Deep X-ray mask with integrated actuator for 3D microfabrication

We present a novel method for 3D microfabrication with LIGA process that utilizes a deep X-ray mask in which a microactuator is integrated. The integrated microactuator oscillates the X-ray absorber, which is formed on the shuttle mass of the microactuator, during the X-ray exposures to modify the absorbed dose profile in X-ray resist, typically PMMA. The 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 wafer. Silicon shuttle mass (<F>1 mm×1</F> mm, 20 μm thick) as a mask blank is supported by four 1 mm long suspension beams and is driven by the comb electrodes. A 10 μm thick, 50 μm 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 μm, respectively, for a dc bias of 100 V and an ac bias of 20 VP–P (peak–peak). Fabricated PMMA microstructure shows 15.4 μm deep, S-shaped cross-section in the case of 1.6 kJ cm−3 surface dose and GG development at 35 °C for 40 min. [Copyright &y& Elsevier]