Formation of palladium silicide in the presence of Al with and without a carbon barrier layer

The formation of Pd silicides in the presence of an Al layer is studied using Al/Pd/Si structures with and without a carbon barrier layer between the Al and Pd layers. Both the reactions between Al and Pd and between Pd and Si start around 200°C, forming Pd2Al3 and Pd2Si, respectively. At higher temperatures, the excess Al present reacts with the Pd2Si formed, converting the latter to Pd2Al3 which is completed at 400°C. In the presence of a carbon barrier layer using an Al/C/Pd/Si structure, the Pd2Si formed stays little changed up to an anneal of 30 min at 500°C. The Pd2Si formed reacts with the Al present at higher temperatures, about two-thirds reacted after an anneal at 550°C, and nearly completely reacted after an anneal at 600°C, both for 30 min. The effectiveness of the carbon barrier layer for the Al/Pd 2Si reaction is compared with that for the Al/PtSi reaction, where little reaction is observed after an anneal of 30 min at 600°C. Application of the carbon barrier layer to device contact metallurgies is also discussed.