Optical film, sputtering target, and method of producing optical film

A method of producing an optical film having transmissivity in a visible wavelength band, having absorbance in a near-infrared wavelength band, and having radio wave transparency, characterized in that the method comprises:

• a first step of repeatedly preparing a plurality of samples of optical films with increased or decreased oxygen content by a sputtering method using a sputtering target composed of a mixture of a cesium source compound and a tungsten source compound and feedback-controlling an oxygen partial pressure of a sputtering film formation atmosphere;
• a second step of selecting samples of optical films having transmissivity in a visible wavelength band, having absorbance in a near-infrared wavelength band, and having radio wave transparency from the prepared samples of optical films;
• a third step of measuring the optical constants (refractive index n and extinction coefficient k) of the selected samples of optical films at wavelengths from 300 nm to 2400 nm by an ellipsometer;
• a fourth step of creating a wavelength dispersion graph from the measured multiple optical constants (refractive index n and extinction coefficient k), and determining the minimum and maximum values of the refractive index n and extinction coefficient k of the optical films at each of 300 nm and wavelengths [400 nm, 600 nm, . . . 2400 nm] specified at 200 nm intervals in a wavelength region from 400 nm to 2400 nm from the wavelength dispersion graph, thereby specifying the numerical ranges of the refractive index n and extinction coefficient k listed in Table 10 below;
• a fifth step of preparing a plurality of types of samples of optical films by setting a plurality of film formation conditions of the film formation apparatus using the sputtering target in order to determine the film formation conditions of the film formation apparatus that forms an optical film that satisfies the numerical ranges of the refractive index n and the extinction coefficient k described in Table 10 below;
• a sixth step of measuring the optical constants (refractive index n and extinction coefficient k) of the prepared samples of optical films at wavelengths from 300 nm to 2400 nm by an ellipsometer to specify samples of optical films whose refractive index n and extinction coefficient k satisfy the numerical ranges shown in Table 10 below;
• a seventh step of producing an optical film having transmissivity in a visible wavelength band, having absorbance in a near-infrared wavelength band, and having radio wave transparency based on the film forming conditions of a film forming apparatus in which the specified sample of optical film is formed
• TABLE 10
• nm
• n-min
• n-max
• nm
• k-min
• k-max
• 300
• 2.6
• 3.2
• 300
• 0.3
• 0.7
• 400
• 2.1
• 2.6
• 400
• 0.0
• 0.2
• 600
• 1.9
• 2.3
• 600
• 0.0
• 0.2
• 800
• 1.8
• 2.1
• 800
• 0.0
• 0.3
• 1000
• 1.7
• 2.1
• 1000
• 0.0
• 0.5
• 1200
• 1.7
• 2.1
• 1200
• 0.0
• 0.7
• 1400
• 1.7
• 2.2
• 1400
• 0.1
• 0.8
• 1600
• 1.7
• 2.3
• 1600
• 0.1
• 0.9
• 1800
• 1.7
• 2.4
• 1800
• 0.2
• 1.0
• 2000
• 1.8
• 2.6
• 2000
• 0.2
• 1.0
• 2200
• 1.9
• 2.7
• 2200
• 0.3
• 1.0
• 2400
• 1.9
• 2.8
• 2400
• 0.3
• 1.0.