A semiconductor method includes providing a silicon semiconductor substrate. A gate and a plurality of source/drain regions are formed on the silicon semiconductor substrate to form at least one pFET. A silicon-germanium layer is formed over the plurality of source/drain regions. The germanium is condensed from the silicon-germanium layer to form a plurality of source/drains in the plurality of source/drain regions by forming an oxide layer over the silicon-germanium layer. An interlevel dielectric layer is formed over the gate and the source/drain regions. A plurality of contacts is formed in the interlevel dielectric layer to the gate and the plurality of source/drain regions.

Semiconductor system using germanium condensation

We propose a complete model for the oxidation of silicon germanium. Our model includes the participation of both silicon and germanium atoms in the oxidation process and the replacement by silicon of germanium in mixed oxides. Our model is capable of predicting, as a function of time, the oxide thickness, the profile of the silicon in the underlying alloy, and the profile of germanium in the oxide. The parameters of the model vary with temperature, alloy composition, and oxidizing ambient. The model shows excellent agreement with published results, with model parameters following trends consistent with the physical phenomena hypothesized. The presence of germanium catalyzes both the silicon and the germanium oxidation rates, and all reaction rates increase with increasing temperature. The resulting effective oxidation rate is enhanced, with respect to the oxidation of pure silicon, at all germanium concentrations. Mixed oxides form only in the case of high germanium concentrations, but at high temperature...

A Kinetic Model for the Oxidation of Silicon Germanium Alloys

The injection of Si self-interstitial atoms during dry oxidation at 815°C of very shallow SiGe layers grown on Si (001) by molecular-beam epitaxy (MBE) has been investigated. We first quantified the oxidation enhanced diffusion (OED) of two boron deltas buried into the Si underlying the oxidized SiGe layers. Then, by simulating the interstitial diffusion in the MBE material with a code developed on purpose, we estimated the interstitial supersaturation (S) at the SiGe∕Si interface. We found that S (a) is lower than that observed in pure Si, (b) is Ge-concentration dependent, and (c) has a very fast transient behavior. After such a short transient, the OED is completely suppressed, and the suppression lasts for long annealing times even after the complete oxidation of the SiGe layer. The above results have been related to the mechanism of oxidation of SiGe in which the Ge piles up at the SiO2∕SiGe interface by producing a thin and defect-free layer with a very high concentration of Ge.

Silicon interstitial injection during dry oxidation of SiGe∕Si layers

Several fundamental aspects of the oxidation-induced redistribution of Ge in thin films of SiGe are studied. This includes the incorporation of Ge into the oxide and the formation of what is alternatively referred to as pile-up, snow-plow, or a germanium-rich layer. Experimental data from the present work shows longer oxidation times leading to an increase of Ge content in the pile-up region and eventually creating a single high Ge content pile-up layer by entirely consuming the initial SiGe layer. The pile-up effect was shown to occur at the oxidation interface, with the highest Ge content occurring at the same interface. For a given oxide thickness, the redistribution of Ge and the formation of a pile-up region was shown experimentally to be independent of temperature in the range between 800 °C and 1000 °C. Simulations using common models for the oxidation of Si and diffusion of Si in SiGe indicate that temperature does have an influence on the composition of the pile-up layer, though the range of achievable compositions is limited. The flux of Si due to diffusion of Si in SiGe relative to the oxidation-induced flux of Si out of the SiGe is integral to the formation and dimensions of a pile-up region. Two predictive relations were derived for describing the dynamics of oxidation of SiGe. The first relation is given for determining the pile-up layer thickness as a function of oxide thickness and the composition of the pile-up layer. The second relation assumes a limited supply of Si and is for determination of the minimum initial thickness of a SiGe layer to avoid oxidation of Ge. The validity of these equations was confirmed experimentally by RBS and XPS data from the present work. The proposed models may be used in nanostructuring of thin films of SiGe by oxidation and in the design of core-shell structures and transistors. This is all done with a focus on oxidation of epitaxial thin films (< 100 nm) of Si1-XGeX in dry O2 at 1 atm between 800 °C and 1000 °C.

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

We have developed a modified technique to fabricate silicon–germanium on insulator (SGOI) starting with a sandwiched structure of Si∕SiGe∕Si. By means of oxidation and annealing, relaxed SiGe-on-insulator (SGOI) with a Ge fraction of 34% has been produced. Our results indicate that oxidation of the silicon cap suppresses Ge loss at the initial stage of the SiGe oxidation and the subsequent annealing process homogenizes the Ge fraction and also reduces Ge enrichment under the oxide. It is found that the strain in the SiGe layer is almost fully relaxed at high oxidation temperature (∼1150°C) without generating any dislocations and crosshatch patterns that are commonly observed on the surface of a relaxed or partially relaxed SiGe layer on bulk Si substrate.

Fabrication and mechanism of relaxed SiGe-on-insulator by modified Ge condensation

We present a study on thin oxides obtained by rapid thermal oxidation of Si1−xGex epitaxial layers. The oxidation processes were performed in dry O2 at 1000 °C for times up to 600 s. Our data show an oxide growth rate enhancement with respect to pure Si. Except for a very small amount of GeO2 that is found at the surface, all the Ge is rejected towards the SiO2/SiGe interface, forming a Ge-enriched layer free of extended defects. The comparison of our results for dry processes with those reported in the literature for wet ambient supports the idea that the kinetics of SiGe oxidation is controlled by similar mechanisms in both cases, in contrast with models and interpretations so far proposed.

G. Privitera

Papers

Oxidation rate enhancement of SiGe epitaxial films oxidized in dry ambient