Multi-object spectroscopy (MOS) allows measuring infrared spectra of faint astronomical objects that provides information on the evolution of the Universe. MOS requires a slit mask for object selection at the focal plane of the telescope. We are developing MEMS-based programmable reflective slit masks composed of 2048 individually addressable micromirrors. Each micromirror measures 100 x 200 mu m(2) and is electrostatically tilted by a precise angle of at least 20 degrees. The main requirements for these arrays are precise and uniform tilt angle over the whole device, uniformity of the mirror electromechanical behavior, a flat mirror deformation and individual addressing capability of each mirror. This capability of our array is achieved using a line-column algorithm based on an optimized tilt angle/voltage hysteresis of the electrostatic actuator.