Experimental evidence of oxidant-diffusion-limited oxidation of SiGe alloys

Abstract

Rate-limiting step, as well as self-limited oxidation of SiGe alloys is so far under controversy. Contrasting to the monoparabolic growth mode for oxidation of Si, a parabolic growth mode and self-limited oxidation of SiGe alloys at different temperature are clearly observed depending on the oxidation time. With modified Deal-Grove model, we extract the parabolic rate constants related to the oxygen diffusion at different temperature and the activation energy of oxygen diffusivity finding that oxygen diffusion is still the rate-limiting step. We attribute this oxidation behavior to the strain effects associated with the volume change in converting Si/SiGe to SiO(2)/mixed oxide at different oxidation stages. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3191382

A comparative analysis of oxidation rates for thin films of SiGe versus Si

“…These models rely on accounting for the disposition of Si and Ge in the various layers formed by the oxidation process, including consumption of Si and Ge by the oxide. The simplifying assumption that the oxide is composed exclusively of SiO 2 is supported by empiric evidence 14, 19, 21–24, 27–32. The exceptions to this assumption, wherein both SiO 2 and GeO 2 are found, are native oxides 19, 27, 33, 34, those formed under high oxidant pressures 14, 27, and those formed at low temperatures 11, 32.…”

“…The lack of consensus about the oxidation rate of SiGe versus that of Si under dry thermal oxidation is clear, given reports of it being the same as 8, 21, 22, faster than 23–27, and slower than 15, 28, 29 that of Si. Discussions of either enhanced or retarded oxidation rates for SiGe, relative to that of Si, commonly focus on two plausible explanations: firstly, interstitial versus vacancy mechanisms for diffusion of Si in SiGe and the implications of the Ge concentration dependent lattice parameter of SiGe, and secondly, the difference in bonding energy of Si to Ge, as opposed to that of Si to Si 8, 18, 22, 23, 25, 26.…”

Ge redistribution in SiO2/SiGe structures under thermal oxidation: Dynamics and predictions

“…This has been examined by modeling the flows of oxidant through the oxide and of Si through a Ge-rich region adjacent to the oxidizing interface. 22,23,32 Low relative Si flows induced by low temperatures or high oxidant pressures have been recognized as leading to formation of GeO 2 . 30,32 Kilpatrick et al 23 have determined a so-called crossover temperature for various oxide thicknesses and oxidation conditions, below which GeO 2 is formed and above which the oxide is exclusively SiO 2 .…”

“…Such concentration gradients are typically characterized by a Ge-rich region adjacent to the SiO 2 growth front and are variously referred to as a pile-up region, snow plow effect, or germanium-rich layer (GRL). The pile-up effect, resulting from dry oxidation of SiGe, has been reported to occur in numerous publications, [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] but these observations are frequently limited to the acknowledgment of the existence of a pile-up layer. Furthermore, the reports do not provide sufficient information to understand how modification of the oxidation conditions may lead to variations in the profile of Ge concentration in the SiGe.…”

Ge concentrations in pile-up layers of sub-100-nm SiGe films for nano-structuring by thermal oxidation

“…Although the oxidation of Si is described by the well established Deal-Grove 6 and Massoud 7 models, the oxidation of SiGe is not as well characterized. 8,15,[20][21][22][23][24][25][26][27][28][29][30][31][32][33] Despite the work that has been done to study oxidation of SiGe, a lack of consensus remains regarding oxidation rates for SiGe as compared to that of Si. 15 Several models have been proposed to describe the oxidation processes in SiGe, 11,[16][17][18][19] all of which consider the relative diffusion of O in SiO 2 and that of Si in SiGe and Ge.…”