A method for controlling an etch process comprises providing a wafer having at least a first layer and a second layer formed over the first layer. The thickness of the second layer is measured. An etch selectivity parameter is determined based on the measured thickness of the second layer. An operating recipe of an etch tool is modified based on the etch selectivity parameter. A processing line includes an etch tool, a first metrology tool, and a process controller. The etch tool is adapted to etch a plurality of wafers based on an operating recipe, each wafer having at least a first layer and a second layer formed over the first layer. The first metrology tool is adapted to measure a pre-etch thickness of the second layer. The process controller is adapted to determine an etch selectivity parameter based on the measured pre-etch thickness of the second layer and modify the operating recipe of the etch tool based on the etch selectivity parameter.