Sputter-Ion Depth Profiling

Sputter-Ion Depth Profiling. Although it is essentially a destructive technique, SIMS depth profiling is rapid, and possesses parts per million or even parts per billion sensitivity to all elements and isotopes, coupled with a depth resolution of a few nanometres. Concentration-depth plots can be accurate to 5%. 

The depth resolution (i.e. the ability to discriminate between atoms in adjacent thin layers) is limited by the primary beam causing redistribution of target atoms prior to their emission as ions, and to segregation and radiation-enhanced diffusion processes. The local topography can also lead to a loss of depth resolution with sputter depth. 

As a first approximation, a simple linear relation may be assumed to convert the time of sputtering to depth. Thus for a constant sputtering rate, the depth of erosion z will be given by  

The value of S will be a complex function of the sample composition, and of the incident ions and their energy, mass and angle of incidence. If the crater depth can be measured independently, the above equation can be used to obtain the value of S. 

Imaging SIMS. Steeds et al. (1999) included this technique in their study of the distribution of boron introduced into diamond, where it is a well-established dopant that controls the electrical conductivity. SIMS was performed with a field-emission liquid gallium ion source interfaced to a magnetic sector mass spectrometer capable of about 0.1 pm spatial resolution. 

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