Chemical liquid preparation device, and substrate processing device

A chemical liquid preparation method of preparing a chemical liquid to be supplied to a substrate,

• the chemical liquid being a TMAH-containing chemical liquid which contains tetramethylammonium hydroxide (TMAH),
• the chemical liquid preparation method comprising:
• a correspondence relationship preparing step of preparing a correspondence relationship between a supply flow rate ratio between an oxygen-containing gas and an inert-gas-containing gas and a convergent dissolved oxygen concentration in the TMAH-containing chemical liquid that is converged to when the oxygen-containing gas and the inert-gas-containing gas are supplied into the TMAH-containing chemical liquid at the supply flow rate ratio,
• a concentration setting step of setting a target dissolved oxygen concentration in the TMAH-containing chemical liquid that corresponds to a desired etching rate,
• a supply-flow-rate-ratio acquiring step of acquiring the supply flow rate ratio between the oxygen-containing gas and the inert-gas-containing gas corresponding to the target dissolved oxygen concentration in accordance with the correspondence relationship prepared in the correspondence relationship preparing step,
• a first gas supplying step of supplying the oxygen-containing gas and the inert-gas-containing gas with a predetermined supply flow rate ratio of the oxygen-containing gas and the inert-gas-containing gas, and
• a second gas supplying step of, after the first gas supplying step, supplying the oxygen-containing gas and the inert-gas-containing gas with the supply flow rate ratio acquired in the supply-flow-rate-ratio acquiring step.