface lead to electrical characteristics worse than those of SiO 2 =Si, while the scatter of the available data [1] suggests poor interface control. Investigations of the thermal oxide film on SiC in its different regions have been pursued [2 -7], indicating that in the surface and bulk regions the oxide is similar to that grown on Si [4,8,9], that the interface is less abrupt [5,10], and that incompletely oxidized C or Si are found near the interface [2,3,6,7,[11][12][13][14]. However, a thorough understanding of the phenomena taking place during the thermal growth of SiO 2 on SiC is still missing.…”

First-principles calculations for the adsorption of water molecules on theCu(100)surface

“…19,20,21,22,23,24 The results reported in this paper were obtained using the Vienna ab-initio simulation package (VASP). 20,21,22 The exchange-correlation effects were treated with the generalized gradient-corrected exchange-correlation functionals (GGA) given by Perdew and Wang.…”

Anodic etching of SiC in alkaline solutions

“…In many application areas, for instance those related to aerospace, automotive and petroleum industries, there is a need for electronic devices that can operate at high power levels, high temperatures, high frequencies and in harsh environments. Silicon (Si) cannot meet these requirements; SiC can [2][3][4]. In addition, because of its exemplary chemical and mechanical properties SiC, in combination with Si, is finding wider application in sensors and micro-electromechanical systems (MEMS) [5][6][7][8][9].…”