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Zone-plate-array lithography (ZPAL): optical maskless lithography for cost-effective patterning

Zone-Plate-Array Lithography (ZPAL) is an optical-maskless-lithography technique, in which an array of tightly focused spots is formed on the surface of a substrate by means of an array of high-numerical-aperture zone plates. The substrate is scanned while an upstream spatial-light modulator, enabling "dot-matrix" style writing, modulates the light intensity in each spot. We have built a proof-of-concept system using an array of zone plates, and the Silicon Light Machines Grating Light Valve (GLVTM) as the light modulator. We have demonstrated fully multiplexed writing, multilevel alignment and resolution corresponding to k1 < 0.3. This system currently operates at l = 400nm and utilizes well-known I-line processes. Diffractive optics such as zone plates offer significant advantages over refractive approaches since near-ideal performance is achieved on axis, reliable planar fabrication techniques are used, costs are low, and the approach can be readily scaled to shorter wavelengths. In this paper, we also developed models and analyzed the cost-of-ownership of maskless lithography (ZPAL) versus that for optical-projection lithography (OPL). In this context, we propose the use of an effective throughput to consider the photomask delivery times in the case of OPL. We believe that ZPAL has the potential to become the most practical and cost-effective method of maskless lithography, enabling circuit designers to fully exploit their creativity, unencumbered by the constraints of mask-based lithography. This may revolutionize custom circuit design as well as research in electronics, NEMS, microphotonics, nanomagnetics and nanoscale science and engineering.