| CPC B67D 7/16 (2013.01) [B67D 7/145 (2013.01); H01L 21/67017 (2013.01)] | 20 Claims |

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1. A liquid preparation method in a liquid supply system, comprising:
supplying a liquid from a liquid tank to a processing tool in which a wafer is located;
measuring, with a detection member, a quantity of the liquid stored in the liquid tank by emitting a detection signal toward a floating member positioned in a tube, wherein the tube extends in a height direction of the liquid tank and fluidly connects to two connecting ports of the liquid tank that are located at opposite sides of a surface of the liquid, and the position of the floating member in the tube varies according to a level of the liquid in the liquid tank; and
regulating the liquid in the liquid tank in response to the quantity of the liquid in the liquid tank,
wherein the detection signal is transmitted to the tube via an upper connecting line that connects an upper end of the tube to the liquid tank, and the detection signal from the detection member in the upper connecting line travels along a longitudinal direction of the tube.
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