Apparatus and method for treating substrate

An apparatus for treating a substrate, the apparatus comprising:

• a substrate support unit to support the substrate;
• and
• a liquid supplying unit to supply a liquid to a substrate supported by the substrate support unit;
• wherein the liquid supplying unit includes:
• a nozzle to discharge the liquid;
• a liquid supplying line to supply the liquid to the nozzle;
• a constant pressure valve installed on the liquid supplying line, wherein the constant pressure valve comprises a diaphragm that can open and close a fluid passage through which the liquid can flow, wherein the diaphragm comprises a locking part that physically contacts a portion of the valve when the fluid passage is closed, and wherein the constant pressure valve comprises a fluid supply member configured to apply fluid pressure or air pressure to move the diaphragm and its locking part;
• a shut-off valve installed on the liquid supplying line while being interposed between the constant pressure valve and the nozzle to supply the liquid or to stop the supply of the liquid;
• and
• a controller configured to control the constant pressure valve and the shut-off valve, and
• wherein the controller is configured to have the fluid supply member of the constant pressure valve supply fluid or air at a first pressure when the shut-off valve is opened, wherein the controller is configured to have the fluid supply member supply fluid or air at a second pressure when the shut-off valve is closed, and wherein the second pressure is greater than the first pressure such that the locking part does not close the fluid passage of the constant pressure valve in response to the shut-off valve being closed.