Water Flow Improvement by Pinhole Outlet in Batch-Type Wet Cleaning Bath for Large-Diameter Wafers

The pinhole water outlet fabricated near the top of bath walls could produce a simple water flow with less water recirculation in the batch-type wet cleaner for 300 mm-diameter silicon wafers. The pinholes having a 2 mm diameter were arranged in three different configurations: ( i ) the right and left side walls have the pinhole outlets, while the front and back side walls did not, ( ii ) the distance between the nearest neighbor pinholes was less than 1.5 cm and (iii) the pinhole arrays were at the depth of 3, 4.5 and 6 cm beneath the water surface. The water motion was studied by computational fluid dynamics and visualization, during the wafer operations. When 10 cm of the wafer bottom was immersed in the water, the calculation showed that 90% of the particles, released from the 1 cm depth beneath the water surface, was removed from the bath within 10 s. By observations throughout the sequential wafer operations of dipping, holding and lifting, the blue-colored tracer ink that had been painted at the wafer surface simply went toward the outlet without any considerable recirculation. The range of the water flow rate without causing any recirculation was additionally studied.