An ion-assisted Mo-Si deposition process for planarizing reticle substrates for extreme ultraviolet lithography

Substrate particles are a serious concern in the fabrication of reticles for extreme ultraviolet lithography (EUVL) because they nucleate defects in the reflective multilayer films that can print in the lithographic image. We have developed a strategy for planarizing reticle substrates with smoothing-layers and, in this letter, we investigate the smoothing properties of an ion-assisted Mo-Si deposition process. We have observed that ion-assistance can significantly improve the particle-smoothing properties of Mo-Si multilayer films and can do so without a significant increase in the high-spatial frequency roughness of the multilayer film. An ion-assisted Mo-Si smoothing-layer approach to reticle substrate planarization, therefore, shows significant promise for defect mitigation in EUVL reticles.