Experimental and Theoretical Studies of the Si(100)/SiO 2 Interface Formed by Wet and Dry Oxidation
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V6.2.1
Experimental and Theoretical Studies of the Si(100)/SiO2 Interface Formed by Wet and Dry Oxidation A. Roy Chowdhuri, Dong-Un Jin, C. G. Takoudis Department of Chemical Engineering, University of Illinois at Chicago, 810 S. Clinton Street, Chicago, Illinois 60607-7000. USA. ABSTRACT Interfacial strain and substoichiometric silicon oxides are the two principal causes that result in the redshift of the transverse and longitudinal optical phonons of the asymmetric stretch of O in the Si-O-Si bridging bond of thermal SiO2 with decreasing oxide thickness. Analyses to comprehend these effects, therefore, require consideration of both strain and interfacial substoichiometry. A method to isolate the contributions of strain and suboxide content towards the observed shifts is proposed. The procedure, which utilizes simple optical model and effective medium approximation, allows estimation of the average strain and suboxide concentration in films of different thickness. Analyses of oxides formed at two different temperatures (550 and 700°C) with dry and wet oxygen reveal how process conditions affect the interface properties.
INTRODUCTION The extensive use of thermally grown SiO2 as the dielectric material in metal-oxide semiconductor (MOS) transistors is justified by the high quality, and both thermodynamically and electrically stable interface formed between thermally grown SiO2 and the Si substrate [1]. With aggressive scaling of MOS devices the dielectric/substrate will constitute a significant part of the device. The two major issues associated with thermally grown ultrathin silicon dioxide films are the presence of substoichiometric oxides (suboxides) [2,3] and strain near the oxide/substrate interface [4]. Understanding these interfacial effects and their dependence on the process conditions has become a topic of paramount importance [5]. The two prominent features characterizing the infrared spectra of SiO2 films appear at ~1075 cm-1 and ~1254 cm-1 and have been assigned to the transverse optical (TO) and longitudinal optical (LO) phonons of asymmetric stretching of O in the Si-O-Si bridging bond [6]. As the film thickness decreases, and the spectra preferentially probe the interface, compressive stress and suboxides may influence the shift of the TO and LO peaks[6-11]. However, the majority of the studies in this context either invoked interfacial strain [9-11] or sub-stoichiometry [6,8,12] as the dominant factor responsible for the thickness dependent changes in the infrared spectra. In this work, a simple procedure for determining the individual contributions of interfacial strain and substoichiometry towards the LO-TO splitting observed in the infrared spectra of ultrathin oxides on Si is proposed. After resolving these two interfacial issues, central force network model and effective medium approximation are used to estimate film strain and suboxide content of oxide films of different thickness.
V6.2.2
EXPERIMENT Oxides of different thickness were grown in a conventional horizontal furnace with either d
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