Provided is a method and system for controlling a fabrication cluster for processing of a substrate in an etch process, the fabrication cluster having equipment settings and process parameters. A correlation of etch stage measurements to actual etch stage data is developed, the etch stage measurements comprising measurements using two or more optical metrology devices and an etch sensor device. An etch stage value is extracted using the developed correlation and the etch stage measurement. If the etch stage measurement objectives are not met, the metrology devices are modified, a different etch sensor device is selected, the etch stage measurements are enhanced, and/or the correlation algorithm is refined. The steps are iterated until the etch stage measurement objectives are met. The extracted etch stage value is used to adjust an equipment setting and/or process parameter of the fabrication cluster.