Mask technologies for deep X-ray LIGA

Masks for LIGA applications requiring deep X-ray lithography have different specifications compared to those masks used in microelectronic applications. Generally, deep X-ray LIGA applications require resist heights greater than 100 mum, whereas accurate pattern transfer in this depth of resist is obtained by using highly parallel synchrotron radiation beam from storage rings in the lithography. Given the unusual nature of the lithography, the requirements for the mask blank and the absorber structures are quite different from those used in optical lithography. This paper discusses different approaches to mask making, and weighs up the advantages and disadvantages of the different approaches. In particular, emphasis will be placed on the changes in critical dimensions and sidewall roughnesses in the resist structures produced by the different mask technologies.