Method for manufacturing a bonded wafer

Abstract

To provide a manufacturing method for bonded type wafer capable of reducing defective parts of an epitaxial layer caused by thermosetting defects of BCB.SOLUTION: A manufacturing method for bonded type wafer bonds an epitaxial wafer containing P (phosphorus) and a wafer to be bonded via benzocyclobutene. The epitaxial wafer includes: a starting substrate having a first surface and a second surface opposite the first surface; and an epitaxial layer formed on the first surface of the starting substrate and containing P. After removing deposits deposited on the second surface of the starting substrate of the epitaxial wafer by detouring around during the epitaxial growth process, thermosetting of the benzocyclobutene is performed.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a bonded wafer in which a support substrate (bonded wafer) is bonded to an epitaxial wafer obtained by epitaxially growing a compound semiconductor functional layer (epitaxial layer) on a growth substrate (starting substrate).

Background Art

[0002] The technique of separating only the epitaxial functional layer from the starting substrate and transferring it to another substrate is an important technique for relaxing the restrictions caused by the physical properties of the starting substrate and increasing the design freedom of the device system. In order to achieve the transfer, a technique is required to bond the epitaxial functional layer to a support substrate (bonded wafer), remove the starting substrate, and realize the transfer.

[0003] Patent Document 1 discloses a technique of thermocompression bonding a semiconductor substrate (epitaxial wafer) having a starting substrate and an epitaxial functional layer structure and a temporary support substrate via a dielectric layer, and a technique of separating the temporary support substrate and the epitaxial functional layer structure from the starting substrate by wet etching. However, no improvement measures for the poor thermal curing of the benzocyclobutene (hereinafter referred to as BCB) layer formed on the dielectric layer are shown.

[0004] When thermally curing BCB, if oxygen (more specifically, 100 ppm or more) is present in the atmosphere, curing failure is likely to occur.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Even when the atmosphere is made vacuum or nitrogen atmosphere during the thermosetting of BCB, it has been found that as the heating progresses, oxygen components are released into the atmosphere from moisture adsorbed on members and the like present in the heating furnace, deteriorating the curability of BCB. To avoid this poor thermosetting property, it is possible to improve the atmosphere of the heat treatment furnace before heating by nitrogen cycle purge or baking at a low temperature before the heat treatment.

[0007] However, even when the atmosphere of the heat treatment furnace before heating was improved, the thermosetting property of BCB sometimes decreased.

[0008] The poor thermosetting of BCB causes local unevenness in the BCB layer, and cracks and other damages are generated in the epitaxial layer due to the stress generated therefrom. The part where the crack occurs becomes a defective part where a device cannot be fabricated, and the area yield decreases.

[0009] The present invention has been made to solve the above problems, and an object thereof is to provide a method for manufacturing a bonded wafer capable of reducing defective parts of an epitaxial layer caused by poor thermosetting property of BCB.

Means for Solving the Problems

[0010] In order to solve the above problems, the present invention provides a method for manufacturing a bonded wafer in which an epitaxial wafer containing P (phosphorus) and a wafer to be bonded are bonded via benzocyclobutene, using, as the epitaxial wafer, an epitaxial wafer including a starting substrate having a first surface and a second surface opposite to the first surface, and an epitaxial layer formed on the first surface of the starting substrate and containing P, After removing deposits that have precipitated by wrapping around during the epitaxial growth process on the second surface of the starting substrate of the epitaxial wafer, the thermosetting of the benzocyclobutene is performed. A method for manufacturing a bonded wafer is provided, which is characterized by this.

[0011] In the manufacturing method of the bonded wafer of the present invention, benzocyclobutene (BCB) can be thermally cured on the second surface, which is the back surface of the starting substrate of the epitaxial wafer, in a state where there are no precipitates. This can prevent the destruction of the epitaxial layer caused by poor thermal curing of BCB, and a bonded wafer can be manufactured with good yield.

[0012] For example, as the epitaxial layer, one having an active layer containing Ga (gallium), In (indium), and P, and a window layer containing P can be used.

[0013] The structure of the epitaxial layer is not particularly limited. As the epitaxial layer, for example, one having an active layer containing Ga, In, and P, and a window layer containing P can be used.

[0014] For example, as the wafer to be bonded, a wafer made of a material selected from the group consisting of germanium, silicon, sapphire, and quartz can be used.

[0015] The wafer to be bonded is not particularly limited. As the wafer to be bonded, for example, a germanium wafer, a silicon wafer, a sapphire wafer, or a quartz wafer can be used.

[0016] For example, the removal of the precipitate can be performed by mechanical grinding or polishing, or mechanical chemical polishing.

[0017] The specific means for removing the precipitate is not particularly limited. For example, the precipitate can be removed by mechanical grinding or polishing, or mechanical chemical polishing.

[0018] In this case, the epitaxial layer includes a window layer, It is preferable that the replacement for the removal of the precipitate is 1 / 10 or more of the thickness of the window layer of the epitaxial layer.

[0019] If the replacement for the removal of the precipitate is set to be 1 / 10 or more of the thickness of the window layer of the epitaxial layer, the precipitate can be completely removed.

[0020] Alternatively, the removal of the precipitate may be performed by a wet etching method or a dry etching method.

[0021] From the viewpoint of the safety of device maintenance, it is desirable to adopt the wet etching method as a specific means for removing the precipitate, but the precipitate may also be removed by the dry etching method.

[0022] In this case, the wet etching method may be performed using a solution obtained by diluting a mixed solution of hydrogen peroxide water and an inorganic acid or an organic acid with water.

[0023] The solution used in wet etching is not particularly limited. For example, a solution obtained by diluting a mixed solution of hydrogen peroxide water and an inorganic acid or an organic acid with water can be used.

[0024] In this case, it is preferable that the dilution ratio (volume of water ÷ volume of mixed solution) of the solution diluted with water is 9 times or more and 49 times or less.

[0025] A solution with a dilution ratio within this range can be manufactured with high precision. Also, by using such a solution, it is possible to remove the precipitate in a sufficiently short processing time while preventing the deterioration of the TTV of the second surface, which is the back surface of the starting substrate.

[0026] Alternatively, the dry etching method may be performed in an atmosphere containing one or more selected from the group consisting of Cl2, BCl3, and SiCl4.

[0027] The atmosphere for performing the dry etching method is not particularly limited. For example, the dry etching method can be performed in an atmosphere containing one or more selected from the group consisting of Cl2, BCl3, and SiCl4.

Advantages of the Invention

[0028] As described above, according to the method for manufacturing a bonded wafer of the present invention, it is possible to prevent the destruction of the epitaxial layer caused by the poor thermosetting of BCB, and to manufacture a bonded wafer with good yield.

Brief Description of the Drawings

[0029]

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Embodiments for Carrying Out the Invention

[0030] As described above, there has been a demand for the development of a method for manufacturing a bonded wafer capable of reducing the defective part of the epitaxial layer generated due to the poor thermosetting property of BCB.

[0031] As a result of repeated studies by the inventors, it has been found that even if the atmosphere of the heat treatment furnace before heating is improved, the thermosetting property of BCB is reduced due to the outgassing from the backside deposits of the epitaxial wafers supplied into the furnace for bonding. There are deposits mainly composed of phosphorus (P) on the backside of the epitaxial wafer. The deposits are in a polycrystalline state, have a weak bonding state, and have many gaps, so it is expected that atmospheric components easily penetrate and easily form phosphorus oxide. As a result, during the heat treatment of the epitaxial wafer, oxygen is released from the deposits into the vacuum atmosphere, and it is considered that the thermosetting property of BCB is reduced.

[0032] As a result of intensive studies on the above problems by the present inventors, in the method for manufacturing a bonded wafer, after removing the deposits that have crept in and deposited on the backside of the starting substrate of the epitaxial wafer during the epitaxial growth process, by performing the thermosetting of benzocyclobutene, which is a bonding material, it has been found that it is possible to reduce the defective portions of the epitaxial layer caused by the poor thermosetting property of BCB, and the present invention has been completed.

[0033] That is, the present invention is a method for manufacturing a bonded wafer in which an epitaxial wafer containing P (phosphorus) and a wafer to be bonded are bonded via benzocyclobutene, using, as the epitaxial wafer, an epitaxial wafer including a starting substrate having a first surface and a second surface opposite to the first surface, and an epitaxial layer formed on the first surface of the starting substrate and containing P, characterized in that, after removing the deposits that have crept in and deposited on the second surface of the starting substrate of the epitaxial wafer during the epitaxial growth process, the thermosetting of the benzocyclobutene is performed.

[0034] Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.

[0035] [First Embodiment] Hereinafter, a first embodiment of a method for manufacturing a bonded wafer of the present invention will be described with reference to FIGS. 1 to 3.

[0036] First, a starting substrate 1 shown in FIG. 1 is prepared. In the example shown in FIG. 1, the starting substrate 1 is a GaAs starting substrate of the first conductivity type. The starting substrate 1 has a first surface 11 as a front surface and a second surface 12 as a back surface opposite to the first surface 11.

[0037] After laminating a 0.5-μm first-conductivity-type GaAs buffer layer (not shown) on the first surface 11 of such a starting substrate 1, a 0.1-μm first-conductivity-type GaInP first etch stop layer and a 0.1-μm first-conductivity-type GaAs second etch stop layer are sequentially grown to form an etch stop layer 3.

[0038] Next, an epitaxial layer 2 having a light-emitting element structure in which a 1-μm first-conductivity-type AlGaInP first cladding layer 21, a 0.2-0.5-μm undoped AlGaInP active layer 22, a 1-μm second-conductivity-type AlGaInP second cladding layer 23, a 0.1-μm second-conductivity-type GaInP intermediate layer (not shown), and a 5-μm second-conductivity-type GaP window layer 25 are sequentially grown is formed on the etch stop layer 3. Thereby, an epitaxial wafer 10 including the starting substrate 1 having the first surface 11 and the second surface 12 and the epitaxial layer 2 formed on the first surface 11 of the starting substrate 1 and containing P (phosphorus) is prepared. Here, the portion from the first cladding layer 21 to the second cladding layer 23 is referred to as a DH (double hetero) structure portion 24.

[0039] Note that the components and thicknesses of the respective layers of the epitaxial wafer 10 described above are specific examples, and the details of the respective layers of the epitaxial wafer 10 used in the present invention are not particularly limited as long as the epitaxial layer 2 contains phosphorus. It can also be said that the epitaxial wafer 10 used in the present embodiment has an active layer 22 containing Ga (gallium), In (indium), and P, and a window layer 25 containing P.

[0040] In the epitaxial growth process described above, deposits (back surface adhering deposits) 5 are deposited by creeping around to the second surface 12 which is the back surface of the starting substrate 1.

[0041] Next, in this example, a protective film (processing protective film) 4 is formed on the epitaxial layer 2 of the epitaxial wafer 10, specifically on the window layer 25, to obtain the epitaxial wafer 10 in the state shown in FIG. 1. As the material of the protective film 4, inorganic films such as SiO2 and SiN x and organic films such as waxes, resists, vinyl chloride, and polymers can be selected. In this embodiment, SiO2 is used as the protective film 4 because of its easy film formation and peelability.

[0042] In this embodiment, the protective film 4 is formed, but in the present invention, the protective film 4 may not be formed. However, if the protective film 4 is formed, it is possible to prevent impurities generated during processing from adhering to or contaminating the surface of the epitaxial layer 2.

[0043] Also, in this embodiment, the protective film 4 has a thickness of 1 μm, but it is not limited to this film thickness, and the same effect can be obtained even if it is thinner or thicker. From the viewpoints of film thickness uniformity and protection effectiveness, the protective film 4 preferably has a film thickness of 0.1 μm or more. Also, from the viewpoint of peelability (ease of removal in the subsequent etching process), it is preferable to set the upper limit to 10 μm.

[0044] However, this film thickness is an example in the case of SiO2, and when an organic film is formed as the protective film 4, for example, the preferable film thickness range is not limited to the above.

[0045] Next, the protective film 4 formed on the epitaxial wafer 10 and the processing plate are adhered via hot wax, and the second surface 12, which is the back surface of the starting substrate 1 of the epitaxial wafer 10, is polished. Thereby, the deposit 5 on the second surface 12 of the starting substrate 1 is removed, and the epitaxial wafer 10 in the state of FIG. 2 is obtained. The replacement (OP value; cutting amount, etc.) may be an amount equal to or more than the amount by which the deposit 5 can be completely removed. Since the deposit 5 tends to become thicker as the epitaxial layer 2 containing P becomes thicker, it mainly depends on the thickness of the window layer 25 that occupies a large thickness ratio. When the OP value is 1 / 10 or more of the thickness of the window layer 25, the deposit 5 can be completely removed. In the present embodiment, since the thickness of the window layer 25 is 5 μm, it may be set to 0.5 μm or more, which is 1 / 10 of the thickness, and the processing is performed so that the OP value at the center position of the wafer is about 0.9 μm.

[0046] In the present embodiment, the case where the removal of the deposit 5 is performed by polishing is exemplified as a specific example. However, the method for removing the deposit 5 from the back surface of the epitaxial wafer 10 is not limited to polishing only. For example, the same effect can be obtained by selecting a lapping method or a surface grinding method. In other words, the removal of the deposit can be performed, for example, by mechanical grinding or polishing, or by mechanical chemical polishing. However, in the case of the lapping method, since the deposit is mixed into the crushed layer generated during processing, a larger replacement than the polishing method is required. Also in the surface grinding method, as in the lapping method, a large cutting amount is required if a large crushed layer is generated. Therefore, in order to reduce the influence of the crushed layer, the grinding number of the grinding wheel is preferably #1,000 or more, and more preferably #5,000 or more.

[0047] Next, the protective film 4 is removed with a hydrofluoric acid solution, and then benzocyclobutene (BCB) is spin-coated onto the window layer 25 of the epitaxial wafer 10 to form a BCB coating film. Next, the epitaxial wafer 10 is overlapped with and opposed to a sapphire wafer, which is the wafer to be bonded 30, through the BCB coating film and thermocompression bonded, that is, by thermosetting the BCB, a bonded wafer 100 (bonded substrate) is fabricated in which the epitaxial wafer 10 and the wafer to be bonded 30 are bonded through a thermoset BCB layer (BCB bonding film) 20 shown in FIG. 3.

[0048] In the present invention, by removing the deposit 5 on the second surface 12 of the starting substrate 1, which is the back surface of the epitaxial wafer 10, the oxygen component contained in the deposit 5 can be removed together with the deposit 5. After removing such a deposit 5, by performing thermosetting of benzocyclobutene, the oxygen content in the atmosphere during the thermosetting process of benzocyclobutene can be reduced, and the curing failure rate of the BCB layer 20 can be improved. Thereby, the occurrence of local unevenness in the BCB layer 20 can be suppressed, and as a result, the occurrence of defective portions due to breakage such as cracks in the epitaxial layer 2 can be prevented.

[0049] In this embodiment, when applying BCB by spin coating, the designed film thickness was 0.6 μm. However, it is not limited to this thickness, and the same effect can be obtained even if it is thicker or thinner than this thickness.

[0050] Also, in this embodiment, a method for removing the protective film 4 has been exemplified, but BCB may be applied and bonded in a state where the protective film 4 is present. Particularly when the protective film 4 is SiO2, since SiO2 has the effect of an adhesion enhancing layer with respect to BCB, higher bonding strength can be obtained by leaving the protective film (SiO2) 4.

[0051] The bonding conditions can be selected under any bonding conditions. For example, the bonding can be thermocompression bonding at 1.2 N / cm 2 or more and at 200 °C or higher and 400 °C or lower. In this embodiment, 2 N / cm 2Bonding was carried out under bonding conditions of 250 °C, but it is not limited to this condition.

[0052] In this embodiment, the wafer 30 to be bonded is exemplified as a sapphire wafer, but the material of the wafer 30 to be bonded is not limited to sapphire, and any material can be selected as long as flatness is ensured. When a transparent substrate is required, sapphire or quartz can be selected, and if an opaque substrate is acceptable, Si or Ge can be selected.

[0053] In this embodiment, BCB is exemplified in a state of being applied in layers, but it is not limited to layers. The same results can be obtained by patterning the photosensitive BCB into island shapes, line shapes, or other shapes and performing the bonding process.

[0054] Further processing can also be performed on the bonded wafer 100 shown in FIG. 3 obtained as described above. Hereinafter, an example of processing the bonded wafer 100 will be described with reference to FIGS. 4 to 7.

[0055] In this example, from the bonded wafer 100 shown in FIG. 3, the GaAs starting substrate 1 is removed by wet etching to expose the first etch stop layer, and then the etchant is switched to remove the first and second etch stop layers to expose the first cladding layer 21, and as shown in FIG. 4, an EP bonded substrate 200 is fabricated that retains only the epitaxial layer 2 including the DH structure portion 24 and the window layer 25.

[0056] Next, a pattern is formed on the epitaxial layer 2 by photolithography, and element isolation processing is performed by inductively coupled plasma (ICP) etching. The gas used for ICP is, for example, chlorine and argon. The ICP processing is performed twice, for example, a step of exposing a part of the surface of the BCB layer 20 and a step of exposing a part of the surface of the GaP window layer 25. By this element isolation processing, for example, as shown in FIG. 5, a separated element 6 bonded to the wafer 30 to be joined via the BCB layer 20, in which a part of the surface of the GaP window layer 25 is exposed, and a part formed on another part of the surface of the window layer 25, including the first cladding layer 21, the active layer 22, and the second cladding layer 23, a separated element 6 including the DH structure portion 24 is obtained.

[0057] In this embodiment, the case where a part of the surface of the GaP window layer 25 is exposed is illustrated, but it is not limited to the case where a part of the surface of the GaP window layer 25 is exposed. At least if the active layer 22 is separated from other elements, the processing purpose is achieved. Even when a part of the surface of the second cladding layer 23 is exposed instead of the exposure of the GaP window layer 25, the same effect can be obtained.

[0058] After the element isolation processing, as shown in FIG. 6, a protective film 40 is formed as an end face treatment. In this embodiment, SiO2 is used as the material of the protective film 40. The protective film is not limited to SiO2, and any material can be selected as long as it can protect the end face of the separated element 6 and has insulating properties. For example, SiN x or titanium oxide, magnesium oxide, etc. can also be selected.

[0059] In this embodiment, as shown in FIG. 6, an opening 40A for exposing a part of the surface of the first cladding layer 21 and an opening 40B for exposing a part of the surface of the GaP window layer 25 are formed in the protective film 40.

[0060] After the formation of the protective film 40, as shown in FIG. 7, electrodes 50 and 60 are formed in contact with the first cladding layer 21 which is a first conductive type layer and the GaP window layer 25 which is a second conductive type layer respectively, and heat treatment is performed to form ohmic contacts. Thereby, the junction device 300 shown in FIG. 7 is obtained. In the present embodiment, the first conductive type is designed as N type and the second conductive type is designed as P type. A metal containing Au and Si is used for the electrode 50 in contact with the N type layer, and a metal containing Au and Be is used for the electrode 60 in contact with the P type layer.

[0061] In the present embodiment, a metal of Au and Si is used as the N type electrode, but it is not limited to this material, and the same result can be obtained by using a metal containing Au and Ge. Also, a metal of Au and Be is used as the P type electrode, but it is not limited to this material, and the same result can be obtained by using a metal containing Au and Zn.

[0062] In the junction device 300 of the present embodiment in which the device (separation element) 6 having the electrodes 50 and 60 formed thereon as shown in FIG. 7 is joined to the wafer to be joined 30 via the BCB layer 20, for example, it is provided as a product for the EZ - PETAMP process of Shin - Etsu Chemical Co., Ltd. After adhering the electrode side of the junction device 300 to the template substrate via silicone, the wafer to be joined 30 is peeled off by irradiating a laser from the side of the wafer to be joined 30 to sublime the BCB, and the device 6 can be transferred from the wafer to be joined 30 to the template substrate. The transferred device 6 can then be re - transferred to a mounting substrate having a drive circuit to form an RGB display device.

[0063] [Second Embodiment] Next, the second embodiment of the present invention will be described.

[0064] The second embodiment is the same as the first embodiment up to the formation of the epitaxial layer 2 and the protective film 4, which was described with reference to FIG. 1.

[0065] In the second embodiment, the epitaxial wafer 10 is immersed in a sulfuric acid-peroxide solution to perform wet etching on the second surface 12, which is the back surface of the starting substrate 1. The sulfuric acid-peroxide solution is a mixture of sulfuric acid and hydrogen peroxide solution (hereinafter referred to as peroxide) (piranha solution) diluted with water. When the dilution ratio is defined as the volume of water divided by the volume of the mixture, in this embodiment, a solution with a dilution ratio of 19 times is used and immersed for 120 seconds. As a result, the precipitate 5 is removed from the second surface 12 of the starting substrate 1 of the epitaxial wafer 10, and the state shown in FIG. 2 is obtained.

[0066] In this embodiment, the precipitate 5 is removed by a wet etching method using a sulfuric acid-peroxide solution. However, the etching solution used in the wet etching method is not limited to the sulfuric acid-peroxide solution, and a similar effect can be obtained by diluting a mixture of other acids and peroxide. For example, the same effect can be obtained by using inorganic acids such as hydrochloric acid or organic acids such as citric acid, malonic acid, and tartaric acid.

[0067] In this embodiment, the case where the wet etching method is performed for 120 seconds is illustrated. However, the time for performing the wet etching method is not limited to 120 seconds, and a shorter processing time may be used as long as the effect is obtained. When the dilution ratio is small, the processing time can be shorter. However, in the case of the sulfuric acid-peroxide solution, the GaAs of the starting substrate 1 is also etched. If the dilution ratio is 4 times or more, more preferably 9 times or more, deterioration of the total thickness variation (TTV) of the second surface 12, which is the back surface of the starting substrate 1, can be prevented. Also, even if the dilution ratio is large, a similar effect can be obtained, but from the viewpoints of longer processing time and production accuracy of the mixture, it is desirable to be up to about 99 times, more preferably up to about 49 times.

[0068] In addition, in this embodiment, the case of wet etching has been exemplified. However, since the effect can be obtained as long as the deposits 5 on the second surface 12 of the starting substrate 1 can be removed, the etching method is not limited to wet etching. The same effect can be obtained by dry etching methods such as inductively coupled plasma (ICP) etching or electron cyclotron resonance (ECR) etching in an atmosphere containing a chlorine-based gas (such as Cl2, BCl3, SiCl4). However, when the starting substrate 1 contains As, it is desirable to use the wet etching method from the viewpoint of safety during equipment maintenance.

[0069] Next, as shown in FIG. 3, a bonded wafer (EPW bonded substrate) 100 is fabricated by bonding an epitaxial wafer 10 to a substrate 30 to be bonded via a BCB layer 20. The thickness of the BCB layer 20 and other conditions such as the wafer 30 to be bonded are the same as those in the first embodiment.

[0070] Also, the details of the removal process of the GaAs starting substrate 1 and the etching stop layer 3, the element isolation process, and the formation processes of the protective film 40 and the electrodes 50 and 60 are the same as those described with reference to FIGS. 4 to 7 in the first embodiment.

Example

[0071] Hereinafter, the present invention will be specifically described using examples and comparative examples, but the present invention is not limited thereto.

[0072] (Example 1) In Example 1, a bonded wafer 100 shown in FIG. 3 was manufactured in accordance with the first embodiment of the present invention described above, and the bonded wafer 100 was processed according to the procedure described with reference to FIGS. 4 to 7 to obtain a bonded device 300. Refer to paragraphs 0037 and 0038 for the material and film thickness of the epitaxial structure. Also, the protective film was a 1-μm SiO2 film.

[0073] More specifically, in Example 1, as methods for removing the deposits 5 on the second surface 12 of the starting substrate 1 of the epitaxial wafer 10, the lapping method, the polishing method, and the surface grinding method were each used. Also, in each of the removal methods, the replacements were changed and a plurality of prototypes were made. A #5,000 grit was used for surface grinding.

[0074] (Example 2) In Example 2, in accordance with the second embodiment of the present invention described above, the bonded wafer 100 shown in FIG. 3 was manufactured, and the bonded wafer 100 was processed according to the procedure described with reference to FIGS. 4 to 7 to obtain a bonded device 300.

[0075] More specifically, in Example 2, as a method for removing the deposits 5 on the second surface 12 of the starting substrate 1 of the epitaxial wafer 10, wet etching using sulfuric acid peroxide was used. Sulfuric acid peroxide with dilution ratios (volume of water ÷ volume of mixed solution) of 4 times, 9 times, 19 times, 49 times, and 99 times was prepared, and these sulfuric acid peroxides were used. Also, using each of these sulfuric acid peroxides, the immersion time was changed and a plurality of prototypes were made.

[0076] (Comparative Example) In the comparative example, as shown in FIG. 8, after growing the epitaxial layer 2 on the first surface 11 of the starting substrate 1, a protective film was not formed before applying BCB, and as shown in FIG. 9, the bonded wafer 100 was manufactured in the same manner as in Example 1 except that the deposits 5 on the second surface 12, which is the back surface of the starting substrate 1, were not removed and bonding was performed via BCB, and the bonded wafer 100 was processed in the same order as in Example 1 to obtain a bonded device.

[0077] Regarding Example 1, Fig. 10 shows the relationship between the replacement (OP value; cutting amount, etc.) and the defective area ratio of the epitaxial layer due to BCB thermosetting failure after bonding in each case of the lap method, polish method, and surface grinding method for removing the deposit 5. Fig. 10 also shows the results of a comparative example where the deposit 5 was not removed, i.e., the replacement was set to 0 μm. The defective area ratio is shown as the ratio of the area where the epitaxial layer 2 was damaged to the effective area excluding the bonding defective area in the outer peripheral part. Also, the exemplified area is for a 10.16 cm (4-inch) wafer.

[0078] The replacement (OP value) shown in Fig. 10 indicates the difference in values before and after cutting after being attached to the cutting plate in the lap method and polish method, and for the surface grinding method, the decrease in the total thickness at the center of the wafer is represented as the OP value.

[0079] From the results shown in Fig. 10, it can be seen that in Example 1 where the deposit 5 on the second surface 12 of the starting substrate 1 of the epitaxial wafer 10 was removed and then BCB thermosetting was performed, the epitaxial layer defects due to the BCB layer 20 could be suppressed compared to the comparative example (OP value = 0 μm) where BCB thermosetting was performed without removing the deposit 5. In particular, in the lap method, it can be seen that the epitaxial layer defects due to the BCB layer 20 do not occur at an OP value of about 1 μm or more, and in other methods, at an OP value of about 0.5 μm (1 / 10 of the thickness of the window layer) or more. In the lap method, it is presumed that more cutting amount (replacement) is required due to the influence of the crushed layer generated during lapping. In the polish method and surface grinding method, the influence of the crushed layer is extremely small, and it is presumed that improvement was achieved with a smaller cutting amount (replacement) than the lap method.

[0080] The grinding amount may be taken larger than described above, but since the effect does not increase even if the grinding amount is increased, there is no positive significance in increasing the grinding amount.

[0081] Regarding Example 2, the relationship between the dilution ratio of persulfuric acid and the etching time, and the area ratio of the defective parts of the epitaxial layer caused by the BCB layer after bonding is shown in FIG. 11. FIG. 11 also shows the results of a comparative example in which the precipitate 5 was not removed, that is, the etching time was set to 0 seconds.

[0082] From the results shown in FIG. 11, in Example 2 in which the BCB was thermally cured after removing the precipitate 5 on the second surface 12 of the starting substrate 1 of the epitaxial wafer 10, compared with the comparative example in which the BCB was thermally cured without removing the precipitate 5 (etching time = 0 seconds), it can be seen that the epitaxial layer defects caused by the BCB layer 20 could be suppressed. In particular, it can be seen that the epitaxial defects can be sufficiently suppressed even with a short etching time as the dilution ratio of persulfuric acid decreases. This is considered to indicate the difference in the etching rate for the precipitate 5 generated on the second surface 12 which is the back surface of the starting substrate 1 of the epitaxial wafer 10. It can be said that the same applies to any dilution ratio and etching time as long as the precipitate 5 can be removed.

[0083] From the viewpoint of controlling the variation in the etching amount, the lower limit of the etching time is preferably 60 seconds or more, and therefore the dilution ratio is preferably 9 times or more. Also, from the viewpoint of productivity, the upper limit of the processing time is preferably around 120 seconds, and therefore the dilution ratio is preferably 49 times or less. However, as shown in FIG. 11, an effect can be obtained even if the treatment is carried out outside this dilution ratio.

[0084] In this example, the case of persulfuric acid was exemplified, but as long as it contains hydrogen peroxide, even a mixed solution containing an inorganic acid or an organic acid of a type different from sulfuric acid is effective for etching the precipitate 5, and the same tendency as in the case of persulfuric acid can be obtained.

[0085] Note that the present invention is not limited to the above-described embodiment. The above-described embodiment is an example, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Explanation of Reference Numerals

[0086] 1…Starting substrate, 2…Epitaxial layer, 3…Etch stop layer, 4 and 40…Protective film, 5…Deposit, 6…Separation element (device), 10…Epitaxial wafer, 11…First surface, 12…Second surface, 20…BCB layer, 21…First cladding layer, 22…Active layer, 23…Second cladding layer, 24…DH structure part, 25…Window layer, 30…Wafer to be bonded, 40A and 40B…Openings, 50 and 60…Electrodes, 100…Bonded wafer, 200…EP bonding substrate, 300…Bonded device.

Claims

1. A method for manufacturing a bonded wafer in which an epitaxial wafer containing P (phosphorus) and a wafer to be bonded are bonded via benzocyclobutene, comprising: using, as the epitaxial wafer, an epitaxial wafer including a starting substrate having a first surface and a second surface opposite to the first surface, and an epitaxial layer formed on the first surface of the starting substrate and containing P; removing deposits that have precipitated by overflowing during the epitaxial growth process from the second surface of the starting substrate of the epitaxial wafer, and then performing thermosetting of the benzocyclobutene, the method for manufacturing a bonded wafer being characterized thereby.

2. The method for manufacturing a bonded wafer according to claim 1, characterized in that, as the epitaxial layer, an epitaxial layer having an active layer containing Ga (gallium), In (indium), and P, and a window layer containing P is used.

3. The method for manufacturing a bonded wafer according to claim 1 or 2, characterized in that, as the wafer to be bonded, a wafer made of a material selected from the group consisting of germanium, silicon, sapphire, and quartz is used.

4. The method for manufacturing a bonded wafer according to any one of claims 1 to 3, characterized in that the removal of the deposits is performed by mechanical grinding or polishing, or by mechanical chemical polishing.

5. The epitaxial layer includes a window layer, the method for manufacturing a bonded wafer according to claim 4, characterized in that the removal allowance for the deposits is set to be 1 / 10 or more of the thickness of the window layer of the epitaxial layer.

6. The method for manufacturing a bonded wafer according to any one of claims 1 to 3, characterized in that the removal of the deposits is performed by a wet etching method or a dry etching method.

7. The method for manufacturing a bonded wafer according to claim 6, characterized in that the wet etching method is performed using a solution obtained by diluting a mixed solution of hydrogen peroxide water and an inorganic acid or an organic acid with water.

8. The method for manufacturing a bonded wafer according to claim 7, characterized in that the dilution ratio (volume of water ÷ volume of mixed solution) of the solution diluted with water is set to be 9 times or more and 49 times or less.

9. The dry etching method is carried out in an atmosphere containing one or more selected from the group consisting of Cl ２ , BCl ３ and SiCl ４ , The manufacturing method of the bonded wafer according to claim 6, characterized in that it is carried out in an atmosphere containing one or more selected from the group consisting of

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