Fabrication of a 35-channel optical scanner integrated by passive-self alignment using through-holes precisely formed by DRIE

A 35-channel optical scanner integrating a mirror array and a collimator-lens array was fabricated. The mirror array consists of a mirror substrate with 35 single-axis-rotational mirrors and an electrode substrate for actuating the corresponding mirror by electrostatic force. Each substrate includes two kinds of through-holes: one for passing a collimated-optical beam through, the other for inserting a precise pin for passive-self alignment of the mirror array and the collimator-lens array. To precisely form the through-holes suitable for passive-self alignment, deep reactive ion etching (DRIE) conditions were optimized. DRIE from both surfaces of a substrate under the optimized conditions - a C₄F₈/SF₆ gas-flow ratio of 90% and a bias power in SF₆ gas of 110 W - can form through-holes with an average undercut of 3.4 μm and an average sidewall angle of 89.9 degrees. By passive-self alignment, namely, inserting a pin into the fabricated through-hole and stacking the mirror array on the collimator-lens array, the measured assembly deviation of each substrate was less than 17.5 μm.