Apparatus and method for processing substrate

An apparatus for processing a substrate, comprising:

• a circulation line connected to a chemical supply unit to circulate a chemical solution;
• a membrane filter installed in the circulation line to filter particles in the chemical solution;
• a supply line connected to a first node of the circulation line and configured to supply the chemical solution to a chamber;
• a drain line connected, in the circulation line, to a second node located between the membrane filter and the first node, and configured to drain the chemical solution;
• a first on-off valve positioned in the circulation line between the first node and the second node;
• and a second on-off valve installed in the drain line;
• and a return line connecting an upstream of the first node at the circulation line and a downstream of the first node at the supply line to return the chemical solution from the supply line to the circulation line;
• and wherein the apparatus is programmed configured to operate in multiple durations and a membrane of the membrane filter has no complete formation of a cake due to the particles during a fourth duration, from when a pump of the chemical supply unit is restarted after the pump had stopped.