Real Time Sputter Depth Measurement for In Situ Surface Microanalysis

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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 create 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. Interferometry is an ideal tool for this type of measurement since it is precise and non-contacting Charles Evans & Associates proposes to develop a tool, adaptable to existing analytical instruments, that provides dynamic depth measurements to a resolution approaching one nanometer. To do this, several issues specific to this unique application must be addressed. During Phase I the researchers will build a demonstration interferometer subject to the constraints of in situ application. They will perform experiments to assess depth resolution and to study the influence of various materials and near-surface structures. A design will be laid out for incorporating this device into an existing analytical instrument in Phase II.