Antireflection film, optical element using same, and film formation method therefor

Abstract

In order to provide an antireflection film with low incident angle dependence and an optical element using the same, the present invention provides a multilayered antireflection film (AR) consisting of only three layers, namely a first layer (L1), a second layer (L2), and a third layer (L3), laminated in the given order from a glass or plastic substrate (S) side, wherein the first layer (L1), the second layer (L2), and the third layer (L3) are all formed from silicon oxide or all formed from aluminum oxide, the refractive index of the first layer (L1) and the third layer (L3) is 1.21 or less, and the refractive index of the second layer (L3) is 1.36 or more.

Description

Anti-reflective coating, optical element using the same, and method for forming the same coating.

[0001] This invention relates to an anti-reflective coating, an optical element using the same, and a method for forming the same coating.

[0002] As an anti-reflective coating, a dielectric multilayer film called a multicoat, which consists of stacked thin films with different refractive indices, is known. This reduces reflected light by adjusting the amplitude and phase of reflected waves generated at the surface and interface of each film and causing them to interfere. As an example of this type of anti-reflective coating, Patent Document 1 describes an anti-reflective coating composed of five dielectric thin films formed on a substrate with a refractive index of 1.90 or higher using vacuum deposition or electron gun deposition.

[0003] Japanese Patent Publication No. 2010-271404

[0004] However, the anti-reflective coating described in Patent Document 1 adjusts the amplitude and phase of reflected waves generated at the surface and interface of each coating, so its anti-reflective properties deteriorate at oblique incidence (especially when the incidence angle is 30 degrees or more) where interference conditions are disrupted. Therefore, there is a need for the development of an anti-reflective coating that has properties independent of the incidence angle.

[0005] The problem that this invention aims to solve is to provide an anti-reflective film with low dependence on the angle of incidence, an optical element using the same, and a method for forming the film.

[0006] The present invention solves the above problem by providing an anti-reflective film consisting of only three layers, in which a first layer, a second layer, and a third layer are laminated in order from the glass or plastic substrate side, wherein the first layer, the second layer, and the third layer are formed from silicon oxide, and the refractive index of the first layer and the third layer is 1.21 or less, and the refractive index of the second layer is 1.35 or more.

[0007] Furthermore, the present invention solves the above problem by providing an anti-reflective film consisting of only three layers, in which a first layer, a second layer, and a third layer are laminated in order from the glass or plastic substrate side, wherein the first layer, the second layer, and the third layer are formed from aluminum oxide, and the refractive index of the first layer and the third layer is 1.21 or less, and the refractive index of the second layer is 1.35 or more.

[0008] Further, the present invention is a multilayer film consisting of only four layers, in which a first layer, a second layer, a third layer, and a fourth layer are sequentially laminated from the side of a glass or plastic substrate, wherein the first layer, the second layer, the third layer, and the fourth layer are formed of silicon oxide, and the above problem is solved by an antireflection film in which the refractive indices of the first layer and the third layer are 1.19 or less, and the refractive indices of the second layer and the fourth layer are 1.36 or more.

[0009] Further, the present invention is a multilayer film consisting of only four layers, in which a first layer, a second layer, a third layer, and a fourth layer are sequentially laminated from the side of a glass or plastic substrate, wherein the first layer, the second layer, the third layer, and the fourth layer are formed of aluminum oxide, and the above problem is solved by an antireflection film in which the refractive indices of the first layer and the third layer are 1.19 or less, and the refractive indices of the second layer and the fourth layer are 1.36 or more.

[0010] In the above invention, it is more preferable that the reflectance is 5% or less when light in the near-infrared wavelength region (780 to 2500 nm) is incident at an incident angle of 0° to 50°.

[0011] In the above invention, it is more preferable that the reflectance is 0.5% or less when light in the visible light wavelength region (400 to 750 nm) is incident at an incident angle of 0°.

[0012] The antireflection film according to the above invention can be applied to an optical element having the antireflection film and a glass or plastic substrate. This optical element includes lenses, prisms, fly's eye integrators and the like. Further, the optical system having this optical element includes an imaging optical system, a scanning optical system, and a projection optical system, and can be used in optical apparatuses such as cameras, video cameras, binoculars, copiers, printers, projectors, and head-mounted displays.

[0013] More preferably, in the antireflection film according to the above invention, the first layer and the third layer having relatively low refractive indices are formed by repeating film formation by a vacuum deposition method and film formation by a sputtering method, and the second layer and the fourth layer having relatively high refractive indices are formed by at least one film formation method selected from the group consisting of a sputtering method, an ion-assisted vacuum deposition method, and a vacuum deposition method.

[0014] As for the film formation method for the second layer, a method of forming a film by the ion-assisted vacuum deposition method after forming a film by the sputtering method is more preferable.

[0015] According to the present invention, it is possible to provide an antireflection film with little incident angle dependency and an optical element using the same.

[0016] This is a cross-sectional view showing an antireflection film according to one embodiment of the present invention. This is a graph showing the spectral reflectance characteristics of the antireflection film of Figure 1. This is a graph showing the spectral reflectance characteristics of the antireflection film of Figure 1 at incident angles of 0° and 50°. This is a graph showing the spectral reflectance characteristics of the antireflection film of a comparative example at incident angles of 0° and 50°. This is a graph showing the spectral reflectance characteristics when the refractive indices of the first layer and the third layer of the antireflection film of Figure 1 are changed. This is a graph showing the spectral reflectance characteristics when the refractive index of the second layer of the antireflection film of Figure 1 is changed. This is a cross-sectional view showing an antireflection film according to another embodiment of the present invention. This is a graph showing the spectral reflectance characteristics of the antireflection film of Figure 7. This is a graph showing the spectral reflectance characteristics of the antireflection film of Figure 7 at incident angles of 0° and 50°. This is a graph showing the spectral reflectance characteristics when the refractive indices of the first layer and the third layer of the antireflection film of Figure 7 are changed. This is a graph showing the spectral reflectance characteristics when the refractive indices of the second layer and the fourth layer of the antireflection film of Figure 7 are changed. This is a schematic cross-sectional view showing an example of a film formation apparatus for forming the antireflection film according to the present invention. This is a view taken along the line XIII-XIII in Figure 12 as viewed in the direction of the arrows. This is a process diagram showing an example of a film formation method using the film formation apparatus shown in Figure 12 and Figure 13. This is a schematic cross-sectional view showing another example of the film formation apparatus for forming the antireflection film according to the present invention. This is a view taken along the line XVI-XVI in Figure 15 as viewed in the direction of the arrows. This is a graph (the vertical axis represents the logarithm of pressure) showing the atmospheric pressures of the first pressure region R1 and the second pressure region R2 shown in Figure 15, and the set pressures of the first exhaust device and the second exhaust device. This is a process diagram showing an example of a film formation method using the film formation apparatus shown in Figure 15.

[0017] 《Anti-reflective coating (Part 1)》 Hereinafter, embodiments of the anti-reflective coating of the present invention will be described based on the drawings. Figure 1 is a cross-sectional view showing an anti-reflective coating AR according to one embodiment of the present invention. As shown in Figure 1, the anti-reflective coating AR according to this embodiment is a multilayer film consisting of only three layers, in which the first layer L1, the second layer L2, and the third layer L3 are laminated in order from the substrate S side. These first layer L1, second layer L2, and third layer L3 are all made of the same predetermined material. The refractive index of the first layer L1 is 1.21 or less, the refractive index of the second layer L2 is 1.35 or more, the refractive index of the third layer L3 is 1.21 or less, and the difference in refractive index between the first layer L1 and the second layer L2 or between the second layer L2 and the third layer L3 is 0.14 or more. As shown in Figure 1, the anti-reflective coating AR of this embodiment is formed on the surface of a substrate S made of glass or plastic, for example.

[0018] In the anti-reflective coating AR of this embodiment, silicon dioxide and aluminum oxide can be exemplified as predetermined materials constituting the first layer L1, the second layer L2, and the third layer L3. When silicon dioxide is used as the predetermined material, the first layer L1, the second layer L2, and the third layer L3 are all composed of silicon dioxide, and when aluminum oxide is used as the predetermined material, the first layer L1, the second layer L2, and the third layer L3 are all composed of aluminum oxide.

[0019] Furthermore, as described above, the anti-reflective coating AR of this embodiment has a refractive index of 1.21 or less for the first layer L1, 1.35 or more for the second layer L2, and 1.21 or less for the third layer L3. In addition, the difference in refractive index between the first layer L1 and the second layer L2, or between the third layer L3 and the second layer L2, is set to 0.14 or more. Regardless of whether silicon dioxide or aluminum oxide is used as the predetermined material, the refractive index conditions for each of these layers L1, L2, and L3 are met during the formation process.

[0020] The anti-reflective film AR of this embodiment is constructed by laminating a first layer L1, a second layer L2, and a third layer L3 in order from the substrate S side. That is, as shown in Figure 1, the first layer L1 is formed on one surface of the substrate S, the second layer L2 is formed on the surface of the first layer L1, and the third layer L3 is formed on the surface of the second layer L2. No other thin films are formed between the substrate S and the first layer L1, no other thin films are formed between the first layer L1 and the second layer L2, and no other thin films are formed between the second layer L2 and the third layer L3. The anti-reflective film AR of this embodiment is a laminated thin film with a three-layer structure consisting only of the first layer L1, the second layer L2, and the third layer L3. However, the present invention is not limited to the laminated thin film with a three-layer structure shown in Figure 1, and may also be a laminated thin film with four or more layers. In that case, the film is a multilayer film of at least three layers, where at least one of these three layers is in contact with a glass or plastic substrate, all of these at least three layers are formed from silicon oxide or aluminum oxide, and the difference in refractive index between two of these at least three layers is 0.14 or more.

[0021] Figure 2 shows silicon dioxide (SiO₂) on the surface of a glass substrate S with a refractive index of 1.52. ２ A first layer L1 is formed consisting of ), and silicon dioxide (SiO₂) is formed on the surface of this first layer L1. ２ A second layer L2 is formed consisting of ), and silicon dioxide (SiO₂) is formed on the surface of this second layer L2. ２ This graph shows the spectral reflectance characteristics of an anti-reflective coating AR having a third layer L3 formed from the above. The anti-reflective coating AR shown in this figure was formed using the film deposition apparatus 1 shown in Figures 12 and 13, which will be described later. It is a laminated coating with a first layer L1 with a low refractive index of 20.7 nm, a second layer L2 with a high refractive index of 53.8 nm, and a third layer L3 with a low refractive index of 127.2 nm. When the refractive index at a wavelength of 550 nm was calculated, the refractive index of the first layer L1 was 1.16, the refractive index of the second layer L2 was 1.45, and the refractive index of the third layer L3 was 1.16. In this specification, the refractive index refers to the value at a wavelength of 550 nm unless otherwise specified.

[0022] As shown in the figure, it was confirmed that the reflectivity is low in the 400 nm to 750 nm band, so it can be used as a practical anti-reflective coating for various types of visible light.

[0023] Figure 3 is a graph showing the spectral reflectance characteristics of the anti-reflective coating AR shown in Figure 1 at incident angles of 0° and 50°. The reflectance characteristics when the incident angle of light is 0° are the same as those shown in Figure 2, but the vertical axis scale has been changed. As shown in Figure 3, with the anti-reflective coating AR shown in Figure 1, even when the incident angle changes to 50°, the reflectance remains below 5% across the entire wavelength range. In particular, it was confirmed that the reflectance is below 5% for light in the near-infrared wavelength range (780 to 2500 nm) when incident at angles of 0° to 50°.

[0024] Figure 4 is a graph showing the spectral reflectance characteristics of an anti-reflective coating fabricated as a comparative example of the anti-reflective coating AR shown in Figure 1, at incident angles of 0° and 50°. The anti-reflective coating in this comparative example was formed using a general vacuum deposition apparatus and is a seven-layer laminated coating with a low refractive index first layer L1 having a thickness of 178.4 nm, a high refractive index second layer L2 having a thickness of 13.4 nm, a low refractive index third layer L3 having a thickness of 34.2 nm, a high refractive index fourth layer L4 having a thickness of 46.1 nm, a low refractive index fifth layer L5 having a thickness of 14.6 nm, a high refractive index sixth layer L6 having a thickness of 33.3 nm, and a low refractive index seventh layer L7 having a thickness of 91.6 nm. When calculating the refractive index at a wavelength of 550 nm, the refractive index of the first layer L1, third layer L3, fifth layer L5, and seventh layer L7 was 1.47, while the refractive index of the second layer L2, fourth layer L4, and sixth layer L6 was 2.46.

[0025] As shown in Figure 4, the anti-reflective coating of the comparative example showed high reflectivity for light in the near-infrared wavelength range (780 to 2500 nm) when incident at angles of incidence from 0° to 50°, and it was confirmed that the reflectivity exceeded 5% when the incident angle changed to 50°.

[0026] The anti-reflective coating AR having spectral reflectance characteristics shown in Figures 2 and 3 is made of silicon dioxide (SiO₂) with a refractive index of 1.16 in the first layer L1, 1.45 in the second layer L2, and 1.16 in the third layer L3. ２The film is a three-layer laminated film consisting of ), and we demonstrated how the spectral reflectance characteristics of the anti-reflective film AR change when the refractive index of each layer is changed. Figure 5 is a graph showing the spectral reflectance characteristics when the refractive index of the first layer L1 and the third layer L3 of the anti-reflective film AR in Figure 1 is changed, and Figure 6 is a graph showing the spectral reflectance characteristics when the refractive index of the second layer L2 of the anti-reflective film AR in Figure 1 is changed.

[0027] Figure 5 is a graph showing the spectral reflectance characteristics (incident angle of light at 0°) of the anti-reflective coating AR when the refractive index of the second layer L2, which has a relatively high refractive index, is fixed at 1.48, and the refractive indices of the first layer L1 and the third layer L3 are set to four levels: 1.17, 1.20, 1.21, and 1.25. As shown in the figure, when the refractive index of the second layer L2 is fixed at 1.48, the reflectance in the 400 nm to 750 nm band is 0.5% or less when the refractive indices of the first layer L1 and the third layer L3 are 1.21 or less, but it was confirmed that the reflectance in the 400 nm to 750 nm band exceeds 0.5% when the refractive index of the first layer L1 and the third layer L3 is 1.25. Therefore, it can be said that it is preferable for the refractive indices of the first layer L1 and the third layer L3 to be 1.21 or less.

[0028] Figure 6 is a graph showing the spectral reflectance characteristics (incident angle of light at 0°) of the anti-reflective coating AR when the refractive indices of the first layer L1 and third layer L3, which have relatively low refractive indices, are fixed at 1.17, and the refractive index of the second layer L2 is set to four levels: 1.30, 1.35, 1.47, and 2.42. As shown in the figure, when the refractive indices of the first layer L1 and third layer L3 are fixed at 1.17, the reflectance in the 400 nm to 750 nm band is 0.5% or less when the refractive index of the second layer L2 is 1.35 or higher, but it was confirmed that when the refractive index of the second layer L2 is 1.30, the reflectance in the 400 nm to 750 nm band exceeds 0.5%. Therefore, it can be said that it is preferable for the refractive index of the second layer L2 to be 1.35 or higher.

[0029] From the above, silicon dioxide (SiO ２) in the three-layer antireflective film AR composed thereof, it was confirmed that when the refractive indices of the first layer L1 and the third layer L3 are 1.21 or less, and the refractive index of the second layer L2 is 1.35 or more, the reflectance in the band of 400 nm to 750 nm is 0.5% or less. In addition, silicon dioxide (SiO ２ ) in the three-layer antireflective film AR composed thereof, it was confirmed that when the difference between the refractive indices of the first layer L1 and the third layer L3 and the refractive index of the second layer L2 is 0.14 or more, the reflectance in the band of 400 nm to 750 nm is 0.5% or less.

[0030] In a similar verification experiment, aluminum oxide (Al ２ O ３ ) also in the three-layer antireflective film AR composed thereof, it was confirmed that when the refractive indices of the first layer L1 and the third layer L3 are 1.21 or less, and the refractive index of the second layer L2 is 1.35 or more, the reflectance in the band of 400 nm to 750 nm is 0.5% or less. In addition, aluminum oxide (Al ２ O ３ ) also in the three-layer antireflective film AR composed thereof, it was confirmed that when the difference between the refractive indices of the first layer L1 and the third layer L3 and the refractive index of the second layer L2 is 0.14 or more, the reflectance in the band of 400 nm to 750 nm is 0.5% or less.

[0031] <<Antireflective Film (Part 2)>> FIG. 7 is a cross-sectional view showing an antireflective film AR according to another embodiment of the present invention. As shown in FIG. 7, the antireflective film AR according to the present embodiment is a multilayer film consisting of only four layers, in which a first layer L1, a second layer L2, a third layer L3, and a fourth layer L4 are sequentially laminated from the substrate S side. All of the first layer L1, the second layer L2, the third layer L3, and the fourth layer L4 are made of the same predetermined material. The refractive index of the first layer L1 is 1.19 or less, the refractive index of the second layer L2 is 1.36 or more, the refractive index of the third layer L3 is 1.19 or less, the refractive index of the fourth layer is 1.36 or more, and the difference in refractive index between the first layer L1 and the second layer L2, or the difference in refractive index between the second layer L2 and the third layer L3, or the difference in refractive index between the third layer L3 and the fourth layer L4 is 0.17 or more. As shown in FIG. 7, the antireflective film AR of the present embodiment is formed, for example, on the surface of a substrate S made of glass or plastic.

[0032] In the anti-reflective coating AR of this embodiment, silicon dioxide and aluminum oxide can be exemplified as predetermined materials constituting the first layer L1, second layer L2, third layer L3, and fourth layer L4. When silicon dioxide is used as the predetermined material, the first layer L1, second layer L2, third layer L3, and fourth layer L4 are all composed of silicon dioxide, and when aluminum oxide is used as the predetermined material, the first layer L1, second layer L2, third layer L3, and fourth layer L4 are all composed of aluminum oxide.

[0033] Furthermore, as described above, the anti-reflective coating AR of this embodiment has the following characteristics: the refractive index of the first layer L1 is 1.19 or less, the refractive index of the second layer L2 is 1.36 or more, the refractive index of the third layer L3 is 1.19 or less, the refractive index of the fourth layer L4 is 1.36 or more, and the difference in refractive index between the first layer L1 and the second layer L2, or between the second layer L2 and the third layer L3, or between the third layer L3 and the fourth layer L4 is 0.17 or more. Regardless of whether silicon dioxide or aluminum oxide is used as the predetermined material, the refractive index conditions of each of these layers L1, L2, L3, and L4 are met.

[0034] The anti-reflective film AR of this embodiment is constructed by laminating a first layer L1, a second layer L2, a third layer L3, and a fourth layer L4 in order from the substrate S side. That is, as shown in Figure 7, the first layer L1 is formed on one surface of the substrate S, the second layer L2 is formed on the surface of the first layer L1, the third layer L3 is formed on the surface of the second layer L2, and the fourth layer L4 is formed on the surface of the third layer L3. No other thin films are formed between the substrate S and the first layer L1, no other thin films are formed between the first layer L1 and the second layer L2, no other thin films are formed between the second layer L2 and the third layer L3, and no other thin films are formed between the third layer L3 and the fourth layer L4. The anti-reflective film AR of this embodiment is a laminated thin film with a four-layer structure consisting only of the first layer L1, the second layer L2, the third layer L3, and the fourth layer L4. However, the present invention is not limited to the four-layer laminated thin film shown in Figure 7, but may also be a laminated thin film with five or more layers. In that case, it is sufficient if it is a multilayer film with at least three layers, one of these at least three layers is in contact with a glass or plastic substrate, all of these at least three layers are formed from silicon oxide or aluminum oxide, and the difference in refractive index between two of these at least three layers is 0.17 or more.

[0035] Figure 8 shows silicon dioxide (SiO₂) on the surface of a glass substrate S with a refractive index of 1.52. ２ A first layer L1 is formed consisting of ), and silicon dioxide (SiO₂) is formed on the surface of this first layer L1. ２ A second layer L2 is formed consisting of ), and silicon dioxide (SiO₂) is formed on the surface of this second layer L2. ２ A third layer L3 is formed consisting of ), and silicon dioxide (SiO₂) is formed on the surface of this third layer L3. ２This graph shows the spectral reflectance characteristics of an anti-reflective coating AR having a fourth layer L4 formed from the above. The anti-reflective coating AR shown in this figure was formed using the film deposition apparatus 1 shown in Figures 12 and 13, which will be described later. It is a laminated coating with a first layer L1 with a low refractive index of 14.6 nm, a second layer L2 with a high refractive index of 67.4 nm, a third layer L3 with a low refractive index of 75.3 nm, and a fourth layer L4 with a high refractive index of 20.0 nm. When the refractive index at a wavelength of 550 nm was calculated, the refractive index of the first layer L1 was 1.16, the refractive index of the second layer L2 was 1.45, the refractive index of the third layer L3 was 1.16, and the refractive index of the fourth layer L4 was 1.45.

[0036] As shown in the figure, it was confirmed that the reflectivity is low in the 400 nm to 750 nm band, so it can be used as a practical anti-reflective coating for various types of visible light.

[0037] Figure 9 is a graph showing the spectral reflectance characteristics of the anti-reflective coating AR shown in Figure 7 at incident angles of 0° and 50°. The reflectance characteristics when the incident angle of light is 0° are the same as those shown in Figure 8, but the vertical axis scale has been changed. As shown in Figure 9, with the anti-reflective coating AR shown in Figure 7, even when the incident angle changes to 50°, the reflectance remains below 5% across the entire wavelength range, and it was confirmed that the reflectance is below 5% for light in the near-infrared wavelength range (780 to 2500 nm) when incident at angles of 0° to 50°. On the other hand, with the anti-reflective coating related to the comparative example shown in Figure 4, the reflectance is high for light in the near-infrared wavelength range (780 to 2500 nm) when incident at angles of 0° to 50°, and it was confirmed that it exceeds 5% when the incident angle changes to 50°.

[0038] The anti-reflective coating AR having spectral reflectance characteristics shown in Figures 8 and 9 is made of silicon dioxide (SiO₂) with a refractive index of 1.16 for the first layer L1, 1.45 for the second layer L2, 1.16 for the third layer L3, and 1.45 for the fourth layer L4. ２The laminated film has a four-layer structure consisting of ), and we demonstrated how the spectral reflectance characteristics of the anti-reflective film AR change when the refractive index of each layer is changed. Figure 10 is a graph showing the spectral reflectance characteristics when the refractive index of the first layer L1 and the third layer L3 of the anti-reflective film AR in Figure 5 is changed, and Figure 11 is a graph showing the spectral reflectance characteristics when the refractive index of the second layer L2 and the fourth layer L4 of the anti-reflective film AR in Figure 5 is changed.

[0039] Figure 10 is a graph showing the spectral reflectance characteristics (incident angle of light at 0°) of the anti-reflective coating AR when the refractive indices of the second layer L2 and fourth layer L4, which have relatively high refractive indices, are fixed at 1.48, and the refractive indices of the first layer L1 and third layer L3 are set to five levels: 1.17, 1.18, 1.19, 1.20, and 1.25. As shown in the figure, when the refractive indices of the second layer L2 and fourth layer L4 are fixed at 1.48, the reflectance in the 400 nm to 750 nm band is 0.5% or less when the refractive indices of the first layer L1 and third layer L3 are 1.19 or less, but it was confirmed that when the refractive indices of the first layer L1 and third layer L3 are 1.20, the reflectance in the 400 nm to 750 nm band exceeds 0.5%. Therefore, it can be said that it is preferable for the refractive indices of the first layer L1 and third layer L3 to be 1.19 or less.

[0040] Figure 11 is a graph showing the spectral reflectance characteristics (incident angle of light at 0°) of the anti-reflective coating AR when the refractive indices of the first layer L1 and the third layer L3, which have relatively low refractive indices, are fixed at 1.17, and the refractive indices of the second layer L2 and the fourth layer L4 are set to three levels: 1.30, 1.36, and 1.47. As shown in the figure, when the refractive indices of the first layer L1 and the third layer L3 are fixed at 1.17, the reflectance in the 400 nm to 750 nm band is 0.5% or less when the refractive indices of the second layer L2 and the fourth layer L4 are 1.36 or higher. However, when the refractive indices of the second layer L2 and the fourth layer L4 are 1.30, it was confirmed that the reflectance in the 400 nm to 750 nm band exceeds 0.5%. Therefore, it can be said that it is preferable for the refractive indices of the second layer L2 and the fourth layer L4 to be 1.36 or higher.

[0041] From the above, silicon dioxide (SiO ２In a four-layer anti-reflective coating AR consisting of silicon dioxide (SiO₂), it was confirmed that when the refractive indices of the first layer L1 and the third layer L3 are 1.19 or less, and the refractive indices of the second layer L2 and the fourth layer L4 are 1.36 or more, the reflectance in the 400 nm to 750 nm band becomes 0.5% or less. ２ In a four-layer anti-reflective coating AR consisting of the above, it was confirmed that when the difference between the refractive indices of the first layer L1 and the third layer L3 and the refractive indices of the second layer L2 and the fourth layer L4 is 0.17 or more, the reflectance in the 400 nm to 750 nm band becomes 0.5% or less.

[0042] Similar demonstration experiments have shown that aluminum oxide (Al ２ O ３ In a four-layer anti-reflective coating AR consisting of aluminum oxide (Al), it was confirmed that if the refractive index of the first layer L1 and the third layer L3 is 1.19 or less, and the refractive index of the second layer L2 and the fourth layer L4 is 1.36 or more, the reflectance in the 400 nm to 750 nm band becomes 0.5% or less. ２ O ３ In a four-layer anti-reflective coating AR consisting of the above, it was confirmed that if the difference between the refractive indices of the first layer L1 and the third layer L3 and the refractive indices of the second layer L2 and the fourth layer L4 is 0.17 or more, the reflectance in the 400 nm to 750 nm band becomes 0.5% or less.

[0043] 《Method for Forming an Anti-Reflective Film (Part 1)》 Next, an example of a method for forming the anti-reflective film AR according to the present invention described above will be explained. Figure 12 is a longitudinal cross-section of the main part of the anti-reflective film forming apparatus 1 of the present invention, and Figure 13 is a view along the line XIII-XIII in Figure 12.

[0044] The film deposition apparatus 1 of this embodiment comprises a housing 2 that constitutes a film deposition chamber 2a which is a substantially sealed space; a first exhaust device 3 for reducing the pressure inside the film deposition chamber 2a; a disc-shaped substrate holder 5 that is rotatable by a drive unit 5c and capable of holding a substrate S on one main surface; a differential pressure vessel 12 provided so as to face a part of the substrate holding surface 5a of the substrate holder 5; a sputtering mechanism 13 provided inside the differential pressure vessel 12; a gas introduction system 14 for introducing sputtering gas into the differential pressure vessel 12; and a vacuum deposition mechanism 6 provided inside the film deposition chamber 2a so as to face the substrate holding surface 5a.

[0045] The substrate S to be deposited is not particularly limited, and in addition to glass substrates, acrylic and other plastic substrates can also be used. In particular, the effects of the present invention are even more pronounced when using substrates for optical applications, which have a high refractive index and therefore require suppression of reflectivity, as well as mechanical strength due to handling and cleaning.

[0046] In this example, a gap G is provided between the substrate holding surface 5a of the substrate holder 5 and the upper end face 12a of the differential pressure container 12, allowing a small amount of gas to flow through. The substrate holder 5 in this example is formed in a disc shape that makes it easy to adjust the appropriate gap G. However, as long as the gap G can be appropriately adjusted, the substrate holder is not limited to a disc shape like in this example, and may be dome-shaped or cylindrical, such as those used in carousel-type rotary film deposition apparatuses.

[0047] The differential pressure vessel 12 is formed in a cylindrical shape, with one axial end face 12b (the lower surface in Figure 12) closed and the other end face 12a (the upper surface in Figure 12) open. The differential pressure vessel 12 separates the internal space of the film deposition chamber 2a into a high vacuum region A outside the differential pressure vessel 12 and a differential pressure region B inside the differential pressure vessel 12.

[0048] The open end face 12a of the differential pressure vessel 12 is, for example, circular and is positioned with a predetermined gap G from the substrate holding surface 5a of the substrate holder 5, as described above. This gap G is such that when sputtering gas is introduced into the differential pressure region B from the gas introduction system 14, the sputtering gas leaks through the gap G into the high vacuum region A, thereby adjusting the differential pressure region B to a predetermined pressure (high pressure / low vacuum) higher than the high vacuum region A. The size of the suitable gap G can be determined mainly by the volume of the differential pressure vessel 12, the flow rate of the sputtering gas, and the pressures of the high vacuum region A and the differential pressure region B to be adjusted.

[0049] The differential pressure vessel 12 is provided with a sputtering mechanism 13. The sputtering mechanism 13 in this example comprises a target 13a arranged inside the differential pressure vessel 12, a sputtering electrode 13b on which the target 13a is mounted, a sputtering power supply 13c that supplies power to the sputtering electrode 13b, and a shutter 13d arranged between the target 13a and the substrate holder 5 to cover or uncover the target 13a. The sputtering mechanism 13 in this example uses a DC (direct current) or RF (radio frequency) sputtering method.

[0050] The target 13a is formed from the film raw material in a flat plate shape and is placed inside the differential pressure vessel 12 so as to face the substrate holding surface 5a of the substrate holder 5. In the film deposition method of this embodiment, a silicon dioxide thin film or aluminum oxide film is deposited, so a metal target of Si or Al can be used as the target 13a. In addition, SiO ２ or Al ２ O ３ Metal oxide targets such as those shown may also be used.

[0051] The gas introduction system 14 introduces sputtering gas into the differential pressure region B inside the differential pressure container 12. The gas introduction system 14 includes gas cylinders 14a and 14d for storing sputtering gas, valves 14b and 14e provided in correspondence with the gas cylinders 14a and 14d, mass flow controllers 14c and 14f for adjusting the flow rate of sputtering gas, and piping 14g as a sputtering gas supply path. In this example, an inert gas such as argon or helium and a reactive gas such as oxygen are introduced as sputtering gas.

[0052] The deposition mechanism 6 consists of an electron beam deposition source and includes a crucible 6a for filling with deposition material and an electron gun 6b for irradiating the deposition material filled in the crucible 6a with an electron beam. A shutter 6c for opening and closing the upper opening of the crucible 6a is movably provided above the crucible 6a. In the film deposition method of this embodiment, a silicon dioxide thin film or aluminum oxide film is deposited, and the deposition material is SiO ２ or Al ２ O ３ This is used.

[0053] An ion source 11 is installed in a high-vacuum region A to the side of the deposition mechanism 6, near the lower surface inside the deposition chamber 2a. The ion source 11 is an ion assist ion source that assists the deposition process of the substrate S by the deposition mechanism 6 and the sputtering mechanism 13 with ions. The irradiation range of the ion beam from the ion source 11 is a predetermined range of all or part of the substrate holding surface 5a of the substrate holder 5. In this embodiment, a part of the substrate S held on the substrate holding surface 5a of the substrate holder 5 is temporarily hidden by the differential pressure container 12 as the substrate holder 5 rotates, so the ion beam from the ion source 11 is irradiated in the area where the ion beam is not shielded by the differential pressure container 12.

[0054] In this embodiment, the ion source 11 is, for example, an ion source that uses a grid-like electrode to extract ions from the plasma, a so-called Kaufman-type ion source. The operating pressure of the Kaufman-type ion source is 0.02 Pa or less. Although not shown in the figures, the Kaufman-type ion source 11 comprises a housing, an anode and filament disposed inside the housing, a magnet for generating a magnetic field disposed outside the housing, a screen electrode disposed at an opening in the housing and kept at the same potential as the housing, and a screen-shaped accelerating electrode disposed outside the screen electrode. When a reactive gas such as oxygen or an inert gas such as argon is supplied into the housing and a positive potential is applied to the anode to heat the filament, a discharge occurs, and plasma is generated inside the housing by collisions between electrons generated by the discharge and the gas. The generated plasma is densely packed by the magnetic field of the magnet disposed outside the housing. In this state, when a negative potential is applied to the accelerating electrode, ions are extracted from the plasma, pass through the screen electrode, are accelerated, and irradiated onto the substrate S.

[0055] By irradiating the thin film deposited on the substrate S by the deposition mechanism 6 and the sputtering mechanism 13 with an ion beam, a dense, high-strength film with a smooth surface can be obtained. A shutter to block ion irradiation to the substrate S, or an adjustment plate to adjust the ion directionality, may be installed above the ion source 11. Furthermore, a neutralizer that irradiates negative electrons towards the substrate S to electrically neutralize the substrate S charged by positive ions irradiated from the ion source 11 may be installed in the deposition chamber 2a. Moreover, the ion source 11 is not limited to a Kaufman-type ion source; an ion source of a different type may be used as long as its operating pressure is 0.05 Pa or less, which is the atmospheric pressure of the high-vacuum region A. Furthermore, in the deposition apparatus 1 of this embodiment, the ion source 11 is not an essential component; it may be omitted as needed if there are no problems with the strength of the anti-reflective film AR produced.

[0056] The film deposition apparatus 1 used in this example has a sputtering mechanism 13 and a deposition mechanism 6 located inside a single deposition chamber 2a. Therefore, sputtering and vacuum deposition can be performed simultaneously, or alternately, repeatedly. In the sputtering method, the pressure at which sputtering is possible is 1 to 10 －１ In contrast to Pa, the pressure at which vacuum deposition is possible is 10 －１ ~10 －６ The pressure is Pa. In the film deposition apparatus 1 of this example, it is necessary to accommodate two film deposition methods, sputtering and vacuum deposition, which require significantly different pressures. The configuration for this is located in the differential pressure vessel 12, which houses the target 13a of the sputtering mechanism 13.

[0057] In other words, by introducing sputtering gas into the differential pressure vessel 12, the pressure in the differential pressure region B of the differential pressure vessel 12 is made higher than the high vacuum region A inside the deposition chamber 2a, thereby setting the pressure in the differential pressure region B to a sputtering-capable pressure of 1 to 10. －１ Set to Pa. At this time, the pressure in the differential pressure region B is controlled by adjusting the flow rate of the sputtering gas and the dimensions of the gap G. For example, if the gap G is set to a very small width, a large amount of gas will not flow from the differential pressure container 12 into the high vacuum region A inside the deposition chamber 2a, so the pressure near the evaporation source of the deposition mechanism 6 can be set to a vacuum level 10 that allows for vacuum deposition. －１ ~10 －６ The pressure can be set to Pa. However, the pressure in the high vacuum region A and the pressure in the differential pressure region B are not set to equal pressure, but a differential pressure is always provided. This configuration makes it possible to perform sputtering deposition and vacuum deposition deposition inside the same deposition chamber 2a. Moreover, unlike conventional technology, there is no need to adjust the internal pressure of the deposition chamber 2a to a pressure suitable for each deposition method when switching between sputtering deposition and vacuum deposition deposition.

[0058] Furthermore, the film deposition apparatus 1 used in this example is equipped with a rotary substrate holder 5 that holds and rotates the substrate S. Therefore, during film deposition, the substrate S rotates inside the deposition chamber 2a around the rotation axis 5b. As a result, the substrate S moves between the differential pressure region B for sputtering deposition and the high vacuum region A for vacuum deposition. However, by controlling the rotation speed of the substrate holder 5 by the drive unit 5c, the time spent in each region A and B can be adjusted to any desired time. This indicates that films deposited by sputtering and films deposited by vacuum deposition can be deposited in the same deposition chamber 2a.

[0059] Furthermore, in this example, by rotating the substrate holder 5, the substrate S is passed through a high-vacuum region A with a vacuum higher than the pressure suitable for the sputtering method while sputtering film deposition is performed. This suppresses the adhesion of particles other than the deposited film particles to the substrate S, leading to the production of a high-quality film.

[0060] Furthermore, when sputtering and vacuum deposition are performed simultaneously, or alternately and repeatedly, the dwell time of the substrate S in the differential pressure region B of sputtering and the high vacuum region A of vacuum deposition, as well as the deposition conditions of the sputtering mechanism 13 or the deposition mechanism 6, can be adjusted to set the ratio of the film weight by sputtering to the film weight by vacuum deposition, and the total film thickness to desired values.

[0061] The control device 10 controls the ON / OFF of the first exhaust device 3, the rotational speed control including the ON / OFF of the drive unit 5c of the substrate holder 5, the operation control of the deposition mechanism 6 including the opening and closing of the shutter 6c, the operation control of the sputtering mechanism 13 including the ON / OFF of the sputtering power supply 13c, the operation control of the gas introduction system 14 including valves 14b and 14e, and the operation control of the ion source 11 including the ON / OFF. Then, with the inside of the deposition chamber 2a controlled to a predetermined atmospheric pressure, it executes deposition control using a hybrid deposition method that combines ion-assisted vacuum deposition and sputtering.

[0062] Next, an embodiment of a method for forming an anti-reflective film AR using the above-described film-forming apparatus 1 will be explained. In the following, the method for forming a three-layer anti-reflective film AR shown in Figure 1 and the method for forming a four-layer anti-reflective film AR shown in Figure 7 will be explained together. Figure 14 is a process diagram showing an example of the method for forming these three-layer or four-layer anti-reflective film ARs.

[0063] The method for forming the three-layer anti-reflective film AR of this embodiment involves repeatedly forming the first layer L1 (SiO₂) on one side of a glass substrate S by vacuum deposition using a deposition mechanism 6 and by sputtering using a sputtering mechanism 13. ２ Membrane or Al ２ O ３ A film is formed, and then the second layer L2 (SiO) is formed by sputtering using the sputtering mechanism 13. ２ Membrane or Al ２ O ３ A film is formed, and then the process of forming a third layer L3 (SiO₂) is repeated using vacuum deposition using the deposition mechanism 6 and sputtering using the sputtering mechanism 13. ２ Membrane or Al ２ O ３ This is a method for forming a film. Furthermore, in this embodiment, the method for forming the four-layer anti-reflective film AR involves repeatedly forming a film on one side of a glass substrate S by vacuum deposition using a deposition mechanism 6 and by sputtering using a sputtering mechanism 13 to form the first layer L1 (SiO ２ Membrane or Al ２ O ３ A film is formed, and then the second layer L2 (SiO) is formed by sputtering using the sputtering mechanism 13. ２ Membrane or Al ２ O ３ A film is formed, and then the process of forming a third layer L3 (SiO₂) is repeated using vacuum deposition using the deposition mechanism 6 and sputtering using the sputtering mechanism 13. ２ Membrane or Al ２ O ３ A film is formed, and then the fourth layer L4 (SiO) is formed by sputtering using the sputtering mechanism 13. ２ Membrane or Al ２ O ３ This is a method for forming a film.

[0064] As preparation, the substrate S is set in the substrate holder 5 and attached to the deposition chamber 2a. Also, a Si target or Al target is set as the target 13a, and SiO is placed in the crucible 6a as the deposition material. ２ or Al ２ O ３ After filling, start the process shown in Figure 14.

[0065] In step ST1, the film deposition chamber 2a is sealed, and the inside of the film deposition chamber 2a is evacuated (reduced pressure) using the first exhaust device 3. In step ST2, a pressure sensor 15, which is positioned to face the high vacuum region A of the film deposition chamber 2a, is used to determine that the inside of the film deposition chamber 2a is at a predetermined pressure (1 × 10⁻¹⁰). －１ ~1 x 10 －６ The range of Pa, for example, 7 × 10 －４ It is determined whether the pressure (Pa) has reached a predetermined level. －４ If Pa) has not been reached, return to step ST1 and 7 × 10 －４ Repeat the vacuum evacuation process until the pressure reaches Pa.

[0066] Once the pressure inside the deposition chamber 2a reaches a predetermined level, the pressure is reduced to a level suitable for vacuum deposition by the deposition mechanism 6, and the process proceeds to step ST3, where the rotation of the substrate holder 5 begins. In this embodiment, the rotation of the substrate holder 5 in step ST3 is started before the introduction of gas in step ST4, but the rotation of the substrate S may be started during or after the introduction of gas. However, since the rotation of the substrate holder 5 affects the flow rate of gas leaking out of the differential pressure container 12 through the gap G between the substrate holder 5 and the differential pressure container 12, it is preferable to start the rotation of the substrate holder 5 before or during the introduction of gas.

[0067] In step ST4, valves 14b and 14e are opened to introduce oxygen gas and argon gas from gas cylinders 14a and 14d, respectively, into the differential pressure region B inside the differential pressure container 12. Once oxygen gas and argon gas are introduced into the differential pressure region B, the first exhaust device 3 will expel 7 × 10⁻¹⁰ gases. －４Within the differential pressure region B, which has been reduced to approximately Pa, oxygen and argon gases are locally introduced, and a small amount of these gases leaks out of the differential pressure container 12 at a constant flow rate through the gap G.

[0068] When the amount of gas introduced into differential pressure region B and the amount of gas leaking out of differential pressure region B through gap G reach a predetermined balance, the pressure in differential pressure region B becomes a desired pressure, and in this embodiment, 1 to 10 suitable for sputtering film deposition. －１ The pressure in differential pressure region B may be detected by installing a pressure sensor inside the differential pressure container 12, but the pressure is between 1 and 10. －１ Experiments have confirmed that plasma is generated when the pressure reaches Pa. Therefore, in this embodiment, when plasma is generated inside the differential pressure container 12, the predetermined pressure is 1 to 10 －１ It is determined that Pa has been reached. If plasma does not occur after waiting for a while in step ST4, it is expected that the pressure inside the differential pressure container 12 has not risen sufficiently because the introduction rate of oxygen gas and argon gas is slower than the leakage rate of gas from gap G. Therefore, the flow rates of oxygen gas and argon gas are increased by adjusting the mass flow controllers 14c and 14f.

[0069] In step ST5, a first layer L1 is deposited on the surface of the substrate S. That is, the shutter 6c that had been blocking the crucible 6a is opened, and an electron beam is irradiated onto the crucible 6a from the electron gun 6b to perform vacuum deposition. Simultaneously or around the same time, the shutter 13d that had been shielding the front of the target 13a is opened, and sputtering deposition is performed. In other words, the first layer L1 is deposited by repeatedly performing deposition by vacuum deposition and deposition by sputtering while rotating the substrate holder 5 at a constant speed.

[0070] In step ST6, a non-contact film thickness sensor 16 determines whether the film thickness of the first layer L1 formed on the surface of the substrate S has reached a predetermined target film thickness. If the film thickness of the first layer L1 formed on the surface of the substrate S has not reached the predetermined target film thickness, the hybrid film deposition of vacuum deposition and sputter deposition in step ST5 is repeated until the target film thickness is reached. Once the film thickness of the first layer L1 formed on the surface of the substrate S has reached the predetermined target film thickness, the electron gun 6b of the deposition mechanism 6 is turned off, the shutter 6c is closed to block the crucible 6a, and the deposition of the first layer L1 is terminated. The process then proceeds to step ST7.

[0071] In step ST7, the second layer L2 is deposited on the surface of the first layer L1. That is, the shutter 13d that opens and closes the front of the target 13a is kept open, and sputtering deposition is performed.

[0072] In step ST8, a non-contact film thickness sensor 16 determines whether the film thickness of the second layer L2 formed on the surface of the first layer L1 has reached a predetermined target film thickness. If the film thickness of the second layer L2 formed on the surface of the first layer L1 has not reached the predetermined target film thickness, the sputtering deposition process in step ST7 is repeated until the target film thickness is reached. Once the film thickness of the second layer L2 formed on the surface of the first layer L1 has reached the predetermined target film thickness, the deposition of the second layer L2 is terminated. The process then proceeds to step ST9.

[0073] In step ST9, a third layer L3 is deposited on the surface of the second layer L2. That is, the shutter 6c, which had been blocking the crucible 6a, is opened, and an electron beam is irradiated onto the crucible 6a from the electron gun 6b to perform vacuum deposition. Simultaneously or around this time, the shutter 13d, which had been open in front of the target 13a, is kept open, and sputtering deposition is performed. In other words, the third layer L3 is deposited by repeatedly performing deposition by vacuum deposition and deposition by sputtering while rotating the substrate holder 5 at a constant speed.

[0074] In step ST10, a non-contact film thickness sensor 16 determines whether the film thickness of the third layer L3 formed on the surface of the second layer L2 has reached a predetermined target film thickness. If the film thickness of the third layer L3 formed on the surface of the second layer L2 has not reached the predetermined target film thickness, the vacuum deposition process in step ST9 is repeated until the target film thickness is reached. Once the film thickness of the third layer L3 formed on the surface of the second layer L2 has reached the predetermined target film thickness, the electron gun 6b of the deposition mechanism 6 is turned off, the shutter 6c is closed to block the crucible 6a, the target 13a is covered with the shutter 13d of the sputtering mechanism 13, and the valves 14b and 14e are closed to complete the deposition of the third layer L3. The process then proceeds to step ST11.

[0075] In step ST11, if the anti-reflective film AR to be deposited is the three-layer anti-reflective film AR shown in Figure 1, the process proceeds to step ST14 and the film deposition is completed. On the other hand, if the anti-reflective film AR to be deposited is the four-layer anti-reflective film AR shown in Figure 7, the process proceeds to step ST12.

[0076] In step ST12, a fourth layer L4 is deposited on the surface of the third layer L3. That is, the shutter 13d that opens and closes the front of the target 13a is kept open, and sputtering deposition is performed.

[0077] In step ST13, a non-contact film thickness sensor 16 determines whether the film thickness of the fourth layer L4 formed on the surface of the third layer L3 has reached a predetermined target film thickness. If the film thickness of the fourth layer L4 formed on the surface of the third layer L3 has not reached the predetermined target film thickness, the sputtering deposition in step ST12 is repeated until the target film thickness is reached. Once the film thickness of the fourth layer L4 formed on the surface of the third layer L3 has reached the predetermined target film thickness, the target 13a is covered with the shutter 13d, and the valves 14b and 14e are closed to complete the deposition of the fourth layer L4. The process then proceeds to step ST14, and the deposition is completed.

[0078] As described in steps ST1 to ST14 above, in the film deposition method of this embodiment, a first layer L1 is deposited on the surface of the substrate S by a hybrid film deposition method of vacuum deposition and sputtering, and a third layer L3 is deposited on the surface of the second layer L2. During this process, the vacuum level of the high vacuum region A decreases due to gas leaking from the differential pressure container 12 (differential pressure region B), which reduces the density of the film and makes it porous, allowing for the deposition of the first layer L1 and the third layer L3, which have low refractive indices. Meanwhile, the second layer L2 is deposited on the surface of the first layer L1 and the fourth layer L4 is deposited on the surface of the third layer L3 by sputtering. When sputtered particles from sputter deposition collide with the first layer L1 or the third layer L3, which are becoming porous due to the vacuum deposition method, physical energy is applied, causing the porous film to be compressed or condensed. As a result, the porous film, which would normally have low strength, becomes high strength.

[0079] The method for forming a three-layer structure shown in Figure 14 involves forming the first layer L1 by repeatedly combining vacuum deposition and sputtering, then forming the second layer L2 by sputtering, and then forming the third layer L3 by repeatedly combining vacuum deposition and sputtering. The method for forming a four-layer structure shown in Figure 14 involves forming the first layer L1 by repeatedly combining vacuum deposition and sputtering, then forming the second layer L2 by sputtering, then forming the third layer L3 by repeatedly combining vacuum deposition and sputtering, and then forming the fourth layer L4 by repeatedly combining vacuum deposition and sputtering. However, the method for forming a film according to the present invention is not limited to the method shown in Figure 14, and may include the following procedure. In the following, a method of forming a film by repeatedly performing film deposition by vacuum deposition and film deposition by sputtering will be abbreviated as the deposition-sputtering hybrid method.

[0080] 《Method for Deposition of a Three-Layer Structure》 First, as an alternative method for the three-layer structure shown in Figure 1, the first layer L1 and the third layer L3 are deposited by a hybrid deposition / sputtering method, as in the embodiment shown in Figure 14. However, the following method can be used for the deposition procedure of the second layer L2. In the following, the ion-assisted vacuum deposition method refers to a deposition method in which ion irradiation by an ion source 11 is performed simultaneously with vacuum deposition by the deposition mechanism 6, while the vacuum deposition method refers to a deposition method in which only vacuum deposition (without ion irradiation) is performed by the deposition mechanism 6.

[0081] The second layer L2 can be deposited by at least one of the following deposition methods: sputtering, ion-assisted vacuum deposition, and vacuum deposition. While the order of these three deposition methods is not limited, typical combinations are listed below. (Step 1) Sputtering method ⇒ Ion-assisted vacuum deposition method (Step 2) Sputtering method ⇒ Vacuum deposition method (Step 3) Sputtering method ⇒ Ion-assisted vacuum deposition method ⇒ Vacuum deposition method (Step 4) Sputtering method ⇒ Vacuum deposition method ⇒ Ion-assisted vacuum deposition method (Step 5) Vacuum deposition method (Step 6) Vacuum deposition method ⇒ Sputtering method (Step 7) Vacuum deposition method ⇒ Ion-assisted vacuum deposition method (Step 8) Vacuum deposition method ⇒ Sputtering method ⇒ Ion-assisted vacuum deposition method (Step 9) Vacuum deposition method ⇒ Ion-assisted vacuum deposition method ⇒ Sputtering method (Step 10) Ion-assisted vacuum deposition method (Step 11) Ion-assisted vacuum deposition method ⇒ Sputtering method (Step 12) Ion-assisted vacuum deposition method ⇒ Vacuum deposition method (Step 13) Ion-assisted vacuum deposition method ⇒ Sputtering method ⇒ Vacuum deposition method (Step 14) Ion-assisted vacuum deposition method ⇒ Vacuum deposition method ⇒ Sputtering method

[0082] 《Method for Deposition of a Four-Layer Structure》 Next, as an alternative method for the four-layer structure shown in Figure 7, the first layer L1 and the third layer L3 are deposited by a hybrid evaporation / sputtering method, as in the embodiment shown in Figure 14. The procedure for depositing the second layer L2 is the same as (procedures 1) to (procedure 14) above. In addition, the procedure for depositing the fourth layer L4 can be described below. Note that procedures 1 to 14 for the second layer L2 and the procedure for the fourth layer L4 shown below can be combined in any way.

[0083] (Step 15) Sputtering method ⇒ Ion-assisted vacuum deposition method (Step 16) Sputtering method ⇒ Vacuum deposition method (Step 17) Sputtering method ⇒ Ion-assisted vacuum deposition method ⇒ Vacuum deposition method (Step 18) Sputtering method ⇒ Vacuum deposition method ⇒ Ion-assisted vacuum deposition method (Step 19) Vacuum deposition method (Step 20) Vacuum deposition method ⇒ Sputtering method (Step 21) Vacuum deposition method ⇒ Ion-assisted vacuum deposition method (Step 22) Vacuum deposition method ⇒ Sputtering method ⇒ Ion-assisted vacuum deposition method (Step 23) Vacuum deposition method ⇒ Ion-assisted vacuum deposition method ⇒ Sputtering method (Step 24) Ion-assisted vacuum deposition method (Step 25) Ion-assisted vacuum deposition method ⇒ Sputtering method (Step 26) Ion-assisted vacuum deposition method ⇒ Vacuum deposition method (Step 27) Ion-assisted vacuum deposition method ⇒ Sputtering method ⇒ Vacuum deposition method (Step 28) Ion-assisted vacuum deposition method ⇒ Vacuum deposition method ⇒ Sputtering method

[0084] 《Method for Forming Anti-Reflective Films (Part 2)》 Next, another example of the manufacturing method for the anti-reflective film AR according to the present invention described above will be explained. Figure 15 is a schematic longitudinal section showing a film deposition apparatus 1 for manufacturing the anti-reflective film AR according to the present invention, and Figure 9 is a view along the line IX-IX in Figure 8.

[0085] The film deposition apparatus 1 of this embodiment comprises a housing 2 that constitutes a film deposition chamber 2a which is a substantially sealed space; a first exhaust device 3 for reducing the pressure of the entire inside of the film deposition chamber 2a; a second exhaust device 4 for locally reducing the pressure of a second pressure region R2 inside the film deposition chamber 2a; a substrate holder 5 for holding a substrate S which is the material to be deposited; a deposition mechanism 6; an air supply device 8 for introducing a predetermined gas into the first pressure region R1; a blocking member 7 for suppressing the flow of the gas supplied from the air supply device 8 toward the second pressure region R2; a control device 10 that controls the atmospheric pressure inside the film deposition chamber 2a while evaporating the deposition material M and depositing the evaporated deposition material M onto the substrate S; and an ion source 11 for ion assistance.

[0086] The first pressure region R1 is any region within the deposition chamber 2a that is set to a higher pressure (lower vacuum) relative to the second pressure region R2, and its range is not clearly defined and is not limited in any way. Similarly, the second pressure region R2 is any region within the deposition chamber 2a that is set to a lower pressure (higher vacuum) relative to the first pressure region R1, and its range is not clearly defined and is not limited in any way. Furthermore, the deposition chamber 2a may or may not include regions other than the first pressure region R1 and the second pressure region R2.

[0087] In the three-layer anti-reflective film AR of this embodiment shown in Figure 1, in the step of forming the first layer L1 and the third layer L3 with a low refractive index of 1.21 or less, the region containing the substrate S inside the film deposition chamber 2a is designated as the first pressure region R1, and the region containing the vapor deposition material M is designated as the second pressure region R2. In contrast, in the step of forming the second layer L2 with a high refractive index of 1.35 or more, both the region containing the substrate S and the region containing the vapor deposition material M inside the film deposition chamber 2a are designated as the second pressure region R2. Furthermore, in the four-layer anti-reflective film AR of this embodiment shown in Figure 7, in the step of forming the first layer L1 and the third layer L3 with a low refractive index of 1.19 or less, the region containing the substrate S inside the film deposition chamber 2a is designated as the first pressure region R1, and the region containing the vapor deposition material M is designated as the second pressure region R2. In contrast, in the process of forming a second layer L2 and a fourth layer L4 with a high refractive index of 1.36 or higher, both the region containing the substrate S and the region containing the deposition material M within the deposition chamber 2a are designated as the second pressure region R2.

[0088] The film deposition apparatus 1 of this embodiment has a housing 2 that is box-shaped with an upper surface (ceiling), a lower surface (bottom), and multiple sides, or cylindrical with an upper surface (ceiling), a lower surface (bottom), and curved sides, and the inside of the housing 2 constitutes a film deposition chamber 2a as a substantially sealed space. In the orientation of the film deposition apparatus 1 shown in Figure 15, the upper surface of the housing 2 is conveniently referred to as the upper surface, the lower surface as the bottom, and the side surface as the side. However, this is merely a convenient definition to explain the relative positional relationship between the housing 2 and the first exhaust device 3, substrate holder 5, and deposition mechanism 6 provided in the housing 2, and does not absolutely define the orientation of the film deposition apparatus 1 when it is actually installed.

[0089] For example, in the embodiment of the film deposition apparatus 1 shown in Figure 15, the substrate holder 5 and the deposition mechanism 6 are arranged in the vertical direction, but the apparatus is not limited to this arrangement, and the substrate holder 5 and the deposition mechanism 6 may be arranged in the left-right direction, horizontal direction, or diagonal direction. Also, in the embodiment of the film deposition apparatus 1 shown in Figure 15, the substrate holder 5 and the deposition mechanism 6 are arranged in the vertical direction, and due to this layout, the first exhaust device 3 is placed on the side of the housing 2 and the second exhaust device 4 is placed on the bottom surface of the housing 2, but the apparatus is not limited to this arrangement, and the first exhaust device 3 and the second exhaust device 4 can be placed at appropriate locations on the housing 2.

[0090] As shown in Figure 15, the first exhaust device 3 is provided near the center of the side surface of the housing 2 via a gate valve 3a. The gate valve 3a is an airtight valve that opens and closes the first exhaust device 3 and the film deposition chamber 2a. When the pressure in the film deposition chamber 2a is reduced, the gate valve 3a is opened. On the other hand, when a substrate S is introduced into the film deposition chamber 2a through an opening (not shown), or when the substrate S has finished deposition is removed from the film deposition chamber 2a, the gate valve 3a is closed. The first exhaust device 3 can be a turbomolecular pump (TMP) or a constant pressure pump (CP), and it is desirable that it has a rated capacity that can reduce the pressure inside the film deposition chamber 2a to 0.01 Pa or less.

[0091] As shown in Figure 15, the second exhaust system 4 is located on the underside of the housing 2, directly below the deposition mechanism 6, via a gate valve 4a. The gate valve 4a is an airtight valve that opens and closes the second exhaust system 4 and the deposition chamber 2a. When the pressure inside the deposition chamber 2a is reduced, the gate valve 4a is opened. On the other hand, when a substrate S is introduced into the deposition chamber 2a through an opening (not shown), or when a substrate S that has finished deposition is removed from the deposition chamber 2a, the gate valve 4a is closed. The second exhaust system 4 can be a turbomolecular pump (TMP) or a constant pressure pump (CP), and it is desirable that it has a rated capacity that can reduce the pressure in the second pressure region R2, which includes the deposition mechanism 6 inside the deposition chamber 2a, to 0.01 Pa or less.

[0092] Inside the deposition chamber 2a, a plate-shaped substrate holder 5 is suspended by a rotating shaft 5b, which is rotatably supported on the upper surface of the housing 2. The substrate holder 5 is rotatable around the rotating shaft 5b, which is rotated by a drive unit 5c. The substrate holding surface 5a of the substrate holder 5 holds the substrate S to be deposited with the deposition material M. The number of substrates S held by the substrate holder 5 is not limited and may be one or multiple. Furthermore, the holding part that holds the substrate S may be configured to rotate relative to the substrate holder 5, and the substrate S may be rotated and revolved by a planetary mechanism. In addition, the drive unit 5c may be omitted, and the substrate holder 5 may be non-rotating. In the embodiment shown in Figure 8, the substrate holder 5 is capable of holding multiple substrates S on its substrate holding surface 5a, and the substrate holder 5 is positioned so that multiple substrates S are located directly above the deposition mechanism 6.

[0093] A deposition mechanism 6 is provided near the lower surface inside the film deposition chamber 2a. The deposition mechanism 6 in this embodiment consists of an electron beam deposition source and includes a crucible 6a filled with deposition material M and an electron gun 6b that irradiates the deposition material M in the crucible 6a with an electron beam. A shutter 6c that opens and closes the upper opening of the crucible 6a is movably provided above the crucible 6a. When performing film deposition on a substrate S held in the substrate holder 5, the electron gun 6b is activated to heat and evaporate the deposition material M in the crucible 6a, and the shutter 6c is opened to deposit the evaporated deposition material M onto the substrate S. Reference numeral 6d in Figure 15 indicates a cooling tube coil of a Meissna trap, which efficiently removes moisture released from the substrate S when the inside of the film deposition chamber 2a is evacuated. The deposition material M used in the film deposition apparatus 1 of this embodiment is a predetermined material that can be used as the anti-reflective film AR described above, and is silicon dioxide or aluminum oxide.

[0094] Furthermore, instead of electron beam heating using an electron gun, resistance heating may be used as the evaporation source for the deposition mechanism 6. Resistance heating is a method of heating by applying a voltage across the ends of a heating element and using Joule heating caused by the current flowing through it. Heating elements that can be used include high-melting-point metals such as tungsten, tantalum, and molybdenum, as well as carbon and boron nitride / titanium boride mixed sintered bodies. The heating element may be processed into a suitable shape depending on the evaporating material, or a heat-resistant crucible may be used in combination.

[0095] An ion source 11 is installed in the second pressure region R2 to the side of the deposition mechanism 6, near the lower surface inside the deposition chamber 2a. The ion source 11 is an ion assist ion source that assists the deposition process of the substrate S by the deposition mechanism 6 with ions. The irradiation range of the ion beam from the ion source 11 is a predetermined range of all or part of the substrate holding surface 5a of the substrate holder 5. In this embodiment, a part of the substrate S held on the substrate holding surface 5a of the substrate holder 5 is temporarily hidden by the shielding member 7 as the substrate holder 5 rotates, so the ion beam from the ion source 11 is irradiated in the area where the ion beam is not shielded by the shielding member 7.

[0096] In this embodiment, the ion source 11 is, for example, an ion source that uses a grid-like electrode to extract ions from the plasma, a so-called Kaufman-type ion source. The operating pressure of the Kaufman-type ion source is 0.02 Pa or less. Although not shown in the figures, the Kaufman-type ion source 11 comprises a housing, an anode and filament disposed inside the housing, a magnet for generating a magnetic field disposed outside the housing, a screen electrode disposed at an opening in the housing and kept at the same potential as the housing, and a screen-shaped accelerating electrode disposed outside the screen electrode. When a reactive gas such as oxygen or an inert gas such as argon is supplied into the housing and a positive potential is applied to the anode to heat the filament, a discharge occurs, and plasma is generated inside the housing by collisions between electrons generated by the discharge and the gas. The generated plasma is densely packed by the magnetic field of the magnet disposed outside the housing. In this state, when a negative potential is applied to the accelerating electrode, ions are extracted from the plasma, pass through the screen electrode, are accelerated, and irradiated onto the substrate S.

[0097] By irradiating the deposited film on the substrate S with an ion beam using the deposition mechanism 6, a dense, high-strength film with a smooth surface can be obtained. A shutter to block ion irradiation to the substrate S, or an adjustment plate to adjust the ion directionality, may be installed above the ion source 11. Furthermore, a neutralizer that irradiates negative electrons towards the substrate S to electrically neutralize the substrate S charged by positive ions irradiated from the ion source 11 may be installed in the deposition chamber 2a. Moreover, the ion source 11 is not limited to a Kaufman-type ion source; an ion source of a different type may be used as long as its operating pressure is 0.05 Pa or less, which is the ambient pressure of the second pressure region R2. Furthermore, in the deposition apparatus 1 of this embodiment, the ion source 11 is not an essential component; it may be omitted as needed if there are no problems with the strength of the anti-reflective film AR produced.

[0098] In this embodiment, the film deposition apparatus 1 can perform deposition processing by setting the atmospheric pressure of the first pressure region R1, which includes the substrate S, within the film deposition chamber 2a to a first pressure, while setting the atmospheric pressure of the second pressure region R2, which includes the deposition material M, within the film deposition chamber 2a to a second pressure lower than the first pressure. The second pressure in the second pressure region R2, which includes the deposition material M, is set by the exhaust of the first exhaust device 3 and the second exhaust device 4 described above. In contrast, the first pressure in the first pressure region R1, which includes the substrate S, is set by the exhaust of the first exhaust device 3 and the second exhaust device 4 described above, as well as the supply of gas by the air supply device 8 and the control of the gas flow by the shut-off member 7.

[0099] In other words, the film deposition apparatus 1 of this embodiment includes an air supply device 8 that introduces a predetermined inert gas or an active gas that does not react with the formed film into a first pressure region R1 including a substrate S held in a substrate holder 5. The air supply device 8 of this embodiment includes a nozzle 8a and a gas supply source 8b. The gas supply source 8b is a supply source for supplying atmospheric gas inside the film deposition chamber 2a, and is a supply source for supplying, for example, argon gas or other inert gas or a gas that does not react with the formed film. The nozzle 8a and gas supply source 8b are solely for the purpose of increasing the atmospheric pressure of the first pressure region R1 relative to the atmospheric pressure of the second pressure region R2, and do not supply a reactive gas to generate a reacted film. Therefore, even if it is an active gas, such as oxygen gas when the deposition material is silicon dioxide, an active gas that hardly reacts with the formed silicon dioxide film may be introduced into the first pressure region R1.

[0100] Figure 15 shows one nozzle 8a and a gas supply source 8b, but multiple nozzles 8a may be connected to one or more gas supply sources 8b, and a predetermined gas may be blown from these multiple nozzles 8a toward the first pressure region R1. The inside of the film deposition chamber 2a is maintained in an inert gas atmosphere or an active gas atmosphere that does not react with the formed film.

[0101] Furthermore, the film deposition apparatus 1 of this embodiment includes a shut-off member 7 that suppresses the flow of gas supplied from the air supply device 8 toward the second pressure region R2 in order to set the first pressure of the first pressure region R1 including the substrate S. The shut-off member 7 of this embodiment has a bottom surface 7a and a side surface 7b rising from the bottom surface 7a, and is formed in a closed-bottom cylindrical shape with all or part of the upper surface 7c facing the bottom surface 7a being open. The cross-section of the shut-off member 7 shown in Figure 15 is circular as shown in Figure 16, but the present invention is not limited to this and may be elliptical or polygonal, and may be set according to the shape of the substrate holder 5. Also, as shown in Figure 15, the nozzle 8a may be fixed by passing through the shut-off member 7.

[0102] In this embodiment, the shut-off member 7 is positioned such that a predetermined gap G is formed between its open upper surface 7c and the substrate holding surface 5a of the substrate holder 5. This gap G is sized so that when gas is introduced from the air supply device 8 into the third pressure region R3 surrounded by the shut-off member 7, the gas leaks through the gap G into the first pressure region R1, and the first pressure region R1 is adjusted to a first pressure higher than the second pressure region R2. By providing this gap G, the gas supplied from the air supply device 8 and blown into the third pressure region R3 has its flow directly toward the second pressure region R2 suppressed by the bottom surface 7a and / or side surface 7b of the shut-off member 7, reaches the opening of the upper surface 7c, and flows out to the first pressure region R1 along the substrate holding surface 5a of the substrate holder 5 through the gap G. The dimensions of the suitable gap G can be determined primarily by the volume of the third pressure region R3 surrounded by the blocking member 7, the flow rate of gas from the air supply device 8, and the first pressure of the adjusted first pressure region R1 and the second pressure of the second pressure region R2.

[0103] The control device 10 controls the following: turning the first exhaust device 3 on / off, opening and closing the gate valve 3a, turning the second exhaust device 4 on / off, opening and closing the gate valve 4a, controlling the rotational speed including turning the drive unit 5c of the substrate holder 5 on / off, controlling the operation of the deposition mechanism 6 including opening and closing the shutter 6c, controlling the gas flow rate including turning the nozzle 8a on / off, and controlling the operation of the ion source 11 including turning it on / off. Then, with the inside of the deposition chamber 2a controlled to a predetermined atmospheric pressure, it executes film deposition control using the ion-assisted vacuum deposition method.

[0104] Next, the operation will be explained. Figure 18 is a process diagram showing the method for forming the anti-reflective film AR according to this embodiment. In the film formation apparatus 1 of this embodiment, first, the substrate S is mounted on the substrate holding surface 5a of the substrate holder 5, and the housing 2 is sealed. Then, the gate valve 3a is opened to activate the first exhaust device 3, and the setting value of the first exhaust device 3 is set to, for example, 0.01 Pa to reduce the overall pressure inside the film formation chamber 2a. Around the same time, the gate valve 4a is opened to activate the second exhaust device 4, and the setting value of the second exhaust device 4 is set to, for example, 0.01 Pa to locally reduce the pressure in the second pressure region R2 including the deposition mechanism 6 (ST1 in Figure 18). Around the same time, gas is supplied from the air supply device 8 to the third pressure region R3 (ST2 in Figure 18). At this point, the drive unit 5c may be driven to start rotating the substrate holder 5 at a predetermined rotational speed (ST1 in Figure 18).

[0105] As time passes, the pressure inside the deposition chamber 2a decreases from atmospheric pressure. However, inert gas and the like that supplied to the third pressure region R3 and leaking out through the gap G flow toward the first pressure region R1, which includes the substrate S held in the substrate holder 5, as shown by the dashed arrows in Figures 15 and 16. As a result, the atmospheric pressure in the first pressure region R1, which includes the substrate S held in the substrate holder 5, becomes higher than that of the general area inside the deposition chamber 2a. In contrast, the gas supplied to the third pressure region R3 is prevented or blocked from flowing directly toward the second pressure region R2 by the bottom surface 7a and / or side surface 7b of the barrier member 7, so the pressure-boosting effect of the air supply device 8 does not extend to the second pressure region R2. As a result, the atmospheric pressure in the second pressure region R2, which includes the deposition mechanism 6 and the ion source 11, is maintained at a lower pressure than the first pressure region R1 because localized exhaust is performed by the second exhaust device 4.

[0106] Through the cooperative action of the first exhaust device 3, the second exhaust device 4, the air supply device 8, and the shut-off member 7, preferably when the ambient pressure in the second pressure region R2 is 0.05 Pa or less and the ambient pressure in the first pressure region R1 is 0.05 to 100 Pa (Y in ST3 in Figure 18), the electron gun 6b of the deposition mechanism 6 is activated to heat and evaporate the deposition material M filled in the crucible 6a, and the shutter 6c is opened to deposit the evaporated deposition material M onto the substrate S (ST4 in Figure 18). Although not shown in the figures, pressure sensors for detecting ambient pressure are provided in each of the first pressure region R1 and the second pressure region R2, and the control device 10 reads the output signals of these pressure sensors to control the opening and closing of the shutter 6c of the deposition mechanism 6.

[0107] Furthermore, the ion source 11 starts operating simultaneously with, or before or after, the operation of the deposition mechanism 6, and irradiates the substrate S with ions. Since the ion source 11 is a Kaufman-type ion source with an operating pressure of 0.05 Pa or less, it operates properly at the atmospheric pressure of the second pressure region R2. The kinetic energy of the ions irradiated from the ion source 11 accelerates the deposition material M that has been evaporated and is floating by the deposition mechanism 6, pressing it against the substrate S, or densifying the surface of the thin film deposited on the substrate S. As a result, the thin film formed on the surface of the substrate S has high adhesion, density, and mechanical strength.

[0108] Figure 17 is a graph showing the ambient pressures of the first pressure region R1 and the second pressure region R2, as well as the set pressures of the first exhaust device 3 and the second exhaust device 4, with the vertical axis representing the logarithm of pressure. As shown in the figure, the reason why the second pressure region R2, which includes the deposition mechanism 6, is set to a pressure such that the mean free path of the second pressure region R2 is greater than the distance between the substrate S and the deposition material M, specifically to 0.05 Pa or less, is that if the ambient pressure is higher than this, the deposition material M will not evaporate. On the other hand, the reason why the first pressure region R1, which includes the substrate S, is set to a pressure such that the mean free path of the first pressure region R1 is greater than the distance between the substrate S and the deposition material M, specifically to 0.05 Pa or more, is that if the ambient pressure is lower than this, a thin film with the desired low refractive index cannot be obtained. Furthermore, the reason why the first pressure region R1, which includes the substrate S, is set to 100 Pa or less is that if the ambient pressure is higher than this, the deposition material M will not reach the substrate S and film formation will not be possible. In this embodiment, the second pressure region R2 including the deposition mechanism 6 should be 0.05 Pa or less, and the first pressure region R1 including the substrate S should be between 0.05 and 100 Pa. Therefore, the specific numerical values ​​for the set pressures of the first exhaust device 3 and the second exhaust device 4, and the amount of gas supplied from the air supply device 8 are not particularly limited.

[0109] As described above, the first layer L1 shown in Figures 1 and 7 is formed (ST4 in Figure 18) with the ambient pressure of the second pressure region R2 containing the deposition material M set to 0.05 Pa or less, and the ambient pressure of the first pressure region R1 containing the substrate S set to 0.05 to 100 Pa. This makes it possible to form the first layer L1 with a low refractive index.

[0110] When the first layer L1 reaches the target film thickness (Y in ST5 in Figure 18), a command signal from the control device 10 is transmitted to the air supply device 8, and the supply of gas from the nozzle 8a is stopped (ST7 in Figure 18). As a result, the ambient pressure of the first pressure region R1, which had been set to a high pressure of 0.05 to 100 Pa, is reduced to 0.05 Pa, the same pressure as the ambient pressure of the second pressure region R2, which includes the evaporation material M. The physical area including the substrate S, which was previously the first pressure region R1, then changes to the second pressure region R2. It is desirable to close the shutter 6c of the evaporation mechanism 6 (ST6 in Figure 18) from the time the supply of gas from the nozzle 8a is stopped until the physical area including the substrate S reaches the same pressure as the second pressure region R2, which includes the evaporation material M, in order to prevent the evaporated material from adhering to the substrate S.

[0111] When the atmospheric pressure in the physical area including the substrate S reaches 0.05 Pa, which is the atmospheric pressure of the second pressure region R2 (Y in ST8 in Figure 18), the shutter 6c of the deposition mechanism 6 is opened, and the second layer L2 shown in Figures 1 and 7 is formed on the substrate S (ST9 in Figure 18). Since the entire inside of the deposition chamber 2a is under a low pressure of 0.05 Pa, a dense thin film with a high refractive index can be formed. When this second layer L2 reaches the target film thickness (Y in ST10 in Figure 18), the shutter 6c of the deposition mechanism 6 is closed (ST11 in Figure 18).

[0112] Next, the air supply device 8 starts supplying gas to the third pressure region R3 again (ST12 in Figure 18). As a result, the atmospheric pressure in the first pressure region R1, which includes the substrate S held in the substrate holder 5, becomes higher than the general area inside the film deposition chamber 2a. In contrast, the gas supplied to the third pressure region R3 is prevented or blocked from flowing directly toward the second pressure region R2 by the bottom surface 7a and / or side surface 7b of the barrier member 7, so the pressure-boosting effect of the air supply device 8 does not extend to the second pressure region R2. Therefore, the atmospheric pressure in the second pressure region R2, which includes the deposition mechanism 6 and the ion source 11, is maintained at a lower pressure than the first pressure region R1 because localized exhaust is performed by the second exhaust device 4.

[0113] Through the cooperative action of the first exhaust device 3, the second exhaust device 4, the air supply device 8, and the shut-off member 7, preferably when the ambient pressure in the second pressure region R2 is 0.05 Pa or less and the ambient pressure in the first pressure region R1 is 0.05 to 100 Pa (Y in ST13 in Figure 18), the shutter 6c of the deposition mechanism 6 is opened, and the evaporated deposition material M is deposited onto the substrate S (ST14 in Figure 18).

[0114] As described above, the third layer L3 shown in Figures 1 and 7 is formed (ST14 in Figure 18) with the ambient pressure of the second pressure region R2 containing the deposition material M set to 0.05 Pa or less, and the ambient pressure of the first pressure region R1 containing the substrate S set to 0.05 to 100 Pa. This makes it possible to form a third layer L3 with a low refractive index.

[0115] If the anti-reflective film AR to be manufactured consists of the first layer L1, second layer L2, and third layer L3 shown in Figure 1, the film formation process is completed at this point. On the other hand, if the anti-reflective film AR to be manufactured consists of the first layer L1, second layer L2, third layer L3, and fourth layer L4 as shown in Figure 7, although not shown in the figure, steps ST6 to ST10 are carried out following step ST15 in Figure 18. This makes it possible to form a dense fourth layer L4 with a high refractive index.

[0116] As described above, the anti-reflective coating AR of this embodiment provides an anti-reflective coating with low reflectivity even when the incident angle varies from 0° to 50°, and an optical element using the same.

[0117] AR...Anti-reflective coating L1...First layer L2...Second layer L3...Third layer L4...Fourth layer S...Substrate 1...Film deposition apparatus 2...Housing 2a...Film deposition chamber 3...First exhaust device 4...Second exhaust device 5...Substrate holder 6...Evaporation mechanism 7...Blocking member 8...Air supply device 8a...Nozzle 10...Control device 11...Ion source 12...Differential pressure vessel 13...Sputtering mechanism 14...Gas introduction system 15...Pressure sensor 16...Film thickness sensor R1...First pressure region R2...Second pressure region R3...Third pressure region M...Evaporation material

Claims

1. An anti-reflective film comprising at least three multilayer films, wherein one of the at least three layers is in contact with a glass or plastic substrate, all of the at least three layers are formed from silicon oxide or aluminum oxide, and the difference in refractive index between two of the at least three layers is 0.17 or more.

2. The anti-reflective film according to claim 1, wherein the first layer, second layer, and third layer films are laminated in order from the substrate side, and the difference in refractive index between the first layer and the second layer is 0.17 or more.

3. The anti-reflective film according to claim 1, wherein the first layer, second layer, third layer, and fourth layer films are laminated in order from the substrate side, and the difference in refractive index between the first layer and the second layer is 0.17 or more.

4. A multilayer film consisting of only three layers, in which a first layer, a second layer, and a third layer are laminated in order from the glass or plastic substrate side, wherein the first layer, the second layer, and the third layer are formed from silicon oxide, and the refractive index of the first layer and the third layer is 1.21 or less, and the refractive index of the second layer is 1.35 or more.

5. A multilayer film consisting of only three layers, in which a first layer, a second layer, and a third layer are laminated in order from the glass or plastic substrate side, wherein the first layer, the second layer, and the third layer are formed from aluminum oxide, and the refractive index of the first layer and the third layer is 1.21 or less, and the refractive index of the second layer is 1.35 or more.

6. A multilayer film consisting of only four layers, in which a first layer, a second layer, a third layer, and a fourth layer are laminated in order from the glass or plastic substrate side, wherein the first layer, the second layer, the third layer, and the fourth layer are formed from silicon oxide, and the refractive index of the first layer and the third layer is 1.19 or less, and the refractive index of the second layer and the fourth layer is 1.36 or more.

7. A multilayer film consisting of only four layers, in which a first layer, a second layer, a third layer, and a fourth layer are laminated in order from the glass or plastic substrate side, wherein the first layer, the second layer, the third layer, and the fourth layer are formed from aluminum oxide, and the refractive index of the first layer and the third layer is 1.19 or less, and the refractive index of the second layer and the fourth layer is 1.36 or more.

8. The anti-reflective coating according to any one of claims 1 to 7, wherein the reflectance when light in the near-infrared wavelength range (780 to 2500 nm) is incident at an incident angle of 0° to 50° is 5% or less.

9. The anti-reflective coating according to any one of claims 1 to 8, wherein the reflectance when light in the visible light wavelength range (400 to 750 nm) is incident at an incident angle of 0° is 0.5% or less.

10. An optical element comprising a glass or plastic substrate and an anti-reflective film according to any one of claims 1 to 9 formed on the substrate.

11. A method for forming an anti-reflective film according to claim 4 or 5, wherein the first layer is formed by repeatedly forming the film by vacuum deposition and by sputtering, the second layer is then formed by at least one of the following methods: sputtering, ion-assisted vacuum deposition and vacuum deposition, and the third layer is then formed by repeatedly forming the film by vacuum deposition and by sputtering.

12. A method for forming an anti-reflective film according to claim 6 or 7, wherein the first layer is formed by repeatedly performing film formation by vacuum deposition and film formation by sputtering; the second layer is then formed by at least one film formation method among sputtering, ion-assisted vacuum deposition, and vacuum deposition; the third layer is then formed by repeatedly performing film formation by vacuum deposition and film formation by sputtering; and the fourth layer is then formed by at least one film formation method among sputtering, ion-assisted vacuum deposition, and vacuum deposition.

13. The method for forming the second layer, comprising forming the film by sputtering and then forming the film by ion-assisted vacuum deposition, according to claim 11 or 12.

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