An analytic expression on the relationship of the mask mean to target (MTT) and the mask uniformity specifications is suggested. The MTT and uniformity (M-U) curve defines the boundary of the specification region, and this curve is explicitly expressed as mask error enhancement factors (MEEFs), dose sensitivities, and critical dimension (CD) tolerances of cell and peripheral patterns. This curve shows linear relationships between mask M-U. The decrease of the mask uniformity allows the increase of the mask MTT margin. M-U specifications are suggested for 63, 73, and 90 nm design rules. In this experiment, the tolerance of the cell pattern is given as the product of the MEEF and the mask uniformity margin which is specified as 60% of the total CD variation at the given design rule, while that of the peripheral pattern is set to be 10% of the design rule. An isolated pattern is selected as a peripheral pattern because its pitch size is infinite. The mask MTT specification for 63 nm is +/- 23 nm at the mask uniformity of 2.23 nm. For 73 nm design rule, specifications of mask MTT are +/- 1.94 and +/- 1.48 nm at the mask uniformities of 2.32 and 3.31 nm at the process constants (k1's) of 0.295 and 0.322, respectively. For 90 nm design rule, the mask MTT specifications are +/- 3.89 and +/- 4.13 nm at mask uniformities of 3.89 and 4.13 nm for k1's of 0.364 and 0.396, respectively. (c) 2006 American Vacuum Society.