Low Temperature Oxynitridation of SiGe in NO/N 2 O Ambients
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Low temperature oxynitridation of SiGe in NO/N2O ambients Anindya Dasgupta and Christos G. Takoudis Department of Chemical Engineering, University of Illinois at Chicago, 810 South Clinton Street, Chicago, Illinois 60607. ABSTRACT X-Ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and spectral ellipsometry have been used to study sub-35 Ǻ low temperature oxynitrides of SiGe. The oxynitridations steps have been performed at 550 oC and 650 oC, while the oxynitridation feed gases have been preheated to 900 oC and 1000 oC, respectively, before entering the reaction zone. XPS and SIMS data suggests that NO-assisted oxynitridation incorporates more nitrogen than the N2O-assisted one, while there is minimal Ge segregation towards the dielectric/substrate interface in both oxynitridation processes. SIMS data suggests that the nitrogen is distributed throughout the film in contrast to high temperature Si oxynitridation where nitrogen incorporation takes place near the dielectric/substrate interface. Spectral Ellipsometry has been used to measure the final thickness of the oxynitrides film. These results are discussed in the context of an overall mechanism of the oxynitridation of SiGe. INTRODUCTION Recently, silicon germanium alloys have received considerable attention due to their tunable band gap, enhanced hole mobility, improved high frequency behavior, and ease of integration with existing silicon technology. However, producing a high quality layer for insulating field effect devices has proved troublesome. Conventional thermal oxidation of SiGe alloys results in undesirable relaxation of strained layers [1,4] and formation of a Ge rich layer below the oxide [1,5,6]. The Ge rich layer causes high interface trap density, high fixed charge, and poor breakdown characteristics [1,5,6]. Also, the scaling of oxide for use in sub-0.1 µm technologies raises fundamental problems (particularly, gate-to-substrate tunneling and dopant diffusion during a high temperature processing step). Thus, it is imperative to study new materials for use as future dielectrics on SiGe. Since oxynitrides are leading contenders to replace oxides in future logic and memory applications, this work is intended to study the growth of hyperthin oxynitride films on SiGe substrates. This study aims at understanding the effect of temperature on N2O- and NO-assisted oxynitridation of SiGe alloys, especially in ultrathin (i.e.,
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