Promising Gate Stacks with Ru & RuO 2 Gate Electrodes and Y-silicate Dielectrics
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Promising Gate Stacks with Ru & RuO2 Gate Electrodes and Y-silicate Dielectrics
Huicai Zhong1, Greg Heuss1, You-Seok Suh1, Shin-Nam Hong2 and Veena Misra1 Jason Kelly3 and Gregory Parsons3
1
Department of Electrical Engineering, North Carolina State University, Raleigh, NC 2
Department of Electrical Engineering, Hankuk Aviation University, Seoul, Korea
3
Department of Chemical Engineering, North Carolina State University, Raleigh, NC
ABSTRACT
In this work, we studied the electrical and thermal stability of Ru and RuO2 electrode on Y-silicate dielectrics in contrast to ZrO2 and Al2O3 dielectrics. Very low resistivity Ru and rutile stoichiometric RuO2 films, deposited via reactive sputtering, were evaluated as gate electrodes on ultrathin Y-silicate, ZrO2 and Al2O3 films for Si-MOS devices. Thermal and chemical stability of the electrodes was studied at annealing temperatures up to 800°C in N2 and subsequently forming gas anneal. XRD and XPS were measured to study grain structure and interface reactions. The morphology of the films was tested by atomic force microscopy (AFM). Electrical properties were evaluated via MOS capacitors. The role of oxygen inside dielectrics was studied by comparing equivalent oxide thickness change as a function of annealing temperature for capacitors with Y-silicate, ZrO2 and Al2O3 dielectrics. Good stability of Ru and RuO2 gate electrodes on all dielectrics studied was found. Flatband voltage and gate current as a
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function of annealing temperature was also studied. It was found that capacitors with Y-silicate after high-temperature anneal had less positive flatband voltage shift than ZrO2 and Al2O3. For capacitors with Ru gate electrode, the significant flatband voltage shift after high temperature anneal could be partially removed by a forming gas anneal.
INTRODUCTION
Aggressive scaling of MOSFET technology makes the evaluation of high-conductivity metal gate electrodes and alternative gate dielectrics important [1]. Gate dielectric materials with high dielectric constant, low leakage current, good thermal stability, and good interface characteristics comparable to Si-SiO2 are needed as alternative dielectrics. High conductivity and excellent thermal stability properties are required for metal gate electrodes to decrease gate depletion effect and to improve interface properties between gate electrode and gate dielectric. Thin films of transition metal oxides such as ruthenium oxide, RuO2 not only have large workfunctions (~5 eV), but also very low resistivity and excellent thermal/chemical stability [2,3,4]. Studies performed by our group have demonstrated that Ru and RuO2 gate electrodes on SiO2 offer good thermal stability [5]. Ru and RuO2 on ZrO2 and ZrSiO4 dielectrics with good thermal stability up to 800oC were recently reported [6]. In this paper, we report the material, electrical and thermal stability properties of Ru and RuO2 gate electrodes on Y-silicate dielectrics and compare them to ZrO2 and Al2O3.
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EXPERIMENTAL DETAILS Ru and RuO2 thin films we
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