OTS (February 2008) -- In parallel to the advancements made in ashless resist stripping using ZETA® system ViPR™ process, FSI now offers the HCl free ViPR™ process for metal silicide stripping (see FSI press release “FSI International Announces Breakthrough in Metal Stripping for Silicide Formation”). In collaboration with several customers, FSI has optimized the ViPR™ baseline process for rapid stripping of cobalt and nickel-platinum alloy metals used for salicide formation.
The ViPR™ process’s high on-wafer sulfuric acid temperature permits dramatically shorter process times for stripping cobalt metal, reducing chemical consumption (more than 70%) and improving process throughput (more than 40%). The unique spray cleaning technology of the ZETA® system ensures that the wafer always sees fresh chemicals and avoids the risk of contamination inherent in the use of recycled chemicals that can load up with metals and other impurities. By achieving the lowest levels of residual metals, the ZETA® system guarantees the lowest device leakage across dielectric features which in turn lead to higher manufacturing yields.
The ViPR™ process also offers a better alternative to HCl based, aqua-regia chemistry for NiPt stripping. In addition to being more difficult to work with, HCl-based chemistries have blocked the industry’s desire to move to lower silicide anneal temperatures (see Figure 1) and have proven incompatible with the SiGe source/drain technology now finding broad application at 45nm. While HCl-based chemistry does strip unreacted nickel and platinum, it can also cause unwanted surface reactions and attack certain regions of the silicide, resulting in higher, rather than lower, sheet resistances. Testing by FSI and customers has demonstrated that the sheet resistance issue can be addressed using an HCl-free metal stripping process. The high temperature (>150°C) achievable in the HCl-free VIPR™ process enables removal of the nickel and platinum layers without attacking the silicide layer. As a result, customers are now able to implement their preferred low temperature silicide anneal process without negative consequences. Although sulfuric acid based processes can be accomplished by either wet bench or single wafer means, the temperature limitation of benches and extensive chemical consumption of single wafer systems make the batch spray ViPR™ process the most economic means of achieving this type of strip.
Figure 1. Normalized NiPt silicide resistivity after metal stripping by HCl-based aqua regia. HCl-based chemistry results in increased resistivity for lower anneal temperature [adapted from Goh et al., “Challenges in Nickel Platinum Silicide Wet Etching for Sub-65nm Device Technology,” ECS Transactions, Vol. 11, No. 2, pp. 321-326 (2007)].
For more information on FSI ViPR™ technology for metal salicide stripping, please click here.