Full sets (8 levels each) of X-ray masks have been made and characterized for overlay, resolution and line- width control. These mask sets have been successfully used to fabricate fully scaled 0.5 μm MOS circuits. The mask absorber included, in addition to the device pattern, test patterns and fiducials. A multilevel resist system was used to pattern the critical levels of the mask set. The precision of the mask set has been characterized by measuring more than 600 fiducials on each mask. Analysis of this data shows a level to level overlay error of less than 0.12 μm (3 σ) including measurement error. SEM measurements show a line-width controlled to within 250 Å (1 σ). Details of the device masks and their characteristics are discussed in this paper. © 1989.