Quantification of the Concentration Scale

Secondary ion emissions are recorded in intensity units. As a result, there can exist the need to relate secondary intensities to concentration. 

The conversion of secondary ion intensities into concentration values is, however, complicated by the fact that all secondary ion emissions exhibit a strong sensitivity to the chemistry of the substrate s surface during sputtering. This is otherwise referred to as the matrix effect. Matrix effects (discussed in Section 3.3.2.2) can result in secondary ion yield variations that span orders of magnitude. 

Quantification is further complicated by the fact that a vast array of analytical conditions can be used in SIMS. This is realized as these can influence the surface chemistry (primary ion implantation, damage, and segregation) and thus introduce 

As SIMS measures the number of secondary ions striking the detector, concentrations are most typically reported in units of atoms per some spatial or volumetric dimension, i.e. atoms/cm (at/cm ) in Static SIMS or atoms/cm (at/cm or at/cc) in Dynamic SIMS. These can be converted into percentage concentration values if the spatial or volume density of the substrate analyzed is known ( 1 x 10 at/cm and 5 X 10 at/cm for Silicon). Likewise, weight percent values can be defined by accounting for the mass of the respective signals. 

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Conversion of the sputter time scale to either the depth (as applies to Dynamic SIMS) or the surface coverage removed (as applies to Static SIMS) can be a relatively straightforward procedure. This is outlined in Section 5.4.2. Owing to the intricate interplay of intrinsic matrix effects with analysis-induced matrix effects, conversion of the intensity scale can be much more difficult. Indeed, effective quantification of the concentration scale requires the complete removal of all matrix... 

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