Nickel Silicide Work Function Tuning Study In Metal-Gate CMOS Applications
- PDF / 260,584 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 74 Downloads / 207 Views
B7.11.1
Nickel Silicide Work Function Tuning Study In Metal-Gate CMOS Applications Jun Yuan, Grant Z. Pan, Yu-Lin Chao, Jason C.S.Woo Electrical Engineering Department, University of California, Los Angeles, CA, 90095 ABSTRACT Mid-gap work function (~4.7eV) for mono-nickel-silicide (NiSi) was obtained by extrapolating flat band voltages of metal-oxide-semiconductor (MOS) capacitors with different gate oxide thickness. Both silicidation temperature and time can affect the nickel silicide work function as a result of different Ni:Si ratio close to the gate oxide interface. Arsenic implantation into the polysilicon before silicidation can shift the NiSi work function towards the silicon conduction band, which makes it suitable for high performance NMOS applications. The physical mechanism responsible for this work function shift is arsenic pileup at the oxide interface during the nickel silicidation process. Therefore, dual work function metal gate can be obtained by using a single gate full silicidation process. Silicidation temperature and time also affect the work function shift from arsenic dopant, and the incomplete gate silicidation can have the maximum work function modification effect. Arsenic activation temperature before silicidation was found to have a significant effect on the work function shift. Un-annealed samples exhibit a minimum shift in work function due to the low dopant pile-up concentration at the oxide interface. INTRODUCTION Metal-oxide-semiconductor-field-effect-transistors (MOSFETs) are the major devices in the very-large-scale-integration circuits due to their high package density, high speed and low power consumption. As MOSFETs are continuously scaled down into nanometer regime, metal gates are expected to replace polysilicon gates in order to eliminate the polydepletion-effect, suppress boron penetration and reduce the gate resistance. In addition, metal gates may be necessary for many high-K gate dielectrics in order to reduce the gate tunneling leakage current [1]. Simplification of process integration requires single metal deposition for both NMOS and PMOS. Full silicidation of polysilicon gate is very promising due to its process compatibility with the self-aligned silicide technology. Mono-nickelsilicide (NiSi) is an excellent candidate due to its low process temperature, lower line-width dependence of sheet resistance, and lower silicon consumption in the source/drain region [24]. However, the NiSi work function is close to the mid-gap of silicon, which makes it unsuitable for high performance MOSFET applications due to high threshold voltages [5]. Metal inter-diffusion gate and nitrogen implantation into a single metal have been suggested to tune the metal gate work function in MOSFETs [6-7]. Recently, doping of the polysilicon gate prior to silicidation has also been reported to modify the nickel silicide work function [8-11]. However, more investigation is needed to fully understand this nickel silicide work function modification effect. In this paper, work function shifts for ni
Data Loading...
