Physical quantity sensor having optical part and method for manufacturing the same

A method for manufacturing a physical quantity sensor having a movable portion, a support portion and an optical part is provided. The method includes steps of: etching a silicon substrate so that a movable-portion-to-be-formed portion, a support-portion-to-be-formed portion, and an optical-part-to-be-formed portion having a plurality of columns and trenches are formed; oxidizing the optical-part-to-be-formed portion so that each column changes to a silicon oxide column and the trench is filled with a silicon oxide layer; and removing a part of the movable-portion-to-be-formed portion connecting to the silicon substrate so that the movable portion is separated from the silicon substrate.