Overlay Error Estimation of Wafer Rear Surface Alignment for 0.1-µm Lithography

Abstract

This paper proposes using the wafer rear surface alignment (RSA) method in a lithography system in order to achieve 0.1-µm lithography. To evaluate alignment limitations, the error due to processed layers, which induces degradation of mark visibility, is measured with two conventional sensors. One is a heterodyne sensor that is stable for grained aluminum samples. The other is a broad-band sensor effective for reducing the multiple interference effect in resist films. With these sensors, the estimated limitation is 0.053 µm (M±3σ), obtained in both experiments and in simulations. The RSA method is effective in overcoming this limitation, because there are no disturbance marks due to resist film or grained aluminum film. The RSA is shown to improve the alignment limitation from 0.053 µm to 0.031 µm (M±3σ).