Method for producing composite substrate

Abstract

Disclosed is a method for producing a composite substrate, including: a step for forming an intermediate layer on a support substrate; a step for irradiating a surface of a piezoelectric material substrate and a surface of the intermediate layer formed on the support substrate with FAB, respectively; a step for further irradiating the surface of the piezoelectric material substrate with FAB to form a sputtered film, which contains a material of the piezoelectric material substrate, on the surface of the intermediate layer; a step for bonding the piezoelectric material substrate and the intermediate layer, on which the sputtered film has been formed to obtain a bonded body that has a waveguide substrate; and a step for irradiating the bonded body with laser light in the surface direction of a composite substrate. A composite substrate is formed using the bonded body that has been irradiated with the laser light.

Description

Composite substrate manufacturing method

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

[0002] Conventionally, LN (LiNbO ３ : lithium niobate) and LT (LiTaO ３ Composite substrates are known that are formed by bonding a piezoelectric substrate made of a material such as lithium tantalate (LTC) to a support substrate made of a material such as silicon, and are used in surface acoustic wave devices and the like. One known method for fabricating such composite substrates involves irradiating the bonding surfaces of the piezoelectric substrate and the support substrate with fast atom beams (FAB) to perform an activation process, and then directly bonding these bonding surfaces together. However, this method suffers from the problem of low bonding strength between the substrates, which can lead to separation during processing after bonding.

[0003] To solve the above problem, the technology disclosed in Patent Document 1 is known. Patent Document 1 describes a method for forming a silicon oxide (SiO ２ ) film is formed on the film, and silicon nitride (Si ３ N ４ This method improves the bonding strength between the piezoelectric substrate and the support substrate and prevents peeling after bonding.

[0004] International Publication No. 2017 / 163722

[0005] In the composite substrate having the structure of Patent Document 1, Si ３ N ４ However, a bonding layer made of LN (LiNbO ３ ) and LT (LiTaO ３ When using piezoelectric material substrates such as SiO 2 , SiO 3 , SiO 4 , SiO 2 ...

[0006] In order to obtain a composite substrate without a bonding layer, even if a piezoelectric substrate and a support substrate on which an intermediate layer of silicon oxide is formed are bonded in the manufacturing process of the composite substrate, sufficient bonding strength cannot be obtained, and improvement is required. The same is true when the piezoelectric substrate and the support substrate are directly bonded. Therefore, a method for bonding an intermediate layer or the support substrate to a LiNbO ３ or LiTaO ３ There was an issue with the bonding strength with the piezoelectric material substrate made of the material.

[0007] The present invention has been made in view of the above, and its main object is to realize a method for manufacturing a composite substrate having good light propagation characteristics while improving the bonding strength between an intermediate layer provided on a support substrate or between the support substrate and a piezoelectric material substrate.

[0008] The method for manufacturing a composite substrate according to the first aspect of the present invention is to ２ , MgF ２ , CaF ２ forming an intermediate layer containing at least one of LiNbO ３ or LiTaO ３ A method for manufacturing a composite substrate according to a second aspect of the present invention includes the steps of: irradiating a surface of a piezoelectric material substrate formed using LiNbO as a material and a surface of the intermediate layer formed on the support substrate with a fast atomic beam; further irradiating the surface of the piezoelectric material substrate with the fast atomic beam to form a sputtered film made of the material of the piezoelectric material substrate on the surface of the intermediate layer; bonding the piezoelectric material substrate and the intermediate layer on which the sputtered film has been formed to obtain a bonded body; and irradiating the bonded body with laser light in a plane direction of the composite substrate, and forming the composite substrate using the bonded body irradiated with the laser light. ３ or LiTaO ３ a surface of a piezoelectric material substrate formed using SiO ２ , MgF ２ , or CaF ２and a surface of a support substrate including the piezoelectric material substrate, with a fast atomic beam; further irradiating the surface of the piezoelectric material substrate with the fast atomic beam to form a sputtered film made of the material of the piezoelectric material substrate on the surface of the support substrate; bonding the piezoelectric material substrate and the support substrate on which the sputtered film has been formed to obtain a bonded body; and irradiating the bonded body with laser light in a plane direction of the composite substrate, and the composite substrate is formed using the bonded body irradiated with the laser light.

[0009] According to the present invention, it is possible to realize a method for manufacturing a composite substrate having good optical propagation characteristics while improving the bonding strength between an intermediate layer provided on a support substrate or between a support substrate and a piezoelectric material substrate.

[0010] FIG. 1 is a diagram showing a schematic configuration of a composite substrate according to a first embodiment of the present invention. FIG. 2 is a diagram showing an example of a manufacturing process for a composite substrate according to the first embodiment of the present invention. FIG. 3 is a diagram showing an example of a manufacturing process for a composite substrate according to the first embodiment of the present invention. FIG. 4 is a diagram showing a schematic configuration of a composite substrate according to a second embodiment of the present invention. FIG. 5 is a diagram showing an example of a manufacturing process for a composite substrate according to the second embodiment of the present invention. FIG. 6 is a diagram showing an example of a manufacturing process for a composite substrate according to the second embodiment of the present invention. FIG. 7 is a diagram showing an example of a manufacturing process for a composite substrate according to the second embodiment of the present invention. FIG. 8 is a diagram showing a characteristic evaluation system for a composite substrate.

[0011] 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 addition, in order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part more schematically than in the embodiments, but these are merely examples and do not limit the interpretation of the present invention.

[0012] First Embodiment Fig. 1 is a diagram showing a schematic configuration of a composite substrate according to a first embodiment of the present invention. A composite substrate 100 in this embodiment is used, for example, as an optical element that constitutes an optical waveguide, and has a structure in which a piezoelectric material substrate is bonded to a support substrate 30 via an intermediate layer 20. Fig. 1(a) is a schematic cross-sectional view of the composite substrate 100, and Fig. 1(b) is a schematic plan view of the composite substrate 100. The x, y, and z coordinate axes shown in Fig. 1 are expressed in accordance with the crystal axes of the waveguide substrate 10.

[0013] In the first embodiment, the piezoelectric material substrate is a waveguide substrate 10 including an optical waveguide, and grooves 60 extending straight in the direction of the crystal axis x of the waveguide substrate 10 are formed by linearly cutting the surface of the substrate in a predetermined width by dry etching, dicing, laser processing, or the like. These grooves 60 are provided at two locations on the surface of the waveguide substrate 10 at a constant interval. As a result, a ridge portion 50 having a trapezoidal cross section is formed in the portion sandwiched between the pair of parallel grooves 60. This ridge portion 50 is used as an optical waveguide.

[0014] The waveguide substrate 10 is made of, for example, LiNbO ３ (lithium niobate) and LiTaO ３ (lithium tantalate) or other piezoelectric materials are used. ３ , LiTaO ３ These may be referred to as "LN" and "LT," respectively. The waveguide substrate 10 includes a bonding interface 40 formed in a bonding step described below.

[0015] The intermediate layer 20 is provided on the support substrate 30 and is disposed between the waveguide substrate 10 and the support substrate 30. The material of the intermediate layer 20 is a low refractive index material from the viewpoint of energy confinement, and a material with a refractive index of 1.8 or less is desirable, such as SiO ２ , MgF ２ , CaF ２ Preferably, the compound contains at least one of SiO ２ The support substrate 30 is made of SiO ２ , MgF ２ , or CaF ２By using a substrate made of the above, if the support substrate 30 has a lower refractive index than the waveguide substrate 10, the intermediate layer 20 does not need to be provided.

[0016] The intermediate layer 20 can be formed by any suitable method, such as sputtering, vacuum deposition, physical vapor deposition such as ion beam assisted deposition (IAD), chemical vapor deposition, or atomic layer deposition (ALD). The intermediate layer 20 can be formed at a temperature of, for example, room temperature (25° C.) to 300° C.

[0017] The support substrate 30 supports the waveguide substrate 10. Any appropriate substrate can be used as the support substrate 30. The support substrate 30 may be made of a single crystal or a polycrystalline material. It may also be made of a metal. The waveguide substrate 10 and the support substrate 30 are bonded to each other via an intermediate layer 20.

[0018] The material constituting the support substrate 30 is preferably silicon, sialon, sapphire, cordierite, mullite, glass, quartz, crystal, alumina, SUS, iron-nickel alloy (42 alloy), MgF ２ , CaF ２ and brass. The thickness of the support substrate 30 is, for example, 0.3 to 1 mm, but any other appropriate thickness may be adopted.

[0019] The silicon may be single crystal silicon, polycrystalline silicon, or high-resistivity silicon. The support substrate 30 may be SOI (Silicon on Insulator).

[0020] Typically, the sialon is a ceramic obtained by sintering a mixture of silicon nitride and alumina, and for example, Si ６ -wAlwOwN ８ Sialon has a composition represented by -w. Specifically, sialon has a composition in which alumina is mixed into silicon nitride, and w in the formula represents the mixing ratio of alumina. w is preferably 0 or more and 4.2 or less, and more preferably 0.5 or more and 4.0 or less.

[0021] Typically, the sapphire is Al２ O ３ The alumina is a single crystal having a composition of Al ２ O ３ The alumina is preferably a translucent alumina.

[0022] Typically, the cordierite is 2MgO.2Al ２ O ３ 5SiO ２ The mullite is a ceramic having a composition of 3Al ２ O ３ 2SiO ２ ~2Al ２ O ３ SiO ２ It is a ceramic having a composition in the range of

[0023] 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.

[0024] The composite substrate 100 can be manufactured in any suitable shape. In one embodiment, the composite substrate 100 can be manufactured in the form of a so-called wafer. The size of the composite substrate 100 can be appropriately set depending on the purpose, for example, with a wafer (substrate) diameter of 50 mm to 150 mm.

[0025] 2, 3 and 4 are diagrams showing an example of a manufacturing process for the composite substrate according to the first embodiment of the present invention.

[0026] 2A shows a preparation step in the manufacturing process of the composite substrate 100. In this step, a support substrate 30 is prepared.

[0027] 2B shows the step of forming the intermediate layer 20 in the manufacturing process of the composite substrate 100. In this step, a SiO 2 film having a predetermined thickness is formed on the surface of the support substrate 30 prepared in the preparation step of FIG. ２ The intermediate layer 20 is formed by depositing the amorphous material.

[0028] FIG. 2( c) shows the activation step in the manufacturing process of the composite substrate 100. In this step, an LN substrate 10A having a predetermined thickness, formed using, for example, LN as a material, is prepared. An activation process is performed by irradiating the surfaces of the intermediate layer 20 formed on the surface of the support substrate 30 in the film formation step of FIG. 2( b) and the LN substrate 10A with a fast atom beam (hereinafter referred to as FAB) using an inert gas such as Ar as the atomic species for a predetermined period of time. The FAB irradiation time is preferably, for example, about 15 seconds. As mentioned above, an LT substrate can be used instead of the LN substrate, but in the following description, the LT substrate will also be referred to as the "LN substrate 10A."

[0029] FIG. 2(d) shows the sputtering step in the manufacturing process of the composite substrate 100. In this step, the FAB irradiation on the intermediate layer 20 side, which was irradiated to both the intermediate layer 20 and the LN substrate 10A in the activation step of FIG. 2(c), is stopped, and the FAB irradiation on the LN substrate 10A side is continued for a predetermined time. The FAB irradiation time at this time, including the irradiation time in the activation step of FIG. 2(c), is, for example, about 3 to 10 minutes, preferably 4 to 7 minutes. As a result, the LN constituting the LN substrate 10A is sputtered and attached to the surface of the intermediate layer 20, forming a sputtered film 21 made of the same material as the LN substrate 10A on the intermediate layer 20 side.

[0030] FIG. 3( e) shows the bonding step of the manufacturing process for the composite substrate 100. In this step, the LN substrate 10A irradiated with FAB in the activation step of FIG. 2( c) is bonded to the intermediate layer 20 on which the sputtered film 21 is formed in the sputtering step of FIG. 2( d) to form a bonded assembly. As a result, the LN substrate 10A and the sputtered film 21 are bonded and integrated, and a bonded interface 40 between them is formed inside the LN substrate 10A. At this time, three layers (a first layer 11, a second layer 12, and a third layer 13) are formed in the LN substrate 10A near the bonded interface 40 (see FIG. 3( f)). The first layer 11 is a layer that does not contain inert gas atoms such as Ar irradiated with FAB in the activation step of FIG. 2( c), and the second layer 12 is a layer that is located closer to the intermediate layer 20 than the first layer 11 and contains the inert gas atoms. The third layer 13 is disposed closer to the intermediate layer 20 than the first layer 11 and the second layer 12, for example, in contact with the intermediate layer 20. The third layer 13 does not contain the inert gas atoms or contains them at a lower content than the second layer 12. The first layer 11 is made of a crystalline LN or LT, which is the material of the LN substrate 10A, and the third layer 13 is an amorphous film of LN or LT. The second layer 12 is either a crystalline LN or LT film of LN or LT, similar to the first layer 11, or an amorphous film of LN or LT, similar to the third layer 13. These layers may contain other atomic species that were mixed into the second layer 12 or the third layer 13 during the sputtering process shown in FIG. 2(d), such as Fe atoms, Al atoms, or Cr atoms that constitute the jig or base used to secure the LN substrate 10A. Details of these layers will be described later. 3(e) and subsequent figures, the positional relationship between the LN substrate 10A, the intermediate layer 20, and the support substrate 30 is shown upside down compared to FIGS. 2(a) to 2(d).

[0031] 3(f) shows a thinning step in the manufacturing process of the composite substrate 100. In this step, the LN substrate 10A is polished to a predetermined thickness to thin the bonded body after the bonding step shown in FIG. 3(e). For example, the LN substrate 10A can be polished to a thin plate using grinding, CMP (Chemical Mechanical Polishing), surface planarization using a gas cluster ion beam, or the like.

[0032] 3( g) shows the ridge processing step in the manufacturing process of the composite substrate 100. In this step, linear grooves 60 are provided at two locations at regular intervals on the surface of the LN substrate 10A thinned in the thinning process of FIG. 3( f), thereby forming a ridge portion 50 that functions as an optical waveguide. For example, the grooves 60 can be formed by processing the surface of the LN substrate 10A using laser light or by dry etching such as RIE (Reactive Ion Etching).

[0033] 4( h) shows the thermal annealing step in the manufacturing process of the composite substrate 100. In this step, the bonded assembly in which the grooves 60 are formed on the surface of the LN substrate 10A by the ridge processing step of FIG. 3( g) is heated to a predetermined temperature. The heating temperature at this time is preferably, for example, about 300 to 450°C, and more preferably 400 to 450°C. As a result, in the composite substrate 100 manufactured from this bonded assembly, the optical propagation characteristics of the waveguide substrate 10 including the ridge portion 50 can be improved, and optical loss can be reduced when the ridge portion 50 is used as a waveguide.

[0034] The inventors of the present invention have experimentally confirmed that the above-mentioned thermal annealing process improves the optical propagation characteristics of the waveguide substrate 10. The reason why the thermal annealing process improves the optical propagation characteristics of the waveguide substrate 10 is thought to be that a portion of the LN or LT in the waveguide substrate 10 that has been made amorphous by FAB irradiation during the activation process shown in Fig. 2(c) or the sputtering process shown in Fig. 2(d) is recrystallized by heating.

[0035] Inert gas atoms and other atomic species introduced into the second layer 12 and the third layer 13 during the sputtering process may diffuse into other layers when the LN substrate 10A is heated during the thermal annealing process shown in FIG. 4( h). The degree of diffusion varies depending on the heating temperature and heating time. That is, the Fe, Al, and Cr atom contents in the first layer 11, the second layer 12, and the third layer 13 vary depending on the heating temperature and heating time during the thermal annealing process. In the second and third layers, the Fe atom content is preferably 0.5 to 20 atomic %, the Al atom content is preferably 0.5 to 8.5 atomic %, and the Cr atom content is preferably 0.5 to 4.5 atomic %. The inert gas atom content in the second layer is preferably 2.5 to 3.5 atomic %, and the inert gas atom content in the third layer is preferably 0 to 1.1 atomic %.

[0036] The thermal annealing step described above may be performed at any timing after the bonding step shown in Fig. 3(e) has been performed. For example, the thermal annealing step may be performed on the bonded assembly of the LN substrate 10A and the intermediate layer 20 obtained by the bonding step shown in Fig. 3(e), and then the thin plate processing step shown in Fig. 3(f) or the ridge processing step shown in Fig. 3(g) may be performed. Furthermore, even if the thermal annealing step is not performed, the optical annealing step described below can be performed to improve the light propagation characteristics of the waveguide substrate 10, so the thermal annealing step may be performed as needed, or may not be performed at all.

[0037] FIG. 4(i) shows the photo-annealing step in the manufacturing process of the composite substrate 100. In this step, grooves 60 are formed on the surface of the LN substrate 10A by the ridge processing step of FIG. 3(g), and the thermal annealing step of FIG. 4(h) is further performed as needed. In this bonded structure, an irradiation area 51 corresponding to the ridge portion 50 sandwiched between the grooves 60 is set, and laser light is irradiated onto this irradiation area 51 in the in-plane direction (x direction) of the composite substrate 100 formed by the bonded structure. The laser light output and irradiation time are preferably 100 mW or more and 4 minutes or more, respectively. This allows the laser light to pass through the ridge portion 50 as an optical waveguide. Note that the entire irradiation area 51 does not necessarily need to be within the ridge portion 50; a portion of the irradiation area 51 may be outside the ridge portion 50.

[0038] In this embodiment, by performing the above-described optical annealing step, it is possible to improve the optical propagation characteristics of the waveguide substrate 10 in the ridge portion 50 and reduce optical loss in the composite substrate 100 manufactured from the bonded body. The reason why the optical propagation characteristics of the waveguide substrate 10 are improved by the optical annealing step will be described later.

[0039] Through the above steps, a composite substrate 100 having the structure shown in FIG. 1 and excellent light propagation characteristics is manufactured.

[0040] Second Embodiment Fig. 5 is a diagram showing a schematic configuration of a composite substrate according to a second embodiment of the present invention. A composite substrate 110 in this embodiment has a structure in which a waveguide substrate 10 is bonded to a support substrate 30 without an intermediate layer 20 therebetween, as compared to the composite substrate 100 of Fig. 1 described in the first embodiment. Fig. 5(a) is a schematic cross-sectional view of the composite substrate 110, and Fig. 5(b) is a schematic plan view of the composite substrate 110. The x, y, and z coordinate axes shown in Fig. 5 are indicated in accordance with the crystal axes of the waveguide substrate 10.

[0041] As described above, the support substrate 30 is made of SiO ２ , MgF ２ , or CaF ２By using a substrate made of the above, when the support substrate 30 has a lower refractive index than the waveguide substrate 10, it is possible to form a composite substrate 110 that can be used as an optical element that constitutes an optical waveguide, even without providing an intermediate layer 20 as in the structure shown in FIG.

[0042] In this embodiment, as in the first embodiment, the composite substrate 110 may further include any layer. The type, function, number, combination, arrangement, etc. of such layers may be appropriately set depending on the purpose. Furthermore, the composite substrate 110 may be manufactured in any appropriate shape depending on the purpose.

[0043] 6, 7 and 8 are diagrams showing an example of a manufacturing process for a composite substrate according to the second embodiment of the present invention.

[0044] 6A shows a preparation step in the manufacturing process of the composite substrate 110. In this step, a support substrate 30 is prepared, similar to the step shown in FIG. 2A described in the first embodiment. Note that, unlike the first embodiment, in this embodiment, the step of forming the intermediate layer 20 on the support substrate 30 is omitted.

[0045] 6B shows an activation step in the manufacturing process of the composite substrate 110. In this step, for example, an LN substrate 10A having a predetermined thickness is prepared, and activation processing is performed by irradiating the surfaces of the support substrate 30 prepared in the preparation step of FIG. 6A and the LN substrate 10A with FAB using an inert gas such as Ar as an atomic species for a predetermined time, similar to the step of FIG. 2C described in the first embodiment.

[0046] FIG. 6(c) shows a sputtering step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 2(d) described in the first embodiment, the FAB irradiation on the support substrate 30 side, which was irradiated on both the support substrate 30 and the LN substrate 10A in the activation step of FIG. 6(b), is stopped, and the FAB irradiation on the LN substrate 10A side is continued for a predetermined time. The FAB irradiation time at this time, including the irradiation time in the activation step of FIG. 6(b), is, for example, about 3 to 10 minutes, preferably 4 to 7 minutes. As a result, the LN constituting the LN substrate 10A is sputtered and attached to the surface of the support substrate 30, forming a sputtered film 21 on the support substrate 30 side made of the same material as the LN substrate 10A.

[0047] FIG. 7(d) shows the bonding step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 3(e) described in the first embodiment, the LN substrate 10A irradiated with FAB in the activation step of FIG. 6(b) and the support substrate 30 on which the sputtered film 21 is formed in the sputtering step of FIG. 6(c) are bonded to form a bonded assembly. As a result, the LN substrate 10A and the sputtered film 21 are bonded and integrated, and a bonded interface 40 between them is formed inside the LN substrate 10A. Note that in FIG. 7(d) and subsequent figures, the positional relationship between the LN substrate 10A and the support substrate 30 is illustrated upside down compared to FIGS. 6(a) to 6(c).

[0048] 7( e) shows a thinning process in the manufacturing process of the composite substrate 110. In this process, similar to the process of FIG. 3( f) described in the first embodiment, the LN substrate 10A is thinned by polishing it to a predetermined thickness from the bonded body after the bonding process shown in FIG.

[0049] Fig. 7(f) shows a ridge processing step in the manufacturing process of the composite substrate 110. In this step, similar to the step of Fig. 3(g) described in the first embodiment, linear grooves 60 are provided at two locations at regular intervals on the surface of the LN substrate 10A thinned in the thinning step of Fig. 7(e), thereby forming a ridge portion 50 that functions as an optical waveguide.

[0050] FIG. 8( g ) shows a thermal annealing step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 4( h ) described in the first embodiment, the bonded assembly in which the grooves 60 are formed on the surface of the LN substrate 10A by the ridge processing step of FIG. 7( f ) is heated to a predetermined temperature. The heating temperature is preferably, for example, approximately 300 to 450°C, and more preferably 400 to 450°C. As in the first embodiment, the thermal annealing step may be performed at any timing after the bonding step of FIG. 7( d ). For example, the thermal annealing step may be performed on the bonded assembly of the LN substrate 10A and the support substrate 30 obtained by the bonding step of FIG. 7( d ), followed by the thin plate processing step of FIG. 7( e ) and the ridge processing step of FIG. 7( f ). The thermal annealing step may be performed as needed, or may not be performed.

[0051] FIG. 8( h) shows the optical annealing step in the manufacturing process of the composite substrate 110. In this step, similar to the step of FIG. 4( i) described in the first embodiment, grooves 60 are formed on the surface of the LN substrate 10A by the ridge processing step of FIG. 7( f), and, if necessary, the thermal annealing step of FIG. 8( g) is performed on the bonded structure. An irradiation area 51 corresponding to the ridge portion 50 sandwiched between the grooves 60 is set, and laser light is irradiated onto this irradiation area 51 in the in-plane direction (x direction) of the composite substrate 110 formed by the bonded structure. The output power and irradiation time of the laser light are preferably 100 mW or more and 4 minutes or more, respectively. As a result, the laser light passes through the ridge portion 50 as an optical waveguide, and in the composite substrate 110 manufactured from the bonded structure, the optical propagation characteristics of the waveguide substrate 10 at the ridge portion 50 are improved, thereby reducing optical loss.

[0052] Through the above steps, a composite substrate 110 having the structure shown in FIG. 5 and good optical propagation characteristics is manufactured.

[0053] 4(i) and 8(h), the reason why the optical propagation characteristics of the waveguide substrate 10 are improved is presumed to be as follows. That is, in the optical annealing process, when laser light is irradiated onto the irradiation area 51 corresponding to the ridge portion 50, the crystalline state of the LN or LT constituting the waveguide substrate 10 within the ridge portion 50 gradually changes due to the energy of the incident laser light. By continuing this state for a predetermined period of time or longer, a crystalline structure that easily transmits laser light is formed within the ridge portion 50, and it is thought that the optical propagation characteristics are improved compared to before the laser light was irradiated.

[0054] Examples for verifying the effect of the photo-annealing process according to the present invention will be specifically described below. Unless otherwise specified, the following procedures were carried out at room temperature.

[0055] Example 1 A bonded structure was fabricated according to the manufacturing process described with reference to Figures 2 and 3. Specifically, an LN substrate 10A having a diameter of 4 inches and a thickness of 500 µm and a silicon substrate were prepared, and the silicon substrate was used as the support substrate 30. Then, a SiO ２ The amorphous material was formed into a film having a thickness of 1.0 μm, thereby forming the intermediate layer 20 .

[0056] Next, after cleaning the surface of the LN substrate 10A and the surface of the support substrate 30 (on the intermediate layer 20 side), both substrates are placed in a vacuum chamber. －６ The chamber was evacuated to a pressure in the Pa range, and the surfaces of both substrates were simultaneously irradiated with FAB using Ar gas (accelerating voltage 1 kV, Ar flow rate 27 sccm) for 15 seconds. The FAB irradiation on the support substrate 30 side was then stopped, and the FAB irradiation on the LN substrate 10A side was continued for an additional 285 seconds (5 minutes in total). As a result, a sputtered film 21 with a thickness of 1.1 nm was formed on the surface of the support substrate 30 facing the intermediate layer 20.

[0057] Next, the LN substrate 10A was directly bonded to the support substrate 30. Specifically, the beam-irradiated surfaces of both substrates were placed one on top of the other, and the two substrates were bonded together by applying a pressure of 10,000 N at room temperature for 2 minutes to obtain a bonded assembly.

[0058] Next, the surface of the LN substrate 10A of the obtained bonded body was polished until its thickness was 3.6 μm, and then ridge processing was performed using laser light to form two 2 μm deep grooves 60 spaced 6 μm apart on the surface of the LN substrate 10A. After that, the bonded body after ridge processing was cut to a predetermined size and the cut end faces were polished to form a bonded body having a length of 1.4 mm in the x direction, a length of 8.5 mm in the z direction, and a ridge portion 50 with a width of 6 μm and a height of 2 μm as an optical waveguide, which had the same structure as the composite substrate 100 shown in FIG.

[0059] Next, the resulting bonded body was placed in a high-temperature furnace, heated from room temperature to 450°C, held at that temperature for a certain period of time, and then returned to room temperature, thereby performing thermal annealing. In the following steps, the bonded body after thermal annealing was used as the composite substrate 100 to be subjected to light annealing.

[0060] Next, in the characteristic evaluation system for the composite substrate 100 shown in FIG. 9 , laser light (output intensity: 150 mW, wavelength: 976 nm) output from a laser 201 was focused by an incident lens 202 and irradiated onto the composite substrate 100 (bonded body after thermal annealing) to be optically annealed. The position of the composite substrate 100 was finely adjusted using a stage or the like so that the irradiation range 51 of the laser light was approximately aligned with the cross section of the ridge portion 50 (see FIG. 4( i)). The laser light irradiated in the in-plane direction of the composite substrate 100 passed through the ridge portion 50. In FIG. 9 , the axial direction of the characteristic evaluation system is defined by taking the z-axis as the direction of propagation of the laser light within the ridge portion 50, i.e., the extension direction of the ridge portion 50 in the in-plane direction of the composite substrate 100. This definition of the axial direction differs from the direction of the crystal axis of the waveguide substrate 10 shown in FIGS. 1 and 5 . At this time, in order to prevent reflected light from returning to the laser 201 when laser light is incident on the ridge portion 50, it is preferable that the angle of incidence of the laser light on the composite substrate 100 be shifted by a predetermined angle with respect to the direction in which the laser light propagates within the ridge portion 50 (z direction). For example, in the composite substrate 100, the angle between the end face (laser light incident surface) and the side face of the ridge portion 50 is formed at 84 degrees, and the laser light is irradiated in a direction such that the laser light refracted at this end face propagates within the ridge portion 50 in the z direction. This allows the laser light to propagate in the z direction within the ridge portion 50 while preventing reflected light from returning to the laser 201. In addition, as long as the angle of incidence of the laser light with respect to the end face of the ridge portion 50 is a predetermined angle (e.g., 84 degrees) shifted from 90 degrees, the composite substrate 100 can be irradiated with laser light in any direction. However, in the following explanation, regardless of the direction in which the laser light is irradiated onto the end face of the ridge portion 50, as long as the laser light irradiated onto the composite substrate 100 in that irradiation direction can propagate along the extension direction of the ridge portion 50, that irradiation direction will be referred to as the surface direction of the composite substrate 100.

[0061] When laser light was incident on ridge portion 50 as described above, the laser light that passed through ridge portion 50 and was output from the opposite surface was narrowed by output lens 203 and input to measuring device 204, and the intensity of the laser light received by measuring device 204 was continuously measured. As a result, a measured value of 63.4 mW was obtained at the start of the measurement. Furthermore, the measured value gradually changed as the measurement time passed, rising to 65.8 mW after 4 minutes. Thereafter, almost no change in the measured value was observed.

[0062] (Example 2) A bonded body obtained by the same method as in Example 1 was placed in a high-temperature furnace, and thermal annealing was performed by heating it from room temperature to a temperature (300°C) lower than that in Example 1, maintaining that temperature for a certain period of time, and then returning it to room temperature. In the following steps, this bonded body after thermal annealing was used as the composite substrate 100 to be subjected to light annealing.

[0063] Thereafter, as in Example 1, in the characteristic evaluation system shown in FIG. 9 , laser light (output intensity: 150 mW, wavelength: 976 nm) output from laser 201 was focused by input lens 202 so that its irradiation area 51 substantially coincided with the cross section of ridge portion 50, and the laser light passed through ridge portion 50. Then, the laser light that passed through ridge portion 50 and was output from the opposite surface was focused by output lens 203 and input to measuring instrument 204, and the intensity of the laser light received by measuring instrument 204 was continuously measured. As a result, a measured value of 34.6 mW was obtained at the start of the measurement, but the measured value gradually changed as the measurement time passed, rising to 34.85 mW after 4.5 minutes. Thereafter, almost no change in the measured value was observed.

[0064] From the above-described second embodiment, it was confirmed that, compared to the first embodiment, when the temperature of thermal annealing is low, the effect of improving the light propagation characteristics by the subsequent optical annealing is low.

[0065] (Example 3) The bonded body obtained by the same method as in Examples 1 and 2 was placed in a high-temperature furnace, heated from room temperature to 450°C, held at that temperature for a certain period of time, and then returned to room temperature, thereby performing thermal annealing. In the following steps, this bonded body after thermal annealing was used as the composite substrate 100 to be subjected to light annealing.

[0066] 9 , laser light (output intensity: 100 mW, wavelength: 976 nm) output from laser 201 was focused by input lens 202 so that its irradiation area 51 substantially coincided with the cross section of ridge portion 50, and the laser light passed through ridge portion 50. Then, the laser light that passed through ridge portion 50 and was output from the opposite surface was focused by output lens 203 and input to measuring instrument 204, and the intensity of the laser light received by measuring instrument 204 was continuously measured. As a result, a measured value of 41.2 mW was obtained at the start of the measurement, but the measured value gradually changed as the measurement time passed, rising to 41.6 mW after 4 minutes and to 41.65 mW after 6 minutes.

[0067] From the above-described Example 3, it was confirmed that, compared to Example 1, when the intensity of the laser light is low, the effect of optical annealing on improving the light propagation characteristics is low, and it takes a long time for the improvement effect to plateau.

[0068] 9 was changed from 100 mW to 200 mW, and measurement was continued using the measuring instrument 204. Immediately after the change in the output intensity of the laser light, a measured value of 85.5 mW was obtained for the composite substrate 100 used in Example 3. However, the measured value did not change much over time, and after 5 minutes, it rose slightly to 85.55 mW.

[0069] Furthermore, the output intensity of the laser light was changed from 200 mW to 150 mW, and measurement was continued using the measuring device 204. At this time, a measured value of 64.1 mW was obtained, and the measured value did not change even after 5 minutes had passed.

[0070] Furthermore, the output intensity of the laser light was changed from 150 mW to 100 mW, and measurement was continued using the measuring device 204. At this time, a measured value of 43.2 mW was obtained, and the measured value did not change even after 5 minutes had passed.

[0071] From the above-described Example 4, it was confirmed that when the improvement effect of the light propagation characteristics by irradiating the laser light reaches a plateau, the light propagation characteristics do not change even if the output intensity of the laser light is subsequently changed.

[0072] According to the embodiment of the present invention described above, the following advantageous effects are achieved.

[0073] (1) The manufacturing method of the composite substrate 100 is as follows. ２ , MgF ２ , CaF ２ the LN substrate 10A and the intermediate layer 20 formed on the support substrate 30 with FAB (FIG. 2(c)); a sputtering process (FIG. 2(d)) in which the surface of the LN substrate 10A is further irradiated with FAB to form a sputtered film 21 containing the material of the LN substrate 10A on the surface of the intermediate layer 20; a bonding process (FIG. 3(e)) in which the LN substrate 10A and the intermediate layer 20 on which the sputtered film 21 is formed are bonded to obtain a bonded body; and a photo-annealing process (FIG. 4(i)) in which laser light is irradiated onto the bonded body in the surface direction of the composite substrate 100, and the composite substrate 100 is formed using the bonded body irradiated with laser light in the photo-annealing process. By doing this, even if the piezoelectric material substrate is directly bonded to the intermediate layer 20 without providing any other layers, it is possible to realize a manufacturing method for a composite substrate 100 having good light propagation characteristics while improving the bonding strength between the intermediate layer 20 provided on the support substrate 30 and the piezoelectric material substrate.

[0074] (2) The manufacturing method of the composite substrate 110 is to form a surface of an LN substrate 10A formed using LN (or LT) as a material and a SiO ２ , MgF ２ , or CaF ２and a surface of a support substrate 30 including the LN substrate 10A, which is irradiated with FAB (FIG. 6( b)), a sputtering step (FIG. 6( c)) of further irradiating the surface of the LN substrate 10A with FAB to form a sputtered film 21 made of the material of the LN substrate 10A on the surface of the support substrate 30, a bonding step (FIG. 7( d)) of bonding the LN substrate 10A and the support substrate 30 on which the sputtered film 21 has been formed to obtain a bonded body, and a photo-annealing step (FIG. 8( h)) of irradiating the bonded body with laser light in the plane direction of the composite substrate 110, and the composite substrate 110 is formed using the bonded body irradiated with laser light in the photo-annealing step. In this way, even when the piezoelectric material substrate is directly bonded to the support substrate 30 without providing any other layer, it is possible to realize a method for manufacturing a composite substrate 110 having good light propagation characteristics while improving the bonding strength between the support substrate 30 and the piezoelectric material substrate.

[0075] (3) The manufacturing method of the composite substrate 100, 110 further includes a thermal annealing step (FIGS. 4(h) and 8(g)) of heating the bonded body to a predetermined temperature. In the photo-annealing step of irradiating laser light, the bonded body may be irradiated with laser light after being heated to the predetermined temperature in the thermal annealing step. This further improves the bonding strength between the piezoelectric material substrate and the intermediate layer 20 or the support substrate 30, thereby reliably preventing these bonds from peeling off in the thin plate processing step and ridge processing step performed before the photo-annealing step.

[0076] (4) The manufacturing method of the composite substrate 100, 110 further includes a ridge processing step of forming a ridge portion 50 in the LN substrate 10A of the bonded body. In the optical annealing step of irradiating laser light, it is preferable to set an irradiation area 51 corresponding to the ridge portion 50 and irradiate the laser light onto this irradiation area 51. In this way, the composite substrate 100, 110 can have a ridge portion 50 that can be used as an optical waveguide with good optical propagation characteristics.

[0077] (5) In the photo-annealing step of irradiating laser light, it is preferable to irradiate the bonded body used in manufacturing the composite substrates 100 and 110 with laser light for at least 4 minutes. It is also preferable to irradiate the bonded body with laser light at an output of at least 100 mW. This ensures that the composite substrates 100 and 110 have good optical propagation characteristics.

[0078] The present invention is not limited to the above-described embodiment, and can be implemented using any components without departing from the spirit of the present invention.

[0079] The above-described embodiments and modifications are merely examples, and the present invention is not limited to these details as long as the features of the invention are not impaired. Furthermore, although various embodiments and modifications have been described above, the present invention is not limited to these details. Other aspects that can be considered within the scope of the technical idea of ​​the present invention are also included within the scope of the present invention.

[0080] 10: Waveguide substrate 10A: LN substrate 11: First layer 12: Second layer 13: Third layer 20: Intermediate layer 21: Sputtered film 30: Support substrate 40: Bonding interface 50: Ridge portion 51: Irradiation area 60: Groove 100, 110: Composite substrate 201: Laser 202: Incident lens 203: Exit lens 204: Measuring device

Claims

1. A method for manufacturing a composite substrate, comprising: ２ , MgF ２ , CaF ２ a step of irradiating a surface of a piezoelectric material substrate formed using LN or LT as a material and a surface of the intermediate layer formed on the support substrate with a fast atomic beam, respectively; a step of further irradiating the surface of the piezoelectric material substrate with the fast atomic beam to form a sputtered film containing the material of the piezoelectric material substrate on the surface of the intermediate layer; a step of bonding the piezoelectric material substrate and the intermediate layer on which the sputtered film is formed to obtain a bonded body; and a step of irradiating the bonded body with a laser beam in a surface direction of the composite substrate, wherein the composite substrate is formed using the bonded body irradiated with the laser beam.

2. A method for manufacturing a composite substrate, comprising: forming a surface of a piezoelectric material substrate formed using LN or LT as a material; and forming a SiO ２ , MgF ２ , or CaF ２ and a surface of a supporting substrate comprising the piezoelectric material substrate and a piezoelectric material layer formed thereon, with a fast atomic beam; further irradiating a surface of the piezoelectric material substrate with the fast atomic beam to form a sputtered film made of a material of the piezoelectric material substrate on the surface of the supporting substrate; bonding the piezoelectric material substrate and the supporting substrate on which the sputtered film has been formed to obtain a bonded body; and irradiating the bonded body with a laser beam in a surface direction of the composite substrate, wherein the composite substrate is formed using the bonded body irradiated with the laser beam.

3. A method for manufacturing a composite substrate as defined in claim 1 or 2, further comprising a step of heating the bonded body to a predetermined temperature, and in the step of irradiating the laser light, the laser light is irradiated onto the bonded body after it has been heated to the predetermined temperature.

4. A method for manufacturing a composite substrate as defined in claim 1 or 2, further comprising a step of forming a ridge portion in the piezoelectric material substrate of the bonded body, and in the step of irradiating the laser light, an irradiation range corresponding to the ridge portion is set, and the laser light is irradiated onto the irradiation range.

5. A method for producing a composite substrate as defined in claim 1 or 2, wherein in the step of irradiating the laser light, the bonded body is irradiated with the laser light for 4 minutes or more.

6. A method for producing a composite substrate according to claim 1 or 2, wherein in the step of irradiating the laser light, the bonded body is irradiated with the laser light at an output of 100 mW or more.

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