NOVELTY - The apparatus (1) has a substrate holding unit (4) that maintains a substrate to horizontal position within an airtight chamber (3). A phosphate supply unit (35) supplies phosphoric acid aqueous solution (60) to an upper surface to form liquid film of phosphoric acid aqueous solution in upper surface of substrate currently maintained at substrate holding unit. A control unit (55) controls phosphoric acid liquid film heating unit and pressurizing unit (50), and performs heating of liquid film of phosphoric acid aqueous solution, and pressurization in the airtight chamber parallely.    USE - Substrate processing apparatus for processing surface of substrate for use in semiconductor device and liquid crystal display device. Can also be used in plasma display, field emission display, optical disk, magnetic disc, magneto optical disc, photomask, ceramic substrate and solar cell.    ADVANTAGE - The fall of etching selectivity is suppressed while raising an etching rate. The etching rate of the silicon nitride film by phosphoric acid is improved. Since the pyrophosphoric acid which is generated replenishment of the water content from area other than substrate interface to substrate interface is returned by phosphoric acid, the etching of the silicon oxide film by a pyrophosphoric acid is suppressed. Since phosphoric acid aqueous solution is supplied to the wafer, the time which raises the temperature of phosphoric acid aqueous solution to predetermined temperature is shortened.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for a substrate processing method for processing surface of substrate.    DESCRIPTION OF DRAWING(S) - The drawings show sectional view illustrating the process of substrate processing apparatus. (Drawing includes non-English language text)    Substrate processing apparatus (1)    Airtight (3)    Substrate holding unit (4)    Phosphate supply unit (35)    Pressurizing unit (50)    Control unit (55)    Phosphoric acid aqueous solution (60)