Bonded wafer and method of manufacturing the same

Abstract

The present invention provides a bonded wafer characterized by having: a plurality of compound semiconductor layers provided on a starting substrate; a peeling prevention layer provided on the plurality of compound semiconductor layers; a resin layer provided on the peeling prevention layer; and an ultraviolet light- and visible light-transmitting substrate bonded via the resin layer. As a result of this configuration, the present invention provides: a bonded wafer in which an epi layer (a plurality of compound semiconductor layers provided on a starting substrate) and an ultraviolet light- and visible light-transmitting substrate are bonded via a bonding resin layer, wherein even if the resin layer is exposed to a temperature process at or above the glass transition point, the resin layer can be prevented from moving and receding from the bonding interface, and thereby epi layer peeling (peeling of the plurality of compound semiconductor layers from the ultraviolet light- and visible light-transmitting substrate) can be suppressed; and a method for manufacturing the bonded wafer.

Description

Bonded wafer and method for manufacturing the same

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

[0002] A μ-LED transfer technology has been disclosed that separates the epitaxial layer (hereinafter also referred to as the epitaxial layer) from the support substrate using laser lift-off (LLO) technology. The starting substrate for a high-brightness red LED is a visible light-absorbing GaAs, and by transferring the epitaxial layer to an ultraviolet and visible light-transmitting substrate, a structure that enables LLO is created. 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 as this minimizes the thermal impact on the epitaxial layer. By combining the thermal sacrificial layer and the bonding layer, LLO can be realized without affecting the LED element. A technology has been disclosed in which ultraviolet-absorbing benzocyclobutene (BCB) is selected as this bonding layer and sacrificial layer (Patent Document 1).

[0003] Japanese Patent Publication No. 2023-083004

[0004] The ultraviolet-absorbing benzocyclobutene (BCB) disclosed in Patent Document 1 as a bonding layer and sacrificial layer is, in other words, a resin layer made of a thermosetting resin used as a bonding material. The epitaxial layer (a compound semiconductor layer provided on the starting substrate) bonded to the ultraviolet and visible light-transmitting substrate via the resin layer (BCB) is converted into an LED element through a device process. The AlGaInP-based material, which is the main material for red LEDs, requires heat treatment of about 400°C to 450°C to form ohmic contacts with metal. Although ohmic formation at lower temperatures is possible, it is not easy and has limitations when considering LED performance.

[0005] To lower the ohmic formation temperature, it is necessary to reduce the depletion layer at the metal-semiconductor interface, requiring high-concentration doping on both the metal and semiconductor sides. Increasing the doping amount increases the amount of impurity diffusion within the semiconductor. As a result, the lifetime characteristics of the LED element tend to deteriorate. To avoid deterioration of lifetime characteristics while maintaining high-concentration doping, it is effective to make the thickness from the high-concentration doping layer to the active layer sufficiently thicker than the diffusion length of the impurities. However, in μ-LEDs where miniaturization is required, this design is the opposite of the desirable direction of thin film reduction, so thick film reduction cannot be easily chosen.

[0006] On the other hand, there are other problems with increasing the film thickness. Devices that separate the epitaxial layer from the support substrate using LLO technology are used for μ-LED applications. These types of devices have a small surface area for the light emission, and are generally about 5 to 50 μm on each side. When the side is about 5 μm, if the height of the element exceeds 4 μm, the center of gravity becomes high, making it difficult to balance, and the LED element may tip over during mounting.

[0007] Therefore, high-concentration doping at the metal-semiconductor interface is difficult in μ-LEDs, including the issue of thick film formation, and there are limitations to lowering the ohmic formation temperature using this method.

[0008] Based on the above, AlGaInP-based μ-LEDs require ohmic formation treatment at a temperature above the glass transition point of the resin layer (BCB). During this process, the BCB softens and becomes fluid when exposed to temperatures above the glass transition point.

[0009] Furthermore, when the compound semiconductor layer provided on the starting substrate is an AlGaInP-based epitaxial layer, GaP is commonly used as a window layer (i.e., it is common to have multiple compound semiconductor layers). Since GaP and AlGaInP have a large lattice mismatch, a high concentration of dislocations occurs in the GaP layer, resulting in the generation of numerous hillocks and pits.

[0010] Hillocks and pits become stress concentration points during bonding, making them prone to crack formation. These cracks can penetrate the AlGaInP layer and reach the GaAs starting substrate. As described later, when manufacturing μLEDs using epitaxial substrates (EPW), the EPW is bonded to the UV and visible light transmitting substrate via a resin layer, and then the starting substrate is removed by selective wet etching. At that time, if there are cracks penetrating from the surface of the epitaxial layer to the substrate as described above, the etching solution can easily penetrate into the cracks inside the epitaxial layer.

[0011] Because the wet etching solution used for GaAs removal is selective, the etching rate of AlGaInP is about two orders of magnitude slower than that of GaAs, but it is not zero. For example, removing a GaAs substrate about 350 μm thick takes a considerable amount of time, during which time the AlGaInP layer is exposed to the etching solution, and the areas around cracks within the AlGaInP layer are etched.

[0012] As a result, through-holes are formed in the epitaxial layer, extending from the surface in contact with the resin layer to the surface where the starting substrate is removed.

[0013] During heat treatment in the glass transition temperature range, the resin layer becomes fluid and moves from the bonding interface through the aforementioned through-holes to the GaAs substrate removal surface. As a result, the resin layer that was present at the bonding interface between the epitaxial layer and the UV and visible light-transmitting support substrate, which was bonding the two together, decreases, leading to a loss of adhesive strength and the problem of the epitaxial layer delaminating from the support substrate. The portion of the epitaxial layer that has delaminated from the support substrate at this stage cannot proceed to the subsequent device processing steps, resulting in a loss of that portion.

[0014] 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, in which an epitaxial layer (a plurality of compound semiconductor layers provided on a starting substrate) and an ultraviolet and visible light transparent substrate are bonded via a bonding resin layer, and the resin layer is prevented from moving away from the bonding interface and decreasing even when the resin layer is exposed to a temperature process above the glass transition point, thereby suppressing epitaxial layer delamination (the delamination of the plurality of compound semiconductor layers from the ultraviolet and visible light transparent substrate).

[0015] To solve the above problems, the present invention provides a bonded wafer characterized by comprising: a plurality of compound semiconductor layers provided on a starting substrate; a peel-preventing layer provided on the plurality of compound semiconductor layers; a resin layer provided on the peel-preventing layer; and an ultraviolet and visible light transparent substrate bonded via the resin layer.

[0016] In such a bonded wafer, since there is a delamination prevention layer between the multiple compound semiconductor layers and the resin layer provided on the starting substrate, even if the resin layer becomes fluid when exposed to a temperature process above its glass transition temperature, the delamination prevention layer prevents it from moving away from the bonding interface with the ultraviolet and visible light-transmitting substrate towards the compound semiconductor layer and decreasing in volume. As a result, bonding with the ultraviolet and visible light-transmitting substrate is maintained, and epitaxial delamination (the delamination of multiple compound semiconductor layers from the ultraviolet and visible light-transmitting substrate) can be suppressed.

[0017] Furthermore, it is preferable that the compound semiconductor layer contains two or more of the following: Al, Ga, In, P, and As.

[0018] Such a compound semiconductor layer can more reliably prevent delamination from ultraviolet and visible light-transmitting substrates.

[0019] Furthermore, it is preferable that the resin layer contains at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

[0020] With such a resin layer, the peel-prevention layer can more reliably block movement from the bonding interface, thereby suppressing epitaxial layer delamination.

[0021] Furthermore, the ultraviolet and visible light-transmitting substrate is preferably made of any of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP.

[0022] Such a UV- and visible-light-transmitting substrate can more reliably suppress the delamination of the compound semiconductor layer.

[0023] Furthermore, it is preferable that the peel-preventing layer is made of a material with a Young's modulus of 100 GPa or higher.

[0024] A delamination prevention layer with such a Young's modulus offers a higher delamination prevention effect and can more reliably suppress epitaxial layer delamination.

[0025] Furthermore, it is preferable that the peel-preventing layer has a Mohs hardness of 7 or higher.

[0026] A delamination prevention layer with this Mohs hardness level offers a higher delamination prevention effect and can more reliably suppress epitaxial layer delamination.

[0027] Furthermore, it is preferable that the peel-preventing layer is composed of at least one layer made of one or more of the following materials: cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond.

[0028] With such materials and number of layers, the peel-prevention layer will have a higher peel-prevention effect and can more reliably suppress epitaxial layer delamination.

[0029] Further, in order to solve the above problems, a method for manufacturing a bonded wafer according to the present invention includes a step of epitaxially growing a plurality of compound semiconductor layers on a starting substrate, a step of forming a release prevention layer on the plurality of compound semiconductor layers, a step of forming a resin layer on the release prevention layer, and a step of bonding an ultraviolet and visible light transmissive substrate through the resin layer. A method for manufacturing a bonded wafer is provided, which is characterized by including these steps.

[0030] With such a method for manufacturing a bonded wafer, since there is a release prevention layer between the plurality of compound semiconductor layers epitaxially grown on the starting substrate and the resin layer, even if the resin layer is exposed to a temperature process above the glass transition point and has fluidity, the release prevention layer prevents the resin layer from moving to the compound semiconductor layer side from the bonding interface with the ultraviolet and visible light transmissive substrate and decreasing. As a result, the bonding with the ultraviolet and visible light transmissive substrate is maintained, and thus epitaxial layer peeling (peeling of the plurality of compound semiconductor layers from the ultraviolet and visible light transmissive substrate) can be suppressed.

[0031] Further, it is preferable that the compound semiconductor layer be made of a material containing any two or more of Al, Ga, In, P, and As.

[0032] With such a compound semiconductor layer, peeling from the ultraviolet and visible light transmissive substrate can be more reliably suppressed.

[0033] Further, it is preferable that the resin layer be made of a material containing at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

[0034] With such a resin layer, it can be more reliably blocked by the release prevention layer and prevented from moving from the bonding interface, and epitaxial layer peeling can be suppressed.

[0035] Further, it is preferable that the ultraviolet and visible light transmissive substrate be made of a material containing any one of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, and GaP.

[0036] Using such an ultraviolet and visible light-transmitting substrate makes it possible to more reliably suppress the delamination of the compound semiconductor layer.

[0037] Furthermore, it is preferable that the peel-preventing layer be made of a material with a Young's modulus of 100 GPa or higher.

[0038] Using a delamination prevention layer with such a Young's modulus provides a higher delamination prevention effect and more reliably suppresses epitaxial layer delamination.

[0039] Furthermore, it is preferable that the peel-preventing layer has a Mohs hardness of 7 or higher.

[0040] Using a delamination prevention layer with such Mohs hardness provides a higher delamination prevention effect and more reliably suppresses epitaxial layer delamination.

[0041] Furthermore, it is preferable that the peel-preventing layer be composed of at least one layer made from one or more of the following materials: cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond.

[0042] Using such materials and layers for the peel-prevention layer provides a higher peel-prevention effect and more reliably suppresses epitaxial layer delamination.

[0043] As described above, in the bonded wafer of the present invention, since there is a delamination prevention layer between the multiple compound semiconductor layers and the resin layer provided on the starting substrate, even if the resin layer becomes fluid when exposed to a temperature process above the glass transition temperature, the delamination prevention layer prevents the resin layer from moving away from the bonding interface with the ultraviolet and visible light-transmitting substrate towards the compound semiconductor layer and decreasing in volume, thereby maintaining bonding with the ultraviolet and visible light-transmitting substrate. As a result, epitaxial delamination (the delamination of multiple compound semiconductor layers from the ultraviolet and visible light-transmitting substrate) can be suppressed.

[0044] Furthermore, in the manufacturing method of the bonded wafer of the present invention, a delamination prevention layer is formed between the multiple compound semiconductor layers epitaxially grown on the starting substrate and the resin layer. Therefore, even if the resin layer becomes fluid when exposed to a temperature process above its glass transition temperature, the delamination prevention layer prevents it from moving away from the bonding interface with the ultraviolet and visible light-transmitting substrate towards the compound semiconductor layer and decreasing in volume. As a result, bonding with the ultraviolet and visible light-transmitting substrate is maintained, and epitaxial delamination (the delamination of multiple compound semiconductor layers from the ultraviolet and visible light-transmitting substrate) can be suppressed.

[0045] In particular, when forming a delamination prevention film on the EPW surface and bonding the EPW to an ultraviolet and visible light-transmitting substrate via a thermosetting resin as a resin layer, it is possible to prevent the thermosetting resin from moving away from the bonding interface through through-holes in the epitaxial layer and decreasing during the ohmic contact formation process, for example, when the temperature range exceeds the glass transition point of the thermosetting resin. This suppresses the delamination of the epitaxial layer during the ohmic contact formation process.

[0046] This is a schematic diagram of a bonded wafer in one embodiment of the present invention. This is a schematic diagram of the epitaxial substrate (EPW) fabrication stage of a bonded wafer in another embodiment of the present invention. This is a schematic diagram of the stage of forming the resin layer. This is a schematic diagram of the stage of bonding an ultraviolet and visible light transparent substrate. This is a schematic diagram of the stage of removing the starting substrate. This is a schematic diagram of the element isolation stage. This is a schematic diagram of the protective film formation stage. This is a schematic diagram of the electrode formation stage. This is a diagram showing the surface state of the bonded wafer in the example. This is a diagram showing the surface state of the bonded wafer in the comparative example. This is a graph showing the number of delamination locations relative to the number of RTA cycles for the example and comparative example.

[0047] The present invention will be described in detail below, but the present invention is not limited to these descriptions.

[0048] As described above, in bonded wafers in which an epitaxial layer (multiple compound semiconductor layers provided on a starting substrate) and an ultraviolet and visible light-transmitting substrate are bonded via a bonding resin layer, there has been a need for a bonded wafer and a method for manufacturing the same that can prevent the resin layer from migrating and decreasing from the bonding interface even when the resin layer is exposed to a temperature process above its glass transition point, thereby suppressing epitaxial layer delamination (the delamination of multiple compound semiconductor layers from the ultraviolet and visible light-transmitting substrate).

[0049] The inventors of this invention have diligently studied the above-mentioned problems and arrived at this invention. First, we will explain the background in detail.

[0050] In typical bonded wafers, an etching stop layer (also called an etch stop layer) made of GaInP or similar material is formed on a starting substrate (e.g., GaAs), an epitaxial growth of a GaAs buffer, which is the same material as the starting substrate, is carried out on top of it, and an AlGaInP-based epitaxial functional layer is grown on top of that to form an epitaxial substrate (EPW). When the AlGaInP-based epitaxial functional layer has 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 (EPWs) with an AlGaInP-based epitaxial functional layer have warping (BOW) due to the lattice mismatch and numerous hillocks and pits on the surface.

[0051] For μ-LED applications, AlGaInP-based light-emitting functional layers are used as starting substrates such as GaAs, Si, and Ge, which are UV- and visible-light transparent substrates, and therefore cannot be used for μ-LED applications in their original form. For this reason, only the epitaxial functional layer is transferred onto the UV- and visible-light transparent substrate before use. After transferring the epitaxial functional layer, it is processed to form a μ-LED die.

[0052] The μ-LED die, processed into the form of a μ-LED die, is separated from the ultraviolet and visible light-transmitting substrate 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 are bonded via a material that is visible light-transmitting and has ultraviolet light-absorbing properties, with the visible light-transmitting and ultraviolet light-absorbing material acting as a sacrificial layer. Since the sacrificial layer has the property of absorbing ultraviolet light, by irradiating it with a laser having an ultraviolet wavelength from the ultraviolet and visible light-transmitting substrate side, the sacrificial layer portion sublimes, and the μ-LED die can be separated from the ultraviolet and visible light-transmitting substrate.

[0053] In this process, materials that are transparent to visible light and absorb ultraviolet light often use a thermosetting resin as the resin layer; for example, benzocyclobutene (BCB) is frequently used. This resin layer is sandwiched between the epitaxial functional layer and the ultraviolet and visible light transparent substrate, and heat and pressure are applied to bond the epitaxial functional layer to the ultraviolet and visible light transparent substrate.

[0054] While the epitaxial functional layer and the ultraviolet and visible light-transmitting substrate can be bonded using the structure and manufacturing method described above, it is common to select GaP as the window layer for the epitaxial functional layer made of AlGaInP-based material, and a large lattice mismatch exists between GaP and the AlGaInP-based material. As a result, numerous hillocks and pits exist on the EPW surface.

[0055] Hillocks and pits are convex or concave areas on the EPW surface, and stress concentrates there when joining them via thermosetting resin using a heat-compression bonding process. As a result, cracks are more likely to occur in the epitaxial layer where hillocks and pits exist. Since these cracks originate from the EPW surface, some may penetrate all the way through to the starting substrate.

[0056] After bonding the EPW and the UV and visible light-transmitting substrate via a resin layer made of thermosetting resin, the starting substrate is removed by selective wet etching to obtain only the epitaxial functional layer. During this process, the etching solution penetrates into the epitaxial functional layer through cracks, and the area around the cracks is etched.

[0057] As a result, through-holes are formed in the epitaxial layer, extending from the surface in contact with the resin layer to the surface where the starting substrate is removed.

[0058] Furthermore, after bonding the EPW and the ultraviolet and visible light-transmitting substrate via a resin layer made of thermosetting resin, the bonded substrate, consisting only of the epitaxial functional layer, requires the formation of ohmic electrodes for current conduction in order to fabricate an LED device.

[0059] To form an ohmic contact, it is necessary to bring the electrode and semiconductor into contact and apply heat treatment. Although it is a short-time RTA treatment, the temperature required is usually in the range of 400°C or higher.

[0060] A resin layer made of thermosetting resin hardens with heat, but it also has the characteristic of having a glass transition point above a certain temperature, during which it softens. When the heat treatment temperature for ohmic formation is reached, the temperature range exceeds the glass transition point of the thermosetting resin, causing it to soften.

[0061] A resin layer made of thermosetting resin is subjected to stress due to epitaxial lattice mismatch, and the thermosetting resin that has softened beyond its glass transition temperature is under stress. If there are no through holes as described above, there is no change even if the thermosetting resin softens, but if there are through holes, the resin layer made of thermosetting resin moves through these through holes due to the stress driven by the epitaxial lattice mismatch.

[0062] As a result, the amount of resin layer made of thermosetting resin in the bonding interface decreases, meaning the amount of bonding material decreases, causing the epitaxial layer to peel off from the ultraviolet and visible light-transmitting substrate.

[0063] This epitaxial layer delamination extends beyond the size of the through-hole. While the area where the through-hole occurs is not suitable for use as an LED, a wider area beyond that becomes unsuitable for LED conversion, resulting in a significant decrease in yield.

[0064] Therefore, the inventors believe that preventing the movement of the resin layer, which is made of thermosetting resin, through the through-holes is effective in preventing such peeling.

[0065] The inventors considered forming a peel-preventing layer on the surface of the EPW (electrolytic wafer) to prevent the movement of the resin layer, which is made of thermosetting resin, from through holes. They hypothesized that by forming a peel-preventing layer on the surface of the EPW, the exit portion of the through hole could be covered with the peel-preventing layer, thereby preventing the movement of the resin layer, which is made of thermosetting resin.

[0066] Furthermore, according to the inventors' studies, it is preferable that the peel-preventing layer has sufficient hardness to withstand the stress concentrated near the through-hole during bonding. For example, SiO with a Young's modulus of 76 to 97 GPa. ２ However, it does have a certain delamination-inhibiting effect. Nevertheless, it has been found that using materials with a Young's modulus of 100 GPa or higher, although not specifically limited to this method, results in a higher delamination-inhibiting effect.

[0067] In other words, materials with a higher Young's modulus are more suitable as delamination prevention films. Materials with a lower Young's modulus are likely to yield and break under load applied through the through-holes, while materials with a higher Young's modulus are less likely to reach their yield point. As a result, the delamination prevention film is less likely to break, or may not break at all, due to the stress passing through the through-holes, thus preventing the through-holes from opening. Consequently, the effect of preventing the movement of the thermosetting resin through the through-holes is enhanced, leading to a higher detergence on epitaxial layer delamination. Therefore, it is preferable, but not limited to, a delamination prevention layer made of a material with a Young's modulus of 100 GPa or higher.

[0068] As described above, the inventors have found that by providing a peeling prevention layer, it is possible to prevent the resin layer made of thermosetting resin from moving away from the bonding interface even after the temperature reaches the softening point of the thermosetting resin, and that peeling of the epitaxial layer can be suppressed even when exposed to high temperatures such as in the ohmic formation process, thus completing the present invention.

[0069] In other words, the bonded wafer of the present invention is characterized by having a plurality of compound semiconductor layers provided on a starting substrate, a peel-preventing layer provided on the plurality of compound semiconductor layers, a resin layer provided on the peel-preventing layer, and an ultraviolet and visible light transparent substrate bonded via the resin layer.

[0070] Furthermore, the present invention provides a method for manufacturing a bonded wafer, characterized by comprising the steps of: epitaxially growing a plurality of compound semiconductor layers on a starting substrate; forming a delamination prevention layer on the plurality of compound semiconductor layers; forming a resin layer on the delamination prevention layer; and bonding an ultraviolet and visible light transparent substrate via the resin layer.

[0071] Embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited thereto.

[0072] (Bonded wafer) Figure 1 shows a schematic diagram of a bonded wafer in one embodiment of the present invention.

[0073] As shown in Figure 1, the bonded wafer 1 of the present invention has a plurality of compound semiconductor layers 3 provided on a starting substrate 2, a peel-preventing layer 4 provided on the plurality of compound semiconductor layers 3, a resin layer 5 provided on the peel-preventing layer 4, and an ultraviolet and visible light transparent substrate 6 bonded via the resin layer 5.

[0074] In such a bonded wafer 1, since there is a delamination prevention layer 4 between the multiple compound semiconductor layers 3 and the resin layer 5 provided on the starting substrate 2, even if the resin layer 5 is exposed to a temperature process above its glass transition temperature and becomes fluid, the delamination prevention layer 4 prevents the resin layer 5 from moving from the bonding interface with the ultraviolet and visible light-transmitting substrate 6 towards the compound semiconductor layer 3, thereby maintaining the bonding with the ultraviolet and visible light-transmitting substrate 6. As a result, epitaxial delamination (the delamination of the multiple compound semiconductor layers 3 from the ultraviolet and visible light-transmitting substrate 6) can be suppressed.

[0075] Furthermore, the compound semiconductor layer 3 is not particularly limited, but it is preferable that it contains two or more of the following: Al, Ga, In, P, and As.

[0076] Such a compound semiconductor layer 3 can more reliably suppress delamination from the ultraviolet and visible light-transmitting substrate 6.

[0077] Furthermore, the resin layer 5 is preferably, although not particularly limited, to contain at least one of benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

[0078] With such a resin layer 5, it can be more reliably blocked by the peel-prevention layer 4, preventing movement from the bonding interface and thus suppressing epitaxial layer peeling.

[0079] The resin layer 5 is preferably a thermosetting resin used as a bonding material, although it is not particularly limited. It may also be UV-absorbing benzocyclobutene (BCB), as disclosed in Patent Document 1 as a bonding layer and sacrificial layer.

[0080] Furthermore, the ultraviolet and visible light transmitting substrate 6 is not particularly limited, but it is preferable that it contains any of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP.

[0081] With such an ultraviolet and visible light-transmitting substrate 6, the delamination of the compound semiconductor layer 3 can be suppressed more reliably.

[0082] Furthermore, the peel-preventing layer 4 is not particularly limited, but it is preferable that it is made of a material with a Young's modulus of 100 GPa or more. Furthermore, the peel-preventing layer 4 is not particularly limited, but it is preferable that it is made of a material with a Young's modulus of 1500 GPa or less.

[0083] With a Young's modulus like this, the peel-prevention layer 4 will have a higher peel-prevention effect and can more reliably suppress epitaxial layer peeling.

[0084] Furthermore, the peel-preventing layer 4 is not particularly limited, but it is preferable that it has a Mohs hardness of 7 or higher. Furthermore, the peel-preventing layer 4 is not particularly limited, but it is preferable that it has a Mohs hardness of 15 or lower.

[0085] With a peel-preventing layer 4 having such a Mohs hardness, the peel-preventing effect is higher, and the peeling of the epitaxial layer can be suppressed more reliably.

[0086] Furthermore, the peel-preventing layer 4 is preferably composed of at least one layer made of one or more of the following materials, although it is not particularly limited: cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond.

[0087] With such a material and number of layers, the peel-preventing layer 4 will have a higher peel-preventing effect and can more reliably suppress epitaxial layer peeling.

[0088] (Method for manufacturing bonded wafers) A method for manufacturing bonded wafers according to one embodiment of the present invention will now be described with reference to Figure 1.

[0089] The method for manufacturing a bonded wafer 1 of the present invention includes the steps of: epitaxially growing a plurality of compound semiconductor layers 3 on a starting substrate 2; forming a peel-preventing layer 4 on the plurality of compound semiconductor layers 3; forming a resin layer 5 on the peel-preventing layer 4; and bonding an ultraviolet and visible light transparent substrate 6 via the resin layer 5.

[0090] With this method of manufacturing a bonded wafer 1, since there is a delamination prevention layer 4 between the multiple compound semiconductor layers 3 epitaxially grown on the starting substrate 2 and the resin layer 5, even if the resin layer 5 is exposed to a temperature process above its glass transition temperature and becomes fluid, the delamination prevention layer 4 prevents the resin layer 5 from moving from the bonding interface with the ultraviolet and visible light-transmitting substrate 6 towards the compound semiconductor layer 3, thus maintaining the bonding with the ultraviolet and visible light-transmitting substrate 6. As a result, epitaxial delamination (the delamination of the multiple compound semiconductor layers 3 from the ultraviolet and visible light-transmitting substrate 6) can be suppressed.

[0091] Furthermore, the compound semiconductor layer 3 is preferably made of a material containing two or more of Al, Ga, In, P, and As, although this is not particularly limited.

[0092] Using such a compound semiconductor layer 3 makes it possible to more reliably suppress delamination from the ultraviolet and visible light-transmitting substrate 6.

[0093] Furthermore, the resin layer 5 is preferably made of a material that includes at least one of the following, although not particularly limited: benzocyclobutene, epoxy resin, wax, silicone, fluororesin, spin-on glass, and polyimide.

[0094] With such a resin layer 5, it can be more reliably blocked by the peel-prevention layer 4, preventing movement from the bonding interface and thus suppressing epitaxial layer peeling.

[0095] The resin layer 5 is preferably a thermosetting resin used as a bonding material, although it is not particularly limited. It may also be UV-absorbing benzocyclobutene (BCB), as disclosed in Patent Document 1 as a bonding layer and sacrificial layer.

[0096] Furthermore, the ultraviolet and visible light transmitting substrate 6 is preferably made of a material that includes, but is not particularly limited, sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, or GaP.

[0097] Using such an ultraviolet and visible light-transmitting substrate 6 makes it possible to more reliably suppress the peeling of the compound semiconductor layer 3.

[0098] Furthermore, the peel-preventing layer 4 is preferably made of a material with a Young's modulus of 100 GPa or more, although this is not particularly limited. Also, the peel-preventing layer 4 is preferably made of a material with a Young's modulus of 1500 GPa or less, although this is not particularly limited.

[0099] Using a Young's modulus like this for the peel-prevention layer 4 provides a higher peel-prevention effect and more reliably suppresses epitaxial layer peeling.

[0100] Furthermore, the peel-preventing layer 4 is preferably configured to have a Mohs hardness of 7 or higher, although this is not particularly limited. Also, the peel-preventing layer 4 is preferably configured to have a Mohs hardness of 15 or lower, although this is not particularly limited.

[0101] Using a peel-preventing layer 4 with such Mohs hardness provides a higher peel-preventing effect and more reliably suppresses epitaxial layer peeling.

[0102] Furthermore, it is preferable that the peel-preventing layer 4 is composed of at least one layer made of one or more of the following materials, although not particularly limited: cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond.

[0103] Using such materials and a certain number of layers for the peel-preventing layer 4, the peel-preventing effect is higher, and epitaxial layer peeling can be suppressed more reliably.

[0104] Next, with reference to Figures 2 to 8, a method for manufacturing a bonded wafer in another embodiment will be described in detail.

[0105] First, with reference to Figure 2, the process for fabricating an epitaxial substrate (EPW) will be explained. An epitaxial substrate (EPW) is fabricated by laminating a first-conductivity GaAs buffer layer (not shown) onto a first-conductivity GaAs starting substrate 2, followed by laminating a light-emitting functional layer consisting of a GaInP / GaAs etching stop layer 11, an AlGaInP lower cladding layer 12, an AlGaInP active layer 13, an AlGaInP upper cladding layer 14, a GaInP intermediate layer (not shown), and a GaP window layer 15.

[0106] In this embodiment, the lower cladding layer 12 and the upper cladding layer 14 are described together as a single cladding layer. However, the doping level is not limited to a single level; there may be two or more levels of doping, or there may be gradient doping, or there may be a doping profile that combines these.

[0107] Similarly, although the lower cladding layer 12 and the upper cladding layer 14 are described together as cladding layers, they are not limited to a single composition and may consist of two or more compositions.

[0108] Furthermore, 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.

[0109] 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.

[0110] In this embodiment, GaP is used as the window layer 15, and the degree of lattice mismatch between the GaP window layer 15 and the material from the starting substrate 2 to the upper cladding layer 14 is large, at approximately 3.7%. As a result, warping occurs in the wafer after the epitaxial fracture is complete. In addition, along with the warping, numerous pits and hillocks are generated due to the lattice mismatch.

[0111] Here, hillocks are irregularly shaped convex objects with a height of about 1 / 10 to 2 times the thickness of the GaP window layer 15. On the other hand, pits are pyramidal concave objects with faceted surfaces and one side of about 1 / 20 to 2 times the thickness of the GaP window layer 15. In addition to hillocks and pits, there are also many inclusion defects where by-products generated in the epitaxial growth furnace fall onto the EPW surface and form irregularly shaped convex portions.

[0112] In this embodiment, the example shows the starting substrate 2 as GaAs, but it 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), then a first GaAs buffer layer and a sacrificial layer such as AlAs may be formed, a second GaAs buffer may be epitaxially grown on top of them, and then an epitaxial functional layer may be grown on top of that. Although the example shows the case where a Ge layer is laminated, the same effect can be obtained without a Ge layer. Alternatively, Ge itself may be used as the starting substrate. Furthermore, the starting substrate 2 is not particularly limited, but it is preferable that it be a (001) plane.

[0113] Next, referring to Figure 3, the process of forming the resin layer as a bonding layer will be explained.

[0114] After the EPW is fabricated, a peel-preventing layer 16 is formed on the EPW surface. Although not particularly limited, the peel-preventing layer 16 is preferably made of a material with a high hardness (Mohs hardness) of 7 or higher and a Young's modulus of 100 GPa or higher. This is because materials with higher hardness and yield point have higher resistance to stress.

[0115] Specifically, these include cordierite (Young's modulus 140 [GPa], Mohs hardness 7), forsterite (Young's modulus 150 [GPa], Mohs hardness 7), gallium nitride (Young's modulus 181 [GPa], Mohs hardness 9), zirconia (Young's modulus 200 [GPa], Mohs hardness 8), gallium oxide (Young's modulus 240-260 [GPa], Mohs hardness 7.5), silicon nitride (Young's modulus 280-300 [GPa], Mohs hardness 8.3-9), and aluminum nitride (Young's modulus 320 [GPa], Mohs hardness 7- 8) It is preferable to form it with one or more layers of film containing one or more of the following: silicon carbide (Young's modulus 408 [GPa], Mohs hardness 13), sapphire (Young's modulus 425-460 [GPa], Mohs hardness 9.5), boron carbide (Young's modulus 450-460 [GPa], Mohs hardness 9.5), tungsten carbide (Young's modulus 550 [GPa], Mohs hardness 9), titanium nitride (Young's modulus 590 [GPa], Mohs hardness 9), diamond (Young's modulus 1,000-1,100 [GPa], Mohs hardness 10), etc.

[0116] The material for the aforementioned peeling prevention layer 16 can be deposited using methods such as EB deposition, sputtering, (plasma or optical) CVD, PLD (pulse laser deposition), ALD (atomic layer deposition), MBE (molecular beam epitaxy), and deposition mode in an MBE furnace.

[0117] While increasing the film deposition temperature to 100°C or higher and increasing the orientation or crystallinity enhances the delamination prevention effect, this is not the only method; sufficient effects can be obtained even when the film is deposited at room temperature.

[0118] The film thickness of the peel-preventing layer 16 is preferably within a range where elastic deformation is possible under stress (a range where plastic deformation does not occur). When the film thickness is thicker, cracks are more likely to occur than when it is thin, so if the film is too thick, the peel-preventing effect is reduced. For this reason, although not particularly limited, a thickness not exceeding 1 μm is preferable. Furthermore, a thickness of less than 0.5 μm is even better.

[0119] However, if the film is too thin, it is undesirable due to insufficient mechanical strength. For this reason, although not particularly limited, it is preferable that the film thickness be at least 1 nm (0.001 μm). A thickness of 5 nm (0.005 μm) or more is even better.

[0120] Furthermore, before forming the BCB coating film that will become the resin layer 17, an adhesion-enhancing treatment material is applied or / or SiO ２ An adhesion-enhancing layer 18 may be formed by creating a film. Alternatively, a similar coating film can be obtained by removing convex defects on the epitaxial layer using the spike crush method, and then using this technique.

[0121] When joining wafers together via BCB as the resin layer 17, SiO ２ The film is sometimes used as an adhesion-enhancing layer 18 for BCB, but SiO ２ The Young's modulus is 76-97 [GPa] and the Mohs hardness is 7. Because the Young's modulus and hardness are relatively high, it has a certain delamination prevention effect. However, the Young's modulus is somewhat low (less than 100), resulting in somewhat low yield resistance to stress. Therefore, SiO2 is released from the through-hole due to stress. ２ The membrane may break (destroy). Therefore, SiO ２ The film is not particularly limited, but it is preferable to use it as an adhesion-enhancing layer 18 for BCB rather than as a peel-preventing layer 16.

[0122] In this embodiment, the example shows a case where the peel-preventing layer 16 is formed as a single layer, but it is not limited to a single layer, and two or more layers may be combined to form it.

[0123] Furthermore, although this embodiment illustrates a case where the peel-preventing layer 16 is formed from one type of material, it is not limited to one type of material and may be formed by mixing two or more types.

[0124] After forming the adhesion-enhancing layer 18, the wafer is vacuum-adsorbed, and a coating film of thermosetting resin is applied by spin coating to form a resin layer 17. A general-purpose spin coater can be used for coating. In this embodiment, the thickness of the BCB coating film, obtained by spin-coating BCB as the thermosetting resin, can be changed from 0.01 to 1.0 μm by adjusting the concentration and viscosity of the BCB solution and the rotation speed during spin coating.

[0125] In this embodiment, the thermosetting resin used in the resin layer 17 is not limited to a substance that hardens upon heating, but may also include a substance that has a glass transition temperature, softens upon heat, and hardens upon cooling. Therefore, it is preferable that it contains at least one of benzocyclobutene (BCB), epoxy resin, wax, silicone, fluororesin (e.g., Cytop® manufactured by AGC Inc.), spin-on glass (SOG), and polyimide. However, it is not limited to these.

[0126] When using a thermosetting resin BCB as the resin layer 17, and especially when using, for example, CYCLOTENE 3022-35 manufactured by Dow Chemical 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 the 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.

[0127] 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 film thickness adjustment by changing the rotation speed is limited to about ±50% or less, 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 ensure a certain degree of film thickness uniformity by compression, so the minimum rotation speed is not limited to this minimum.

[0128] In this embodiment, although the method of thinning BCB with a thinning liquid to adjust the concentration and viscosity and to adjust the film thickness of the coating film has been exemplified, the present invention is not limited to BCB, and the same method can be applied to any coating film that can be thinned with a thinning liquid. Epoxy resin, wax, silicone, fluororesin (for example, Cytop (registered trademark) manufactured by AGC), spin-on glass (SOG), and polyimide are also mixed with a liquid corresponding to the aforementioned thinning liquid, and the same method can be used.

[0129] Next, referring to FIG. 4, the process of bonding an ultraviolet and visible light transmissive substrate through a resin layer will be described.

[0130] After forming the resin layer 17, the ultraviolet and visible light transmissive substrate 20 and the resin layer 17 are opposed to each other through the adhesion enhancing layer 19, and thermocompression bonding is performed in a vacuum. Here, the adhesion enhancing layer 19 may be the same as the adhesion enhancing layer 18, or may be formed in advance on the ultraviolet and visible light transmissive substrate 20. In this embodiment, sapphire is used as the ultraviolet and visible light transmissive substrate 20. The bonding pressure is 60 N / cm ２ and the adhesion (curing) condition of the resin layer 17 (BCB) is to hold at 250° C. for 30 minutes, and the curing treatment is performed in a reduced pressure atmosphere.

[0131] In this embodiment, sapphire is exemplified as the ultraviolet and visible light transmissive substrate 20, but the present invention is not limited to sapphire, and any material having ultraviolet and visible light transmissivity can be selected. For example, it is preferable to select quartz, glass, lithium tantalate (LT), lithium niobate (LN), ZnO, SiC, GaN, or GaP because the same effect can be obtained. However, the present invention is not limited thereto.

[0132] In this embodiment, the bonding pressure is 60 N / cm ２ However, the present invention is not limited to this pressure. In particular, it is preferable that the pressure is 5 N / cm ２ or more and 300 N / cm ２ or less because the same effect can be obtained.

[0133] The hardening treatment was performed in a reduced pressure atmosphere of 0.01 atm, but it is not limited to a reduced pressure atmosphere. It may also be performed in a vacuum atmosphere of 1E-2 Pa or less, or in a nitrogen atmosphere with an oxygen concentration of 100 ppm or less, to obtain similar effects.

[0134] Next, referring to Figure 5, the process of removing the starting substrate 2 will be explained.

[0135] After thermocompression bonding, the starting substrate 2 is etched off with ammonia hydrogen peroxide. After removing the starting substrate 2, the GaInP / GaAs etching stop layer 11 is removed. First, the InGaP first etching stop layer is removed with hydrochloric acid solution. Next, the GaAs second 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.

[0136] Next, the process of element isolation will be explained with reference to Figure 6.

[0137] After leaving only the light-emitting functional layer on the ultraviolet and visible light-transmitting substrate 20, an etching mask is formed by photolithography, and the epitaxial layer of the element isolation region and electrode contact region is partially removed by dry etching using a chlorine-based gas.

[0138] In the conventional case, the epitaxial layer (adhesion-enhancing layer 18 is SiO ２ If a layer is formed, SiO ２ If oxygen remains at the interface between the layer and the resin layer 17 (BCB layer), partial curing defects will occur during thermocompression bonding. These areas of curing defects become charged by the plasma and release gas, which generates gas during dry etching and causes the epitaxial layer to peel off.

[0139] In contrast, in this embodiment, by using the peel-preventing layer 16, in principle, the resin layer 17 (BCB layer) and the epitaxial layer (adhesion-enhancing layer 18 as SiO ２ If a layer is formed, SiO ２ Since no oxygen remains between the layers, curing defects do not occur, and epitaxial layer delamination can be suppressed.

[0140] Next, the process of forming the protective film will be explained with reference to Figure 7.

[0141] After the dry etching process, a protective film 21 is formed to protect at least the sides of the light-emitting functional layer.

[0142] Next, the electrode formation process will be explained with reference to Figure 8.

[0143] After forming the protective film 21, the ohmic electrode 22 is formed from metal using photolithography, vapor deposition, and lift-off method, and then heat-treated to form the ohmic contact.

[0144] The temperature during ohmic contact formation is typically around 350 to 450°C, and it is common to perform the treatment at a temperature higher than the glass transition temperature of, for example, BCB, which constitutes the resin layer 17 (350°C).

[0145] Through the above process, it is possible to manufacture bonded wafers that maintain good delamination resistance against laser lift-off and suppress epitaxial layer delamination even during heat treatment during ohmic formation.

[0146] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0147] (Example) As shown in Figure 2, a first conductivity type GaAs buffer layer (not shown) is laminated on a first conductivity type GaAs starting substrate 2, then an etching stop layer 11 is laminated (Ga0.5In0.5P first etching stop layer of 0.3 μm, GaAs second etching stop layer of 0.3 μm), and a (AlxGa1-x)yIn1-yP (0 < x ≤ 1, 0.4 ≤ y ≤ 0.6) lower cladding layer 12 of 1 μm, An epitaxial wave substrate (EPW) was fabricated by laminating a light-emitting functional layer consisting of a 0.6 μm (AlxGa1-x)yIn1-yP (0 ≤ x < 0.6, 0.4 ≤ y ≤ 0.6) active layer 13, a 0.6 μm (AlxGa1-x)yIn1-yP (0 < x ≤ 1, 0.4 ≤ y ≤ 0.6) upper cladding layer 14, a 0.05 μm (GayIn1-yP (0.5 ≤ y ≤ 1) intermediate layer (not shown)) and a 6 μm (GaP window layer 15).

[0148] In this embodiment, the conductivity type from the starting substrate 2 to the lower cladding layer 12 was N-type, and from the upper cladding layer 14 to the GaP window layer 15 it was P-type. The average doping concentration of the lower cladding layer 12 was 5E + 17 / cm³. ３The average doping concentration in the upper cladding layer 14 was 1E+17 / cm³. ３ The average doping concentration in layers other than the cladding layer, excluding the active layer 13, was 0.8 to 3E+18 / cm³. ３ That's what I decided.

[0149] After the EPW was fabricated, a peel-preventing layer 16 was formed as shown in Figure 3. A material with a high Young's modulus is preferred for the peel-preventing layer 16, and the SiO of the adhesion-enhancing layer 18 is also preferred. ２ Materials with a higher Young's modulus are desirable. In this embodiment, silicon nitride (SiNx), aluminum nitride (AlN), and sapphire (Al ２ O ３ Cordillerite was used. Each film was deposited by sputtering and formed to a thickness of 50 nm.

[0150] Next, using the P-CVD method, a 20 nm thick adhesion-enhancing layer 18 is formed using SiO ２ The film was deposited on EPW on which a peel-preventing layer 16 had been formed. Similarly, a sapphire substrate used as an ultraviolet and visible light transmitting substrate 20 also had SiO as an adhesion-enhancing layer 19. ２ A film was deposited. TEOS and oxygen were used as materials for P-CVD deposition.

[0151] Next, in order to form the resin layer 17, SiO is used as the adhesion-enhancing layer 18. ２ BCB was dropped onto EPW with a film deposited on it and spin-coated. The spinning speed was 5,000 rpm, and the amount of BCB solution dropped was 0.5 ml. At that time, the concentration and viscosity of the BCB solution were adjusted by diluting it, and the coating was controlled to achieve the desired film thickness. Specifically, using CYCLOTENE 3022-35 manufactured by Dow Chemical as the BCB raw material, a BCB film with a thickness of 0.2 μm was obtained as the resin layer 17 by mixing the diluent and the BCB solution in a ratio of 1:2.

[0152] Next, as shown in Figure 4, SiO is used as the adhesion-enhancing layer 19 in advance by P-CVD. ２ A 0.02 μm film-deposited ultraviolet and visible light-transmitting substrate 20 and the aforementioned EPW substrate were placed facing each other in a vacuum chamber and thermocompressed to bond the epitaxial layer and the ultraviolet and visible light-transmitting substrate 20.

[0153] In this embodiment, sapphire is used as the ultraviolet and visible light transmitting substrate 20, and the bonding pressure is 60 N / cm². ２ The bonding (curing) conditions for the BCB were set to 250°C for 30 minutes, and the curing treatment was performed in a reduced pressure atmosphere of 0.01 atm.

[0154] After bonding with the ultraviolet and visible light-transmitting substrate 20, the starting substrate 2 was etched off with ammonia hydrogen peroxide. After removing the starting substrate 2, the etching stop layer 11 was removed (first the InGaP etching stop layer was removed with hydrochloric acid water, and then the GaAs etching stop layer was removed with sulfuric acid hydrogen peroxide). A bonded wafer for device fabrication was then prepared, as shown in Figure 5, in which only the light-emitting functional layer remained on the ultraviolet and visible light-transmitting substrate 20.

[0155] After fabricating a bonded wafer as shown in Figure 5, SiO for hard mask ２ A film was deposited to a thickness of 1.2 μm using the P-CVD method, and a resist pattern was formed using the photolithography method. The openings in the resist pattern were etched with a hydrofluoric acid-based solution to create a pattern, and the resist was removed. After removal, the material 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 embodiment, chlorine was used as the chlorine-based gas, and the substrate temperature was 30°C during the process. The same process was repeated to partially remove the lower cladding layer 12, the active layer 13, and the upper cladding layer 14, exposing the GaP window layer 15 as shown in Figure 6.

[0156] Next, a protective film 21 was formed. First, SiO ２ A film with a thickness of 0.5 μm was deposited using the P-CVD method, and a resist pattern was formed using the photolithography method. Next, the openings of the resist pattern were etched with a hydrofluoric acid-based solution to create a pattern, and the resist was peeled off to form a protective film 21 as shown in Figure 7.

[0157] Next, the electrode 22 was formed. First, a resist pattern was formed by photolithography, metal was deposited into the openings, and the pattern was formed by the lift-off method. After forming the metal pattern, RTA treatment in a nitrogen atmosphere (400°C, 5 minutes) was performed to form an ohmic contact between the metal pattern and the semiconductor layer, thereby forming the ohmic electrode 22 as shown in Figure 8.

[0158] (Comparative Example) The procedure for preparing the epitaxial substrate (EPW) was the same as in the example, but no peeling prevention layer was formed on the EPW, and SiO was used as the adhesion enhancing layer. ２ Only a film was formed. Other aspects, such as spin coating of BCB, bonding method, removal method of the starting substrate after bonding with the ultraviolet and visible light transmitting substrate, and device formation process, were the same as in the example.

[0159] (Evaluation) In the example, no epitaxial delamination occurred, but in the comparative example, epitaxial delamination occurred. For reference, Figure 9 shows the surface condition of the bonded wafer in the example, and Figure 10 shows the surface condition of the bonded wafer in the comparative example. There was no delamination in the example, but numerous delaminations occurred in the comparative example. It is thought that epitaxial delamination occurred in the comparative example in areas where cracks caused by hillocks or pits were present. When delamination occurs in this way, the effective area of ​​the bonded wafer decreases.

[0160] The results suggest that, firstly, the heat treatment during ohmic contact formation (RTA treatment: 400°C, 5 minutes) exposed the resin layer to a temperature process above its glass transition temperature, resulting in fluidity. Secondly, in the comparative example without a delamination prevention layer, the resin layer migrated away from the bonding interface through cracks, weakening the bond and leading to epitaxial layer delamination. In contrast, in the example with a delamination prevention layer, the resin layer did not migrate away from the bonding interface, thus maintaining the bond and preventing epitaxial layer delamination.

[0161] The delamination-inhibiting effect of the example remains effective even after repeated heat treatments. Although heat treatment for ohmic contact formation needs to be performed approximately 1 to 4 times depending on the conditions, as shown in Figure 11, even after repeated heat treatments (horizontal axis: number of RTAs), the number of delamination points in the epitaxial layer (vertical axis) is clearly less in the example than in the comparative example, indicating that delamination is effectively inhibited.

[0162] The materials used for the peel-preventing layer in the example are silicon nitride (SiNx), aluminum nitride (AlN), and sapphire (AlN), as shown in Figure 11. ２ O ３ ), it is cordierite.

[0163] This specification includes the following embodiments: [1] A bonded wafer characterized by having a plurality of compound semiconductor layers provided on a starting substrate, a peel-preventing layer provided on the plurality of compound semiconductor layers, a resin layer provided on the peel-preventing layer, and an ultraviolet and visible light-transmitting substrate bonded via the resin layer. [2] The bonded wafer according to [1], characterized in that the compound semiconductor layers contain two or more of Al, Ga, In, P, and As. [3] The bonded wafer according to [1] or [2], 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 any one of [1] to [3], characterized in that the ultraviolet and visible light-transmitting substrate contains one of sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, and GaP. [5]: The bonded wafer according to any one of [1] to [4] above, characterized in that the peel-preventing layer is made of a material with a Young's modulus of 100 GPa or more. [6]: The bonded wafer according to any one of [1] to [5] above, characterized in that the peel-preventing layer has a Mohs hardness of 7 or more. [7]: The bonded wafer according to any one of [1] to [6] above, characterized in that the peel-preventing layer is made of at least one layer of one or more materials selected from cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond. [8]: A method for manufacturing a bonded wafer, characterized in that it includes the steps of: epitaxially growing a plurality of compound semiconductor layers on a starting substrate; forming a peel-preventing layer on the plurality of compound semiconductor layers; forming a resin layer on the peel-preventing layer; and bonding an ultraviolet and visible light transmitting substrate via the resin layer. [9]: The method for manufacturing a bonded wafer according to [8] above, characterized in that the compound semiconductor layer is made of a material containing two or more of Al, Ga, In, P, and As.

[10] : A method for manufacturing a bonded wafer according to [8] or [9] above, 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.

[11] : A method for manufacturing a bonded wafer according to any one of [8] to

[10] above, characterized in that the ultraviolet and visible light transmitting substrate is made of a material comprising sapphire, quartz, glass, lithium tantalate, lithium niobate, ZnO, SiC, GaN, and GaP.

[12] : A method for manufacturing a bonded wafer according to any one of [8] to

[11] above, characterized in that the peel-preventing layer is made of a material with a Young's modulus of 100 GPa or more.

[13] : A method for manufacturing a bonded wafer according to any one of [8] to

[12] above, characterized in that the peel-preventing layer has a Mohs hardness of 7 or more.

[14] : A method for manufacturing a bonded wafer according to any one of [8] to

[13] above, characterized in that the peel prevention layer is composed of at least one layer of one or more materials selected from cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond.

[0164] 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.

Claims

1. A bonded wafer characterized by comprising: a plurality of compound semiconductor layers provided on a starting substrate; a peel-preventing layer provided on the plurality of compound semiconductor layers; a resin layer provided on the peel-preventing layer; and an ultraviolet and visible light transparent substrate bonded via the resin layer.

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 bonded wafer according to any one of claims 1 to 4, characterized in that the peel prevention layer is made of a material with a Young's modulus of 100 GPa or more.

6. The bonded wafer according to claim 5, characterized in that the peel-preventing layer has a Mohs hardness of 7 or higher.

7. The bonded wafer according to claim 5, characterized in that the peel prevention layer is composed of at least one layer of one or more materials selected from cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond.

8. 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 delamination prevention layer on the plurality of compound semiconductor layers; forming a resin layer on the delamination prevention layer; and bonding an ultraviolet and visible light transparent substrate via the resin layer.

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

10. The method for manufacturing a bonded wafer according to claim 8, 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.

11. The method for manufacturing a bonded wafer according to claim 8, 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.

12. The method for manufacturing a bonded wafer according to any one of claims 8 to 11, characterized in that the peel prevention layer is made of a material with a Young's modulus of 100 GPa or more.

13. The method for manufacturing a bonded wafer according to claim 12, characterized in that the peel prevention layer has a Mohs hardness of 7 or higher.

14. The method for manufacturing a bonded wafer according to 12, characterized in that the peel prevention layer is composed of at least one layer of one or more materials selected from cordierite, forsterite, gallium nitride, zirconia, silicon nitride, gallium oxide, aluminum nitride, silicon carbide, sapphire, boron carbide, tungsten carbide, titanium nitride, and diamond.

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