Low resistance contacts to laser annealed junctions for nano-scaled MOS devices.

摘要

As MOS devices scale down to smaller dimensions, contact resistance will dominate the overall series resistance associated with current flow from source to drain. This thesis research has concentrated on issues of reducing the contact resistance, which include contact resistance measurement, contact material formation, and methods to increase doping concentration in silicon.;By performing two dimensional current flow simulations, we have found that common structures do not ensure accuracy in extracting contact resistivities from measured contact resistances, due to parasitic and intrinsic current crowding. In order to accurately extract contact resistivities for this study, the transmission line structure was modified by etching silicide to avoid the sidewall contact contribution.;As a contact material to silicon, nickel silicide (NiSi) has become our choice because it forms at temperatures as low as 400 °C with small silicon consumption. We have investigated the reaction between 10 nm-thick Ni films and Si. By performing rapid thermal anneals (RTA) at temperatures from 270 to 400 °C, we have observed the formation of Ni2Si and its transformation into the low resistivity phase of NiSi. Compared two RTA schemes of spike and soak in terms of the effective time, the spike anneals, which can be performed at higher temperatures with shortened anneal time, show reduced effective times for Ni diffusion. This suggests that spike anneals can improve junction characteristics while maintaining low resistance silicide films in the source/drain region.;The use of millisecond laser annealing has been investigated in this work. Low contact resistivities between 5 x 10-8 and 1 x 10-7 O-cm2 have been demonstrated on NiSi contacts to the laser annealed silicon, while a limit at 1 x 10-7 O-cm2 was noticed from the RTA samples. The obtained contact resistivities below 1 x 10-7 O2-cm2 represent that active concentrations above the solubility limit (2 x 1020/cm3) were achieved at the contact interface by the laser. Because of the ability to form NiSi contacts at low temperatures, supersaturated dopings maintain active and thus reduce the contact resistance. The laser annealing technique combined with low temperature NiSi contact formation shows promise in creating low resistance contacts for devices in technology nodes smaller than 45 nm.