Trapezoidal SOI FinFET analog parameters' dependence on cross-section shape

Abstract

The trapezium is often a better approximation for the FinFET cross-section shape, rather than the design-intended rectangle. The frequent width variations along the vertical direction, caused by the etching process that is used for fin definition, may imply in inclined sidewalls and the inclination angles can vary in a significant range. These geometric variations may cause some important changes in the device electrical characteristics. This work analyzes the influence of the FinFET sidewall inclination angle on some relevant parameters for analog design, such as threshold voltage, output conductance, transconductance, intrinsic voltage gain (A V ), gate capacitance and unit-gain frequency, through 3D numeric simulation. The intrinsic gain is affected by alterations in transconductance and output conductance. The results show that both parameters depend on the shape, but in different ways. Transconductance depends mainly on the sidewall inclination angle and the fixed average fin width, whereas the output conductance depends mainly on the average fin width and is weakly dependent on the sidewall inclination angle. The simulation results also show that higher voltage gains are obtained for smaller average fin widths with inclination angles that correspond to inverted trapeziums, i.e. for shapes where the channel width is larger at the top than at the transistor base because of the higher attained transconductance. When the channel top is thinner than the base, the transconductance degradation affects the intrinsic voltage gain. The total gate capacitances also present behavior dependent on the sidewall angle, with higher values for inverted trapezium shapes and, as a consequence, lower unit-gain frequencies.

Analog Parameters of Strained Non-Rectangular Triple Gate FinFETs

“…Due to accuracy problems in these steps, it is very usual some fin width variations along the vertical direction, leading to nearly trapezoidal cross-sections on most cases (5). Some previous works (6,7) showed some consequences of these shape variations at room temperature.…”

Influence of Fin Shape and Temperature on Conventional and Strained MuGFETs’ Analog Parameters

“…Due to technological problems in these steps, it is very usual the occurrence of some fin width variations along the vertical direction, leading on most cases to nearly trapezoidal, non-rectangular, cross-sections [5]. Some previous works [6,7,8] showed some consequences of these shape variations at room temperature.…”

Suppression of subthreshold characteristics variation for junctionless multigate transistors using high-k spacers

“…Nevertheless, during the fabrication, the cross section of the photo resist is not always ideally rectangular and more likely trapezoidal due to the post lithography baking processes [13] and the optical absorption [14]. Then its shape would be transferred to Fin etching [13,15,16]. At the same time, the non-ideal anisotropic over-etching also induces the cross section of the Fin body being trapezoidal shape [17].…”