A INTRODUCTION

Silicide formation is a key process step in current integrated circuit (IC) fabrication. The silicides are introduced to lower sheet resistance of poly-runners and to shunt the highly doped source/drain regions. In this Datareview, an overview will be given of the various materials aspects of silicidation of Co and Ti and their implementation in a full IC fabrication process.

B THERMAL PROCESS WINDOW EVOLUTION OF TiSi ₂ AND CoSi ₂

The technological implementation of a material in a full IC process is built on a detailed knowledge about the material and its formation [1,2]. This is particularly so for silicidation, since the reaction is very sensitive to many factors that change its kinetics. From a thermodynamic point of view, a system consisting of a thin metal film on a Si substrate is far from equilibrium. When kinetic constraints are removed, e.g. by heating and allowing elements to diffuse, the system will evolve in order to lower its free energy by the formation of intermetallic compounds. For Co on Si, a CO-rich phase, Co ₂Si, forms prior to the monosilicide, CoSi. These reactions are diffusion controlled. The final phase of the reaction is CoSi ₂ and its formation is nucleation controlled. The specific resistivity of CoSi and CoSi ₂ are 180 ?? cm and 18 ?? cm, respectively.

In the case of Ti on Si, the TiSi ₂