Laser bandwidth effect on overlay budget and imaging for the 45 nm and 32nm technology nodes with immersion lithography

The laser bandwidth and the wavelength stability are among the important factors contributing to the CD Uniformity budget for a 45 nm and 32nm technology node NV Memory. Longitudinal chromatic aberrations are also minimized by lens designers to reduce the contrast loss among different patterns. In this work, the residual effect of laser bandwidth and wavelength stability are investigated and quantified for a critical DOF layer. Besides the typical CD implications we evaluate the "image placement error" (IPE) affecting specific asymmetric patterns in the device layout. We show that the IPE of asymmetric device patterns can be sensitive to laser bandwidth, potentially resulting in nanometer-level errors in overlay. These effects are compared to the relative impact of other parameters that define the contrast of the lithography image for the 45nm node. We extend the discussion of the contributions to IPE and their relative importance in the 32 nm double-patterning overlay budget.