Charging effects in spatial light modulators based on micromirrors

This paper describes charging effects on spatial light modulators (SLM). These light modulators consist of up to one million mirrors that can be addressed individually and are operated at a frame rate of up to 2 kHz. They are used for DUV mask writing where they have to meet very high requirements with respect to accuracy. In order to be usable in a mask-writing tool, the chips have to be able to work under DUV light and maintain their performance with high accuracy over a long time. Charging effects are a problem frequently encountered with MEMS, especially when they are operated in an analog mode. In this paper, the issue of charging effects in SLMs used for microlithography, their causes and methods of their reduction or elimination, by means of addressing methods as well as technological changes, will be discussed. The first method deals with the way charges can accumulate within the actuator, it is a simple method that requires no technological changes but cannot always be implemented. The second involves the removal of the materials within the actuator where charges can accumulate.