Research Review: Metal-semiconductor Alloy Boosts MOSFET Performance
JAPANESE engineers have turned to a metallic nickel-InGaAs alloy to cut the source and drain resistance of InGaAs channel MOSFETs, which are promising contenders to maintain the march of Moore’s Law at the 11 nm mode.
Forming low resistance contacts with conventional methods is tough due to low dopant solubility, according to corresponding author SangHyeon Kim from the University of Tokyo. If source and drain resistances are too high, they saturate the on resistance in deeply scaled MOSFETs with a gate length of 30 nm or less.
The team, which includes researchers from Sumitomo Chemical Company and Tsukuba’s National Institute of Advanced Industrial Science and Technology, produced their transistors using a type of self-aligned salicide source/drain process, which is used to reduce contact resistance in silicon MOSFETs.
“Using salicide – an alloy between silicon and a metal like nickel-InGaAs – we can reduce the source-drain resistance due to a very low resistivity of salicide," explains Kim.
With this approach, it is possible to control the indium content of the contact during epitaxial growth and ultimately reduce the Schottky barrier height between the contacts and the channel. This promises to increase the drive current produced by the MOSFET.
The researchers produced their novel contacts for their InP-based MOSFETs by directly reacting nickel and InGaAs during a rapid thermal annealing step at 250 °C. There is a high degree of uniformity in this alloy, according to transmission electron microscopy measurements.
Engineers have fabricated a portfolio of transistors with gate lengths of 5 μm, gate widths of 150 μm and a range of InGaAs compositions. On-off ratios are 104, peak mobilities hit 2000 cm2 V-1s-1, and source and drain resistances are five times lower than that in p-n junctions. “We are planning to optimise our devices and scale them," says Kim.
SH Kim et al. (2011) App. Phys. Express 4 0242017
InGaAs MOSFETS are fabricated with a self-aligned metal source-drain structure