Surface treatment agent, surface treatment method, and region selective film formation method for surface of substrate

A surface treatment agent used for treating a substrate which has a surface having two or more regions made of materials that are different from each other, the agent comprising:

• a compound (H) represented by Formula (H-1),
• wherein R1 represents a linear or branched alkyl group having 1 to 30 carbon atoms which may have a substituent, a linear or branched fluorinated alkyl group having 1 to 30 carbon atoms which may have a substituent, an aromatic hydrocarbon group which may have a substituent, or a cycloalkyl group having 3 to 12 carbon atoms which may have a substituent, and R2 represents a hydrogen atom, a linear or branched alkyl group having 1 to 8 carbon atoms which may have a substituent, or a cycloalkyl group having 3 to 12 carbon atoms which may have a substituent.