Static EUV micro-exposures using the ETS Set-2 optics

While interferometry is routinely used for the characterization and alignment of lithographic optics, the ultimate measure of performance for these optical systems is the transfer of an image or pattern into photoresist. Simple yet flexible exposure systems play an important role in this task because they allow complex system-dependent effects to be isolated from the printing results. This enables the most direct lithography evalaution of the optical system under investigation. To address tehse issues for commercial-class EUV optics, a synchrotron-based programmable illuminator exposrue station has been implemented at Lawrence Berkeley National Laboratory (the Advanced Light Source). As previously presented, this static microfield exposure system has been used to lithography characterize a 4-mirror optical system designed for the EUV Engineering Test Stand (ETS) prototype stepper. Based on the lithographic characterization, here we present a detailed performance analysis of the 0.1-NA ETS Set-2 optic. Operation of the static printing system with the Set-2 optic yielded approximately 330 exposed wafers, where each wafer contains one or more focus-exposure matrices. A wide variety of parameters were studied includign, among others, illumination conditions, resist thickness, and mask tone. Here we present a subset of this data in terms of process-window results. The resutls demonstrate a depth of focus (DOF) approximately 2μm for isolated 70-nm line features, 1 μm for nested 70-nm line features, and 0.5μm for 70-nm contacts on 270-nm pitch.