Abstract: An etching solution has a high etching selectivity of silicon with respect to silicon-germanium and having high stability over time at a treating temperature in surface processing in manufacturing various semiconductor devices, particularly in various silicon composite semiconductor devices containing silicon-germanium. The silicon etching solution contains a compound having at least one carboxy group and having all pKa of 3.5 or more and 13 or less, or a salt thereof; an organic alkali; and water.

Abstract: In etching of a single crystal silicon substrate having a Si crystal plane ((100) plane, (110) plane, and (111) plane) as a main plane, an etching rate on the (110) plane cannot be sufficiently reduced, and there is room for improvement in an etching rate ratio between the (110) plane and the (111) plane. An object of the present invention is to provide a silicon etching solution having excellent crystal plane isotropy in silicon etching and having a high etching selectivity ratio of silicon to a silicon oxide film. The problem is solved by a silicon etching solution containing: an acid group-containing compound having at least one acid group selected from the group consisting of a carboxy group, a sulfonic acid group, a phosphoric acid group, and a phosphonic acid group, and having pKa of 3.5 or more and 13 or less; a quaternary ammonium hydroxide; an oxidizing agent; and water.

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.