Work Function Tuning of Mo x Si y N z metal gate electrode for Advanced CMOS Technology
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Work Function Tuning of MoxSiyNz metal gate electrode for Advanced CMOS Technology Pommy Patel1, Douglas A Buchanan1, and Robert M Wallace2 1 Dept of Electrical and Computer Engineering, University of Manitoba, Winnipeg, R3T6C9, Canada 2 Dept. of Elect. Eng. and Physics, University of Texas at Dallas, Richardson, Texas 75083, Richardson, TX, 75083 ABSTRACT Due to continued transistor scaling, the work function tuning of metal gates has become important for advanced CMOS applications. The primary objective of this research is to understand the tuning of the MoxSiyNz (also referred to as MoSiN) gate work function through the incorporation of nitrogen. A molybdenum silicide (MoSi2) target was reactively sputtered in nitrogen (N2) and argon (Ar) plasma. The amount of nitrogen in the MoSiN films was varied by controlling the gas flow ratio, RN = N2/(N2+Ar). Capacitance-voltage (CV) and internal photoemission (IPE) measurements were performed to extract the work function (φm) of the MoSiN gate. The MoSiN work function was observed to decrease from ~ 4.67 ± 0.02eV to ~ 4.44 ± 0.025eV for an increase in the gas flow ratios from 10% to 40%. The SIMS depth profiles suggested a uniform distribution of nitrogen throughout the films. The XPS surface analysis confirmed a steady increase in the total nitrogen concentration in the MoSiN films as gas flow ratio was increased. The increase in N2 concentration corresponded directly with the lowering of the MoSiN work function. These results clearly demonstrated that the MoSiN work function maybe altered over ~0.3 eV tuning window by adjusting the N2 concentration in these films. INTRODUCTION Gate depletion, dopant penetration and high gate resistance issues in conventional poly-Si gates have necessitated the use of metal gate electrodes for advanced MOS devices. To maintain low threshold voltages levels, the work function (φm) of metal gate(s) must be close of that of n+ poly and p+ poly-silicon [1]. The ability to tune the work function (φm) of a mid-gap metal gate electrode over the desired range may be preferable over a dual metal approach. Molybdenum (Mo) is a transition metal with a mid-gap (φm ~ 4.5eV) work function. Recently, the work function tuning of Mo based gates has been implemented using various techniques including alloying [2], metal inter-diffusion [3], dopant implantation [4], sillicidation [5] and nitridation [6, 7]. The reactively sputtered MoxSiyNz (MoSiN) films were found to have good thermal stability on SiO2 when used as a diffusion barrier for aluminum interconnects [8]. Recently, the work function (φm) of reactively sputtered MoSiN gate was found to exhibit a dependence on the resultant Mo/Si/N ratio and subsequent thermal processing [9]. The present study extends past results and demonstrates the ability to tune the MoSiN work function over a wide range. Additionally, material characterization techniques including xray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were performed to understand the surface and interfa
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