Patent ID: 7582219

Claim:
A method of fabricating by an etching technique a plate-shaped reflective mirror having a reflective surface on which light is incident, the method comprising: a coating step of coating at least one of opposite faces of a plate-shaped etchable material made of a single crystal material, with an etching mask; a mask-pattern forming step of forming a mask pattern on at least one of opposite faces of the etching mask which has been deposited on the etchable material, the mask pattern having a planar shape which is more similar to a circle than to a quadrangle; and a wet-etching step of wet-etching the etchable material on which the etching mask has been deposited, by immersing the etchable material in an etchant having a predetermined temperature and a predetermined concentration, whereby the reflective mirror is fabricated so as to have a silhouette of a planar shape which is more similar to a circle than to a quadrangle, when viewed in a direction normal to the reflective surface, the method further comprising a determining step of determining the planar shape of the mask pattern, based on a desired planar shape of the reflective mirror, by allowing for differences in wet etch rate between crystallographic planes in the etchable material, wherein an ultimate planar shape of the reflective mirror is more rounded than the planar shape of the mask pattern.