During fluid treatment of a substrate surface, a carrier/wafer assembly containing a substrate wafer closes the top of a microcell container. The carrier/wafer assembly and the container walls define a thin enclosed treatment volume that is filled with treating fluid, such as electroless plating solution. The thin fluid-treatment volume typically has a volume in a range of about from 100 ml to 500 ml. Preferably a container is heated and the treating fluid is pre-heated before being injected into the container. Preferably, the chemical composition, temperature, and other properties of fluid in the thin enclosed fluid-treatment volume are dynamically variable. A rinse shield and a rinse nozzle are located above the container. A carrier/wafer assembly in a rinse position substantially closes the top of the rinse shield.