Large-field, high-resolution photolithography

Holographic lithography's unique capacity for high-resolution and large-area pattern transfer offers significant advantages for fabricating a range of optical microsystems. Two industrialised models of lithographic system have been constructed. The first has an imaging resolution of 0.25 mu m over an exposure field of 6 '' x 6 '' and can print onto a variety of substrate types of dimensions up to 6 '' x 6 ''. It includes an alignment system permitting a pattern-to-pattern overlay accuracy of 0.3 mu m (3 sigma value). The second model combines an imaging resolution of 0.25 mu m with an exposure field of 10 '' x 12 '' and prints onto substrates up to 470 mm x 370 mm. This system has a substrate stepping capability allowing a pattern to be replicated many times onto the substrate, and an alignment system providing 0.5 mu m overlay accuracy. Both models operate at an exposure wavelength of 364 nm, making them compatible with standard i-line photoresist processing. The technology has been successfully employed for printing grating structures with periods down to 0.5 mu m for such applications as high-resolution encoders and optical interconnects.