WO2014123097A1 - Method for manufacturing composite substrate and semiconductor wafer using said substrate - Google Patents

Abstract

A composite substrate (1) includes: a support substrate (11) including, as a crystal phase, 35-65% by mass of a mullite phase, and 35-65% by mass of an alumina phase; and a semiconductor film (13) disposed on the main surface (11m) of the support substrate (11). A method for manufacturing a semiconductor wafer (3) includes: a step for preparing the composite substrate (1); a step for growing at least one semiconductor layer (20) on the semiconductor film (13) of the composite substrate to form a composite substrate (2) having a semiconductor layer; and a step for removing the support substrate (11) from the composite substrate (2) having a semiconductor layer to form the semiconductor wafer (3). A method is thus provided for manufacturing a composite substrate suitable for manufacturing a high-quality semiconductor wafer with high yield and good efficiency, and a semiconductor wafer using same.

Description

Composite substrate and method for manufacturing semiconductor wafer using the same

The present invention relates to a composite substrate suitable for efficiently producing a high-quality semiconductor wafer with high yield and a method for producing a semiconductor wafer using the same.

Group III nitride semiconductor wafers such as GaN wafers are suitably used as substrates and semiconductor layers for semiconductor devices such as light-emitting devices and electronic devices. As a base substrate for manufacturing such a semiconductor wafer, the chemical composition is the same as or close to that of the semiconductor wafer from the viewpoint of making the lattice constant and the thermal expansion coefficient match or close to match between the base substrate and the semiconductor wafer. What you have is excellent. However, when the semiconductor wafer is a GaN wafer or the like, the most excellent GaN substrate as the base substrate is very expensive, and it is difficult to obtain a large-diameter GaN substrate having a main surface diameter exceeding 2 inches.

Therefore, a sapphire substrate is generally used as a base substrate for forming a GaN wafer. However, sapphire crystals and GaN crystals have greatly different lattice constants and thermal expansion coefficients.

For this reason, in order to relax the mismatch of the lattice constant between the sapphire crystal and the GaN crystal and form a GaN wafer with good crystallinity, for example, Japanese Patent Laid-Open No. 04-297023 (Patent Document 1) It is disclosed that when a GaN crystal is grown on a sapphire substrate, a GaN buffer layer is formed on the sapphire substrate and the GaN crystal layer is grown on the GaN buffer layer.

In order to obtain a GaN-based film having a high crystallinity and a small warpage by using a composite substrate of a support substrate having a thermal expansion coefficient close to that of GaN crystal and a GaN single crystal film, for example, Japanese Unexamined Patent Application Publication No. 2012-121788. (Patent Document 2) discloses that an oxide sintered body supporting substrate having a thermal expansion coefficient in the main surface larger than 0.8 times and smaller than 1.2 times the thermal expansion coefficient of the GaN crystal, Disclosed is a growth of a GaN-based film on a GaN single crystal film of a composite substrate including a GaN single crystal film disposed on the main surface side.

Japanese Patent Laid-Open No. 04-297023 JP 2012-121788 A

In the above-mentioned Japanese Patent Application Laid-Open No. 04-297023 (Patent Document 1), since the thermal expansion coefficient of sapphire crystal is much larger than the thermal expansion coefficient of GaN crystal, the larger the diameter of the main surface, the smaller the warpage of GaN. It is difficult to obtain a film.

On the other hand, in the above Japanese Unexamined Patent Publication No. 2012-121788 (Patent Document 2), the composite substrate used has a low flatness after polishing of the oxide sintered body supporting substrate, and the oxide sintered body supporting substrate. There is a region where the bonding between the GaN-based film and the GaN single crystal film is insufficient, and the uniform growth of the GaN-based film is inhibited on the region, which hinders the improvement of the yield of the GaN-based film.

An object of the present invention is to solve the above problems and provide a composite substrate suitable for efficiently producing a high-quality semiconductor wafer with high yield and a method for producing a semiconductor wafer using the same. To do.

According to an aspect of the present invention, a support substrate including a mullite phase of 35% to 65% by mass and an alumina phase of 35% to 65% by mass as crystal phases is disposed on the main surface side of the support substrate. And a semiconductor substrate.

In the composite substrate according to this aspect of the present invention, the support substrate may further include 10% by mass or less of a silica phase as an amorphous phase.

According to another aspect of the present invention, a support substrate containing a mullite phase of 35% by mass to 65% by mass and an alumina phase of 35% by mass to 65% by mass as crystal phases, and a main surface of the support substrate A step of preparing a composite substrate including a semiconductor film disposed on the side, a step of growing at least one semiconductor layer on the semiconductor film of the composite substrate to form a composite substrate with a semiconductor layer, and a semiconductor layer And a step of forming a semiconductor wafer by removing the supporting substrate from the attached composite substrate.

In the method for manufacturing a semiconductor wafer according to this aspect of the present invention, the support substrate can further include 10% by mass or less of a silica phase as an amorphous phase.

According to the present invention, it is possible to provide a composite substrate suitable for efficiently producing a high-quality semiconductor wafer with high yield and a method for producing a semiconductor wafer using the same.

It is a schematic sectional drawing which shows an example of the composite substrate concerning this invention. It is a schematic sectional drawing which shows an example of the process of preparing the composite substrate concerning this invention. It is a schematic sectional drawing which shows another example of the process of preparing the composite substrate concerning this invention. It is a schematic sectional drawing which shows the manufacturing method of the semiconductor wafer concerning this invention.

[Embodiment 1: Composite substrate]
Referring to FIG. 1, a composite substrate 1 according to an embodiment of the present invention includes a support substrate including a mullite phase of 35% to 65% by mass and an alumina phase of 35% to 65% by mass as crystal phases. 11 and a semiconductor film 13 disposed on the main surface 11m side of the support substrate 11. In the composite substrate 1 of this embodiment, the support substrate 11 includes a mullite phase and an alumina phase as crystal phases, the mullite phase content is 35 mass% to 65 mass%, and the alumina phase content is 35 mass%. Since the amount is 65% by mass or less, the flatness of the main surface after polishing of the support substrate 11 is increased, and the ratio α _S of the thermal expansion coefficient α _S of the support substrate 11 to the thermal expansion coefficient α _F of the semiconductor film 13 is increased. / Α _F is close to 1. Thereby, since the composite substrate 1 has high bonding properties between the support substrate 11 and the semiconductor film 13 and the occurrence of warping and cracking is suppressed, a high-quality semiconductor wafer can be efficiently produced on the semiconductor film 13 with high yield. Can be well formed.

(Support substrate)
With reference to FIG. 1, the support substrate 11 included in the composite substrate 1 of the present embodiment has a crystal phase of 35% by mass or more and 65% by mass from the viewpoint of increasing the flatness of the main surface after polishing of the support substrate 11. % Of mullite phase and 35% by mass or more and 65% by mass or less of alumina phase are necessary. Furthermore, the support substrate 11 has a mullite phase content of preferably 40% by mass or more and 63% by mass or less, and 45% by mass or more and 61% by mass or less from the viewpoint of further increasing the flatness of the main surface after polishing. More preferred. In addition, the content of the alumina phase of the support substrate 11 is preferably 37% by mass or more and 55% by mass or less, and more preferably 39% by mass or more and 49% by mass or less.

In the support substrate 11, the chemical composition of the mullite phase is Al ₆ Si ₂ O ₁₃ (3Al ₂ O ₃ .2SiO ₂ ) or a composition in the vicinity thereof, and the chemical composition of the alumina phase is Al ₂ O ₃ . The contents of the mullite phase and the alumina phase which are crystal phases can be measured by X-ray diffraction. Further, the flatness of the main surface after polishing of the support substrate 11 can be evaluated by measuring the arithmetic average roughness Ra defined in JIS B0601 of the main surface after polishing. The smaller the arithmetic average roughness Ra, the higher the flatness degree, and the higher the arithmetic average roughness Ra, the lower the flatness degree.

From the viewpoint of improving the removability from the composite substrate 1 by increasing the etchability with respect to an etchant such as hydrofluoric acid while maintaining the flatness of the main surface after polishing high, the support substrate 11 is an amorphous phase. It is preferable to further contain 10 mass% or less of silica phase. When the content of the silica phase in the support substrate 11 exceeds 10% by mass, the degree of planarization of the main surface after polishing of the support substrate 11 tends to decrease. Further, from the viewpoint of enhancing the removability of the support substrate 11 from the composite substrate 1, the content of the silica phase in the support substrate 11 is preferably 0.02% by mass or more. Further, the support substrate 11, the chemical composition of the silica phase is SiO _2. The content of the silica phase that is an amorphous phase can be calculated by measuring the Si concentration in the etchant after sufficiently etching the support substrate 11 by ICP-OES (inductively coupled plasma-luminescence) analysis.

The supporting substrate 11 is not particularly limited in its production method and form as long as it has the above-mentioned characteristics, but from the viewpoint of easy physical property adjustment by adjusting the content of each chemical composition, alumina powder is used as a raw material. It is preferable to form a sintered body obtained by sintering these raw materials using a mixed powder of silica powder and a mixed powder of mullite powder, alumina powder and silica powder.

(Semiconductor film)
Referring to FIG. 1, the thickness of the semiconductor film 13 included in the composite substrate 1 of the present embodiment is the thickness from the viewpoint of growing at least one semiconductor layer having high crystallinity on the semiconductor film 13. However, 10 micrometers or more are required, 20 micrometers or more are preferable and 50 micrometers or more are more preferable. In addition, the thickness of the semiconductor film 13 is preferably 250 μm or less, and more preferably 200 μm or less, from the viewpoint of obtaining an inexpensive composite substrate.

The semiconductor film 13 included in the composite substrate 1 of the present embodiment is not particularly limited, but from the viewpoint of growing at least one semiconductor layer having high crystallinity on the semiconductor film 13, a semiconductor layer to be grown. And the chemical composition is preferably the same or similar. For example, when the semiconductor layer to be grown is a GaN-based (Group III nitride containing Ga) layer, the semiconductor film 13 is preferably a GaN film.

(Bonding film)
With reference to FIG. 1, in the composite substrate 1 of this embodiment, a bonding film 12 is formed between the support substrate 11 and the semiconductor film 13 from the viewpoint of increasing the bonding strength between the support substrate 11 and the semiconductor film 13. Preferably it is. The bonding film 12 is not particularly limited, but an SiO ₂ layer, a TiO ₂ layer, or the like is preferable from the viewpoint that the effect of increasing the bonding strength between the support substrate 11 and the semiconductor film 13 is high. Furthermore, a SiO ₂ layer is more preferable from the viewpoint that it can be removed by etching with hydrofluoric acid.

[Embodiment 2: Manufacturing Method of Semiconductor Wafer]
2, 3, and 4, a method for manufacturing a semiconductor wafer according to another embodiment of the present invention includes a mullite phase of 35 mass% or more and 65 mass% or less and a crystal phase of 35 mass% or more and 65 mass% or more. Step of preparing a composite substrate 1 including a support substrate 11 containing no more than% alumina phase and a semiconductor film 13 disposed on the main surface 11m side of the support substrate 11 (FIGS. 2A to 2D) 3 (A) to 3 (D) and FIG. 4 (A)), and a step of growing at least one semiconductor layer 20 on the semiconductor film 13 of the composite substrate 1 to form the composite substrate 2 with a semiconductor layer (FIG. 4B) and a step of removing the support substrate 11 from the composite substrate with semiconductor layer 2 to form a semiconductor wafer (FIG. 4C). The manufacturing method of the semiconductor wafer 3 of the present embodiment includes a support substrate 11 including a mullite phase of 35 mass% to 65 mass% and an alumina phase of 35 mass% to 65 mass% as crystal phases on the main surface 11 m side. After growing at least one semiconductor layer 20 on the semiconductor film 13 of the composite substrate 1 including the semiconductor film 13 disposed, the support substrate is removed to obtain a high-quality semiconductor wafer 3 with high yield. It can be manufactured efficiently at a high rate.

(Preparation process of composite substrate)
With reference to FIG. 4A, in the step of preparing the composite substrate 1, the method for disposing the semiconductor film 13 on the main surface 11 m side of the support substrate 11 of the composite substrate 1 is not particularly limited. A method of growing the semiconductor film 13 on the main surface 11m (first method), and bonding the semiconductor film 13 formed on the main surface of the base substrate to the main surface 11m of the support substrate 11 and then the base substrate (Second method), a semiconductor film donor substrate (not shown) is bonded to the main surface 11m of the support substrate 11, and then the semiconductor film donor substrate is bonded at a predetermined depth from the bonding surface. For example, a method (third method) of forming the semiconductor film 13 on the main surface 11m of the support substrate 11 by cutting. When the support substrate 11 is formed of an oxide sintered body, the first method is difficult, and therefore any one of the second and third methods is preferably used. In the second method, the method for bonding the semiconductor film 13 to the support substrate 11 is not particularly limited, and the method for bonding the semiconductor film 13 directly to the main surface 11m of the support substrate 11 or the main surface of the support substrate 11 is not limited. For example, a method of bonding the semiconductor film 13 with the bonding film 12 interposed in 11 m may be used. In the third method, the method for bonding the semiconductor film donor substrate to the support substrate 11 is not particularly limited. The method for bonding the semiconductor film donor substrate directly to the main surface 11m of the support substrate 11, For example, a method may be used in which the semiconductor film donor substrate is bonded to the main surface 11m with the bonding film 12 interposed therebetween.

The step of preparing the composite substrate 1 is not particularly limited, but from the viewpoint of efficiently preparing a composite substrate 1 with high quality, for example, referring to FIG. A sub-process for preparing the support substrate 11 (FIG. 2A), a sub-process for forming the semiconductor film 13 on the main surface 30n of the base substrate 30 (FIG. 2B), the support substrate 11 and the semiconductor film 13 can be included, and a sub-process for removing the base substrate 30 (FIG. 2D).

In FIG. 2C, in a sub-process for bonding the support substrate 11 and the semiconductor film 13, a bonding film 12a is formed on the main surface 11m of the support substrate 11 (FIG. 2C1). After forming the bonding film 12b on the main surface 13n of the semiconductor film 13 grown on the surface 30n (FIG. 2 (C2)), the main surface 12am of the bonding film 12a formed on the support substrate 11 and the base substrate By bonding the main surface 12bn of the bonding film 12b formed on the semiconductor film 13 formed on the semiconductor film 13, the bonding film 12a formed by bonding the bonding film 12a and the bonding film 12b is interposed. Then, the support substrate 11 and the semiconductor film 13 are bonded together (FIG. 2 (C3)). However, as long as the support substrate 11 and the semiconductor film 13 can be bonded to each other, the support substrate 11 and the semiconductor film 13 can be directly bonded together without the bonding film 12 interposed.

A specific method for bonding the support substrate 11 and the semiconductor film 13 is not particularly limited, but from the viewpoint of maintaining the bonding strength even at a high temperature after bonding, the bonded surfaces are washed and bonded as they are, and then, 600 ° C. Direct bonding method in which bonding is performed by raising the temperature to about 1200 ° C., and surface activation method in which bonding surfaces are cleaned and activated with plasma or ions and then bonded at a low temperature of room temperature (for example, 25 ° C.) to about 400 ° C. Etc. are preferably used.

The step of preparing the composite substrate 1 includes, for example, referring to FIG. 3, in the third method, the sub-step of preparing the support substrate 11 (FIG. 3A), the semiconductor film Sub-step for preparing donor substrate 13D (FIG. 3B), sub-step for bonding support substrate 11 and semiconductor film donor substrate 13D (FIG. 3C), and bonding of semiconductor film donor substrate 13D A sub-process (FIG. 3D) for cutting the semiconductor film donor substrate 13D along a surface located at a predetermined distance from the surface 13n.

The semiconductor film donor substrate 13D shown in FIG. 3B is a substrate that provides the semiconductor film 13 to the support substrate 11 in order to form the composite substrate 1. Referring to FIG. 3B, in the step of preparing the semiconductor film donor substrate 13D, the method of manufacturing the semiconductor film donor substrate 13D is not particularly limited, and the semiconductor film donor substrate 13D is not limited to the III-V group compound semiconductor film donor. In the case of a substrate, HVPE (hydride vapor deposition) method, MOCVD (metal organic chemical vapor deposition) method, MBE (molecular beam growth) method, sublimation method, flux method, high nitrogen pressure solution method, etc. are preferably used. In addition, when the semiconductor film donor substrate 13D is a group IV element semiconductor film donor substrate or a group IV compound semiconductor film donor substrate, it can be suitably performed by an LPE (liquid phase growth) method, an MOCVD method, an MBE method, a sublimation method, or the like. .

In FIG. 3C, in a sub-process for bonding the support substrate 11 and the semiconductor film 13, the bonding film 12a is formed on the main surface 11m of the support substrate 11 (FIG. 3C1), and the semiconductor film donor substrate 13D is formed. After forming the bonding film 12b on the main surface 13n (FIG. 3 (C2)), the bonding film 12b formed on the main surface 12am of the bonding film 12a formed on the support substrate 11 and the semiconductor film donor substrate 13D. The main surface 12bn is bonded to each other, whereby the supporting substrate 11 and the semiconductor film 13 are bonded to each other with the bonding film 12 formed by bonding the bonding film 12a and the bonding film 12b interposed therebetween (FIG. 3C3). )). However, as long as the support substrate 11 and the semiconductor film 13 can be bonded to each other, the support substrate 11 and the semiconductor film 13 can be directly bonded together without the bonding film 12 interposed. Here, as described in FIG. 2C above, a direct bonding method, a surface activation method, or the like is preferably used as a specific method for bonding the supporting substrate 11 and the semiconductor film 13 together. Thus, a bonded substrate 1L in which the support substrate 11 and the semiconductor film donor substrate 13D are bonded together is obtained.

Referring to FIG. 3D, in the sub-process for cutting the semiconductor film donor substrate 13D, the semiconductor is a surface located at a predetermined distance from the bonding main surface 13n of the semiconductor film donor substrate 13D of the bonding substrate 1L. The composite substrate 1 is formed by cutting the film donor substrate 13D.

The method for cutting the semiconductor film donor substrate 13D is not particularly limited, and examples thereof include a wire saw, blade saw, laser processing, electric discharge processing, and water jet. When the semiconductor film donor substrate 13D is cut with a wire saw, it is preferable to use a fixed abrasive wire in order to cut the large-diameter semiconductor film donor substrate 13D flatly, in order to reduce the cutting allowance. It is preferable to use a fine wire. In order to reduce the cutting allowance, the loose abrasive method is preferred. Also, when cutting the semiconductor film donor substrate 13D with a wire saw, the wire tension is increased and the wire speed is increased in order to reduce the bending of the wire due to the cutting resistance and increase the accuracy and flatness of the thickness. It is preferable to make it. For this purpose, a highly rigid wire saw device is preferable.

Also, in order to reduce the cutting resistance and increase the accuracy and flatness of the thickness, it is preferable to vibrate the wire and vibrate the semiconductor film donor substrate 13D in synchronization therewith. Specifically, when the wire saw is positioned at an angle perpendicular to or close to the cutting progress direction of the semiconductor film donor substrate 13D, the semiconductor film donor substrate 13D moves in the cutting progress direction, and the semiconductor film donor substrate When the wire saw is positioned at an angle far from perpendicular to the cutting progress direction of 13D, the semiconductor film donor substrate 13D moves in the direction opposite to the cutting progress direction, thereby reducing the cutting resistance.

When the semiconductor film donor substrate 13D is a group III nitride film donor substrate such as a GaN film donor substrate, it is more brittle and easier to break than a sapphire substrate and an SiC substrate. The method cannot be cut well. In cutting the group III nitride film donor substrate, it is necessary to further reduce the cutting resistance. In order to reduce cutting resistance and increase thickness accuracy and flatness, viscosity η (unit: Pa · s) of machining fluid for slicing, flow rate Q (unit: m ³ / s) of machining fluid, wire wire Using speed V (unit: m / s), maximum cutting length L (unit: m), cutting speed P (unit: m / s), and simultaneous cutting number n, R = (η × Q × V) It is preferable that the resistance coefficient R (unit: N) represented by / (L × P × n) is in an appropriate range, specifically 4000 or more and 5000 or less.

The composite substrate 1 obtained by cutting can obtain a desired thickness and uniformity by polishing the main surface of the semiconductor film 13 and the support substrate 11. Specifically, the composite substrate 1 can be affixed to the polishing apparatus during polishing by suction fixation or back pad fixation. Alternatively, the composite substrate 1 can be attached to the holding plate and then attached to the polishing apparatus. By mechanical pressurization such as vacuum chuck, air bag pressurization, weight, etc., the tilt can be suppressed and the warp can be corrected and pasted. The composite substrate 1 can also be adsorbed and fixed. By uniformly bonding the composite substrate 1 to the polishing apparatus, the thickness distribution after polishing can be reduced.

As described above, in the step of preparing the composite substrate, the thickness distribution of the semiconductor film 13 of the composite substrate 1 is reduced, the damaged layer due to the cutting of the semiconductor film 13 is removed, and the crystal quality is maintained high. From the viewpoint of smoothing, it is preferable to polish the main surface of the semiconductor film 13 of the composite substrate 1 obtained by cutting.

For this reason, in the step of preparing the composite substrate, a predetermined value on a surface located at a predetermined distance from the main bonding surface of the semiconductor film donor substrate 13D, which is a surface for cutting the semiconductor film donor substrate 13D of the bonding substrate 1L. The distance is preferably a distance obtained by adding the thickness of the polishing margin to the thickness of the semiconductor film 13 of the composite substrate 1 to be manufactured. Here, the polishing allowance is not particularly limited, but is preferably 10 μm or more, more preferably 20 μm or more, and even more preferably 30 μm or more from the viewpoint of reducing the thickness distribution and off-angle distribution and removing the damaged layer. The polishing allowance is preferably 100 μm or less, more preferably 80 μm or less, and further preferably 60 μm or less from the viewpoint of reducing material loss of the semiconductor film donor substrate 13D.

Referring to FIGS. 3D and 3B, the remaining semiconductor film donor substrate 13Dr can be repeatedly used by polishing its main surface.

In the composite substrate 1 thus obtained, the materials of the support substrate 11, the semiconductor film 13, and the bonding film 12 are as described above, and thus are not repeated here.

(Process for forming a composite substrate with a semiconductor layer)
Referring to FIG. 4B, the step of obtaining composite substrate 2 with a semiconductor layer is performed by growing at least one semiconductor layer 20 on semiconductor film 13 of composite substrate 1. The method for growing at least one semiconductor layer 20 is not particularly limited. When the semiconductor layer 20 is a III-V compound semiconductor layer, the HVPE (hydride vapor phase epitaxy) method, MOCVD (metal organic chemical vapor deposition) is used. And MBE (molecular beam growth) method, sublimation method, flux method, high nitrogen pressure solution method, PLE (phase control growth) method, etc., and when the semiconductor layer 20 is a group IV element semiconductor layer It can be suitably performed by CVD (chemical vapor deposition), MBE, solution growth, etc. When the semiconductor layer 20 is a group IV compound semiconductor layer, CVD, MBE, sublimation, LPE (liquid phase growth) ) Method or the like.

At least one semiconductor layer 20 grown on the semiconductor film 13 of the composite substrate 1 is similar in chemical composition to the semiconductor layer 20 compared to the semiconductor film 13 from the viewpoint of growing the semiconductor layer 20 with good quality. Are preferable, and the same is more preferable. Here, the approximate chemical compositions are not the same, but all are III-V group compounds, IV group elements, or IV group compounds. The same chemical composition means that the constituent elements are the same.

From the viewpoint of improving the crystallinity of the semiconductor layer 20 to be grown, the step of growing at least the semiconductor layer 20 on the main surface 13m of the semiconductor film 13 of the composite substrate 1 includes a semiconductor buffer on the main surface 13m of the semiconductor film 13. It is preferable to include a sub-process for growing the layer 21 and a sub-process for growing the semiconductor crystal layer 23 on the main surface 21 m of the semiconductor buffer layer 21. Here, the semiconductor buffer layer 21 refers to a layer of low crystallinity or non-crystalline (amorphous) grown at a lower temperature than the semiconductor crystal layer 23.

In this way, the composite substrate with semiconductor layer 2 in which at least one semiconductor layer 20 is disposed on the semiconductor film 13 of the composite substrate 1 is obtained.

(Process for obtaining a semiconductor wafer)
Referring to FIG. 4C, the step of obtaining semiconductor wafer 3 including semiconductor layer 20 is performed by removing support substrate 11 from composite substrate 2 with a semiconductor layer. The method for removing the support substrate 11 is not particularly limited, but from the viewpoint of efficiently removing the support substrate 11, a method for removing the support substrate 11 by etching, or removing the support substrate 11 by grinding or polishing. The method is preferred. When the silica phase of the amorphous phase contained in the support substrate 11 is 0.05 mass% or more, a method of removing the support substrate 11 by etching with hydrofluoric acid is preferable. When the amorphous silica phase contained in the support substrate 11 is less than 0.05 mass or no amorphous silica phase is contained, a method of removing the support substrate 11 by grinding or polishing is preferable.

(Example 1)
1. Measurement of thermal expansion coefficient of GaN crystal forming semiconductor film of composite substrate In order to measure the thermal expansion coefficient of GaN crystal forming semiconductor film of composite substrate, the dislocation density grown by the substrate HVPE method is 1 × 10 GaN single crystal with ⁶ cm ^-2 , silicon (Si) concentration of 1 x 10 ¹⁸ cm ^-2 , oxygen (O) concentration of 1 x 10 ¹⁷ cm ^-2 and carbon (C) concentration of 1 x 10 ¹⁶ cm ^-2 To 2 × 2 × 20 mm in size (the longitudinal direction is a-axis, the plane parallel to the longitudinal direction is either c-plane or m-plane, and the accuracy of the plane orientation is within ± 0.1 °) A sample was cut out.

About said sample for evaluation, the average thermal expansion coefficient when it heated up from room temperature (25 degreeC) to 800 degreeC was measured by TMA (thermomechanical analysis). Specifically, the thermal expansion coefficient of the evaluation sample was measured in a nitrogen gas flow atmosphere by a differential expansion method using TMA8310 manufactured by Rigaku Corporation. The average thermal expansion coefficient α _{F (GaN)} in the a-axis direction from 25 ° C. to 800 ° C. of the GaN crystal forming the semiconductor film of the composite substrate obtained by such measurement was 5.84 × 10 ⁻⁶ / ° C. It was.

2. Preparation Step of Composite Substrate (1) Sub-Step of Preparing Support Substrate With reference to FIG. 2 (A), alumina (Al ₂ O ₃ ) powder and silica (SiO ₂ ) powder are used as materials for the support substrate 11. Thirteen types of sintered bodies 1A to 1M were prepared by sintering 13 types of raw materials 1A to 1M mixed at the following mass ratios in an air atmosphere at 1700 ° C. for 20 hours. Here, the mass ratio Al ₂ O ₃ : SiO ₂ between the Al ₂ O ₃ powder and the SiO ₂ powder is 65:35 for the raw material 1A, 70:30 for the raw material 1B, 73:27 for the raw material 1C, and 77 for the raw material 1D. : 23, Raw material 1E is 79:21, Raw material 1F is 81:19, Raw material 1G is 83:17, Raw material 1H is 85:15, Raw material 1I is 87:13, Raw material 1J is 89:11, Raw material 1K is 92: 8. Raw material 1L was 95: 5, and raw material 1M was 98: 2.

The prepared 13 types of sintered bodies 1A to 1M were confirmed by X-ray diffraction. As a result, mullite (Al ₆ Si ₂ O ₁₃ ) phase and alumina (Al ₂ O ₃ ) phase existed as crystal phases. It was. The silica (SiO ₂ ) phase, which is an amorphous phase, is not detected by X-ray diffraction, but the sintered body is processed into a size of 20 mm × 10 mm × thickness 0.15 mm, and a 45 mass% hydrofluoric acid aqueous solution The solution obtained by dissolving in 200 ml for 20 hours was evaluated by ICP-OES (inductively coupled plasma-luminescence) analysis, and the silica content in the sintered body was calculated from the detected amount of Si. This result and the result of X-ray diffraction were combined to determine the composition ratio of the support substrate 11.

Further, measurement samples having a size of 2 × 2 × 20 mm (longitudinal direction is a direction substantially parallel to the main surface of the support substrate cut out from the sintered body) from each of the 13 types of sintered bodies 1A to 1M are prepared. Cut out. Here, since the sintered bodies 1A to 1M have no direction specificity, the cutting direction is arbitrary. For these measurement samples, the average thermal expansion coefficient α _S when the temperature was raised from room temperature (25 ° C.) to 800 ° C. was measured in the same manner as described above.

In the sintered body 1A, the mass ratio Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of the mullite phase, which is a crystalline phase, and the silica phase, which is an amorphous phase, is 89: 1: 10, The average thermal expansion coefficient α _S (hereinafter simply referred to as average thermal expansion coefficient α _S ) from 25 ° C. to 800 ° C. is 4.0 × 10 ⁻⁶ / ° C., and the average thermal expansion coefficient α in the a-axis direction of the GaN crystal is The ratio of the thermal expansion coefficient α _S of the sintered body to _{F (GaN)} (hereinafter referred to as α _S / α _{F (GaN)} ratio) was 0.683. The sintered body 1B has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 96: 1: 3, an average thermal expansion coefficient α _S of 4.5 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.768. The sintered body 1C has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 95: 4: 1 and an average thermal expansion coefficient α _S of 4.8 × 10 ⁻⁶ / ° C. The α _S / α _{F (GaN)} ratio was 0.819. The sintered body 1D has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 80: 19: 1, an average thermal expansion coefficient α _S of 5.1 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.870. The sintered body 1E has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 73.9: 26: 0.1 and an average thermal expansion coefficient α _S of 5.4 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.922. The sintered body 1F has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 67.92: 32: 0.08 and an average thermal expansion coefficient α _S of 5.6 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.956. The sintered body 1G has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 60.94: 39: 0.06 and an average thermal expansion coefficient α _S of 5.8 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.990. The sintered body 1H has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 52.94: 47: 0.06 and an average thermal expansion coefficient α _S of 6.0 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.024. The sintered body 1I has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 45: 54.95: 0.05 and an average thermal expansion coefficient α _S of 6.2 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.058. The sintered body 1J has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 38: 61.95: 0.05, and an average thermal expansion coefficient α _S of 6.5 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.109. The sintered body 1K has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 28: 71.96: 0.04 and an average thermal expansion coefficient α _S of 6.9 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.177. The sintered body 1L has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 17: 82.97: 0.03 and an average thermal expansion coefficient α _S of 7.3 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.246. The sintered body 1M has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 7: 92.99: 0.01 and an average thermal expansion coefficient α _S of 7.9 × 10 ⁻⁶ / The α _S / α _{F (GaN)} ratio was 1.348.

From the 13 kinds of sintered bodies 1A to 1M, support substrates each having a diameter of 4 inches (101.6 mm) and a thickness of 0.40 mm were cut out, and both main surfaces of each support substrate were polished into mirror surfaces. Various types of support substrates 1A to 1M were prepared. The flatness of the main surfaces of the support substrates 1A to 1M after polishing was evaluated by the value of the arithmetic average roughness Ra defined in JIS B0601 measured in the range of 20 μm × 20 μm using an AFM (Electron Force Microscope). . The evaluation of the flatness of the main surface is such that the arithmetic average roughness Ra is 10 nm or less, the arithmetic average roughness Ra is greater than 10 nm and less than 20 nm, and the arithmetic average roughness Ra is greater than 20 nm. Low. The flatness of the main surface was low for the support substrate 1A, medium for the support substrates 1B to 1D, and high for the support substrates 1E to 1M.

(2) Sub-Process for Forming Semiconductor Film on Base Substrate With reference to FIG. 2B, the base substrate 30 has a diameter of 5 inches (127 mm) having a (111) principal surface 30n polished to a mirror surface. ) To prepare a Si substrate having a thickness of 0.5 mm.

A GaN film having a thickness of 0.4 μm was formed as the semiconductor film 13 on the main surface 30n of the base substrate 30 by the MOCVD method. The film formation conditions were as follows: TMG gas and NH ₃ gas were used as the source gas, H ₂ gas was used as the carrier gas, the film formation temperature was 1000 ° C., and the film formation pressure was 1 atm. The main surface 13m of the semiconductor film 13 obtained in this way had a plane orientation with an off angle of ± 1 ° from the (0001) plane.

(3) Sub-Process for Bonding Supporting Substrate and Semiconductor Film Referring to (C1) in FIG. 2 (C), each main surface of supporting substrate 1A-1M which is supporting substrate 11 in FIG. 2 (A) A SiO ₂ film having a thickness of 2 μm was formed on 11 m by a CVD (chemical vapor deposition) method. Next, the SiO ₂ film having a thickness of 2 μm on each main surface 11 m of each of the support substrates 1A to 1M is polished using CeO ₂ slurry, so that only the SiO ₂ film having a thickness of 0.2 μm is left. The bonding film 12a was obtained. As a result, the voids of the main surfaces 11m of the support substrates 1A to 1M were filled, and a 0.2 μm thick SiO ₂ film having a flat main surface 12am as the bonding film 12a was obtained.

Further, referring to (C2) in FIG. 2 (C), a thickness is formed on the main surface 13n of the GaN film which is the semiconductor film 13 formed on the Si substrate which is the base substrate 30 in FIG. 2 (B). A 2 μm thick SiO ₂ film was formed by CVD. Next, the SiO ₂ film having a thickness of 2 μm was polished using a CeO ₂ slurry, so that only the SiO ₂ film having a thickness of 0.2 μm was left to form the bonding film 12b.

2C, the main surface 12am of the bonding film 12a formed on each of the support substrates 1A to 1M as the support substrate 11 and the Si substrate as the base substrate 30 are referred to. The main surface 12bn of the bonding film 12b formed on the formed semiconductor film 13 is cleaned and activated by argon plasma, and then the main surface 12am of the bonding film 12a and the main surface 12bn of the bonding film 12b are pasted. In addition, heat treatment was performed at 300 ° C. for 2 hours in a nitrogen atmosphere.

(4) Sub-process for removing base substrate Referring to FIG. 2 (D), the main surface and side surfaces of the back side (side where semiconductor film 13 is not bonded) of support substrates 1A to 1M as support substrate 11 Then, the Si substrate as the base substrate 30 was removed by etching using a mixed acid aqueous solution containing 10% by mass of hydrofluoric acid and 5% by mass of nitric acid. Thus, the composite substrates 1A to 1M, which are the composite substrates 1 in which the GaN films as the semiconductor films 13 are arranged on the main surfaces 11m side of the support substrates 1A to 1M as the support substrates 11 as shown in FIG. was gotten.

3. Step of Forming Semiconductor Layer Referring to FIG. 4B, the main surface 13m of the GaN film that is the semiconductor film 13 of the composite substrate 1A to 1M that is the composite substrate 1 (the main surface is the (0001) surface). A GaN layer was grown as a semiconductor layer 20 by MOCVD on the top and the main surface of a sapphire substrate having a diameter of 4 inches (101.6 mm) and a thickness of 1 mm (the main surface is the (0001) plane). . In the growth of the semiconductor layer 20, TMG (trimethylgallium) gas and NH ₃ gas are used as source gases, and H ₂ gas is used as a carrier gas. A GaN buffer layer having a thickness of 0.1 μm was grown, and then a GaN crystal layer having a thickness of 5 μm was grown as the semiconductor crystal layer 23 at 1050 ° C. Here, the growth rate of the GaN crystal layer was 1 μm / hr. Thereafter, the composite substrate with semiconductor layer 1A to 1M in which the GaN layer as the semiconductor layer 30 was formed on each of the composite substrates 1A to 1M was cooled to room temperature (25 ° C.) at a rate of 10 ° C./min.

The warpage shape and the warpage amount of the composite substrate with semiconductor layer 1A to 1M taken out from the film forming apparatus after cooling to room temperature are observed using the Corning Tropel FM200EWafer on the main surface of the semiconductor layer 20 on the GaN layer side. Measured by optical interference fringes.

The semiconductor substrate 1A with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the warpage amount was 700 μm. In the composite substrate with a semiconductor layer 1B, the semiconductor layer side warped in a concave shape, and the amount of warpage was 650 μm. In the composite substrate with a semiconductor layer 1C, the semiconductor layer side warped in a concave shape, and the amount of warpage was 630 μm. The composite substrate 1D with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the amount of warpage was 450 μm. In the composite substrate 1E with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 350 μm. The composite substrate 1F with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the amount of warpage was 230 μm. In the composite substrate with a semiconductor layer 1G, the semiconductor layer side warped in a concave shape, and the amount of warpage was 150 μm. The composite substrate with a semiconductor layer 1H warped in a concave shape on the semiconductor layer side, and the amount of warpage was 10 μm. In the composite substrate with a semiconductor layer 1I, the semiconductor layer side warped in a convex shape, and the amount of warpage was 13 μm. In the composite substrate with a semiconductor layer 1J, the semiconductor layer side warped convexly, and the amount of warpage was 100 μm. In the composite substrate with a semiconductor layer 1K, the semiconductor layer side warped in a convex shape, and the amount of warpage was 220 μm. In the composite substrate with a semiconductor layer 1L, the semiconductor layer side warped in a convex shape, and the amount of warpage was 750 μm. In the composite substrate 1M with a semiconductor layer, the semiconductor layer side warped in a convex shape and the support substrate was cracked, so that it was difficult to measure the amount of warpage. These results are summarized in Table 1. In Table 1, “-” indicates that the physical property value is not measured.

4). Step of removing support substrate Referring to FIG. 4C, the composite substrate with semiconductor layer 1A to 1M obtained above is immersed in a 45% by mass hydrofluoric acid aqueous solution to form support substrate 11. The semiconductor wafers 1A to 1M which are the semiconductor layers 20 grown on the main surface 13m of the GaN film which is the semiconductor film 13 are removed by dissolving the support substrates 1A to 1M and the SiO ₂ film which is the bonding film 12. Obtained. As shown in Table 1, the removal time of the base substrate was less than 500 hours for the composite substrates with semiconductor layers 1A to 1L and 500 hours or more for the composite substrate with semiconductor layers 1M.

It should be noted that warpage in the semiconductor wafers 1A to 1M is recognized by measurement by optical interference fringes observed using FM 200E Wafer manufactured by Corning Tropel, and the magnitude relationship of the warpage of the semiconductor wafers 1A to 1M is related to the composite substrate with semiconductor layer 1A. The magnitude relationship of warpage at ˜1M was maintained.

(Example 2)
1. Measurement of thermal expansion coefficient of GaN crystal forming semiconductor film of composite substrate When the thermal expansion coefficient of GaN crystal forming semiconductor film of composite substrate was measured in the same manner as in Example 1, the semiconductor film of composite substrate was formed. The average coefficient of thermal expansion α _{F (GaN)} from 25 ° C. to 800 ° C. in the a-axis direction of the GaN crystal was 5.84 × 10 ⁻⁶ / ° C.

2. Preparation Step of Composite Substrate (1) Sub-Step of Preparing Support Substrate Referring to FIG. 2 (A), as materials for the support substrate 11, mullite (Al ₆ Si ₂ O ₁₃ ) powder and alumina (Al ₂ O ₃ ) By sintering 10 kinds of raw materials 2A to 2J obtained by mixing powder and silica (SiO ₂ ) powder in the following mass ratio at 1700 ° C. for 2 hours under a pressure of 50 MPa in a uniaxial direction under an argon gas atmosphere. Ten types of sintered bodies 2A to 2J were prepared. Here, the mass ratio between the Al ₆ Si ₂ O ₁₃ powder, the Al ₂ O ₃ powder, and the SiO ₂ powder is Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ , and the raw material 2A is 50:22:28. 2B is 50:30:20, Raw material 2C is 50:32:18, Raw material 2D is 50:35:15, Raw material 2E is 50:39:11, Raw material 2F is 50: 42: 8, and Raw material 2G is 50:44. : 6, raw material 2H was 50: 46: 4, raw material 2I was 50: 48: 2, and raw material 2J was 50: 50: 0.

The 10 types of sintered bodies 2A to 2J prepared were confirmed by X-ray diffraction. As a result, mullite (Al ₆ Si ₂ O ₁₃ ) phase and alumina (Al ₂ O ₃ ) phase existed as crystal phases. It was. The silica (SiO ₂ ) phase, which is an amorphous phase, is not detected by X-ray diffraction, but the sintered body is processed into a size of 20 mm × 10 mm × thickness 0.15 mm, and a 45 mass% hydrofluoric acid aqueous solution The solution obtained by dissolving in 200 ml for 20 hours was evaluated by ICP-OES (inductively coupled plasma-luminescence) analysis, and the silica content in the sintered body was calculated from the detected amount of Si. This result and the result of X-ray diffraction were combined to determine the composition ratio of the support substrate 11.

Further, a measurement sample having a size of 2 × 2 × 20 mm (longitudinal direction is a direction substantially parallel to the main surface of the support substrate cut out from the sintered body) from each of the above-described 10 types of sintered bodies 2A to 2J. Cut out. Here, since the sintered bodies 2A to 2J have no direction specificity, the cutting direction is arbitrary. For these measurement samples, the average thermal expansion coefficient α _S when the temperature was raised from room temperature (25 ° C.) to 800 ° C. was measured in the same manner as described above.

In the sintered body 2A, the mass ratio of the mullite phase, which is a crystalline phase, and the alumina phase and the amorphous silica phase, Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ is 80: 1: 19, 25 ° C. To 800 ° C., the average thermal expansion coefficient α _S (hereinafter simply referred to as the average thermal expansion coefficient α _S ) is 3.5 × 10 ⁻⁶ / ° C., and the average thermal expansion coefficient α _{F (} The ratio of the thermal expansion coefficient α _S of the sintered body to _GaN) (hereinafter referred to as α _S / α _{F (GaN)} ratio) was 0.597. The sintered body 2B has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 90: 1: 9, an average thermal expansion coefficient α _S of 3.9 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.666. The sintered body 2C has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 93: 1: 6, an average thermal expansion coefficient α _S of 4.3 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.734. The sintered body 2D has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 97: 1: 2, an average thermal expansion coefficient α _S of 4.8 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.819. The sintered body 2E has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 88.5: 11: 0.5 and an average coefficient of thermal expansion α _S of 5.0 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.853. The sintered body 2F has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 78.9: 21: 0.1 and an average thermal expansion coefficient α _S of 5.2 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.887. The sintered body 2G has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 71.92: 28: 0.08 and an average thermal expansion coefficient α _S of 5.6 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.956. The sintered body 2H has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 64.94: 35: 0.06 and an average thermal expansion coefficient α _S of 5.8 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.990. The sintered body 2I has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 55.96: 44: 0.04 and an average thermal expansion coefficient α _S of 6.1 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 1.041. The sintered body 2J has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 50: 50: 0, an average thermal expansion coefficient α _S of 6.2 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 1.058.

A support substrate having a diameter of 4 inches (101.6 mm) and a thickness of 0.40 mm was cut out from each of the 10 types of sintered bodies 2A to 2J, and both main surfaces of each support substrate were polished into mirror surfaces. Various types of support substrates 2A to 2J were prepared. The flatness of the main surfaces of the support substrates 2A to 2J after polishing was evaluated in the same manner as in Example 1. The flatness of the main surface was low for the support substrate 2A, medium for the support substrates 2B to 2D, and high for the support substrates 2E to 2J.

(2) Sub-Process for Forming Semiconductor Film on Base Substrate Referring to FIG. 2 (B), as the base substrate 30, the main surface of the (111) surface polished to a mirror surface in the same manner as in Example 1 A Si substrate having a diameter of 5 inches (127 mm) and a thickness of 0.5 mm having 30n was prepared.

A GaN film having a thickness of 0.4 μm was formed as the semiconductor film 13 on the main surface 30n of the base substrate 30 by the MOCVD method in the same manner as in Example 1. The main surface 13m of the obtained semiconductor film 13 had a plane orientation whose off angle from the (0001) plane was within ± 1 °.

(3) Sub-step of bonding support substrate and semiconductor film Referring to FIG. 2C, the support substrate 11 and the semiconductor film 13 are bonded together with the bonding film 12 interposed in the same manner as in the first embodiment. It was.

(4) Sub-Process for Removing the Base Substrate With reference to FIG. 2D, the Si substrate as the base substrate 30 was removed in the same manner as in Example 1. Thus, the composite substrates 2A to 2J, which are the composite substrate 1, in which the GaN film that is the semiconductor film 13 is arranged on the main surface 11m side of each of the support substrates 2A to 2J that are the support substrates 11 as shown in FIG. was gotten.

3. Step of Forming Semiconductor Layer Referring to FIG. 4B, the main surface 13m of the GaN film that is the semiconductor film 13 of the composite substrate 2A to 2J that is the composite substrate 1 (refer to FIG. 4B). A GaN layer was grown as the semiconductor layer 20 by the MOCVD method. Thus, composite substrates with semiconductor layers 2A to 2J in which the GaN layer as the semiconductor layer 20 was formed on each of the composite substrates 2A to 2J were obtained.

The warpage shape and the amount of warpage of the composite substrates with semiconductor layers 2A to 2J taken out from the film forming apparatus after cooling to room temperature were measured in the same manner as in Example 1.

In the composite substrate with semiconductor layer 2A, the semiconductor layer side warped in a concave shape and the support substrate was cracked, so that it was difficult to measure the amount of warpage. In the composite substrate 2B with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 690 μm. In the composite substrate with a semiconductor layer 2C, the semiconductor layer side warped in a concave shape, and the amount of warpage was 670 μm. The composite substrate 2D with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the amount of warpage was 620 μm. The composite substrate 2E with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the amount of warpage was 500 μm. The composite substrate 2F with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the amount of warpage was 400 μm. The semiconductor substrate with a semiconductor layer 2G warped in a concave shape on the semiconductor layer side, and the amount of warpage was 230 μm. In the composite substrate 2H with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 150 μm. In the composite substrate with semiconductor layer 2I, the semiconductor layer side warped convexly, and the amount of warpage was 12 μm. In the composite substrate 2J with a semiconductor layer, the semiconductor layer side warped convexly, and the amount of warpage was 13 μm. These results are summarized in Table 2.

4). Step of removing support substrate With reference to FIG. 4C, the composite substrate 2A to 2J with a semiconductor layer obtained above is immersed in a 45% by mass hydrofluoric acid aqueous solution to form the support substrate 11. The support wafers 2A to 2J and the SiO ₂ film as the bonding film 12 are removed by grinding and polishing, and the semiconductor wafer 2A as the semiconductor layer 20 grown on the main surface 13m of the GaN film as the semiconductor film 13 is obtained. 2J was obtained.

It should be noted that warpage in the semiconductor wafers 2A to 2J is also recognized by measurement by optical interference fringes observed using FM 200E Wafer manufactured by Corning Tropel, and the magnitude relation of warpage of the semiconductor wafers 1A to 1M is related to the composite substrate with semiconductor layer 1A. The magnitude relationship of warpage at ˜1M was maintained.

(Example 3)
1. Measurement of thermal expansion coefficient of GaN crystal forming semiconductor film of composite substrate When the thermal expansion coefficient of GaN crystal forming semiconductor film of composite substrate was measured in the same manner as in Example 1, the semiconductor film of composite substrate was formed. The average coefficient of thermal expansion α _{F (GaN)} from 25 ° C. to 800 ° C. in the a-axis direction of the GaN crystal was 5.84 × 10 ⁻⁶ / ° C.

2. Preparation Step of Composite Substrate (1) Sub-Step of Preparing Support Substrate With reference to FIG. 3 (A), alumina (Al ₂ O ₃ ) powder and silica (SiO ₂ ) powder are used as materials for the support substrate 11. Thirteen types of sintered bodies 3A to 3M were prepared by sintering 13 types of raw materials 3A to 3M mixed at the following mass ratios in an air atmosphere at 1700 ° C. for 20 hours. Here, the mass ratio Al ₂ O ₃ : SiO ₂ between the Al ₂ O ₃ powder and the SiO ₂ powder is 65:35 for the raw material 3A, 70:30 for the raw material 3B, 73:27 for the raw material 3C, and 77 for the raw material 3D. : 23, Raw material 3E 79:21, Raw material 3F 81:19, Raw material 3G 83:17, Raw material 3H 85:15, Raw material 3I 87:13, Raw material 3J 89:11, Raw material 3K 92: 8. Raw material 3L was 95: 5, and raw material 3M was 98: 2.

The prepared 13 types of sintered bodies 3A to 3M were confirmed by X-ray diffraction. As a result, mullite (Al ₆ Si ₂ O ₁₃ ) phase and alumina (Al ₂ O ₃ ) phase existed as crystal phases. It was. The silica (SiO ₂ ) phase, which is an amorphous phase, is not detected by X-ray diffraction, but the sintered body is processed into a size of 20 mm × 10 mm × thickness 0.15 mm, and a 45 mass% hydrofluoric acid aqueous solution The solution obtained by dissolving in 200 ml for 20 hours was evaluated by ICP-OES (inductively coupled plasma-luminescence) analysis, and the silica content in the sintered body was calculated from the detected amount of Si. This result and the result of X-ray diffraction were combined to determine the composition ratio of the support substrate 11.

In addition, a measurement sample having a size of 2 × 2 × 20 mm (longitudinal direction is a direction substantially parallel to the main surface of the support substrate cut out from the sintered body) from each of the 13 types of sintered bodies 3A to 3M. Cut out. Here, since the sintered bodies 3A to 3M have no direction specificity, the cutting direction is arbitrary. For these measurement samples, the average thermal expansion coefficient α _S when the temperature was raised from room temperature (25 ° C.) to 800 ° C. was measured in the same manner as described above.

The sintered body 3A has a mass ratio Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 89: 1: 10 between the mullite phase, which is a crystalline phase, and the alumina phase and the amorphous silica phase, and 25 ° C. The average thermal expansion coefficient α _S (hereinafter simply referred to as the average thermal expansion coefficient α _S ) from 4.0 to 800 ° C. is 4.0 × 10 ⁻⁶ / ° C., and the average thermal expansion coefficient α _{F (} The ratio of the thermal expansion coefficient α _S of the sintered body to _GaN) (hereinafter referred to as α _S / α _{F (GaN)} ratio) was 0.683. The sintered body 3B has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 96: 1: 3, an average thermal expansion coefficient α _S of 4.5 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.768. The sintered body 3C has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 95: 4: 1, an average thermal expansion coefficient α _S of 4.8 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.819. The sintered body 3D has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 80: 19: 1, an average thermal expansion coefficient α _S of 5.1 × 10 ⁻⁶ / ° C., The α _S / α _{F (GaN)} ratio was 0.870. The sintered body 3E has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 73.9: 26: 0.1 and an average thermal expansion coefficient α _S of 5.4 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.922. The sintered body 3F has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 67.92: 32: 0.08 and an average thermal expansion coefficient α _S of 5.6 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.956. The sintered body 3G has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 60.94: 39: 0.06 and an average thermal expansion coefficient α _S of 5.8 × 10 ⁻⁶ / ° C and the α _S / α _{F (GaN)} ratio was 0.990. The sintered body 3H has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 52.94: 47: 0.06 and an average thermal expansion coefficient α _S of 6.0 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.024. The sintered body 3I has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 45: 54.95: 0.05 and an average thermal expansion coefficient α _S of 6.2 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.058. The sintered body 3J had a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 38: 61.95: 0.05 and an average thermal expansion coefficient α _S of 6.5 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.109. The sintered body 3K has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 28: 71.96: 0.04 and an average thermal expansion coefficient α _S of 6.9 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.177. The sintered body 3L has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 17: 82.97: 0.03 and an average thermal expansion coefficient α _S of 7.3 × 10 ⁻⁶ / And the α _S / α _{F (GaN)} ratio was 1.246. The sintered body 3M has a mass ratio of Al ₆ Si ₂ O ₁₃ : Al ₂ O ₃ : SiO ₂ of 7: 92.99: 0.01 and an average thermal expansion coefficient α _S of 7.9 × 10 ⁻⁶ / The α _S / α _{F (GaN)} ratio was 1.348.

A support substrate having a diameter of 4 inches (101.6 mm) and a thickness of 0.40 mm was cut out from each of the 13 types of sintered bodies 3A to 3M, and both main surfaces of each support substrate were polished into mirror surfaces. Various types of support substrates 3A to 3M were prepared. The flatness of the main surfaces of the support substrates 3A to 3M after polishing was evaluated based on the value of the arithmetic average roughness Ra defined in JIS B0601 measured in the range of 20 μm × 20 μm using an AFM (electron force microscope). . The evaluation of the flatness of the main surface is such that the arithmetic average roughness Ra is 10 nm or less, the arithmetic average roughness Ra is greater than 10 nm and less than 20 nm, and the arithmetic average roughness Ra is greater than 20 nm. Low. The flatness of the main surface was low for the support substrate 3A, medium for the support substrates 3B to 3D, and high for the support substrates 3E to 3M.

(2) Step of Preparing Semiconductor Film Donor Substrate Referring to FIG. 3B, a GaN crystal body having a diameter of 4 inches (101.6 mm) and a thickness of 8 mm is prepared as a semiconductor film donor substrate 13D. The bonded surface of the substrate 13D was mirror-polished to an arithmetic average roughness Ra of 10 nm or less by mechanical polishing and preferably by CMP. Here, the semiconductor film donor substrate 13D was grown by HVPE using a GaAs substrate as a base substrate.

(3) Sub-Process for Bonding Supporting Substrate and Semiconductor Film Donor Substrate Referring to (C1) in FIG. 3C, each of the supporting substrates 3A to 3M, which are the supporting substrate 11 in FIG. A SiO ₂ film having a thickness of 2 μm was formed on the main surface 11 m by a CVD (chemical vapor deposition) method. Next, the SiO ₂ film having a thickness of 2 μm on each main surface 11m of the supporting substrates 3A to 3M is polished with CeO ₂ slurry, so that only the SiO ₂ film having a thickness of 0.2 μm is left. The bonding film 12a was obtained. As a result, the voids of the main surfaces 11m of the support substrates 3A to 3M were filled, and a 0.2 μm thick SiO ₂ film having the flat main surface 12am as the bonding film 12a was obtained.

Further, referring to (C2) in FIG. 3 (C), an SiO ₂ film having a thickness of 2 μm is formed by CVD on the main surface 13n of the GaN crystal body which is the semiconductor film donor substrate 13D in FIG. 3 (B). A film was formed. Next, the SiO ₂ film having a thickness of 2 μm was polished using a CeO ₂ slurry, so that only the SiO ₂ film having a thickness of 0.2 μm was left to form the bonding film 12b.

Next, referring to (C3) in FIG. 3 (C), formed on the main surface 12am of the bonding film 12a and the semiconductor film donor substrate 13D formed on each of the support substrates 3A to 3M as the support substrate 11. After cleaning and activating the main surface 12bn of the bonding film 12b with argon plasma, the main surface 12am of the bonding film 12a and the main surface 12bn of the bonding film 12b are bonded together, and then at 300 ° C. for 2 hours in a nitrogen atmosphere. Heat treated.

Thus, the bonded substrate 1L was obtained in which the semiconductor film donor substrate 13D was bonded to the support substrate 11 with the bonding film 12 interposed.

3. Sub-Process for Cutting Semiconductor Film Donor Substrate Referring to FIG. 3D, the surface of semiconductor substrate donor substrate 13D of bonding substrate 1L located at a depth of 400 μm from the bonding surface with bonding film 12 inside By cutting with a wire saw, a composite substrate 1 was obtained in which a support substrate 11 as shown in FIG. 4A and a GaN film as a semiconductor film 13 were bonded together with a bonding film 12 interposed therebetween. The wire used was a fixed abrasive wire electrodeposited with diamond abrasive grains. In order to reduce the cutting resistance and increase the accuracy and flatness of the thickness, the cutting method is a method in which the wire is swung and the semiconductor film donor substrate 13D is vibrated in synchronization therewith. The resistance coefficient of wire saw cutting was 4200N. After cutting, the semiconductor film 13 of the composite substrate 1 was subjected to mechanical polishing and CMP. In order to make the thickness of the semiconductor film 13 uniform, the composite substrate is attached to the apparatus by CMP by preliminarily correcting the substrate shape by vacuum chuck adsorption and then adsorbing and fixing to the apparatus.

4). Step of Forming Semiconductor Layer Referring to FIG. 4B, the main surface 13m of the GaN film that is the semiconductor film 13 of the composite substrate 3A to 3M that is the composite substrate 1 (refer to FIG. 4B). A GaN layer was grown as the semiconductor layer 20 by the MOCVD method. In this way, composite substrates with semiconductor layers 3A to 3M in which the GaN layers as the semiconductor layers 20 were formed on the composite substrates 3A to 3M were obtained.

The warpage shape and the amount of warpage of the composite substrates with semiconductor layers 2A to 2J taken out from the film forming apparatus after cooling to room temperature were measured in the same manner as in Example 1.

The semiconductor substrate 3A with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the warpage amount was 700 μm. In the composite substrate 3B with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 650 μm. In the composite substrate with a semiconductor layer 3C, the semiconductor layer side warped in a concave shape, and the amount of warpage was 630 μm. In the composite substrate 3D with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 450 μm. In the composite substrate 3E with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 350 μm. The composite substrate 3F with a semiconductor layer warped in a concave shape on the semiconductor layer side, and the amount of warpage was 230 μm. In the composite substrate 3G with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 150 μm. In the composite substrate 3H with a semiconductor layer, the semiconductor layer side warped in a concave shape, and the amount of warpage was 10 μm. In the composite substrate with semiconductor layer 3I, the semiconductor layer side warped in a convex shape, and the amount of warpage was 13 μm. The composite substrate 3J with a semiconductor layer warped in a convex shape on the semiconductor layer side, and the amount of warpage was 100 μm. The composite substrate 3K with a semiconductor layer warped in a convex shape on the semiconductor layer side, and the warpage amount was 220 μm. In the composite substrate with a semiconductor layer 3L, the semiconductor layer side warped in a convex shape, and the amount of warpage was 750 μm. In the composite substrate 3M with a semiconductor layer, the semiconductor layer side warped in a convex shape, and the support substrate was cracked. These results are summarized in Table 3. In Table 3, “-” indicates that the physical property value is not measured.

5. Step of removing support substrate Referring to FIG. 4C, the composite substrate 3A to 3M with a semiconductor layer obtained above is immersed in a 45% by mass hydrofluoric acid aqueous solution to form the support substrate 11. The semiconductor wafers 3A to 3M which are the semiconductor layers 20 grown on the main surface 13m of the GaN film which is the semiconductor film 13 are removed by dissolving the support substrates 3A to 3M and the SiO ₂ film which is the bonding film 12. Obtained. As shown in Table 3, the removal time of the base substrate was less than 500 hours for the composite substrates with semiconductor layers 3A to 3L and 500 hours or more for the composite substrate with semiconductor layers 3M.

It should be noted that the warpage of the semiconductor wafers 3A to 3M is also recognized by the measurement by optical interference fringes observed using the FM 200E Wafer manufactured by Corning Tropel, and the magnitude relation of the warpage of the semiconductor wafers 3A to 3M is as follows. The magnitude relationship of warpage at ~ 3M was maintained.

Referring to Tables 1 to 3, a support substrate containing a mullite phase of 35% by mass to 65% by mass and an alumina phase of 35% by mass to 65% by mass as crystal phases, and disposed on the main surface side of the support substrate The composite substrate including a semiconductor film having a thickness of 10 μm or more has high flatness after polishing of the support substrate, and the ratio α _S of the thermal expansion coefficient α _S of the support substrate to the thermal expansion coefficient α _F of the semiconductor film By using such a composite substrate, / α _F is 0.99 or more and 1.11 or less close to 1, a composite substrate with a semiconductor layer with small warpage and a semiconductor wafer with small warpage were obtained. Further, from the viewpoint of improving the removability by etching of the support substrate while maintaining a high degree of flatness of the main surface of the support substrate after polishing in the composite substrate, the support substrate further includes a silica phase of 10% by mass or less as an amorphous phase. It was preferable to include.

The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 Composite substrate, 1L bonded substrate, 2 Composite substrate with semiconductor film, 3 Semiconductor wafer, 11 Support substrate, 1m, 11m, 12am, 12bn, 13m, 13n, 20m, 21m, 23m, 30n Main surface, 12, 12a, 12b Bonding film, 13 semiconductor film, 13D semiconductor film donor substrate, 20 semiconductor layer, 21 semiconductor buffer layer, 23 semiconductor crystal layer, 30 base substrate.

Claims (4)

1. A support substrate including a mullite phase of 35% by mass to 65% by mass and an alumina phase of 35% by mass to 65% by mass as a crystal phase, and a semiconductor having a thickness of 10 μm or more disposed on the main surface side of the support substrate A composite substrate including a film.
2. The composite substrate according to claim 1, wherein the support substrate further includes a silica phase of 10% by mass or less as an amorphous phase.
3. A support substrate including a mullite phase of 35% by mass to 65% by mass and an alumina phase of 35% by mass to 65% by mass as crystal phases, and a thickness of 10 μm or more disposed on the main surface side of the support substrate A step of preparing a composite substrate including a semiconductor film;
   Growing at least one semiconductor layer on the semiconductor film of the composite substrate to form a composite substrate with a semiconductor layer;
   Removing the support substrate from the composite substrate with a semiconductor layer to form a semiconductor wafer.
4. 4. The method for producing a semiconductor wafer according to claim 3, wherein the support substrate further includes a silica phase of 10% by mass or less as an amorphous phase.

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