A diffusional model for the oxidation behavior of Si1−xGex alloys

Abstract

We have developed a kinetic model to describe the oxidation behavior of Si1−xGex alloys during Ge segregation, which compares the Deal–Grove flux of oxidant diffusing through the oxide to the maximum flux of Si diffusing through the Ge-rich layer. This is motivated by thermal oxidation experiments on Si1−xGex alloys (x<0.17) using a fluorine-containing ambient (O2 and 200 ppm of NF3). The fluorine is known to modify point defect generation during oxidation of pure Si toward vacancy production, which is also the case for Ge in Si. We demonstrate that fluorinated oxidation of Si1−xGex enhances the oxidation rate by 25%–40% in the temperature range of 700–800 °C. Oxides formed at these temperatures were SiO2, while those formed at 600 °C exhibited a transition from SiO2 to mixed oxide growth at some point during the very early phase of oxidation, depending on the alloy composition. Consideration of these data suggests that other factors in addition to oxidation temperature must be considered in predicting which oxide type will be produced, in contrast to most previous reports. Our model, indeed, shows that alloy composition, oxide thickness, and oxidant partial pressure are also important parameters. We believe that the model is very useful in predicting the oxide type that should result from a given set of growth conditions, and in particular, it suggests that a changeover from SiO2 to mixed oxide formation is likely at some point during the oxidation process, particularly if carried to larger thicknesses.

Photonic effects during low-temperature ultraviolet-assisted oxidation of SiGe

“…First, there is an enhancement of the SiGe dryoxidation rate over that of pure Si, which was previously observed only for thermal-wet oxidation. Recently, fluorine-assisted dry oxidation 6 and atomic-oxygen oxidation 12 studies reported a similar enhancement. It has been suggested 9 that because The behavior of Ge atoms during dry oxidation of Si 0.8 Ge 0.2 films at 300°C under 10 mbar of oxygen induced by vacuum-ultraviolet (VUV) illumination from an array of Xe 2 * excimer lamps ( ϭ 172 nm) has been studied.…”

“…23,24 However, this effect can only explain the enhancement of the semiconductor-oxidation rate. The trapping of Ge during SiGe-oxidation experiments has been explained by a competition between the oxidant flux from the surface and the Si atoms flux from the substrate: 5,6,[9][10][11][12] as long as the flux of Si atoms is equal or greater than the oxidant flux, the grown oxide layer will contain only SiO 2 , while all Ge atoms will be segregated from this newly formed oxide layer. Because the growth rates in our VUV-assisted oxidation experiment and ozone-assisted oxidation are very similar one can infer that the oxidant fluxes should also be very similar.…”

“…This is quite an unexpected result and can be understood as follows. There is always some Ge oxidation occurring at the interface at this low temperature but once formed most of the GeO 2 is immediately reduced by Si according to the following reaction: 6 Si ϩ GeO 2 → SiO 2 ϩ Ge (1)…”

“…Thermal oxidation usually produces Ge segregation at the interface between the grown oxide and the remaining SiGe layer, which degrades the electrical properties of the structure. [5][6][7] Several low-temperature oxidation techniques, such as plasma, electron-cyclotron resonance plasma, and atomic oxygen, 4,6-13 have been investigated to prevent Ge segregation, thermal relaxation of SiGe-strained layers, or unwanted-dopant redistribution.…”

The Effect of HfO2 Overlayer on the Thermal Stability of SiGe Substrate

“…3 Oxidation of SiGe layers leads to some Ge segregation, to an increase of the SiO 2 /SiGe interface roughness, and to the presence of numerous interface electrical defects. 4,5 Typically, an interfacial layer is formed due to uncontrolled chemical reaction at the interface with the substrate. The common procedure to reduce interfacial trap density in the developed layer is post deposition annealing (PDA), 6,7 which has a wide range of effects on the HfO 2 /Si based interface.…”