JP7563434B2 - Substrate for electronic device and method for producing same - Google Patents

Description

The present invention relates to a substrate for an electronic device and a manufacturing method thereof, and in particular to a substrate for an electronic device in which a nitride semiconductor is formed on a silicon substrate and a manufacturing method thereof.

Nitride semiconductors such as GaN and AlN can be used to create high electron mobility transistors (HEMTs) that use two-dimensional electron gas and high-voltage electronic devices.

It is difficult to produce nitride semiconductor wafers by growing these nitride semiconductors on a substrate, and traditionally, sapphire and SiC substrates have been used as growth substrates. However, epitaxial growth of nitride semiconductors by vapor growth on silicon single crystal substrates has also been performed to increase the diameter of the substrate (large aperture) and to reduce the cost of the substrate. The production of epitaxially grown films of nitride semiconductors by vapor growth on silicon single crystal substrates is advantageous in that larger diameter substrates can be used than sapphire and SiC substrates, making the device more productive and easier to process. However, when vapor growing nitride semiconductors on silicon single crystal substrates, stress due to differences in lattice constants and thermal expansion coefficients can easily cause increased warping, slippage, cracks, etc., so stress is reduced by changing growth conditions and using relaxation layers.

For example, in epitaxial growth on a silicon single crystal substrate, an AlN buffer layer is stacked on a bare Si substrate, and then a GaN-HEMT structure epitaxial layer is stacked to produce an epitaxial substrate for power devices or RF devices. In particular, to make an epitaxial substrate for a power device with a high withstand voltage, it is necessary to produce GaN on Si (GaN on silicon single crystal) with a thicker GaN epitaxial layer. To thicken the epitaxial layer, the silicon single crystal substrate, which is the growth substrate, can be thickened and epitaxial growth can be performed. As a method for thickening the silicon single crystal substrate, two silicon single crystal substrates are bonded together. Patent Document 1 discloses that the thickness of the bonded substrates is 2 mm or more. Patent Document 2 also discloses a combination of two substrates to be bonded together, in which the bond wafer has a surface orientation of {111} and the base wafer has a surface orientation of {100} and a resistivity of 0.1 Ωcm or less.

JP 2021-014376 A JP 2021-027186 A

As described above, it is known to use a bonded substrate (laminate substrate) in which two substrates are bonded together as a growth substrate, as disclosed in Patent Documents 1 and 2. However, there has been a demand for a substrate for electronic devices with even higher fracture strength.

The present invention has been made to solve the above problems, and aims to provide a substrate for an electronic device in which a nitride semiconductor is formed on a silicon single crystal, and which has higher fracture strength, and a method for manufacturing the same.

In order to solve the above problems, the present invention provides a substrate for electronic devices in which a nitride semiconductor film is formed on a bonded substrate of silicon single crystals, the bonded substrate being 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 a crystal plane orientation of {111} are bonded via an oxide film, the oxide film having a thickness of 2 nm to 470 nm.

In this way, in a substrate for electronic devices in which a nitride semiconductor film is formed on a bonded substrate of single crystal silicon, if the bonded substrate is a substrate bonded via an oxide film and the thickness of the oxide film is thin, between 2 nm and 470 nm, the substrate for electronic devices can have a higher fracture strength.

The present invention also provides a substrate for electronic devices in which a nitride semiconductor film is formed on a bonded substrate of silicon single crystals, the bonded substrate being a substrate in which a first silicon single crystal substrate having a crystal plane orientation of {111} and a second silicon single crystal substrate are bonded via an oxide film, the oxide film having a thickness of 2 nm or more and 470 nm or less.

Even in such an embodiment, if the substrate for an electronic device is formed by forming a nitride semiconductor film on a bonded substrate of silicon single crystal, and the bonded substrate is a substrate bonded via an oxide film, and the thickness of the oxide film is thin, ranging from 2 nm to 470 nm, the substrate for an electronic device can have a higher fracture strength.

In this case, the crystal plane orientation of the second silicon single crystal substrate can be {100}.

Even with such a combination of crystal plane orientations, the first silicon single crystal substrate and the second silicon single crystal substrate can be made into a substrate for electronic devices with high fracture strength.

In addition, in the electronic device substrate of the present invention, the thickness of the oxide film can be 2 nm or more and 190 nm or less.

In the electronic device substrate of the present invention, the thickness of the oxide film is set within this range, making it possible to obtain an electronic device substrate with high fracture strength.

In this case, it is preferable that the bonded substrate is a substrate in which the notch of the first silicon single crystal substrate and the notch of the second silicon single crystal substrate are bonded together with a rotational misalignment of 15° to 165°.

Such a material would result in a substrate for electronic devices with higher fracture strength.

The diameter of the combined substrate may be 300 mm or more.

As such, the high fracture strength substrate of the present invention is particularly effective for large-diameter electronic device substrates, such as those with a diameter of 300 mm or more.

The present invention also provides a method for manufacturing a substrate for electronic devices, which includes the steps of: preparing a first silicon single crystal substrate having a crystal plane orientation of {111} and a second silicon single crystal substrate having a crystal plane orientation of {111}; forming an oxide film on at least one surface of the first silicon single crystal substrate and the second silicon single crystal substrate; stacking the first silicon single crystal substrate and the second silicon single crystal substrate with the oxide film interposed therebetween and performing a heat treatment to bond the first silicon single crystal substrate and the second silicon single crystal substrate to produce the bonded substrate; and epitaxially growing the nitride semiconductor film on the surface of the first silicon single crystal substrate of the bonded substrate, wherein the thickness of the oxide film formed in the step of forming the oxide film is formed so that the thickness of the oxide film through the first silicon single crystal substrate and the second silicon single crystal substrate is 2 nm or more and 470 nm or less.

With the method for manufacturing a substrate for an electronic device of the present invention, the bonded substrate is a substrate bonded via an oxide film, and the thickness of the oxide film can be made thin, ranging from 2 nm to 470 nm, making it possible to manufacture a substrate for an electronic device with higher fracture strength.

The present invention also provides a method for manufacturing a substrate for electronic devices, which includes forming a nitride semiconductor film on a bonded substrate of silicon single crystal, comprising the steps of: preparing a first silicon single crystal substrate having a crystal plane orientation of {111} and a second silicon single crystal substrate; forming an oxide film on at least one surface of the first silicon single crystal substrate and the second silicon single crystal substrate; stacking the first silicon single crystal substrate and the second silicon single crystal substrate with the oxide film interposed therebetween and performing a heat treatment to bond the first silicon single crystal substrate and the second silicon single crystal substrate to produce the bonded substrate; and epitaxially growing the nitride semiconductor film on the surface of the first silicon single crystal substrate of the bonded substrate, wherein the thickness of the oxide film formed in the step of forming the oxide film is formed so that the thickness of the oxide film through the first silicon single crystal substrate and the second silicon single crystal substrate is 2 nm or more and 470 nm or less.

Even in such an embodiment, the manufacturing method of the electronic device substrate of the present invention allows the bonded substrate to be a substrate bonded via an oxide film, and the thickness of the oxide film can be made thin, from 2 nm to 470 nm, so that an electronic device substrate with higher fracture strength can be manufactured.

In this case, the crystal plane orientation of the second silicon single crystal substrate can be {100}.

Even when the first silicon single crystal substrate and the second silicon single crystal substrate are combined with such crystal plane orientations, it is possible to manufacture a substrate for an electronic device with high fracture strength.

In addition, in the method for manufacturing a substrate for an electronic device of the present invention, the thickness of the oxide film formed in the step of forming the oxide film can be formed so that the thickness of the oxide film through the first silicon single crystal substrate and the second silicon single crystal substrate is 2 nm or more and 190 nm or less.

In the present invention, the thickness of the oxide film is set within this range, making it possible to manufacture substrates for electronic devices with high fracture strength.

In this case, it is preferable that the notch of the first silicon single crystal substrate and the notch of the second silicon single crystal substrate are joined with a rotational misalignment of 15° to 165°.

This manufacturing method makes it possible to produce substrates for electronic devices with higher breaking strength.

The diameter of the first silicon single crystal substrate and the second silicon single crystal substrate to be prepared can be 300 mm or more.

Substrates with high fracture strength, such as those for electronic devices manufactured by the manufacturing method of the present invention, are particularly effective for manufacturing substrates for electronic devices with large diameters, such as those with diameters of 300 mm or more.

The electronic device substrate of the present invention is a substrate in which the bonded substrate is bonded via an oxide film, and the oxide film has a thickness of 2 nm to 470 nm, so that an electronic device substrate with higher fracture strength can be provided. Furthermore, the manufacturing method of the electronic device substrate of the present invention can manufacture such an electronic device substrate. Therefore, the quality of the electronic device substrate on which the nitride semiconductor film is formed can be improved, and the productivity can be increased.

1 is a schematic cross-sectional view showing an example of a substrate for an electronic device of the present invention. FIG. 2 is a conceptual diagram illustrating the positional relationship of notches of a first silicon single crystal substrate and a second silicon single crystal substrate as viewed from the main surface side of a bonded substrate in the electronic device substrate of the present invention. FIG. 1 is a flow chart showing an outline of an example of a method for producing a substrate for an electronic device according to the present invention. 1A and 1B are schematic diagrams showing a breaking load test, in which (a) is a view from above in the vertical direction, and (b) is a view from the side. 1 is a graph showing the results of Examples 1-1 to 1-9 and Comparative Examples 1-1 and 1-2, and Examples 3-1 to 3-8 and Comparative Examples 3-1 and 3-2. 1 is a graph showing the results of Examples 2-1 to 2-8 and Examples 4-1 to 4-8.

The present invention will be described in detail below with reference to the drawings, but the present invention is not limited to these.

[Substrate for electronic devices]
As shown in FIG. 1, the electronic device substrate 20 of the present invention has a nitride semiconductor film 21 formed on a bonded substrate 10 of silicon single crystals. In the description of the present invention, the bonded substrate 10 of silicon single crystals is also simply referred to as a "bonded substrate". In this case, 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 a crystal plane orientation of {111} 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. The electronic device substrate 20 of the present invention is characterized in that the thickness of the oxide film 13 is 2 nm or more and 470 nm or less.

The bonded substrate 10 may also be a substrate in which a first silicon single crystal substrate 11 having a {111} crystal plane orientation and a second silicon single crystal substrate 12 are bonded via an oxide film 13. In this case as well, as shown in FIG. 1, a nitride semiconductor film 21 is formed on the first silicon single crystal substrate 11. The electronic device substrate 20 of the present invention is characterized in that the thickness of the oxide film 13 is 2 nm or more and 470 nm or less.

In this case, the crystal plane orientation of the second silicon single crystal substrate 12 can be {100}.

Miller indices are written as usual. That is, { } is the general term for equivalent crystal plane orientations, and ( ) is each of the crystal plane orientations. Also, < > is the general term for equivalent crystal axis directions, and [ ] is each of the crystal axis directions.

The crystal plane orientations of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 may each have an off angle of several degrees (approximately 5° or less).

As described above, in order to make the epitaxial substrate for power devices with high breakdown voltage, it is necessary to fabricate an electronic device substrate in which a nitride semiconductor film is formed thick on a silicon single crystal substrate (for example, GaN on Si in which the thickness of the GaN epitaxial layer is increased). To increase the thickness of the epitaxial layer, the silicon single crystal substrate can be made thicker and epitaxially grown. As a method for increasing the thickness of the silicon substrate, a bonded substrate is formed by bonding two silicon single crystal substrates together, but when using such a bonded substrate (bonded substrate), a substrate with higher fracture strength is desired.

In the present invention, in order to obtain a substrate 20 for electronic devices with a stronger fracture strength, the thickness of the oxide film 13 is set to 2 nm or more and 470 nm or less, as described above. By using a bonded substrate 10 with an oxide film 13 having a thickness in this range interposed therebetween, the fracture strength of the bonded substrate 10 can be improved compared to a case where no oxide film is formed. Therefore, even if the nitride semiconductor film 21 is formed on the bonded substrate 10, the fracture strength can be improved. It is considered that the oxide film 13 can play the role of a buffer layer when stress is applied by interposing the oxide film 13. The thickness of the oxide film 13 is preferably set to 2 nm or more and 190 nm or less in view of the magnitude of the effect and the ease of controlling the oxide film thickness. Even if the thickness of the oxide film 13 is made thicker, such as a thickness exceeding 470 nm, the effect of forming the oxide film 13 is gradually reduced, and the oxidation time for forming the oxide film 13 is also lengthened, so there is no merit.

Furthermore, in the present invention, the bonded silicon single crystal substrate 10 is preferably a substrate in which the notch of the first silicon single crystal substrate 11 and the notch of the second silicon single crystal substrate 12 are bonded together with a rotational misalignment of 15° to 165°. In this way, by misaligning the position of the notch in the bonded substrate 10, the fracture strength can be further improved.

The diameter of the combined substrate may be 300 mm or more.

As such, the high fracture strength substrate of the present invention is particularly effective for large-diameter electronic device substrates, such as those with a diameter of 300 mm or more.

In the electronic device substrate 20 of the present invention, since the substrate strength is high as described above, the diameter of the combined substrate 10 (and the electronic device substrate 20) can be as large as 300 mm or more. Conventionally, substrates with such a large diameter have sometimes not had sufficient substrate strength, leading to the occurrence of cracks, etc., but in the present invention, as described above, it is possible to obtain an electronic device substrate 20 with higher fracture strength. There is no particular upper limit on the diameter of the combined substrate 10 (and the electronic device substrate 20), but it can be, for example, 450 mm or less.

When the diameter of the bonded substrate 10 (and the substrate 20 for electronic devices) is 300 mm or more, the diameters of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are also 300 mm or more. The thickness of each of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is not particularly limited, but substrates conforming to the standard can be suitably used. In particular, when the diameter is 300 mm, the thickness can be 775 μm. Such silicon single crystal substrates are used as ordinary substrates for devices, are inexpensive, and can be used without any problems. The thickness of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 can be, for example, 500 μm to 1500 μm. The thicknesses of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 do not have to be the same, that is, the thickness ratio of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is not limited to 1. Even if the thickness ratio is other than 1, the same effect can be obtained as long as the total thickness of the bonded substrate 10 is the same.

The thickness of the bonded substrate 10 in which the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are bonded is not limited to 775 μm×2. It is known that the strength against the breaking load is stronger as the substrate thickness is thicker. Therefore, in the configuration of the present invention, for example, if the bonded bonded substrate 10 is made to correspond to the spec thickness of 775 μm of a single substrate with a diameter of 300 mm that is normally distributed, the strength does not reach the strength of the bonded first silicon single crystal substrate 11 and second silicon single crystal substrate 12, both of which are 775 μm in the configuration of the present invention (thickness is about 1550 μm), but the strength is greatly increased compared to a single substrate of the same thickness (775 μm). Of course, in this case, the thickness ratio of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is not limited to 1. As a method for manufacturing such a bonded substrate 10 having a thickness of 775 μm, two thin first and second silicon single crystal substrates 11 and 12 may be bonded together to a total thickness of 775 μm, or two normal specification products (thickness 775 μm) may be bonded together and ground to adjust the thickness to 775 μm.

The positional relationship between the notch of the first silicon single crystal substrate 11 and the notch of the second silicon single crystal substrate 12 in the bonded substrate 10 will be described with reference to FIG. 2. In all of FIGS. 2(a) to (f), the crystal plane orientation of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is {111}, and the notch position is in the <110> direction as an example. In FIGS. 2(a), (b), (c), (d), (e), and (f), the notch position is shown as being rotated no (0° rotation), 10° rotation, 15° rotation, 20° rotation, 30° rotation, and 60° rotation, respectively. That is, in each of FIGS. 2(a) to (f), the position of the notch of the first silicon single crystal substrate 11 is shown facing directly downward for convenience, and the position of the notch of the second silicon single crystal substrate 12, represented by a dashed line, is shifted according to the angle of each figure.

In the electronic device substrate 20 of the present invention, in addition to having the bonded substrate 10 bonded via the oxide film 13 as described above, the notch of the first silicon single crystal substrate 11 and the notch of the second silicon single crystal substrate 12 are rotationally misaligned as shown in Figures 2(b) to (f), which can further increase the fracture strength. The angle of rotational misalignment is preferably 15° or more as shown in Figures 2(c) to (f), rather than 10° as shown in Figure 2(b). In addition, the rotational misalignment between the positions of the notch of the first silicon single crystal substrate 11 and the notch of the second silicon single crystal substrate 12 is preferably 15° or more and 165° or less.

The orientation of the notch of each of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is not particularly limited. The position of the notch of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is not limited to the <110> direction, and may be in other directions. Since the difference in strength due to the angular misalignment of the notch occurs due to the relative position of the notch, which is a part that has a physically weak characteristic against the breaking load, the present invention has the same effect even if the notch is in an orientation other than the <110> direction.

In addition, in the electronic device substrate 20 of the present invention, 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}, so that a good nitride semiconductor film 21 is formed.

[Method of manufacturing a substrate for electronic devices]
A method for producing the above-described electronic device substrate 20 of the present invention will now be described with reference to FIG.

First, as shown in S11 of FIG. 3, a first silicon single crystal substrate 11 and a second silicon single crystal substrate 12 are prepared (step S11). At this time, silicon single crystal substrates having a crystal plane orientation of {111} are prepared as the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12. At this time, the diameters of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 prepared can be 300 mm or more.

In another embodiment, in step S11, a first silicon single crystal substrate 11 having a crystal plane orientation of {111} can be prepared, and a second silicon single crystal substrate 12 having a crystal plane orientation other than {111} can be prepared. In this case, the crystal plane orientation of the second silicon single crystal substrate 12 is preferably {100}. Even with such a combination of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12, the subsequent steps can be performed in the same manner.

In addition, since the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are bonded together to form a single silicon single crystal substrate 20, the first silicon single crystal substrate 11 can also be called a bond wafer and the second silicon single crystal substrate 12 can also be called a base wafer.

The thickness of each of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is not particularly limited, but substrates that comply with standards can be suitably used. In addition, the resistivity and impurity concentration of each of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 can be set appropriately.

Next, as shown in S12 of FIG. 3, an oxide film is formed on at least one surface of the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 (step S12). The oxide film formed here will become the oxide film 13 shown in FIG. 1 after the two silicon single crystal substrates are bonded. The method of forming this oxide film is not particularly limited, but for example, an oxide film (thermal oxide film) can be formed on the surface by performing an oxidation heat treatment. The thickness of the oxide film is formed so that the film thickness of the oxide film 13 between the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is 2 nm or more and 470 nm or less after the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are bonded in step S13 described later. An oxide film may be formed on each of the two silicon single crystal substrates, or an oxide film may be formed on one of the silicon single crystal substrates. In addition, the oxide film formed here may be formed as a natural oxide film as long as it is 2 nm or more when bonded.

Next, as shown in S13 of FIG. 3, the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are bonded (step S13). At this time, the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are superimposed via the oxide film formed in step S12, and bonded by heat treatment. In this way, the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are firmly bonded to each other, and the bonded substrate 10 (see FIG. 1) is produced.

As described above, by forming the oxide film in step S12 so that the thickness of the oxide film 13 between the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 is 2 nm or more and 470 nm or less, it is possible to make the thickness of the oxide film 13 after the two substrates are bonded in step S13 2 nm or more and 470 nm or less. It is preferable that the thickness of the oxide film formed in step S12 is 2 nm or more and 190 nm or less.

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

In addition, in the bonding process of step S13, it is preferable that the notch of the first silicon single crystal substrate 11 and the notch of the second silicon single crystal substrate 12 are bonded with a rotational misalignment of 15° to 165° (see Figure 2).

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 below. In particular, it is preferable to remove the oxide film formed on the surface of the bonded substrate 10 (particularly the surface of the first silicon single crystal substrate 11) by hydrofluoric acid spin cleaning or the like.

In this way, the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 are bonded to produce the bonded substrate 10, and then, as shown in S14 of FIG. 3, the 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). Note that the first silicon single crystal substrate 11 may be polished on both sides before this bonding, or even if it is not polished on both sides before bonding, one side of the main surface to be grown can be polished after bonding and before epitaxial growth. 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 a normal method. In addition, an intermediate layer (buffer layer) may be formed as appropriate. In this manner, the electronic device substrate 20 shown in FIG. 1 can be manufactured.

The present invention will be explained in more detail below with examples and comparative examples, but the present invention is not limited to the following examples.

(Examples 1-1 to 1-9, Comparative Example 1-1)
According to the method for producing a substrate for an electronic device of the present invention shown in FIG. 3, the substrate for an electronic device 20 shown in FIG. 1 was produced.

First, a double-sided polished silicon single crystal substrate 11 having a diameter of 300 mm, a thickness of 775 μm, a crystal plane orientation of {111}, p-type, a resistivity of 5000 Ωcm, and a notch formed in the <110> direction was prepared (step S11). The interstitial oxygen concentration Oi was 16 ppm (JEIDA standard) for both the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12.

A surface oxide film was formed on these two prepared silicon single crystal substrates (step S12). The oxide film was formed so that the thickness of the oxide film when the two silicon single crystal substrates were bonded together was 2 nm (Example 1-1), 23 nm (Example 1-2), 80 nm (Example 1-3), 150 nm (Example 1-4), 190 nm (Example 1-5), 220 nm (Example 1-6), 280 nm (Example 1-7), 350 nm (Example 1-8), 470 nm (Example 1-9), and 600 nm (Comparative Example 1-1). As for the specific formation method, first, in Example 1-1, a natural oxide film was formed. Also, the oxidation heat treatment in Examples 1-2 to 1-9 and Comparative Example 1-1 was a pyrogenic oxidation method. The conditions for the pyrogenic oxidation method were 900°C for 15 minutes (Example 1-2), 900°C for 60 minutes (Example 1-3), 900°C for 142 minutes (Example 1-4), 900°C for 199 minutes (Example 1-5), 900°C for 214 minutes (Example 1-6), 900°C for 256 minutes (Example 1-7), 900°C for 301 minutes (Example 1-8), 1000°C for 213 minutes (Example 1-9), and 1000°C for 275 minutes (Comparative Example 1-1).

Next, the two silicon single crystal substrates were stacked with their notches aligned, and a bonding heat treatment was performed at 500°C in a nitrogen atmosphere to produce the bonded substrate 10 (step S13). After that, the bonded substrate 10 was spin-cleaned with hydrofluoric acid to remove the oxide film on the surface of the bonded substrate 10.

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

As a result, in Examples 1-1 to 1-9, the nitride semiconductor film 21 could be formed without cracks or the like. In this manner, the electronic device substrate 20 was manufactured.

In addition, bonded substrates were produced before the nitride semiconductor film was formed under the same conditions as in each of Examples 1-1 to 1-9 and Comparative Example 1-1, and the strength of each bonded substrate was measured.

To measure the strength of this bonded substrate, the breaking load was examined using an Instron precision universal testing machine, as shown in Figure 4. Figure 4(a) is a view from above in the vertical direction, and Figure 4(b) is a view from the side.

As shown in Figures 4(a) and (b), three fulcrum jigs J (with a radius of curvature R of the crimping point of 15 mm) were placed above and below the bonded substrate. Since the notch position in the bonded substrate is weak in terms of strength, the notch position N was set to be directly below the central fulcrum jig J (see Figures 4(a) and (b)).

(Comparative Example 1-2)
The bonded substrate was produced in the same manner as in Example 1-1, with the following changes. After the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 were prepared, the oxide film formation in step S12 was not performed on either substrate. In addition, the native oxide film on the bonding surfaces of both substrates was removed by HF spin cleaning. Then, the two substrates were bonded together with the native oxide film removed. The breaking load of this substrate (bonded substrate without an oxide film) was investigated in the same manner as above.

(Comparative Example 1-3)
A single first silicon single crystal substrate 11 similar to that in Example 1-1 was prepared. The breaking load of this single substrate was examined in the same manner as above.

The above results of the breaking load (strength) are summarized in Table 1. In addition, for Examples 1-1 to 1-9 and Comparative Examples 1-1 and 1-2, the results are plotted in Figure 5 (Figure 5 also shows Examples 3-1 to 3-8 and Comparative Examples 3-1 and 3-2, which will be described later).

Thus, the strength of the bonded substrate 10 in Examples 1-1 to 1-9 was higher than that in Comparative Examples 1-1 to 1-3. In addition, the strength of the bonded substrate 10 in Comparative Example 1-2, in which two silicon single crystal substrates were bonded without an oxide film, was only about twice the strength of a single unbonded silicon single crystal substrate in Comparative Example 1-3. In contrast, in Examples 1-1 to 1-9, in which bonded substrates 10 bonded via an oxide film 13 were used, the strength was significantly improved, far exceeding twice the strength of a single unbonded silicon single crystal substrate. In Comparative Example 1-1, in which the oxide film was thicker than 470 nm (600 nm), the effect of the oxide film was attenuated, sufficient strength was not obtained, and it took a long time to form the oxide film.

(Example 2-1)
Steps S11 to S14 were carried out in the same manner as in Example 1-1 (natural oxide film formation, oxide film 13 having a thickness of 2 nm after bonding), to manufacture a substrate 20 for an electronic device.

(Examples 2-2 to 2-8)
Substrates 20 for electronic devices were manufactured in the same manner as in Example 2-1, except that the positions of the notches of the first single crystal silicon substrate 11 and the second single crystal silicon substrate 12 were rotated and shifted. The magnitudes of the rotational shift were 10° (Example 2-2), 15° (Example 2-3), 20° (Example 2-4), 30° (Example 2-5), 60° (Example 2-6), 170° (Example 2-7), and 180° (Example 2-8).

In Examples 2-1 to 2-8, the nitride semiconductor film 21 could be formed without cracks or other defects.

In addition, bonded substrates 10 were produced before the nitride semiconductor film was formed under the same conditions as in each of Examples 2-1 to 2-8, and the strength (breaking load) of each bonded substrate was measured. The strength of each bonded substrate 10 was measured in the same manner as in Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-3. The results of the breaking load (strength) are summarized in Table 2 and Figure 6 (Figure 6 also shows Examples 4-1 to 4-8, which will be described later).

The bonded substrates 10 of Examples 2-1 to 2-8 all had improved strength compared to Comparative Examples 1-1 to 1-3.

Of Examples 2-1 to 2-8, the bonded substrates 10 of Examples 2-3 to 2-6 were particularly strong, and were even stronger than Examples 2-1 and 2-2, in which the rotational misalignment of the notches of both substrates was less than 15°.

In addition, in Examples 2-7 and 2-8, the rotational misalignment of the notches of both substrates is 170° and 180°, and the notches are located on the opposite side of the substrate from the cases where the misalignment is 10° and 0° (i.e., Examples 2-2 and 2-1), respectively. When comparing the strength of Example 2-1 (0°) and Example 2-8 (180°), the values are close, and when comparing the strength of Example 2-2 (10°) and Example 2-7 (170°), the values are close. Therefore, when the rotational misalignment of the notches of both substrates is 170° and 180°, it is considered to be equivalent to when the rotational misalignment of the notches of both substrates is 10° and 0°, respectively. From this, for example, when the rotational misalignment of the notches of both substrates is 15° and when it is 165°, it is considered to be equivalent. From the above, it is considered preferable that the rotational misalignment of the notches of both substrates is 15° to 165°.

(Examples 3-1 to 3-8, Comparative Example 3-1)
The electronic device substrate 20 shown in Fig. 1 was manufactured according to the manufacturing method of the electronic device substrate of the present invention shown in Fig. 3. Unlike Example 1-1 and the like, the second silicon single crystal substrate 12 used here had a crystal plane orientation of {100} and had a notch formed in the <100> direction.

First, a double-sided polished silicon single crystal substrate 11 having a diameter of 300 mm, a thickness of 775 μm, a crystal plane orientation of {111}, p-type, a resistivity of 5000 Ωcm, and a notch formed in the <110> direction was prepared (step S11). The interstitial oxygen concentration Oi was 16 ppm (JEIDA standard) for both the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12.

A surface oxide film was formed on these two prepared silicon single crystal substrates (step S12). The oxide film was formed so that the thickness of the oxide film when the two silicon single crystal substrates were bonded together was 2 nm (Example 3-1), 25 nm (Example 3-2), 83 nm (Example 3-3), 148 nm (Example 3-4), 189 nm (Example 3-5), 223 nm (Example 3-6), 295 nm (Example 3-7), 468 nm (Example 3-8), and 599 nm (Comparative Example 3-1). As for the specific formation method, first, in Example 3-1, a natural oxide film was formed. Also, the oxidation heat treatment in Examples 3-2 to 3-8 was a pyrogenic oxidation method. The conditions for the pyrogenic oxidation method were 900°C for 15 minutes (Example 3-2), 900°C for 60 minutes (Example 3-3), 900°C for 142 minutes (Example 3-4), 900°C for 199 minutes (Example 3-5), 900°C for 214 minutes (Example 3-6), 900°C for 256 minutes (Example 3-7), 1000°C for 213 minutes (Example 3-8), and 1000°C for 275 minutes (Comparative Example 3-1).

Next, the two silicon single crystal substrates were stacked with their notches aligned, and a bonding heat treatment was performed at 500°C in a nitrogen atmosphere to produce the bonded substrate 10 (step S13). After that, the bonded substrate 10 was spin-cleaned with hydrofluoric acid to remove the oxide film on the surface of the bonded substrate 10.

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

As a result, in Examples 3-1 to 3-8, the nitride semiconductor film 21 could be formed without cracks or the like. In this manner, the electronic device substrate 20 was manufactured.

In addition, bonded substrates before the formation of the nitride semiconductor film were produced under the same conditions as in Examples 3-1 to 3-8 and Comparative Example 3-1, and their strength was measured in the same manner as above.

(Comparative Example 3-2)
The bonded substrate was produced in the same manner as in Example 3-1, with the following changes. After the first silicon single crystal substrate 11 and the second silicon single crystal substrate 12 were prepared, the oxide film formation in step S12 was not performed on either substrate. In addition, the natural oxide film on the bonding surfaces of both substrates was removed by HF spin cleaning. Then, with the natural oxide film removed, the two substrates were bonded together. The breaking load of this substrate (bonded substrate without an oxide film) was investigated in the same manner as above.

The results of the above breaking load (strength) are summarized in Table 3. The results for Examples 3-1 to 3-8 and Comparative Examples 3-1 and 3-2 are plotted in Figure 5.

Thus, the strength of the bonded substrate 10 in Examples 3-1 to 3-8 was higher than that in Comparative Examples 3-1 and 3-2. Furthermore, the strength of the bonded substrate 10 in Comparative Example 3-2, in which two silicon single crystal substrates were bonded without an oxide film, was only about twice the strength of the single unbonded silicon single crystal substrate in Comparative Example 1-3. In contrast, in Examples 3-1 to 3-8, in which bonded substrates 10 bonded via an oxide film 13 were used, the strength was significantly improved, far exceeding twice the strength of a single unbonded silicon single crystal substrate.

(Example 4-1)
Steps S11 to S14 were carried out in the same manner as in Example 3-1 (natural oxide film formation, oxide film 13 having a thickness of 2 nm after bonding), to manufacture a substrate 20 for an electronic device.

(Examples 4-2 to 4-8)
Substrates 20 for electronic devices were manufactured in the same manner as in Example 4-1, except that the positions of the notches of the first single crystal silicon substrate 11 and the second single crystal silicon substrate 12 were rotated and shifted. The magnitudes of the rotational shift were 10° (Example 4-2), 15° (Example 4-3), 20° (Example 4-4), 30° (Example 4-5), 60° (Example 4-6), 170° (Example 4-7), and 180° (Example 4-8).

In Examples 4-1 to 4-8, the nitride semiconductor film 21 was formed without any cracks or other defects.

In addition, bonded substrates 10 before the formation of the nitride semiconductor film were produced under the same conditions as in each of Examples 4-1 to 4-8, and the strength (breaking load) of each bonded substrate was measured. The strength measurements of each bonded substrate 10 were performed in the same manner as in Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-3. The above results of the breaking load (strength) are summarized in Table 4 and shown in Figure 6.

The bonded substrates 10 of Examples 4-1 to 4-8 all had improved strength compared to Comparative Examples 3-1, 3-2, and 1-3. Note that, although Example 4-1 was performed under the same conditions as Example 3-1, there were differences in the data due to experimental variability.

Of Examples 4-1 to 4-8, the bonded substrates 10 of Examples 4-3 to 4-6 were particularly strong, and were even stronger than Examples 4-1 and 4-2, in which the rotational misalignment of the notches of both substrates was less than 15°.

In addition, in Examples 4-7 and 4-8, the rotational misalignment of the notches of both substrates is 170° and 180°, and the notches are located on the opposite side of the substrate from the cases where the misalignment is 10° and 0° (i.e., Examples 4-2 and 4-1), respectively. When comparing the strength of Example 4-1 (0°) and Example 4-8 (180°), the values are close, and when comparing the strength of Example 4-2 (10°) and Example 4-7 (170°), the values are close. Therefore, when the rotational misalignment of the notches of both substrates is 170° and 180°, it is considered to be equivalent to when the rotational misalignment of the notches of both substrates is 10° and 0°, respectively. From this, for example, when the rotational misalignment of the notches of both substrates is 15° and when it is 165°, it is considered to be equivalent. From the above, it is considered preferable that the rotational misalignment of the notches of both substrates is 15° to 165°.

Example 5
The bonded substrate 10 manufactured under the conditions of Example 2-5 was adjusted to a thickness of 775 μm by grinding, polishing, and etching after bonding. The strength (breaking load) of this bonded substrate 10 was measured in the same manner as in Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-3. As a result, the breaking load (strength) of Example 5 was 912 N. The breaking load (strength) of Comparative Example 1-3 (i.e., an example having the same total thickness of 775 μm as Example 5 but consisting of one substrate) was 305 N as shown in Table 1, so the breaking load of Example 5 was improved compared to Comparative Example 1-3.

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

10...silicon single crystal bonded substrate,
11...first silicon single crystal substrate,
12...second silicon single crystal substrate,
13... oxide film,
20...Substrate for electronic device,
21...Nitride semiconductor film.

Claims (10)

A substrate for an electronic device in which a nitride semiconductor film is formed on a silicon single crystal bonded substrate,
The bonded substrate is a substrate in which a first silicon single crystal substrate having a {111} crystal plane orientation and a second silicon single crystal substrate having a {111} crystal plane orientation are bonded via an oxide film;
The substrate for electronic devices, wherein the oxide film has a thickness of 2 nm or more and 190 nm or less. A substrate for an electronic device in which a nitride semiconductor film is formed on a silicon single crystal bonded substrate,
The bonded 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 are bonded via an oxide film;
The substrate for electronic devices, wherein the oxide film has a thickness of 2 nm or more and 190 nm or less. The substrate for electronic devices according to claim 2, characterized in that the crystal plane orientation of the second silicon single crystal substrate is {100}. The substrate for electronic devices according to claim 1 or 2, characterized in that the bonded substrate is a substrate in which the notch of the first silicon single crystal substrate and the notch of the second silicon single crystal substrate are bonded together with a rotational misalignment of 15° to 165°. The substrate for electronic devices according to claim 1 or 2, characterized in that the diameter of the bonded substrate is 300 mm or more. A method for manufacturing a substrate for an electronic device, comprising forming a nitride semiconductor film on a bonded substrate of silicon single crystal,
Preparing a first silicon single crystal substrate having a {111} crystal plane orientation and a second silicon single crystal substrate having a {111} crystal plane orientation;
forming an oxide film on a surface of at least one of the first silicon single crystal substrate and the second silicon single crystal substrate;
a step of overlapping the first silicon single crystal substrate and the second silicon single crystal substrate with the oxide film interposed therebetween and performing a heat treatment to bond the first silicon single crystal substrate and the second silicon single crystal substrate to produce the bonded substrate;
epitaxially growing the nitride semiconductor film on a surface of the first silicon single crystal substrate of the bonded substrate;
and forming the oxide film such that a thickness of the oxide film formed in the step of forming the oxide film is 2 nm or more and 190 nm or less through the first silicon single crystal substrate and the second silicon single crystal substrate. A method for manufacturing a substrate for an electronic device, comprising forming a nitride semiconductor film on a bonded substrate of silicon single crystal,
Providing a first silicon single crystal substrate having a {111} crystal plane orientation and a second silicon single crystal substrate;
forming an oxide film on a surface of at least one of the first silicon single crystal substrate and the second silicon single crystal substrate;
a step of overlapping the first silicon single crystal substrate and the second silicon single crystal substrate with the oxide film interposed therebetween and performing a heat treatment to bond the first silicon single crystal substrate and the second silicon single crystal substrate to produce the bonded substrate;
epitaxially growing the nitride semiconductor film on a surface of the first silicon single crystal substrate of the bonded substrate;
and forming the oxide film such that a thickness of the oxide film formed in the step of forming the oxide film is 2 nm or more and 190 nm or less through the first silicon single crystal substrate and the second silicon single crystal substrate. 8. The method for producing a substrate for an electronic device according to claim 7 , wherein the crystal plane orientation of the second silicon single crystal substrate is {100}. 8. The method for manufacturing a substrate for electronic devices according to claim 6 or 7 , wherein the notch of the first silicon single crystal substrate and the notch of the second silicon single crystal substrate are joined together with a rotational misalignment of 15° to 165°. 8. 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 each have a diameter of 300 mm or more.

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