Capping layers, cleaning method, and rapid thermal processing temperature on cobalt silicide formation

Abstract

The effect of some key variables such as rapid thermal processing (RTP) temperature, substrate cleaning method and capping layers, on cobalt silicide formation has been investigated. The in-situ RF sputter etch is found to give a post RTP2 R sh that is equivalent to a wet cleaned wafer. The temperature transformation curve of cobalt films, analyzed with R sh data and XRD, reveal the formation of Co 2 Si-CoSi-CoSi 2 phases in that order. The transformation curves of TiN capped films match those of blanket cobalt but the Ti capped films show the CoSi phase to be stable over a broader temperature range. There is no effect of dopants on the final cobalt disilicide R sh values for either the single of polycrystalline substrates. Controlled oxygen leak studies in the RTP ambient reveal that the R sh after RTP1 is degraded if a capping layer is not present. Electrical test results confirm the need for capping layers. This is indicated by lower R sh and R c values on both n+ and p+ junctions and poly structures. Furthermore the electrical results are comparable for Ti and TiN layers used as the cap films although the R sh /R c values are in general lower for the TiN capped films. Poly gate length vs R sh plots show the extendibility of the capped cobalt silicide process to the 0.18 um node.