Explicit expression on specifications of mask mean to target and mask uniformity

Abstract

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 90nm 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 63nm is ±2.3nm at the mask uniformity of 2.23nm. For 73nm design rule, specifications of mask MTT are ±1.94 and ±1.48nm at the mask uniformities of 2.32 and 3.31nm at the process constants (k1’s) of 0.295 and 0.322, respectively. For 90nm design rule, the mask MTT specifications are ±3.89 and ±4.13nm at mask uniformities of 3.89 and 4.13nm for k1’s of 0.364 and 0.396, respectively.