Water Outlet Design of Wet Cleaning Bath for 300-mm Diameter Silicon Wafers

Abstract

Water motions influenced by an outlet of a batch-type 300-mm diameter silicon wafer wet cleaning bath were experimentally and numerically studied in order to quickly remove the contaminants from the bath. The outlet consisting of a pinhole arrays (PA) near the top edge of the bath side wall was designed and evaluated along with an ordinary overflow (OF) outlet. The experiment showed that the amount of a blue-colored ink, used as a tracer, in the bath having both the OF-and the PA-outlets decreased faster than that in the bath having only the OF-outlet. Simultaneously, the amount of the blue-colored ink that returned to the bath bottom was reduced by using both the PA-outlet and the OF-outlet. The numerical calculations also showed that particles in the bath quickly went out through the PA-outlet. An advanced semiconductor material surface should be maintained clean for the electronic device fabrication.1,2 The batch-type wet cleaning method, using ultrapure water and chemical reagents in a bath, has been very popular for cleaning the surface of small and large diameter wafers. [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The water flow in the wet cleaning bath has been continuously studied [16][17][18][19] in order to improve the productivity of the cleaning process. While the contaminants, such as small particles, were detached and transported away from the wafer surface, they frequently returned to the wafers following the water recirculation. Thus, the water flow in the bath should be further studied in detail.The water recirculation is considered to be formed by an asymmetric water injection and the insufficient cross section of the outlet. 19,20 In our previous study, 19 the water injection nozzle consisting of dual tubes was designed taking into account the pressure distribution in the nozzle for injecting the water in the normal direction with the symmetric water velocity distribution. While the efficiency of contamination removal from wafers is dominated by the direct water injection to the wafers from the water nozzles, the recontamination is influenced by the recirculation which may be caused by the outlet design. The water outlet design should be studied, next.The wet cleaning bath for the semiconductor materials process has preferred the overflow outlet in order to effectively remove many particles floating on the water surface. The overflow outlet is equivalent to the outlet having a significantly thin cross section along the top edge of the four side walls. In order to remove the contaminants through the overflow outlet, a large and fast stream is necessary near and toward the top edge of the bath side wall. Consequently, such a fast stream requires large and fast recirculations which simultaneously and unfortunately take some contaminants back to the wafers. Thus, a new water outlet design is expected for governing the entire water flow in the bath.In this study, the water outlet of the wafer wet cleaning bath was studied both experimentally and numerically from the viewpoint of expan...

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

“…The water flow rate was mainly 17 l min −1 , similar to the previous studies. [12][13][14] For studying the appropriate water flow rate, rates between 5 and 30 l min −1 were evaluated. A blue-colored ink was used as a tracer for visualizing the water motion, which was captured using a video camera from the front and right sides.…”

“…The previous studies [7][8][9][10][11][12][13] showed that the water recirculation, a kind of stable vortex, could be managed by means of a simple measure, such as employing pinholes near the top of the bath wall as a water outlet. When the nearest neighbor pinholes were within 1.5 cm or less, they could behave and work as an integrated wide water outlet.…”