Liquid supply system and liquid preparation method

A liquid preparation method in a liquid supply system, comprising:

• supplying a liquid from a liquid tank to a processing tool through a discharging piping;
• determining whether an abnormal of the supplying of the liquid occurs by measuring a height of chemical liquid in a tube which is connected to the liquid tank, wherein the measurement of the height of chemical liquid comprises:
• emitting, by a signal source, a detection signal toward a floating member which is positioned in the tube that positioned outside of the liquid tank;
• and
• calculating a time interval (Δt) between a first time point (t1) when the detection signal is generated by the signal source and a second time point (t2) when a signal receiver receives the detection signal reflected from the floating member, wherein when the time interval (Δt) is greater than a predetermined value, a controller determines the abnormality occurs.

A liquid preparation method in a liquid supply system, comprising:

• preparing a liquid mixture by the following operations:
• supplying a liquid tank with a first type of liquid;
• measuring, with a detection member, the amount of the first type of liquid filled into 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 mixture, and the position of the floating member in the tube varies according to a level of the liquid mixture in the liquid tank;
• and
• stopping the supply of the first type of liquid when the amount of the first type of liquid filled into the liquid tank reaches a desired amount;
• and
• supplying the liquid mixture in the liquid tank to a processing tool for processing a semiconductor wafer after the preparation of the liquid mixture.