Fabrication of high-aspect-ratio stepped Cu microcolumn array using UV-LIGA technology

A stepped copper microcolumn array was fabricated based on the UV-LIGA technology and microelectroforming process using THB-151N photoresist. In order to solve the problems of difficult development of 20 μm blind microvia and “resist retention” at the bottom during THB-151N photoresist development, a submerged bidirectional megasonic assisted development method was proposed. Comsol Multiphysics software was used to analyze the mass transfer process of developer in blind microvia under different megasonic power densities and aspect ratios, and the mass transfer coefficient was used to characterize the process. According to the actual working conditions, the optimized megasonic power density of 3.2 W/cm2 and aspect ratio of 1.5 are selected and the megasonic assisted development was studied experimentally. Besides, aiming at the poor verticality of side wall of the blind microvia due to inappropriate exposure dose of THB-151N photoresist film, the effect of exposure dose on the verticality of side wall of the blind microvia was discussed by lithography experiment and the Angle β is introduced to measure the verticality of the side wall. The empirical equation between exposure dose and thickness of the film was fitted.On the basis of the above technological methods and experimental study, stepped Cu microcolumn arrays of 4 × 6 with a height of 300 μm, overall aspect ratio of 15:1 and minimum side length of 20 μm were fabricated.