Thin film producing method and light bulb having such thin film

摘要

When forming an optical thin film on a surface of a bulb of a light source such as an electric lamp or a discharge lamp, a thin film whose interface/surface is less rough is formed on a base having a spheroid shape. When forming a thin film on a base 2 with a spheroid shape, which is disposed in a vacuum chamber 4 of a film-forming device and spun on its rotation axis, an interface or a surface of the thin film is made less rough and the thickness distribution of the thin film is made smaller by setting a sputtering gas pressure to be in a range from 0.04 Pa to 5.0 Pa; by using, as a sputtering gas, a mixed gas of Ar gas and N₂ gas in which the N₂ gas is present at a partial pressure ratio of 1 to 6 assuming a partial pressure of the Ar gas is 100, or a mixed gas of Ar gas, N₂ gas, and O₂ gas in which the N₂ gas is present at a partial pressure ratio of 1 to 6 and O₂ gas is present at a partial pressure ratio of 6 or less assuming a partial pressure of the Ar gas is 100; by setting an input power applied at the start of thin film formation to be the greatest throughout a sputtering process; or by applying a negative bias to the base.