Modelling the Influence of the Silicon Doping Profile on a Silicide Well Ohmic Contact

Abstract

AbstractLow values of contact resistance Rc(Ω) and specific contact resistance, ρc(Ωcm2) are essential for ohmic contacts to devices with ULSI dimensions. The incorporation of silicides into contact structures has made a substantial contribution towards this goal. However the modelling and characterisation of these more complex silicide contact structures still requires considerable development. The variation of doping density in the vertical direction will cause a strong local variation in silicon resistivity with depth as well as a pronounced variation in the silicon-silicide barrier layer as a function of depth.In this paper we use a three dimensional (3-D) finite element analysis of sub-micron silicide contacts to illustrate the influence on Rc of the silicon doping profile in the sourcedrain contact regions. In addition, the influence of the doping profile on the current density distribution at the silicon-silicide interface is presented. A comparison of results is made between a uniform doping profile and two ion-implanted profiles. In order to improve the model's accuracy, the often neglected contribution of the metal-silicide barrier (ρca) to Rc is taken into account. Experimental measurements using a Cross Kelvin Resistor (CKR) test structure, have been used to determine ρca (∼3–5 × 10−9Ω.cm2 ) of the aluminium-TiSi2 interface.