Channel engineering for the reduction of random-dopant-placement-induced threshold voltage fluctuation

Abstract

A simple model is proposed, which is able to calculate VTH standard deviation due to random dopant placement in the channel, for arbitrary vertical impurity distributions. Substantial decrease in VTH fluctuation, while keeping VTH the same, is confirmed for low surface impurity channel MOSFETs, in agreement with the model prediction.

Suppression of random dopant-induced threshold voltage fluctuations in sub-0.1-μm MOSFET's with epitaxial and δ-doped channels

“…When the channel length is scaled down to dimensions below 0.1 m, the doping concentration in the channel region has to be increased to levels above 1 10 cm . The results of our atomistic simulations show that the doping concentration dependence of the random dopant-induced threshold voltage fluctuations in sub-0.1-m MOSFET's with conventional architecture is stronger than the dependence suggested by most of the analytical models [3], [11], [15], [16]. Fig.…”

“…Results of continuous-charge 3-D numerical simulations [9], [11] have shown that the introduction of a thin, low doped layer in the MOSFET channel, immediately below the interface, can efficiently suppress the threshold voltage fluctuations. This approach has been successfully demonstrated experimentally in MOSFET's with low doped epitaxial channels [15]. The introduction of a low doped region in the channel, however, makes the corresponding devices more susceptible to short channel effects.…”

“…The initial drive behind the introduction of lowdoped epitaxial channels was the expectation for mobility and transconductance enhancement, together with the introduction of new means for threshold voltage and subthreshold slope control. Later, based on continuous charge numerical simulations [9], [11] and elaborated analytical models [11], [15], [28], it has been realized that the retrograde channel doping profile in the epitaxial devices will also significantly suppress the random dopant-induced threshold voltage fluctuations. These theoretical predictions were also confirmed experimentally [15].…”

“…have also been developed [3], [11], [15], [16]. At the same time, the integrated circuits are becoming more sensitive to the fluctuation in the MOSFET characteristics due to the reduction in the supply voltage to reduce the power consumption and to sustain the reliability.…”

Statistical 3D ‘atomistic’ simulation of decanano MOSFETs

“…These architectures have additional benefits in terms of optimal threshold voltage control and improved mobility [19][20][21][22]. The undoped epitaxial layer thickness is restricted to approximately one-fifth of the effective channel length, due to short channel effects.…”