Antireflection film and method of producing the same

1. An antireflection film that is provided on a surface of a substrate, the film comprising:

a surface layer having an alumina hydrate as a main component,

wherein the surface layer has only an uneven structure in which a volume proportion of the alumina hydrate per unit volume decreases in a direction from a substrate side to a surface side, and a period of apexes distributed to the uneven structure on the surface side is configured to be equal to or less than a wavelength of light of which reflection is to be suppressed,

an adhesion layer adjacent to the substrate side of the surface layer and formed of hydrogenated metal oxide, metal oxide, or metal fluoride is provided, and

a thermal expansion coefficient value of the adhesion layer at a reference temperature of 25° C. is in a range of 0.65×10 −6 to 19×10 −6 /K, and a difference in refractive index between the adhesion layer and the surface layer at an interface is 0.2 or more and 1.15 or less.

2. The antireflection film according to claim 1 ,

wherein a multilayer film in which at least one or more layers of each of at least two kinds of layers of a first thin layer formed of hydrogenated metal oxide, metal oxide, or metal fluoride, and a second thin layer having a different refractive index from a refractive index of the first layer are laminated is provided between the substrate and the surface layer, and the first thin layer adjacent to the substrate side of the surface layer is the adhesion layer.

3. The antireflection film according to claim 2 ,

wherein the first thin layer and the second thin layer are formed of hydrogenated silicon oxides having different refractive indexes due to different hydrogen concentrations in each thin film layer.

4. The antireflection film according to claim 3 ,

wherein the hydrogen concentration of the thin layers formed of the hydrogenated silicon oxides or the adhesion layer has any value in a range of 0.01 atomic % to 5.02 atomic %.

5. The antireflection film according to claim 3 ,

wherein the multilayer film is constituted of four or more thin layers of hydrogenated silicon oxide.

6. The antireflection film according to claim 1 ,

wherein a multilayer film in which at least one or more layers of each of at least two kinds of layers of a first thin layer formed of hydrogenated metal oxide, metal oxide, or metal fluoride, and a second thin layer having a different refractive index from a refractive index of the first layer are laminated is provided between the adhesion layer and the substrate, and the adhesion layer and the thin film layer adjacent to the adhesion layer have different refractive indexes.

7. The antireflection film according to claim 6 ,

wherein the adhesion layer is formed of hydrogenated silicon oxide.

8. The antireflection film according to claim 6 ,

wherein the first thin layer and the second thin layer are formed of hydrogenated silicon oxides having different refractive indexes due to different hydrogen concentrations in each thin film layer.

9. A method of producing an antireflection film comprising:

subjecting a surface layer portion formed on a surface of a substrate and having aluminum or alumina as a main component to a hydrothermal treatment,

wherein the surface layer portion is subjected to the hydrothermal treatment until the surface layer portion has only an uneven structure having an alumina hydrate as a main component,

the uneven structure is a structure in which a volume proportion of the alumina hydrate which forms the surface layer portion per unit volume decreases in a direction from a substrate side to a surface side of the surface layer portion, and

a multilayer film in which a plurality of hydrogenated silicon oxide layers having different refractive indexes formed by changing a hydrogen concentration in each thin film layer is laminated, is formed to be adjacent to the substrate side of the surface layer portion having the aluminum or alumina as a main component, before forming the surface layer portion.

10. The method of producing an antireflection film according to claim 9 ,

wherein a thickness of the surface layer portion having the aluminum or alumina as a main component before the surface layer portion is subjected to a hydrothermal treatment is 20 nm or less.