One aspect of the present invention relates to a method of dual damascene processing, involving forming a plurality of via openings in the insulation structure containing a single layer of a dielectric material; and simultaneously (i) forming a plurality of trenches in the insulation structure, each trench positioned along the substantially straight line of a group of via openings, and (ii) monitoring the formation of trenches using a scatterometry system to determine trench depth, and terminating forming the trenches when a desired trench depth is attained.