Linear V _FB Modulation and Interface Improvement in La ₂ O ₃ Dipole-First Gate Stack via TMA Pre-Treatment Without EOT Deterioration

This letter presents a novel pre-treatment approach using trimethylaluminum (TMA) as the precursor of Al<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub>, to compensate for the modulation effects of La-dipoles, thereby enabling linear tuning of flat-band voltage (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FB</sub>) in a La<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dipole-first process. Specifically, 5 cycles of TMA pre-treatment prior to La<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> deposition facilitate the realization of five distinct V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FB</sub> levels. By varying the deposition of La<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layers from 3 to 9 cycles during Atomic Layer Deposition (ALD), a linear tuning step of ~40 mV per cycle is achieved, resulting in a total V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FB</sub> shift range of 280 mV. Compared to an un-treated reference, the maximum modulation range can be as high as 460 mV. Furthermore, the TMA pre-treatment significantly improves the Si/SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> interfacial quality without deteriorating the equivalent oxide thickness (EOT). For La<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layers deposited using 3, 6 and 9 cycles, with 5 cycles of TMA pre-treatment, the trap/detrap electron density (N<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ot</sub>) is reduced by 45.7%, 42.9% and 42.6%, respectively, while the interface states (D<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">it</sub>) are reduced by 34.3%, 46.7% and 54.6%, compared to un-treated references. Achieved results demonstrate that the joint effort of both La<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub>O<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dipole and TMA pre-treatment paves a promising way for linear threshold voltage (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">th</sub>) tuning in state-of-the-art nanosheet gate-all-around field-effect transistors (NS GAA-FETs).