Ni/sub x/Ta/sub 1-x/Si and Ni/sub x/Pt/sub 1-x/Si ternary alloys for work function tuning on SiO/sub 2/, HfSiO/sub x/ and HfO/sub 2/ dielectrics

We present two new ternary alloy silicides with tunable work function ranging between 4.27eV to 4.7eV and 4.8eV to 5.0eV respectively for dual metal gate CMOS applications. Ni_xTa_1-xSi gates were investigated for NMOS and Ni_xPt_1-xSi gates were investigated for PMOS applications on SiO₂, HfO ₂ and HfSiO_x dielectrics. A large degree of tuning was observed on SiO₂ however the tuning range decreased as Hf content of the dielectric increased. It was also found that the thermal stability of nickel silicide was enhanced due to the incorporation of tantalum. Device results demonstrate thermally stable characteristics at 900degC, making them eligible candidate for gate first application. X-ray diffraction (XRD) confirmed presence of alloy silicide phases that were responsible for the work function tuning

Introduction

Metal gates may be required for 45nm technology to suppress boron penetration and poly depletion, as well as Fermi level pinning typically seen with hafnium-based silicates (1). Nickel silicide gates formed by full silicidation (FUSI) offer compatibility with conventional CMOS processing, low formation temperature and low resistivity. While work function tuning has been achieved on SiO₂-based dielectrics by changing the poly-si layer doping concentration (2), the mechanism by which the work function of nickel silicide on high-k is tuned is not clear. Reports indicate pinning of work function of NiSi to 4.5eV on HfSiON dielectrics on a wide range of doping concentration (3). Tuning has also been achieved by Ni_xPt_1-x xSi but the study was limited to SiO₂ (4). In this work, we utilize the full silicidation of Ni_xTa_y alloys (NMOS) and Ni_xPt_y alloys (PMOS) on high-k dielectrics of verying composition. We demonstrate that the degree of tuning depends on the Hf content of the dielectric with the maximum range of 800meV. Ni_xPt_1-xSi gates exhibited thermal stability up to 700°C while Ni_xTa_1-xSi gates were stable up to 900°C.