Method for forming coating film on epitaxial substrate and manufacturing method for junction type wafer

Abstract

To provide a method of forming a coating film on an epitaxial substrate, in which when a coating film is formed for bonding an ultraviolet ray and visible ray transmitting substrate to a compound semiconductor where a convex defect or a concave defect exists on a surface, the thickness of the coating film can be homogenized and the curing defect of the coating film can be suppressed.SOLUTION: In a method for forming a coating film on an epitaxial substrate 1, when a coating film 15 is formed by applying resin in an environment filled with an atmospheric gas on a surface of the epitaxial substrate 1 where a plurality of compound semiconductor layers 2 are grown or deposited on a starting substrate 3, the surface thereof having a convex defect 31 with a side of 100 μm or more or a concave defect 33 with a side of 200 μm or less formed on or near the surface of the compound semiconductor layer 2, the oxygen concentration of the coating atmosphere is 100 ppm or less.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for forming a coating film on an epitaxial substrate and a method for manufacturing a bonded wafer. [Background technology]

[0002] A μ-LED transfer technology has been 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 GaAs, which absorbs visible light, and LLO is made possible by transferring the epitaxial layer to a substrate that is transparent to ultraviolet and visible light.

[0003] When transferring the epitaxial layer to the UV- and visible-light-transmitting substrate, direct bonding is possible, but providing a thermal sacrificial layer for the LLO is preferable because it minimizes the thermal effect on the epitaxial layer. By using the thermal sacrificial layer as both a bonding layer and a bonding layer, the LLO can be realized without affecting the LED element. A technology has been disclosed in which UV-absorbing benzocyclobutene (BCB) is selected as the bonding layer and sacrificial layer (Patent Document 1).

[0004] When an EPW (epitaxial wafer) on which a light-emitting diode is formed using BCB as a bonding layer and sacrificial layer is bonded to a substrate of a different material via BCB, BCB is applied by spin coating. The major prerequisite for application by spin coating is that it must be applied to a flat wafer.

[0005] On the other hand, since the EPW for light-emitting diodes is epitaxially grown from a material different from that of the starting substrate, the lattice constant does not usually match that of the starting substrate at the temperature range during growth or at room temperature. Furthermore, the epitaxial layer may also be made of multiple different materials, and a structure may be selected for growth in a lattice mismatched system. When such a structure is selected, the surface of the epitaxial layer is not a mirror surface but a rough surface known as a matte finish due to the lattice mismatch.

[0006] In the case of AlGaInP-based LEDs, GaP is often selected as the final epitaxial layer. When GaP is used as the final layer, it grows in a lattice mismatch with the underlying AlGaInP-based material, so the surface of the final epitaxial layer has pits (concave portions).

[0007] In addition to the pits, the surface of the final epitaxial layer has particles (hereinafter referred to as inclusions) that become convex parts on the surface of the final epitaxial layer due to the fall of precipitates inside the furnace during epitaxial growth. Such pits and inclusions hinder the uniformity of the film thickness of the coating film and cause bonding defects, resulting in a decrease in the bonding yield.

[0008] In order to eliminate the unevenness of the pits (concave portions) or the inclusions (convex portions), SiO2 or SiN, which is transparent to visible light and has low absorption rate for ultraviolet light, is used. x It is also possible to consider depositing the above to eliminate the unevenness.

[0009] However, SiO2 and SiN x Due to the design structure, the deposited film such as the above will inevitably become part of the sacrificial layer and will eventually need to be removed. The thicker the deposited film, the more work it will take to remove it after peeling off the sacrificial layer.

[0010] Specifically, the removal process time will be extended, leading to increased processing costs and reduced yields. Therefore, it is preferable that the deposited film is thin or not at all. For the above reasons, even if the deposition film is designed and selected, the thickness must not exceed 1 μm. With a deposited film of this thickness, it may be possible to reduce the degree of unevenness, but it is far from eliminating the unevenness, and it is not possible to choose a method of eliminating the unevenness with a deposited film.

[0011] The pits present on the surface of the final epitaxial layer have a concave shape, and are basically approximately pyramidal. The greater the side length of the pyramidal portion, the deeper the depth. The coating method is essentially a method in which it is difficult to obtain uniformity in film thickness on a surface having an uneven shape, and it is difficult to obtain uniformity in film thickness near concave portions such as pits and convex portions such as inclusions. The deeper the concave portions, the more difficult it is for the coating liquid to penetrate.

[0012] In particular, if the wettability between BCB and the surface to be coated is poor, the coating liquid will not easily penetrate into the recesses, and as a result, atmospheric gas will easily be trapped between the coating film and the surface. Here, only the spin coating method has been described in detail, but the same phenomenon occurs with other coating methods such as the dip method.

[0013] Regarding the improvement of filling of a coating film in a deep concave shape, a technology has been disclosed in which BCB is applied in a vacuum to enhance filling. The prior art described in Patent Document 2 discloses a technology for applying BCB in a vacuum to fill vias (concave holes) formed on a surface.

[0014] However, BCB contains a solvent, and there is a problem that the concentration changes over time in a vacuum as the solvent evaporates. As a result of the change in BCB concentration, the viscosity changes and the thickness of the BCB coating film changes. Although forming a coating film in a vacuum is effective in filling recesses, coating in a vacuum atmosphere is not preferable in terms of the reproducibility and stability of the film thickness.

[0015] Inclusions are convex defects. When forming a coating film by spin coating, the dropped coating liquid is moved toward the outer periphery of the rotation by centrifugal force, but if an inclusion exists, it becomes an obstruction and the film thickness in the outer periphery of the rotation will inevitably be different from other places (in many cases it will be thinner).

[0016] Furthermore, when the height of the convex portion is high (for example, 10 μm or more), it is difficult to coat the side surface with the coating liquid. Furthermore, the side surface and surface of the inclusion portion, which is a convex shape, have an irregular and complex uneven shape. With a coating method that has poor unevenness tracking ability, it is difficult to uniformly coat the inclusion portion and its surrounding area during coating. Furthermore, since the coating is not uniform, air is likely to be trapped at the interface between the BCB layer and the inclusion portion.

[0017] Although the method of coating in a vacuum as shown in Patent Document 2 has problems with the reproducibility and stability of the film thickness as described above, it is effective in solving the problem of air being present near the surface of the uneven portion. However, this method is not preferable when it is desired to form a thin BCB layer with a uniform film thickness.

[0018] First, the reason why the BCB layer should be thinned is explained. The BCB layer (hereinafter also referred to as the BCB film) is a sacrificial layer in terms of the design structure, and should be removed eventually. The thicker the BCB layer, the more work is required for the removal process after peeling off the sacrificial layer. Specifically, the longer the removal process time, the higher the processing cost and the lower the yield.

[0019] Therefore, it is preferable that the BCB layer is as thin as possible. For the above reasons, it is preferable that the thickness of the BCB layer does not exceed 1 μm, and it is preferable that the thickness is 3 μm or less at most. For the above reasons, it is preferable to set an upper limit on the thickness of the BCB layer.

[0020] In addition, the BCB layer is ablated by laser in LLO. In this case, differences in film thickness depending on the processing position (site) on the wafer change the LLO processing efficiency and cause a decrease in the yield during assembly. Therefore, it is preferable that the coating method is one that guarantees film thickness uniformity between wafers and batches as well as the distribution of film thickness within the surface, and has good reproducibility.

[0021] When coating is performed in a vacuum as shown in Patent Document 2, the solvent evaporates in the vacuum, resulting in a high BCB concentration. Vacuum production times generally vary, making it difficult to reproducibly control the amount of solvent that evaporates. As the solvent evaporates, the viscosity increases, and as the viscosity increases, the film thickness also increases.

[0022] If you want to form a coating film with a certain thickness or more, the design can accommodate changes in viscosity and film thickness, but if you want to maintain a thin film of less than 1 μm, this becomes a major problem. Therefore, it is not a preferred method for forming a thin, uniform BCB film suitable for LLO.

[0023] A technique has been disclosed in which, when curing BCB, the curing and bonding process is carried out in a vacuum or in a nitrogen atmosphere with an oxygen concentration of 100 ppm or less (Patent Document 3). This is because the presence of oxygen during the curing of BCB (cycloaddition reaction) inhibits curing. However, when the epitaxial layer surface is uneven, there is a problem that poor curing occurs and the epitaxial layer peels off even if the low oxygen concentration condition during curing described in Patent Document 3 is satisfied. [Prior art documents] [Patent documents]

[0024] [Patent Document 1] JP 2023-066285 A [Patent Document 2] JP 2015-166736 A [Patent Document 3] Japanese Patent Application Publication No. 7-14701 Summary of the Invention [Problem to be solved by the invention]

[0025] The inventors presumed that the reason why the epitaxial layer peels off after the BCB hardens when the epitaxial layer surface is uneven is that oxygen remains around the uneven parts of the epitaxial layer surface during the BCB application process.

[0026] The present invention has been made to solve the above problems, and has an object to provide a method for forming a coating film on an epitaxial substrate, which can provide a coating film with a uniform thickness and suppress poor curing of the coating film when forming a coating film for bonding an ultraviolet and visible light transmissive substrate to a compound semiconductor having a convex defect or a concave defect on its surface.

[0027] Another object of the present invention is to provide a method for producing a bonded wafer in which peeling of the epitaxial layer is unlikely to occur. [Means for solving the problem]

[0028] The present invention has been made to achieve the above-mentioned object, and provides a method for forming a coating film on an epitaxial substrate, which is obtained by growing or depositing a plurality of compound semiconductor layers on a starting substrate, and which comprises applying a resin to a surface of the epitaxial substrate having a convex defect with a side of 100 μm or more or a concave defect with a side of 200 μm or less formed on or near the surface of the compound semiconductor layer, in an environment filled with atmospheric gas to form a coating film, the method being characterized in that the oxygen concentration of the coating atmosphere is set to 100 ppm or less.

[0029] According to this method for forming a coating film on an epitaxial substrate, by performing coating in an environment in which the oxygen concentration of the coating atmosphere is 100 ppm or less, oxygen can be removed from the coating film and from the gas remaining in the convex defect or concave defect.

[0030] If the oxygen present at the interface between the coating film and the epitaxial substrate is 100 ppm or more, it inhibits the cycloaddition reaction of the coating film such as BCB, and inhibits the coating film from being thermally cured, but gases other than oxygen do not inhibit the cycloaddition reaction, so the thermal curing process of the coating film can be carried out as designed. In other words, by eliminating as much oxygen as possible from the atmosphere in which the resin is applied, it is possible to prevent poor curing of the resin caused by the presence of oxygen.

[0031] In this case, the thickness of the coating film can be set to 1 μm or less.

[0032] This allows a thickness suitable for LLO. In addition, when coating a film thickness of 1 μm or less, the coverage rate tends to worsen, so the effect of the present invention, which allows the coating film to have a uniform thickness, is particularly high.

[0033] At this time, when the coating film is formed, the oxygen concentration in the coating atmosphere can be set to 100 ppm or less by replacing the atmosphere in a sealed container in which the epitaxial substrate is housed with a purge gas.

[0034] As a result, the coating atmosphere during resin coating is replaced from air to purge gas, and coating is performed, making it possible to eliminate oxygen contained in the air.

[0035] In this case, the purge gas may be one or more selected from the group consisting of helium, hydrogen, nitrogen, neon, and argon.

[0036] This allows the selection of gases that do not contain oxygen, such as helium, hydrogen, nitrogen, neon, or argon, as the purge gas, making it easy to maintain the oxygen concentration in the coating atmosphere at 100 ppm or less.

[0037] At this time, the coating atmosphere can be a pressure atmosphere of 10 kPa or more.

[0038] This makes it possible to maintain the chucking force when the wafer is vacuum-chucked during coating, and also suppresses the volatilization of the organic solvent added to adjust the resin viscosity, thereby suppressing changes in viscosity.

[0039] In this case, the coating film may be made of a thermosetting resin.

[0040] This makes it possible to adjust the timing for curing the coating film by adjusting the temperature.

[0041] In this case, the thermosetting resin may be one or more selected from the group consisting of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluorine resin, spin-on glass, and polyimide.

[0042] This allows the support substrate to be reliably bonded to the epitaxial substrate.

[0043] In this case, the concave defect may be a pit generated during epitaxial growth, and the convex defect may be a defect generated by a particle that falls onto the compound semiconductor layer during epitaxial growth.

[0044] This makes it possible to form a coating film even on an epitaxial substrate having pits or particles on the surface.

[0045] The present invention has been made to achieve the above-mentioned object, and provides a method for producing a bonded wafer, the method including a coating film formation step of coating a resin in an environment filled with atmospheric gas on a surface of an epitaxial substrate obtained by growing or depositing a plurality of compound semiconductor layers on a starting substrate, the surface of the epitaxial substrate having a convex defect with a side of 100 μm or more or a concave defect with a side of 200 μm or less formed on or near the surface of the compound semiconductor layer to form a coating film, and a bonding / adhering step of bonding or adhering the compound semiconductor layer and an ultraviolet and visible light transmissive substrate via the coating film to produce a bonded wafer, characterized in that the coating atmosphere in the coating film formation step has an oxygen concentration of 100 ppm or less.

[0046] According to this method for manufacturing a bonded wafer, oxygen can be removed from between the unevenness defects of the epitaxial substrate and the coating film, and poor curing of the coating film can be prevented. Therefore, peeling of the epitaxial layer from the coating film after bonding is less likely to occur.

[0047] In this case, in the bonding / adhering step, the bonding or adhesion can be performed using one or more of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluorine resin, spin-on glass, and polyimide.

[0048] This allows the ultraviolet and visible light transmissive substrate to be reliably bonded to the epitaxial substrate.

[0049] In this case, the ultraviolet and visible light transmissive substrate can be any of sapphire, quartz, glass, lithium tantalate (LT), lithium niobate (LN), ZnO, SiC, GaN, and GaP, which are ultraviolet and visible light transmissive.

[0050] As a result, even when light-receiving and light-emitting elements such as PDs (photodiodes), APDs (avalanche photodiodes), LDs (laser diodes), and LEDs are formed on the epitaxial substrate, light can be received and emitted between the light-receiving and light-emitting elements and the outside via the support substrate formed in a later process. Effect of the Invention

[0051] As described above, according to the method for forming a coating film on an epitaxial substrate of the present invention, when a coating film for bonding an ultraviolet and visible light transmissive substrate to a compound semiconductor having a convex defect or a concave defect on its surface is formed, the coating film can be made to have a uniform thickness and poor curing of the coating film can be suppressed.

[0052] Furthermore, according to the method for producing a bonded wafer of the present invention, it is possible to produce a bonded wafer in which peeling of the epitaxial layer is unlikely to occur. [Brief description of the drawings]

[0053] [Figure 1] 1 shows an epitaxial substrate on which a coating film is to be formed by the method for forming a coating film on an epitaxial substrate of the present invention. [Diagram 2] 1 shows a state in which a coating film is formed on an epitaxial substrate, with convex and concave defects not shown. [Diagram 3] 1 shows a state in which a bonded wafer is formed by bonding or adhering a compound semiconductor layer of an epitaxial substrate and an ultraviolet and visible light transmissive substrate via a coating film. [Figure 4] This shows a state in which the starting substrate and the etching stop layer have been removed from the state shown in FIG. [Diagram 5] This shows the state after ICP (Inductively Coupled Plasma) processing from the state shown in Figure 4. [Figure 6] This shows the state after deposition of SiO2 and pattern formation from the state shown in FIG. [Figure 7] This shows the state after electrodes have been formed in the state shown in FIG. [Figure 8] The procedure of the embodiment will be described below. [Figure 9] FIG. 13 is a diagram showing a comparison of the number of epitaxial peelings at each process step in the formation of a device in a compound semiconductor layer of a bonded wafer between an embodiment and a comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] The present invention will be described in detail below, but the present invention is not limited thereto.

[0055] As described above, when forming a coating film for bonding an ultraviolet and visible light transmissive substrate to a compound semiconductor having a surface with convex or concave defects, there has been a demand for a method for forming a coating film on an epitaxial substrate that can provide a coating film with a uniform thickness and can suppress poor curing of the coating film.

[0056] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that a method for forming a coating film on an epitaxial substrate, in which a plurality of compound semiconductor layers are grown or deposited on a starting substrate, the method comprising: applying a resin to a surface of the epitaxial substrate having a convex defect with a side of 100 μm or more or a concave defect with a side of 200 μm or less formed on or near the surface of the compound semiconductor layer, in an environment filled with atmospheric gas to form a coating film, wherein the oxygen concentration of the coating atmosphere is set to 100 ppm or less, and the method makes it possible to form a coating film with a uniform thickness and to suppress poor curing of the coating film when forming a coating film for bonding an ultraviolet and visible light transmissive substrate to a compound semiconductor having a convex defect or concave defect on its surface, and thus completed the present invention.

[0057] As described above, there has also been a demand for a method of manufacturing a bonded wafer in which peeling of the epitaxial layer is less likely to occur.

[0058] As a result of intensive investigations into the above-mentioned problems, the present inventors have found that a bonded wafer in which peeling of the epitaxial layer is unlikely to occur can be produced by a method for producing a bonded wafer, the method including a coated film formation step of coating a resin in an environment filled with atmospheric gas on a surface of an epitaxial substrate having a plurality of compound semiconductor layers grown or deposited on a starting substrate, the surface of the epitaxial substrate having a convex defect with a side of 100 μm or more or a concave defect with a side of 200 μm or less formed on or near the surface of the compound semiconductor layer to form a coated film, and a bonding / adhering step of bonding or adhering the compound semiconductor layer and an ultraviolet and visible light transmissive substrate via the coated film, the method being characterized in that the coating atmosphere in the coated film formation step has an oxygen concentration of 100 ppm or less, and thus completed the present invention.

[0059] The following description will be given with reference to the drawings. Hereinafter, a method for forming a coating film on an epitaxial substrate and a method for manufacturing a bonded wafer according to an embodiment of the present invention will be described with reference to FIGS.

[0060] First, an example of an epitaxial substrate on which a coating film is formed will be described with reference to FIG. As shown in FIG. 1, the epitaxial substrate 1 comprises a starting substrate 3 and a plurality of compound semiconductor layers 2 . The starting substrate 3 is a substrate that supports the compound semiconductor layer 2 and serves as a base during growth or deposition, and is, for example, a GaAs substrate.

[0061] The compound semiconductor layer 2 is an epitaxial layer grown or deposited on a starting substrate 3. The epitaxial substrate 1 shown in Fig. 1 is a substrate for forming an LED structure as a device layer by separating the compound semiconductor layer 2 from the starting substrate 3, and therefore illustrates a structure in which an etching stop layer 5, a lower cladding layer 7, an active layer 9, an upper cladding layer 11, and a GaP window layer 13 are laminated in this order as the compound semiconductor layer 2.

[0062] The epitaxial substrate 1 can be manufactured, for example, by epitaxially growing a GaAs buffer layer (not shown) made of the same material as the starting substrate 3 on a GaAs substrate as the starting substrate 3, forming an etching stop layer 5 such as GaInP on top of that, and further growing a lower cladding layer 7, an active layer 9, an upper cladding layer 11, and a GaP window layer 13 as AlGaInP-based epitaxial functional layers on top of that.

[0063] In this manner, FIG. 1 illustrates an example in which an epitaxial substrate 1 is fabricated by laminating a first-conductivity-type GaAs buffer layer on a first-conductivity-type GaAs starting substrate 3, and then laminating a light-emitting functional layer consisting of a GaInP / GaAs etching stop layer 5, an AlGaInP lower cladding layer 7, an AlGaInP active layer 9, an AlGaInP upper cladding layer 11, a GaInP intermediate layer (not shown), and a GaP window layer 13.

[0064] In this embodiment, the lower cladding layer 7 and the upper cladding layer 11 are illustrated as a single layer in FIG. 1, but the doping level is not limited to being constant, and the doping level may be two or more steps, may have a graded doping, or may have a doping profile that is a combination of these.

[0065] Although FIG. 1 illustrates the lower cladding layer 7 and the upper cladding layer 11 as a single layer, the cladding layers are not limited to one type of composition, and may be cladding layers made of two or more types of compositions.

[0066] The active layer 9 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 barrier layer and / or the well layer may have a thickness of 10 nm or more, which has a low quantum effect.

[0067] Although the window layer is described as a GaP window layer 13, it is not limited to GaP, and it is sufficient that the window layer is transparent to the emission wavelength. Therefore, even if AlGaAs or AlAs is selected, the same effect as that of GaP can be obtained as a window layer.

[0068] In this embodiment, an LED structure in which the epitaxial functional layer is made of AlGaInP is shown as an example, but this structure is not limited to this, and other structures such as an InGaP / GaAs solar cell structure, an InGaP / GaAs HBT structure, and an AlGaAs / GaAs HEMT structure can be selected.

[0069] These functional layer structures are merely examples, and any structure can be selected as long as it is approximately lattice-matched to the starting substrate 3. In addition, although the case where the etching stop layer 5 is inserted is illustrated here, this is not necessarily required depending on the method selected for peeling off the substrate and the epitaxial functional layer, and when selectively wet etching the starting substrate 3 and the epitaxial layer, a similar structure can be ultimately obtained by inserting a sacrificial layer such as AlAs instead of the etching stop layer 5.

[0070] In this embodiment, the starting substrate 3 is GaAs, but it is not limited to GaAs, and any substrate can be selected as long as it is epitaxially grown. For example, after growing a buffer layer such as Ge on the starting substrate 3 (Si), a GaAs first buffer layer and a sacrificial layer such as AlAs may be formed, a second GaAs buffer layer may be epitaxially grown thereon, and an epitaxial functional layer may be grown thereon. In this case, a Ge layer is stacked as the buffer layer, but the same effect can be obtained even if there is no Ge layer.

[0071] In addition, the surface orientation of the starting substrate 3 is preferably a (001) plane. The epitaxial functional layer can be an AlGaInP-based LED structure, an InGaP / GaAs-based solar cell structure, an InGaP / GaAs-based HBT structure, an AlGaAs / GaAs-based HEMT structure, or the like.

[0072] This functional layer structure is merely an example, and any structure can be selected as long as it is approximately lattice-matched to the starting substrate 3. Also, although the case where a sacrificial layer is inserted is exemplified here, this is not necessarily necessary depending on the method selected for peeling off the substrate and epitaxial layer, and if the entire starting substrate 3 after epitaxial growth is chemically etched off, the same effect can be obtained without inserting a sacrificial layer.

[0073] Alternatively, instead of using GaAs or Si as the starting substrate, InP may be used as the starting substrate 3. In this case, a sacrificial layer such as InGaAs is formed on the starting substrate 3 (InP), an InP buffer layer made of the same material as the starting substrate is epitaxially grown on top of that, and an epitaxial functional layer is grown on top of that.

[0074] This epitaxial functional layer can be configured as a photodetector structure made of InGaAs / InP, a photodetector (PD, APD) structure made of InGaAsP / InP, a light-emitting element (LD, LED) structure made of InGaAsP / InP, a photodetector (PD, APD) structure made of InAlAs / InGaAs, or a field effect transistor structure made of InAlAs / InGaAs.

[0075] These functional layer structures are merely examples, and any structure can be selected as long as it is approximately lattice-matched to the starting substrate 3. In addition, although the case where a sacrificial layer is inserted is exemplified here, this is not necessarily required depending on the method selected for peeling off the substrate and the epitaxial functional layer, and when the starting substrate 3 is chemically etched off, a similar structure can be ultimately obtained by inserting an etching stop layer such as InGaAs instead of the sacrificial layer without inserting the sacrificial layer.

[0076] As shown in FIG. 1, concave defects 33 (pits) are formed on or near the surface of the epitaxial top layer of the epitaxial substrate 1 (EPW), in this case the GaP window layer 13, due to lattice mismatch or different stoichiometry during epitaxial growth.

[0077] When the AlGaInP-based epitaxial functional layer is an LED structure, the concave defect 33 (pit) has a pyramidal concave shape. The pyramidal surface of the pit often has a (11x) face (x=1 to 7), and the apex of the pyramidal portion is often acute. In addition, since the depth of the pyramidal portion does not exceed the total thickness of the epitaxial layer, each side has a length of 200 μm or less, and the depth is also 50 μm or less.

[0078] Furthermore, on the surface or near the surface of the GaP window layer 13, there are many convex defects 31 (inclusions) each having a side of 100 μm or more, which are caused by particles that have fallen from the inner wall of the growth furnace during epitaxial growth. The above is a description of one example of epitaxial substrate 1 on which coating film 15 is formed.

[0079] Next, a method for forming a coating film on epitaxial substrate 1 will be described with reference to FIGS. In the method for forming a coated film of the present invention, a resin is applied to the surface of the epitaxial top layer, GaP window layer 13 in this case, of epitaxial substrate 1 shown in Fig. 1 in an environment filled with atmospheric gas, to form coated film 15 as shown in Fig. 2. At this time, the oxygen concentration of the coating atmosphere is set to 100 ppm or less. The reason is as follows.

[0080] When a thermosetting resin such as BCB is applied to form coating film 15, wettability during application is poor, and it is difficult to improve coverage of concave defect 33 even for a concave defect 33 with a depth of about 50 μm. Therefore, atmospheric gas during application is likely to remain at the interface between concave defect 33 and coating film 15, particularly at the apex of the pyramid.

[0081] Furthermore, in most cases, the convex defect 31 (inclusion) has a height of 1 μm or more due to the size of the original particle, as well as subsequent abnormal growth. (The particle that falls just before the end of epitaxial growth does not grow very tall, as the time of abnormal growth is short.) The convex defect 31 has irregular sides, a very large surface area, and is also tall.

[0082] Furthermore, the coating film 15 is generally formed by spin coating, but the coating method using spin coating is a film formation method in which the film thickness uniformity from the position where the convex defect 31 exists to the outer periphery as viewed from the center of rotation becomes very poor. The higher the height of the convex defect 31, the more remarkable this tendency becomes.

[0083] Furthermore, some coating films 15, such as BCB, have poor wettability during coating, and the coverage rate worsens as the surface area of ​​the side surface of convex defect 31 increases. Therefore, it is difficult to improve the coverage rate and coating film uniformity of convex defect 31 and its surrounding area, and atmospheric gas during coating tends to remain at the interface between the side surface of convex defect 31 and coating film 15.

[0084] In order to solve the above problems, the oxygen concentration of the coating atmosphere is set to 100 ppm or less so that no problems will arise even if the atmospheric gas used during the coating process remains at the interface between the pit (concave defect 33) or inclusion (convex defect 31) portion and the coating film 15.

[0085] By performing coating in an environment where the oxygen concentration of the coating atmosphere is 100 ppm or less, oxygen can be removed from the gas remaining at the interface between the coating film 15 and the convex defect 31 or at the concave defect 33. If the oxygen concentration of the gas present at this interface exceeds 100 ppm, it inhibits the cycloaddition reaction and inhibits the thermal curing of BCB, particularly when the coating film 15 is BCB, but gases other than oxygen do not inhibit the cycloaddition reaction, so by setting the oxygen concentration to 100 ppm or less, the curing process of the coating film 15 can be performed as designed. This is the reason for setting the oxygen concentration of the coating atmosphere to 100 ppm or less.

[0086] Although there are no particular limitations on the specific method for reducing the oxygen concentration in the coating atmosphere to 100 ppm or less, the following method can be exemplified. First, the epitaxial substrate 1 is introduced into a glove box having an oxygen concentration of 100 ppm or less through a load lock. In this embodiment, a glove box is exemplified, but the present invention is not limited to a glove box, and any other equipment having airtightness may be selected.

[0087] For example, if the equipment can mechanically move the epitaxial substrate 1 from the load lock and mechanically move it to the spin coater described later, it is not necessary to have a glove, and an airtight resin container such as a metal chamber or a desiccator may be used. However, since an environment with few particles is preferable and the resin of the coating film 15 contains an organic solvent, an airtight container mainly made of metal is preferable rather than an all-resin container.

[0088] An example of a method for reducing the oxygen concentration to 100 ppm or less is a continuous flow of a purge gas, i.e., a method in which the oxygen concentration of the coating atmosphere is reduced to 100 ppm or less by replacing the atmosphere inside a sealed container in which epitaxial substrate 1 is housed with a purge gas when coating film 15 is formed.

[0089] In this manner, by replacing the atmosphere during resin application with purge gas, oxygen contained in the atmosphere can be eliminated.

[0090] The type of purge gas is not particularly limited, but for example, one or more gases selected from helium, hydrogen, nitrogen, neon, and argon can be used.

[0091] This allows the selection of gases that do not contain oxygen, such as helium, hydrogen, nitrogen, neon, or argon, as the purge gas, making it easy to maintain the oxygen concentration in the coating atmosphere at 100 ppm or less.

[0092] A continuous flow of purge gas may be performed during the process of forming the coating film 15, but is not limited to a continuous flow. After an environment with an oxygen concentration of 100 ppm or less is obtained, the continuous flow may be stopped and the process of forming the coating film 15 may be performed in an airtight environment. This provides the same effect as when the coating film 15 is formed in a continuous flow environment, that is, no oxygen is present at the interface between the epitaxial layer (compound semiconductor layer 2) and the coating film 15.

[0093] The method for forming the coating film 15 is not particularly limited, but an example is a method in which the epitaxial substrate 1 introduced into a glove box is vacuum-adsorbed, and a coating film 15 of a thermosetting resin or the like is applied by a spin coating method. Since the inside of the glove box is an atmosphere at a pressure close to atmospheric pressure, a conventional spin coater can be used as is.

[0094] On the other hand, the formation of the coating film is carried out in an environment filled with atmospheric gas. In other words, it is not carried out in an environment such as a vacuum that excludes atmospheric gas. This is because if the coating film is formed in a vacuum, the solvent in the coating film evaporates, changing the concentration and viscosity, which in turn changes the film thickness, resulting in poor reproducibility and stability of the film thickness. To obtain such an environment, it is desirable that the pressure atmosphere during coating be 0.1 atmosphere (10 kPa) or higher, that is, atmospheric pressure, that is, close to 1 atmosphere (100 kPa).

[0095] By setting the pressure atmosphere within this range, the solvent that adjusts the viscosity of the resin to be applied is less likely to volatilize, and it is possible to prevent changes in the designed coating thickness due to changes in viscosity. This makes it unnecessary to control the low-oxygen atmosphere and environmental temperature in order to maintain the designed thickness, making the manufacturing process simpler, improving process capacity and yield.

[0096] Furthermore, when forming the coating film 15 by spin coating, the epitaxial substrate 1 is generally vacuum chucked and rotated to coat the resin, but by setting the pressure atmosphere at 0.1 atmospheres or more, the relative pressure difference can be maintained and the vacuum chucking force on the epitaxial substrate 1 can be maintained. This also makes it possible to maintain the holding force of the epitaxial substrate 1 during rotation. This makes it difficult for the epitaxial substrate 1 to be damaged during rotation. For this reason, it is preferable to perform the spin coating process in a pressure environment of 0.1 atmospheres or more.

[0097] Although serious problems are unlikely to occur if the pressure of the atmosphere is higher than atmospheric pressure, there is no need to process in a pressurized atmosphere. Although it is effective to perform the process in a slightly pressurized atmosphere to prevent the inclusion of air, the upper limit of the pressure atmosphere is, for example, about 3 atmospheres (300 kPa).

[0098] Although there is no particular limitation on the thickness of the coating film 15, when BCB is used as the thermosetting resin, the thickness of the spin-coated BCB coating film is, for example, about 0.5 μm. However, the thickness is not limited to 0.5 μm, and may be 0.01 μm or more and 3 μm or less.

[0099] In particular, a thickness of 1 μm or less can be a thickness suitable for LLO. Furthermore, when coating with a thickness of 1 μm or less, the coverage rate changes in a worsening direction, so the effect of the present invention, which can make the coating film 15 have a uniform thickness, is particularly high.

[0100] The type of coating film 15 is not particularly limited, but by using a thermosetting resin, the timing at which coating film 15 is cured can be adjusted by temperature.

[0101] When the coating film 15 is made of a thermosetting resin, the resin may be one or more selected from the group consisting of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluororesin, spin-on glass, and polyimide. This allows the supporting substrate to be reliably bonded to the epitaxial substrate 1 in a later process.

[0102] A similar coating film 15 can be obtained by applying an adhesion enhancing treatment material to the surface on which the coating film 15 is to be applied before the formation of the coating film 15, and / or by forming an adhesion enhancing layer such as a SiO2 film 17a as shown in Fig. 2. Also, a similar coating film 15 can be obtained by applying the coating film 15 after removing the convex defects 31 on the epitaxial layer (compound semiconductor layer 2) by a known spike crush method. The above is an explanation of the procedure for forming a coating film on epitaxial substrate 1.

[0103] Next, the steps of a method for manufacturing a bonded wafer using epitaxial substrate 1 will be described with reference to FIGS.

[0104] First, a resin is applied to the surface of the epitaxial substrate 1 shown in Fig. 1 in an environment filled with atmospheric gas to form a coating film 15 as shown in Fig. 2 (coating film forming step). The specific coating film forming step is as described above in the explanation of the procedure of the coating film forming method, and in particular, the coating atmosphere must have an oxygen concentration of 100 ppm or less.

[0105] Next, as shown in FIG. 3, compound semiconductor layer 2 of epitaxial substrate 1 is bonded or adhered to ultraviolet and visible light transmissive substrate 19, which is a supporting substrate, via coating film 15, to produce bonded wafer 41 (bonding and adhesion process).

[0106] Specifically, after applying a coating film 15 such as BCB, an ultraviolet and visible light transmissive substrate 19 is pressed against the coating film 15 while applying heat to harden it, thereby bonding and adhering the epitaxial substrate 1 and the ultraviolet and visible light transmissive substrate 19, which is the wafer to be bonded (support substrate).

[0107] More specifically, after the coating film is formed, the ultraviolet and visible light transmissive substrate 19 on which the SiO2 film 17b is formed by the P-CVD (plasma CVD) method is placed opposite the coating film 15, and the pressure is reduced to perform thermocompression bonding in a vacuum. When sapphire is used as the ultraviolet and visible light transmissive substrate 19, the bonding pressure is, for example, 60 N / cm 2 When BCB is used as the coating film 15, the adhesion (curing) conditions may be, for example, 250° C. for 30 minutes, and the curing process may be carried out by holding in a reduced pressure atmosphere.

[0108] However, the bonding pressure is 60N / cm 2 Not limited to, for example, 5N / cm 2 More than 300N / cm 2 The same effect can be obtained in the following manner.

[0109] The curing process can be performed in a reduced pressure atmosphere of 0.01 atm, but is not limited to reduced pressure atmospheres. -2The treatment may be carried out in a vacuum atmosphere of less than 1 Pa, and the same effect can be obtained even if the treatment is carried out in an atmosphere with an oxygen concentration of 100 ppm or less.

[0110] In the bonding / adhesion step, it is preferable to use the coating film 15 described in the description of the procedure of the coating film formation method, specifically, one or more of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluororesin, spin-on glass, and polyimide for bonding or adhesion.

[0111] Furthermore, as the ultraviolet and visible light transmissive substrate 19, any of sapphire, quartz, glass, lithium tantalate (LT), lithium niobate (LN), ZnO, SiC, GaN, and GaP, which are ultraviolet and visible light transmissive, can be used. The above is an explanation of the procedure for the method of manufacturing bonded wafer 41 using epitaxial substrate 1.

[0112] Next, a procedure for forming a device layer on a bonded wafer will be briefly described with reference to FIGS. After the joining and bonding process, the starting substrate 3 is removed as shown in Fig. 4. In the case of a structure in which an etching stop layer 5 is provided as in Fig. 1, the etching stop layer 5 is also removed.

[0113] Specifically, when the starting substrate 3 is GaAs, after thermocompression bonding, the starting substrate 3 is etched off with ammonia / hydrogen peroxide. After removing the starting substrate 3, the first etching stop layer such as InGaP is removed with hydrochloric acid. 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 transmissive substrate 19.

[0114] After leaving only the light-emitting functional layer on the ultraviolet and visible light transmissive substrate 19, an etching mask is formed by photolithography, and the epitaxial layer in the element isolation region and electrode contact region is partially removed by dry etching using a chlorine-based gas such as ICP, as shown in Figure 5.

[0115] In this case, if oxygen remains at the interface between the epitaxial layer (SiO2 film 17a in the case where SiO2 film 17a is formed) and the coating film 15, partial curing failure occurs during thermocompression bonding. This cured failure portion becomes charged by plasma and releases gas, which generates gas during dry etching and causes the epitaxial layer to peel off. However, by using this technology, oxygen does not remain between the coating film 15 and the epitaxial layer in principle, so curing failure does not occur and peeling of the epitaxial layer can be prevented.

[0116] After the dry etching process, a SiO2 layer 21 is formed on the epitaxial layer as shown in FIG. 6, and then an ohmic electrode 23 is formed of metal by photolithography, vapor deposition, and lift-off as shown in FIG. 7, and an ohmic contact is formed by performing a heat treatment.

[0117] The temperature during ohmic contact formation is about 350 to 450°C, and it is common to perform processing at a temperature higher than the glass transition point of BCB, which is 350°C. If there are areas where the BCB curing process is insufficient, it is believed that poor curing has occurred due to the presence of oxygen. In a heat treatment environment above the glass transition point, the poorly cured areas release gas, causing the epitaxial layer to peel off.

[0118] More specifically, if the coating atmosphere is not kept at 100 ppm or less when forming coating film 15, oxygen will remain at the pyramidal apex of the pit (concave defect 33), and if coating film 15 is, for example, BCB, the cyclic addition reaction will be inhibited, resulting in a poorly cured portion in which BCB is retained in an uncured state.

[0119] If oxygen remains on the side of the inclusion (protruding defect 31), the cycloaddition reaction is inhibited when the coating film 15 is, for example, BCB, resulting in a poorly cured portion in which the BCB remains in an uncured state.

[0120] In addition, the heat treatment temperature during device fabrication, such as when forming ohmic contacts, is generally 350°C or higher, and in many cases 400°C or higher. In addition, the heat resistance temperature (glass transition point) of BCB is 350°C, and BCB begins to decompose at temperatures above 350°C.

[0121] Therefore, when a device is formed in the compound semiconductor layer 2 in the atmosphere while a cured portion has occurred, the epitaxial thickness at the pyramidal apex (pit bottom) of the pit (concave defect 33) is thin, causing a crack to open and the BCB to come into contact with the atmosphere. This triggers the air to enter from the BCB pyramidal apex (pit bottom) when the previous heat treatment temperature (350°C or higher) is reached, causing an explosive reaction with the cured portion, resulting in peeling off of the epitaxial layer.

[0122] Furthermore, when a device is formed in the compound semiconductor layer 2 in the atmosphere while the incompletely cured portion exists, the inclusion portion (protruding defect 31) is convex, so stress causes a crack to form in the epitaxial layer, opening it up and exposing the BCB to the atmosphere. This triggers an explosive reaction between the incompletely cured portion around the inclusion portion (protruding defect 31) and the air that has entered through the crack, causing the epitaxial layer to peel off, as the inclusion portion (protruding defect 31) is convex.

[0123] However, in the present invention, the coating atmosphere is set to 100 ppm or less when forming coating film 15, so that poor thermal curing does not occur in the BCB in the areas adjacent to the pits (concave defects 33) or inclusions (convex defects 31), and peeling of the epitaxial layer during heat treatment in the device process can be prevented.

[0124] In this way, in the present invention, almost no oxygen exists between the coating film 15 and the epitaxial layer (compound semiconductor layer 2), and as a result, poor curing does not occur. Therefore, even if heat treatment is performed under heat treatment conditions above the glass transition point during ohmic contact formation, peeling of the epitaxial layer does not occur.

[0125] As described above, in the present invention, when a coating film 15 such as benzocyclobutene (BCB) is applied, particularly to a thickness of 1 μm or less, to an epitaxial substrate 1 having a pit (concave defect 33) with a side of 200 μm or less or a convex defect 31 with a side of 100 μm or more on the surface or near the surface of a compound semiconductor layer 2, which is an epitaxial layer, a stable film thickness can be obtained relative to the designed film thickness, and a state in which oxygen is excluded from the interface between the coating film 15 and the epitaxial layer can be obtained.

[0126] Furthermore, according to the method for manufacturing a bonded wafer of the present invention, a coating film 15 such as benzocyclobutene (BCB) is formed, particularly with a thickness of 1 μm or less, on an epitaxial substrate 1 having a pit (concave defect 33) with a side of 200 μm or less or a convex defect 31 with a side of 100 μm or more on the surface or near the surface of the epitaxial layer, and when bonding to an ultraviolet and visible light transmissive substrate 19 via the coating film 15, it is possible to obtain a stable thickness of the coating film 15 after bonding relative to the designed thickness, and by obtaining a state in which oxygen is excluded from the interface between the coating film 15 and the epitaxial layer, a stable bonded wafer 41 in which the epitaxial layer does not peel off during device formation can be manufactured. EXAMPLES

[0127] The present invention will be specifically described below with reference to examples, but the present invention is not limited thereto.

[0128] A bonded wafer was manufactured by forming a coating film 15 on an epitaxial substrate 1 and bonding it to a support substrate, and then the starting substrate 3 was removed, a device layer was formed, and the number of pieces of the epitaxial layer that peeled off during each step of forming the device layer was evaluated. The specific procedure was as follows.

[0129] (Example) The process sequence is shown in Figure 8.

[0130] First, as shown in FIG. 1, a first conductivity type GaAs buffer layer is laminated on a first conductivity type GaAs starting substrate 3, and then a Ga 0.5 In 0.5The P first etch stop layer is 0.3 μm, the GaAs second etch stop layer is 0.3 μm each, (Al x Ga 1-x ) y In 1-y P (0 < x ≤ 1, 0.4 ≤ y ≤ 0.6) lower cladding layer 7 is 1 μm, (Al x Ga 1-x ) y In 1-y P (0 ≤ x < 0.6, 0.4 ≤ y ≤ 0.6) active layer 9 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 11 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 1 (EPW) with a light-emitting functional layer formed by laminating a GaP window layer 13 of 8 μm was fabricated (S1 in FIG. 8).

[0131] The conductivity type from the starting substrate 3 to the lower cladding layer 7 was N-type in the example, and P-type from the upper cladding layer 11 to the GaP window layer 13. The average doping concentration of the lower cladding layer 7 was 5.0 × 10 17 / cm 3 , and the average doping concentration of the upper cladding layer 11 was 1.0 × 10 17 / cm 3 . The average doping concentration of the layers other than the cladding layers excluding the active layer 9 was 0.8 to 3.0 × 10 18 / cm 3 .

[0132] After fabricating the epitaxial substrate 1, a SiO2 film 17a with a thickness of 0.02 μm was formed on the epitaxial substrate 1 by the P-CVD method (S2 in FIG. 8). In the P-CVD film formation, TEOS (tetraethoxysilane) and oxygen were used as raw materials.

[0133] Next, the epitaxial substrate 1 on which the SiO2 film 17a was formed was introduced into a glove box in which the oxygen concentration was kept at 100 ppm or less via a load lock (S3 in FIG. 8). In order to keep the oxygen concentration in the glove box at 100 ppm or less, a continuous flow of nitrogen was introduced as a purge gas and purged for 8 hours or more. The oxygen concentration was measured to be 100 ppm or less by an oxygen concentration meter, and was continuously measured during the process.

[0134] Next, the epitaxial substrate 1 was moved onto a spin coater installed in a glove box maintained at about 1 atmosphere, vacuum-adsorbed onto a rotating stage, and while rotating the epitaxial substrate 1, BCB was dropped onto it as a thermosetting resin, spin-coating a coating film 15 of BCB (S4 in FIG. 8). The rotation speed was 5,000 rpm, and the amount of BCB dropped was 0.5 ml. The thickness of the spin-coated BCB was 0.5 μm.

[0135] After the BCB coating film 15 was spin-coated, the epitaxial substrate 1 was moved onto a hot plate installed in a glove box, and a solvent volatilization process (solvent removal process) was performed (S5 in FIG. 8). The temperature for the volatilization process was 80° C. This state is shown in FIG.

[0136] After the volatilization process, the epitaxial substrate 1 was removed from the glove box through the load lock (S6 in FIG. 8). On the other hand, a sapphire wafer was prepared as a support substrate (S7 in FIG. 8), and a SiO2 film 17b (thickness: 0.02 μm) was formed by the P-CVD method (S8 in FIG. 8). This support substrate and the epitaxial substrate 1 were stacked facing each other (S9 in FIG. 8), introduced into a vacuum chamber (S10 in FIG. 8), and thermocompression bonded (S11 in FIG. 8), thereby bonding the epitaxial layer (compound semiconductor layer 2) and the support substrate (ultraviolet and visible light transparent substrate 19) as shown in FIG. 3.

[0137] The bonding pressure is 60N / cm 2 The BCB bonding (curing) conditions were 250°C for 30 minutes, and the curing process was performed in a reduced pressure atmosphere of 0.01 atm.

[0138] After bonding to the support substrate, the starting substrate 3 was etched off with an ammonia hydrogen peroxide mixture to remove the starting substrate 3 (S12 in FIG. 8). Thereafter, the InGaP etching stop layer was removed with a hydrochloric acid solution, and then the GaAs etching stop layer was removed with a sulfuric acid hydrogen peroxide mixture to produce an epitaxially bonded substrate for device fabrication in which only the light-emitting functional layer remained on the support substrate as shown in FIG.

[0139] After preparing the epitaxial bonded substrate, a SiO2 film for a hard mask was formed to a thickness of 1.2 μm by P-CVD, and a resist pattern was formed by photolithography. The openings of the resist pattern were etched with a hydrofluoric acid solution to form a pattern, and the resist was peeled off.

[0140] After the resist was peeled off, the epitaxial junction substrate was introduced into an ICP device and dry etched with chlorine-based plasma to remove the epitaxial layer at the opening and separate the elements (S13 in FIG. 8). In this example, chlorine was used as the chlorine-based gas and the substrate temperature was 30° C. The same process was repeated to remove the lower cladding layer 7, the active layer 9, and the upper cladding layer 11, exposing the upper cladding layer 11 as shown in FIG. 5.

[0141] Next, a SiO2 layer 21 was formed to a thickness of 0.5 μm by P-CVD, and a resist pattern was formed by photolithography. The openings of the resist pattern were etched with a hydrofluoric acid solution to form a pattern as shown in FIG. 6, and the resist was peeled off (S14 in FIG. 8).

[0142] Furthermore, a resist pattern was formed by photolithography, metal was evaporated into the openings, and patterning was performed by lift-off (S15 in FIG. 8). As shown in Fig. 7, after forming the metal pattern, RTA treatment (400°C for 5 minutes) was performed in a nitrogen atmosphere to form an ohmic contact between the metal pattern and the semiconductor layer (ohmic treatment) (S16 in Fig. 8). The device structure was formed by the above steps.

[0143] (Comparative Example) A coating film 15 was formed on an epitaxial substrate 1 under the same conditions as in the example, except that the BCB spin coating was performed in air rather than in an atmosphere with an oxygen concentration of 100 ppm or less, and a bonded wafer was produced by bonding the epitaxial substrate 1 to a supporting substrate, and then the starting substrate 3 was removed to form a device structure.

[0144] [Evaluation of number of epitaxial layer peelings] FIG. 9 shows a comparison of the number of epitaxial layer peelings that occurred during each process of device formation, namely substrate removal (S12 in FIG. 8), ICP processing (S13 in FIG. 8), SiO2 film formation (S14 in FIG. 8), electrode deposition (S15 in FIG. 8), and ohmic processing (S16 in FIG. 8), in the embodiment in which BCB was spin-coated in nitrogen (oxygen concentration 100 ppm or less), and the number of epitaxial layer peelings that occurred during each process in the comparative example in which BCB was spin-coated in air.

[0145] As shown in FIG. 9, in the comparative example, epitaxial layer peeling occurred (increased) at each process in which a plasma atmosphere or heat treatment was performed, such as ICP processing after substrate removal, SiO2 film formation, and ohmic processing, whereas in the example, epitaxial layer peeling did not occur and did not increase.

[0146] The present specification includes the following aspects. [1]: An epitaxial substrate in which a plurality of compound semiconductor layers are grown or deposited on a starting substrate, the epitaxial substrate having a convex defect with a side of 100 μm or more or a concave defect with a side of 200 μm or less formed on or near the surface of the compound semiconductor layer, the surface of the epitaxial substrate having a convex defect with a side of 100 μm or more formed on or near the surface of the compound semiconductor layer, the surface of the epitaxial substrate having a convex defect with a side of 1 ... A method for forming a coating film on an epitaxial substrate, characterized in that the oxygen concentration in the coating atmosphere is 100 ppm or less. [2]: The method for forming a coating film on an epitaxial substrate according to [1] above, characterized in that the coating film has a thickness of 1 μm or less. [3]: The method for forming a coating film on an epitaxial substrate according to [1] or [2] above, characterized in that, when forming the coating film, an airtight container in which the epitaxial substrate is housed is replaced with a purge gas, thereby setting the oxygen concentration of the coating atmosphere to 100 ppm or less. [4]: The method for forming a coating film on an epitaxial substrate according to [3] above, characterized in that the purge gas is one or more selected from the group consisting of helium, hydrogen, nitrogen, neon, and argon. [5]: The method for forming a coating film on an epitaxial substrate according to any one of [1] to [4] above, wherein the coating atmosphere is an atmosphere having a pressure of 10 kPa or more. [6]: The method for forming a coating film on an epitaxial substrate according to any one of [1] to [5] above, wherein the coating film is made of a thermosetting resin. [7]: The method for forming a coating film on an epitaxial substrate according to [6] above, characterized in that the thermosetting resin is selected from one or more of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluororesin, spin-on glass, and polyimide. [8]: The method for forming a coating film on an epitaxial substrate according to any one of [1] to [7] above, characterized in that the concave defect is a pit generated during epitaxial growth, and the convex defect is a defect generated by a particle falling onto the compound semiconductor layer during epitaxial growth. [9]: A method for producing a bonded wafer, comprising: a coating film forming step of coating a resin on a surface of an epitaxial substrate having a plurality of compound semiconductor layers grown or deposited on a starting substrate, the surface of the epitaxial substrate having a convex defect with a side of 100 μm or more or a concave defect with a side of 200 μm or less formed on or near the surface of the compound semiconductor layer in an environment filled with atmospheric gas to form a coating film; and a bonding / adhering step of bonding or adhering the compound semiconductor layer and an ultraviolet and visible light transmissive substrate via the coating film to produce a bonded wafer, A method for producing a bonded wafer, characterized in that the coating atmosphere in the coating film forming step has an oxygen concentration of 100 ppm or less.

[10] : A method for producing a bonded wafer according to the above [9], characterized in that in the bonding / adhering step, the bonding or adhering is carried out using one or more of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluororesin, spin-on glass, and polyimide.

[11] : A method for producing a bonded wafer according to [9] or

[10] above, characterized in that the ultraviolet and visible light transmissive substrate is any one of sapphire, quartz, glass, lithium tantalate (LT), lithium niobate (LN), ZnO, SiC, GaN, and GaP, which are ultraviolet and visible light transmissive.

[0147] The present invention is not limited to the above-described embodiment. The above-described embodiment is merely an example, and anything that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits similar effects is included in the technical scope of the present invention. [Explanation of symbols]

[0148] 1...epitaxial substrate, 2...compound semiconductor layer, 3...starting substrate, 5...etching stop layer, 7...lower cladding layer, 9...active layer, 11...upper cladding layer, 13...GaP window layer, 15...coating film, 17a...SiO2 film, 17b...SiO2 film, 19...visible light transmissive substrate, 21...SiO2 layer, 23...ohmic electrode, 31...convex defect, 33...concave defect, 41...bonded wafer.

Claims

1. An epitaxial substrate is formed by growing or depositing a plurality of compound semiconductor layers on a starting substrate, the epitaxial substrate having a convex defect having a side of 100 μm or more or a concave defect having a side of 200 μm or less formed on or near the surface of the compound semiconductor layer, the surface of the epitaxial substrate being coated with a resin in an environment filled with an atmospheric gas to form a coating film, A method for forming a coating film on an epitaxial substrate, comprising the steps of: setting the oxygen concentration in the coating atmosphere to 100 ppm or less.

2. 2. The method for forming a coating film on an epitaxial substrate according to claim 1, wherein the coating film has a thickness of 1 [mu]m or less.

3. 2. The method for forming a coating film on an epitaxial substrate according to claim 1, wherein the oxygen concentration of the coating atmosphere is set to 100 ppm or less by replacing the atmosphere inside a sealed container in which the epitaxial substrate is housed with a purge gas when forming the coating film.

4. 4. The method for forming a coating film on an epitaxial substrate according to claim 3, wherein the purge gas is at least one selected from the group consisting of helium, hydrogen, nitrogen, neon, and argon.

5. 2. The method for forming a coating film on an epitaxial substrate according to claim 1, wherein the coating atmosphere is an atmosphere having a pressure of 10 kPa or more.

6. 2. The method for forming a coating film on an epitaxial substrate according to claim 1, wherein the coating film is made of a thermosetting resin.

7. 7. The method for forming a coating film on an epitaxial substrate according to claim 6, wherein the thermosetting resin is selected from one or more of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluororesin, spin-on glass, and polyimide.

8. 8. The method for forming a coating film on an epitaxial substrate according to claim 1, wherein the concave defect is a pit generated during epitaxial growth, and the convex defect is a defect generated by a particle that has fallen onto the compound semiconductor layer during epitaxial growth.

9. A method for producing a bonded wafer, comprising: a coating film forming step of coating a surface of the epitaxial substrate, in which a plurality of compound semiconductor layers are grown or deposited on a starting substrate, with a convex defect having a side of 100 μm or more or a concave defect having a side of 200 μm or less formed on or near the surface of the compound semiconductor layer, with a resin in an environment filled with an atmospheric gas to form a coating film; and a bonding / adhering step of bonding or adhering the compound semiconductor layer and an ultraviolet and visible light transmissive substrate via the coating film to produce a bonded wafer, A method for producing a bonded wafer, characterized in that the coating atmosphere in the coating film forming step has an oxygen concentration of 100 ppm or less.

10. 10. The method for producing a bonded wafer according to claim 9, wherein in the bonding / adhering step, the bonding or adhering is performed using one or more of benzocyclobutene, epoxy resin, wax, silicone, amorphous fluororesin, spin-on glass, and polyimide.

11. 11. The method for manufacturing a bonded wafer according to claim 9 or 10, wherein the ultraviolet and visible light transmissive substrate is made of any one of sapphire, quartz, glass, lithium tantalate (LT), lithium niobate (LN), ZnO, SiC, GaN, and GaP, each of which is ultraviolet and visible light transmissive.

Images