Quality control for deep x-ray lithography (LIGA): a preliminary metrology study

The x-ray lithography process is time-consuming and costly. The use of process design rules is essential along with CAD designs that should fulfil the specifications of dimension and roughness. Parameters such as the material of mask membrane, the technique to produce the mask, the resist used (poly (methyl-methacrylate) [PMMA], epoxy based photoresist SU-8), the synchrotron power and synchrotron spectrum do have an effect on the final geometry of the fabricated parts. To evaluate these parts, high accuracy metrology is essential. KIT/IMT and NPL have two different co-ordinate measuring machines (CMMs) designed for millimetre scale geometry measurements to micrometer accuracy. Test structures of various sized holes and columns, made by deep x-ray lithography in PMMA and electroformed in metal, have been measured by these two different CMMs. A comparison of the measurements taken from these two micro-CMMs will be presented and discussed. The outcome of these preliminary results on the x-ray lithography process will be shortly described.