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

Continuing developments in semiconductor process and materials technology h ave enabled significant reductions to be achieved in the contact resistance R-c of devices. This reduction is commonly assessed in terms of the specif ic contact resistance (SCR) parameter rho(c) (Omega cm(2)) of the metal-sem iconductor interface. Such a reduction in SCR is essential, for as device d imensions decrease, then so also must rho(c) and the corresponding contact resistance in order not to compromise the down-scaled ULSI device performan ce. Thus the ability to accurately model contacts and measure rho(c) is ess ential to ohmic contact development. The cross kelvin resistor (CKR) test s tructure is commonly used to experimentally measure the Kelvin resistance o f an ohmic contact and obtain the specific contact resistance rho(c). The e rror correction curves generated from computer modelling of the CKR test st ructure are used to compensate for the semiconductor parasitic resistance, thus giving the SCR value. In this paper the increased difficulty in measur ing lower rho(c) values, due to trends in technology, is discussed. The cha llenges presented by the presence of two interfaces in silicided contacts ( metal-silicide-silicon) is also discussed. Experimental values of the SCR o f an aluminium-titanium silicide interface is determined using multiple CKR test structures. (C) 2000 Elsevier Science Ltd. All rights reserved.