Phase shifted addressing using a spatial light modulator

Spatial light modulator (SLM)-based microlithography has been developed into a mask writer system with state of the art performance. The system is conceptually a stepper with a programmable mask where the discrete mirror structure on the SLM is filtered out by an aperture in the Fourier plane. The SLM-chip consist of 1 million flat tilting micro-mirrors which are electrostatically actuated by means of an analog grayscale voltage map that is sequentially loaded into a CMOS circuit integrated with the micro-mirror device. The system is inherently sensitive to phase errors setting very high demands on micro-mirror planarity. Tilting micro-mirrors enable grayscaling in the amplitude range from −20% to +100% limiting the magnitude of phase-shift lithography for feature enhancement. A new micro-mirror design with a phase-step in the middle of the mirror has the advantages of covering a full address range from −100% to +100% amplitude which allows for strong phase shifting enabling similar lithographic performance as for instance using an alternating phase shift mask in a stepper. A lithography system with the new micro-mirror design also turns out to be less sensitive to micro-mirror non-planarity.