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.
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