A review of SIMS techniques for characterization of ultra low energy ion implants

SIMS (secondary ion mass spectrometry) is the most commonly used analytical technique for characterizing low energy ion implants. To obtain accurate near-surface SIMS profiles, instrumental depth resolution must be optimized, and transient ion yield changes during primary ion beam equilibration must be minimized. Best depth resolution is obtained by sputtering with a low energy primary ion beam incident on the sample at a large angle with respect to the surface normal. These analytical conditions also reduce the depth range over which transient ion yield changes occur. For oxygen primary ion bombardment, flooding the sample surface with oxygen gas during analysis can largely eliminate transient ion yield changes. Of the readily available SIMS instrument configurations, Quadrupole SIMS can deliver the best depth resolution. However, the low mass resolving power of Quadrupole SIMS results in important limitations due to its inability to resolve mass interferences from surface contamination. Magnetic Sector SIMS can eliminate the interference problem by operating in a high mass resolution mode. SurfaceSIMS, using oxygen flooding, provides high sensitivity and uniform near-surface ion yields required for accurate and reproducible depth profiling of shallow ion implants and surface contaminants related to ion implantation