WSix for polycide applications

In 1983 an extensive review of silicides for IC s applications was published by Murarka86. This work focused mainly on sputter techniques as the deposition method. As we will see, after 1983 the CVD technique became the most popular method for polycide applications. Much literature on the technique itself and on the film properties has been published. It seems appropriate here to summarize from the literature the most significant results reported after 1983 on CVD-WSix. 

In this chapter we will briefly mention the use of WSix for polycide structures to overcome line delay problems and the attractiveness of the CVD technique to deposit WSix. In addition, we will elaborate on the two pertinent chemistries for CVD-WSix namely SiH4/WF6 and SiH2Cl2/WF6. 

One remark about using WSix rather than WSi2 is in order. We will see that seldom is pure WSi2 deposited but rather a mixture of WSi2 and Si. The composite film is then more accurately described by WSix. From a chemical point of view this notation is meaningless and does not imply a real compound with a silicon over tungsten ratio of x  

In VLSI-MOS based circuits, where doped poly-crystalline silicon (poly-Si) is used as the gate electrode, the performance of the IC is limited by the RC time delays in the poly-Si runners (see for detailed discussions Murarka86, Sachdev et al.212). The main reason for this delay is the high resistivity (500 fiftcm) of n+ doped poly-Si. In addition, the trend to a larger die size worsens the problem because these poly-Si lines become longer. 

Several approaches to decreasing the RC value of this gate electrode can be followed, such as replacing the entire poly-Si gate by a metal or a 

---