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 Accuracy: Layers thickness: The crater depth is measured with a stylus profilometer. When a multilayer has been analyzed, the sputtering ratio are introduced into the processing and we end up with layers thickness accuracy better than 3% . Sputtering ratio correction must be applied to prevent large errors as in the following example:  Concentrations measurement: The so-called SIMS formula allows to convert raw signals into concentrations, provided that a standard is available.  Below is an example: Silicon in InP. 115In signal is taken as a reference.  The error on concentration is:  The relative error due to the counting statistics is, in the gaussian approximation: DN/N(%) = 100/(N)1/2 Generally, NM >> NI , the statistic error in about 1% if NI is in the 1.E4 counts/cycle range. The error is then due mainly to D(RSF)/RSF, which depends on the quality of the standard, the way the standard and the sample are mounted, and generally the quality of the measure. With a good protocol, we proved that a long term reproducibility as good as 3% can be obtained. |
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