Tool for treating microelectronic workpieces with one or more treatment materials, including liquids, gases, fluidized solids, dispersions, combinations of these, and the like. The invention provides an approach for rapid, efficient rinsing of wetted surface(s), and is particularly advantageous when used to rinse the lower surface of moveable barrier structures such as a barrier plate that overlies a workpiece being treated in such a manner to define a tapering flow channel over the workpiece. Rather than spray rinsing liquid onto the surface in a manner that generates undue splashing, droplet, or mist generation, the liquid is flowingly dispensed, preferably under laminar flow conditions, onto a surface that is in fluid communication with the surface to be rinsed. A smooth, uniform wetting and sheeting action results to accomplish rinsing with a significantly reduced risk of generating particle contamination.