Liquid supply method, liquid supply apparatus, substrate polishing apparatus, and method of measuring supply flow rate of liquid

An apparatus for supplying a liquid from a liquid supply source to a predetermined liquid-supply area at a predetermined flow rate, said apparatus comprising:

• at least one supply tube for retaining the liquid supplied from the liquid supply source, said at least one supply tube being vertically oriented;
• a pressurized gas supply mechanism for supplying a pressurized gas from a gas source to said at least one supply tube;
• a gas pressure adjusting mechanism for adjusting pressure of the pressurized gas to be supplied from the gas source to said at least one supply tube;
• a level sensor configured to continuously detect a level of the liquid in a respective one of said at least one supply tube;
• a control unit configured to:
• determine a flow rate of the liquid discharged from said at least one supply tube based on a level of the liquid detected by said level sensor;
• and
• operate said gas pressure adjusting mechanism so as to maintain the predetermined flow rate based on a difference between the determined flow rate and the predetermined flow rate;
• and
• a pipe having no narrow portion, said pipe extending from the liquid supply source to said at least one supply tube, and from said at least one supply tube to the predetermined liquid-supply area;
• wherein said gas pressure adjusting mechanism is configured to control a pressure of the gas supplied to said at least one supply tube by said pressurized gas supply mechanism so as to force the liquid out of said at least one supply tube and supply the liquid to the predetermined liquid-supply area via said pipe at the predetermined flow rate.