Abstract: The invention involves new etch monitoring and thickness measurement techniques which are more accurate than previous techniques. In accordance with the invention, the etch depth of a substrate region undergoing etching is monitored, or the thickness of the region is measured, by impinging the region with light and detecting the intensity of the reflected light. In contrast to the previous techniques, the incident light is chosen so that a substrate region underlying, and/or a patterned substrate region overlying the substrate region of interest is substantially opaque to the incident light, which precludes the formation of signals unrelated to etch depth or thickness.

Abstract: Mask-to-wafer alignment in X-ray lithography is advantageously carried out utilizing zone plate marks formed on the mask and wafer. In practice, it has been observed that the intensity and in some cases even the location of the centroid of the light spot formed by a zone plate mask can vary during alignment as the mask-to-wafer spacing is changed.The present invention is based on the discovery and analysis of the causes of such variations. Based thereon, applicants have devised a modified mask structure which, when used with a wafer in a zone plate alignment system, enables mask-to-wafer alignment to be made more easily and more reliably than was possible heretofore. The modified mask structure includes a localized blocking layer over each zone plate on the mask. This layer allows only a negligible portion of the light employed to illuminate the zone plates on the mask to propagate into the mask-to-wafer space.