Particles are a serious concern in the fabrication of reticles for extreme ultraviolet lithography because they nucleate perturbations in the reflective multilayer film that can print in the lithographic image. We call these perturbations defects. It has been suggested that reticle substrates can be planarized and the high-spatial-frequency roughness of the multilayer film can be reduced by using an ion-assisted Mo-Si deposition process. In this article we discuss the cleanliness of this ion-assisted deposition process. Within one cleaning cycle, we improved the cleanliness of the deposition process without ion assist from 3-4 to 0.26 particles/cm(2). Of these, 0.09 particles/cm(2) are due to. manual handling of the wafers. We found that in our experimental setup, the added particle density using a process with ion assist is more then six times larger than the added density without ion-assist, suggesting that further work is necessary to develop a clean ion-assisted deposition process. We char, acterized the chemical composition of some of the added particles and found that they contain Al, C, Fe, Mo, and Si. (C) 2003 American Vacuum Society.