Rigorous modeling of scattered light in EUV cameras

Summary form only given. In this paper we make use of both a fitted Power Spectral Density (PSD) function for an EUV system based on earlier published results and also an empirically derived PSD function over the spatial frequencies range from 5E-8 to 0. 1 (1/nm). From the radially symmetric PSD response a flare Point Spread Function (PSF/sub flare/) is constructed from which the impact on the aerial image can be directly computed through a convolution operation on the ideal aerial image without flare. It is shown that if the system PSD is stationary and the "chrome density" is uniform, the flare variation is essentially constant over the static exposure field except for distances several hundred microns from the edge of the exposure field. The main impact of flare is then a loss of overall aerial image contrast that can be significant, e.g. greatly exceeding 15% depending on mirror quality. The variation in critical dimension (CD) as a result of localized "chrome density" variation can be computed. We show that, through an iterative process, critical dimensions on the mask can be resized in a similar way to Optical Proximity Correction (OPC) to minimize the effects of flare on CD control.