Comparison of secondary ion mass spectroscopy analysis of ultrashallow phosphorus using Cs + , O 2 + , and CsC 6 − primary ion beams

It is well known that reducing the work function of the sample surface using Cs + ions increases the negative ion yield of phosphorus. It is also well known that a shallow primary beam implantation depth (R P ) is required for achieving high depth resolution during the analysis of ultrashallow implant profiles. The combination of the opposite polarities of the positive Cs + primary ion beam and the negatively biased sample (the combination most often used for P analysis using magnetic sector secondary ion mass spectroscopy) unfortunately accelerates the Cs + ions towards the sample thus limiting the degree to which the primary ion impact energy can be reduced [R. Loesing, G. M. Guryanov, J. L. Hunter, and D. P. Griffis, J. Vac. Sci. Technol. B 18, 509 (2000)]. A low primary ion beam impact energy and high impact angle, both of which result in lower R P , can be obtained using a negatively charged cluster ion such as CsC 6 − (Peabody negative ion source) impacting on a negatively biased sample [G. Gillen, L. King, B. Freibaum, R. Lareau, and J. Bennett, in Secondary Ion Mass Spectrometry, SIMS XII, edited by A. Benninghoven et al. (Elsevier, Amsterdam, 2000), p. 279; R. Loesing, G. M. Guryanov, and D. P. Griffis, in Proceedings of the 13th Annual SIMS Workshop, Lake Tahoe, 2000, p. 36]. If, however, Cs is not required to improve secondary ion yield, a low energy O 2 + primary beam impacting on a positively biased sample can be used [I. M. Abdelrehim, T. H. Büyüklimanli, S. P. Smith, and C. W. Magee, in Secondary Ion Mass Spectrometry SIMS XII, edited by A. Benninghoven (Elsevier, Amsterdam, 2000), p. 279; S. P. Smith, C. J. Hitzman, and C. W. Magee, in Secondary Ion Mass Spectrometry, SIMS XI, edited by G. Gillen (Wiley, Chichester, 1998), p. 277]. In this case, the reduction in sensitivity for P due to the loss of the negative ion yield enhancing Cs can be partly compensated by flooding the sample surface with oxygen. In this study Cs + , CsC 6 − , and O 2 + primary ions are compared for depth profiling of ultrashallow phosphorus in Si in terms of decay length, sensitivity, and crater bottom roughness.