Recent developments in deep x-ray lithography

Deep x-ray lithography (DXRL) with synchrotron radiation represents the technological core of the Lithographie, Galvanoformung, Abformung (LIGA) microfabrication process, thus defining the lateral shape and the accuracy of the final product. High aspect ratio microcomponents with a height of some micrometers up to several millimeters can be manufactured with submicron precision. We report on recently performed theoretical investigations on the structure transfer accuracy in the shadow printing process. Model calculations revealed the importance of photoelectron emission compared to Fresnel diffraction and beam divergence for typical DXRL conditions. The parameters used to model the effects correspond to the spectral distribution of the BESSY I wavelength shifter, Berlin (0.8 GeV, 5 T) equipped with several vacuum windows and a mask membrane made of beryllium with a thickness of 500 mu m. A poly(methylmethacrylate) resist layer of 300 mu m thickness with a bottom dose of 5 kJ cm(-3) is assumed. The calculated dose profiles are supplemented by a detailed experimental analysis confirming the calculation results which indicate a microstructure precision of less than 0.05 mu m per 100 mu m resist height. Additionally, advanced irradiation techniques like multiple tilted exposures and aligned double exposures are discussed with respect to their technological capacity. Resist side walls exposed under an inclination angle of 45 degrees turned out to follow an accuracy of approximately 1 mu m over a height of up to 500 mu m, where overlay accuracy for multiple aligned irradiations can be achieved within submicron scale using an internal alignment system in the DEX2 JENOPTIK scanner. Both specially treated beryllium masks and optically transparent LIGA masks made of thin silicon nitride membranes have been utilized. Finally, novel applications of microproducts using DXRL as a prerequisite for mass production will be given. (C) 1998 American Vacuum Society. [S0734-211X(98)11106-X].