Product, Adhesive, And Carrier Wafer Thickness Measurement
Authors: David Marx, David Grant, and Russ Dudley Company: Tamar Technology Date Published: 10/3/2011
IWLPC (Wafer-Level Packaging)
Abstract: In the “via first” or “via middle” processes, finished wafers containing through silicon vias (TSV) are bonded to carrier wafers and thinned to expose the TSV contacts. Wafer thickness and total thickness variation (TTV) are important measurements to track before, during, and after the thinning process. The thinning process may include grinding, etching, and/or polishing. Not only might each of these steps impress its own thickness variation, but potentially could correct the thickness variation of the previous step. Therefore, accurate and rapid characterization of the wafer thickness enables process control and improves yield. In addition, thickness variation of the carrier and adhesive can cause unacceptable thickness variation in the product wafer during thinning. We will present the measurement method and example thickness map results for the simultaneous measurement of the product wafer, carrier wafer, and adhesive layer thicknesses. The measurement system is the Tamar Technology WaferScan system, which utilizes multiple sensors to directly measure multiple layer thicknesses. The thickness sensors, capable of measuring silicon thickness from 1µm to 1200µm, used in the WaferScan system can also be used in situ in some grinding and polishing systems. The uses and limitations of in situ measurements will also be described.