Composite substrate and method for producing composite substrate

Abstract

Provided is a composite substrate excellent in reflection characteristics of a wavelength conversion layer interface. A composite substrate according to an embodiment of the present invention includes: a wavelength conversion layer that converts incident light into light having a different wavelength; and a multilayer film that is disposed adjacent to the wavelength conversion layer. The multilayer film is a laminate having a plurality of refractive index layers. The thickness-direction central section of one of the refractive index layers included in the multilayer film has formed therein an amorphous region in which inert gas atoms are present.

Description

Composite substrate and method for manufacturing the same

[0001] The present invention relates to a composite substrate and a method for manufacturing the composite substrate.

[0002] Solid-state lasers capable of outputting short pulsed light are widely used. Lasers with extremely high optical output power at shorter pulse widths are expected to be applied in various fields such as sensing, precision machining, and medicine. As such a laser, for example, as disclosed in Patent Document 1, a laser configuration has been proposed that combines a semiconductor laser, a solid-state laser gain medium layer that can function as a wavelength conversion layer, and a saturable absorber.

[0003] International Publication No. 2020 / 166420

[0004] In the above laser configuration, the light reflection characteristics at the wavelength conversion layer interface can significantly affect the performance of the laser.

[0005] The present invention has been made in view of the above, and a main object of the present invention is to provide a composite substrate having excellent reflection characteristics at the interface of the wavelength conversion layer.

[0006] 1. A composite substrate according to an embodiment of the present invention includes a wavelength conversion layer that converts incident light into light of a different wavelength, and a multilayer film disposed adjacent to the wavelength conversion layer, the multilayer film being a stack of multiple refractive index layers, and one refractive index layer included in the multilayer film having an amorphous region containing inert gas atoms formed in a central portion in the thickness direction. 2. In the composite substrate described in 1 above, the amount of inert gas atoms present in the region may be 0.5 atomic % or more and 10 atomic % or less. 3. In the composite substrate described in 1 or 2 above, the wavelength conversion layer may be selected from doped yttrium aluminum garnet crystal, doped yttrium vanadate crystal, and doped yttrium lithium fluoride crystal. 4. In the composite substrate described in any one of 1 to 3 above, the refractive index layer having the amorphous region containing inert gas atoms formed therein may contain an oxide containing at least one selected from tantalum, titanium, aluminum, yttrium, zirconium, hafnium, lanthanum, cerium, tungsten, zinc, niobium, and magnesium. 5. In the composite substrate described in any one of 1 to 4 above, the refractive indexes of two adjacent layers included in the multilayer film may be different. 6. In the composite substrate described in any one of 1 to 5 above, the refractive indexes of the multiple refractive index layers included in the multilayer film may each be 1.3 to 2.4, and the multilayer film may include one or more refractive index layers having a refractive index of 2.1 or more. 7. In the multilayer film of the composite substrate described in any one of 1 to 6 above, the difference between the refractive index of the layer with the highest refractive index and the refractive index of the layer with the lowest refractive index may be 0.5 or more. 8. In the composite substrate described in any one of 1 to 7 above, the thickness of each layer included in the multilayer film may be 50 nm or more and 300 nm or less. 9. The composite substrate described in any one of 1 to 8 above may include the wavelength conversion layer, the multilayer film, and a surface-emitting laser substrate, in this order. 10. The composite substrate described in any one of 1 to 9 above may include the wavelength conversion layer, the multilayer film, and a saturable absorbing layer, in this order.11. A composite substrate according to another embodiment of the present invention comprises a surface-emitting laser substrate, a wavelength conversion layer that converts incident light into light of a different wavelength, and a saturable absorbing layer, in that order, and a multilayer film disposed adjacent to the wavelength conversion layer at least either between the surface-emitting laser substrate and the wavelength conversion layer or between the saturable absorbing layer and the wavelength conversion layer, the multilayer film being a stack of multiple refractive index layers, and one refractive index layer included in the multilayer film has an amorphous region in which inert gas atoms are present in a central portion in the thickness direction. 12. A laser structure according to an embodiment of the present invention includes the composite substrate according to any one of 1 to 11 above.

[0007] 13. A method for manufacturing a composite substrate according to an embodiment of the present invention is the method for manufacturing a composite substrate described in any one of 1 to 8 above, comprising: preparing a first portion constituting the stack of the plurality of refractive index layers; stacking a second portion constituting the stack of the plurality of refractive index layers on the wavelength conversion layer; performing an activation treatment on each of a surface of the first portion and a surface of the second portion; and bonding the first portion and the second portion after the activation treatment, wherein the material constituting the outermost layer of the first portion and the material constituting the outermost layer of the second portion are substantially the same. 14. In the method for manufacturing a composite substrate described in 13 above, the activation treatment on each of the surfaces of the first portion and the second portion may be performed for 10 to 30 seconds.

[0008] According to an embodiment of the present invention, a composite substrate having excellent reflection characteristics at the interface of the wavelength conversion layer can be provided.

[0009] 3B is a schematic cross-sectional view showing an outline of a configuration of a composite substrate according to one embodiment of the present invention; FIG. 3C is a partially enlarged cross-sectional view of a first refractive index layer; FIG. 3D is a diagram showing an example of a manufacturing process for a composite substrate according to one embodiment; FIG. 3E is a diagram continuing from FIG. 3A; FIG. 3F is a diagram continuing from FIG. 3C; FIG. 3G is a graph showing a simulation result of the reflection characteristics of a multilayer film of Example 1; FIG. 3H is a graph showing a simulation result of the reflection characteristics of a multilayer film of Comparative Example 1; FIG. 3I is a graph showing a simulation result of the reflection characteristics of a multilayer film of Example 2; FIG. 3J is a graph showing a simulation result of the reflection characteristics of a multilayer film of Example 3; FIG. 3L is a graph showing a simulation result of the reflection characteristics of a multilayer film of Example 4.

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments. In order to clarify the description, the drawings may schematically show the width, thickness, shape, etc. of each part compared to the embodiments, but these are merely examples and do not limit the interpretation of the present invention. Furthermore, in the drawings, the same or equivalent elements are given the same reference numerals, and redundant explanations may be omitted.

[0011] [Composite Substrate] Fig. 1 is a schematic cross-sectional view showing the general configuration of a composite substrate according to one embodiment of the present invention. Note that hatching of some components is omitted in Fig. 1 to make the drawing easier to see.

[0012] The composite substrate 100 has a first main surface 1 and a second main surface 2 facing each other, and includes a wavelength conversion layer 10 that converts incident light into light of a different wavelength, a first multilayer film 21 arranged adjacent to the first main surface 1 of the wavelength conversion layer 10, a second multilayer film 22 arranged adjacent to the second main surface 2 of the wavelength conversion layer 10, a substrate 30 arranged on the first multilayer film 21 side of the wavelength conversion layer 10, and a functional layer 40 arranged on the second multilayer film 22 side of the wavelength conversion layer 10.

[0013] The composite substrate 100 can be applied to, for example, a laser device. The substrate 30 is, for example, a substrate constituting a surface-emitting laser (e.g., a vertical-cavity surface-emitting laser (VCSEL) or a vertical-external-cavity surface-emitting laser (VECSEL)). For example, the wavelength conversion layer 10 can convert a first wavelength of laser light incident on the first main surface 1 side into a second wavelength. Although not shown, the substrate 30 can be provided with a resonator structure.

[0014] The substrate that constitutes the surface-emitting laser may be, for example, a gallium arsenide substrate, an indium phosphide substrate, or a gallium nitride substrate. The thickness of the substrate that constitutes the surface-emitting laser is, for example, 100 μm to 1000 μm.

[0015] The wavelength conversion layer 10 is made of any suitable wavelength conversion material capable of converting incident light into light of a different wavelength. A typical material for the wavelength conversion layer 100 is doped yttrium aluminum garnet (hereinafter referred to as YAG) crystal. Specific examples of doped YAG crystal include Yb ３＋ YAG crystal doped with Nd (Yb:YAG), ３＋ Other materials that can be used to form the wavelength conversion layer 10 include, for example, doped yttrium vanadate (hereinafter, referred to as YVO ４ Doped YVO4 crystals are used. ４ Specific examples of crystals include Yb ３＋ Doped YVO ４ Crystal (Yb: YVO ４ ), Nd ３＋ Doped YVO ４ Crystal (Nd:YVO ４ ) Specific examples of doped YLF crystals include Yb ３＋ YLF crystal doped with Nd (Yb:YLF), ３＋ Doped YVO ４Other examples of the material for the wavelength conversion layer 10 include Nd:glass, Yb:FAP, Yb:SFAP, Yb:glass, Yb:KYW, Yb:BCBF, Yb:YCOB, Yb:GdCOB, and Yb:YAB. Among these, examples of the material for the wavelength conversion layer 10 include doped YAG crystal and doped YVO ４ Preferably, a doped YLF crystal is used, which may exhibit, for example, comparable adhesion to adjacent layers. The thickness of the wavelength conversion layer 10 is, for example, 10 μm to 600 μm.

[0016] The first multilayer film 21 is a laminate of a plurality of refractive index layers. In the illustrated example, the first multilayer film 21 is formed by stacking the first refractive index layer 21 from the wavelength conversion layer 10 side. １ , second refractive index layer 21 ２ , third refractive index layer 21 ３ , ..., and the n-th refractive index layer 21 ｎ Specifically, the refractive index layer located closest to the wavelength conversion layer 10 is the first refractive index layer 21. １ The refractive index layer closest to the substrate 30 is the n-th refractive index layer 21 ｎ n is, for example, 10 to 50, and preferably 15 to 40. The thickness of each of the layers included in the first multilayer film 21 is, for example, 50 nm or more and 300 nm or less.

[0017] The first multilayer film 21 includes a plurality of refractive index layers having different refractive indices, including a high refractive index layer having a relatively high refractive index and a low refractive index layer having a relatively low refractive index. For example, two adjacent layers included in the first multilayer film 21 have different refractive indices, one being a high refractive index layer and the other being a low refractive index layer. Also, for example, at least a portion of the first multilayer film 21 may be configured by alternately stacking high refractive index layers and low refractive index layers. As a specific example, the second refractive index layer 21 ２ The refractive index of the first refractive index layer 21 １ and the third refractive index layer 21 ３ In this case, the refractive index of the first refractive index layer 21 may be smaller or larger than that of the first refractive index layer 21. １ and the third refractive index layer 21 ３The refractive indexes of the first and second layers may be substantially the same or different.

[0018] The first multilayer film 21 is configured to transmit light of a first wavelength emitted from the substrate 30 side. Specifically, the first multilayer film 21 is configured to function as a transmission layer or an anti-reflection layer for light of the first wavelength. The first multilayer film 21 is configured to suppress emission of light of a second wavelength from the wavelength conversion layer 10 toward the substrate 30 side, for example, from the viewpoint of improving light utilization efficiency. Specifically, the first multilayer film 21 is configured to function as a reflective layer for light of the second wavelength. Such a function of the first multilayer film 21 can be realized, for example, by adjusting the number of refractive index layers (the above n) constituting the first multilayer film 21, the thickness of each refractive index layer, and the refractive index of each layer.

[0019] Laser light incident from the first main surface 1 (substrate 30) side can be emitted from the second main surface 2 side. For example, light of a second wavelength converted by the wavelength conversion layer 10 can be emitted after passing through the functional layer 40. The functional layer 40 can function as, for example, a saturable absorbing layer. In this case, the functional layer (saturable absorbing layer) 40 is typically made of Cr ４＋ YAG crystal doped with V (Cr:YAG), ３＋ The functional layer (saturable absorbing layer) 40 may be made of a material such as a YAG crystal (V:YAG) doped with V. The thickness of the functional layer (saturable absorbing layer) 40 is, for example, 10 μm to 600 μm.

[0020] The second multilayer film 22 is a laminate of a plurality of refractive index layers. In the illustrated example, the second multilayer film 22 is formed by stacking the first refractive index layer 22 from the wavelength conversion layer 10 side. １ , second refractive index layer 22 ２ , third refractive index layer 22 ３ , . . . and the n-th refractive index layer 22 ｎ Specifically, the layer located closest to the wavelength conversion layer 10 is the first refractive index layer 22 １ The layer closest to the functional layer 40 is the n-th refractive index layer 22 ｎ n is, for example, 10 to 50, and preferably 15 to 40. The thickness of each of the refractive index layers included in the second multilayer film 22 is, for example, 50 nm or more and 300 nm or less.

[0021] The second multilayer film 22 includes a plurality of refractive index layers having different refractive indices, including a high refractive index layer having a relatively high refractive index and a low refractive index layer having a relatively low refractive index. For example, two adjacent layers included in the second multilayer film 22 have different refractive indices, one being a high refractive index layer and the other being a low refractive index layer. Also, for example, at least a portion of the second multilayer film 22 may be configured by alternately stacking high refractive index layers and low refractive index layers. As a specific example, the second layer 22 ２ The refractive index of the first refractive index layer 22 １ and the third refractive index layer 22 ３ In this case, the refractive index of the first refractive index layer 22 may be smaller or larger than that of the first refractive index layer 22. １ and the third refractive index layer 22 ３ The refractive indexes of the first and second layers may be substantially the same or different.

[0022] The second multilayer film 22 is configured to transmit light of the second wavelength emitted from the wavelength conversion layer 10. Specifically, the second multilayer film 22 is configured to function as a transmission layer or an anti-reflection layer for light of the second wavelength. The second multilayer film 22 is configured to suppress emission of light of the first wavelength from the wavelength conversion layer 10 toward the functional layer 40, for example, from the viewpoint of improving light utilization efficiency. Specifically, the second multilayer film 22 is configured to function as a reflective layer for light of the first wavelength. Such a function of the second multilayer film 22 can be realized, for example, by adjusting the number of refractive index layers (the above n) constituting the second multilayer film 22, the thickness of each refractive index layer, and the refractive index of each refractive index layer.

[0023] As described above, each of the first multilayer film 21 and the second multilayer film 22 (hereinafter sometimes simply referred to as a multilayer film) is a laminate of multiple refractive index layers, and may include high-refractive index layers and low-refractive index layers with different refractive indices. The refractive index of each refractive index layer included in the multilayer film (the refractive index of the material constituting each refractive index layer included in the multilayer film) is, for example, 1.3 to 2.4, preferably 1.4 to 2.4, and more preferably 1.45 to 2.35. The refractive index may be a value measured using a spectroscopic ellipsometer or spectrophotometer. The refractive index of the high-refractive index layer is relatively higher than the refractive index of the low-refractive index layer. Specifically, the refractive index of the material constituting the high-refractive index layer is higher than the refractive index of the material constituting the low-refractive index layer. The refractive index of the low-refractive index layer is, for example, 1.3 to 1.8. The refractive index of the high-refractive index layer is, for example, 1.55 to 2.4.

[0024] The plurality of low refractive index layers that may be included in the multilayer film may each have the same configuration (e.g., material, thickness) or may have different configurations. Similarly, the plurality of high refractive index layers that may be included in the multilayer film may each have the same configuration (e.g., material, thickness) or may have different configurations.

[0025] The multilayer film preferably includes one or more refractive index layers having a refractive index of 2.1 or more. By including such a refractive index layer, desired transmission characteristics (reflection characteristics) can be favorably achieved. In the multilayer film, the difference in refractive index between the layer having the highest refractive index and the layer having the lowest refractive index is preferably 0.5 or more, more preferably 0.6 or more, and even more preferably 0.7 or more. From the viewpoint of satisfying such a difference, the multilayer film preferably includes one or more refractive index layers having a refractive index of 1.5 or less.

[0026] Dielectric materials are typically used as materials for forming each refractive index layer included in the multilayer film. Specific examples of materials for forming each refractive index layer included in the multilayer film include silicon oxide, tantalum oxide, titanium oxide, aluminum oxide, yttrium oxide, zirconium oxide, hafnium oxide, lanthanum oxide, cerium oxide, tungsten oxide, zinc oxide, niobium oxide, and magnesium oxide. These may be used alone or in combination of two or more (for example, as a composite oxide). Specifically, the refractive index layer may be composed of an oxide containing at least one selected from silicon, tantalum, titanium, aluminum, yttrium, zirconium, hafnium, lanthanum, cerium, tungsten, zinc, niobium, and magnesium.

[0027] Each refractive index layer included in the multilayer film can be formed by any suitable method, such as sputtering, physical vapor deposition such as ion beam assisted deposition (IAD), chemical vapor deposition, or atomic layer deposition (ALD).

[0028] Inert gas atoms are present in one of the refractive index layers (for example, the first refractive index layer) included in the multilayer film. Typical examples of inert gas atoms include argon and xenon. For example, an amorphous region in which inert gas atoms are present is formed in one of the refractive index layers (for example, the first refractive index layer) included in the multilayer film. FIG. 2 is a partially enlarged cross-sectional view of the first refractive index layer. First refractive index layer 21 １ An amorphous region where inert gas atoms exist can be formed in the central portion 21 a in the thickness direction of the first refractive index layer 21. １ For example, the first refractive index layer 21 １In the first refractive index layer 21, an amorphous layer containing inert gas atoms may be formed in the central portion 21a in the thickness direction. The amount of inert gas atoms present in the region (layer) containing inert gas atoms is, for example, 0.5 atomic % or more and 10 atomic % or less, and preferably 0.7 atomic % or more and 5 atomic % or less. The thickness of the region (layer) containing inert gas atoms is, for example, 0.5 nm or more, and may be 1 nm or more. On the other hand, the thickness of the region (layer) containing inert gas atoms is, for example, 100 nm or less, and preferably 50 nm or less. The first refractive index layer 21 １ The elements contained in the thickness direction end portion 21b may also be contained in the thickness direction central portion 21a where an amorphous region (layer) containing inert gas atoms is formed.

[0029] It is preferable that other layers included in the multilayer film (e.g., layers other than the first refractive index layer) are substantially free of inert gas atoms. The amount of inert gas atoms present in the other layers included in the multilayer film is, for example, less than 0.5 atomic %, and may be 0.4 atomic % or less. Note that, for convenience, in the example shown in FIG. 2, the state of presence of inert gas atoms is described using the first refractive index layer as an example, but inert gas atoms may be selectively present in the other layers included in the multilayer film.

[0030] It is preferable that substantially no inert gas atoms are present in the wavelength conversion layer 10. The amount of inert gas atoms present in the wavelength conversion layer 10 is, for example, less than 0.5 atomic %, and may be 0.4 atomic % or less.

[0031] The abundance of the inert gas atoms can be determined by, for example, composition analysis using energy dispersive X-ray spectroscopy (EDX).

[0032] Specific examples of materials constituting the refractive index layer containing the inert gas atoms include tantalum oxide, titanium oxide, aluminum oxide, yttrium oxide, zirconium oxide, hafnium oxide, lanthanum oxide, cerium oxide, tungsten oxide, zinc oxide, niobium oxide, and magnesium oxide. These may be used alone or in combination (e.g., as a composite oxide). Specifically, the refractive index layer containing the inert gas atoms may be composed of an oxide containing at least one selected from tantalum, titanium, aluminum, yttrium, zirconium, hafnium, lanthanum, cerium, tungsten, zinc, niobium, and magnesium. Such a configuration can provide excellent adhesion (e.g., adhesion at the bonding interface). Among these, the layer may be composed of an oxide containing at least one of tantalum and titanium, thereby achieving even better adhesion.

[0033] The composite substrate 100 may omit the functional layer 40 and the second multilayer film 22, or may omit the substrate 30 and the first multilayer film 21. Although not shown, the composite substrate 100 may further include any layer. The type, function, number, combination, arrangement, etc. of such layers may be appropriately set depending on the purpose. For example, the composite substrate 100 may have another functional layer (e.g., an optical scanner layer) provided on the functional layer 40.

[0034] The composite substrate 100 can be manufactured in any suitable shape. In one embodiment, it can be manufactured in the form of a wafer. The size of the composite substrate 100 can be appropriately set depending on the purpose. For example, the diameter of the wafer is 50 mm to 150 mm. Also, for example, the diameter of the wafer is 3 inches to 6 inches.

[0035] [Manufacturing method] The composite substrate can be obtained, for example, by preparing a first portion constituting a stack of multiple refractive index layers, stacking a second portion constituting a stack of multiple refractive index layers on the wavelength conversion layer, and bonding the first portion and the second portion together.

[0036] 3A to 3D are diagrams showing an example of a manufacturing process for a composite substrate according to one embodiment. ２ to the n-th refractive index layer 21 ｎ The nth layer is the nth refractive index layer 21 ｎ 1, films are formed in this order, forming a stacked structure 20 of n-1 layers on a substrate 30.

[0037] Next, as shown in FIG. 3B, a first refractive index layer 21 is formed on the surface of the laminated structure 20. １ Then, a first portion 61 including the laminated structure 20 and the first outermost layer 51 is formed. Then, a first refractive index layer 21 is formed on a wavelength converting layer (wavelength converting material substrate) 10 prepared separately. １ A second outermost layer 52 (second portion 62) is formed from the material constituting the above.

[0038] The material constituting the first outermost layer 51 and the material constituting the second outermost layer 52 are substantially the same. In one embodiment, the first outermost layer 51 and the second outermost layer 52 are formed by sputtering using the same target under the same conditions. The material constituting the first outermost layer 51 and the material constituting the second outermost layer 52 preferably contain an oxide containing at least one selected from tantalum, titanium, aluminum, yttrium, and lanthanum. Use of such a material enables good bonding, as described below.

[0039] Next, the first portion 61 and the second portion 62 are directly bonded to each other. When directly bonding the first portion 61 and the second portion 62, it is preferable that the first portion 61 and the second portion 62 are each activated by any appropriate activation treatment.

[0040] The activation process is typically performed by irradiating a neutralizing beam. Preferably, a neutralizing beam is generated using an apparatus such as that described in JP 2014-086400 A, and the activation process is performed by irradiating this beam. Specifically, a saddlefield fast atom beam (FAB) source is used as the beam source, an inert gas such as argon or xenon is introduced into the chamber, and a high voltage is applied to the electrode from a DC power supply. This generates a saddlefield electric field between the electrode (positive electrode) and the housing (negative electrode), causing electrons to move and generating a beam of atoms and ions from the inert gas. Of the beams that reach the grid, the ion beam is neutralized by the grid, and a beam of neutral atoms is emitted from the fast atom beam source. The voltage during the activation process by beam irradiation is preferably 0.5 kV to 2.0 kV, and the current during the activation process by beam irradiation is preferably 50 mA to 200 mA.

[0041] 3C shows a state in which activation treatment is being performed on the surface 61 a of the first portion 61 and the surface 62 a of the second portion 62. Typically, activation of the surface 61 a of the first portion 61 and activation of the surface 62 a of the second portion 62 can be performed simultaneously. The activation treatment time for each surface (e.g., the irradiation time of the beam) is preferably 10 to 30 seconds.

[0042] After the activation treatment, the first portion 61 and the second portion 62 are brought into contact with each other and pressurized to directly bond them together. In this way, the bonded body (composite substrate) 102 shown in FIG. 3D is obtained. The contact and pressurization are preferably carried out in a vacuum atmosphere. The temperature at this time is typically room temperature. Specifically, a temperature of 20°C or higher and 40°C or lower is preferred, and a temperature of 25°C or higher and 30°C or lower is more preferred. The pressure applied is preferably 100N to 20,000N.

[0043] The first outermost layer 51 and the second outermost layer 52 are bonded together, and the first refractive index layer 21 １ The resulting first refractive index layer 21 １ The thickness of the first outermost layer 51 and the second outermost layer 52 may be adjusted to a desired thickness of the first refractive index layer 21. １The thickness of the first outermost layer 51 and the second outermost layer 52 can be appropriately set depending on the thickness of the first outermost layer 51 and the second outermost layer 52. The thickness of each of the first outermost layer 51 and the second outermost layer 52 is preferably 20 nm or more and 200 nm or less, and more preferably 30 nm or more and 175 nm or less. The ratio of the thickness of the second outermost layer 52 to the thickness of the first outermost layer 51 is, for example, 0.3 to 2.4. Inert gas atoms used in the activation treatment may be present near the bonding interface. Furthermore, an amorphous structure (e.g., an amorphous region containing inert gas atoms) may be generated near the bonding interface due to the activation treatment.

[0044] By positioning the bonding interface within one of the refractive index layers included in the multilayer film, the influence of an activation process on the multilayer film, which may require highly precise control of the refractive index, can be significantly reduced. For example, the wavelength conversion layer is substantially free of inert gas atoms used in the activation process, and the incorporation of wavelength conversion materials, substrate and / or functional layer constituent materials into the multilayer film due to the activation process can be suppressed. As a result, the refractive index layers included in the multilayer film can have the desired refractive index, and the multilayer film as a whole can, for example, satisfies the desired reflection characteristics. Note that although the refractive index can also change due to the generation of an amorphous structure by the activation process, the influence of the incorporation of wavelength conversion materials due to the activation process is considered to be greater.

[0045] After direct bonding, the bonded body 102 may be subjected to an annealing treatment. Specifically, the bonded body 102 may be heated. The annealing treatment may diffuse and volatilize inert gas atoms and impurities (e.g., impurities derived from the jigs and base of the activation treatment device). Furthermore, the annealing treatment may be expected to crystallize the amorphous state, and, for example, further improve the reflection characteristics. The temperature (heating temperature) of the annealing treatment may be, for example, 300°C to 450°C.

[0046] When bonding, the surfaces of the first portion 61 and the second portion 62 are preferably flat. Specifically, the arithmetic mean roughness Ra of the surfaces of the first portion 61 and the second portion 62 is preferably 5 nm or less, more preferably 2 nm or less, even more preferably 1 nm or less, and particularly preferably 0.3 nm or less. Examples of methods for flattening the surfaces include mirror polishing by chemical mechanical polishing (CMP), lap polishing, etc.

[0047] During the film formation and bonding, it is preferable to clean the surface of each layer, for example, to remove abrasive residue. Examples of cleaning methods include wet cleaning, dry cleaning, and scrub cleaning. Among these, scrub cleaning is preferred because it allows for simple and efficient cleaning. A specific example of scrub cleaning is a method in which a cleaning agent (e.g., the Sun Wash series manufactured by Lion Corporation) is used, followed by cleaning with a scrub cleaner using a solvent (e.g., a mixed solution of acetone and isopropyl alcohol (IPA)).

[0048] 3 shows the production of a bonded body of the wavelength conversion layer 10 and the first multilayer film 21 by forming a first portion 61 on the substrate 30. Similar to the example shown in FIG. 3 , the first portion 61 can be formed on the functional layer 40 and then bonded to the wavelength conversion layer 10 to obtain a bonded body of the wavelength conversion layer 10 and the second multilayer film 22. When obtaining the composite substrate shown in FIG. 1 , the stacking order of the substrate 30 and the functional layer 40 relative to the wavelength conversion layer 10 is not particularly limited. Specifically, the functional layer 40 may be bonded to the wavelength conversion layer 10 after the substrate 30 has been bonded, or the functional layer 40 may be bonded to the wavelength conversion layer 10 after the substrate 30 has been bonded.

[0049] The present invention will be specifically explained below with reference to examples, but the present invention is not limited to these examples.

[0050] [Example 1] A tantalum oxide (Ta ２ O ５ ) layer, silicon oxide (SiO ２ ) layer and aluminum oxide (Al ２ O ３) layers were formed in the order and with the thicknesses shown in Table 1, forming a laminate including 28 layers of the 29th to 2nd refractive index layers and a tantalum oxide layer with a thickness of 100 nm. A tantalum oxide layer with a thickness of 100 nm was formed on the Yb:YAG substrate, and the two substrates were bonded together by the method shown in FIG. 3 to obtain a composite substrate. The refractive indexes of the layers are summarized in Table 1.

[0051] As shown in Table 1, in the first refractive index layer (tantalum oxide layer having a thickness of 200 nm), the influence (generation of an amorphous structure) of the activation treatment (beam irradiation) is extremely small, and a desired refractive index can be obtained.

[0052] Comparative Example 1: A tantalum oxide (Ta) was deposited on a substrate (GaAs substrate) in the same manner as in Example 1. ２ O ５ ) layer, silicon oxide (SiO ２ ) layer and aluminum oxide (Al ２ O ３ A tantalum oxide layer having a thickness of 200 nm is then formed. The surface of the tantalum oxide layer having a thickness of 200 nm on the GaAs substrate and the surface of a separately prepared Yb:YAG substrate are then subjected to an activation treatment. The refractive indexes of the layers of the composite substrate obtained by bonding the two substrates are summarized in Table 1.

[0053] As shown in Table 1, the activation treatment (beam irradiation) forms a layer (50 nm thick) on the Yb:YAG layer side of the first refractive index layer (tantalum oxide layer) with a refractive index lower than that of tantalum oxide (2.23). The constituent components of YAG can be confirmed in this layer (region).

[0054]

[0055] The simulation results of the reflection characteristics of the multilayer film of Example 1 are shown in FIG. 4, and the simulation results of the reflection characteristics of the multilayer film of Comparative Example 1 are shown in FIG.

[0056] Yb:YAG has an effective excitation wavelength of 935 nm to 945 nm and can convert it to light with a wavelength of 1030 nm. The multilayer films of Example 1 and Comparative Example 1 transmit light with the effective excitation wavelength of the wavelength conversion layer (Yb:YAG layer) and suppress the emission of light with a wavelength of 1030 nm emitted from the wavelength conversion layer (Yb:YAG layer). The multilayer film of Example 1 had a reflectance of 0.1% at a wavelength of 940 nm, while the multilayer film of Comparative Example 1 had a reflectance of 1.5% at a wavelength of 940 nm. This indicates that the multilayer film of Example 1 can more effectively allow light with the effective excitation wavelength of the wavelength conversion layer (Yb:YAG layer) to enter.

[0057] (Composition Analysis of Example 1) The 29th to 2nd refractive index layers shown in Table 1 were sequentially formed on a GaAs substrate with the materials and thicknesses shown in Table 1, and finally, a 100 nm thick tantalum oxide layer was formed to form a laminated structure. Furthermore, a 100 nm thick tantalum oxide layer was formed on a Yb:YAG substrate (YAG crystal). Next, the surface (tantalum oxide layer side) of the Yb:YAG substrate on which the tantalum oxide layer was formed and the surface (tantalum oxide layer side) of the GaAs substrate on which the laminated structure was formed were cleaned, and then both substrates were placed in a vacuum chamber and heated for 10 min. －６ The chamber was evacuated to the Pa range, and the surfaces of both substrates were simultaneously irradiated with Ar gas using FAB (accelerating voltage 1 kV, Ar flow rate 27 sccm) for 20 seconds. The GaAs substrate and the Yb:YAG substrate were then directly bonded. Specifically, the FAB-irradiated surfaces of both substrates were placed on top of each other, and the two substrates were bonded together by applying a pressure of 10,000 N at room temperature for 2 minutes, resulting in a bonded structure as shown in Figures 2 and 3D. The resulting bonded structure was then subjected to an annealing treatment. Specifically, the resulting bonded structure was placed in a high-temperature furnace, and the temperature in the furnace was raised from room temperature to a temperature above 100°C, maintained for a certain period of time, and then returned to room temperature, thereby performing annealing.

[0058] In order to measure the Ar content (abundance) of each layer constituting the bonded structure, the bonded structure was thinned by a focused ion beam (FIB) method, while exposing the surface of each layer, and energy dispersive X-ray analysis (EDX) was performed. Specifically, using an atomic resolution analytical electron microscope (JEOL, JEM-ARM200F Dual-X) and an energy dispersive X-ray analyzer (JEOL, JED-2300), analysis was performed by STEM-EDX observation at an acceleration voltage of 200 kV and a beam spot size of approximately 0.2 nmΦ. The measurement results are shown below. The Ar content indicates the ratio of Ar atoms to all atoms present at the measurement point. Measurement point 1 (YAG crystal corresponding to wavelength conversion layer 10): 0 atomic % Measurement point 2 (first refractive index layer 21): 0 atomic % １ , first outermost layer 51 side): 0.7 atomic % Measurement point 3 (first refractive index layer 21 １ , second outermost layer 52 side): 0.7 atomic % Measurement point 4: (second refractive index layer 21 ２ silicon oxide layer corresponding to ): 0 atomic %

[0059] [Example 2] A tantalum oxide (Ta ２ O ５ ) layer, silicon oxide (SiO ２ ) layer and aluminum oxide (Al ２ O ３ ) layers were formed in the order and with the thicknesses shown in Table 2, a laminate including 32 layers of the 33rd to 2nd refractive index layers and a tantalum oxide layer with a thickness of 80 nm was formed, a tantalum oxide layer with a thickness of 80 nm was formed on the Yb:YAG substrate, and the two substrates were bonded together by the method shown in Figure 3 to obtain a composite substrate whose refractive indexes of the layers are summarized in Table 2.

[0060]

[0061] As shown in Table 2, the first refractive index layer (tantalum oxide layer) is significantly less affected by the activation treatment (beam irradiation), and a desired refractive index can be obtained.

[0062] The simulation results of the reflection characteristics of the multilayer film of Example 2 are shown in FIG.

[0063] The multilayer film of Example 2 can transmit light with a wavelength of 1030 nm emitted from the wavelength conversion layer (Yb:YAG layer) and suppress the emission of light with the effective excitation wavelength of the wavelength conversion layer (Yb:YAG layer).

[0064] [Example 3] A titanium oxide (TiO ２ ) layer, silicon oxide (SiO ２ ) layer and aluminum oxide (Al ２ O ３ ) layers were formed in the order and with the thicknesses shown in Table 3, forming a laminate including 28 layers of the 29th to 2nd refractive index layers and a titanium oxide layer with a thickness of 91 nm. A titanium oxide layer with a thickness of 91 nm was formed on the Yb:YAG substrate, and the two substrates were bonded together by the method shown in Figure 3 to obtain a composite substrate. The refractive indexes of the layers are summarized in Table 3.

[0065] As shown in Table 3, in the first refractive index layer (titanium oxide layer with a thickness of 182 nm), the influence (generation of an amorphous structure) of the activation treatment (beam irradiation) is extremely small, and a desired refractive index is obtained.

[0066]

[0067] The simulation results of the reflection characteristics of the multilayer film of Example 3 are shown in FIG.

[0068] Yb:YAG has an effective excitation wavelength of 935 nm to 945 nm and can convert this to light with a wavelength of 1030 nm. The multilayer film of Example 3 transmits light with the effective excitation wavelength of the wavelength conversion layer (Yb:YAG layer) and suppresses the emission of light with a wavelength of 1030 nm emitted from the wavelength conversion layer (Yb:YAG layer). The multilayer film of Example 3 had a reflectance of 0.1% at a wavelength of 940 nm.

[0069] (Composition Analysis of Example 3) As in Example 1, composition analysis was performed at the following locations by STEM-EDX observation. Measurement location 2 (first refractive index layer 21 １ , first outermost layer 51 side) Measurement point 3 (first refractive index layer 21 １ , second outermost layer 52 side) As a result, at measurement points 2 and 3, the constituent elements of Yb:YAG (Y, Al, Yb) and the constituent element of the second refractive index layer (Si) were not confirmed.

[0070] [Example 4] A substrate (GaAs substrate) was coated with zirconium oxide (ZrO ２ ) layer, silicon oxide (SiO ２ ) layer and aluminum oxide (Al ２ O ３ ) layers were formed in the order and with the thicknesses shown in Table 4, forming a laminate including 28 layers of the 29th to 2nd refractive index layers and a 100 nm thick zirconium oxide layer, forming a 100 nm thick zirconium oxide layer on the Yb:YAG substrate, and bonding the two substrates together by the method shown in Figure 3 to obtain a composite substrate whose refractive indexes of the layers are summarized in Table 4.

[0071] As shown in Table 4, in the first refractive index layer (zirconium oxide layer having a thickness of 200 nm), the influence (generation of an amorphous structure) of the activation treatment (beam irradiation) is extremely small, and a desired refractive index can be obtained.

[0072]

[0073] The simulation results of the reflection characteristics of the multilayer film of Example 4 are shown in FIG.

[0074] Yb:YAG has an effective excitation wavelength of 935 nm to 945 nm and can convert it to light with a wavelength of 1030 nm. The multilayer film of Example 4 transmits light with the effective excitation wavelength of the wavelength conversion layer (Yb:YAG layer) and suppresses the emission of light with a wavelength of 1030 nm emitted from the wavelength conversion layer (Yb:YAG layer). The multilayer film of Example 4 had a reflectance of 0.1% at a wavelength of 940 nm.

[0075] (Composition Analysis of Example 4) As in Example 1, composition analysis was performed at the following locations by STEM-EDX observation: Measurement location 2 (first refractive index layer 21 １ , first outermost layer 51 side) Measurement point 3 (first refractive index layer 21 １ , second outermost layer 52 side) As a result, at measurement points 2 and 3, the constituent elements of Yb:YAG (Y, Al, Yb) and the constituent element of the second refractive index layer (Si) were not confirmed.

[0076] The composite substrate according to the embodiment of the present invention can be suitably used in laser devices for sensing, precision machining, medical applications, and the like.

[0077] REFERENCE SIGNS LIST 10 Wavelength conversion layer 21 First multilayer film 22 Second multilayer film 30 Substrate 40 Functional layer 51 First outermost layer 52 Second outermost layer 61 First portion 62 Second portion 100 Composite substrate 102 Bonded body (composite substrate)

Claims

1. A composite substrate comprising: a wavelength conversion layer that converts incident light into light of a different wavelength; and a multilayer film disposed adjacent to the wavelength conversion layer, the multilayer film being a laminate of a plurality of refractive index layers, one of the refractive index layers included in the multilayer film having an amorphous region containing inert gas atoms formed in a central portion in a thickness direction.

2. The composite substrate according to claim 1, wherein the amount of inert gas atoms present in said region is 0.5 atomic % or more and 10 atomic % or less.

3. The composite substrate of claim 1, wherein the wavelength converting layer is selected from doped yttrium aluminum garnet crystals, doped yttrium vanadate crystals, and doped yttrium lithium fluoride crystals.

4. The composite substrate according to claim 1, wherein the refractive index layer in which the amorphous region in which the inert gas atoms are present is formed includes an oxide containing at least one selected from the group consisting of tantalum, titanium, aluminum, yttrium, zirconium, hafnium, lanthanum, cerium, tungsten, zinc, niobium, and magnesium.

5. The composite substrate according to claim 1, wherein the refractive indexes of two adjacent layers included in said multilayer film are different.

6. The composite substrate according to claim 1, wherein the refractive index of each of the plurality of refractive index layers included in the multilayer film is 1.3 to 2.4, and the multilayer film includes at least one refractive index layer having a refractive index of 2.1 or more.

7. The composite substrate according to claim 1, wherein in said multi-layer film, the difference in refractive index between the layer having the highest refractive index and the layer having the lowest refractive index is 0.5 or more.

8. The composite substrate according to claim 1, wherein the thickness of each layer included in said multilayer film is not less than 50 nm and not more than 300 nm.

9. The composite substrate according to claim 1, comprising, in this order, the wavelength conversion layer, the multilayer film, and a surface emitting laser substrate.

10. The composite substrate according to claim 1, comprising, in this order, the wavelength conversion layer, the multilayer film, and a saturable absorbing layer.

11. A composite substrate comprising a surface-emitting laser substrate, a wavelength conversion layer that converts incident light into light of a different wavelength, and a saturable absorbing layer, in that order, and a multilayer film disposed adjacent to the wavelength conversion layer at least either between the surface-emitting laser substrate and the wavelength conversion layer or between the saturable absorbing layer and the wavelength conversion layer, the multilayer film being a laminate of a plurality of refractive index layers, and one of the refractive index layers included in the multilayer film has an amorphous region in which inert gas atoms are present in the center of the thickness direction.

12. A laser structure comprising the composite substrate of claim 1.

13. A method for manufacturing a composite substrate as described in claim 1, comprising: preparing a first part constituting a stack of the plurality of refractive index layers; stacking a second part constituting the stack of the plurality of refractive index layers on the wavelength conversion layer; performing an activation treatment on each of a surface of the first part and a surface of the second part; and bonding the first part and the second part after the activation treatment, wherein a material constituting the outermost layer of the first part and a material constituting the outermost layer of the second part are substantially the same.

14. The method for producing a composite substrate according to claim 13, wherein the activation treatment time for each of the surfaces of the first portion and the second portion is 10 to 30 seconds.

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