Thermally-Stable High Effective Work Function TaCN and Ta 2 N Films for pMOS Metal Gate Applications
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1073-H01-08
Thermally-Stable High Effective Work Function TaCN and Ta2N Films for pMOS Metal Gate Applications C. Adelmann1, P. Lehnen2, L.-Å. Ragnarsson1, T. Conard1, A. Franquet1, V. S. Chang1, E. Rohr1, J. Meersschaut1, O. Boissière2, C. Lohe2, T. Schram1, S. Van Elshocht1, and S. De Gendt1,3 1 IMEC vzw., Kapeldreef 75, Leuven, B-3001, Belgium 2 Aixtron AG, Aachen, 52072, Germany 3 Dept. of Chemistry, KU Leuven, Leuven, B-3001, Belgium ABSTRACT TaCN-based metal films were grown by metal-organic chemical-vapor deposition (MOCVD) and atomic vapor-deposition (AVD). Thermal decomposition at 500ºC leads to compositions of approximately Ta0.50C0.4N0.1 (“TaCN”), whereas a reactive process using NH3 leads to the formation of Ta0.65C0.1N0.25 (“Ta2N”) films. All films are nearly amorphous as grown and recrystallize only weakly after spike annealing at 1050°C. The thermal stability of TaCN/HfSiO4 and Ta2N/HfSiO4 stacks during spike annealing at 1050°C was studied and Si and Hf outdiffusion into TaCN or Ta2N was observed. The effective work functions of TaCN and Ta2N on HfSiO4 were found to be as high as 4.9 eV after high thermal budget. It is demonstrated that the effective work function can be further increased to 5.1 eV after high thermal budget by the insertion of a thin Al2O3 capping layer between HfSiO4 and the metal films. INTRODUCTION In order to limit leakage currents in complementary metal-oxide-semiconductor (CMOS) devices to acceptable levels, current generations require the introduction of high dielectric constant (high-κ) materials, such as HfO2 or HfSiO4, as oxide layers into the gate stack. This also requires replacing polycrystalline Si as the customary electrode materials by appropriate metals to eliminate the carrier depletion of the Si electrode and the resulting increase of the equivalent oxide thickness (EOT) of the gate stack [1]. However, the adjustment of the threshold voltage (VT) of MOS transistors cannot be anymore simply achieved by adjusting the doping level as in the case of polycrystalline Si. For metal gates, the threshold will depend on effective work function (EWF) of the metal in contact with the high-κ dielectric. In practice, it is observed that the EWF often deviates considerably from the bulk (vacuum) work function [2,3]. Generally, for a given metal, it is found to depend not only on the considered dielectric but also on the deposition method and conditions and on the thermal budget of the process flow. High-temperature annealing during device processing is often observed to shift the effective work function [4-6]. This shift is most often towards the “midgap” position of Si, leading to an unfavorable increase of VT. The thermal stability of the EWF during high temperature annealing is thus a decisive factor for the selection of a metal as a gate electrode. In this paper, we describe the growth of TaCN and Ta2N by metal-organic chemicalvapor deposition (MOCVD) and atomic vapor-deposition (AVD®) [7,8]. Both TaCN and Ta2N
show a high EWF of 4.9 eV on HfSiO4, which can be preserved du
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