Manufacturing method of bonded wafer

Abstract

The present invention is a bonded wafer obtained by bonding, via a bonding material, a support substrate and an epitaxial wafer that has a heterojunction structure in which materials having different coefficients of thermal expansion are stacked through epitaxial growth upon a growth substrate. The bonded wafer is characterized in that the average thickness of the bonding material is 0.01 μm to 0.6 μm. Due to this configuration, provided are a bonded wafer and a method for manufacturing the same with which, when a thermosetting bonding material is used to bond a warped semiconductor epitaxial substrate and a support substrate to each other, the film thickness distribution of the bonding material caused by the warpage of the semiconductor epitaxial substrate and the warpage that changes with thermal changes is improved.

Description

[Technical field]

[0001] The present invention relates to a bonded wafer in which a support substrate is bonded to an epitaxial wafer in which a compound semiconductor functional layer is epitaxially grown on a growth substrate (starting substrate). [Background technology]

[0002] The technology to separate only the epitaxial functional layer from the starting substrate and transfer it to another substrate is important for alleviating the constraints imposed by the physical properties of the starting substrate and increasing the design freedom of the device system. In order to achieve this transfer, a technology is required to remove the starting substrate after bonding the epitaxial functional layer to the support substrate and then transfer the layer to another substrate.

[0003] Patent Document 1 discloses a technique for thermocompression bonding a semiconductor epitaxial substrate and a temporary support substrate via a dielectric layer, and a technique for separating the temporary support substrate and the epitaxial functional layer by wet etching, but there is a problem that the bonding quality after bonding decreases if the semiconductor epitaxial substrate is significantly warped. In particular, although the problem does not become apparent immediately after bonding, there is a problem that after the starting substrate is removed, unevenness occurs on the substrate removal surface, and height differences occur within the surface (concave or convex).

[0004] Although not directly related to improving the bonding property, Patent Document 2 discloses a technique in which a transparent conductive layer is inserted between an adhesive layer and a functional layer as one form of bonding.

[0005] When an optically functional layer such as a light receiving or emitting element is bonded with a bonding material transparent to incident or emitted light, there is a limit to the thickness that can be optically selected. In order to suppress multiple reflections in the transparent bonding layer, it is advantageous to make the transparent bonding layer thicker.

[0006] In addition, thickening the bonding layer increases its mechanical strength, so that even if the semiconductor epitaxial substrate is subjected to design stress, the strength of the bonding layer will not be compromised, and the epitaxial layer will be held after the starting substrate is removed, and there is an effect of preventing the remaining epitaxial layer from peeling off from the bonded substrate when the starting substrate is removed. Therefore, increasing the thickness of the bonding layer is advantageous in terms of optical design and mechanical properties.

[0007] However, thickening the bonding layer tends to cause unevenness in the thickness of the bonding layer during bonding. The bonding material has the property of being thermosetting, in other words, the temperature must be raised above room temperature to harden. The semiconductor epitaxial substrate is a laminate of materials different from the starting substrate, and each material has a different thermal expansion coefficient. Therefore, raising the temperature is essentially synonymous with changing the warp of the semiconductor epitaxial substrate.

[0008] The bonding material is soft before it is thermally hardened, and the warping of the semiconductor epitaxial substrate causes a film thickness distribution. The film thickness distribution of the bonding material immediately after coating is within ±5%, but if the semiconductor epitaxial substrate has a convex warp, the bonding material at the center of the wafer will be thinner, and if it has a concave warp, it will be thicker. This warping also changes with temperature changes.

[0009] Applying pressure to the semiconductor epitaxial substrate is an effective way to correct warpage, but this results in a distribution of thickness in the bonding material along the warped shape before compression bonding. Once this distribution of thickness occurs, it is not significantly improved even if a softening treatment is subsequently performed.

[0010] As a result, when a warped semiconductor epitaxial substrate and a support substrate are bonded with a thermosetting bonding material, there is a problem in that there is a large distribution in the thickness of the bonding material. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent Publication No. 2021-27301 [Patent Document 2] Patent 4159421 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention has been made to solve the above-mentioned problems, and has an object to provide a bonded wafer and a manufacturing method thereof that improve the warpage of a semiconductor epitaxial substrate and the film thickness distribution of a bonding material caused by the warpage that changes with thermal change when a warped semiconductor epitaxial substrate is bonded to a support substrate with a bonding material. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention provides A bonded wafer is an epitaxial wafer having a heterojunction structure in which materials having different thermal expansion coefficients are epitaxially grown on a growth substrate, and a support substrate are bonded to each other via a bonding material, The bonded wafer has an average thickness of the bonding material of 0.01 μm or more and 0.6 μm or less.

[0014] By setting the thickness of the bonding material to 0.01 μm or more and 0.6 μm or less in this way, the ratio of the maximum film thickness to the minimum film thickness of the bonding material can be kept to less than two, even when a warped wafer, such as an epitaxial wafer with a heterojunction structure, is bonded to a support substrate.

[0015] It is also preferable that the bonding material is a thermosetting material and has a thermal softening point lower than the thermosetting temperature.

[0016] The bonding material is preferably made of one or more of epoxy resin, benzocyclobutene (BCB), SOG (spin-on-glass), PI (Polyimide), and fluororesin.

[0017] In the present invention, such a bonding material can be suitably used.

[0018] The bonding material may be in a softened state.

[0019] If the bonding material is in a softened state, the support substrate can be easily separated even if peeling becomes necessary.

[0020] In addition, in the present invention, (1) A process for producing an epitaxial wafer having a heterojunction structure by epitaxially growing materials having different thermal expansion coefficients on a growth substrate; (2) preparing a support substrate; and (3) A step of bonding the epitaxial growth layer of the epitaxial wafer to the support substrate via a bonding material. A method for producing a bonded wafer, comprising: The present invention provides a method for producing a bonded wafer in which the average thickness of the bonding material is 0.01 μm or more and 0.6 μm or less.

[0021] By setting the thickness of the bonding material to 0.01 μm or more and 0.6 μm or less in this manner, it is possible to relatively easily manufacture a bonded wafer in which the ratio of the maximum film thickness to the minimum film thickness of the bonding material is 2:000 or less, even when a warped wafer, such as an epitaxial wafer having a heterojunction structure, is bonded to a support substrate.

[0022] It is also preferable that the bonding material is a thermosetting material and has a thermal softening point lower than the thermosetting temperature.

[0023] The bonding material is preferably made of one or more of epoxy resin, benzocyclobutene (BCB), SOG (spin-on-glass), PI (Polyimide), and fluororesin.

[0024] In the present invention, such a bonding material can be suitably used.

[0025] In addition, in the present invention, (1) A process for producing an epitaxial wafer having a heterojunction structure by epitaxially growing materials having different thermal expansion coefficients on a growth substrate; (2) preparing a support substrate; and (3) A step of bonding the epitaxial growth layer of the epitaxial wafer to the support substrate via a bonding material. A method for producing a bonded wafer, comprising: The present invention provides a method for manufacturing a bonded wafer, which comprises applying a thermosetting material onto the epitaxial growth layer and curing it, and then bonding the support substrate onto the epitaxial growth layer via the bonding material having an average thickness of 0.01 μm or more and 0.6 μm or less.

[0026] With such a manufacturing method, even when the bonding material is required to have a certain thickness, it is possible to improve the film thickness distribution of the bonding material. Effect of the Invention

[0027] As described above, the present invention can provide a bonded wafer and a manufacturing method thereof that improve the warpage of a semiconductor epitaxial substrate and the film thickness distribution of a bonding material that is caused by the warpage that changes with thermal change when a warped semiconductor epitaxial substrate is bonded to a support substrate with a bonding material. [Brief description of the drawings]

[0028] [Figure 1] 1 is a graph showing the relationship between the design film thickness of a bonding material and the in-plane thickness distribution (maximum film thickness and minimum film thickness) discovered in the present invention. [Diagram 2] 1 is a graph showing the relationship between the diameter of an epitaxial wafer and the in-plane thickness distribution (maximum film thickness and minimum film thickness) of a bonding material when the wafer is bonded to a supporting substrate via the bonding material. [Diagram 3] FIG. 2 is a schematic diagram showing the production of an epitaxial wafer by growing an epitaxial growth layer on a growth substrate in the first embodiment of the method for producing a bonded wafer of the present invention. [Figure 4]FIG. 2 is a schematic diagram showing a bonded wafer produced by bonding a support substrate (silicon wafer) to an epitaxial growth layer via a bonding material (BCB) in the first embodiment of the method for producing a bonded wafer of the present invention. [Diagram 5] FIG. 2 is a schematic diagram showing a state where a growth substrate is removed from a bonded wafer in the first embodiment of the method for producing a bonded wafer of the present invention. [Figure 6] 11 is a graph showing the relationship between the total film thickness (design thickness) of the lower hardened layer and the bonding material layer and the in-plane thickness distribution (maximum film thickness and minimum film thickness) in a second embodiment of the method for manufacturing a bonded wafer of the present invention. [Figure 7] FIG. 11 is a schematic diagram showing the production of an epitaxial wafer by growing an epitaxial growth layer on a growth substrate in a second embodiment of the method for producing a bonded wafer of the present invention. [Figure 8] FIG. 11 is a schematic diagram showing the state where a thermosetting material (BCB) is applied onto an epitaxial growth layer and cured in a second embodiment of the method for producing a bonded wafer of the present invention. [Figure 9] FIG. 11 is a schematic diagram showing a state where a bonding material (BCB) is applied onto a cured thermosetting material (BCB) in a second embodiment of a method for producing a bonded wafer of the present invention. [Figure 10] FIG. 11 is a schematic diagram showing a process for producing a bonded wafer by bonding a supporting substrate (silicon wafer) via a bonding material (BCB) in a second embodiment of the method for producing a bonded wafer of the present invention. [Figure 11] FIG. 11 is a schematic diagram showing a state where a growth substrate is removed from a bonded wafer in a second embodiment of the method for producing a bonded wafer according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] As described above, when a warped semiconductor epitaxial substrate and a supporting substrate are bonded with a thermosetting bonding material, there has been a demand for a bonded wafer and a manufacturing method thereof that improves the warpage of the semiconductor epitaxial substrate and the film thickness distribution of the bonding material caused by the warpage that changes with thermal changes.

[0030] After extensive research, the inventors discovered that by setting the design (average) thickness of the bonding material to between 0.01 μm and 0.6 μm, the in-plane thickness variation of the bonding material layer can be reduced to a maximum thickness of no more than twice the minimum thickness, and thus completed the present invention.

[0031] That is, the present invention is a bonded wafer in which an epitaxial wafer having a heterojunction structure in which materials with different thermal expansion coefficients are epitaxially grown on a growth substrate and a supporting substrate are bonded together via a bonding material, and the average thickness of the bonding material is 0.01 μm or more and 0.6 μm or less.

[0032] The present invention will be described in detail below, but the present invention is not limited thereto.

[0033] [Bonded wafer] The bonded wafer of the present invention is a bonded wafer in which an epitaxial wafer having a heterojunction structure and a support substrate are bonded together via a bonding material, and is characterized in that the average thickness of the bonding material is 0.01 μm or more and 0.6 μm or less. By making the average thickness of the bonding material 0.6 μm or less, it is possible to reduce the warpage of the wafer and the thickness distribution of the bonding material caused by the warpage due to thermal change.

[0034] The inventors investigated the thickness distribution of the bonding material layer when bonding a warped wafer and a support substrate with a heat-curing bonding material layer, and found that in the past, the bonding material layer had a thickness distribution due to the influence of the warp. Figure 2 shows the relationship between the in-plane thickness variation (maximum value - minimum value) of the bonding material for each wafer diameter when an epitaxial wafer with concave warpage in the epitaxial growth direction and a support substrate are bonded via a bonding material. The thickness of the bonding material layer in Figure 2 is the value when the design thickness is constant at 1 μm, and the bonding material hardening treatment conditions are standardized at 250°C for 1 hour.

[0035] The epitaxial wafers had relatively large residual warpage, with a bow of ≒ 100 μm for a diameter of 2”Φ (50 mm), a bow of ≒ 400 μm for a diameter of 4”Φ (100 mm), and a bow of ≒ 1400 to 1600 μm for a diameter of 6”Φ (150 mm).

[0036] Thermosetting bonding materials harden when held at a constant temperature at the hardening treatment temperature, but they always pass through their softening point once before reaching the hardening point. While the temperature is rising, pressure is applied from above and below to suppress thermal deformation (warpage deformation) of the wafer, but as the bonding material layer that contacts the base softens, the effect of suppressing wafer deformation disappears, and the thickness of the bonding material layer changes along with the deformation of the wafer. If the wafer has a concave warp, the thickness of the bonding material layer on the periphery of the wafer becomes thinner and the thickness of the bonding material layer on the center of the wafer becomes thicker.

[0037] Once the bonding material layer is deformed, it cannot be corrected by applying vertical press pressure and reaches the hardening temperature as is, so the thickness distribution of the bonding material layer is preserved. As a result, the bonding material layer hardens with the thickness distribution remaining unchanged.

[0038] Although not shown in the figure, the thicker the bonding layer is, the worse this tendency becomes. In the case of light-emitting elements, the optical characteristics (particularly the light distribution characteristics) change when the element height changes, which causes characteristic variations and is problematic.

[0039] On the other hand, as shown in Figure 1, by gradually thinning the design thickness (average thickness) of the bonding material layer from 1 μm, the in-plane thickness distribution of the bonding material layer tends to be minimized. In particular, in the thickness range of 0.6 μm or less, the maximum film thickness can be kept to less than twice the minimum film thickness, and also to less than twice the design thickness. In order to maintain uniformity in the light distribution characteristics, it is necessary to maintain a height variation of ±1 μm or less, but in the region of the bonding material layer design thickness (spin-coated thickness) of 0.6 μm or less in Figure 1, this height distribution can be maintained, making it possible to keep the variation in element characteristics within an acceptable range.

[0040] In addition, the bonding material such as BCB described below is a material transparent to the emission wavelength, and a technology has been disclosed in which sapphire or quartz, which is transparent to the emission wavelength, is used as a support substrate to extract light from the support substrate. In this case, since the refractive index of the bonding material is different from that of the transparent support substrate, if the bonding material layer is too thin, multiple reflections may occur within the bonding material layer, resulting in a decrease in the light extraction efficiency. In order to avoid this, the design thickness of the bonding material layer can be increased to mitigate the effect of multiple reflections.

[0041] In the bonded wafer of the present invention, the average thickness of the bonding material is 0.01 μm or more. If it is thinner than 0.01 μm, problems such as a decrease in light extraction efficiency due to the influence of multiple reflections and a decrease in area yield after bonding processing may occur.

[0042] The bonding material is preferably a thermosetting material having a thermal softening point lower than the thermosetting temperature, and is preferably made of one or more of epoxy resin, benzocyclobutene (BCB), SOG (spin-on-glass), PI (Polyimide), and fluororesin.

[0043] The bonding material may be hardened or softened, so that the support substrate can be easily separated from the bonding material when it becomes necessary to separate the support substrate from the bonding material.

[0044] In the bonded wafer of the present invention, there are no particular limitations on the growth substrate, the material for epitaxial growth, and the support substrate.

[0045] [Manufacturing method of bonded wafers] The present invention also provides a method for producing a bonded wafer. Hereinafter, the method for producing a bonded wafer of the present invention will be described in more detail with reference to the drawings in relation to an embodiment, but the present invention is not limited thereto.

[0046] First embodiment A first embodiment of a method for producing a bonded wafer of the present invention includes: (1) A process for producing an epitaxial wafer having a heterojunction structure by epitaxially growing materials having different thermal expansion coefficients on a growth substrate; (2) preparing a support substrate; and (3) A step of bonding the epitaxial growth layer of the epitaxial wafer to the support substrate via a bonding material. A method for producing a bonded wafer, comprising: The method for producing a bonded wafer is such that the average thickness of the bonding material is 0.01 μm or more and 0.6 μm or less.

[0047] A first embodiment of a method for producing a bonded wafer will be described with reference to FIGS.

[0048] 3, a first-conductivity-type GaAs buffer layer 2 is laminated on a first-conductivity-type GaAs growth substrate 1, and then a first-conductivity-type GaInP first etch stop layer 3 is formed to a thickness of, for example, 0.3 μm, a first-conductivity-type GaAs second etch stop layer 4 is formed to a thickness of, for example, 0.3 μm, a first-conductivity-type AlGaInP first cladding layer 5 is formed to a thickness of, for example, 1.0 μm, a non-doped AlGaInP active layer 6, a second-conductivity-type AlGaInP second cladding layer 7 is formed to a thickness of, for example, 1.0 μm, a second-conductivity-type GaInP intermediate layer 8 is formed to a thickness of, for example, 0.1 μm, and a second-conductivity-type GaP window layer 9 is formed to a thickness of, for example, 4 μm, to prepare a semiconductor epitaxial wafer 100 having a light-emitting device structure as epitaxially grown layers (functional layers). Here, the layers from the AlGaInP first cladding layer 5 to the AlGaInP second cladding layer 7 are referred to as a double heterostructure.

[0049] 4, for example, benzocyclobutene (BCB) is spin-coated onto the epitaxial growth layer of the epitaxial wafer 100 as a thermosetting bonding material 10, and then the epitaxial wafer 100 is placed face-to-face with a silicon wafer 11 serving as a supporting substrate, and then thermocompression-bonded to produce a bonded wafer 101 in which the epitaxial wafer 100 and the silicon wafer 11 are bonded together via the bonding material 10. When applying BCB by spin-coating, the designed film thickness is 0.01 μm or more and 0.6 μm or less.

[0050] The support substrate is not limited to a silicon wafer, and any material can be selected as long as flatness is guaranteed. Compound semiconductor wafers such as GaAs and InP can also be selected, but from the viewpoint of price, it is preferable to select silicon, sapphire, quartz, or Ge.

[0051] The thermosetting bonding material 10 is not limited to BCB, and any material having thermosetting properties may be used. In addition to BCB, epoxy resin, SOG (spin-on-glass), PI (Polyimide), fluororesin, etc. may be used.

[0052] In the present embodiment, the case where the thermosetting bonding material 10 is thermally cured by thermocompression is illustrated, but as long as the bonding is established, the bonding is not limited to the state where the bonding material 10 is thermally cured. In the case of the illustrated BCB, the bonding is established even if the temperature is lowered to room temperature after the softening point of 150°C is reached.

[0053] Next, as shown in Fig. 5, the GaAs growth substrate 1 is removed by wet etching using a selective etchant such as ammonia / hydrogen peroxide mixture to expose the GaInP first etch stop layer 3. The etchant is switched to a hydrochloric acid-based solution to selectively remove the GaInP first etch stop layer 3 and expose the GaAs second etch stop layer 4. The etchant is switched to a sulfuric acid / hydrogen peroxide-based solution to selectively remove the GaAs second etch stop layer 4 and expose the first cladding layer 5. By carrying out the above processes, a bonded wafer that retains only the double hetero layer and the window layer is produced.

[0054] Here, the design thickness of the bonding material such as BCB is set to 0.01 μm or more and 0.6 μm or less, but since the bonding material is formed by spin coating, if it is too thin, the area yield after bonding processing tends to decrease. In order to maintain an area yield of 90% or more after bonding, it is preferable to design the bonding material layer thickness to be 0.05 μm or more. Also, if it is sufficient to maintain a bonding area yield of 70% or more, this can be achieved by designing the bonding material layer thickness to be 0.01 μm or more.

[0055] Second Embodiment A second embodiment of the method for producing a bonded wafer of the present invention includes: (1) A process for producing an epitaxial wafer having a heterojunction structure by epitaxially growing materials having different thermal expansion coefficients on a growth substrate; (2) preparing a support substrate; and (3) A step of bonding the epitaxial growth layer of the epitaxial wafer to the support substrate via a bonding material. A method for producing a bonded wafer, comprising: This is a method for manufacturing a bonded wafer, in which a thermosetting material is applied onto the epitaxial growth layer and cured, and the support substrate is then bonded onto the epitaxial growth layer via the bonding material having an average thickness of 0.01 μm or more and 0.6 μm or less.

[0056] There is a trade-off between improving the film thickness distribution of the bonding material layer after bonding by thinning the bonding material layer and improving the light extraction efficiency (external quantum efficiency) by thickening the bonding material layer. However, the above trade-off can be avoided by providing a lower hardened layer formed by hardening a thermosetting material, forming a bonding material layer on top of the lower hardened layer, and bonding the layers together.

[0057] Figure 6 shows the relationship between the total thickness (design thickness) of the lower hardening layer and the bonding material layer and the in-plane thickness distribution (maximum and minimum values) in bonding of 2"Φ wafers. Figure 6 (1) shows data showing the distribution of the total thickness of the bonding material layer and the lower hardening layer after bonding when the design thickness of the bonding material layer is 0.2 μm and the design thickness of the lower hardening layer is changed from 0.4 to 2.2 μm. The designed thickness is 0.6 to 2.4 μm. In the case of the conventional technology, a film thickness distribution of 0.6 to 6 μm occurs for a design thickness of 1 μm, so the film thickness distribution can be significantly improved. In addition, the deviation from the design thickness is relatively small.

[0058] FIG. 6(2) shows data showing the distribution of the total thickness of the bonding material layer and the lower hardening layer after bonding when bonding two 2"Φ wafers with a designed thickness of the bonding material layer of 0.6 μm and a thickness of the lower hardening layer of 0.0 to 4.0 μm. Although the variation is larger than that in FIG. 6(1), the thickness does not exceed twice the designed thickness. In other words, by using the method of the present invention, it is possible to bond a warped epitaxial wafer via a thick bonding material layer without increasing the thickness distribution of the bonding material layer.

[0059] A second embodiment of the method for producing a bonded wafer will be described with reference to FIGS.

[0060] 7, a first-conductivity-type GaAs buffer layer 2 is laminated on a first-conductivity-type GaAs growth substrate 1, and then a first-conductivity-type GaInP first etch stop layer 3 is formed to a thickness of, for example, 0.3 μm, a first-conductivity-type GaAs second etch stop layer 4 is formed to a thickness of, for example, 0.3 μm, a first-conductivity-type AlGaInP first cladding layer 5 is formed to a thickness of, for example, 1.0 μm, a non-doped AlGaInP active layer 6, a second-conductivity-type AlGaInP second cladding layer 7 is formed to a thickness of, for example, 1.0 μm, a second-conductivity-type GaInP intermediate layer 8 is formed to a thickness of, for example, 0.1 μm, and a second-conductivity-type GaP window layer 9 is formed to a thickness of, for example, 4.0 μm, to prepare a semiconductor epitaxial wafer 100 having a light-emitting device structure as epitaxial growth layers (functional layers) sequentially grown. Here, the AlGaInP first cladding layer 5 to the AlGaInP second cladding layer 7 are referred to as a double heterostructure.

[0061] Next, as shown in Fig. 8, benzocyclobutene (BCB) is spin-coated as a thermosetting material 12 onto the epitaxial growth layer of the epitaxial wafer 100. The designed film thickness at this time can be, for example, 0.5 µm. After spin-coating, the substrate is held on a hot plate heated to 250°C for 1 hour to form a lower hardened layer by hardening the BCB.

[0062] 9, after forming a lower hardened layer, a bonding material layer is formed by spin-coating benzocyclobutene (BCB) as a bonding material 10. At this time, the design thickness of the bonding material layer is set to 0.01 μm or more and 0.6 μm or less.

[0063] Next, after forming a bonding material layer as shown in FIG. 10, the bonding material 10 and a silicon wafer 11, which is a supporting substrate, are placed opposite each other and then thermally compressed to produce a bonded wafer 101 in which the epitaxial wafer 100 and the silicon wafer 11 are bonded via the bonding material 10 and the thermosetting material 12.

[0064] The support substrate is not limited to a silicon wafer, and any material can be selected as long as flatness is guaranteed. Compound semiconductor wafers such as GaAs and InP can also be selected, but from the viewpoint of price, it is preferable to select silicon, sapphire, quartz, or Ge.

[0065] In addition, the thermosetting bonding material 10 and the thermosetting material 12 for forming the lower hardened layer are not limited to BCB, and any material having thermosetting properties can be selected. In addition to BCB, epoxy resin, SOG (spin-on-glass), PI (Polyimide), fluororesin, etc. may be used. In addition, it is preferable that the bonding material 10 and the thermosetting material 12 are made of the same material.

[0066] In the present embodiment, the case where the thermosetting bonding material 10 is thermally cured by thermocompression is illustrated, but as long as the bonding is established, the bonding is not limited to the state where the bonding material 10 is thermally cured. In the case of the illustrated BCB, the bonding is established even if the temperature is lowered to room temperature after the softening point of 150°C is reached.

[0067] 11, the GaAs growth substrate 1 is removed by wet etching using a selective etchant such as ammonia / hydrogen peroxide mixture to expose the GaInP first etch stop layer 3. The etchant is switched to a hydrochloric acid-based solution to selectively remove the GaInP first etch stop layer 3 and expose the GaAs second etch stop layer 4. The etchant is switched to a sulfuric acid / hydrogen peroxide-based solution to selectively remove the GaAs second etch stop layer 4 and expose the first cladding layer 5. By carrying out the above processes, a bonded wafer that retains only the double hetero layer and the window layer is produced.

[0068] In the present embodiment, the thickness of the lower hardened layer made of a thermosetting material that has been subjected to a hardening treatment and disposed under the bonding material layer is exemplified as 0.5 μm, but the thickness is not limited to this thickness and can be, for example, 0.01 μm to 5.0 μm. The thickness of the lower hardened layer can be freely selected. If the thickness of the lower hardened layer is increased, the mechanical strength of the remaining epitaxial layer after removing the growth substrate is increased, and the effect of preventing peeling is enhanced.

[0069] In addition, since the bonding material is formed by spin coating, if the thickness of the bonding material is too thin, the area yield after bonding processing tends to decrease. In order to maintain an area yield of 90% or more after bonding, it is preferable to design the bonding material thickness to be 0.05 μm or more. Also, if it is sufficient to maintain a bonding area yield of 70% or more, this can be achieved by designing the bonding material layer thickness to be 0.01 μm or more. EXAMPLES

[0070] The present invention will be specifically described below using examples and comparative examples, but the present invention is not limited to these.

[0071] Example 1 A first conductivity type GaAs buffer layer is laminated on a first conductivity type GaAs growth substrate, and then a first conductivity type Ga x In 1-x The first etch stop layer is 0.3 μm thick, the second etch stop layer is 0.3 μm thick, and the second etch stop layer is 0.3 μm thick. yGa 1-y ) x In 1-x P(0.4 ≦ x ≦ 0.6, 0 < y ≦ 1) first cladding layer of 1.0 μm, undoped (Al y Ga 1-y ) x In 1-x P(0.4 ≦ x ≦ 0.6, 0 ≦ y ≦ 0.6) active layer, p-type (Al y Ga 1-y ) x In 1-x P(0.4 ≦ x ≦ 0.6, 0 < y ≦ 1) second cladding layer of 1.0 μm, p-type GaInP intermediate layer of 0.1 μm, p-type GaP window layer of 4 μm, and a semiconductor epitaxial wafer having a light-emitting element structure as an epitaxially grown layer grown sequentially was prepared.

[0072] Benzocyclobutene (BCB) was spin-coated on the semiconductor epitaxial wafer as a thermosetting bonding material to form a bonding material layer, and it was superposed facing a silicon wafer as a support substrate and thermocompression bonded to fabricate a first bonded wafer in which the semiconductor epitaxial wafer and the silicon wafer were bonded via BCB. When applying BCB by spin coating, the designed film thickness was 0.6 μm.

[0073] The GaAs growth substrate was removed by wet etching treatment with aqueous ammonia peroxide to expose the GaInP first etch stop layer. The etchant was switched to a hydrochloric acid system to selectively remove the GaInP first etch stop layer and expose the GaAs second etch stop layer. The etchant was switched to a sulfuric acid peroxide system to selectively remove the GaAs second etch stop layer and expose the first cladding layer. By performing the above treatments, a second bonded wafer retaining only the double hetero layer and the window layer was fabricated.

[0074] When the thickness distribution of the bonded portion of this bonded wafer was examined, the ratio of the maximum film thickness to the minimum film thickness was 1.9 times. It was found that the thickness distribution was significantly improved compared to the comparative example described later.

[0075] (Example 2) After laminating a GaAs buffer layer of the first conductivity type on a GaAs growth substrate of the first conductivity type, Ga of the first conductivity type x In 1-x P (0.4 ≤ x ≤ 0.6) first etch stop layer of 0.3 μm, GaAs second etch stop layer of the first conductivity type of 0.3 μm, (Al of the first conductivity type y Ga 1-y ) x In 1-x P (0.4 ≤ x ≤ 0.6, 0 < y ≤ 1) first cladding layer of 1.0 μm, non-doped (Al y Ga 1-y ) x In 1-x P (0.4 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.6) active layer, (Al of the second conductivity type y Ga 1-y ) x In 1-x P (0.4 ≤ x ≤ 0.6, 0 < y ≤ 1) second cladding layer of 1.0 μm, GaInP intermediate layer of the second conductivity type of 0.1 μm, GaP window layer of the second conductivity type of 4.0 μm, and a semiconductor epitaxial wafer having a light-emitting element structure as an epitaxial growth layer grown in sequence was prepared.

[0076] Benzocyclobutene (BCB) is spin-coated as a thermosetting material on the semiconductor epitaxial wafer. The designed film thickness at that time was 0.5 μm. After spin coating, it was held on a hot plate heated to 250 °C for 1 hour to form a lower cured layer in which BCB was cured.

[0077] After forming the lower cured layer, benzocyclobutene (BCB) is spin-coated as a bonding material to form a bonding material layer. At that time, the designed film thickness of the bonding material layer was 0.1 μm.

[0078] After forming the bonding material layer, it is overlapped with the bonding material layer facing the silicon wafer as a support substrate and thermocompression bonded to fabricate a first bonded wafer in which the semiconductor epitaxial wafer and the silicon wafer are bonded via BCB.

[0079] The GaAs growth substrate is removed by wet etching with aqueous ammonia peroxide to expose the GaInP first etch stop layer. The etchant is switched to a hydrochloric acid-based one to selectively remove the GaInP first etch stop layer and expose the GaAs second etch stop layer. The etchant is switched to a sulfuric acid peroxide-based one to selectively remove the GaAs second etch stop layer and expose the first cladding layer. By performing the above processes, a second junction wafer that retains only the DH layer and the window layer was fabricated.

[0080] When the thickness distribution of the junction part of this junction wafer was examined, the ratio of the maximum film thickness to the minimum film thickness was 1.3 times.

[0081] (Comparative Example) On a GaAs growth substrate of the first conductivity type, after laminating a GaAs buffer layer of the first conductivity type, Ga x In 1-x P (0.4 ≤ x ≤ 0.6) first etch stop layer of 0.3 μm, GaAs second etch stop layer of the first conductivity type of 0.3 μm, (Al y Ga 1-y ) x In 1-x P (0.4 ≤ x ≤ 0.6, 0 < y ≤ 1) first cladding layer of 1.0 μm, non-doped (Al y Ga 1-y ) x In 1-x P (0.4 ≤ x ≤ 0.6, 0 ≤ y ≤ 0.6) active layer, (Al y Ga 1-y ) x In 1-x P (0.4 ≤ x ≤ 0.6, 0 < y ≤ 1) second cladding layer of 1.0 μm, GaInP intermediate layer of the second conductivity type of 0.1 μm, GaP window layer of the second conductivity type of 4.0 μm were sequentially grown as an epitaxial growth layer having a light-emitting element structure to prepare a semiconductor epitaxial wafer.

[0082] A semiconductor epitaxial wafer was spin-coated with 1.0 μm of BCB as a bonding material, and then placed face-to-face with a sapphire wafer and thermally bonded to produce a bonded wafer in which the epitaxial wafer and the sapphire wafer were bonded via BCB. During bonding, the temperature of the BCB was set to be higher than 150°C and lower than 350°C. Furthermore, the wafer was hardened by holding it at 250°C for 1 hour.

[0083] The GaAs growth substrate is removed by wet etching using ammonia / hydrogen peroxide water to expose the GaInP first etch stop layer. The etchant is switched to a hydrochloric acid-based solution to selectively remove the GaInP first etch stop layer and expose the GaAs second etch stop layer. The etchant is switched to a sulfuric acid / hydrogen peroxide water-based solution to selectively remove the GaAs second etch stop layer and expose the first cladding layer. By carrying out the above processes, a bonded wafer that retains only the double hetero layer and window layer was produced.

[0084] When the thickness distribution of the bonded portion of this bonded wafer was examined, the ratio of the maximum film thickness to the minimum film thickness was 8.5 times.

[0085] As shown by the results of Examples 1 and 2, in the present invention, by fabricating a bonded wafer with a design thickness (average thickness) of the bonding material of 0.6 μm or less, it is possible to significantly improve the thickness distribution of the bonding material caused by warpage. On the other hand, as shown by the result of Comparative Example 1, when a bonded wafer is fabricated with a design thickness of the bonding material of more than 0.6 μm, the thickness distribution of the bonding material becomes large.

[0086] 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.

Claims

[Claim 1] (1) A process for producing an epitaxial wafer having a heterojunction structure by epitaxially growing materials having different thermal expansion coefficients on a growth substrate; (2) preparing a support substrate; and (3) A step of bonding the epitaxial growth layer of the epitaxial wafer to the support substrate via a bonding material. A method for producing a bonded wafer, comprising: A method for manufacturing a bonded wafer, comprising applying a thermosetting material onto the epitaxial growth layer and hardening the material, and then bonding the support substrate onto the epitaxial growth layer via the bonding material having an average thickness of 0.01 μm or more and 0.6 μm or less.

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