Patent attributes
A film of aluminum 2 is formed on a glass substrate (BK7) 1 by vacuum evaporation, and a multilayer optical thin film 3 is formed by an ion sputtering method on this aluminum film 2. Afterwards, such a member is cut into small pieces by means of dicing, and the aluminum 2 is then etched by a sodium hydroxide solution, so that the glass substrate 1 and the multilayer optical thin film 3 are separated. When the aluminum thickness exceeds 90 nm, clouding occurs in the multilayer optical thin film 3, and when the aluminum thickness is less than 10 nm, the separation of the glass substrate and multilayer optical thin film cannot be performed cleanly. Accordingly, the aluminum thickness is set in a range of 10 to 90 nm.