Enhancement on forming complex three dimensional microstructures by a double-side multiple partial exposure method

This study presents a novel batch process based on standard lithography technology, called the double-side multiple partial exposure (DoMPE) method, which enhances the fabrication capability of three dimensional (3D) photoresist microstructures. By incorporating gray-tone lithography and double-side exposure techniques, the proposed DoMPE scheme extends the multilevel morphology on both the front side and back side of the suspended photoresist microstructures. Back-side gray-tone lithography is achieved by depositing various appropriate thicknesses of Ti film on glass substrate that acts as the gray-tone mask. The process parameters, including metal film thickness, developed depth, exposure dosage, development time, and soft-bake time, are experimentally characterized. Different 3D photoresist microstructures with multiple levels on the front and back sides are successfully fabricated and presented here to show the enhancement effect using the proposed technique, including a microinductor structure and a vertical comb drive structure that demonstrate potential applications even on electrically conductive devices.