High immunity to threshold voltage variability in undoped ultra-thin FDSOI MOSFETs and its physical understanding

Abstract

Sources responsible for local and inter-die threshold voltage (V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> ) variability in undoped ultra-thin FDSOI MOSFETs with a high-k/metal gate stack are experimentally discriminated for the first time. Charges in the gate dielectric and/or TiN gate workfunction fluctuations are determined as major contributors to the local V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> variability and it is found that SOI thickness (T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Si</inf> ) variations have a negligible impact down to T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Si</inf> =7nm. Moreover, T <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Si</inf> scaling is shown to limit both local and inter-die V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> variability induced by gate length fluctuations. The highest matching performance ever reported for 25nm gate length MOSFETs is achieved (A <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Vt</inf> =0.95mV.µm), demonstrating the effectiveness of the undoped ultra-thin FDSOI architecture in terms of V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">t</inf> variability control.