Abstract: [Problem to be solved] Provided is a method for processing a substrate having high etching selectivity of silicon with respect to silicon-germanium and further having a high selection ratio of silicon with respect to a silicon oxide film and/or a silicon nitride film in surface processing when manufacturing various types of silicon devices, particularly various types of silicon composite semiconductor devices containing silicon-germanium. [Solution] A method for processing a substrate includes: bringing an etching solution into contact with a substrate including a silicon film and a silicon-germanium film to perform etching; and selectively removing the silicon film, in which the etching solution contains an organic alkali and water and has a dissolved oxygen concentration of 0.20 ppm or less.

Abstract: A silicon etching solution including an aqueous alkaline solution containing a hypohalite ion in a range of 0.05 mmol/L or greater and 5 mmol/L or less and having a pH of 12.5 or greater at 24° C.