A plasma treatment method which is capable of extending the MTF of metal interconnects fabricated on a semiconductor wafer substrate, is disclosed. At least one embodiment includes a mode locked waveguide laser system. The connection region is formed into such an arcuate shape in cross-section that an upper surface corresponding to a valley side of the M-shape is a concave surface and an opposite lower surface is a convex surface. The input selection circuit selects a predetermined reference voltage for driving the liquid crystals from a plurality of reference voltages provided from an input voltage generation circuit or a plurality of reference voltages generated within the input selection circuit based on an input signal representative of gray-scale data and the polarity control signal.