Quantification of the Depth Scale

Secondary ion emissions are collected as a function of sputter time, or more precisely, the primary ion dose. This is a result of the fact that each primary ion impact has a statistical likelihood of removing atoms and/or molecules from the surface of the substrate of interest. If more than one atomic layer is removed per analytical cycle, as is carried out in Dynamic SIMS, quantification of the depth scale may be required. For obvious reasons, this requirement does not extend to the Static SIMS regime. 

Conversion of the sputter time to depth units can be carried out once an understanding of the rate at which material is removed from the substrate s surface is reached. This rate is referred to as etch rate or the sputter rate, with the latter more conunonly used in SIMS (for definitions, see Section 3.2.2). Commonly used sputter rate units include A/s, nm/s, and nm/min. In some cases, the primary ion 

As discussed in Section 3.2.2, sputter rates depend on the following  

The dynamics (mechanism) of energy transfer which in itself depends on the masses of the colliding species, as well as the impact energy and angle, and 

The material examined, inclusive of long range lattice structure (amorphous versus crystallinity), the crystal orientation, the temperature of the sample, 

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