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

Abstract

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 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 G). For multi-gate fin field-effect transistors (FinFETs) which require smaller EWF shifts from mid-gap for low-V T: 1) conformal, lower-J 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.

Metal gate work function tuning by Al incorporation in TiN

“…Using TiAl as an Al diffusion source, low TiN work function values around 4.1-4.2 eV can be expected. 10 The extracted TiN EWF from TiN/TiAl devices with 5 nm of TiAl was 3.96 eV, while for the same metal gate stack with 2 nm of TiAl the TiN EWF value was about 4.13 eV. Literature reports that a reduction of 0.60 eV on TiN EWF can be achieved using TiAl layer, 10 the Al dif.…”

“…Solutions for the nMOS EWF in the range of 4.1-4.4 eV can be obtained by doping the TiN film with different materials (such as Al and N). [8][9][10] Literature reports had shown that the addition of Al ions into TiN layer can significantly change the TiN EWF. 8,10 The metal gate EWF shift is related to formation of different dipoles at the interface between metal gate and high-k due Al diffusion.…”

“…[8][9][10] Literature reports had shown that the addition of Al ions into TiN layer can significantly change the TiN EWF. 8,10 The metal gate EWF shift is related to formation of different dipoles at the interface between metal gate and high-k due Al diffusion. 8 The amount of Al ions at the interface between high-k dielectric and TiN layer will determine the shift on metal gate work function and a decrease of 0.60 eV on TiN EWF can be achieved using Al diffusion approach.…”

“…Aluminum and TiAl films have been used as an Al diffusion source for tuning the metal gate electrode work function. 8,10 The objective of this work is to decrease the TiN EWF by the incorporation of Al into TiN metal electrode using an AlN layer between HfO 2 and TiN films as an alternative material for Al diffusion source. The usage of AlN to control the metal gate EWF has been reported as a promising approach for work function engineering for CMOS technology.…”

Low-Frequency-Noise-Based Oxide Trap Profiling in Replacement High-k/Metal-Gate pMOSFETs

“…One wafer received a post-HfO 2 -ALD 9 min SF 6 -plasma exposure to introduce F in the gate stack. This was followed by a 1 min anneal in N 2 at 500 o C [10]. One reference wafer did not receive a post-high-k treatment, while wafer 5 received a post-HfO 2 -ALD heat treatment.…”