Microprocessing treatment agent and microprocessing treatment method

Provided are: a microprocessing treatment agent with which it is possible, in a laminated film including at least a silicon oxide film and a silicon nitride film, to satisfactorily perform selective microprocessing of the silicon nitride film while suppressing microprocessing of the silicon oxide film; and a microprocessing treatment method. This microprocessing treatment agent includes at least a compound represented by chemical formula (1), an inorganic phosphoric acid, a hexafluorosilicic acid compound, and water, said agent selectively microprocessing the silicon nitride film in relation to the silicon oxide film. (X is any one of H, Si, and functional groups represented by chemical formulas (2) to (4). R1 to R3 each independently represent any one of H, F, Cl, Br, I, alkyl groups, alkenyl groups, alkynyl groups, hydroxyalkyl groups, alkoxy groups, aminoalkoxy groups, phosphate groups, sulfate groups, nitrile groups, carboxyl groups, or acetoxy groups. n ranges from 1 to 4.).