Comparison of tilting and piston mirror elements for 65nm node spatial light modulator optical maskless lithography

Spatial light modulator (SLM) maskless lithography, an optical technology that replaces photomasks with an adjustable array of microelectromechanical mirrors can potentially complement conventional, mask-based, lithography. The usefulness of this technology depends on whether it can print features at least as well as conventional tools and can keep pace with the International Technology Roadmap for Semiconductors. In particular, any SLM-based tool developed now must be capable of printing 50nm or smaller gates and 130nm pitch lines and spaces using 193nm light as is being planned for the 65nm half-pitch node. SLM mirrors may be designed to tilt or shift in depth (piston). Aerial image simulations presented here show that 65nm node features formed by piston mirrors have the same process latitude as tilt mirrors with a numerical aperture (NA) of 1.1. In addition, piston mirrors exhibit the added benefit that they may be arranged to mimic alternating aperture phase shift photomasks. Isolated and dense features of 65nm node dimensions can be printed with a reduced NA of 0.90. This form of phase shifting may be required at the 65nm ITRS node both for conventional and maskless lithography applications.