A substrate processing method according to the invention includes a supercritical process step of processing a substrate by a processing fluid in a supercritical state by introducing the processing fluid into an internal space of the chamber accommodating the substrate, a decompression step of decompressing the internal space by discharging the processing fluid, a carry-out step of carrying out the substrate from the chamber, and a temperature adjustment step of adjusting a temperature of the internal space to a target temperature by introducing and discharging the processing fluid to and from the internal space after the substrate is carried out. Stable processing efficiency can be obtained also particularly in the case of processing a plurality of substrates in turn by properly controlling a temperature in a chamber after a process in a technique for processing a substrate by a processing fluid in a supercritical state in the chamber.

A cleaning agent composition for use in removal of an adhesive residue, the composition containing a quaternary ammonium salt and a solvent, wherein the solvent consists of an organic solvent, and the organic solvent includes an N,N,N,N-tetra(hydrocarbyl)urea.