To estimate the multi-layer surface profile and to detect the inter-layer surface defects, a gated wavefront sensing approach has been proposed in previous work. However, that methodology measures the wavefront that has been distorted by its prior surfaces (reflected wavefront) or post surfaces (transmitted wavefront).

 Analysis has to be performed to estimate the multi-layer wavefront sensing by taking into consideration the multi-layer surface conditions. We will design a reconstruction correction algorithm by retrieving multi-layer wavefront information using the range gated system.

The correction model resulting from this project can be used to develop a multilayer gated wavefront sensing inspection system.  The system has the potential to discriminate and take measurements over large multi-layer wafer surfaces.

This is a novel application that has not been introduced in the commercial market. Nevertheless, the wavefront sensing technique has the capability to provide high local sensitivity with large area measurements using a relatively lower-cost solution.