Rutherford backscattering depth resolution

The discussion of Rutherford backscattering spectrometry starts with an overview of the experimental target chamber, proceeds to the particle kinematics that detennine mass identification and depth resolution, and then provides an example of the analysis of a silicide. 

Rutherford Backscattering (RBS) provides quantitative, nondestructive elemental depth profiles with depth resolutions sufficient to satisfy many requirements however, it is generally restricted to the analysis of elements heavier than those in the substrate. The major reason for considering depth profiling using FIXE is to remove this restrictive condition and provide quantitative, nondestructive depth profiles for all elements yielding detectable characteristic X rays (i.e.,Z> 5 for Si(Li) detectors). 

The use of nuclear techniques allows the determination of C, N, H, O, and heavier contaminants relative fractions with great accuracy, and of the elements depth profile with moderate resolution (typically 10 nm). Rutherford backscattering spectroscopy (RBS) of light ions (like alpha particles) is used for the determination of carbon and heavier elements. Hydrogen contents are measured by forward scattering of protons by incident alpha particles (ERDA) elastic recoil detection analysis [44,47]. 

The distribution of species normal to the surface can be obtained nondestructively by variation of the emission angle in XPS or AES (limited to a total depth of about 50 nm), by Rutherford backscattering spectrometry (applying only to elements with Z > 10) and by nuclear reaction analysis (Z < 20 only). Depth resolution in both RBS and NRA is in the range 5-50 nm. 

There are three approaches for a subnanometer depth resolution [223] (1) Use of extremely low energies down to 100 eV. Although this generally increases the depth resolution and produces, for instance, profiles of As or P implants that resemble results from HR Rutherford backscattering spectrometry (RBS), the main drawbacks are a small ion current with bad focus-ability and a low sputter yield that can lead to erosion... 

Quantification in shallow profiles is another issue for quantitative analysis with SIMS. Matrix effects and sputtering rate changes are necessary considerations in quantification of shallow profiles to obtain an accurate profile with concentration and depth scales [14]. Comparison to high resolution Rutherford backscattering (HRBS) data helps in evaluating shallow SIMS profiles [36]. 

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