Substrate for electronic device and method for manufacturing the same

Abstract

To provide: a substrate for electronic devices, the substrate having a nitride semiconductor formed on a single-crystal silicon, and being suppressed in the occurrence of slipping, cracking and the like, thereby achieving high fracture strength; and a method for producing the substrate.SOLUTION: Provided is a substrate for electronic devices, which is obtained by forming a nitride semiconductor film on a bonded substrate of silicon single crystal, wherein the bonded substrate is obtained by bonding a first silicon single-crystal substrate that has a (111) crystal plane orientation and a second silicon single-crystal substrate that has a main surface having an off angle with respect to a (100) crystal plane orientation by the intermediary of an oxide film, and the nitride semiconductor film is formed on the surface of the first silicon single-crystal substrate of the bonded substrate.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a substrate for an electronic device and a method for manufacturing the same, and more particularly to a substrate for an electronic device in which a nitride semiconductor is formed on a silicon substrate and a method for manufacturing the same.

Background Art

[0002] Nitride semiconductors such as GaN and AlN can be used for manufacturing high electron mobility transistors (HEMTs) and high breakdown voltage electronic devices using two-dimensional electron gases.

[0003] It is difficult to fabricate a nitride semiconductor wafer in which these nitride semiconductors are grown on a substrate. Conventionally, sapphire substrates and SiC substrates have been used as growth substrates. However, due to the increase in the diameter (large aperture) of the substrate or the reduction of the substrate cost, epitaxial growth of a nitride semiconductor by vapor phase growth on a silicon single crystal substrate has also been carried out. The fabrication of an epitaxial growth film of a nitride semiconductor by vapor phase growth on a silicon single crystal substrate is advantageous in that a substrate with a larger diameter can be used compared to a sapphire substrate or an SiC substrate, so the productivity of the device is high and it is easy to process. However, in the vapor phase growth of a nitride semiconductor on a silicon single crystal substrate, due to stress caused by the difference in lattice constant and the difference in thermal expansion coefficient, warping, slip, cracking, etc. are likely to occur, and stress reduction is performed by growth conditions and relaxation layers.

[0004] In particular, to increase the breakdown voltage of an epitaxial substrate for a power device, it is necessary to fabricate GaN on Si (GaN on a single crystal silicon substrate) with a thick GaN epitaxial layer. To increase the thickness of the epitaxial layer, it is sufficient to thicken the single crystal silicon substrate as the growth substrate and perform epitaxial growth. And, as a method of thickening the single crystal silicon substrate, bonding two single crystal silicon substrates together has been performed. Patent Document 1 discloses that the thickness of the bonded substrate should be 2 mm or more. Further, Patent Document 2 discloses that as a combination of two substrates to be bonded, the bond wafer has a plane orientation of {111}, and the base wafer has a plane orientation of {100} and a resistivity of 0.1 Ωcm or less.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] As described above, it is known to use a bonded substrate as a growth substrate as disclosed in Patent Document 1 and Patent Document 2. However, even when these bonded substrates are used, an increase in warpage, slip, cracking, etc. cannot be completely suppressed. Further, slip, cracking, etc. often occurred mainly at the notch portion of the substrate. Generally, a notch is formed in the <110> direction on a {111} single crystal silicon substrate, and is formed in the <110> direction or <100> direction on a {100} single crystal silicon substrate.

[0007] The present invention has been made to solve the above problems, and provides a substrate for an electronic device in which a nitride semiconductor is formed on a silicon single crystal, the substrate for an electronic device having a high fracture strength with suppression of occurrence of slip, crack, etc., and a method for manufacturing the same.

Means for Solving the Problems

[0008] In order to solve the above problems, the present invention provides a substrate for an electronic device in which a nitride semiconductor film is formed on a bonding substrate of a silicon single crystal, wherein the bonding substrate is a substrate in which a first silicon single crystal substrate having a crystal plane orientation of {111} and a second silicon single crystal substrate having an off-angle with respect to a main plane having a crystal plane orientation of {100} are bonded via an oxide film, and the nitride semiconductor film is formed on the surface of the first silicon single crystal substrate of the bonding substrate.

[0009] Regarding the crystal plane orientation, it is not just one without an off-angle like a normal second silicon single crystal substrate, but by providing an off-angle like the second silicon single crystal substrate in the present invention, the cleavage plane becomes non-perpendicular to the main plane (the bonding plane with the first silicon single crystal substrate) (the cleavage plane is inclined). Even with only one second silicon single crystal substrate, since the cleavage plane is inclined, compared with the conventional product in which the cleavage plane of the second silicon single crystal substrate is perpendicular to the bonding plane, an increase in warpage, slip, and crack (hereinafter also referred to as crack, etc.) can be suppressed, and a substrate for an electronic device having a high fracture strength can be obtained.

[0010] In this case, the second silicon single crystal substrate can be nitrogen-doped.

[0011] If it is such a thing, it will become a substrate for an electronic device with higher fracture strength.

[0012] Further, the first silicon single crystal substrate has a notch formed in the <110> direction, The second single-crystalline silicon substrate has a notch formed in the <110> direction, The bonding substrate can be a substrate bonded such that the position of the notch of the first single-crystalline silicon substrate coincides with the position of the notch of the second single-crystalline silicon substrate.

[0013] If it is such a structure, due to the positional relationship between the cleavage planes of the first single-crystalline silicon substrate and the second single-crystalline silicon substrate to be bonded, a substrate for an electronic device with a higher fracture strength in which the occurrence of cracks and the like is further suppressed is obtained.

[0014] Further, the diameter of the bonding substrate can be 300 mm or more.

[0015] Thus, the substrate with high fracture strength of the present invention is particularly effective for substrates for large-diameter electronic devices with a diameter of 300 mm or more.

[0016] The present invention also relates to a method for manufacturing a substrate for an electronic device, in which a nitride semiconductor film is formed on a bonded substrate of single-crystalline silicon, A step of preparing a first single-crystalline silicon substrate with a crystal plane orientation of {111} and a second single-crystalline silicon substrate whose main surface has an off-angle with respect to the crystal plane orientation {100}; A step of thermally oxidizing at least one of the first single-crystalline silicon substrate and the second single-crystalline silicon substrate to form an oxide film on the surface; A step of bonding the first single-crystalline silicon substrate and the second single-crystalline silicon substrate by overlapping them via the oxide film and performing a heat treatment to produce the bonding substrate; A step of epitaxially growing the nitride semiconductor film on the surface of the first single-crystalline silicon substrate of the bonding substrate; A method for manufacturing a substrate for an electronic device, characterized by comprising the above steps.

[0017] In the manufacturing method of the substrate for an electronic device of the present invention as described above, since it includes the second single-crystalline silicon substrate in which the cleavage plane is inclined with respect to the bonding surface, it is possible to manufacture a substrate for an electronic device with high fracture strength in which the occurrence of cracks and the like is suppressed.

[0018] In this case, the second single-crystalline silicon substrate to be prepared can be nitrogen-doped.

[0019] In this way, it is possible to manufacture a substrate for an electronic device with higher fracture strength.

[0020] Further, the first single-crystalline silicon substrate to be prepared is formed with a notch in the <110> direction, the second single-crystalline silicon substrate to be prepared is formed with a notch in the <110> direction, and they can be overlapped and bonded so that the positions of the notches of the first single-crystalline silicon substrate and the positions of the notches of the second single-crystalline silicon substrate coincide.

[0021] In this way, depending on the positional relationship between the cleavage planes of the first single-crystalline silicon substrate and the second single-crystalline silicon substrate to be bonded, it is possible to manufacture a substrate for an electronic device with high fracture strength in which the occurrence of cracks and the like is further suppressed.

[0022] Further, the diameters of the first single-crystalline silicon substrate and the second single-crystalline silicon substrate to be prepared can be 300 mm or more.

[0023] A substrate with high fracture strength such as the substrate for an electronic device manufactured by the manufacturing method of the present invention is particularly effective for manufacturing a large-diameter substrate for an electronic device with a diameter of 300 mm or more.

Advantages of the Invention

[0024] In the case of a substrate for an electronic device and a method for manufacturing the same according to the present invention, since a second single-crystalline silicon substrate having an off-angle with a cleavage plane inclined with respect to the bonding surface is provided, it is possible to provide a substrate for an electronic device with high fracture strength in which the occurrence of cracks and the like is suppressed.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0026] Hereinafter, the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. [Substrate for Electronic Device] As shown in FIG. 1, in the substrate 20 for an electronic device of the present invention, a nitride semiconductor film 21 is formed on a bonded substrate 10 of a silicon single crystal. In the description of the present invention, the bonded substrate 10 of a silicon single crystal is also simply referred to as the "bonded substrate". At this time, the bonded substrate 10 is a substrate in which a first silicon single crystal substrate 11 having a crystal plane orientation of {111} and a second silicon single crystal substrate 12 having an off-angle with respect to the crystal plane orientation {100} of the main surface are bonded via an oxide film 13. As shown in FIG. 1, the nitride semiconductor film 21 is formed on the first silicon single crystal substrate 11.

[0027] In this specification, the line attached above the number in the notation of normal Miller indices is replaced by "-" before the number. That is, for example, the notation [1-10] is

Number

[0028] Also, the notation of Miller indices is as usual. That is, {} represents the general term of equivalent crystal plane orientations, () represents each orientation of the crystal plane orientation. Also, <> represents the general term of equivalent crystal axis directions, and [] represents each direction of the crystal axis direction.

[0029] Here, as described above, in order to increase the breakdown voltage of the epitaxial substrate for a power device, it is necessary to fabricate a substrate for an electronic device in which a nitride semiconductor film is thickly formed on a silicon single crystal substrate (for example, GaN on Si with a thick GaN epitaxial layer). In order to increase the thickness of the epitaxial layer, the silicon single crystal substrate may be thickened and epitaxially grown. As a method of thickening the silicon substrate, two silicon single crystal substrates are bonded together, but the occurrence of cracks and the like could not be completely suppressed even when using the bonded substrate.

[0030] However, in the substrate 20 for electronic devices of the present invention, as described above, a combined substrate (seed crystal) formed by bonding two silicon single crystal substrates 11 and 12, the first and the second, is used (bonded substrate 10). Further, in the second silicon single crystal substrate 12, since the main surface has an off-angle with respect to the crystal plane orientation {100}, the cleavage plane is non-perpendicular to the bonding surface with the first silicon single crystal substrate. In this case, compared with the conventional product using a just one without an off-angle, it is possible to obtain a substrate for electronic devices with high fracture strength in which the occurrence of cracks and the like (increase in warpage, slip, crack) is suppressed.

[0031] FIG. 2 shows an example of the positional relationship between the cleavage plane in the first silicon single crystal substrate 11 and the cleavage plane in the second silicon single crystal substrate 12. Here, the case where these cleavage planes are in positions close to each other in the direction perpendicular to the main surface (that is, when the positions are close in plan view) is taken as an example for explanation, but the present invention is not limited to such a positional relationship. Also, the case where there is an off-angle in the left-right direction on the paper surface in FIG. 2 is taken as an example, but the direction of the off-angle in the present invention is not particularly limited. That is, in plan view, whether the positions of the cleavage planes of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are close or far from each other, and also regardless of the direction of the off-angle of the second silicon single crystal substrate 12 (for example, even in the front-rear direction on the paper surface of FIG. 2), the effect of preventing the above-described cracks and the like can be achieved. On the other hand, if both substrates are just ones without an off-angle, cracks and the like are likely to occur. The magnitude of the off-angle is not particularly limited, but for example, it can be greater than 0° and 12° or less, preferably 2° to 8°, and particularly 4°.

[0032] In the present invention, the formation positions of the notches of each of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are not particularly limited. In the example described below, the first single-crystalline silicon substrate 11 has a notch formed in the <110> direction, and the second single-crystalline silicon substrate 12 also has a notch formed in the <110> direction. Further, the bonded substrate 10 is bonded such that the positions of the notches of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 coincide with each other. In such a case, not only can the effect (improvement in fracture strength) due to the off-angle as described above be obtained, but also the fracture strength can be further improved by the displacement of the cleavage plane positions in the plan view of the first single-crystalline silicon substrate and the second single-crystalline silicon substrate.

[0033] More specifically, regarding the bonding state of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 as described above, with reference to FIG. 3 as a view seen from the main surface (principal surface) side of each substrate, it will be described. Here, as the first single-crystalline silicon substrate 11, an example will be described in which the crystal plane orientation is {111} and the notch is at the <110> position, and as the second single-crystalline silicon substrate 12, an example will be described in which the crystal plane orientation is {100} and the notch is at the <110> position.

[0034] In FIG. 3, the cleavage plane of the first single-crystalline silicon substrate 11 is schematically shown by a dotted line, and the cleavage plane of the second single-crystalline silicon substrate 12 is schematically shown by a broken line. As shown in FIG. 1, when the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are overlapped, it can be seen that the cleavage planes in the vertical direction in the figure are displaced. The cleavage planes in the horizontal direction in the figure overlap. However, in the entire bonded substrate 10, due to the effect of the displacement of the cleavage planes in the vertical direction in the figure, the substrate strength of the bonded substrate 10 is improved. As a result, even if the nitride semiconductor film 21 is formed on the surface of the first single-crystalline silicon substrate 11 of the bonded substrate 10, it is possible to obtain a substrate 20 for an electronic device having a high fracture strength with further suppression of the occurrence of cracks and the like.

[0035] In the substrate 20 for an electronic device of the present invention, since the nitride semiconductor film 21 is formed on the surface of the first silicon single crystal substrate 11 having a crystal plane orientation of {111}, a good nitride semiconductor film 21 is formed.

[0036] Fig. 4 shows an example of another bonding substrate. In Fig. 4, as the first silicon single crystal substrate, an example is described in which the crystal plane orientation is {111} and the notch is at the <110> position, and as the second silicon single crystal substrate, an example is described in which the crystal plane orientation is {100} and the notch is at the <100> position. In this case, although the crystal axis direction in which the notch of the second silicon single crystal substrate is formed is different from that in the case of Fig. 3, the others are the same as in Fig. 3. As can be seen from Fig. 4, when the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are overlapped, the cleavage planes are all in a close positional relationship. Even in the case of Fig. 4 like this, since two silicon single crystal substrates having crystal plane orientations of {111} and {100} respectively are joined, and since the second silicon single crystal substrate 12 has the above-mentioned off-angle, the strength of the bonding substrate and the substrate for an electronic device is increased, but the strength in the case of Fig. 3 is higher than that in Fig. 4.

[0037] In the substrate 20 for an electronic device of the present invention, since the substrate strength is high as described above, the diameter of the bonding substrate 10 (and the substrate 20 for an electronic device) can also be a large diameter of 300 mm or more. Such a large-diameter substrate conventionally may not have sufficient substrate strength and may have cracks or the like, but in the present invention, it can be made into a substrate for an electronic device having high fracture strength in which these are suppressed. The upper limit of the diameter of the bonding substrate 10 (and the substrate 20 for an electronic device) is not particularly limited, but for example, it can be 450 mm or less.

[0038] When the diameter of the bonding substrate 10 (and the substrate 20 for electronic devices) is 300 mm or more, the diameters of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are also 300 mm or more. The respective thicknesses of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are not particularly limited, but those according to the standards can be preferably used. In particular, when the diameter is 300 mm, the thickness can be 775 μm. Such a single-crystalline silicon substrate is used as a normal device substrate, is inexpensive, and can be used without particular problems. As the thickness of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12, for example, those having a thickness of 500 μm to 1500 μm can be used.

[0039] Further, the second single-crystalline silicon substrate 12 can be nitrogen-doped. By doping with nitrogen, the strength of the second single-crystalline silicon substrate 12 becomes higher, and the substrate 20 for electronic devices having a higher fracture strength is obtained. The nitrogen concentration is not particularly limited, and for example, it can be 5×10 13 ~5×10 15 atoms / cm 3 .

[0040] [Method for manufacturing a substrate for electronic devices] Hereinafter, a method for manufacturing the substrate 20 for electronic devices of the present invention as described above will be described with reference to FIG. 5.

[0041] First, as shown in S11 of FIG. 5, the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are prepared (step S11). At this time, as the first single-crystalline silicon substrate 11, a single-crystalline silicon substrate having a crystal plane orientation of {111} and a notch formed in the <110> direction is prepared. Further, as the second single-crystalline silicon substrate 12, a single-crystalline silicon substrate having a main surface with an off-angle with respect to the crystal plane orientation {100} and a notch formed in the <110> direction is prepared. When preparing the second single-crystalline silicon substrate 12 having the off-angle, for example, it can be obtained by manufacturing one ingot with the growth axis direction of <100> and slicing it at a desired off-angle. At this time, the diameters of the first single-crystalline silicon substrate and the second single-crystalline silicon substrate to be prepared can be 300 mm or more. Further, the second single-crystalline silicon substrate can be particularly a nitrogen-doped one. The method of nitrogen doping is not particularly limited, and known methods can be used. For example, in the production of a single-crystalline silicon by the CZ method, a nitrogen-doped silicon ingot can be produced and cut out by using a silicon wafer with a nitride film on the raw material or the like. Of course, the first single-crystalline silicon substrate may also be nitrogen-doped.

[0042] Since the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are bonded together to form a bonded substrate 20 of a single single-crystalline silicon substrate, the first single-crystalline silicon substrate 11 can also be referred to as a bond wafer, and the second single-crystalline silicon substrate 12 can also be referred to as a base wafer.

[0043] The thicknesses of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are not particularly limited, but those according to the standards can be preferably used. Also, the resistivity and impurity concentration of each of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 can be set as appropriate.

[0044] Next, as shown in S12 of FIG. 5, at least one of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 is thermally oxidized to form an oxide film on the surface (step S12). The oxide film formed here will become the oxide film 13 shown in FIG. 1 after the bonding of both single-crystalline silicon substrates. The method for forming this oxide film is not particularly limited. For example, an oxide film with a thickness of about 100 nm can be formed on the surface by performing an oxidation heat treatment. The thickness of the oxide film is not particularly limited, but for example, it can be 10 nm or more and 1000 nm or less. An oxide film may be formed on each of the two single-crystalline silicon substrates, or an oxide film may be formed on either one of the single-crystalline silicon substrates.

[0045] Next, as shown in S13 of FIG. 5, the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are bonded (step S13). At this time, first, it is preferable to overlap the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 so that the positions of the notches of the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 coincide. At that time, both single-crystalline silicon substrates are overlapped via the oxide film formed in step S12. By performing a heat treatment in this state, the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 are bonded to produce a bonded substrate 10 (see FIG. 1).

[0046] The conditions (atmosphere, temperature, time, etc.) of the heat treatment (bonding heat treatment) are not particularly limited as long as the first single-crystalline silicon substrate 11 and the second single-crystalline silicon substrate 12 can be bonded. The temperature of this bonding heat treatment can be, for example, 400°C or more and 1200°C or less in a nitrogen atmosphere, and a bonding heat treatment for 1 to 12 hours can be performed.

[0047] After this bonding heat treatment, it is preferable to clean the surface of the bonded substrate 10 before the epitaxial growth of the nitride semiconductor film described later. In particular, it is preferable to remove the oxide film generated on the surface of the bonded substrate 10 (especially the surface of the first single-crystalline silicon substrate 11) by spin cleaning with hydrofluoric acid or the like.

[0048] In this way, after bonding the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 to fabricate the bonded substrate 10, as shown in S14 of FIG. 5, a nitride semiconductor film 21 (see FIG. 1) is epitaxially grown on the surface of the first silicon single crystal substrate 11 of the bonded substrate 10 (step S14). Regarding the first silicon single crystal substrate 11, it may be polished on both sides before bonding, or even if it is not polished on both sides before bonding, it can be polished on one side on the main surface to be grown before epitaxial growth after bonding. Naturally, the second silicon single crystal substrate 12 may also be polished on both sides. As the nitride semiconductor film 21, an AlN layer, a GaN layer, an AlGaN layer, etc. can be formed. This nitride semiconductor film 21 can be formed by an ordinary method. Also, an intermediate layer (buffer layer) may be formed as appropriate. In this way, the substrate 20 for electronic devices shown in FIG. 1 can be manufactured.

Example

[0049] Hereinafter, examples and comparative examples will be shown to more specifically explain the present invention, but the present invention is not limited to the following examples.

[0050] (Example 1) Following the manufacturing method of the substrate for electronic devices of the present invention shown in FIG. 5, the substrate 20 for electronic devices shown in FIG. 1 was manufactured.

[0051] First, as the first silicon single crystal substrate 11, a silicon single crystal substrate that was polished on both sides, had a diameter of 300 mm, a thickness of 775 μm, a crystal plane orientation of {111}, was p-type, had a resistivity of 1 kΩcm, and had a notch formed in the <110> direction, and as the second silicon single crystal substrate 12, a silicon single crystal substrate that was polished on both sides, had a diameter of 300 mm, a thickness of 775 μm, a crystal plane orientation of {100}, was p-type, had a resistivity of 30 Ωcm, and had a notch formed in the <110> direction were prepared (step S11). These first silicon single crystal substrate 11 and second silicon single crystal substrate 12 each have a cleavage plane as conceptually shown in FIG. 3. Regarding the crystal plane orientation, the first silicon single crystal substrate 11 has no off-angle and is just flat, while the second silicon single crystal substrate 12 has an off-angle (4°). The direction of the off-angle is the direction opposite to the notch (0 o'clock direction in Fig. 3). Also, the first silicon single crystal substrate 11 is not nitrogen-doped, and the second silicon single crystal substrate 12 is nitrogen-doped, with a nitrogen concentration of 5×10 13 atoms / cm 3 .

[0052] Oxidation heat treatment was performed on these two prepared silicon single crystal substrates to form oxide films with a thickness of 100 nm each (step S12).

[0053] Next, the notch positions of the two silicon single crystal substrates were aligned and bonded together, and bonding heat treatment was performed at 500 °C in a nitrogen atmosphere to produce a bonded substrate 10 (step S13). Thereafter, the bonded substrate 10 was spin-cleaned with hydrofluoric acid to remove the oxide film on the surface. Fig. 6 shows the state placed in the wafer BOX after the oxide film removal.

[0054] Next, on the surface of the first silicon single crystal substrate 11 of the bonded substrate 10, as a nitride semiconductor film 21, a 150-nm AlN layer, a 160-nm AlGaN layer, a superlattice structure in which 25 pairs of GaN layers and AlN layers are alternately stacked, a 1000-nm GaN layer, a 20-nm AlGaN layer, and a 3-nm GaN layer were epitaxially grown to a total film thickness of 1.8 μm (step S14).

[0055] As a result, cracking and slipping did not occur, and GaN could be formed. In this way, a substrate 20 for electronic devices was manufactured.

[0056] (Comparative Example 1) As follows, as the second silicon single crystal substrate, except that a flat one without an off-angle was used, which is different from Example 1, a substrate for electronic devices was manufactured in the same manner as in Example 1.

[0057] First, as the first silicon single crystal substrate, a double-sided polished silicon single crystal substrate with a diameter of 300 mm, a thickness of 775 μm, a crystal plane orientation of {111}, p-type, a resistivity of 1 kΩcm, and a notch formed in the <110> direction, and as the second silicon single crystal substrate, a double-sided polished silicon single crystal substrate with a diameter of 300 mm, a thickness of 775 μm, a crystal plane orientation of {100}, p-type, a resistivity of 30 Ωcm, and a notch formed in the <110> direction were prepared. These first silicon single crystal substrate and second silicon single crystal substrate each have a cleavage plane as shown conceptually in FIG. 3. Regarding the crystal plane orientation, both the first silicon single crystal substrate and the second silicon single crystal substrate are just ones without an off-angle. Also, the first silicon single crystal substrate is not nitrogen-doped, and the second silicon single crystal substrate is nitrogen-doped, and the nitrogen concentration is 5×10 13 atoms / cm 3 is.

[0058] Oxidation heat treatment was performed on these two prepared silicon single crystal substrates to form oxide films with a thickness of 100 nm each.

[0059] Next, the notch positions of the two silicon single crystal substrates were aligned and bonded, and bonding heat treatment was performed at 500 °C in a nitrogen atmosphere to produce a bonded substrate. Note that this heat treatment step was performed simultaneously with the bonding heat treatment step in Example 1 as shown in FIG. 6. Thereafter, the bonded substrate 10 was spin-cleaned with hydrofluoric acid to remove the oxide film on the surface. Note that after removing the oxide film, it was placed in a wafer BOX (see FIG. 6).

[0060] Next, a GaN film as a nitride semiconductor film was epitaxially grown on the surface of the first silicon single crystal substrate of the bonded substrate under the same conditions as in Example 1.

[0061] As a result, slip etc. did not occur, but the fracture strength was inferior compared to Example 1 as described later.

[0062] Next, under the same conditions as in each of Example 1 and Comparative Example 1, a bonded substrate before forming a nitride semiconductor film was produced, and the strength of each bonded substrate was measured.

[0063] In the measurement of the strength of this bonded substrate, as shown in FIG. 7, the breaking load and flexural strength were investigated using an Instron precision universal testing machine. FIG. 7(a) is a view seen from the upper side in the vertical direction, and FIG. 7(b) is a view seen from the side.

[0064] As shown in FIGS. 7(a) and 7(b), three fulcrum jigs J (the radius of curvature R of the crimping point is 15 mm) were arranged above and below the bonded substrate. In the bonded substrate, since the notch position is weak in strength, the notch position N was installed so as to be directly below the central fulcrum jig J (see FIGS. 7(a) and 7(b)). The calculation formula for flexural strength is as follows.

[0065] Flexural strength = 3PL / 2WT 2 (Calculation formula) P: Breaking load, L = Distance between fulcrums (150 mm) W: Width 300 mm T: Thickness 1.55 mm

[0066] As a result, the breaking load of the notch portion of the bonded substrate 10 in Example 1 was 784 N, and the flexural strength was 245 Mpa. On the other hand, the breaking load of the notch portion of the bonded substrate in Comparative Example 1 was 732 N and the flexural strength was 228 MPa. From this, it was found that the bonded substrate 10 of Example 1 had a higher fracture strength than Comparative Example 1.

[0067] (Example 2, Comparative Example 2) As the second single-crystalline silicon substrate, an undoped one was used, which was different from Example 1, and a substrate for an electronic device was manufactured in the same manner as in Example 1 (Example 2). As a result, no cracks or slips occurred, and GaN could be formed. Further, as the second single-crystalline silicon substrate, a substrate not doped with nitrogen was used, which was different from Comparative Example 1, and a substrate for an electronic device was manufactured in the same manner as in Comparative Example 1 (Comparative Example 2). As a result, slips or the like did not occur, but the fracture strength was inferior to that of Example 2 as described later.

[0068] Further, under the same conditions as in each of Example 2 and Comparative Example 2, a bonded substrate before forming the nitride semiconductor film was produced, and the strength of each bonded substrate was measured. The measurement method was the same as in Example 1 and Comparative Example 1.

[0069] As a result, the fracture load of the notch portion of the bonded substrate 10 in Example 2 was 713 N, and the flexural strength was 223 Mpa. On the other hand, the fracture load of the notch portion of the bonded substrate in Comparative Example 2 was 663 N and the flexural strength was 207 MPa. From this, it was found that the bonded substrate 10 of Example 2 had a higher fracture strength than Comparative Example 2.

[0070] The above results of the fracture load and flexural strength are summarized in Table 1.

[0071]

Table 1

[0072] As described above, and as can be seen from Table 1, in terms of the fracture load and flexural strength, in the case of having nitrogen doping (Example 1 and Comparative Example 1), Example 1 in which the present invention was implemented showed superior results compared to Comparative Example 1. Also, even in the case of no nitrogen doping (Example 2 and Comparative Example 2), Example 2 in which the present invention was implemented showed superior results compared to Comparative Example 2. Note that Comparative Example 1 has a superior value compared to Example 2, but this is due to the difference in the presence or absence of nitrogen doping. When conditions other than the off-angle, such as the presence or absence of nitrogen doping, are the same, if the second single-crystalline silicon substrate has an off-angle as in the present invention, it is superior in terms of the fracture load and flexural strength compared to the case where there is no off-angle, and it is clear from the above that it is extremely effective in suppressing conventional problems such as an increase in warpage and cracking.

[0073] (Examples 3-6) As the second single-crystalline silicon substrate, different from Example 1, substrates for electronic devices were manufactured in the same manner as in Example 1 except that those with an off-angle of 2° (Example 3) and 8° (Example 4) were used. Also, as the second single-crystalline silicon substrate, different from Example 2, substrates for electronic devices were manufactured in the same manner as in Example 2 except that those with an off-angle of 2° (Example 5) and 8° (Example 6) were used. As a result, none of them cracked or slipped, and GaN could be formed.

[0074] Also, under the same conditions as in each of Examples 3-6, bonding substrates before forming the nitride semiconductor film were prepared, and the strength of each bonding substrate was measured. The measurement method was the same as in Example 1.

[0075] As a result, the breaking load and flexural strength of the notch portion of the bonding substrate 10 in Examples 3-6 were (753 N, 235 MPa), (803 N, 251 MPa), (697 N, 218 MPa), and (731 N, 228 MPa). From this, it was found that the bonding substrates 10 of Examples 3 and 4 had higher fracture strength than Comparative Example 1. Also, it was found that the bonding substrates 10 of Examples 5 and 6 had higher fracture strength than Comparative Example 2.

[0076] The results of the breaking load and flexural strength of Examples 3-6 are summarized in Table 2.

[0077]

Table 2

[0078] As described above, and as can be seen from Tables 1 and 2, in terms of the breaking load and bending strength, in the case of having nitrogen doping (Examples 3 and 4 and Comparative Example 1), Examples 3 and 4 in which the present invention was implemented showed superior results compared to Comparative Example 1. Also, even in the case of having no nitrogen doping (Examples 5 and 6, Comparative Example 2), Examples 5 and 6 in which the present invention was implemented showed superior results compared to Comparative Example 2. Furthermore, as can be seen from the comparison within Examples 1, 3, and 4 and the comparison within Examples 2, 5, and 6, the greater the off-angle, the more excellent the fracture strength. Although Comparative Example 1 has a value superior to or equivalent to Examples 5 and 6, this is due to the difference in the presence or absence of nitrogen doping, similar to the reason when comparing Comparative Example 1 and Example 2. If the conditions other than the off-angle are the same, when the second single-crystalline silicon substrate has an off-angle as in the present invention, it has a higher fracture strength compared to the case where there is no off-angle, and it can be used to suppress the increase in warpage and the occurrence of cracks.

[0079] This specification includes the following aspects. [1]: A substrate for an electronic device in which a nitride semiconductor film is formed on a bonding substrate of a single-crystalline silicon, The bonding substrate is a substrate in which a first single-crystalline silicon substrate having a crystal plane orientation of {111} and a second single-crystalline silicon substrate having a main surface with an off-angle with respect to the crystal plane orientation {100} are bonded via an oxide film, A substrate for an electronic device in which the nitride semiconductor film is formed on the surface of the first single-crystalline silicon substrate of the bonding substrate. [2]: The substrate for an electronic device according to [1] above, wherein the second single-crystalline silicon substrate is nitrogen-doped. [3]: The first single-crystalline silicon substrate has a notch formed in the <110> direction, The second single-crystalline silicon substrate has a notch formed in the <110> direction, The bonding substrate is the substrate for an electronic device according to the above [1] or [2], which is bonded such that the positions of the notches of the first silicon single crystal substrate and the positions of the notches of the second silicon single crystal substrate coincide with each other. [4]: The substrate for an electronic device according to any one of the above [1] to [3], wherein the diameter of the bonding substrate is 300 mm or more. [5]: A method for manufacturing a substrate for an electronic device, which forms a nitride semiconductor film on a bonding substrate of silicon single crystals, a step of preparing a first silicon single crystal substrate having a crystal plane orientation of {111} and a second silicon single crystal substrate whose main surface has an off-angle with respect to the crystal plane orientation {100}; a step of thermally oxidizing at least one of the first silicon single crystal substrate and the second silicon single crystal substrate to form an oxide film on the surface; a step of bonding the first silicon single crystal substrate and the second silicon single crystal substrate by overlapping them via the oxide film and performing heat treatment, thereby producing the bonding substrate; a step of epitaxially growing the nitride semiconductor film on the surface of the first silicon single crystal substrate of the bonding substrate; A method for manufacturing a substrate for an electronic device having the above steps. [6]: The method for manufacturing a substrate for an electronic device according to the above [5], wherein the second silicon single crystal substrate to be prepared is nitrogen-doped. [7]: The first silicon single crystal substrate to be prepared has a notch formed in the <110> direction, the second silicon single crystal substrate to be prepared has a notch formed in the <110> direction, The method for manufacturing a substrate for an electronic device according to the above [5] or [6], wherein the first silicon single crystal substrate and the second silicon single crystal substrate are overlapped and bonded so that the positions of the notches of the first silicon single crystal substrate and the positions of the notches of the second silicon single crystal substrate coincide with each other. [8]: The method for manufacturing a substrate for an electronic device according to any one of the above [5] to [7], wherein the diameters of the first silicon single crystal substrate and the second silicon single crystal substrate to be prepared are 300 mm or more.

[0080] Note that the present invention is not limited to the above-described embodiments. The above-described embodiments are examples, and any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and exhibits the same operational effects is included in the technical scope of the present invention.

Description of Reference Numerals

[0081] 10... Bonding substrate of single-crystal silicon, 11... First single-crystal silicon substrate, 12... Second single-crystal silicon substrate, 13... Oxide film, 20... Substrate for electronic devices, 21... Nitride semiconductor film.

Claims

1. A substrate for an electronic device having a nitride semiconductor film formed on a bonded substrate of single-crystalline silicon, wherein the bonded substrate is a substrate in which a first single-crystalline silicon substrate having a crystal plane orientation of {111} and a second single-crystalline silicon substrate having a main surface with an off-angle with respect to the crystal plane orientation {100} are bonded via an oxide film, and the nitride semiconductor film is formed on the surface of the first single-crystalline silicon substrate of the bonded substrate. A substrate for an electronic device characterized by this.

2. The substrate for an electronic device according to claim 1, wherein the second single-crystalline silicon substrate is nitrogen-doped.

3. The first single-crystalline silicon substrate has a notch formed in the <110> direction, The second single-crystalline silicon substrate has a notch formed in the <110> direction, and the bonded substrate is a substrate bonded such that the position of the notch of the first single-crystalline silicon substrate coincides with the position of the notch of the second single-crystalline silicon substrate. The substrate for an electronic device according to claim 1, characterized by this.

4. The first single-crystalline silicon substrate has a notch formed in the <110> direction, The second single-crystalline silicon substrate has a notch formed in the <110> direction, and the bonded substrate is a substrate bonded such that the position of the notch of the first single-crystalline silicon substrate coincides with the position of the notch of the second single-crystalline silicon substrate. The substrate for an electronic device according to claim 2, characterized by this.

5. The substrate for an electronic device according to any one of claims 1 to 4, wherein the diameter of the bonded substrate is 300 mm or more.

6. A method for manufacturing a substrate for an electronic device for forming a nitride semiconductor film on a bonded substrate of single-crystalline silicon, A step of preparing a first silicon single crystal substrate having a crystal plane orientation of {111} and a second silicon single crystal substrate having an off-angle with respect to a crystal plane orientation of {100} on a main surface, A step of thermally oxidizing at least one of the first silicon single crystal substrate and the second silicon single crystal substrate to form an oxide film on the surface, A step of bonding the first silicon single crystal substrate and the second silicon single crystal substrate by overlapping them via the oxide film and performing heat treatment to produce the bonded substrate, A step of epitaxially growing the nitride semiconductor film on the surface of the first silicon single crystal substrate of the bonded substrate, A method for manufacturing a substrate for an electronic device, characterized by comprising:

7. The method for manufacturing a substrate for an electronic device according to claim 6, wherein the second silicon single crystal substrate to be prepared is nitrogen-doped.

8. The first silicon single crystal substrate to be prepared has a notch formed in the <110> direction, The second silicon single crystal substrate to be prepared has a notch formed in the <110> direction, The method for manufacturing a substrate for an electronic device according to claim 6, wherein the first silicon single crystal substrate and the second silicon single crystal substrate are overlapped and bonded so that the positions of the notches of the first silicon single crystal substrate and the second silicon single crystal substrate coincide with each other.

9. The first silicon single crystal substrate to be prepared has a notch formed in the <110> direction, The second silicon single crystal substrate to be prepared has a notch formed in the <110> direction, The method for manufacturing a substrate for an electronic device according to claim 7, wherein the first silicon single crystal substrate and the second silicon single crystal substrate are overlapped and bonded so that the positions of the notches of the first silicon single crystal substrate and the second silicon single crystal substrate coincide with each other.

10. The method for manufacturing a substrate for an electronic device according to any one of claims 6 to 9, characterized in that the diameters of the first silicon single crystal substrate and the second silicon single crystal substrate to be prepared are 300 mm or more.

Images