An apparatus for processing wafer-shaped articles, comprises a closed process chamber providing a gas-tight enclosure. A rotary chuck is located within the closed process chamber, and is adapted to hold a wafer shaped article thereon. A lid is secured to an upper part of the closed process chamber, and comprises a lower surface facing inwardly of the chamber. At least one heating element heats the lower surface of the lid to a desired temperature, so as to prevent condensation of process vapor on the inwardly facing surface of the lid.