Analysis of precise CD control for 45nm node and beyond

Semiconductor device shrink progresses steadily at a speed of one generation every two years and CD uniformity (CDU) requirement becomes severer as shown in ITRS. Higher level of CD control performance is the most important item for semiconductor exposure tools to meet 45nm node requirements. For this higher accuracy it is of course necessary to brush up the projection optics and the illuminator system in every detail. We need to reassess items which were ignored as error factor until now and include them into the CD budget and thereby control in high accuracy. These small factors include the effects of birefringence caused by glass materials and coating, transmission distribution at the pupil of projection optics and influence of spectrum stability of a laser used in Hyper NA lens, and so on. They will come into the budget in addition to the conventional aberration and illuminator uniformity as we start to use new exposure technology such as immersion or polarized illumination after 45nm node. In this paper, we list up items which influence CDU in the node after 45nm, and estimate sensitivity for CDU for each item. Then we set the target values of every item by breaking the CDU target value of ITRS in terms of projection optics, illumination system, and total performance of exposure equipment. We show data for some items, and describe a prospect for 45nm node era and beyond.