| 摘要 |
PROBLEM TO BE SOLVED: To obtain a magnesium fluoride optical thin film which can be preferably used as an antireflection film or a protective film of optical parts and which can decrease the reflective when it is used as an antireflection film, by controlling the refractive index to a specified range. SOLUTION: The refractive index of the magnesium fluoride optical thin film is controlled to 1.36 to 1.37. The optical thin film is produced by the following method. A Is wafer 2 (2 inch) is mounted on a MgF2 target 1, and gases of Ar, Ar+O2 , O2 +CF4 , O2 are introduced as the sputtering gas into a vacuum chamber 3. The pressure in the vaccum chamber 3 is controlled by changing the evacuation rate of a cryopump 7 with a variable orifice 6. By varying the sputtering conditions, a thin film is formed on the substrate 8. By controlling the pressure in the back ground to a specified value by using O2 gas, a magnesium fluoride thin film having a low refractive index as about 1.36 to 1.37 is obtd. |
