Lithographic apparatus and method for illumination uniformity correction and uniformity drift compensation

A lithographic apparatus including a uniformity correction system is disclosed. The system fingers configured to be movable into and out of intersection with a radiation beam so as to correct an intensity of respective portions of the radiation beam. The system further includes actuating devices coupled a corresponding ones of the fingers and configured to move the corresponding fingers. A width of a tip of each of the fingers is half that of a width of the actuating devices. Systems and methods are provided for compensating for uniformity drift caused by, for example, illumination beam movement, optical column uniformity, uniformity compensator drift, etc. An illumination slit uniformity caused by system drift is measured. First respective positions of uniformity compensators are determined based on the uniformity. Uniformity compensators are moved to the first respective positions. A substrate is exposed. Alternatively, another illumination system slit uniformity is measured. The another illumination slit u