SURFACE TREATING METHOD

摘要

PROBLEM TO BE SOLVED: To provide a surface treating method by which a spindle shape with a high aspect ratio is formed on an optical element so as to form an antireflection structure having antireflection effect to light having a wider wavelength range and small dependency on incident angle. SOLUTION: A metallic mask is formed on an optical element in a dot array shape and the optical element is subjected to reactive ion etching. At this time, the optical element is etched until the metallic mask vanishes after the gradual reduction of the diameter of the mask and a spindle shape is formed on the optical element.