Effective Work Function Engineering for Aggressively Scaled Planar and Multi-Gate Fin Field-Effect Transistor-Based Devices with High-k Last Replacement Metal Gate Technology

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This work reports on aggressively scaled replacement metal gate, high-k last devices (RMG-HKL), exploring several options for effective work function (EWF) engineering, and targeting logic high-performance and low-power applications. Tight low-threshold voltage (V_{\text{T}}) distributions for scaled NMOS devices are obtained by controlled TiN/TiAl-alloying, either by using RF-physical vapor deposition (RF-PVD) or atomic layer deposition (ALD) for TiN growth. The first technique allows optimization of the TiAl/TiN thicknesses at the bottom of gate trenches while maximizing the space to be filled with a low-resistance metal; using ALD minimizes the occurrence of preferential paths, at gate sidewalls, for Al diffusion into the high-k dielectric, reducing gate leakage (J_{\text{G}}). For multi-gate fin field-effect transistors (FinFETs) which require smaller EWF shifts from mid-gap for low-V_{\text{T}}: 1) conformal, lower-J_{\text{G}} ALD-TiN/TaSiAl; and 2) Al-rich ALD-TiN by controlled Al diffusion from the fill-metal are demonstrated to be promising candidates. Comparable bias temperature instability (BTI), improved noise behavior, and slightly reduced equivalent oxide thickness (EOT) are measured on Al-rich EWF-metal stacks.
2013-04-25