Apparatus and method for processing substrate

A method of processing a substrate, comprising:

• a first step of supplying an organic developing solution onto a substrate with an exposed photoresist (PR) film formed thereon, while rotating the substrate at a first revolutions per minute (rpm) over a first period of time;
• a second step of reducing a rotation speed of the substrate from the first rpm to a second rpm that is lower than the first rpm over a second period of time following the first period of time;
• and
• a third step of removing PR reactants, generated from a reaction of the PR film with the organic developing solution, by raising the rotation speed of the substrate from the second rpm to a third rpm that is higher than the second rpm and lower than the first rpm,
• wherein the organic developing solution is substituted with a rinse solution during the second step or during the third step by stopping the supplying of the organic developing solution while starting a supplying of the rinse solution onto the substrate during the second step or during the third step,
• wherein the organic developing solution is continued to be supplied onto the substrate for a portion of the second period of time and stopped when the rinse solution is starting to be supplied onto the substrate during the second period of time.