Composite substrate, device, and method for manufacturing composite substrate

Abstract

A composite substrate 1 comprises: a functional layer 21a; a support substrate 23 that supports the functional layer 21a; a coating layer 22 that covers at least a main surface of the support substrate 23 on the functional layer 21a side; and a beveled region 12 that is formed in an outer peripheral part so as to extend from the functional layer 21a to a part of the coating layer 22. Herein, the coating layer 22 preferably covers the entire peripheral surface of the support substrate 23. Thereby, provided is a composite substrate in which damage to a support substrate is less likely to occur during polishing of a functional layer, for example, even if beveling is performed.

Description

Composite substrate, device, and method for manufacturing a composite substrate

[0001] The present invention relates to composite substrates, devices, and methods for manufacturing composite substrates. In particular, the present invention relates to composite substrates having a beveled region on the outer periphery.

[0002] It is known that when fabricating composite substrates, the unadhered region formed at the wafer edge can be removed by beveling the outer edge of the composite substrate in a circular pattern during the fabrication process, thereby suppressing the peeling of the thin film from the unadhered region.

[0003] Patent Document 1 describes a semiconductor substrate having a semiconductor layer on a support, wherein at least the outer edge of the semiconductor layer is located inward from the outer edge of the support, and at least the periphery of the side of the semiconductor layer opposite to the support is chamfered.

[0004] Japanese Patent Application Publication No. 1-227441

[0005] However, in conventional composite substrates where the outer periphery is ground, the support substrate is exposed as a result of beveling. In this case, for example, when processing the functional layer by polishing, etching, or ion implantation, damage occurs to the exposed portion of the support substrate, resulting in contamination such as chipping or peeling. As a result, yield decreases and device performance deteriorates. The present invention aims to provide a composite substrate that, even when beveling is performed, is less prone to damage to the support substrate and contamination such as chipping or peeling that occurs when polishing the functional layer.

[0006] To solve the above problems, the present invention provides a composite substrate comprising a functional layer, a support substrate supporting the functional layer, a coating layer covering at least the main surface of the support substrate on the functional layer side, and a beveling region formed on the outer periphery extending from the functional layer to a part of the coating layer. The present invention also provides a device comprising the above composite substrate. Furthermore, the present invention provides a method for manufacturing a composite substrate, comprising a coating layer formation step of forming a coating layer that covers the entire circumferential surface of the support substrate supporting the functional layer, a bonding step of bonding a functional layer wafer, which will be the basis of the functional layer, and the support substrate via the coating layer, a beveling step of performing beveling on the outer periphery of the bonded functional layer wafer and support substrate extending from the functional layer wafer to a part of the coating layer to form a beveling region, and a polishing step of polishing the functional layer wafer to form a functional layer.

[0007] The objective is to provide composite substrates that are less prone to damage to the support substrate when beveling or polishing the functional layer.

[0008] Figures illustrating the composite substrate of the first embodiment. Figures (a) to (b) illustrate the composite substrate of the first embodiment. Figures (a) to (b) illustrate a conventional composite substrate. Figures illustrating a modified example of the composite substrate in the first embodiment. Figures (a) to (b) illustrate the composite substrate of the second embodiment. Figures illustrating the composite substrates of the third and fourth embodiments. Figures illustrating the composite substrate of the fifth embodiment. Figures (a) to (h) illustrate the manufacturing method of the composite substrate of the first embodiment. Figures (a) to (h) illustrate the manufacturing method of the composite substrate of the second embodiment. Figures (a) to (i) illustrate the manufacturing method of the composite substrate of the third embodiment. Figures (a) to (i) illustrate the manufacturing method of the composite substrate of the fourth embodiment. Figures (a) to (h) illustrate the manufacturing method of the composite substrate of the fifth embodiment.

[0009] The embodiments of the present invention will be described in detail below with reference to the attached drawings. Here, the composite substrate 1 will be described according to the first to fifth embodiments.

[0010] [First Embodiment] <Description of the Composite Substrate Configuration> Figures 1 and 2(a) to 2(b) show the composite substrate 1 of the first embodiment. Of these, Figure 1 is a top view of the composite substrate 1, and Figure 2(a) is a cross-sectional view of Figure 1 taken along IIa-IIa, schematically showing the layer structure of the composite substrate 1. Figure 2(b) is a diagram that further describes the outer periphery of the composite substrate 1. As shown in Figure 1, the composite substrate 1 has a substantially circular shape with an orientation flat (orifura) portion 11. The orientation flat portion 11 is a planar portion formed on the side surface of the composite substrate 1 to indicate the crystal orientation of the composite substrate 1. The composite substrate 1 has an outer diameter of, for example, 4 inches or more and 12 inches or less, and a thickness of, for example, 200 μm or more and 1000 μm or less. The composite substrate 1 also has a beveling region 12 on its outer periphery. Here, "outer periphery" refers to the edge when the composite substrate 1 is viewed from above. The beveling region 12 is formed by chamfering the outer periphery of the composite substrate 1. This suppresses sagging of the outer periphery when forming the functional layer 21a of the composite substrate 1. The region other than the beveling region 12, which is inside the beveling region 12, is the effective region 13 that is used when actually fabricating the device.

[0011] Furthermore, as shown in Figures 2(a) to 2(b), the composite substrate 1 has a structure in which a functional layer 21a, a coating layer 22, and a support substrate 23 are stacked from top to bottom in the figure.

[0012] The functional layer 21a is selected for the application in which the composite substrate 1 is used. The functional layer 21a is made of, for example, a piezoelectric material. The piezoelectric material is, for example, lithium niobate (LiNbO). ３ (LN)), Lithium tantalate (LiTaO) ３ (LT)), a solid solution of lithium niobate and lithium tantalate. In this case, the direction normal to the main surface of the functional layer 21a is LiNbO ３ When consisting of (LN), it is preferable to use one that is rotated 37.8° from the Z-axis to the -Y-axis around the X-axis, which is the propagation direction of the surface acoustic wave, i.e., one that is (0°, 37.8°, 0°) in Euler angle notation, because it results in a large electromechanical coupling coefficient. Also, if the functional layer 21a is LiTaO ３When the substrate is made of (LT), it is preferable to use a substrate cut in a direction rotated by 32° to 50° from the Y axis to the Z axis around the X axis, which is the propagation direction of surface acoustic waves, that is, a substrate with Euler angles of (180°, 58° to 40°, 180°), because this results in low propagation loss. It should be noted that materials used for the functional layer 21a are not limited to these; quartz, sapphire, gallium arsenide (GaAs), silicon carbide (SiC), gallium nitride (GaN), zinc oxide (ZnO), solid solution ceramics (PZT) and the like are appropriately selected.

[0013] For the thickness of the functional layer 21a, for example, the lower limit can be set to 100 nm or more, preferably 300 nm or more, and the upper limit can be set to 20000 nm or less, preferably 2000 nm or less. The thickness of the functional layer 21a is appropriately set according to the function exhibited by the functional layer 21a.

[0014] The covering layer 22 covers the entire peripheral surface of the support substrate 23. Here, "covers the entire peripheral surface" means that the upper and lower surfaces and the entire side surface are covered by the covering layer 22. In other words, due to the covering layer 22, there is no exposed portion of the support substrate 23 including the beveling region 12. The material of the covering layer 22 is determined by the combination of the functional layer 21a and the support substrate 23. According to the combination of the functional layer 21a and the support substrate 23, silicon oxide (SiO ２ ), tantalum pentoxide (Ta ２ O ５ ), and SiCN can be used. Further, depending on the combination of the functional layer 21a and the support substrate 23, niobium oxide (Nb ２ O ５ ), aluminum oxide (Al ２ O ３ ), aluminum nitride (AlN), silicon nitride (Si ３ N ４ ), hafnium oxide (HfO ２ ), etc. can also be used.

[0015] The thickness (T) of the coating layer 22 between the functional layer 21a and the support substrate 23 can be, for example, 1 μm or more and 30 μm or less. If the thickness (T) between the functional layer 21a and the support substrate 23 is less than 1 μm, exposed portions are likely to occur on the support substrate 23. Also, if the thickness (T) between the functional layer 21a and the support substrate 23 exceeds 30 μm, the performance of the functional layer 21a is likely to deteriorate. The ratio T / t of the thickness (T) between the functional layer 21a and the support substrate 23 to the thickness (t) of the side portion of the coating layer 22 can be 0.995 or more and 1.05 or less. If T / t is within this range, the thickness (T) of the coating layer 22 is likely to be uniform, and if it is outside this range, the thickness (T) of the coating layer 22 is likely to be uneven. The thickness between the functional layer 21a and the support substrate 23 (T) / the thickness of the side portion (t) can be, for example, 1.00 μm / 1.02 μm, 5.01 μm / 5.02 μm, or 9.99 μm / 9.97 μm. In this case, T / t will be 0.980, 0.998, and 1.02, respectively.

[0016] The support substrate 23 serves as the support for the entire composite substrate 1. The support substrate 23 is covered by the coating layer 22 and supports the functional layer 21a and the coating layer 22. Any suitable substrate can be used as the support substrate 23. The support substrate 23 may be composed of a single crystal, a polycrystalline material, or a composite in which a polycrystalline layer is provided on a single crystal.

[0017] The materials constituting the support substrate 23 are preferably silicon (Si), glass, sapphire, quartz glass, crystal, or silicon carbide (SiC). However, it is not limited to these, and may also be Sialon, cordierite, mullite, alumina, SUS, iron-nickel alloy (42 alloy), brass, etc. The outer diameter of the support substrate 23 is, for example, 4 inches or more and 12 inches or less, and the thickness is, for example, 200 μm or more and 1000 μm or less, but any other appropriate thickness can be adopted. When the support substrate 23 is silicon (Si), it is preferable that the resistivity is 1000 Ω / m or more. This improves the RF (Radio Frequency) characteristics when the composite substrate 1 is used to manufacture high-frequency devices such as surface acoustic wave filters (SAW (Surface Acoustic Wave) filters) or optical modulators.

[0018] As shown in Figures 2(a) to (b), the beveling region 12 is formed on the outer periphery of the composite substrate 1, extending from the functional layer 21a to a portion of the coating layer 22. In other words, the beveling region 12 is formed by removing the entire outer periphery of the functional layer 21a in the thickness direction, and for the outer periphery of the coating layer 22, removing a portion of the upper part in the thickness direction as shown in the figure, while leaving the lower part as is. The beveling region 12 may be stepped or curved. Furthermore, it may be inclined or may be a stepped shape composed of multiple steps. Among these, the stepped shape shown in Figures 2(a) to (b) is preferred. As shown in Figure 2(b), if the width of the beveling region 12 is defined as the beveling width, the beveling width can be 1 mm or more and 4 mm or less. If the beveling width is less than 1 mm, an unadhered area is likely to remain on the outer periphery. On the other hand, if the beveling width exceeds 4 mm, the effective area 13 that can be used as a device is reduced too much. Furthermore, as shown in Figure 2(b), if the amount removed in the lamination direction of the functional layer 21a and the coating layer 22 is defined as the beveling depth, it is preferable that the beveling depth be 1 μm or more. If the beveling depth is less than 1 μm, the functional layer 21a may not be sufficiently removed. The ratio T / T' of the thickness (T') in the beveling region 12 (shown as the coating layer thickness (T') in Figure 2(b)) and the thickness (T) between the functional layer 21a and the support substrate 23 (shown as the coating layer thickness (T) in Figure 2(b)) can be 1.1 or more and 200 or less. It is also preferable that T / T' be 1.33 or more and 20 or less. If T / T' is less than 1.1, an unbonded area may remain depending on the mechanical tolerance. On the other hand, if T / T' exceeds 200, there is a possibility of cracking or breakage during heating (heating process such as Figure 8(f) described later).

[0019] Figures 3(a) and 3(b) show a conventional composite substrate. Of these, the composite substrate 2 shown in Figure 3(a) has a structure in which a functional layer 21a, an intermediate layer 22A, and a support substrate 23 are laminated. The intermediate layer 22A is made of the same material as the coating layer 22. Compared to the composite substrate 1 shown in Figure 2(a), the composite substrate 2 shown in Figure 3(a) has a beveled region 12 formed on the outer periphery of the composite substrate 2, extending from the functional layer 21a and intermediate layer 22A to a part of the support substrate 23. In other words, the composite substrate 2 shown in Figure 3(a) has a beveled region 12 that extends to a deeper area than the composite substrate 1 shown in Figure 2(a). In this case, the support substrate 23 is exposed by the beveled region 12.

[0020] Furthermore, the composite substrate 3 shown in Figure 3(b) has a structure in which a functional layer 21a, a coating layer 22, and a support substrate 23 are laminated, similar to the composite substrate 1 shown in Figure 2(a). On the other hand, in the composite substrate 2 shown in Figure 3(b), compared to the composite substrate 1 shown in Figure 2(a), the beveling region 12 is formed on the outer periphery of the composite substrate 3, extending from the functional layer 21a and the coating layer 22 to a part of the support substrate 23. In other words, in the composite substrate 2 shown in Figure 3(a), the beveling region 12 is formed in a deeper region compared to the composite substrate 1 shown in Figure 2(a). In this case as well, similar to the case in Figure 3(a), the support substrate 23 is exposed by the beveling region 12.

[0021] In the structures shown in Figures 3(a) and 3(b), the beveling region 12 exposes the support substrate 23, making it susceptible to damage to the exposed portion of the support substrate 23 when polishing the functional layer 21a, for example. In this case, contamination caused by the damage can lead to reduced yield and decreased device performance when processing the functional layer 21a by polishing, etching, or ion implantation. In the composite substrate 1 shown in Figure 2(a), a coating layer 22 is provided, covering the support substrate 23 without exposing it. This suppresses damage when polishing the functional layer 21a, for example. As a result, reduced yield and decreased device performance are less likely to occur when processing the functional layer 21a.

[0022] For example, when polishing the functional layer 21a, damage is most likely to occur around the beveling region 12, so it is not necessarily required to provide the coating layer 22 in the areas excluding this region.

[0023] Figure 4 shows a modified example of the composite substrate 1 in the first embodiment. The composite substrate 1 shown in Figure 4 has a structure in which a functional layer 21a, a coating layer 22, and a support substrate 23 are laminated, similar to the composite substrate 1 shown in Figure 2(a). On the other hand, in the composite substrate 2 shown in Figure 4, compared to the composite substrate 1 shown in Figure 2(a), the coating layer 22 does not cover the side or bottom portions of the support substrate 23, but only covers the main surface on the functional layer 21a side. As a result, the beveling region 12 of the support substrate 23 is covered by the coating layer 22, making the damage described above less likely to occur. In other words, the coating layer 22 only needs to cover the main surface on the functional layer 21a side of the support substrate 23. However, it is more preferable for the coating layer 22 to cover the entire circumferential surface of the support substrate 23, as shown in Figure 2(a). This makes it possible to suppress deformation of the composite substrate 1 due to film stress.

[0024] [Second Embodiment] Figures 5(a) and 5(b) show a composite substrate 1 according to the second embodiment. Of these, Figure 5(a) is a schematic diagram showing the layer structure of the composite substrate 1 according to the second embodiment. Figure 5(b) is a diagram that further explains the outer periphery of the composite substrate 1. The composite substrate 1 according to the second embodiment shown in Figures 5(a) and 5(b) differs from the composite substrate 1 according to the first embodiment shown in Figure 2(a) in that it has a stepped portion 23a on the outer periphery of the support substrate 23. The stepped portion 23a can have a shape similar to the step formed by the beveling region 12. In this case, the thickness of the outer periphery of the support substrate 23 is smaller than the thickness of the central portion. By providing such a stepped portion 23a, the step can be created without considering the thickness of the functional layer 21a, and production can be carried out efficiently. In this case, the thickness of the coating layer 22 in the beveling region 12 (T'') and the thickness between the functional layer 21a and the support substrate 23 (T) can be set to T / T'' of 0.95 or more and 1.06 or less. When T / T'' is within this range, the stress difference due to the film thickness is reduced, and wafer deformation can be suppressed.

[0025] [Third Embodiment] Figure 6 shows the composite substrate 1 of the third and fourth embodiments. The composite substrate 1 shown in Figure 6 differs from the composite substrate 1 of the first embodiment shown in Figure 2(a) in that it has an electron trapping layer 24 that traps electrons on the main surface of the support substrate 23 on the functional layer 21a side. In the third embodiment, the electron trapping layer 24 is made of polycrystalline silicon (polysilicon). By providing the electron trapping layer 24, for example, when the composite substrate 1 is used to manufacture a surface acoustic wave filter (SAW filter), the RF characteristics are improved.

[0026] [Fourth Embodiment] In the fourth embodiment, the composite substrate 1 is made of amorphous silicon for the electron trapping layer 24. This provides the same effects as in the third embodiment. In the third and fourth embodiments, the electron trapping layer 24 is preferably 5 nm or more and 2000 nm or less in thickness. Furthermore, the electron trapping layer 24 is more preferably 50 nm or more and 500 nm or less in thickness. If the thickness of the electron trapping layer 24 is less than 5 nm, the electron trapping effect will not be fully exhibited. If the thickness of the electron trapping layer 24 exceeds 2000 nm, the manufacturing cost will increase.

[0027] [Fifth Embodiment] Figure 7 shows a composite substrate 1 according to the fifth embodiment. The composite substrate 1 of the fifth embodiment is one in which a protective layer 25 is further provided compared to the composite substrate 1 of the first embodiment. In this case, the protective layer 25 is formed on the main surface of the functional layer 21a on the support substrate 23 side. The protective layer 25 is made of the same material as the coating layer 22 and is bonded to the coating layer 22. As will be described in detail later, the functional layer 21a and the support substrate 23 are bonded by activating the main surfaces that form the bonding surface of both with plasma. By providing the protective layer 25 and activating the protective layer 25 with plasma, no plasma damage remains on the main surface of the functional layer 21a on the support substrate 23 side. The thickness of the protective layer 25 can be 0.1 μm or more and 5 μm or less. If the thickness of the protective layer 25 is less than 0.1 μm, there is a possibility that the protective layer 25 will be completely polished away during the bonding surface polishing process (the bonding surface polishing process shown in Figure 12(c) later). If the thickness of the protective layer 25 exceeds 5 μm, the wafer on which the protective layer 25 is formed (the functional layer wafer 21 described later) will warp due to film stress, making it impossible to perform post-processing after the formation of the protective layer 25.

[0028] In the first to fifth embodiments described above, a coating layer 22 is formed on the support substrate 23, and the beveling region 12 is not formed all the way to the support substrate 23, but only on a portion of the coating layer 22. This prevents the support substrate 23 from being exposed and suppresses damage to the support substrate 23.

[0029] <Device> The structure of the composite substrate 1 shown in the figure can be used as the structure of various devices. Examples of devices include high-frequency devices, power semiconductors, semiconductor lasers, surface acoustic wave filters (SAW filters), optical modulation devices, thin-film piezoelectric MEMS (Micro Electro Mechanical Systems), etc.

[0030] <Description of Method for Manufacturing Composite Substrate 1> Next, a method for manufacturing composite substrate 1 will be described. FIGS. 8(a) to 8(h) are diagrams illustrating the method for manufacturing composite substrate 1 according to the first embodiment. First, a functional layer wafer 21 that serves as a base of the functional layer 21a and a supporting substrate 23 are prepared (1. Substrate preparation step, FIG. 8(a)). Here, as the functional layer wafer 21, a substrate having a diameter of 4 inches or more and 12 inches or less and a thickness of 100 μm or more and 500 μm or less is prepared. Also, as the supporting substrate 23, a substrate having the same diameter as that of the functional layer wafer 21 and a thickness of 100 μm or more and 2000 μm or less is prepared. It is assumed herein that the functional layer wafer 21 is LN and the supporting substrate 23 is Si.

[0031] Next, the supporting substrate 23 is thermally oxidized to form a coating layer 22 on the entire circumferential surface of the supporting substrate 23 (2. Thermal oxidation step, FIG. 8(b)). Here, the surface of the supporting substrate 23 made of Si is oxidized to form SiO ２ 2, thereby forming the coating layer 22. Dry oxygen is used as the oxidizing atmosphere when performing thermal oxidation (dry oxidation); if necessary, oxygen added with water vapor (wet oxidation) or hydrochloric acid (hydrochloric acid oxidation) is used. The coating layer 22 is configured to have a thickness of 5 μm or more and 20 μm or less.

[0032] Further, the main surfaces serving as bonding surfaces of the functional layer wafer 21 and the coating layer 22 are polished (3. Bonding surface polishing step, FIG. 8(c)). Here, the bonding surfaces are polished such that the arithmetic mean height (Sa) is 1.0 nm or less. This improves the bonding strength in the subsequent bonding step (step 4). It is more preferable to set the arithmetic mean height (Sa) to 0.2 nm or less. Setting the arithmetic mean height (Sa) to 0.2 nm or less significantly improves the bonding strength. FIG. 8(c) shows the case where the arithmetic mean height (Sa) is set to 0.2 nm.

[0033] Next, the bonding surfaces of the functional layer wafer 21 and the covering layer 22 are respectively bonded (4. Bonding step, FIG. 8(d)). The bonding method is not particularly limited, and can be performed by, for example, Surface Activated Bonding (SAB) or Plasma Activated Bonding (PAB), but it is preferably performed by Plasma Activated Bonding (PAB). In the case of plasma activated bonding, a plasma activation treatment is performed to activate at least one of the respective bonding surfaces of the functional layer wafer 21 and the covering layer 22 with plasma. Examples of gases used for generating plasma include Ar, O ２ , N ２ , H ２ O, H ２ and combinations thereof. At this time, for example, the pressure during activation is set to 1 Pa or more and 100 Pa or less, and the temperature is set to 30°C or more and 100°C or less. Further, the plasma irradiation energy is set to 100 W or more and 500 W or less. Then, bonding is performed in atmospheric pressure or vacuum. When bonding in vacuum, the pressure is 1.0×10 －７ Pa or more and 1.0×10 －１ Pa or less. Then, the respective bonding surfaces are brought into contact with each other and pressed at a predetermined pressure. Thereby, the functional layer wafer 21 and the supporting substrate 23 are bonded via the covering layer 22.

[0034] Next, the main surface opposite to the bonding surface of the functional layer wafer 21 is ground (5. Grinding step, FIG. 8(e)). In this case, the functional layer wafer 21 is thinned to a thickness of 3 μm or more and 30 μm or less. Grinding can be performed by a known method using a grinding machine. In FIG. 8(e), the portion removed by grinding is indicated by a dotted line.

[0035] Next, the bonded functional layer wafer 21 and supporting substrate 23 are heated (6. Heating step, FIG. 8(f)). Heating is performed, for example, at a temperature of 100°C or more and 250°C or less for 1 hour or more and 10 hours or less.

[0036] Furthermore, the outer periphery of the functional layer wafer 21 and the support substrate 23, which are joined via the coating layer 22, is ground from the functional layer wafer 21 to a portion of the coating layer 22 to form a beveling region 12 (7. Outer Peripheral Grinding Process, Figure 8(g)). At this time, the beveling width is set to be between 1 mm and 4 mm, and the roughness after grinding is set to be between 100 nm and 500 nm in arithmetic mean height (Sa). The grinding depth of the coating layer 22 is adjusted so that the ratio T / T' of the thickness in the beveling region 12 (T') to the thickness between the functional layer 21a and the support substrate 23 (T) is between 1.33 and 20. Grinding can be performed, for example, by a grinding device that rotates a disc-shaped grinding wheel at high speed, and moves the grinding wheel along the sides while bringing it into contact with the sides of the functional layer wafer 21 and the coating layer 22 to grind the outer periphery. In Figure 8(g), the areas to be removed by grinding are indicated by dotted lines.

[0037] Then, the main surface of the functional layer wafer 21 is polished to the desired thickness to form the functional layer 21a (8. Polishing (thinning) process, Figure 8(h)). At this time, the thickness of the functional layer 21a is set to be between 100 nm and 2000 nm. Polishing can be performed by a known method using a polishing machine. In Figure 8(h), the areas to be removed by polishing are indicated by dotted lines. This allows the composite substrate 1 to be manufactured.

[0038] Figures 9(a) to 9(h) illustrate the manufacturing method of the composite substrate 1 according to the second embodiment. The manufacturing method of the composite substrate 1 shown in Figure 9 differs from the manufacturing method of the composite substrate 1 shown in Figure 8 in the position of the outer peripheral grinding step. Specifically, the outer peripheral grinding step is added after the substrate preparation step, resulting in the following sequence: 1. Substrate preparation step (Figure 9(a)) → 2. Outer peripheral grinding step (Figure 9(b)) → 3. Thermal oxidation step (Figure 9(c)) → 4. Bonding surface polishing step (Figure 9(d)) → 5. Bonding step (Figure 9(e)) → 6. Grinding step (Figure 9(f)) → 7. Heating step (Figure 9(g)) → 8. Polishing (thinning) step (Figure 9(h)).

[0039] 2. In the outer peripheral grinding process, the beveling width shall be 2 mm or more and 4 mm or less, and the roughness after grinding shall be 100 nm or more and 500 nm or less in arithmetic mean height (Sa). In this order, the beveling region 12 of the coating layer 22 is formed in advance in 2. outer peripheral grinding process (Figure 9(b)) and 3. thermal oxidation process (Figure 9(c)). Also, a stepped portion 23a with a shape similar to the step formed by the beveling region 12 is formed on the support substrate 23. Then, in the final 8. polishing (thinning) process (Figure 9(h)), the outer peripheral portion of the functional layer 21a is removed during polishing, and the beveling region 12 of the functional layer 21a is formed. In the bonding surface polishing process, the bonding surface is polished so that the arithmetic mean height (Sa) is 1.0 nm or less. It is more preferable that the arithmetic mean height (Sa) be 0.2 nm or less. Furthermore, the grinding process thins the film to a thickness of 3 μm to 20 μm.

[0040] Figures 10(a) to 10(i) illustrate the manufacturing method of the composite substrate 1 according to the third embodiment. The manufacturing method of the composite substrate 1 shown in Figure 10 differs from the manufacturing method of the composite substrate 1 shown in Figure 8 in that 2. a polysilicon film deposition process is added after 1. the substrate preparation process, but otherwise it is the same. That is, the order is 1. Substrate preparation process (Figure 10(a)) → 2. Polysilicon film deposition process (Figure 10(b)) → 3. Thermal oxidation process (Figure 10(c)) → 4. Bonding surface polishing process (Figure 10(d)) → 5. Bonding process (Figure 10(e)) → 6. Grinding process (Figure 10(f)) → 7. Heating process (Figure 10(g)) → 8. Outer edge grinding process (Figure 10(h)) → 9. Polishing (thin film formation) process (Figure 10(i)).

[0041] 2. The polysilicon film deposition process involves depositing a polycrystalline silicon (polysilicon) film as an electron trapping layer 24 on the main surface of the support substrate 23 on the bonding surface side. At this time, the polycrystalline silicon (polysilicon) film is deposited with a thickness of 1 μm or more and 3 μm or less. The method of depositing the polycrystalline silicon (polysilicon) film is not particularly limited and any film deposition method such as sputter deposition, ion-assisted deposition, or CVD (Chemical Vapor Deposition) may be used.

[0042] Figures 11(a) to 11(i) illustrate the manufacturing method of the composite substrate 1 according to the fourth embodiment. The manufacturing method of the composite substrate 1 shown in Figure 11 differs from the manufacturing method of the composite substrate 1 shown in Figure 8 in that a laser irradiation step is added after the thermal oxidation step, 2. The other difference is that the steps are as follows: 1. Substrate preparation step (Figure 11(a)) → 2. Thermal oxidation step (Figure 11(b)) → 3. Laser irradiation step (Figure 11(c)) → 4. Bonding surface polishing step (Figure 11(d)) → 5. Bonding step (Figure 11(e)) → 6. Grinding step (Figure 11(f)) → 7. Heating step (Figure 11(g)) → 8. Outer peripheral grinding step (Figure 11(h)) → 9. Polishing (thinning) step (Figure 11(i)).

[0043] 3. The laser irradiation step involves irradiating the main surface of the support substrate 23 on the bonding surface side with a laser to form a modified layer of Si constituting the support substrate 23. In this case, the Si constituting the support substrate 23 becomes amorphous, forming amorphous silicon (a-Si), which is the modified layer. This amorphous silicon functions as the electron trapping layer 24. The laser irradiation method can be arbitrary; for example, a pulsed laser can be used. The wavelength of the laser light used is, for example, 300 nm to 1200 nm. The laser energy density is, for example, 1 μJ / cm². ２ 50 μJ / cm or more ２ The following applies. Furthermore, the laser pulse width is between 1 fs and 100 ps.

[0044] Figures 12(a) to 12(h) illustrate the manufacturing method of the composite substrate 1 according to the fifth embodiment. Compared with the manufacturing method of the composite substrate 1 shown in Figure 8, the manufacturing method of the composite substrate 1 shown in Figure 12 includes a 2. film formation step after the 1. preparation step for the functional layer wafer 21 (Figure 12(b)). This allows for the formation of a protective layer 25. Here, the protective layer 25 is made of SiO ２The thickness of the protective layer 25 is set to 0.1 μm or more and 5 μm or less. The method of forming the protective layer 25 is not particularly limited and any method of film formation such as sputter deposition, ion-assisted deposition, or CVD may be used. Furthermore, in step 3, the bonding surface polishing step (Figure 12(c)), the protective layer 25 is polished instead of the functional layer wafer 21. In addition, in step 4, the bonding step (Figure 12(d)), a plasma activation treatment is performed to activate at least one of the bonding surfaces of the protective layer 25 and the coating layer 22 with plasma. Then, the bonding surfaces are brought into contact with each other and pressed with a predetermined pressure under room temperature conditions. As a result, the functional layer wafer 21 and the support substrate 23 are bonded via the protective layer 25 and the coating layer 22. Furthermore, in step 7, the outer peripheral grinding step (Figure 12(g)), the protective layer 25 is also ground. The rest is the same as in Figure 8.

[0045] The manufacturing method of the composite substrate 1 shown in Figures 8 to 12 above can be understood as a manufacturing method of a composite substrate that includes: a coating layer formation step (corresponding to the thermal oxidation step above) in which a coating layer 22 is formed to cover the entire circumferential surface of a support substrate 23 that supports the functional layer 21a; a bonding step in which the functional layer wafer 21, which will be the basis of the functional layer 21a, and the support substrate 23 are bonded together via the coating layer 22; a beveling step (corresponding to the outer periphery grinding step above) in which beveling is performed from the functional layer wafer 21 to a part of the coating layer 22 on the outer periphery of the bonded functional layer wafer 21 and support substrate 23 to form a beveled region 12; and a polishing step (corresponding to the polishing (thinning) step above) in which the functional layer wafer 21 is polished to form the functional layer 21a.

[0046] Here, the manufacturing method of the composite substrate 1 in the second embodiment shown in Figure 9 can be understood as further including a step portion formation step (corresponding to the outer peripheral grinding step in Figure 9) in which the outer peripheral of the support substrate 23 is ground to form a step portion 23a before the coating layer formation step (corresponding to the thermal oxidation step in Figure 9). Furthermore, the manufacturing method of the composite substrate 1 in the third embodiment shown in Figure 10 and the manufacturing method of the composite substrate 1 in the fourth embodiment shown in Figure 11 can be understood as further including an electron capture layer formation step (corresponding to the polysilicon film formation step in Figure 10 and the laser irradiation step in Figure 11) in which an electron capture layer 24 is created on the main surface of the support substrate 23 that is joined to the functional layer wafer 21. And the manufacturing method of the composite substrate 1 in the third embodiment shown in Figure 12 can be understood as further including a protective layer formation step (corresponding to the film formation step in Figure 12) in which a protective layer 25 made of the same material as the coating layer 22 is created on the main surface of the functional layer wafer 21 that is joined to the support substrate 23, before the joining step.

[0047] In the manufacturing method of the composite substrate 1 shown in Figures 8, 10 to 12 above, a coating layer 22 is formed on the support substrate 23, and in the outer peripheral grinding process, the grinding is stopped at a portion of the coating layer 22, without grinding down to the support substrate 23. In the manufacturing method of the composite substrate 1 shown in Figure 9 above, the coating layer 22 is formed on the support substrate 23 after the outer peripheral has been ground. This allows the polishing (thinning) process to be performed without exposing the support substrate 23. As a result, a composite substrate 1 can be provided that can suppress damage to the support substrate 23.

[0048] Furthermore, the manufacturing method of the composite substrate 1 is not limited to the above-described form. For example, the functional layer 21a can be formed by forming a thin film by ion implantation. This is a technique for transferring a thin film from the functional layer wafer 21 to the support substrate 23. Specifically, light ions are implanted into the functional layer wafer 21 at an arbitrary depth to form a fragile layer (ion implantation step). Then, after bonding with the support substrate 23 via the coating layer 22, the fragile layer is peeled off by heating and transferred as the functional layer 21a (transfer step). The ion implantation energy is adjusted so that spontaneous separation occurs by applying heat treatment at an appropriate temperature after bonding.

[0049] (Example 1) In Example 1, the composite substrate 1 of the first embodiment was manufactured by the method shown in Figures 8(a) to (h). A lithium niobate substrate (LN substrate) with a diameter of 4 inches and a thickness of 250 μm was prepared as the functional layer wafer 21 which would form the basis of the functional layer 21a. In addition, a Si substrate with the same diameter as the functional layer wafer 21 and a thickness of 500 μm was prepared as the support substrate 23 (substrate preparation step).

[0050] Next, the support substrate 23 is thermally oxidized, and SiO ２ A coating layer 22 made of the above material was formed on the entire circumferential surface of the support substrate 23 (thermal oxidation process). In this process, the support substrate 23 was thermally oxidized using water vapor (wet oxidation) to make the coating layer 22 10 μm thick. The coating layer 22 on the side surfaces of the support substrate 23 was also made 10 μm thick.

[0051] Furthermore, the main surface that would become the bonding surface between the functional layer wafer 21 and the coating layer 22 was polished (bonding surface polishing step). Here, the bonding surface was polished so that the arithmetic mean height (Sa) was 0.2 nm. Next, the bonding surfaces of the functional layer wafer 21 and the coating layer 22 were bonded (bonding step). Here, bonding was performed in a chamber by plasma-activated bonding (PAB). At this time, H was used as the gas for the plasma activation treatment. ２ Using oxygen (O), the chamber pressure during activation was set to 5 Pa, the plasma irradiation energy to 400 W, and the chamber temperature to 40°C. The bonding was then performed in a vacuum at a pressure of 100 Pa.

[0052] Next, the main surface of the functional layer wafer 21 opposite to the bonding surface was ground to create a thin film (grinding step). In this case, the film was thinned to a thickness of 30 μm. Then, the bonded functional layer wafer 21 and the support substrate 23 were heated (heating step). Heating was performed using a clean oven at a temperature of 150°C for 10 hours.

[0053] Furthermore, the unadhered area on the outer periphery was removed by grinding to form a beveled area 12 (outer periphery grinding step). At this time, the beveling width was set to 2 mm, and the roughness after grinding was set to an arithmetic mean height (Sa) of 100 nm. The grinding depth of the coating layer 22 was adjusted so that the ratio T / T' of the thickness in the beveled area 12 (T') to the thickness between the functional layer 21a and the support substrate 23 (T) was 2.0. Specifically, T' = 5 μm and T = 10 μm. Note that the thickness of the coating layer 22 in the beveled area 12 does not need to be uniform across the entire surface. Finally, the main surface of the functional layer wafer 21 was polished to the desired film thickness to form the functional layer 21a (polishing (thinning) step). The thickness of the functional layer 21a was set to 500 nm. In this way, the composite substrate 1 of the first embodiment was manufactured.

[0054] (Example 2) In Example 2, the composite substrate 1 of the second embodiment was manufactured by the method shown in Figures 9(a) to (h). In this case, after the substrate preparation step, an outer edge grinding step was performed. At this time, the beveling width was set to 2 mm, and the roughness after grinding was set to an arithmetic mean height (Sa) of 100 nm. The coating layer 22 was formed such that the ratio T / T'' of the thickness in the beveling region 12 and the thickness between the functional layer 21a and the support substrate 23 was 1.0. Specifically, T'' = 10 μm and T = 10 μm. The composite substrate 1 of the second embodiment was manufactured in the same manner as in Example 1.

[0055] (Example 3) In Example 3, the composite substrate 1 of the third embodiment was manufactured by the method shown in Figures 10(a) to (i). In this case, a polysilicon film deposition process was performed after the substrate preparation process. At this time, polycrystalline silicon (polysilicon) was deposited on the support substrate 23 to a thickness of 3.0 μm as the electron trapping layer 24. Here, the film deposition was performed by CVD. Then, in the subsequent thermal oxidation process, the support substrate 23 was thermally oxidized so that the coating layer 22 was 2 μm thick. The composite substrate 1 of the third embodiment was manufactured by proceeding in the same manner as in Example 1.

[0056] (Example 4) In Example 4, the composite substrate 1 of the fourth embodiment was manufactured by the method shown in Figures 11(a) to (i). In this case, a laser irradiation step was performed after the thermal oxidation step. At this time, the wavelength of the laser was 350 nm and the energy density was 20 J / cm². ２ The thickness of the electron trapping layer 24, which is made of amorphous silicon, was set to 10 nm. The composite substrate 1 of the fourth embodiment was manufactured in the same manner as in Example 1.

[0057] (Example 5) In Example 5, the composite substrate 1 was manufactured in the same manner as in Example 1, except that the functional layer 21a and the functional layer wafer 21 were made of sapphire instead of LN.

[0058] (Example 6) In Example 6, the composite substrate 1 of the fifth embodiment was manufactured by the method shown in Figures 12(a) to (h). In this case, a film deposition process was performed on the functional layer wafer 21 after the preparation process to form a protective layer 25. At this time, as the protective layer 25, SiO was applied to the functional layer wafer 21. ２ A film was deposited to a thickness of 200 nm. In this case, the film was deposited by CVD. Then, the composite substrate 1 of the fifth embodiment was manufactured in the same manner as in Example 1.

[0059] (Comparative Example 1) A composite substrate was manufactured in the same manner as in Example 1, except that the thermal oxidation process was eliminated and the coating layer 22 was not formed.

[0060] (Results) In the composite substrates 1 of Examples 1 to 6, it was confirmed that no peeling occurred between the functional layer 21a and the support substrate 23, and that the outer peripheral removal surface was the coating layer 22. It was also confirmed that no damage occurred to the support substrate 23. In contrast, in the composite substrate of Comparative Example 1, damage sometimes occurred to the support substrate 23.

[0061] Although this embodiment has been described above, the technical scope of the present invention is not limited to the scope described in the above embodiment. It is clear from the claims that various modifications or improvements made to the above embodiment are also included in the technical scope of the present invention.

[0062] 1...Composite substrate, 12...Beveling region, 21...Functional layer wafer, 21a...Functional layer, 22...Coating layer, 23...Support substrate, 23a...Stepped portion, 24...Electron trapping layer, 25...Protective layer

Claims

1. A composite substrate comprising: a functional layer; a support substrate for supporting the functional layer; a coating layer covering at least the main surface of the support substrate on the functional layer side; and a beveling region formed on the outer periphery, extending from the functional layer to a portion of the coating layer.

2. The composite substrate according to claim 1, wherein the coating layer covers the entire circumferential surface of the support substrate.

3. The composite substrate according to claim 1, wherein the thickness of the coating layer between the functional layer and the support substrate is 1 μm or more and 30 μm or less.

4. The composite substrate according to claim 1, wherein the coating layer has a ratio T / t of the thickness between the functional layer and the support substrate (T) to the thickness of the side portion (t) of the coating layer being 0.995 or more and 1.05 or less.

5. The composite substrate according to claim 1, wherein the ratio T / T' of the thickness (T') of the coating layer in the beveling region to the thickness (T) between the functional layer and the support substrate is 1.33 or more and 20 or less.

6. The composite substrate according to claim 1, wherein the support substrate has a stepped portion on its outer periphery having a shape similar to the step formed by the beveling region.

7. The composite substrate according to claim 6, wherein the ratio T / T'' of the thickness (T'') of the coating layer in the beveling region to the thickness (T) between the functional layer and the support substrate is 0.95 or more and 1.06 or less.

8. The composite substrate according to claim 1, wherein the support substrate has an electron trapping layer on the main surface on the functional layer side for trapping electrons.

9. The composite substrate according to claim 8, wherein the electron trapping layer is made of polycrystalline silicon or amorphous silicon.

10. The composite substrate according to claim 8, wherein the electron trapping layer has a thickness of 50 nm or more and 500 nm or less.

11. The functional layer is LiNbO ３ (LN), LiTaO ３ The composite substrate according to claim 1, comprising any one of (LT), solid solution ceramics, quartz, sapphire, and silicon carbide (SiC).

12. The support substrate is silicon (Si), and the coating layer is silicon oxide (SiO ２ The composite substrate according to claim 1, which is the composite substrate described in claim 1.

13. The composite substrate according to claim 12, wherein the resistivity of the support substrate, which is silicon (Si), is 1000 Ω / m or more.

14. The composite substrate according to claim 1, wherein the functional layer is formed on the main surface on the support substrate side, is made of the same material as the coating layer, and has a protective layer that is bonded to the coating layer.

15. A device comprising a composite substrate according to any one of claims 1 to 14.

16. A method for manufacturing a composite substrate, comprising: a coating layer forming step of forming a coating layer that covers the entire circumferential surface of a support substrate that supports a functional layer; a bonding step of bonding a functional layer wafer, which will be the basis of the functional layer, and the support substrate via the coating layer; a beveling step of performing beveling from the functional layer wafer to a part of the coating layer on the outer periphery of the bonded functional layer wafer and the support substrate to form a beveled region; and a polishing step of polishing the functional layer wafer to form the functional layer.

17. The method for manufacturing a composite substrate according to claim 16, further comprising a step-forming step of grinding the outer periphery of the support substrate to form a stepped portion before the coating layer forming step.

18. The method for manufacturing a composite substrate according to claim 16, further comprising an electron trapping layer formation step of creating an electron trapping layer on the main surface of the support substrate that is joined to the functional layer wafer.

19. The method for manufacturing a composite substrate according to claim 16, further comprising a protective layer formation step, before the bonding step, creating a protective layer on the main surface of the functional layer wafer that is bonded to the support substrate, which is made of the same material as the coating layer and is bonded to the coating layer.

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