Reaction kinetics in tungsten/barrier metal/silicon systems

Abstract

The reaction kinetics and electrical properties of the W/TiN/TiSi 2/Si and W/TiN/Si systems are described. By using the TiN/TiSi 2 and TiN diffusion barrier layer, the tungsten silicidation rate is successfully lowered by 2 orders and 4.5 orders of magnitude respectively, compared with the silicidation rate of the W/Si system. The tungsten resistivity is 8 μΩ cm after 950°C annealing in N 2. By considering the activation energy of WSi 2 formation, the reaction rate for the W/TiN/TiSi 2 system is found to be controlled by the silicon supply at the bottom of the tungsten layer, and the rate-limiting process is considered to be silicon bond breaking at the TiSi 2-Si interface. The driving force for silicon diffusion is considered to be the reduction caused by tungsten silicidation at the W-TiN interface. 100 Å TiN films are thick enough to maintain the thermal stability, i.e. to suppress reactions and to maintain adhesion even after annealing at 950°C for 5 h. A good ohmic contact resistivity of the order of 10 -6 Ω cm 2 could be obtained for the TiN/p +-Si contact by increasing the interfacial hole density up to (8–10) × 10 19 cm -3. Some application examples are proposed with W/barrier layer/Si systems.