In acid processing of substrates, such as silicon wafers in the manufacture of electronic devices, such as integrated circuit chips, the method of mixing separate chemicals together in the processing chambers and as the separate chemicals are sprayed in atomized and directional spray patterns toward and across the surfaces of the substrates, the directional spray patterns emanating from different sources and having oblique directions with respect to each other to traverse each other at the surfaces of the substrates for thorough mixing and immediate application to the wafer faces to accomplish the processing. A vented housing defines the processing chamber with spray posts spaced from each other around the periphery of the housing and mounted on the sidewall and directing atomized liquid chemical sprays toward the center at which the substrates are mounted as to cause the spray patterns to traverse each other as they sweep across the wafers.