Deep X-ray Mask with Integrated Micro-Actuator for 3D Microfabrication via LIGA Process

We present a novel method for 3D microfabrication with LIGA process that utilizes a deep X-ray mask in which a micro-actuator is integrated. The integrated micro-actuator oscillates the X-ray absorber, which is formed on the shuttle mass of the micro-actuator, during X-ray exposures to modify the absorbed dose profile in X-ray resist, typically PMMA. 3D PMMA microstructures according to the modulated dose contour are revealed after GG development. An X-ray mask with integrated comb drive actuator is fabricated using deep reactive ion etching, absorber electroplating, and bulk micromachining with silicon-on-insulator (SOI) wafer. 1mm 1 mm, 20 m thick silicon shuttle mass as a mask blank is supported by four 1 mm long suspension beams and is driven by the comb electrodes. A 10 m thick, 50 m line and spaced gold absorber pattern is electroplated on the shuttle mass before the release step. The fundamental frequency and amplitude are around 3.6 kHz and 20 m, respectively, for a do bias of 100 V and an ac bias of 20 (peak-peak). Fabricated PMMA microstructure shows 15.4 m deep, S-shaped cross section in the case of 1.6 kJ surface dose and GG development at 35 for 40 minutes.