Physical and electrical properties of CoSi 2 thin films on silicon, and on silicon substrates buffered with SiO 2 and yttria-stabilized zirconia, using the laser physical vapor deposition technique

Abstract

Laser physical vapor deposition (LPVD) has been used to deposit thin CoSi 2 films on silicon, and on silicon buffered with SiO 2 and yttria-stabilized zirconia (YSZ). Silicide films were deposited by ablating a solid target of CoSi 2 in vacuum with a pulsed KrF excimer laser laser ( λ = 248 nm ). Particulate-free silicide thin films were deposited at an optimized substrate temperature of 600 °C. X-ray diffraction, Auger electron spectroscopy, Rutherford backscattering (RBS), scanning electron microscopy and transmission electron microscopy (TEM) were used to characterize the quality of silicide films and of the silicide-Si interface. The room temperature resistivity of an approximately 400 Å CoSi 2 thin film was found to be 23 μΩ cm. Growth of CoSi 2 thin films on SiO 2- and YSZ-buffered silicon under the same processing conditions as for silicon substrates was carried out to investigate if the underlying substrate was playing a role in the silicidation process. It was found by cross-sectional TEM (XTEM) and RBS that the stoichiometry of the film and the nature of the silicide-Si interface were independent of the nature of the substrate used. These results suggest that the LPVD technique could be used for the deposition of stoichiometric silicide thin films using lower thermal budgets as far as phase and stoichiometry are concerned on a variety of substrates without any need for an equilibrium with the underlying substrates as is the case with other silicidation techniques. Contacts of CoSi 2 to p +-Si were ohmic in nature and showed a linear behavior over a large range of current densities. The measured specific contact resistance of the as-deposited silicide ohmic contacts was of the order of 10 −5 Ω cm 2 . The quality of the silicide contacts was not affected by high temperature annealing treatments. Thus LPVD offers the possibility of fabricating low resistance silicide interconnects and ohmic contacts at a low deposition temperature without any need for a high-temperature annealing step, as required in other conventional silicidation processes.