Sources of variability in alpha emissivity measurements at LA and ULA levels, a multicenter study

Alpha emissivity measurements are important in the semiconductor industry for assessing the suitability of materials for use in production processes. A recently published round-robin study that circulated the same samples to several alpha counting centers showed wide center-to-center variations in measured alpha emissivity. A separate analysis of these results hypothesized that much of the variation might arise from differences in sample-to-entrance window separations. XIA recently introduced an ultra low background counter, the UltraLo-1800(" UltraLo"), that operates in a fundamentally different manner from the proportional counters used at most of the centers in the original study. Inparticular, by placing the sample within the counting volume, it eliminates the sample-to-entrance window separation issue noted above, and so offers an opportunity to test this hypothesis. In this work we briefly review how the UltraLo operates and describe a new round-robin study conducted entirely on UltraLo instruments using a set of standard samples that included two samples used in the original study. This study shows that, for LA (" Low Alpha" between 2 and 50 alpha/ khr-cm(2)) sample measurements, the only remaining site-to-site variations were due to counting statistics. Variations in ULA(" Ultra-Low Alpha" < 2 a/ khr-cm(2)) sample measurements were reduced three- fold, compared to the earlier study, with the measurements suggesting that residual activity variations now primarily arise from site-to-site differences in the cosmogenic background. (C) 2014 Elsevier B. V. All rights reserved.