Bonded wafer and method for manufacturing the same

Abstract

The objective is to provide a bonded wafer and a method for manufacturing the same that can maintain both sublimation and bonding properties well, by focusing on the thickness of the epitaxial layer, particularly the relationship between the layer thickness that causes wafer warping and the bonding layer / sacrificial layer thickness. [Solution] A bonded wafer comprising a plurality of compound semiconductor layers provided on a starting substrate, a resin layer provided on the plurality of compound semiconductor layers, and an ultraviolet and visible light transparent substrate bonded via the resin layer, wherein the plurality of compound semiconductor layers each have a first compound semiconductor layer having an active layer function and a second compound semiconductor layer which is the uppermost layer bonded to the resin layer, and the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T > 0.3845 × ln(G) - 0.464 and T ≤ 1.0 μm.

Description

[Technical Field]

[0001] The present invention relates to a bonded wafer and a method for manufacturing the same. [Background technology]

[0002] A μ-LED transfer technology is disclosed that separates the epitaxial layer from the support substrate using laser lift-off (LLO) technology. The starting substrate for high-brightness red LEDs is visible light-absorbing GaAs, and LLO is possible by transferring the epitaxial layer to an ultraviolet and visible light-transmitting substrate. When transferring the epitaxial layer to an ultraviolet and visible light-transmitting substrate, direct bonding is possible, but it is preferable to provide a thermal sacrificial layer for LLO to minimize the thermal impact on the epitaxial layer. By combining the thermal sacrificial layer and bonding layer, LLO can be realized without affecting the LED element. A technology is disclosed in which ultraviolet-absorbing benzocyclobutene (BCB) is selected as this bonding layer and sacrificial layer (Patent Document 1).

[0003] Patent Document 2 discloses a technique for bonding an epitaxial wafer on which light-emitting diodes (LEDs) are formed to a substrate of a different material via a BCB (Body Core Block) which serves as both a bonding layer and a sacrificial layer, and then separating only the LEDs from the substrate of the different material by sublimating the bonding layer and sacrificial layer with a laser. When using a bonded wafer to which this technique has been applied, it is necessary to reliably sublimate and remove the BCB by laser sublimation, and the thinner the BCB, the higher the removal efficiency. In other words, from the standpoint of sublimation, the bonding layer and sacrificial layer must be as thin as possible.

[0004] On the other hand, making the bonding layer thinner reduces the adhesive strength, leading to a decrease in the area of ​​the epitaxial layer that is maintained without abnormalities after bonding. In other words, from the perspective of yield after bonding, the bonding layer and sacrificial layer should be as thick as possible.

[0005] In other words, there is a trade-off between the requirements for sublimation properties and the requirements for bonding yield for the bonding layer and sacrificial layer.

[0006] On the other hand, GaP is the layer that primarily causes warping of the epitaxial wafer, and this warping significantly affects bonding performance. In other words, GaP thickness greatly affects bonding performance and bonding yield, so in order to maintain bonding performance, the BCB thickness needs to be adjusted according to the GaP thickness. While Patent Documents 2 to 4 provide examples of GaP thicknesses ranging from 4 to 15 μm, there are no prior documents that disclose the relationship between GaP thickness and BCB thickness from the perspective of maintaining good bonding yield. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-083004 [Patent Document 2] Japanese Patent Publication No. 2024-029034 [Patent Document 3] Japanese Patent Publication No. 2023-163011 [Patent Document 4] International Publication No. 2024 / 034480 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The present invention has been made to solve the above problems, and aims to provide a bonded wafer and a method for manufacturing the same that can maintain both sublimation and bonding properties well, by focusing on the relationship between the thickness of the epitaxial layer, in particular the layer thickness that causes wafer warping, and the bonding layer / sacrificial layer thickness.

[0009] More specifically, in a compound epitaxial bonded substrate in which an epitaxial layer and an ultraviolet and visible light-transmitting substrate are bonded via a thermosetting resin, the present invention discloses conditions for the thickness of the bonding thermosetting resin, which also possesses visible light transmittance, and the thickness of the epitaxial layer that are less likely to cause bonding defects, thereby disclosing a technology that improves bonding yield. In particular, when bonding an epitaxial substrate of a lattice mismatch system in which the warp of the wafer changes depending on the thickness of the epitaxial layer to an ultraviolet and visible light transmissive substrate, a technique for improving the yield is disclosed by restricting the film thicknesses of the visible light transmissive resin and the epitaxial layer. In other words, an object of the present invention is to provide a structure and a manufacturing method thereof that optimize the film thickness of a bonding material and the film thickness of an epitaxial wafer when bonding a compound semiconductor epitaxial wafer and a different substrate with a resin material to improve the yield.

Means for Solving the Problems

[0010] The present invention has been made to achieve the above object, and includes a bonding type wafer having a plurality of compound semiconductor layers provided on a starting substrate, a resin layer provided on the plurality of compound semiconductor layers, and an ultraviolet and visible light transmissive substrate bonded via the resin layer, wherein the plurality of compound semiconductor layers include a first compound semiconductor layer having an active layer function and a second compound semiconductor layer which is the uppermost layer bonded to the resin layer, and the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T>0.3845×ln(G)-0.464 and T≦1.0 μm.

[0011] According to such a bonding type wafer, it is possible to obtain a bonding type wafer having the minimum resin layer thickness corresponding to the thickness of the second compound semiconductor layer. As a result, the good product area after epitaxial layer bonding can be made 70% or more.

[0012] At this time, the compound semiconductor layer can include any two or more of Al, Ga, In, P, and As.

[0013] Thereby, it can be applied to various bonding wafers.

[0014] At this time, the resin layer can include at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

[0015] As a result, in addition to substances that cure upon heating, substances that soften upon heating and cure upon cooling can be used as materials.

[0016] At this time, the ultraviolet and visible light transmissive substrate can include any one of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, and GaP.

[0017] Thus, any of the above materials having ultraviolet and visible light transmissivity can be selected.

[0018] At this time, the second compound semiconductor layer can be the thickest layer among the plurality of compound semiconductor layers.

[0019] Thus, the present invention is suitable when there is a thick layer in the uppermost layer such as a window layer or a current diffusion layer.

[0020] At this time, the second compound semiconductor layer can be GaP.

[0021] Since GaP is generally used for semiconductor devices for LED applications, the present invention is suitable.

[0022] The present invention has also been made to achieve the above objective, and provides a method for manufacturing a bonded wafer, comprising the steps of: epitaxially growing a plurality of compound semiconductor layers on a starting substrate; forming a resin layer on the plurality of compound semiconductor layers; and bonding an ultraviolet and visible light transparent substrate to the plurality of compound semiconductor layers via the resin layer, wherein the step of epitaxially growing the plurality of compound semiconductor layers includes the steps of epitaxially growing a first compound semiconductor layer having an active layer function and epitaxially growing a second compound semiconductor layer which is the uppermost layer to be bonded to the resin layer, and in the step of forming the resin layer, the resin layer is formed such that the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T>0.3845×ln(G)-0.464 and T≦1.0μm.

[0023] According to this method for manufacturing bonded wafers, it is possible to manufacture bonded wafers having a minimum resin layer thickness corresponding to the thickness of the second compound semiconductor layer. This makes it possible to achieve a good product area of ​​70% or more after epitaxial layer bonding.

[0024] In this case, the compound semiconductor layer can be made of a material containing two or more of Al, Ga, In, P, and As.

[0025] This allows the method to be applied to various types of bonded wafers.

[0026] In this case, the resin layer may be made of a material containing at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, or polyimide.

[0027] This allows for the use of materials that harden with heating, as well as materials that soften with heat and harden with cooling.

[0028] In this case, the ultraviolet and visible light transmitting substrate can be made of any of the following materials: sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP.

[0029] This allows for the selection of either of the above materials that transmit ultraviolet light or visible light.

[0030] In this case, the second compound semiconductor layer can be the thickest layer among the plurality of compound semiconductor layers.

[0031] Thus, the present invention is suitably applicable when the uppermost layer, such as a window layer or current diffusion layer, is thick.

[0032] In this case, the second compound semiconductor layer can be GaP.

[0033] Since GaP is commonly used in semiconductor devices for LED applications, the present invention is suitable. [Effects of the Invention]

[0034] As described above, the bonded wafer of the present invention allows for the formation of a thermosetting resin film with a minimum thickness, while simultaneously improving the sublimation performance of the thermosetting resin when sublimated by laser irradiation, reducing the amount of thermosetting resin residue, and enabling a bonded product area of ​​70% or more relative to the bonded area after bonding.

[0035] Furthermore, according to the method for manufacturing bonded wafers of the present invention, it is possible to form a thermosetting resin film with a minimum thickness, improve the sublimation properties of the thermosetting resin when sublimating it by laser irradiation, reduce the amount of thermosetting resin residue, and make it possible to achieve a bonded product area of ​​70% or more of the bonded area after bonding. [Brief explanation of the drawing]

[0036] [Figure 1]A schematic diagram of an example of the bonded wafer of the present invention is shown. [Figure 2] A schematic diagram of an example of a bonded wafer according to an embodiment of the present invention is shown. [Figure 3] A schematic diagram of the manufacturing process for the bonded wafer in the example is shown. [Figure 4] A schematic diagram of the manufacturing process for the bonded wafer in the example is shown. [Figure 5] A schematic diagram of the processing stages of a bonded wafer in a reference example is shown. [Figure 6] A schematic diagram of the processing stages of a bonded wafer in a reference example is shown. [Figure 7] A schematic diagram of the processing stages of a bonded wafer in a reference example is shown. [Figure 8] A schematic diagram of the processing stages of a bonded wafer in a reference example is shown. [Figure 9] This shows the relationship between the area yield between the GaP layer thickness and the BCB layer thickness according to the present invention. [Modes for carrying out the invention]

[0037] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0038] As described above, there was a need for a bonded wafer and a method for manufacturing the same that could maintain both sublimation and bonding properties, focusing on the relationship between the thickness of the epitaxial layer, particularly the layer thickness that causes wafer warping, and the thickness of the bonding layer and sacrificial layer.

[0039] As a result of diligent study on the above problems, the present inventors have found that a bonded wafer having a plurality of compound semiconductor layers provided on a starting substrate, a resin layer provided on the plurality of compound semiconductor layers, and an ultraviolet and visible light transparent substrate bonded via the resin layer, wherein the plurality of compound semiconductor layers have a first compound semiconductor layer having an active layer function and a second compound semiconductor layer which is the uppermost layer bonded to the resin layer, and the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T>0.3845×ln(G)-0.464 and T≦1.0μm, thereby enabling the formation of a thermosetting resin film with a minimum thickness, improving the sublimation performance of the thermosetting resin when sublimating the thermosetting resin by laser irradiation, reducing the amount of thermosetting resin residue, and making it possible to achieve a good product range of 70% or more of bond defects after bonding, thus completing the present invention.

[0040] The present inventors have also conducted extensive research on the above-mentioned problems and have come up with a method for manufacturing a bonded wafer, comprising the steps of: epitaxially growing a plurality of compound semiconductor layers on a starting substrate; forming a resin layer on the plurality of compound semiconductor layers; and bonding an ultraviolet and visible light transparent substrate to the plurality of compound semiconductor layers via the resin layer, wherein the step of epitaxially growing the plurality of compound semiconductor layers comprises the steps of epitaxially growing a first compound semiconductor layer having an active layer function and epitaxially growing a second compound semiconductor layer which is the uppermost layer bonded to the resin layer. A method for manufacturing a bonded wafer, comprising the step of forming the resin layer, wherein the resin layer is formed such that the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T > 0.3845 × ln(G) - 0.464 and T ≤ 1.0 μm, has been found to be able to form a thermosetting resin film with a minimum thickness, improve the sublimation performance of the thermosetting resin when sublimating the thermosetting resin by laser irradiation, reduce the amount of residue of the thermosetting resin, and make it possible to reduce the good area of ​​bonded products to 70% or more after bonding, thus completing the present invention.

[0041] Hereinafter, a bonded wafer and a method for manufacturing a bonded wafer according to an embodiment of the present invention will be described using a wafer for LED (μLED) applications as an example.

[0042] (Bonded wafer) Figure 1 shows a schematic diagram of an example of a bonded wafer of the present invention. As shown in Figure 1, the bonded wafer 1 of the present invention is a bonded wafer 1 having a plurality of compound semiconductor layers 3 provided on a starting substrate 2, a resin layer 4 provided on the plurality of compound semiconductor layers 3, and an ultraviolet and visible light transparent substrate 5 bonded via the resin layer 4, wherein the plurality of compound semiconductor layers 3 have a first compound semiconductor layer 3a having an active layer function and a second compound semiconductor layer 3b which is the uppermost layer bonded to the resin layer 4.

[0043] In this case, the compound semiconductor layer 3 may contain two or more of the following elements: Al, Ga, In, P, and As. These are commonly used, and this allows the above relationships to be applied to various types of bonded wafers. The same applies to the method for manufacturing bonded wafers according to the present invention, which will be described later.

[0044] In this case, the second compound semiconductor layer 3b can be the thickest of the multiple compound semiconductor layers 3. Thus, the present invention is suitable when the uppermost layer has a thick layer, such as a window layer or current diffusion layer. This is also true for the method of manufacturing a bonded wafer according to the present invention, which will be described later.

[0045] Figure 2 shows a schematic diagram of an example of a bonded wafer according to an embodiment of the present invention. As shown in Figure 2, the bonded wafer 10 according to an embodiment of the present invention is an epitaxial substrate in which a first conductivity type GaAs buffer layer (not shown) made of the same material as the starting substrate 2, a GaInP / GaAs etching stop layer 11, an AlGaInP-based epitaxial light-emitting functional layer (AlGaInP lower cladding layer 12, AlGaInP active layer 13, AlGaInP upper cladding layer 14, GaInP intermediate layer (not shown), GaP window layer (window layer) 15), a resin layer 4, and a light-emitting functional layer 5 that transmits ultraviolet and visible light are laminated on a first conductivity type GaAs starting substrate 2.

[0046] The starting substrate 2 is not limited to GaAs; any substrate that can be epitaxially grown can be selected. For example, a buffer layer such as Ge may be grown on the starting substrate (Si), a first GaAs buffer layer, a sacrificial layer such as AlAs, and a second GaAs buffer layer may be grown on top of that, and then the epitaxial functional layer may be grown on top of that. Although a configuration with a Ge layer has been shown, the same effect can be obtained without the Ge layer. Alternatively, Ge itself may be used as the starting substrate 2. Furthermore, the starting substrate 2 is preferably (001) plane.

[0047] Although cladding layers 12 and 14 are described together, the doping level is not limited to a single level. It is possible to have two or more levels of doping, or to have a gradient doping pattern, or to have a doping profile that combines the above. Furthermore, the cladding layer is not limited to a single composition; it may consist of two or more different compositions.

[0048] The active layer 13 is not limited to a single composition and may have a so-called multiple quantum well structure having a barrier layer and a well layer, and the thickness of the barrier layer and / or the well layer may be 10 nm or more, which is the thickness at which quantum effects are low. In this embodiment, an emissive layer is used as an example, but the present invention is not limited to this, and may include, for example, a layer having a light-receiving function.

[0049] When an AlGaInP-based epitaxial functional layer is used in an LED structure, it is common to form a window layer on the light-emitting layer made of AlGaInP-based material, and GaP is generally selected as the material for this window layer. GaP and AlGaInP-based materials have a large lattice mismatch, and therefore, epitaxial wafers with an AlGaInP-based epitaxial functional layer exhibit warping (BOW) due to this lattice mismatch.

[0050] The window layer 15 is literally a layer that acts as a window for light extraction. The thicker the window layer 15, the higher the external quantum efficiency, so the thicker the window layer 15, the better the function as a light-emitting element. In this embodiment, GaP is the window layer 15, and in this case, the lattice mismatch compared to the material from the starting substrate 2 to the upper cladding layer 14 is large at approximately 3.7%. Therefore, warping occurs in the wafer after epitaxial growth is complete. This warping tends to increase as the thickness of the GaP window layer 15 increases. For example, in the case of a 4-inch wafer, if the thickness of the GaP window layer 15 is 4 μm, the warp (BOW) is 60-70 μm, and if it is 10 μm, the warp (BOW) is about 100-120 μm.

[0051] As the resin layer 4, a thermosetting resin is used, but it is not limited to a substance that hardens upon heating. It may also include a substance that has a glass transition temperature, softens upon heat, and hardens upon cooling. Therefore, it is acceptable as long as it contains at least one of benzocyclobutene (BCB), epoxy resin, wax, silicone, fluororesin [e.g., Cytop® manufactured by AGC Inc.], spin-on glass, or polyimide. This also applies to the method of manufacturing bonded wafers, which will be described later.

[0052] The ultraviolet and visible light transmitting substrate 5 can be any material that transmits ultraviolet and visible light. It may contain any of the following: sapphire, quartz, glass, lithium tantalate (LT), lithium niobate (LN), ZnO, SiC, GaN, or GaP. This also applies to the method of manufacturing bonded wafers, which will be described later.

[0053] Next, we will explain the relationship between the thickness of the resin layer 4 and the second compound semiconductor layer 3b.

[0054] The bonded wafer 1 of the present invention is further characterized in that the relationship between the thickness T of the resin layer 4 and the thickness G of the second compound semiconductor layer 3b satisfies T > 0.3845 × ln(G) - 0.464 and T ≤ 1.0 μm.

[0055] According to this relationship, if the second compound semiconductor layer 3b (GaP window layer 15) is thick, the thickness of the resin layer 4 needs to be increased, while if the second compound semiconductor layer 3b (GaP window layer 15) is thin, the thickness of the resin layer 4 can be decreased. By maintaining the above relationship between T and G, a bonded wafer (compound epitaxial bonded substrate) can be made that has the minimum thickness of the resin layer 4 corresponding to the thickness of the second compound semiconductor layer 3b (GaP window layer 15). This makes it possible to achieve a good product area of ​​70% or more after epitaxial layer bonding.

[0056] As mentioned above, in this embodiment, the window layer 15 is GaP. Since GaP and the AlGaInP-based material constituting the active layer 13 have a lattice mismatch of approximately 3.7% at room temperature, the epitaxial wafer exhibits significant warping. Although this warping can be corrected by compression, this is only possible when the substrate is a hard surface; the effect of correcting warping is limited when the substrate is a thermosetting resin before heat curing. Therefore, when bonding an epitaxial wafer with a large lattice mismatch to a different substrate using a thermosetting resin, if the film thickness of the thermosetting resin is too thick, the thermosetting resin layer before curing acts as a cushion layer, resulting in insufficient warping correction of the wafer, thus maintaining the warping, and the warping of the wafer becomes fixed after heat curing. Therefore, while a thicker thermosetting resin improves the bonding yield, there is an upper limit to the applicable thickness of the thermosetting resin from the viewpoint of insufficient warping correction. From the viewpoint of warping correction, the upper limit for the thickness of the resin layer 4 is 1 μm.

[0057] On the other hand, when bonding to a different substrate via a thermosetting resin for μ-LED applications, the μ-LED portion and the thermosetting resin are separated by laser irradiation and sublimation. Sublimation is easier the thinner the thermosetting resin is, and from the viewpoint of sublimation, a thinner thickness is preferable. The lower limit of the film thickness of the resin layer 4 is preferably 0.01 μm or more. A range of 0.01 μm or more and less than 0.1 μm is more preferable in relation to the bonding yield.

[0058] Furthermore, the film thickness in terms of the peelability of the thermosetting resin by laser irradiation and the yield required to maintain a good bonding yield are inversely related to the warp correction of the epitaxial wafer. In this invention, we explored the range of GaP window layer thickness and thermosetting resin film thickness that satisfy both conditions for good peelability of the thermosetting resin by laser irradiation and good bonding yield, while keeping the thickness of the resin layer 4 within the range of 0.01 to 1 μm.

[0059] The minimum required effective area after bonding is 70% or more of the substrate area. A preferred effective area is 90% or more.

[0060] Figure 9 shows the relationship between the area yield between the GaP layer thickness and the BCB layer thickness according to the present invention. In the figure, ○ marks indicate conditions where the area yield exceeds 90%, × marks indicate conditions where the area yield is less than 70%, and △ marks indicate conditions with an intermediate area yield (70-90%). It is shown that when the GaP layer is thick, a thicker BCB layer is more likely to yield a good yield, and when the GaP layer is thin, a good yield can be obtained even with a thin BCB layer.

[0061] To achieve bonding that maintains an effective area of ​​70% or more after bonding, bonding is performed while maintaining the relationship T > 0.3845 × ln(G) - 0.464 (dotted line). The upper limit of T is 1.0 μm, but the thinner the resin layer 4, the higher the sublimation performance during laser sublimation (lower residue generation). Therefore, by forming the resin layer 4 with the minimum film thickness according to the above relationship, both peelability and adhesion can be achieved.

[0062] To achieve bonding that maintains an effective area of ​​90% or more after bonding, it is more preferable to bond while maintaining the relationship T > 0.4033 × ln(G) - 0.4277. The upper limit of T is 1.0 μm, but the thinner the thermosetting resin layer, the higher the sublimation performance (lower residue generation) during laser sublimation processing. Therefore, forming the resin layer 4 with the minimum film thickness according to the above relationship is more preferable for achieving both peelability and adhesion.

[0063] The relationship between the thickness of the resin layer 4 and the second compound semiconductor layer 3b described above is the same in the method for manufacturing a bonded wafer according to the present invention, which will be described later.

[0064] Furthermore, in this invention, the present invention can be suitably used when the lattice mismatch between the first compound semiconductor layer 3a and the second chemical semiconductor layer 3b is 0.5% or more. When the lattice mismatch is 3% or more, the problems become more pronounced, and the effects of using this invention become greater.

[0065] (Method for manufacturing bonded wafers) Next, the method for manufacturing a bonded wafer according to the present invention will be described with reference to Figure 1. The method for manufacturing a bonded wafer according to the present invention is a method for manufacturing a bonded wafer that includes the steps of: epitaxially growing a plurality of compound semiconductor layers 3 on a starting substrate 2; forming a resin layer 4 on the plurality of compound semiconductor layers 3; and bonding an ultraviolet and visible light transparent substrate 5 to the plurality of compound semiconductor layers 3 via the resin layer 4, wherein the step of epitaxially growing a plurality of compound semiconductor layers 3 includes the step of epitaxially growing a first compound semiconductor layer 3a having an active layer function, and the step of epitaxially growing a second compound semiconductor layer 3b which is the uppermost layer to be bonded to the resin layer 4.

[0066] In this embodiment, as shown in Figure 2, a GaAs buffer layer (not shown) of the same material as the starting substrate 2, a GaInP / GaAs etching stop layer 11, and an AlGaInP-based epitaxial light-emitting functional layer (AlGaInP lower cladding layer 12, AlGaInP active layer 13, AlGaInP upper cladding layer 14, GaInP intermediate layer (not shown), GaP window layer 15) are epitaxially grown on a GaAs starting substrate 2 of the first conductivity type, a resin layer 4 is formed thereon, and an ultraviolet and visible light-transmitting substrate 5 is bonded via the resin layer 4. Here, the first compound semiconductor layer 3a is the active layer 13, and the second compound semiconductor layer 3b is the GaP window layer 15.

[0067] For μ-LED applications, the AlGaInP-based light-emitting functional layer is used as a starting substrate 2, which is made of GaAs, Si, Ge, etc., that have ultraviolet and visible light absorbing properties and cannot be used in its original form for μ-LED applications. Therefore, only the epitaxial light-emitting functional layer is transferred onto an ultraviolet and visible light-transmitting substrate 5 for use. After transferring only the epitaxial light-emitting functional layer, the epitaxial light-emitting functional layer is processed to form a μ-LED die.

[0068] The μ-LED die, once processed into the form of a μ-LED die, is separated from the ultraviolet and visible light-transmitting substrate 5 and transferred to the drive substrate. To separate the μ-LED die, a structure is adopted in which the epitaxial functional layer and the ultraviolet and visible light-transmitting substrate 5 are bonded via a resin layer 4, which is a material that is transparent to visible light and has ultraviolet light-absorbing properties, and the material with visible light transparency and ultraviolet light-absorbing properties is used as a sacrificial layer. Since the sacrificial layer has the property of absorbing ultraviolet light, by irradiating the ultraviolet and visible light-transmitting substrate 5 with a laser having an ultraviolet wavelength, the sacrificial layer portion sublimes, and the μ-LED die can be separated from the ultraviolet and visible light-transmitting substrate 5.

[0069] As mentioned above, when an AlGaInP-based epitaxial functional layer is used in an LED structure, it is common to form a window layer on the light-emitting layer made of AlGaInP-based material, and GaP is generally selected as the material for this window layer. GaP and AlGaInP-based materials have a large lattice mismatch, and therefore, warping (BOW) due to lattice mismatch occurs in epitaxial wafers in which the AlGaInP-based epitaxial functional layer and GaP window layer have been epitaxially grown.

[0070] An epitaxial wafer with warping has its warping corrected to some extent by the pressure applied when the thermosetting resin (resin layer 4) is thermocompressed. Although the epitaxial functional layer and the ultraviolet and visible light-transmitting substrate 5 are bonded by the resin layer 4, the stress due to the warping inside the epitaxial functional layer remains, and tensile stress continues to be applied to the resin layer 4. If the adhesion or curing of the resin layer 4 is insufficient, delamination will occur between the epitaxial functional layer and the resin layer 4, or between the resin layer 4 and the ultraviolet and visible light-transmitting substrate 5, resulting in a defective bond.

[0071] One method to improve the curability of thermosetting resins is to increase the curing temperature. However, the warpage of epitaxial wafers tends to increase with rising temperature, and bonding at high temperatures results in bonding while retaining large residual stresses. Therefore, increasing the temperature to improve the curability of thermosetting resins is not generally done, and curing is typically performed using the low to medium temperature range. In the case of benzocyclobutene (BCB), curing is generally performed in the range of 200 to 300°C. The above temperature range is an example and is not limited to this range; curing at 350°C is also possible. However, at this temperature, the residual stress in the epitaxial functional layer becomes large, making delamination more likely. For these reasons, it is difficult to employ a treatment that increases the temperature to improve curability.

[0072] One method to improve adhesion is to increase the thickness of the resin layer 4. Increasing the thickness of the resin layer 4 improves buffering and thus improves adhesion. However, the thermosetting resin is a sacrificial layer used to separate the μ-LED die from the ultraviolet and visible light-transmitting substrate. Increasing the thickness of the thermosetting resin reduces the sublimation rate during laser irradiation, which increases the possibility of thermosetting resin remaining on the μ-LED after laser sublimation, or increases the amount of resin remaining. Therefore, there are limitations to the method of improving adhesion by increasing the thickness of the thermosetting resin. Due to the limitations of the sublimation process, resin layers 4 with a thickness exceeding 1.0 μm are not used.

[0073] From the standpoint of sublimation properties, a thinner resin layer 4 is preferable. However, as mentioned above, reducing the thickness of the resin layer 4 reduces the cushioning properties and thus the adhesion. The minimum film thickness required for bonding without considering the area of ​​bonding defects is preferably 0.01 μm or more.

[0074] The warpage of epitaxial wafers is primarily caused by a large lattice mismatch between GaP and AlGaInP-based materials. The adhesion of the resin layer 4 is greatly influenced by residual stress generated from the epitaxial wafer side during bonding. In other words, the warpage caused by the lattice mismatch constrains the adhesion and optimal film thickness of the resin layer 4. However, there is no prior art regarding the design of the epitaxial functional layer thickness that causes warpage of epitaxial wafers or the constraints on the film thickness of the resin layer 4.

[0075] In the method for manufacturing a bonded wafer of the present invention, in the step of forming the resin layer 4, the resin layer 4 is formed such that the relationship between the thickness T of the resin layer 4 and the thickness G of the second compound semiconductor layer 3b satisfies T > 0.3845 × ln(G) - 0.464 and T ≤ 1.0 μm. The relationship between T and G described above is the same as the relationship explained in the description of the bonded wafer mentioned earlier.

[0076] After epitaxial growth of multiple compound semiconductor layers 3, the fabricated epitaxial wafer is vacuum adsorbed, and a coating film of thermosetting resin is applied by spin coating to form a resin layer 4. A general-purpose spin coater can be used for coating.

[0077] When changing the coating thickness, the film is formed such that the above relationship is satisfied with respect to the thickness of the main semiconductor layer that causes warping in the wafer (in the case of an epitaxial functional layer having an AlGaInP-based light-emitting layer as exemplified in this embodiment, this is the GaP layer).

[0078] When BCB is used as the thermosetting resin, and for example, when CYCLOTENE 3022-35 manufactured by Dow Chemical is used as the BCB raw material, the thickness of the coated film is approximately 1 μm when applied as is. However, by mixing the thinner and BCB solution in a 1:1 ratio, a BCB film with a thickness of 0.5 μm can be obtained. In this way, the concentration and viscosity of the BCB solution can be adjusted by diluting the BCB solution with the thinner, and the film thickness can be freely changed.

[0079] In addition to adjusting the concentration and viscosity, it is also possible to change the film thickness by changing the rotation speed during coating. However, the range of film thickness that can be adjusted by changing the rotation speed is limited to about ±50%, and adjusting the concentration and viscosity is more effective for significantly changing the film thickness. Also, since the uniformity of the coated film decreases at low rotation speeds, it is preferable to perform the coating at 2,000 rpm or higher. However, when using thermosetting resins for bonding, it is possible to produce a certain degree of film thickness uniformity by compression, so this minimum rotation speed is not strictly limited.

[0080] In this embodiment, a method of adjusting the film thickness of the coating by diluting BCB with a thinner to adjust its concentration and viscosity was illustrated. However, this method is not limited to BCB, and the same method can be applied to any coating that can be diluted with a thinner. Epoxy resins, waxes, silicones, fluororesins [e.g., AGC's Cytop®], spin-on glass, and polyimides are also mixed with a liquid equivalent to the aforementioned thinner, and the same method can be used.

[0081] A similar coating can be obtained by applying an adhesion-enhancing treatment material before forming the BCB coating film, or by forming an adhesion-enhancing layer such as an SiO2 film 16. Furthermore, a similar coating can be obtained by removing convex defects on the epitaxial layer using the spike-crushing method before applying the above technique.

[0082] After forming the coated film, the UV- and visible light-transmitting substrate 5 and the coated film are placed facing each other, and the material is sandwiched between the epitaxial functional layer and the UV- and visible light-transmitting substrate 5. By applying heat and pressure in a vacuum, bonding between the epitaxial functional layer and the UV- and visible light-transmitting substrate 5 can be achieved. In this embodiment, sapphire is exemplified as the UV- and visible light-transmitting substrate 5. The bonding pressure is 60 N / cm². 2 The bonding (curing) conditions for BCB are holding at 250°C for 30 minutes, and the curing process can be performed in a reduced-pressure atmosphere.

[0083] In this embodiment, the bonding pressure is 60 N / cm². 2However, this pressure is not limited to 5 N / cm². 2 More than 300N / cm 2 The following conditions can achieve the same effect:

[0084] The hardening treatment can be carried out in a reduced pressure atmosphere of 0.01 atm, but is not limited to a reduced pressure atmosphere. 1 × 10 -2 The procedure may be carried out in a vacuum atmosphere below Pa, or in a nitrogen atmosphere with an oxygen concentration of 100 ppm or less, to obtain the same effect.

[0085] By performing the above steps, it is possible to realize a bonded wafer (compound epitaxial bonded wafer) held by a resin layer 4 of minimal thickness while maintaining good peelability.

[0086] After thermocompression bonding, the starting substrate can be etched off with ammonia hydrogen peroxide. After removing the starting substrate, the first InGaP etching stop layer is removed with hydrochloric acid solution. Next, the second GaAs etching stop layer is removed with sulfuric acid hydrogen peroxide, leaving only the light-emitting functional layer on the ultraviolet and visible light-transmitting substrate.

[0087] After leaving only the light-emitting functional layer on an ultraviolet and visible light-transmitting substrate, an etching mask can be formed by photolithography, and the epitaxial layer of the element isolation region and electrode contact region can be partially removed by dry etching using a chlorine-based gas. In this case, if oxygen remains at the interface between the epitaxial layer (or the SiO2 layer if an SiO2 layer is formed) and the BCB layer, partial curing defects will occur during thermocompression bonding. These areas with curing defects become charged by the plasma and release gas, generating gas during dry etching and causing the epitaxial layer to peel off. However, by using the manufacturing method of the present invention, oxygen does not remain between the BCB layer and the epitaxial layer in principle, so curing defects do not occur, and the above-mentioned epitaxial layer peeling can be prevented.

[0088] After dry etching, an ohmic electrode can be formed of metal by photolithography, evaporation, and lift-off methods, and an ohmic contact can be formed by heat treatment. The temperature at the time of forming the ohmic contact is about 350 to 450 °C, and it is common to perform a treatment at a temperature higher than the glass transition point of BCB, which is 350 °C.

Example

[0089] Hereinafter, the present invention will be specifically described with reference to examples, but this does not limit the present invention.

[0090] (Example) As shown in FIG. 3, after laminating a first-conductivity-type GaAs buffer layer (not shown) on a first-conductivity-type GaAs starting substrate 2, an etching stop layer 11 is laminated (Ga 0.5 In 0.5 P first etching stop layer is 0.3 μm, GaAs second etching stop layer is 0.3 μm), (Al x Ga 1-x )) y In 1-y P (0 <x ≦ 1, 0.4 ≦ y ≦ 0.6) lower cladding layer 12 is 1 μm, (Al x Ga 1-x )) y In 1-y P (0 ≦ x <0.6, 0.4 ≦ y ≦ 0.6) active layer 13 is 0.6 μm, (Al x Ga 1-x )) y In 1-y P (0 <x ≦ 1, 0.4 ≦ y ≦ 0.6) upper cladding layer 14 is 0.6 μm, Ga y In 1-y P (0.5 ≦ y ≦ 1) intermediate layer (not shown) is 0.05 μm, and an epitaxial substrate on which a light-emitting functional layer with a GaP window layer 15 changed from 3 to 10 μm is laminated is produced.

[0091] The conductivity type from the starting substrate to the lower cladding layer is N-type in this example, and P-type from the upper cladding layer to the GaP window layer. The average doping concentration of the lower cladding layer is 5 × 10 17 / cm 3The average doping concentration in the upper cladding layer is 1 × 10⁻⁶. 17 / cm 3 The average doping concentration in layers other than the cladding layer, excluding the active layer, was calculated as (0.8~3) × 10⁻⁶. 18 / cm 3 That's what I decided.

[0092] After fabricating epitaxial wafers, a 0.02 μm thick SiO2 film was deposited on the epitaxial wafers using plasma CVD. TEOS and oxygen were used as materials for the plasma CVD deposition.

[0093] As shown in Figure 4, a resin layer 4 was formed by dropping BCB solution onto an epitaxial wafer on which an SiO2 film 16 had been deposited and spin-coating it. The rotation speed was 5,000 rpm, and the amount of BCB solution dropped was 0.5 ml. At that time, the viscosity of the BCB solution was adjusted by diluting it, and the coating was controlled to achieve the desired film thickness. For example, when using CYCLOTENE 3022-35 manufactured by Dow Chemical as the BCB raw material, a BCB film with a thickness of 0.5 μm can be obtained by mixing the diluent and BCB solution in a 1:1 ratio. The thickness of the resin layer 4 was varied from 0.01 to 0.6 μm. The relationship between the thickness of the resin layer 4 and the thickness of the GaP window layer 15 was maintained as follows: (thickness of resin layer 4) > 0.3845 × ln(thickness of GaP window layer 15) - 0.464.

[0094] As shown in Figure 2, a 0.02 μm thick SiO2 film 16 was deposited by plasma CVD on an ultraviolet and visible light-transmitting substrate 5. The substrate was then placed in a vacuum chamber and thermocompressed to bond the epitaxial layer to the ultraviolet and visible light-transmitting substrate 5.

[0095] In this embodiment, sapphire is used as the ultraviolet and visible light transmitting substrate 5, and the bonding pressure is 60 N / cm². 2 The BCB bonding (curing) conditions were set to hold at 250°C for 30 minutes, and the curing treatment was performed in a reduced pressure atmosphere of 0.01 atm.

[0096] The area yield of the fabricated bonded wafers was measured and was found to be in the range of 87-98%.

[0097] (Reference example) The bonded wafers prepared in the examples were subsequently subjected to the following processing steps.

[0098] After bonding an epitaxial wafer to an ultraviolet and visible light-transmitting substrate, the starting substrate was etched off with ammonia hydrogen peroxide. After removing the starting substrate, the InGaP etching stop layer was removed with hydrochloric acid solution, and then the GaAs etching stop layer was removed with sulfuric acid hydrogen peroxide, leaving only the light-emitting functional layer on the ultraviolet and visible light-transmitting substrate to create an epitaxial bonded substrate for device fabrication (Figure 5).

[0099] After fabricating the epitaxial junction substrate, a 1.2 μm thick SiO2 film for the hard mask was deposited by plasma CVD, and a resist pattern was formed by photolithography. The openings in the resist pattern were etched with a hydrofluoric acid solution to create the pattern, and the resist was removed. After removal, the substrate was introduced into an ICP apparatus and dry-etched with a chlorine-based plasma to remove the epitaxial layer at the openings and separate the elements. In this reference example, chlorine was used as the chlorine-based gas, and the substrate temperature was 30°C during processing. The same process was repeated to remove the lower cladding layer, active layer, and upper cladding layer, exposing the GaP window layer (Figure 6).

[0100] A 0.5 μm thick film of SiO2 was deposited using plasma CVD, and a resist pattern was formed using photolithography. The openings in the resist pattern were etched with a hydrofluoric acid-based solution to create a pattern (Figure 7), and the resist was removed.

[0101] A resist pattern was formed using photolithography, metal was deposited into the openings, and the pattern was completed using the lift-off method.

[0102] After forming the metal pattern, RTA treatment (400°C, 5 minutes) was performed in a nitrogen atmosphere to form ohmic contact between the metal pattern and the semiconductor layer (Figure 8).

[0103] (Comparative example) The resin layer thickness was in the range of 0.01 to 1.0 μm, and the relationship between the resin layer thickness and the GaP window layer thickness was within the range of (resin layer thickness) ≤ 0.3845 × ln(GaP window layer thickness) - 0.464. Aside from this, the bonded wafer was manufactured under the same conditions as in the examples.

[0104] When the area yield of the fabricated bonded wafers was measured, it was in the range of 30% to less than 70%. Figure 9 plots the results including those of the examples and comparative examples.

[0105] As described above, according to the embodiments of the present invention, it was possible to form a resin layer with a minimum thickness while achieving a good product area of ​​70% or more in terms of bonding defects after bonding.

[0106] This specification includes the following embodiments: [1]: A bonded wafer comprising a plurality of compound semiconductor layers provided on a starting substrate, a resin layer provided on the plurality of compound semiconductor layers, and an ultraviolet and visible light transparent substrate bonded via the resin layer, wherein the plurality of compound semiconductor layers include a first compound semiconductor layer having an active layer function and a second compound semiconductor layer which is the uppermost layer bonded to the resin layer, and the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T>0.3845×ln(G)-0.464 and T≦1.0μm. [2]: The junction wafer according to [1], wherein the compound semiconductor layer contains two or more of Al, Ga, In, P, and As. [3]: The bonded wafer according to [1] or [2] above, wherein the resin layer comprises at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide. [4]: The bonded wafer according to [1], [2], or [3] above, wherein the ultraviolet and visible light transmitting substrate comprises any of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP. [5]: The junction wafer according to [1], [2], [3], or [4], wherein the second compound semiconductor layer is the thickest of the plurality of compound semiconductor layers. [6]: The junction wafer according to [1], [2], [3], [4] or [5], wherein the second compound semiconductor layer is GaP. [7]: A method for manufacturing a bonded wafer, comprising the steps of: epitaxially growing a plurality of compound semiconductor layers on a starting substrate; forming a resin layer on the plurality of compound semiconductor layers; and bonding an ultraviolet and visible light transparent substrate to the plurality of compound semiconductor layers via the resin layer, wherein the step of epitaxially growing the plurality of compound semiconductor layers includes the steps of epitaxially growing a first compound semiconductor layer having an active layer function and epitaxially growing a second compound semiconductor layer which is the uppermost layer to be bonded to the resin layer, and the step of forming the resin layer includes forming the resin layer such that the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T>0.3845×ln(G)-0.464 and T≦1.0μm. [8]: A method for manufacturing a junction wafer according to [7], comprising making the compound semiconductor layer a material containing two or more of Al, Ga, In, P, and As. [9]: A method for manufacturing a bonded wafer according to [7] or [8], comprising making the resin layer a material comprising at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

[10] : A method for manufacturing a bonded wafer according to [7], [8], or [9], wherein the ultraviolet and visible light transmitting substrate is made of a material containing any of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP.

[11] : A method for manufacturing a junction wafer according to [7], [8], [9], or

[10] , comprising making the second compound semiconductor layer the thickest of the plurality of compound semiconductor layers.

[12] : A method for manufacturing a junction wafer according to [1], [7], [8], [9],

[10] or

[11] , comprising the second compound semiconductor layer being GaP.

[0107] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0108] 1...Jolted wafer of the present invention, 2...Starting substrate, 3...Compound semiconductor layer, 3a...First compound semiconductor layer, 3b...Second compound semiconductor layer, 4...Resin layer, 5…A substrate that transmits ultraviolet and visible light, 10…A bonded wafer according to an embodiment of the present invention, 11...Etching stop layer, 12...Lower cladding layer, 13...Activating layer, 14…Upper cladding layer, 15…GaP window layer (window layer), 16…SiO2 film.

Claims

1. Multiple compound semiconductor layers are provided on the starting substrate, A resin layer provided on the plurality of compound semiconductor layers, A bonded wafer having an ultraviolet and visible light-transmitting substrate bonded via the aforementioned resin layer, The plurality of compound semiconductor layers include a first compound semiconductor layer having an active layer function and a second compound semiconductor layer which is the uppermost layer bonded to the resin layer. A bonded wafer characterized in that the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T > 0.3845 × ln(G) - 0.464 and T ≤ 1.0 μm.

2. The junction wafer according to claim 1, characterized in that the compound semiconductor layer contains two or more of Al, Ga, In, P, and As.

3. The bonded wafer according to claim 1, characterized in that the resin layer contains at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

4. The bonded wafer according to claim 1, characterized in that the ultraviolet and visible light transmitting substrate contains any of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP.

5. The junction wafer according to claim 1, characterized in that the second compound semiconductor layer is the thickest layer among the plurality of compound semiconductor layers.

6. The junction wafer according to any one of claims 1 to 5, characterized in that the second compound semiconductor layer is GaP.

7. A process of epitaxially growing multiple compound semiconductor layers on a starting substrate, A step of forming a resin layer on the plurality of compound semiconductor layers, A method for manufacturing a bonded wafer, comprising the step of bonding an ultraviolet and visible light-transmitting substrate to a plurality of compound semiconductor layers via a resin layer, The process of epitaxially growing the plurality of compound semiconductor layers includes the step of epitaxially growing a first compound semiconductor layer having an active layer function, and the step of epitaxially growing a second compound semiconductor layer which is the uppermost layer bonded to the resin layer. A method for manufacturing a bonded wafer, characterized in that, in the step of forming the resin layer, the resin layer is formed such that the relationship between the thickness T of the resin layer and the thickness G of the second compound semiconductor layer satisfies T > 0.3845 × ln(G) - 0.464 and T ≤ 1.0 μm.

8. The method for manufacturing a junction wafer according to claim 7, characterized in that the compound semiconductor layer is made of a material containing two or more of Al, Ga, In, P, and As.

9. The method for manufacturing a bonded wafer according to claim 7, characterized in that the resin layer is made of a material comprising at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

10. The method for manufacturing a bonded wafer according to claim 7, characterized in that the ultraviolet and visible light transmitting substrate is made of a material containing any of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP.

11. The method for manufacturing a junction wafer according to claim 7, characterized in that the second compound semiconductor layer is the thickest layer among the plurality of compound semiconductor layers.

12. A method for manufacturing a junction wafer according to any one of claims 7 to 11, characterized in that the second compound semiconductor layer is GaP.

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