Research Projects

Air Spacer MOSFET technology

Jemin Park and Chenming Hu

Samsung and ERSO Chair fund

In a 20nm-gate MOSFET with oxide spacer, 77% of the gate charge is due to the gate to plug/diffusion capacitances. Reducing these capacitances will be an increasingly important way to improve the device speed and switching energy/power at 20nm and beyond. Compared to an air-spacer inverter, a conventional nitride-spacer inverter has 82% longer delay and 85% larger switching energy (power consumption). Even a pure-oxide-spacer inverter has 41% longer delay and 48% larger switching energy than the air-spacer inverter. High density memories employ the SAC technology that requires the use of nitride spacers. This significantly raises the gate to plug/diffusion capacitance and increases the delay and switching energy by about 60%. A novel air-spacer SAC device can preserve the 35% area benefit of SAC device while reducing the delay and power by over 75% to levels even better than the non-SAC conventional device. It also reduces the bit-line and word-line capacitances. The result is increased DRAM and SRAM speed, reduced power, and reduced chip size. These air spacer technologies are promising key technology for 20nm generation and beyond.

Figure 1
Figure 1: Figure 1: MOSFETs constructed with 3D simulator. In (b) (c) part of ILD is removed to show the outlines of SAC. Lgate = 20nm, nitride/oxide/air spacer thickness= 12nm. (a) Non-SAC MOSFET (Oxide spacer)(b) SAC MOSFET (Nitride spacer) (c) SAC MOSFET (Air spacer)

Figure 2
Figure 2: Figure 2: The mixed-mode simulation of inverter delay. The delay of air-spacer is decreased by 45% and 30% compared with nitride-spacer and oxide-spacer respectively.

[1]
M. Togo, A. Tanabe, A.Furukawa, K.Tokunaga, and T. Hashimoto. : ‘A Gate-side Air-gap Structure (GAS) to Reduce the Parasitic Capacitance in MOSFETs’, Symposium on VLSI Tech. Dig., p. 38, 1996.
[2]
TSUPREM4 User Manual, Synopsys, Mountain View, CA.
[3]
SENTAURUS User Manual, Synopsys, Mountain View, CA