In situ ATR - FTIR spectroscopy of Hf(IV) tert butoxide adsorption on Si and Ge
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0917-E09-03
In situ ATR - FTIR spectroscopy of Hf(IV) tert butoxide adsorption on Si and Ge Shilpa Dubey, Keijing Li, Harish Bhandari, Zheng Hu, C. Heath Turner, and Tonya M. Klein Department of Chemical Engineering, The University of Alabama, A127, Bevill Building, Tuscaloosa, Alabama, 35487 ABSTRACT Hafnium oxide ultra thin films on Si (100) are being developed to replace thermally grown SiO2 gates in CMOS devices. In this work, a specially designed Attenuated Total Reflectance Fourier Transform Infra Red Spectroscopy (ATR-FTIR) reaction cell has been developed to observe chemisorption of hafnium (IV) t-butoxide onto a Si and Ge ATR crystal heated up to 250°C and under 1 torr of vacuum to observe the initial reaction pathways and species on the substrate surface in real time and under typical process conditions. Chemisorption spectra were compared to spectra of the liquid precursor and to spectra generated by density functional theory (DFT) calculations of liquid, monodentate and bidentate absorbed precursor. An asymmetric stretching mode located at ~1017 cm-1 present in the chemisorbed spectra but not in the liquid spectra indicates that the adsorbed hafnium containing group is prevalent as a bidentate ligand according to calculations. Surface concentration of the chemisorbed species was dependant on the substrate temperature and precursor partial pressure allowing for determination of heats of adsorption which was 26.5 kJ/mol on Si.
INTRODUCTION Scaling of metal oxide semiconductor (MOS) transistors used in advanced electronic devices will require a new gate material with a higher dielectric constant perhaps by the 45 nm node. To effectively replace SiO2, the material needs to have sufficient band offsets with the gate as well as the semiconductor substrate, and it must be able to withstand high temperature processing of up to 1000ºC without reaction or inter-diffusion with the gate metal or substrate. Researchers have not only studied various metal oxides such as HfO2, TiO2, ZrO2, Al2O3, La2O3, but also have explored a wide variety of precursors like amides, halides, β-diketonates and alkoxides [1,2]. Hafnium (IV) tert-butoxide (HtB) is a widely used organometallic precursor for HfO2, is easily oxidized and therefore is an appropriate precursor for atomic layer deposition (ALD) [3,4,5]. In addition, Hf[OC(CH3)3]4, which decomposes at 225°C, has 4 oxygen atoms in the molecular structure allowing for stoichiometric deposition of HfO2 in the absence of an external O2 supply. Its relatively high vapor pressure, ~0.07 torr at 25°C and 1 Torr at 65°C, is an added advantage in that it can be handled at low temperatures, minimizing the heating of precursor and delivery lines [6]. In situ ATR-FTIR spectroscopy is an efficient and non-invasive tool for observing metal organometallic reactions on Si [7,8,9,10]. In this study, the adsorption of HtB on Si and Ge ATR crystal elements was observed as a function of substrate temperature.
EXPERIMENT The experiment set up as shown in figure 1 consists of a Harrick Scientific
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