Gettering in Low Temperature VLSI Processes

For gettering in silicon we have discussed a mechanism that depends on the injection of silicon interstitials. At low temperatures, where this mechanism is important, the time to getter effectively is only weakly dependent on temperature. We have cited data from the literature reporting effective getteringin 1 hour at both 1000°C and 800°C for the case of phosphorus diffusion. For backside getters, such as polysilicon, which do not inject silicon interstitials, temperatures much below 1000°C can not be used. Thus as processing temperatures drop, the efficacy of polysicon as a gettering treatment must be questioned. Backside treatments such as argon implantation and phosphorus diffuision, because they do inject silicon interstitials,will be effective down to very low temperatures. Intrinsic gettering will also be effective at low temperatures, as long as one insures that oxygen precipitation continuesthrough the Process.