Maskless Optical Lithography using MEMs-based Spatial-Light Modulators

摘要

The semiconductor industry has been driven by significant improvements in optical-lithographic capability. Asfeature sizes on the wafer shrink faster than the wavelength of the exposing illumination, increasingly complex andexpensive steps such as immersion, resolution-enhancement techniques, and optical-proximity correction (OPC) arerequired. Traditionally, high costs have been amortized over large volumes of chips, and by progressive technologicalmaturity. Optical lithography using MEMs-based spatial-light modulators provides an alternative means of lithography.Significantly lower costs-of-ownership coupled with throughputs acceptable for mask manufacturing, mask prototyping,and low-volume-chip manufacturing are the enabling attributes of such techniques. At MIT, we have pursued a uniqueversion of this technology, which we call Zone-Plate-Array Lithography (ZPAL). In ZPAL, an array of high-numericalaperturediffractive lenses (for example, zone plates) is used to create an array of tightly focused spots on the surface of aphotoresist-coated substrate. Light directed to each zone plate is modulated in intensity by one pixel on an upstreamspatial-light modulator. The substrate is scanned, and patterns of arbitrary geometry are written in a “dot-matrix”fashion. In this paper, we describe results from our proof-of-concept ZPAL system and its future potential. Lithographyusing distributed, tightly focused spots presents a different set of advantages and challenges compared to traditionaloptical-projection lithography. We discuss some of these issues and how they bear on practical system designs.