The present invention relates to a method for cleaning wafers while preventing pattern collapse of the wafers in semiconductor device fabrication, the wafer having at its surface an uneven pattern and containing silicon element at least on surfaces of recessed portions. Provided is: a liquid chemical for forming a protective film which allows efficient cleaning; and a method for cleaning wafers, using the liquid chemical. A liquid chemical for forming a water repellent protective film is provided for forming a protective film on a wafer (having at its surface an uneven pattern and containing silicon element at least at a part of the uneven pattern), the protective film being formed at least on surfaces of recessed portions of the uneven pattern at the time of cleaning the wafer. The liquid chemical contains a dialkylsilyl compound represented by the formula [1] and does not contain an acid and a base. R2(H)SiX  [1]