Surface treatment agent, silicon compound, and method for suppressing pattern collapse when substrate surface is cleaned with cleaning liquid

A surface treatment agent for use in treating a surface of a substrate having a pattern,

• the surface treatment agent comprising a reactive silane compound, and a solvent,
• the reactive silane compound comprising a compound represented by the following formula (1):
• wherein in the formula (1), R1 and R2 are each independently a monovalent hydrocarbon group having 1 or more and 15 or less carbon atoms, optionally having a substituent, or a hydrogen atom, R1 and R2 are not simultaneously a hydrogen atom, R1 and R2 are optionally bonded to each other to form a hydrocarbon ring, a total number of carbon atoms of R1 and R2 is 2 or more and 20 or less, R3 is an alkylene group having 1 or more and 5 or less carbon atoms, R4 is an alkyl group having 1 or more and 4 or less carbon atoms, or a hydrogen atom, X is a hydrocarbon group having 1 or more and 6 or less carbon atoms, and a is an integer of 0 or more and 2 or less, and the solvent comprising water.