Polycide structures

The first problem occurs with the gate electrode. The solution that has been developed has been to create a "polycide structure. Here, a thin layer... 

As mentioned earlier, the "polycide" structure can be used to replace the traditional gate poly. A sketch of such a configuration is shown in Figure 4, when x > 2.0, the WSix is stable on the poly. Otherwise, it cracks and/or peels off during high temperature processing. 

The same effect is seen when the polycide structure of Figure 4 is annealed. In Figure 6 we see the effect of furnace annealing Figure 7 shows similar effects for rapid thermal annealing. 

One of the primary advantages of the polycide concept is that the silicide top layer oxidizes readily to form a dense adherent Si02 overlayer, and the polycide structure underneath remains intact. Also, the oxide film forms within a reasonable time. Oxide thicknesses formed by dry 02 oxidation are shown in Figure 10, as a function of time and temperature. 

The hot-wall study11 introduced TaCI5 with an evaporator operating in the temperature range of 120° to 140 C with a small H2 flow (about 5 seem) as the carrier gas. A SiH4 flow of 24 seem is used at a pressure of 280 mTorr. Deposition rates of 120 A/min were achieved at temperatures of 615°to 635°C, with uniformity of 10%. Actually, a polysilicon layer is deposited first, so that a polycide structure could be studied. 

Figure 22 TEM cross section through TaSi polycide structure.20...

At present, tungsten silicide is usually used on the top of gate polysilicon as polycide structure which is an abbreviated name for polysilicon-silicide as shown in Fig. 6. 

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. 

Figure 9.1. MOS gate structure a) after deposition of poly-Si and the silicide b) after patterning the polycide stack c) after S/D implantations and spacer formation.

Figure 9.19 Schematic representation of a SIMS analysis of the fluorine profile in a polycide gate structure before and after anneal.

---