One of the key components of a full-field 150-mm exposure system is a properly specified and fabricated mask. The Micralign Model 661 HT uses a 71/4-inch diameter mask substrate with a 150-mm patterned field. While low distortion, electron beam generated full-field masks for 150-mm wafers will become more common in the future, it is expected that many of those masks fabricated in the near term will be optically stepped. Present 71/4-inch fabrication techniques can meet the critical dimension and defect density requirements consistent with the specified lithographic capabilities of the Micralign system. Pattern registration is the primary requirement affecting the specification of optically stepped masks. Die placement results in a random error, a systematic error (runout), and an orthogonality error. This distortion is commonly measured for each mask, and the relative magnitude is part of the specification. The burden on optically stepped masks can be minimized by relaxing this registration specification based on the Micralign's ability to correct for isotropic and anisotropic runout, as well as for orthogonality errors. A description of mask registration errors, how they are measured and subsequently compensated for by the offset and magnification capabilities of the Micralign exposure system, and the experiment designed to quantify those capabilities, is presented. Design characteristics of the Micralign subsystems providing error compensation are outlined. Experimental techniques and results demonstrating the correction of actual mask registration errors are described and data presented.