Automated Metrology Improves Productivity and Yields for Wafer Level Packaging in High Volume Manufacturing

Wafer Bumping In-line Process control of Wafer-Level Chip Scale Package (WLCSP) requires accurate measurement of bump features during processing. These bump features include critical dimension of Redistribution Layer (RDL), Under Bump Metal (UBM) and transparent polyimide thickness. For a 4-Mask Layer Cu plated WLCSP, accurate feature thickness measurement is required for both the Redistribution Layer (RDL) and Under Bump Metal (UBM) to ensure consistent delivery of good electrical performance and package reliability. This is especially important as WLCSP is moving towards finer feature size and pitch to meet increasing demand for smaller form factor. This paper reports the development of an automated Critical Dimension (CD) measurement solution capable of measuring features at pre-defined locations on different topology both under sampling and full inspection mode on wafer. The solution is fully scalable to meet the requirement of high product-mix HVM environment, by highly adaptive to different features...