SUBSTRATE PROCESSING APPARATUS, SUBSTRATE PROCESSING METHOD, AND STORAGE MEDIUM

PROBLEM TO BE SOLVED: To provide a technique which allows for accurate detection of the fact that a process liquid existing on the surface of a substrate was replaced by a process liquid supplied later.SOLUTION: In a substrate processing apparatus 1 where a second process liquid is supplied to a substrate W, held horizontally in a substrate holding unit 31, after a first process liquid is supplied thereto, a process liquid distribution unit 53 is provided between the substrate W and a recovery cup 50 provided around the substrate W, and includes a distribution surface on which the process liquid flows. A concentration detector 604 irradiates the distribution surface with concentration detection light from a projection unit 61, and detects the concentration of at least one of the first process liquid and second process liquid, based on the results of a light reception unit 62 receiving the reflection light thereof.SELECTED DRAWING: Figure 3 【課題】基板の表面に存在する処理液が、後から供給された処理液に置換されたことを正確に検出することができる技術を提供する。【解決手段】基板保持部３１に水平に保持された基板Ｗに対し第１処理液が供給された後、第２処理液が供給される基板処理装置１において、処理液通流部５３は、基板Ｗと、この基板Ｗの周囲に設けられた回収カップ５０との間に設けられ、処理液が流れる通流面を備える。濃度検出部６０４は、投光部６１から前記通流面に濃度検出用の光を照射し、その反射光を受光部６２にて受光した結果に基づいて、前記第１処理液または第２処理液の少なくとも一方の濃度を検出する。【選択図】図３