JP2005219962A - Diamond single crystal substrate and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a low cost large-sized diamond single crystal substrate by forming a diamond single crystal film on a silicon substrate from which a low cost maximum-area single crystal can be obtained. <P>SOLUTION: In the diamond single crystal substrate and the manufacturing method of the single crystal substrate of this invention, the residual stress due to a lattice mismatch between a silicon single crystal substrate and a diamond single crystal is buffered by having intermediate layers of an oxide single crystal layer 11 and a metal single crystal layer 12 between the diamond single crystal film 13 and the silicon single crystal substrate 10, while using a silicon single crystal from which the low cost large-sized diamond single crystal substrate is easily obtainable, as a substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a diamond single crystal substrate and a method for manufacturing the same. It is particularly suitable for materials used for semiconductor materials, electronic parts, optical parts and the like.

Diamond has excellent properties such as high thermal conductivity, wide band gap, high breakdown electric field, and high light transmittance. Therefore, diamond is expected as a material for electronic devices and sensors for high temperature, high frequency, high electric field, and high output.
In order to put these various types into practical use, a single crystal diamond film having a large area with a diameter of several inches or more is required at low cost. Further, it is required to synthesize a high quality diamond film with reduced crystal structure defects.

  So far, artificial diamond single crystal substrates have been made by high temperature and high pressure synthesis. However, since the diamond single crystal obtained by the high-temperature and high-pressure method has a large size of the synthesis apparatus and is expensive, there is a limit in reducing the manufacturing cost of the single crystal. Also, the size of the single crystal obtained is limited to a small size of about 1 cm square because the volume of the portion that can be made high pressure is small.

  In addition to the high-temperature and high-pressure synthesis method, a single crystal production method using epitaxial growth by a gas phase synthesis method is being developed as a technique established as a diamond production method. In general, epitaxial growth is divided into homoepitaxial growth that grows on a single crystal substrate of the same type as the material to be grown and heteroepitaxial growth that grows on a single crystal substrate of a different type. Homoepitaxial growth requires a diamond substrate, and it takes time to make a thin film larger than the substrate. At present, it is difficult to obtain a large single crystal with a diameter of several inches.

  Therefore, there is an expectation for heteroepitaxial growth in which diamond is grown on different materials. To date, attempts have been made to heteroepitaxially grow diamond using cubic boron nitride (C-BN), silicon carbide (SiC), silicon (Si), iridium (Ir), and platinum (Pt) as substrates. Has been. For example, Patent Literature 1, Patent Literature 2, Patent Literature 3, and the like. There has also been reported an attempt to heteroepitaxially grow diamond by depositing the above-mentioned metal single crystal film on an oxide single crystal, for example, a magnesium oxide or strontium titanate substrate. However, magnesium oxide and strontium titanate single crystal substrates are expensive and difficult to obtain a large area. Among these heteroepitaxial substrates, silicon is regarded as particularly important because a single crystal substrate having a large diameter of several inches can be easily obtained.

In Non-Patent Document 1, diamond was directly formed on a silicon single crystal substrate, but the half-value width was 4.6 ° in the [111] X-ray pole figure measurement. In Patent Document 4, if the half width is 6 seconds or less (less than 1/600 °), the distortion in the crystal is almost eliminated. In Patent Document 5, a diamond single film is formed after a silicide single crystal is grown on a silicon single crystal substrate. In Non-Patent Document 2, a diamond film is formed on a silicon substrate using a microwave plasma CVD method using negative bias applied to the silicon substrate. In Non-Patent Document 3, silicon carbide (SiC) is formed on silicon, and a diamond film is formed thereon.
JP-A-63-224225 JP-A-2-233591 JP-A-4-132687 JP-A-7-148426 JP 7-41385 A X.Jiang et al Appl. Phys. Lett. 67 (1995) 1197 J. Plitzko et al. Diamond. Relate. Mater. 6 (1997) 935 K. Kawarada et al. J. Appl. Phys. 81 (1997) 3490

As described above, there is an expectation for heteroepitaxial growth in which diamond is grown on a different material, but depending on the substrate, it is expensive and difficult to obtain a large area.
In Non-Patent Document 1, a diamond film was formed directly on a silicon single crystal substrate, but the half-value width was 4.6 ° in the [111] X-ray pole figure measurement. If the value width is 6 seconds or less (less than 1/600 °), it is said that the distortion in the crystal is almost eliminated. Therefore, the diamond in this example is insufficient for use in a semiconductor or the like. Moreover, when the diamond film by patent document 5 was observed by the Raman scattering spectroscopic analysis, the half value width of Raman shift became large with 3.2 cm < ^-1 >, and it is difficult to utilize for a semiconductor etc. The film prepared in Non-Patent Document 2 was not fully oriented with a half-value width of 9 ° in [111] X-ray pole figure measurement. Further, the diamond film produced in Non-Patent Document 3 has a half width of 1.5 ° in the [111] X-ray pole figure measurement, which is not yet sufficient.
Therefore, the present invention aims to obtain a large-sized diamond single crystal substrate at a low cost by forming a diamond single crystal film on a silicon substrate from which a single crystal having the maximum area can be obtained at low cost. is there.

  The diamond single crystal substrate or the single crystal substrate manufacturing method of the present invention uses a silicon single crystal as a substrate, which is easy to manufacture a large single crystal substrate at a low cost, and an oxide single crystal between the diamond single crystal and the silicon single crystal substrate. By having an intermediate layer between the crystal layer and the metal single crystal layer, the residual stress due to lattice mismatch or the like between the silicon single crystal substrate and the diamond single crystal is buffered.

That is, the present invention has the following configuration.
(1) A diamond single crystal substrate in which an oxide single crystal is stacked on a silicon single crystal substrate, a metal single crystal layer is stacked on the oxide single crystal layer, and a diamond single crystal is stacked on the metal single crystal layer. .
(2) The oxide single crystal is one or two selected from the group consisting of magnesium oxide, nickel oxide, zirconium oxide, barium titanate, lead titanate, strontium titanate, potassium tantalate and lithium niobate. The diamond single crystal substrate according to (1) above, which is a laminate of the above single crystals.
(3) The metal single crystal was selected from elements of groups VIA, VIIA, VIIIA and IB of the periodic table containing iron, cobalt, iridium, nickel, palladium, rhodium, platinum, gold, silver and copper. The diamond single crystal substrate according to (1) or (2) above, wherein the diamond single crystal substrate is a laminate of one type or two or more types of single crystals.

(4) The diamond single crystal substrate according to any one of (1) to (3), wherein the oxide single crystal layer has a thickness of 100 nm or less.
(5) The diamond single crystal substrate according to any one of (1) to (4), wherein the metal single crystal layer has a thickness of 100 to 5000 nm.
(6) The diamond single crystal substrate according to any one of (1) to (5), wherein an amorphous layer is provided between the silicon single crystal substrate and the oxide single crystal substrate.

(7) A diamond single crystal substrate characterized in that an oxide single crystal layer is formed on a silicon single crystal substrate, a metal single crystal layer is further formed thereon, and a diamond single crystal film is further formed thereon. Production method.
(8) The diamond single crystal substrate according to (7), wherein the diamond single crystal is manufactured using any one of a microwave plasma CVD method, a filament CVD method, a high frequency CVD method, and a direct current arc plasma method. Production method.
(9) The above-mentioned (7) or (8), wherein the oxide single crystal is produced using any one of a high-frequency sputtering method, a direct current sputtering method, a molecular beam epitaxy method, an electron gun vapor deposition method, and a laser ablation method. ) Diamond single crystal substrate manufacturing method.

The diamond single crystal manufacturing method of the present invention can obtain a large-sized diamond single crystal substrate at low cost by forming a diamond single crystal film on a silicon substrate on which a single crystal having the maximum area can be obtained at low cost. it can.
A typical layer structure of the diamond single crystal substrate of the present invention is as shown in FIG. In FIG. 1, 10 is a Si substrate, 11 is an oxide single crystal layer, 12 is a metal single crystal layer, and 13 is a diamond single crystal film.
The metal single crystal layer 12 is selected from a simple substance or an alloy of a VIA group, a VIIA group, a VIIIA group, or an IB group element. These have a small lattice mismatch with the diamond film, and can form the diamond single crystal film 13 having crystal orientation. Among these, iridium is preferable because it has a small lattice mismatch with the diamond film and a small carbon diffusion coefficient. Alternatively, platinum having a small lattice mismatch is preferable. As a result, a diamond film having a small residual stress and a good orientation of particles in the film can be obtained.

The oxide single crystal layer 11 is selected from the group consisting of magnesium oxide, nickel oxide, zirconium oxide, barium titanate, lead titanate, strontium titanate, potassium tantalate, and lithium niobate having a small lattice mismatch with diamond or silicon. It is a laminate of one type or two or more types of single crystals. In particular, strontium titanate and magnesium oxide are preferable because they have close lattice constants with silicon and diamond and thus have a small lattice mismatch. This reduces the residual stress and prevents the diamond film from peeling off.
For example, a strontium titanate single crystal film is formed on a silicon single crystal substrate, and an iridium single crystal film is further formed thereon. Further, a diamond single crystal film 13 is formed thereon. Since the intermediate layer between the silicon substrate and the diamond film buffers the lattice mismatch, the diamond single crystal film can be formed on the large silicon single crystal substrate.

If the oxide single crystal layer 11 is thicker than 100 nm, the residual stress similarly increases, and the oxide single crystal peels off. For this reason, the oxide single crystal film 11 preferably has a thickness of 100 nm or less.
If the film thickness of the metal single crystal is less than 100 nm, it will not be a continuous film. When diamond is deposited, the nucleation density of diamond will be low, and the diamond layer will not be a continuous film. On the other hand, when the film thickness is 5000 nm or more, the residual stress increases and the metal single crystal layer 12 is peeled off. For this reason, the metal single crystal film 12 is preferably 100 nm to 5000 nm.

  It is preferable that an amorphous layer exists between the silicon single crystal and the oxide single crystal. This buffers the lattice mismatch between the silicon single crystal and the oxide single crystal, and improves the orientation of the oxide single crystal layer.

The metal single crystal layer 12 can be suitably formed using a high frequency sputtering method, a direct current sputtering method, a molecular beam epitaxy method, an electron gun vapor deposition method, a laser ablation method, or the like. In any method, the metal single crystal layer 12 having orientation can be obtained.
The oxide single crystal layer 11 is formed on the silicon substrate by suitably using a high frequency sputtering method, a direct current sputtering method, a molecular beam epitaxy method, an electron gun vapor deposition method, a laser ablation method, or the like. it can. Thereby, the high-quality oxide single crystal layer 11 having orientation can be obtained at low cost.

The diamond single crystal film 13 can be formed by suitably using a microwave plasma CVD method, a filament CVD method, a high frequency CVD method, a direct current arc plasma method, and the like. It becomes possible. The raw material is hydrogen and a hydrocarbon gas such as methane, ethane or acetylene. These may be mixed with an active gas such as hydrogen or an inert gas such as helium, argon, neon, xenon, or nitrogen. As the pressure, a suitable pressure of 1 Pa to 10000 Pa is used. As a result, a diamond substrate having high adhesion and high orientation can be obtained. It is also more convenient to bias the substrate to a negative voltage in order to generate diamond nuclei on the substrate. The negative voltage is about −10V to −400V.
The substrate temperature during diamond growth is about 500 ° C to 1200 ° C. Thereby, a high quality diamond single crystal can be obtained.

  In the diamond single crystal substrate of the present invention, a metal single crystal layer or an oxide single crystal layer having a small lattice mismatch and / or a low carbon diffusion coefficient is formed between the diamond single crystal film and the silicon single crystal. By reducing the stress, the diamond film does not peel off. Therefore, a high-quality single crystal diamond film having no grain boundary is synthesized in a wide area with no peeling.

Next, examples of the present invention will be described.
Example 1
A silicon (100) wafer was used as the substrate. FIG. 2 shows the layer structure of the diamond single crystal substrate of Example 1. In FIG. 2, 20 is the silicon single crystal substrate. The plane orientation of the silicon single crystal substrate 20 was 4 ° from the (100) plane. The oxide layer on the substrate surface was removed with a 1% aqueous hydrofluoric acid solution. This silicon wafer was heated in an ultra-high vacuum chamber to obtain a silicon (100) 2 × 1 cleaning surface. This silicon wafer was put in a molecular beam epitaxy tank, and the pressure was set to 1 × 10 ⁴ Pa and the substrate temperature was 850 ° C. in an oxygen atmosphere, and the strontium titanate layer 21 was formed by molecular beam epitaxy. When reflection high-energy electron diffraction (RHEED) measurement was performed, it was confirmed that the strontium titanate layer 21 was a single crystal. The film thickness of this strontium titanate layer 21 was 100 nm. On the substrate on which this strontium titanate was formed, the substrate temperature was set to 650 ° C. using a DC sputtering apparatus, and iridium was formed to a thickness of 1500 nm in argon gas. When this iridium layer 22 was measured by reflection high-energy electron diffraction (RHEED), it was confirmed to be a single crystal. Thereafter, the substrate was set in a microwave plasma CVD apparatus, and a diamond single crystal film 23 was formed while flowing hydrogen and methane as source gases. The growth conditions were a methane concentration of 4%, a substrate temperature of 800 ° C., and a substrate bias of −200V. Under these conditions, diamond growth was performed for 10 hours. Result of the synthesized film was evaluated by Raman spectroscopy, the 1333 cm ^-1 confirmed peak by diamond, broad peak due to non-diamond components in the 1150 cm ^-1 and 1550 cm ^-1 was not observed. In addition, when observed with SEM, no crystal grains having misoriented were observed. When the X-ray rocking curve measurement was performed, the half width was 3 to 5 seconds. That is, a diamond single crystal substrate could be obtained.

Comparative Example 1
Under almost the same conditions as in Example 1, strontium titanate was not formed, but iridium was directly formed on the silicon single crystal substrate. However, the iridium film had poor adhesion to the silicon substrate, and the iridium film was peeled off before the diamond film was formed. As a result, diamond could not be formed. From the above, the usefulness of the oxide single crystal layer was shown.

Comparative Example 2
A diamond film was formed under almost the same conditions as in Example 1 without forming an iridium film. An attempt was made to form a diamond film directly on strontium titanate, but diamond nucleation hardly occurred and various plane orientations were exposed, so that only a polycrystalline diamond film could be produced. Thereby, the usefulness of the metal single crystal layer was shown.

Ｎｏ．１〜７のダイヤモンド層を反射電子線回折により評価したところ、スポット状の回折点が認められ、単結晶であることが確認された。Ｎｏ．８の二酸化シリコン単結晶を中間層とした場合、ダイヤモンド層の反射電子線回折により、多結晶であることが確認された。 Example 2
Films were formed in almost the same manner as in Example 1 while changing the type of oxide on the silicon single crystal substrate. FIG. 3 shows the layer structure. An iridium single crystal layer 32 was formed on the oxide single crystal layer 31, and a diamond single crystal film 33 was formed thereon. The diamond single crystal film 33 was evaluated by reflected electron diffraction. The results are shown in Table 1.

No. When the 1 to 7 diamond layers were evaluated by backscattered electron diffraction, spot-like diffraction spots were observed, and it was confirmed to be a single crystal. No. When 8 silicon dioxide single crystal was used as the intermediate layer, it was confirmed to be polycrystalline by reflection electron diffraction of the diamond layer.

Ｎｏ．８〜１７では、反射電子線回折により、スポット状の回折点が認められ、単結晶であることが確認された。Ｎｏ．１８のアルミニウムを中間層とした場合、ダイヤモンド層の反射電子線回折を行ったところ、多結晶であることが確認された。 Example 3
A substrate having the layer structure shown in FIG. 3 was obtained in substantially the same manner as in Example 1. The diamond single crystal film 43 was formed by changing the type of the metal single crystal layer 32 between the strontium titanate layer 31 and the diamond single crystal film 33 to various metals shown in Table 2. Each was confirmed to be a single crystal by observation of reflection high-energy electron diffraction. The results are shown in Table 2.

No. In 8-17, the spot-like diffraction point was recognized by the backscattered electron diffraction, and it was confirmed that it is a single crystal. No. When 18 aluminum was used as the intermediate layer, it was confirmed that the diamond layer was polycrystalline by reflection electron diffraction of the diamond layer.

Ｎｏ．１９、２０は、チタン酸ストロンチウム層の厚みが１００ｎｍ以下であり、層間の剥離もなくダイヤモンド単結晶を得ることができた。Ｎｏ．２１、２２ではチタン酸ストロンチウム層が１００ｎｍ以上となり、イリジウムを成膜する前に、チタン酸ストロンチウム層とシリコン層との間で剥離が起こった。 Example 4
A diamond layer was formed by changing the thickness of the strontium titanate layer in substantially the same manner as in Example 1. The results are shown in Table 3.

No. In Nos. 19 and 20, the thickness of the strontium titanate layer was 100 nm or less, and a diamond single crystal could be obtained without peeling between layers. No. In Nos. 21 and 22, the strontium titanate layer was 100 nm or more, and peeling occurred between the strontium titanate layer and the silicon layer before forming the iridium film.

成膜したダイヤモンド層を、走査電子顕微鏡で観察したところ、Ｎｏ．２３〜２４のイリジウムの厚みが１００ｎｍ以下のものは、ダイヤモンド層が不連続となっていた。Ｎｏ．２５〜２６を同様に観察したところ、連続膜となっていた。 Example 1
A diamond layer was formed by changing the thickness of the iridium layer in substantially the same manner as in Example 1. The results are shown in Tables 4 and 5.

When the formed diamond layer was observed with a scanning electron microscope, no. When the thickness of iridium of 23 to 24 was 100 nm or less, the diamond layer was discontinuous. No. When 25-26 was observed similarly, it was a continuous film.

Ｎｏ．３０、３１のように膜厚を５０００ｎｍ以上にしたところ、ダイヤモンド成膜前にイリジウム層とチタン酸ストロンチウム層との間で剥離が起こった。これにより、ダイヤモンド単結晶を得ることができなかった。

No. When the film thickness was set to 5000 nm or more as in 30 and 31, peeling occurred between the iridium layer and the strontium titanate layer before the diamond film formation. Thereby, a diamond single crystal could not be obtained.

Example 6
A diamond film formed by almost the same method as in Example 1 was prepared so as to have an amorphous silicon dioxide layer between a silicon single crystal and a strontium titanate layer. When the X-ray rocking curve of the diamond layer was measured, the half-width of the diamond (100) peak was 3 to 5 seconds, although it did not have an amorphous layer. A diamond single crystal having a narrow orientation of 2 seconds and higher orientation could be obtained.

Ｎｏ．３２〜３４の方法で成膜したものは、反射電子線回折でダイヤモンド層を評価したところスポット状の回折点が認められ、単結晶であることが確認された。Ｎｏ．３５の光ＣＶＤで成膜したものは、評価したところ様々な面方位を持った多結晶であることが分かった。 Example 7
Film formation was performed in almost the same manner as in Example 1, except that the diamond film formation method was changed. The diamond layer was evaluated using backscattered electron diffraction. The results are shown in Table 6.

No. When the diamond layer was evaluated by reflection electron diffraction, the film formed by the methods 32 to 34 was found to have a spot-like diffraction point and was confirmed to be a single crystal. No. As a result of evaluation, the film formed by 35 photo CVD was found to be polycrystalline with various plane orientations.

Ｎｏ．３６〜４０の方法で成膜したものは、反射電子線回折でチタン酸ストロンチウム層を評価したところスポット状の回折点が認められ、単結晶であることが確認された。Ｎｏ４１のＲＦプラズマＣＶＤ法で成膜したものは、チタン酸ストロンチウム層を評価したところ様々な面方位を持った多結晶であることが分かった。 Example 8
Film formation was performed in almost the same manner as in Example 1, except that the film formation method of the strontium titanate layer was changed. The strontium titanate layer was evaluated using backscattered electron diffraction. The results are shown in Table 7.

No. When the strontium titanate layer was evaluated by reflection electron diffraction, the film formed by the methods 36 to 40 was found to have spot-like diffraction spots and was confirmed to be a single crystal. The film formed by the No. 41 RF plasma CVD method was evaluated as a strontium titanate layer and was found to be polycrystalline with various plane orientations.

It is explanatory drawing of the layer structure of the board | substrate of this invention. 3 is an explanatory diagram of a layer configuration of Example 1. FIG. 3 is an explanatory diagram of a layer configuration of Example 2. FIG.

Explanation of symbols

10, 20, 30 Silicon single crystal substrate 11 Oxide single crystal layer 12 Metal single crystal layers 13, 23, 33 Diamond single crystal layer 21 Strontium titanate layers 22, 32 Iridium layer 31 Oxide single crystal layer

Claims (9)

  A diamond single crystal substrate in which an oxide single crystal is stacked on a silicon single crystal substrate, a metal single crystal layer is stacked on the oxide single crystal layer, and a diamond single crystal is stacked on the metal single crystal layer.   The oxide single crystal is one or two or more types selected from the group consisting of magnesium oxide, nickel oxide, zirconium oxide, barium titanate, lead titanate, strontium titanate, potassium tantalate and lithium niobate. 2. The diamond single crystal substrate according to claim 1, wherein the diamond single crystal substrate is a stacked layer of crystals. The metal single crystal may be one kind selected from elements of Group VIA, Group VIA, Group VIIIA, Group IB of the periodic table containing iron, cobalt, iridium, nickel, palladium, rhodium, platinum, gold, silver and copper, or 3. The diamond single crystal substrate according to claim 1, wherein the diamond single crystal substrate is a laminate of two or more types of single crystals.   The diamond single crystal substrate according to any one of claims 1 to 3, wherein the oxide single crystal layer has a thickness of 100 nm or less.   The diamond single crystal substrate according to any one of claims 1 to 4, wherein the metal single crystal layer has a thickness of 100 to 5000 nm.   The diamond single crystal substrate according to any one of claims 1 to 5, wherein an amorphous layer is provided between the silicon single crystal substrate and the oxide single crystal substrate.   A method for producing a diamond single crystal substrate, comprising: producing an oxide single crystal layer on a silicon single crystal substrate; further producing a metal single crystal layer thereon; and further producing a diamond single crystal film thereon.   The diamond single crystal substrate manufacturing method according to claim 7, wherein the diamond single crystal is manufactured using any one of a microwave plasma CVD method, a filament CVD method, a high frequency CVD method, and a direct current arc plasma method. The diamond single crystal according to claim 7 or 8, wherein the oxide single crystal is manufactured using any one of a high frequency sputtering method, a direct current sputtering method, a molecular beam epitaxy method, an electron gun vapor deposition method, and a laser ablation method. Crystal substrate manufacturing method.

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