The X-Ray Metrology of TSVs and Wafer Bumps

ABSTRACT The emergence, development and use of Through Silicon Vias (TSVs) for the 2.5D and 3D integration of new products requires the availability of new inspection and measurement tools to validate TSV and 3D integration manufacturing procedures so as to ensure and optimise production yields and to provide high quality QA data. The areas where this need is most acute is in the measurement of the level of voiding that can be created during TSV fill, recognized as one of the major causes of poor yield in the TSV manufacturing process, and the level of voiding caused during the formation of wafer bumps. In particular, with TSV production most likely to be undertaken during the Middle End of Line (MEOL) or Back End of Line (BEOL) process flow, optical or infra-red techniques cannot provide this void data. Therefore, the use of x-rays offers a valuable, non-destructive method of inspecting and measuring TSVs and wafer bumps, not just for voiding, but also for a range of other critical dimensions. Historically, x-ray inspection / measurement has not been available for use in these applications owing to the limitations of x-ray source resolution for the features of interest and the limited quantity of x-rays (or flux) that has been available to give fast data acquisition. However, this paper will present the results of non-destructive, on-wafer measurements of TSV voids, solder bump voids and other features using a new, production-ready x-ray metrology tool