An analytical model for sidewall parasitic capacitance of nano-scale trench isolated MOSFETs

Abstract

This paper presents a physics-based, analytical model for sidewall parasitic capacitance of nano-scale MOSFETs. Trench isolated MOSFETs have been considered in the 90 nm technology node. An analytical expression for the trench oxide parasitic capacitance is derived by taking into account the enhanced depletion depth caused due to gate fringing field at the trench oxide sidewalls and dopant redistribution in the channel. The sidewall parasitic capacitance is calculated using conformal mapping technique. The developed model has been validated by comparing the results predicted from the derived model with simulation data and with a similar model available in literature. It has been demonstrated that our model determines more correctly the parasitic capacitance of nano-scale devices compared to the existing model.Keywords-nano-scale MOSFETs; shallow trench isolation; inverse narrow width effect; gate fringing field; dopant redistribution; edge effect.

New Analytic Model of Coupling and Substrate Capacitance in Nanometer Technologies

“…The average reported error is around 5%-8%. The sidewall parasitic capacitance in nanoscale trench-isolated MOSFETs [16] and gate capacitance in gateall-around cylindrical silicon nanowire MOSFETs [17] were also modeled by using a conformal mapping method, which is similar to [1] and [6]. Furthermore, capacitance modeling is important in chemical mechanical polishing (CMP) and density analysis.…”

“…We repeated this type of experiments for different block sizes. The curve-fitting technique is applied to tune the template equations in terms of technologydependent parameters, that is, x/t in (11) and β in (16). The tuning of β for coupling capacitance is done for several fixed geometry sizes, such as 1 μnd 10 μm.…”

“…For CMOS 0.18 μm technology, (16) is not applicable because there is no extracted capacitance for the case where two metal blocks have no overlap. From the curve-fitting process, x/t in (11) tends to be a constant.…”

“…12 also shows that there is no need to use x/t for less than 25% displacement and more displacement needs to be compensated in capacitance calculation represented by larger x/t ratio. More than 100% displacement changes the equation to (16).…”

“…To tune (16) for this technology, β is also obtained from the curve-fitting process as follows: β = −0.0898 × displace + 1.233 (20) where displace is the amount of displacement between two metal edges. In this case, commercial tools do not extract any coupling capacitance for distances more than 3 μm.…”