Abstract: The present invention provides a dynamic-flow system that uses a vacuum to pull an etchant or other processing agent through a nozzle onto the surface of the work object. The processing agent can only communicate with the vacuum and be pulled onto the wafer surface when the nozzle is sealed against the work object. Therefore, the processing agent is dispensed onto the surface of the wafer or other work object under a negative rather than a positive pressure. Accordingly, the dispensation of the processing agent is self-stopping in the event that seal of the nozzle against the work object fails. The present invention also provides a novel nozzle for dispensing a processing agent onto a selected area of a work object. The nozzle of the present invention provides a substantially unidirectional flow of processing agent along the surface of a work object and maximizes the contact time of the processing agent at the surface of the work object.