Simultaneous nuclear reaction analyses of boron and phosphorus in thin borophosphosilicate glass films using (alpha, p) reactions

A method combining (alpha, p) nuclear reaction analysis (NRA) and ellipsome try has been developed for measuring the boron and phosphorus content of bo rophosphosilicate glass (BPSG) used for interlevel dielectrics in integrate d circuits. Yields from the P-31(alpha, p(0))S-34 (Q = 0.63 MeV) and B-10(a lpha, p(0))C-13 (Q = 4.06 MeV) reactions are coupled with ellipsometry thic kness measurements to determine the average atomic percent of B and P in th e film. We have determined that 6.0 MeV incident alpha's with a detector an gle of 135 degrees and about 100 mu m of Mylar range foil are optimum for o ur system. The yield for the B-10(alpha, p(0))C-13 reaction is quite consta nt in our energy range of interest (similar to 5.8-6 MeV) but the yield for the P-31(alpha,p(0))S-34 is not. Consequently, a simple conversion from "s tandard" BPSG reference samples (independently quantified by ICP mass spect rometry) is adequate to calculate a film's %B content. The %P calculation i s more complex, involving a three-dimensional fit of the P yield data and m easured film thickness to the him %P content. This fit is based upon yield data from a matrix of standard film samples. The technique is sensitive to 0.1% with an accuracy of +/-10% depending on the sample. This measurement m ethod is now used routinely at Sandia National Laboratories in support of o ur fabrication process lines. (C) 2000 Published by Elsevier Science B.V. A ll rights reserved.