AVS 45th International Symposium
    Applied Surface Science Division Thursday Sessions
       Session AS-ThP

Paper AS-ThP11
Quantitative Wafer Surface Trace Metal Analysis by TXRF and Surface SIMS

Thursday, November 5, 1998, 5:30 pm, Room Hall A

Session: Aspects of Applied Surface Science Poster Session
Presenter: M.J. Edgell, Charles Evans & Associates
Authors: J.M. Metz, Charles Evans & Associates
S.P. Smith, Charles Evans & Associates
M.J. Edgell, Charles Evans & Associates
V.K.F. Chia, Charles Evans & Associates
Correspondent: Click to Email
Ultra-clean Si wafer surfaces are critical to the fabrication of ULSI devices. This is reflected by the stringent contamination limits for polished and epitaxial substrates, and surface preparation (i.e. before gate oxide growth) suggested by the National Technology Roadmap for Semiconductors (NTRS). Today's requirement for surface metals is typically in the range of 10@super 10@ atoms/cm@super 2@. Future needs in the year 2003 are anticipated to be 1x10@super 10@ atoms/cm@super 2@ for Al, Ca, and Zn, and 2x10@super 10@ atoms/cm@super 2@ for Fe, Ni, Cu, and Na. The transition metals Fe, Ni, Cu, and Na are considered to be very damaging at the gate oxide level, and therefore requirements for these are becoming more stringent. It is even considered that surface metals on epi substrates before gate oxidation may have to be as tight as for polished substrates, because the low temperature processing at small design rules leads to less effective gettering in the p+ substrate of p/p+ epi. Al is important to monitor because at concentrations below 10@super 11@ atoms/cm@super 2@ it can increase the oxide growth rate in the very thin gate oxide regime. This is a different effect compared to higher levels of Al (e.g. >10@super 12@ atoms/cm@super 2@) decreasing gate oxide thickness for thicker gate oxides. TXRF and SurfaceSIMS are two of the most powerful analytical techniques available for substrate and interface engineering. Both these techniques provide quantitative trace metal information at the surface of wafers. TXRF is an excellent survey tool capable of analyzing 300 mm wafers to a depth of about 50 Å. Quantification at the Si/SiO@sub 2@ interface is very important and may be performed accurately using SurfaceSIMS. The information provided by these two techniques allows pre-clean technologies used on silicon substrates to be evaluated. This presentation reviews the two techniques and illustrates with examples how they compliment each other.