The effect of the earth's magnetic field on auger analysis

Semi-quantitative analyses of thin films or surfaces are commonly obtained from the peak intensities in the differentiated Auger spectrum. To reduce effects of surface roughness, beam focus and electron current, ratios of peak heights are used rather than absolute values. In performing analysis of CdSe single crystal and thin film samples in a commercial Auger analyzer fitted with a cylindrical mirror analyzer (CMA), the ratio of the Cd(376 eV) to Se(1315 eV) peaks was found to vary by as much as 15% when the diameter of the incident electron beam was increased from 5 to 60 μm. The effect was found to be due to an energy-dependent shift of the electron beam caused by the earth's magnetic field. The electron transmission of the CMA was measured as a function of the primary electron beam spot position on the sample. The transmission decreases rapidly once the spot falls outside an area with a radius ～25 μm. Due to this response, the relative shift in position caused by the magnetic field produces variations in peak ratios when the spot size is changed. This effect will produce inaccurate analysis if the Auger peaks differ significantly in energy and the primary electron beam spot size is large, and accounts for the observed 15% variation in $\text{Cd}\text{Se}$ ratio.