Photolithography equipment manufacturers are continuously developing machines with ever increasing resolution and wafer throughput. The development has shown that previously less dominant performance limiting factors are increasingly impacting the conformity between the projected image and the object plane. It is evisaged that active optical elements are required for the correction of these non-conformities. This paper introduces the concept of active transmissive optical element shape control to improve focus whilst minimizing the effect of stress-biregringence and overlay.@en

Photolithography is the critical step in realizing a smaller feature size of Integrated Circuits (IC). Manufacturing beyond the 30 [nm] node requires tighter focus budgets in ArF immersion lithography systems [1]. Wafer non-flatness and lens heating are main focus-budget contributors [2, 3]. Their contribution can be reduced by exposing the wafer with a curved instead of the conventional flat focal plane (Figure 1). This effect is achieved by manipulating the photomask curvature during the exposure process. A piezoelectric actuation system has been developed for this purpose which can control the photomask curvature [4]. This paper revisits the actuation principle and presents the experimental validation of the concept in a functional model.@en