Thickness Characterization of Ultra Thin Wafers on Carrier

For high density 3D integration to become reality, wafers must be drastically thinned to less than 100 mum. In this thickness range, the ultra thin Si wafers cannot be handled as such anymore and a carrier must be introduced for mechanical stability. However, this also introduces a difficulty in measuring the precise thickness and thickness variation of the device wafer only. In this paper, we present results about thickness measurements of ultra thin wafers on carrier using Spectral Coherence Interferometry (SCI) of a near-infrared (NIR) light source. This technique is equivalent to a time-of- flight method where the of the device and carrier wafers can be measured independently and simultaneously.