Polycide

Diamyceline Polfungicid zasypka Futrican Myco-Polycid Unifungicid Polfungicid plyn... 

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. 

The tungsten silicide films, when deposited by CVD as contrasted to sputtering, are very conformal. This behavior is shown in Figure 9, where a 5000 A polycide film (2500 A WSi2 + 2500 A poly is deposited over a small step. On steps with vertical walls, the thickness of the polycide on the vertical wall was at least 75% of its thickness on the horizontal surface. 

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. 

Instead, the approach taken was to anneal the polycide films at temperatures over 800°C. In this case. Si diffused up to the TasSi3 film in sufficient quantity to convert it to TaSi2. An anneal at 1000°C for 15 minutes in argon produced a resistivity of 48 n l-cm in 2500 A thick TaSi2 layers. 

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. 

Proprietary Names. Benzalchlor-50 Cetal Cone. A and B Empigen BAC Hyamine 3500 Laudamonium Morpan BC Ovules Pharmatex Quartamon Roccal Sabol Silquat BIO Silquat B50 Vantoc CL Zephiran. It is an ingredient of Polycide, Stomosol, and Timodine. 

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. 

The sheet resistance of the polycide stack should be as low as possible. 

The patterning of the polycide stack should give no additional problems compared with the patterning of poly-Si. 

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.

After 1983, CVD-WSi2 became because of the above mentioned reasons popular and is now worldwide in use in large volume production (almost exclusively in polycide applications). Besides CVD also sputtered WSi2 is still in use in production. In the following sections we will elaborate on the CVD technique. 

Good results have been reported [Saraswat et al.225, Deal et al.227, Trammel228, Metz228] for CVD-WSix-polycide MOS devices. Even in the case where there was no poly-Si and thus the silicide was in direct contact with the gate oxide, very low levels of fixed oxide charge and interface traps were present. It is interesting how the workfunction found for polycide MOS... 

In a detailed study of polycide stack behavior during anneal, Kottke... 

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

Figure 9.20. WSi delamination of 0.6 and 0.7Jim wide polycide lines. Top SiH2Cl2 (x=2.9) SiH4 (x=2.6) bottom. [Ellwanger et al.244, reprinted with permission].

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