pouring hydrofluoric acid solution into a container having an opening defined by a rim on a top of the container;

placing the silicon wafer at the opening of the container, one side of the silicon wafer having the passivation layer facing the hydrofluoric acid solution, the silicon wafer being in direct contact with the rim on the top of the container;

introducing an inert gas to a bottom of the hydrofluoric acid solution at a bottom of the container from the bottom of the container and heating the hydrofluoric acid solution; and

corroding the passivation layer of the silicon wafer using hydrogen fluoride gas volatilized from the hydrofluoric acid solution,

wherein a distance between a liquid surface of the hydrofluoric acid solution and the side of the silicon wafer having the passivation layer ranges 15-30 cm,

wherein a time of the corroding is greater or equal to a ratio of a thickness of the passivation layer to a corrosion rate; the thickness has a unit of centimeter and the corrosion rate has a unit of angstrom/min; the silicon wafer comprises a main body defining a plurality of back cavities; the passivation layer is formed between the back cavities and the main body; the passivation layer covers the entire surface on the one side of the silicon wafer facing the hydrofluoric acid solution; the passivation layer directly contacts the back cavities and forms a bottom of the back cavities; and the hydrogen fluoride gas goes through the back cavities and corrodes the passivation layer.