Evaluating 10B- and 11B-implanted standards for the analysis of boron in silicon with ultralow energy SIMS

Measurement standards are a prerequisite for accurate quantification of boron in silicon by secondary ion mass spectrometry (SIMS). We report about the comparison between the 10B reference SRM® 2137 from NIST and an 11B reference tailored for ultralow energy SIMS developed at IMEC. Depth profiles were acquired on two SIMS platforms (magnetic sector and time-of-flight) and using both O2+ and Cs+ primary ion beams of 350 eV. First, the relative sensitivity factors (RSFs) for 10B and for 11B were derived from measuring the two standards. The RSFs were consistent across instruments and sputter conditions, with the ratio of the RSFs for 10B and 11B close to unity. Second, the derived RSFs were used to analyze an in situ boron-doped epitaxial silicon sample. It was found that the concentration obtained using both references was mutually consistent. Notably, the IMEC standard led to a lower uncertainty compared to the NIST standard, and it required probing a shallower depth to realize the calibration. This renders the new IMEC standard for B in silicon suitable to calibrate SIMS instruments for modern ultrashallow SIMS metrology.