Developing a viable multilayer coating process for extreme ultraviolet lithography reticles

Reticle blanks for extreme ultraviolet lithography (EUVL) are fabricated by depositing reflective Mo/Si multilayer films on superpolished substrates. To obtain a reasonable cost of ownership for EUVL, the multilayer films must be nearly defect free, have excellent reflectance/thickness uniformity, and have a high EUV reflectance. Small particle contaminants on the substrate that can nucleate printable Mo/Si phase defects are a serious concern. We develop an ion-beam thin film planarization process for mitigating the effect of small substrate contaminants that relies on enhancing the smoothing capability of Mo/Si multilayer films; we observe that etching of the Si layers in between deposition steps can yield a significant improvement in smoothing. Using this process substrate particles as large as 50 nm in diameter are smoothed to similar to1 nm in height, rendering them harmless. We further develop this process so that it retains these particle-smoothing capabilities while also achieving a high EUV reflectance and excellent uniformity. (C) 2004 Society of Photo-Optical Instrumentation Engineers.