A method is provided for controlling substrate thickness. At least one etchant is dispensed from at least one dispenser to a plurality of different locations on a surface of a spinning substrate to perform etching. A thickness of the spinning substrate is monitored at the plurality of locations, so that the thickness of the substrate is monitored at each individual location while dispensing the etchant at that location. A respective amount of etching performed at each individual location is controlled, based on the respective monitored thickness at that location.