Chemical agent for forming water repellent protective film and surface treatment method for wafers

A surface treatment method for a wafer, comprising:

• a water-repellent protective film-forming step of, in a state that at least one kind of liquid selected from the group consisting of a cleaning liquid and a rinse liquid is retained on a surface of the wafer, replacing the liquid with a water-repellent protective film-forming liquid chemical and retaining the water-repellent protective film-forming liquid chemical on the surface of the wafer;
• and a drying step,
• wherein the water-repellent protective film-forming liquid chemical comprises the following components:
• (I) an aminosilane compound of the following general formula [1];
• (II) a silicon compound of the following general formula [2];
• and
• (III) an aprotic solvent, and
• wherein the amount of the component (I) contained in the liquid chemical is 0.02 to 0.5 mass % based on the total amount of the components (I) to (III),
• (R1)aSi(H)b(NH2)4-a-b [1]
• where R1 is each independently a monovalent organic group having a monovalent hydrocarbon structure of 1 to 18 carbon atoms in which a part or all of hydrogen atoms may be substituted with a fluorine atom;
• a is an integer of 1 to 3;
• b is an integer of 0 to 2;
• and the sum of a and b is 1 to 3,
• (R2)cSi(H)dX4-c-d [2]
• where R2 is each independently a monovalent organic group having a monovalent hydrocarbon structure of 1 to 18 carbon atoms in which a part or all of hydrogen atoms may be substituted with a fluorine atom;
• X is at least one group selected from the group consisting of a halogen atom, a —OC(═O)R3 group, a —OS(═O)2—R3 group, a —N(S(═O)2—R3)2 group and a —C(S(═O)2—R3)3 group;
• R3 is a monovalent perfluoroalkyl group of 1 to 6 carbon atoms;
• c is an integer of 1 to 3;
• d is an integer of 0 to 2;
• and the sum of c and d is 1 to 3.