Wafer Thickness Sensor (WTS) for etch depth measurement of TSV

The wafer thickness sensor (WTS) is an optical, non-destructive sensor that directly measures the etch depth of vias, without regard to aspect ratio. The high throughput measurements of via depth after the etching of through silicon vias (TSV) will allow timely feedback for process control, process development, and the prevention of process excursions in 3D IC process technology. In this paper, we report the capabilities and limitations of the WTS for the measurement of TSV etched depth. Etch depth measurement results are presented for a variety of vias, including 1 mum, 3 mum, and 5 mum diameter vias, vias with an aspect ratio of 28:1, and both isolated and densely packed vias. Results include accuracy and repeatability data, with a route towards providing a high volume manufacturing TSV etch metrology solution for 3D IC process technology.