Factors Affecting Precision and Accuracy in Quantitative Analysis by Secondary Ion Mass Spectrometry

In quantitative analysis by secondary ion mass spectrometry (SIMS) using external standards, precision and accuracy are affected by sample misalignment and different secondary ion energy distributions. To Investigate this, depth profiles of four pieces of a B-Implanted silicon wafer were obtained with samples mounted fiat, or intentionally misaligned. The B⁺ signal was referenced to ³⁰Si⁺ and ²⁸SI₃⁺. In comparative analyses of four nominally Identical samples, the relative standard deviation (RSD) was 5.9% for nominally flat samples compared to 13% for misaligned samples for the ³⁰SI⁺ reference ion. When ²⁸SI₃⁺ was used as the reference species, internal agreement was much worse (150% for misaligned samples compared to 13% for flat samples). The best results (RSD 1.9%) were obtained for analyses from the center of one large sample with ³⁰Si⁺ as a reference. This study has shown that random sample misalignments lead to discrimination between analyte and reference ion species with differing energy distributions, which cause significant errors In the comparison of two samples.