SBIR Phase II: Real Time Sputter Depth Measurement for In Situ Surface Microanalysis

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DMI-9627857 Colvard This Small Business Innovation Research Phase II project addresses the problem of knowing what subsurface level of a sample is being analyzed at any given moment during an analytical depth profile. Depth profile analysis of elemental composition at solid surfaces with secondary ion mass spectrometry (SIMS) and Auger electron spectrometry requires ion beam sputtering of material from the surface to form a crater of increasing depth. Only after the measurement is completed can the crater depth be measured by profilometry, the sputter rate averaged, and the calibration of composition versus depth completed. Unfortunately, sputter rates can vary widely in different materials, which shifts the apparent position of interfaces. Sputter rate has also been linked to ion yield, which affects the relative sensitivity factors used to quantify impurity data in SIMS. As industrial demands increase for higher levels of spatial and compositional accuracy, and for faster analytical turn around, it is important to measure crater depth and sputter rate in situ and in real time. We demonstrated in Phase I an interferometric technique that can perform this measurement. In Phase II we propose to use this approach to create a new tool, adaptable to existing analytical instruments, that will provide dynamic depth measurements, during an analysis, with a resolution approaching one nanometer. We will build a prototype instrument, adapted to an analytical SIMS spectrometer, that will monitor sputter depths at a single point during depth profile analyses. Its performance and functionality will be characterized, and shortcomings will be addressed. Experiments will be conducted to explore its behavior with different sample types, and multi-point extensions to the technique will be examined. Immediate applications exist for incorporation of this tool into commercial secondary ion mass spectrometers and Auger microprobes, both in new instruments and as retrofits into the large installed base.