Effects of microscopic fluctuations in dopant distributions on MOSFET threshold voltage

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

“…This problem, recognized almost three decades ago [1], [2], is confirmed now experimentally [3]- [8] and in three-dimensional (3-D) continuous charge [9]- [11] and "atomistic" device simulations [12]- [14]. Simple analytical models, describing, for example, the random dopant-induced threshold voltage fluctuations, Manuscript received January 19, 1999;revised March 31, 1999.…”

“…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].…”

“…A relatively easy way to reduce the intrinsic parameter fluctuations, without a major change in the MOSFET architecture, is the appropriate tailoring of the channel doping profile. 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].…”

Quantum and Coulomb Effects in Nano Devices

“…The empirical analytical expression by Mizuno was generalized by Stolk et al [71] by taking into account the finite thickness of the inversion layer, the depth-distribution of the charge in the depletion layer and the influence of the source and drain impurity distributions. Numerical drift-diffusion and hydrodynamic simulations [72,73,74,75] have also confirmed the existence of the fluctuations in the threshold voltage in ultra-small devices. Two-dimensional (2D) [76] and three-dimensional (3D) [77,78,79,80] ensemble Monte Carlo (EMC) particle-based simulations have also been carried out.…”

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.…”