David Bernard

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Being able to look inside an object without opening it up or destroying it, and separating the different features within that would otherwise overlap each other when seen in a standard 2D X-ray image, are the same for the needs of electronics inspection on wafers and on printed circuit boards, as they are in the medical sphere. If there is a problem on a wafer (or a person!) ideally we want to analyze and measure the situation as much as possible, with everything in its natural and existing state before we opt, if necessary, to halt or modify a production process and/or take more radical action to probe the issues further with more invasive techniques and, possibly, a ‘surgical’, or destructive, inspection. If the fault / failure has been modified through an external analytical intervention then some important information might be lost from the subsequent analysis and thereby possibly obscure the root cause of the issue; for example, such as the need to modify process parameters.The above reasons are why non-destructive 2D and 3D x-ray inspection has become, for many years, an important part of the inspection regime in electronics manufacturing, both for failure analysis and process development and control.

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 optimize 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.

Download The X-ray Metrology of TSVs and Wafer Bumps here. 

This white paper, co-authored by David Bernard, John Tingay, Philip Moyse, Simon White, Evstatin Krastev & Will Heeley, Nordson DAGE was originally published in the proceedings of the Pan Pacific Microelectronics Symposium, Kauai, Hawaii, February 3- 5, 2015

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