A non-destructive measurement of ball limiting metallurgy (BLM) undercut is demonstrated by using C-mode scanning acoustic microscopy. The results from CSAM measurements agree well with the optical and cross-section data. The implementation of the method in manufacturing will not only save time and cost on destructive failure analysis such as cross section and chemical un-layering, but also provide a way for monitoring process trend for early detection and correction of process abnormalities.

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