Linewidth design rules for microstructures manufactured in PMMA resist using X-ray LIGA

During the past decade, individual simulation modules for the LIGA process have been developed, such as the power spectrum of the X-rays available from a given synchrotron, the effect of various components in the beam line, the image structure in the resist and image development. This has lead to an understanding of the parameters affecting the basic dimensional relationship between the mask and the 3D image in the resist itself. The commercialization of X-ray LIGA now requires knowledge of the parameters affecting the production engineering of micro devices. Foremost among these parameters are the manufacturing tolerances arising from variations in key microfabrication steps. This paper seeks to integrate the various physical simulation models into a single interactive program, whereby the design engineer can see the effect of different synchrotron output spectra, different beamline constructions and different resist parameters on the dimensions of the planned 3D microstructure. A novel approach to estimating the dimensional tolerances to be expected with large scale production is developed and comparison made with data available from the literature. Predicted results from using a particular synchrotron with a beamline designed to approximate to a “standard” exposure spectra at the rest surface are calculated, showing the microstructure shape and tolerance expected in large scale production. From these data a basic set of equations are established from which “Linewidth Design rules for LIGA” can be established. The steps following definition of the resist structure, for example electrodeposition, injection moulding or hot embossing, are not studied here.