Low temperature Si 0.85 Ge 0.15 oxynitridation in wet-nitric oxide ambient
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Low temperature Si0.85Ge0.15 oxynitridation in wet-nitric oxide ambient Anindya Dasgupta and Christos G. Takoudis Department of Chemical Engineering, University of Illinois at Chicago, 810 South Clinton Street, Chicago, Illinois 60607. ABSTRACT
Nitric oxide (NO) aided Si0.85Ge0.15 wet-oxynitridation has been performed at 400 700 °C, while the wet-NO feed gas was preheated to higher temperatures before entering the reaction zone. X-Ray photoelectron spectroscopy (XPS) and secondary ion mass spectroscopy (SIMS) data suggests that both nitrogen and oxygen incorporation increases within the dielectric bulk with increasing wet-oxynitridation temperature, while there is no apparent germanium segregation towards the dielectric/substrate interface at all temperatures studied. Angle-resolved XPS analysis shows that increase in wetoxynitridation temperature above 600 °C is likely to volatilize some germanium oxide from the surface region. Nitrogen incorporation is found to hinder germanium segregation. These results are discussed in the context of an overall mechanism of SiGe wet-oxynitridation. INTRODUCTION Recently, SiGe 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, conventional high temperature (> 400 °C) thermal oxidation of SiGe alloys in dry and wet O2, O3 and atomic oxygen results in undesirable relaxation of strained layers [1,2] and formation of a Ge rich layer below the oxide [1,3,4], which causes high interface trap density, high fixed charge, and poor breakdown characteristics [1,3,4]. Since oxynitrides are leading contenders to replace oxides in future logic and memory applications, this work is intended to study the growth of hyper-thin oxynitride films on SiGe substrates. It aims at understanding the effect of temperature on wet NO-assisted oxynitridation of SiGe alloys, especially in ultrathin (i.e., < 40 Å) dielectrics. Wet oxynitridation is used in this work, since the rate of oxidation of SiGe alloys is reported to be significantly higher than that of pure Si during wet oxidation [5-11], whereas the oxidation rates of SiGe is the same as that of bulk Si in dry oxygen [5, 12, 13]. It has been demonstrated that the Ge acts as a catalyst during the wet oxidation of SiGe [9, 10]. Holland et at. [6] have suggested that the enhancement of wet oxidation rate is the result of weak Si—Ge binding energy. The wet oxynitridation processing is studied at 400 – 700 °C. X-ray photoelectron spectroscopy (XPS) is used to determine the extent, nature and role of bonding states of N, Si and Ge, while secondary ion mass spectroscopy (SIMS) is utilized for the elemental concentration profiles at all conditions investigated. EXPERIMENT A resistively heated horizontal furnace (Lindberg/Blue, STF 55346C) is used for all processes. It consists of a quartz tube 3" in diameter and 39" in length. A removable cap
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