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SIMS Theory: Standards for RSF Measurement
Quantitative SIMS analysis requires standard materials from which to measure RSF values. Because ion yields depend on the analyte element, the sputtering species, and the sample matrix, separate RSF's must be measured for each. Ion implants are good standards. It is possible to implant virtually any element into any matrix. Ions can be passed through a mass analyzer before implantation to insure implant purity. Typical implant ion energies range from 50 to 300 keV. Higher energies are usually used for heavier ions, producing typical implant depths centered around 0.2 um. Most importantly, the implant ion current can be integrated to determine total ion dose. However, care must be taken to exclude secondary electron and ion currents from the total measurement.
The phosphorous implant raw data shown in the Depth Profile section can be used to calculate an RSF value for phosphorous in silicon. The shaded area is the total signal from the phosphorous implant (3.68e6 phosphorous ions).
Dividing the total signal by the measurement time gives Ii, the average phosphorous secondary ion signal during the measurement (2.69e4 / s). The implant dose (1e15 ions per square centimeter in this example) and the crater depth (0.74 um) are required to calculate the average implant concentration, CI (1.35e19 atom/cc).
Inclusion of the silicon matrix current, IM, (2.18E8 / s) provides for RSF calculation according to the rearranged RSF equation.
The calculated RSF value (1.09e23) is in close agreement with the value cited (1.07e23) in the RSF Tables section.
