Backside Infrared Interferometric Patterned Wafer Thickness Sensing for Through-Silicon-Via (TSV) Etch Metrology

A quantitative metrology technique is required to provide quality control necessary for production-worthy through-silicon-via (TSV) etch. This paper reports on backside infrared interferometric wafer thickness sensing for highly repeatable, nondestructive, and high-throughput determination of TSV depth, unlimited by aspect ratio (AR). Selected etch depth measurements for 1-18 mu m critical dimension TSVs with AR up to 28: 1 are demonstrated with 3sigma measurement repeatability of less than 50 nm. On the 5 mu m x 25 mu m TSV etch process baseline on 300mm wafers, lot-to-lot, run-to-run, and within wafer etch depth variations have been quantified in a production-worthy fashion. This technique has found no appreciable depth differences between dense and isolated TSVs within run, and has identified improvements in run-to-run variability when using oxide conditioning wafers.