Method for controlling chemical species concentration

摘要

A method is described for maintaining constant chemical composition in solutions used for wet chemical processing. All chemical species that are deliberately included in the bath are kept at constant concentration primarily by a method of compensating for their depletion or generation with a set of feed solutions that are formulated and dosed into the bath in accordance with an overall material balance. Further, all chemical species not deliberately included in the bath are kept at constant concentration primarily by keeping the aggregate volume of replenishing stocks in strict proportion to the process service performed by the bath (e.g. the charge passed in an electroplating cell). Finally, a time-based scheme completes the control of the concentration of all bath species by controlling any species (whether deliberately included in the bath or not) that is depleted or generated as the result of chemical reactions which occur independently and/or spontaneously with time. Maintaining all bath chemical species at constant concentration prevents bath aging and permits production of more uniform work pieces from the bath.