A device manufacturing method includes: forming a layer on a substrate by a layer-forming process; determining a value of a metric at a plurality of positions across the substrate, wherein variation of the values across the substrate is indicative of variation of layer thickness across the substrate; controlling the layer-forming parameter based on the values so as to reduce variation of layer thickness in a subsequent layer-forming process on a different substrate; and repeating the layer-forming process on a different substrate according to the controlled layer-forming parameter.