ABSTRACT
Lithographic tools have played a pivotal role in the fabrication of metamaterials since the pioneering work of D. R. Smith, where printed circuit boards were used in structures operating at radio frequencies. Masks are generally made using electron-beam lithography, which has been employed as the tool of choice in the fabrication of near-infrared or optical-frequency metamaterials because of its high resolution, moderate cost, and flexibility. A variation on the lift-off technique, which allows fabrication of multiple layers in a single lithographic step, involves the deposition of multiple layers into the same lithographically defined window. Optical lithography techniques have primarily been developed to enable the mass production of integrated circuits, and can be considered as the backbone of the silicon industry. With successive generations of exposure tools, the wavelength of the light has been reduced and the wafer size increased to accommodate ever-larger production volumes.
