The impact of a thinner binary mask absorber on 22nm and beyond mask inspectability and defect sensitivity

Abstract

As part of 20 nm/22 nm process development, an evaluation was performed to determined the impact of Thin OMOG on mask inspection. Despite significant improvements in mask inspectability and reduced database modeling errors, thin OMOG demonstrated lower defect sensitivity as compared to Standard OMOG at the same inspection conditions (calibration, sensitivity). Stack height aside, the primary difference between standard and thin OMOG is attenuator reflectivity. It is surmised that the reduction in sensitivity is due to a lower reflected light contrast on thin-OMOG. This characteristic was noted for both 257 nm and 193 nm inspection wavelengths.In addition to the reduction in defect sensitivity, an unexpected phase interference was noted at the image edge with a 193 nm inspection wavelength, for Standard OMOG, but not for Thin OMOG. This interference, or undershoot is due in part to the low difference in reflectivity and phase between the quartz and the attenuator on the Standard OMOG substrate. This difference is more than five times greater for the Thin OMOG attenuator.The primary focus of this paper is on the characterization of thin OMOG relative to the interaction between attenuator reflectivity, image quality, database modeling and tool calibrations as they relate to mask inspectability and defect sensitivity. This paper will also address the changes required to compensate for the loss of sensitivity induced by the introduction of the thin OMOG absorber.