Metalorganic chemical vapor deposition of aluminum oxide on silicon nitride
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Metalorganic chemical vapor deposition of aluminum oxide on silicon nitride Anindya Dasgupta, Abhijit Roy Chowdhuri and Christos G. Takoudis Department of Chemical Engineering, University of Illinois at Chicago, 810 South Clinton Street, Chicago, Illinois 60607. ABSTRACT Thin films of aluminum oxide were deposited on silicon nitride thin films using trimethylaluminum and oxygen at 0.5 Torr and 300 °C. Fourier transform infrared (FTIR) and x-ray photoelectron spectroscopic (XPS) analyses of these films showed no aluminum silicate phase at the film-substrate interface. The O/Al ratio in the deposited film was found to be higher than that in stoichiometric Al2O3 indicating the presence of excess oxygen. FTIR spectroscopy and XPS of the annealed samples did not show any formation of silicon oxide, oxynitride or silicate at the aluminum oxide/silicon nitride interface. In contrast to aluminum oxide on clean silicon substrates, using ultrathin silicon nitride as a barrier layer could prevent excess oxygen migration towards the Si substrate and formation of any interfacial layers. INTRODUCTION In complementary metal-oxide-semiconductor (CMOS) devices, aluminum oxide has emerged as one of the promising substitutes for SiO2 as the dielectric layer [1]. It has a dielectric constant (εAl2O3 ~ 9) more than twice that of SiO2 (εSiO2 ~ 3.9). With a band gap of ~ 9 eV, a 2.8 eV conduction band offset to Si, and its robustness to withstand high temperature wafer processing steps, Al2O3 provides many advantages over other potential candidates. Al2O3 is known to be amorphous at < 750 oC, although γ-Alumina (cubic) may form at higher temperatures [2,3]. Both amorphous Al2O3 (< 350 °C) and cubic Alumina (>750°C) form a thermodynamically stable interface over Si [2]. Atomic layer controlled deposition using trimethylaluminum (TMA) and H2O showed that aluminum oxide was formed on HF treated Si without the formation of any aluminum silicate phase at the dielectric/Si interface [4]. However, another study [5] reported aluminum silicate phase formation at the oxide/substrate interface when triethyldialuminum tri-sec-butoxide (TEDA-TSB) and O2 (at ~ 400 °C) was used. Recently, deposition using TMA and O2 has shown that no silicon oxide or aluminum silicate phase is formed during deposition. However, the O/Al ratio has been found to be higher than the stoichiometric one in Al2O3. Subsequent high temperature annealing in an inert Ar ambient forms SiO2 at the alumina/Si interface without the formation of any aluminum silicate phase [6]. It is understood that the excess oxygen in the aluminum oxide film diffuses and reacts with Si to form SiO2 [6]. In this work we explore low temperature metal-organic chemical vapor deposition (MOCVD) of Al2O3 films using TMA and O2 on chemical vapor deposited Si3N4. The deposited films and aluminum oxide/silicon nitride interfaces are characterized using Fourier transform infrared (FTIR) spectroscopy and x-ray photoelectron spectroscopy
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(XPS). Low pressure CVD Si3N4 has a dielectric constant
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