Maskless EUV lithography via optically addressed modulator

A new approach [1] to maskless EUV lithography is presented. It is based on a modulator that converts a deep ultraviolet (DUV) intensity pattern into an EUV phase pattern. The EUV phase pattern is then imaged with reduction via a 'conventional' EUV projection optic to create an intensity pattern on a wafer with pixel size of the order of 20nm and feature size of the order of 35nm [2]. The modulator consists, in one version, of a two-dimensional array of small EUV multilayer mirrors, each mounted on an elastomer pad. The required phase information is generated when the pads expand in response to the heat input pattern of the DUV programming beam. The fastest DUV writing method uses a mask, as in present day production lithography, so the proposed process is really a hybrid and is only maskless in the EUV stage. If the modulator is scanned this imaging process has the usual advantage of redundancy [3] in that as many as 100 different mirrors contribute on successive pulses to the intensity at a single feature on the wafer. Throughput is high and will be discussed for a typical case. Higher throughput may require larger DUV field size than is currently used in production. Modulator fabrication will be discussed.