The invention provides a method for forming a surface oxide layer on an amorphous silicon including steps: using a HF acid to clean a surface of the amorphous silicon; using a water to clean the surface of the amorphous silicon being cleaned by the HF acid; drying the surface of the amorphous silicon after being cleaned by the water; using an extreme ultraviolet lithography to form a first oxide layer on the surface of the amorphous silicon after being dried; using an oxidizing solution to clean the surface of the amorphous silicon with the first oxide layer to thereby form a second oxide layer; and drying the surface of the amorphous silicon with the second oxide layer. By using the extreme ultraviolet lithography to form the first oxide layer, the surface of the amorphous silicon is given with strong hydrophilicity and therefore the distribution of water would be uniform.