Performance of the ASML EUV Alpha Demo Tool

The 22nm technology node is the target for insertion of Extreme Ultra-Violet (EUV) lithography into pre-production. To prepare this insertion, the issues that arise with the use of an EUV lithographic scanner in a pre-production environment need to be addressed. To gain better understanding of the issues that come with an EUV lithographic scanner, the Alpha Demo Tool (ADT) from ASML was installed at IMEC and is now in use since mid of 2008. In July 2009, the source was upgraded to a 170W/2 pi source to allow for higher uptime and wafer output by means of the semi-automatic tin refill. Also a new advanced resist, the SEVR-59 resist was introduced after the installation of the 170W/2 pi source to allow printing of 32nm Lines-Spaces (LS). After these changes, the ADT has been monitored closely with respect to the imaging performance. In this paper, we report on both the CD fingerprint analysis and the exposure tool stability. For 32nm dense LS, the ADT shows a wafer CD Uniformity (CDU) of 2.5nm 3 sigma, without any corrections for process or reticle. As for 40nm LS, the wafer CDU is correlated to different factors that are known to influence the CD fingerprint from traditional lithography: reticle CD error, slit intensity uniformity, focal plane deviation but also EUV specific reticle shadowing. The ADT shows excellent wafer-to-wafer stability (<0.5nm CD range in a 5-wafer lot) and the average CD as a function of exposure sequence is stable (<0.5nm 3 sigma in a 5-wafer lot). The ADT shows good CD stability over 5 months of operation with the 170W/2p source, both intrafield and across wafer. There is a 5nm difference in overlay performance (measured or after corrections) between the ADT and the XT:1900Gi production tool (using the same etched silicon wafers as a reference). Below 32nm, the ADT shows good wafer CDU for 30nm dense LS (60nm pitch). First 27nm dense line CDU data are achieved (54nm pitch). The results indicate that the ADT can be used effectively for EUV process development before installation of the pre-production tool, the ASML NXE:3100 at IMEC.