Depth resolution measurements were made using a custom "delta layer" sample consisting of a silicon substrate with thin phosphorus-rich layers of up to 5% P atoms per Si atoms (2.5 x 10 21 P at./cm 3 ) laid down by vapor deposition between silicon layers. The P-rich layers were at 30, 90, 180 and 330 nm depth from the surface (ihp-microelectronics.com). Depth profiles were acquired by using a Cs + primary beam from 16 keV to 4 keV at 500 pA and by rastering a 20 x 20 µm 2 area. MRP was >9000 at 8 keV of secondary ions energy as reported by the NanoSIMS software (based on peak side slope width from 10% to 90% of peak height; equivalent to ~6000 MRP for peak width at 10% height) . 31 P -and 30 Si - images were acquired with a counting time per frame of 4 s for a total acquisition time of about an hour. Images were processed with WinImage by defining a ROI of 8 x 8 µm 2 in the image center to extract the counts rates of phosphorus with minimal ion contributions from the analysis periphery. Profiles were then processed with WinCurve to scale the depth and extract depth resolution. Because P is known to diffuse into the overlying Si during deposition but not into the deeper layer (verified by IMS-7f), depth resolution was based on the rate at which the 31 P -counts drop off after each layer.