6 – Maskless photolithography

: The virtues of using photons for maskless lithography rather than charged particles are discussed briefly. Two generic forms of maskless photolithography, image projection and focal-spot writing, are compared. A particular form of focal-spot writing, zone-plate-array lithography (ZPAL), is highlighted. In this approach, an array of diffractive-optical microlenses is employed to produce stationary, discrete focal spots. Patterns are created by modulating the focal-spot intensities under computer control as the substrate is scanned. The reasons behind the design choices in ZPAL, experimental results, commercialization efforts, and prospects for circumventing the diffraction barrier are described.