THERMAL CVD OF METALLIC CONDUCTORS

As before, we observe that there are many metallic conducting films that can be deposited by CVD.1 It is not our intention to catalogue all of these. Rather, we will restrict our attention to those films either in use in integrated circuit manufacture, or that have good potential for such use. 

In contrast to the films described in the last chapter, the ones to be discussed in this chapter have only become of interest recently. Up to the present, the integrated circuit gate electrodes have been fabricated from LPCVD polysilicon, which is heavily doped with phosphorus in a separate step (either by diffusion or ion implantation). Such heavily doped polysilicon can have resistivities as low as 500 juJ2-cm, so it behaves as a conductor, although not a very good one. Its compatibility with standard processing steps, however, make it a very attractive gate material. 

The final metallization of the standard single-layer metal conductor circuits has been provided by sputtered aluminum. As required, the sputtered Al can be doped with Si to minimize spiking of Al into the Si that it must contact. It can also be doped with copper to minimize electromigration effects. 

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 a point of interest, approximate values of the thin film resistivities of these materials are tabulated in Table 1. 

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