New challenges to the modelling and electrical characterisation of ohmic contacts for ULSI devices

Continuing developments in semiconductor process and materials technology have enabled significant reductions to be achieved in the contact resistance Rc of devices. This reduction is commonly assessed in terms of the specific contact resistance (scr) parameter ρ_c (Ω·cm²). Such a reduction is essential, for as device dimensions decrease, then so also must ρ_c in order not to compromise down-scaled ULSI device performance. Thus the ability to accurately model contacts and measure ρ_c is essential to ohmic contact development. In this paper the increased difficulty in measuring lower ρ_c values, due to trends in technology, is discussed. The challenges presented by the presence of two interfaces in silicided contacts (metal-silicide-silicon) is also discussed. Experimental values of the scr of an aluminium-titanium silicide interface is determined using multiple cross Kelvin resistor test structures