Abstract:
MOSFETs are extensively used in Ie fabrications. Improvement
of the VLSI technology has resulted in device dimens-ions of the
order of fractions of a micron. With increased substrate doping
levels and reduced gate oxide thicknesses the classical treatment
of MOSFETs is no longer accurate. If the substrate is heavily
doped then the inversion layer thickness falls below the
classica1 critical width and under that situation the
quantization effects cannot be neglected. The effects of
quantization can be most accurately modeled by numerically
solving Schrodinger's and Poisson's equations self-consistently.
But this approach involves much computational time. It is
important to develop a computer efficient method that can derive
a result that approximates the quantum mechanical calculation
resul ts. In this thesis WKB approximate method is used to
determine the eigen energy of the inversion layer potential well.
The average penetration of the inversion layer charges in the
potential well from the semiconductor-insul<;ltor interface is
determined using the results of the WKB method. The surface
potential at the semiconductor-insulator interface is then
related to the threshold voltage by using the calculated_ eigen
energy and the average penetration of the inversion layer charges
from the semiconductor-insulator interface. The derived relations
. , ~.
-are used to develop a computer efficient analytical model to
study the quantum mechanical effects in various parameters of
MOSFETs including threshold voltage. The threshold voltage is
found to be larger than the classical value if quantization
effects are considered. Also quantization effects are found to
become prominent for higher substrate doping levels and thinner
gate oxide thicknesses.
