(Invited) Replacement Metal Gate/High-k Last Technology for Aggressively Scaled Planar and FinFET-Based Devices
Focusing next on gate dielectric scaling, we report a thorough evaluation of the impact of HfO2 doping , post high-k deposition thermal (PDA) and SF6-based plasma treatments [4,5] for planar vs. FinFET devices with different Si crystal orientations for the fin top and sidewall surfaces, providing a deeper insight into underlying degradation mechanisms. Higher k-value HfO2 (k~30) is achieved by introducing a metallic dopant during HfO2 growth, followed by an 800°C PDA which crystallizes HfO2 into its cubic phase. Up to 103× JG reduction at ~9.7Å EOT and net performance (ION) and reliability (BTI, TDDB) improvements when normalized to JG make this material attractive for low-power applications. F incorporation into the gate stack through exposure of HfO2 to a SF6-plasma results in substantially reduced Nit and noise values, improved mobility, and no EOT penalty down to narrow fin devices (WFin≥5nm), mitigating the impact of fin patterning, fin corners and fin sidewalls crystal orientations due to defects passivation by Hf-F and Si-F bonds formation. The plasma was optimized by increasing the number of ions reaching the bottom of narrow, high aspect-ratio gate trenches such that it can be used to incorporate F in the gate stack and to selectively remove the p-EWF/barrier metals (TiN/TaN) from NMOS areas in a simplified, highly scalable dual-EWF metal CMOS scheme  suitable for 2D and 3D device architectures and which maximizes the space for gate metallization. NBTI lifetime improvement with SF6 at 125°C is however fairly modest in the (sub-)1nm EOT regime, substantially increasing upon PDA introduction in the process flow, and for higher PDA temperatures (760°C→800°C). PDA devices exhibit reduced JG (enabling nFETs with ~10× lower JG at given VT) and show considerably smaller total effective trap density values, despite an increase in Nit (~1.4-1.8×), thanks to reduced bulk traps/defects. The latter seem thus to play a key and dominant role in NBTI for ultra-thin EOT, being mostly pre-existing defects contributing to charge trapping and de-trapping during stress and relaxation as inferred by the larger recoverable (R) vs. permanent BTI degradation components, calculated assuming universality of relaxation. Less steep R vs.stress time dependence in PDA devices also indicate less generation of new defects during stress, with improved hot-carrier immunity due to less charge trapping into bulk defects corroborating reduced presence of the latter. Further reliability gain is obtained for PMOS with (100) fin sidewalls in agreement with LF-noise results (Fig. 2).
 C. Auth et al., VLSI Tech. Dig., p.131 (2012);
 A. Veloso et al., VLSI Tech. Dig., p.194 (2013);
 L.-Å. Ragnarsson et al., VLSI Tech. Dig., p.27 (2012);
 A. Veloso et al., VLSI Tech. Dig., p.33 (2012);