JP5929520B2 - Method for producing diamond film and composite substrate used therefor - Google Patents

Description

  The present invention relates to a method for producing a diamond-based film having a large principal surface area, small warpage, and few cracks, and a composite substrate used therefor.

  The diamond-based film is preferably used as a substrate and a semiconductor layer of a semiconductor device such as a light emitting device or an electronic device. As a substrate for depositing such a diamond-based film, a diamond substrate is most excellent from the viewpoint of matching or approaching the lattice constant and the thermal expansion coefficient between the substrate and the diamond-based film. However, the diamond substrate is very expensive, and it is difficult to obtain a large-diameter diamond substrate having a main surface diameter exceeding 1 inch.

  For this reason, as a method for forming a diamond-based film, for example, Japanese Patent Laid-Open No. 2006-250767 (Patent Document 1) discloses CVD (chemical) using a single crystal silicon substrate having a surface formed with an oxide film and a quartz substrate. JP-A-2007-284285 (Patent Document 2) discloses a CVD method using single crystal silicon and single crystal silicon carbide as a substrate.

JP 2006-250767 A JP 2007-284285 A

  In the diamond film forming method disclosed in Japanese Patent Application Laid-Open No. 2006-250767 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2007-284285 (Patent Document 2), a diamond film to be formed and a single film used as a substrate are used. Since the thermal expansion coefficients of crystalline silicon, quartz, and single crystal silicon carbide are different, there has been a problem that the diamond film is warped or cracked.

  The present invention solves the above-described problems, and forms a diamond-based film using a low-cost composite substrate including a support substrate that has a thermal expansion coefficient that matches or approximates that of a diamond crystal and is easy to remove, A diamond-based film having a large main surface area, small warpage, small cracks and good crystallinity can be obtained, and then the support substrate is removed, so that the main surface area is large and the warpage is small and cracks are generated. It is an object of the present invention to provide a method for producing a diamond-based film that can efficiently extract a diamond-based film having a good crystallinity at a low cost, and a composite substrate used therefor.

According to one aspect, the present invention includes a support substrate that dissolves in an acid, and a single crystal film disposed on a main surface side of the support substrate, and the thermal expansion coefficient in the main surface of the support substrate is diamond. compared to the thermal expansion coefficient of the crystal, rather less than the 1.2 times greater than 0.8 times, the single crystal film, Si film is major surface (001) plane, a major surface (001) plane diamond The composite substrate is a film or any one of GaAs films whose main surface is the (001) plane .

  In the composite substrate according to the present invention, the support substrate may include a composite oxide containing silicon.

According to another aspect, the present invention includes a support substrate that dissolves in an acid, and a single crystal film disposed on the main surface side of the support substrate, and the thermal expansion coefficient in the main surface of the support substrate is compared to the thermal expansion coefficient of diamond crystals, rather less than the 1.2 times greater than 0.8 times, the single crystal film, Si film is major surface (001) plane, the principal surface is a (001) plane A diamond substrate, a step of preparing a composite substrate which is any one of a GaAs film whose principal surface is a (001) surface, and a diamond-based material on the principal surface of the single crystal film disposed on the principal surface side of the support substrate Forming a film, and a method for producing a diamond-based film.

The method for producing a diamond-based film according to the present invention may further include a step of removing the support substrate by dissolving it in an acid after the step of forming the diamond-based film. Further, the area of the main surface of the single crystal film of the supporting substrate can be 5 cm ² or more. Further, the step of forming the diamond-based film includes a sub-step of forming a diamond-based buffer layer on the main surface of the single-crystal film and a sub-step of forming a diamond-based single crystal layer on the main surface of the diamond-based buffer layer. And can be included.

  According to the present invention, the area of the main surface is increased by forming a diamond-based film using a low-cost composite substrate including a support substrate that has a thermal expansion coefficient that matches or approximates that of a diamond crystal and is easy to remove. A diamond-based film with low warpage, less cracking, and good crystallinity can be obtained. Thereafter, by removing the supporting substrate from the composite substrate, a diamond-based film having a large principal surface area, small warpage, few cracks and good crystallinity can be efficiently and inexpensively taken out.

It is a schematic sectional drawing which shows an example of the composite substrate concerning this invention. It is a schematic sectional drawing which shows an example of the manufacturing method of the diamond-type film | membrane concerning this invention. Here, (A) shows a step of preparing a composite substrate, (B) shows a step of forming a diamond-based film, and (C) shows a step of removing the support substrate. It is a schematic sectional drawing which shows an example of the process of preparing the composite substrate in this invention.

[Composite substrate]
Referring to FIG. 1, a composite substrate 10 according to an embodiment of the present invention includes a support substrate 11 that dissolves in an acid, and a single crystal film 13 that is disposed on the main surface 11 m side of the support substrate 11. The thermal expansion coefficient in the main surface 11m of the support substrate 11 is larger than 0.8 times and smaller than 1.2 times compared with the thermal expansion coefficient of the diamond crystal.

  In the composite substrate 10 of the present embodiment, the thermal expansion coefficient in the main surface 11m of the support substrate 11 is larger than 0.8 times and smaller than 1.2 times the thermal expansion coefficient of the diamond crystal. Even if the area of the main surface 13m is large on the main surface 13m of the single crystal film 13 formed on the main surface 11m, the warp is small, the generation of cracks is small, the crystallinity is good, the dislocation density is low, and the crystallinity is good. A diamond-based film can be formed. In addition, since the support substrate 11 is dissolved in an acid, a diamond-based film is formed on the main surface 13m of the single crystal film 13 of the composite substrate 10, and then the support substrate 11 is removed with an acid, whereby the single crystal film 13 is removed. Thus, a diamond-based film having a large surface area formed on the main surface 13m and having a large warp, a small amount of cracking, and good crystallinity can be obtained efficiently and at low cost.

(Support substrate)
The support substrate 11 of the composite substrate 10 of the present embodiment has a large area on the main surface on the main surface 13m of the single crystal film 13 formed on the main surface 11m of the support substrate 11, and the occurrence of cracks is small. From the viewpoint of forming a diamond-based film having good crystallinity, the thermal expansion coefficient in the main surface 11m of the support substrate 11 is larger than 0.8 times and larger than 1.2 times compared with the thermal expansion coefficient of the diamond crystal. It is necessary to be small and is preferably larger than 0.9 times and smaller than 1.1 times, more preferably larger than 0.98 times and smaller than 1.02 times. The support substrate 11 needs to be dissolved in an acid from the viewpoint of efficiently removing the support substrate from the formed diamond-based film at low cost.

  The support substrate 11 has a thermal expansion coefficient in the main surface 11m of the support substrate 11 that is greater than 0.8 times and less than 1.2 times the thermal expansion coefficient of the diamond crystal, and is soluble in acid. There is no particular limitation, and it may be single crystal, polycrystal, or amorphous, but a sintered body that is polycrystalline is preferred from the viewpoint of easy adjustment of the thermal expansion coefficient.

The support substrate 11 preferably contains a complex oxide containing silicon (Si) from the viewpoint of easy adjustment of its thermal expansion coefficient and dissolution in an acid. Here, the composite oxide refers to an oxide containing oxides of a plurality of types of elements. That is, the composite oxide containing silicon (Si) refers to an oxide containing silicon oxide and an oxide of an element other than silicon. For example, silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) SiO ₂ —Al ₂ O ₃ composite oxide formed, SiO ₂ —MgO composite oxide formed from silica (SiO ₂ ) and magnesia (MgO), silica (SiO ₂ ) and alumina (Al ₂ O ₃ ) Preferred examples include SiO ₂ —Al ₂ O ₃ —MgO composite oxides formed of MgO and magnesia (MgO). Here, the support substrate 11 containing silica (SiO ₂ ) is dissolved in hydrofluoric acid (HF) or the like. The support substrate 11 containing magnesia (MgO) is dissolved in hydrofluoric acid (HF), nitric acid (HNO ₃ ), sulfuric acid (H ₂ SO ₄ ), phosphoric acid (H ₃ PO ₄ ), and the like.

  Note that in the support substrate 11, the type and ratio (for example, molar ratio) of silicon (Si) and other elements (for example, metal elements) in the composite oxide are determined by ICP-AES (Inductively Coupled Plasma-Emission Spectroscopy) method. , ICP-MS (inductively coupled plasma-mass spectrometry) method, GDMS (glow discharge mass spectrometry) method, and the like.

Further, the support substrate 11 can be easily adjusted in its expansion coefficient by changing the type and ratio of the raw material, and is in the range of more than 0.8 times and less than 1.2 times the thermal expansion coefficient of the diamond crystal. From the viewpoint that the thermal expansion coefficient can be easily obtained, silica (SiO ₂ ) having a lower thermal expansion coefficient than that of the tiremond crystal, alumina (Al ₂ O ₃ ) having a higher thermal expansion coefficient than that of the diamond crystal, and / or Alternatively, silicon oxide and metal such as SiO ₂ —Al ₂ O ₃ composite oxide, SiO ₂ —MgO composite oxide, and SiO ₂ —Al ₂ O ₃ —MgO composite oxide formed by combining with magnesia (MgO) A sintered body containing an oxide complex oxide is particularly preferable.

At this time, since the thermal expansion coefficients of the support substrate 11 and the diamond crystal generally vary greatly depending on their temperatures, it is important to determine the temperature or thermal expansion coefficient in any temperature range. The object of the present invention is to produce a diamond-based film having a small warp on a composite substrate, and the diamond-based film is formed on the composite substrate at the film-forming temperature of the diamond-based film by raising the temperature from room temperature. After the film formation, the temperature is lowered to room temperature and the diamond-based film formed on the composite substrate is taken out, so that the average thermal expansion coefficient of the support substrate and the diamond crystal from room temperature to the film formation temperature of the diamond-based film is It is considered appropriate to handle them as the thermal expansion coefficient of diamond crystals. For this reason, in the present invention, the thermal expansion coefficients of the support substrate and the diamond crystal have an average heat in a N ₂ gas atmosphere from room temperature (specifically, 25 ° C.) to 800 ° C. which is the film formation temperature of the diamond-based film. It will be determined by the expansion coefficient.

(Single crystal film)
The single crystal film 13 disposed on the main surface 11m side of the support substrate 11 of the composite substrate 10 of this embodiment is a diamond crystal (from the viewpoint of growing a diamond-based film having low warpage, low dislocation density, and good crystallinity. Those having the same tetragonal crystal structure as that of (tetragonal diamond type structure) are preferred, and a Si film (tetragonal diamond type structure) having a main surface 13m of (001) plane and main surface 13m of (001). ) Surface diamond film (tetragonal diamond type structure), and GaAs film (tetragonal zinc blende type structure) having a main surface 13m of (001) surface are preferable.

The area of the main surface 13m of the single crystal film 13 in the composite substrate 10 is not particularly limited, from the viewpoint of growing a diamond-based film is large area of the main surface, is preferably 5 cm ² or more, 15cm ² More preferably, it is more preferably 45 cm ² or more.

(Adhesive layer)
In the composite substrate 10 of the present embodiment, the adhesive layer 12 is preferably formed between the support substrate 11 and the single crystal film 13 from the viewpoint of increasing the bonding strength between the support substrate 11 and the single crystal film 13. The adhesive layer 12 is not particularly limited, from the viewpoint of removing the effect of high acid to increase the bonding strength between the supporting substrate 11 and the single crystal film 13, a silicon oxide layer such as a SiO _2, Si ₃ N ₄ layers A silicon nitride layer such as a metal oxide layer such as a MgO layer, a metal nitride layer such as a TiN layer, and the like are preferable. Here, the SiO ₂ layer is dissolved in hydrofluoric acid (HF), and the Si ₃ N ₄ layer is hydrofluoric acid (HF) or heated phosphoric acid (phosphoric acid (H ₃ heated to 150 ° C. to 160 ° C.). refers to PO _4), hereinafter the same. dissolved in), MgO layer is dissolved in nitric acid (HNO _3), sulfuric acid (H ₂ SO _4), or phosphoric acid (H ₃ PO _4), TiN layer is nitric acid (HNO ₃ ) Dissolve in.

(Production method of composite substrate)
The manufacturing method of the composite substrate is the same as the preparation step of the composite substrate in the diamond-based film manufacturing method described later.

[Diamond production method]
Referring to FIG. 2, a diamond-based film manufacturing method according to another embodiment of the present invention includes a support substrate 11 that dissolves in an acid, and a single crystal film 13 that is disposed on the main surface 11 m side of the support substrate 11. And a step of preparing the composite substrate 10 having a thermal expansion coefficient in the main surface 11m of the support substrate 11 larger than 0.8 times and smaller than 1.2 times compared to the thermal expansion coefficient of the diamond crystal (FIG. 2 (A)) and a step of forming a diamond-based film 20 on the main surface 13m of the single crystal film 13 disposed on the main surface 11m side of the support substrate 11 (FIG. 2B). . Here, the diamond-based film refers to a film containing diamond, and examples thereof include a diamond film and a diamond-like carbon (DLC) film.

  According to the method for producing a diamond-based film of the present embodiment, the support substrate 11 that dissolves in an acid and the single crystal film 13 disposed on the main surface 11 m side of the support substrate 11 are included. The main surface 13m of the single crystal film 13 of the composite substrate 10 using the composite substrate 10 having a thermal expansion coefficient in the surface 11m larger than 0.8 times and smaller than 1.2 times the thermal expansion coefficient of the diamond crystal. By forming the diamond-based film 20 thereon, the diamond-based film 20 having a large principal surface area, small warpage, less cracking, and good crystallinity can be obtained efficiently.

(Preparation process of composite substrate)
Referring to FIG. 2A, in the method of manufacturing a diamond-based film according to this embodiment, first, a support substrate 11 that dissolves in an acid, and a single crystal film 13 disposed on the main surface 11m side of the support substrate 11 are used. And a step of preparing a composite substrate 10 having a thermal expansion coefficient in the main surface 11m of the support substrate 11 that is larger than 0.8 times and smaller than 1.2 times that of the diamond crystal. .

  In the composite substrate 10, the support substrate 11 and the single crystal film have a thermal expansion coefficient in the main surface 11 m of the support substrate 11 that is larger than 0.8 times and smaller than 1.2 times that of the diamond crystal. 13 can be formed on the main surface 13m of the single crystal film 13 with the diamond-based film 20 having a large crystal surface area, large warpage, small cracks, and good crystallinity. In the composite substrate 10 described above, since the support substrate 11 is dissolved in an acid, the support substrate 11 is removed, so that a diamond-based film having a large principal surface area, less warpage, less cracking, and good crystallinity. Can be taken out efficiently and at low cost.

  In addition, the method of disposing the single crystal film 13 on the main surface 11m side of the support substrate 11 of the composite substrate 10 is not particularly limited, and a method of growing the single crystal film 13 on the main surface 11m of the support substrate 11 (first step). 1), a method of removing the base substrate after the single crystal film 13 formed on the main surface of the base substrate (not shown) is bonded to the main surface 11m of the support substrate 11 (second method) ), A single crystal (not shown) is bonded to the main surface 11m of the support substrate 11, and then the single crystal is separated from the bonding surface by a surface having a predetermined depth to be formed on the main surface 11m of the support substrate 11. A method of forming the single crystal film 13 (third method) is exemplified. When the support substrate is a polycrystalline sintered body, the first method is difficult, and therefore any one of the second and third methods is preferably used. In the second method, the method for bonding the single crystal film 13 to the support substrate 11 is not particularly limited. The method for bonding the single crystal film 13 directly to the main surface 11m of the support substrate 11, Examples thereof include a method in which the single crystal film 13 is bonded to the main surface 11m with the adhesive layer 12 interposed. In the third method, the method for attaching the single crystal to the support substrate 11 is not particularly limited, and the method of attaching the single crystal directly to the main surface 11m of the support substrate 11 or the main surface 11m of the support substrate 11 may be used. Examples thereof include a method of bonding single crystals with the adhesive layer 12 interposed.

  The step of preparing the composite substrate 10 is not particularly limited. From the viewpoint of efficiently preparing the composite substrate 10 with low cost and high quality, for example, the second method described above with reference to FIG. , A sub-process for preparing the support substrate 11 (FIG. 3A), a sub-process for forming the single crystal film 13 on the main surface 30n of the base substrate 30 (FIG. 3B), a support substrate, 11 and the single crystal film 13 (FIG. 3C) and a sub-process of removing the base substrate 30 (FIG. 3D).

  Referring to FIG. 3C, in the sub-step of bonding the support substrate 11 and the single crystal film 13, an adhesive layer 12a is formed on the main surface 11m of the support substrate 11 (FIG. 3C1). After forming the adhesive layer 12b on the main surface 13n of the single crystal film 13 grown on the main surface 30n of the base substrate 30 (FIG. 3 (C2)), the adhesive layer 12a formed on the support substrate 11 By bonding the main surface 12am and the main surface 12bn of the adhesive layer 12b formed on the single crystal film 13 formed on the base substrate 30, the adhesive layer 12a and the adhesive layer 12b are bonded to each other. Then, the supporting substrate 11 and the single crystal film 13 are bonded to each other with the adhesive layer 12 interposed therebetween (FIG. 3 (C3)). However, as long as the support substrate 11 and the single crystal film 13 can be bonded to each other, the support substrate 11 and the single crystal film 13 can be directly bonded together without the adhesive layer 12 interposed.

  A specific method for bonding the support substrate 11 and the single crystal film 13 is not particularly limited, but from the viewpoint of maintaining the bonding strength even at a high temperature after bonding, the bonded surface is washed and bonded as it is. Direct bonding method in which bonding is performed by raising the temperature to about 1 to 1200 ° C., surface activation for bonding at a low temperature of about room temperature (for example, 25 ° C.) to about 400 ° C. after cleaning the bonded surfaces and activating them with plasma or ions. The method is preferably used.

In the composite substrate 10 thus obtained, the materials and physical properties of the support substrate 11, the single crystal film 13, and the adhesive layer 12 are as described above, and thus are not repeated here. Here, the area of the main surface 13m of the single crystal film 13 in the composite substrate 10 is not particularly limited, but is preferably 5 cm ² or more from the viewpoint of forming a diamond-based film having a large main surface area. More preferably, it is 15 cm ² or more, and further preferably 45 cm ² or more.

(Diamond film deposition process)
Referring to FIG. 2B, the method for manufacturing a diamond-based film according to this embodiment includes a step of forming a diamond-based film 20 on the main surface 13m of the single crystal film 13 in the composite substrate 10 next. .

  In the composite substrate 10 prepared in the composite substrate preparation step, the thermal expansion coefficient in the main surface 11m of the support substrate 11 is larger than 0.8 times and 1.2 times larger than the thermal expansion coefficient of the diamond crystal. Since the smaller support substrate 11 and the single crystal film 13 are included, the diamond-type film 20 having a large crystal surface with a large area of the main surface 20m on the main surface 13m of the single crystal film 13 and a small warp and less cracking. Can be formed.

  The method for forming the diamond-based film is not particularly limited, but from the viewpoint of forming a diamond-based film having a low dislocation density and good crystallinity, a CVD (chemical vapor deposition) method is preferable. The film formation temperature of the diamond film is not particularly limited, but is preferably 700 ° C. or higher and 1000 ° C. or lower from the viewpoint of forming a diamond film having a low dislocation density and good crystallinity.

  The step of forming the diamond-based film 20 is not particularly limited, but from the viewpoint of forming the diamond-based film 20 having a low dislocation density and good crystallinity, the main surface 13m of the single crystal film 13 of the composite substrate 10 is formed. It is preferable to include a sub-process for forming the diamond-based buffer layer 21 and a sub-process for forming the diamond-based single crystal layer 23 on the main surface 21 m of the diamond-based buffer layer 21. Here, the diamond-based buffer layer 21 is a part of the diamond-based film 20, another part of the diamond-based film 20, and crystallinity that can be grown at a temperature lower than the growth temperature of the diamond-based single crystal layer 23. Refers to a low or amorphous layer.

  The diamond-based single crystal layer 23 can also be grown as the diamond-based film 20 on the single-crystal film 13 without growing the diamond-based buffer layer 21. Such a method is suitable when the mismatch in lattice constant between the single crystal film 13 and the diamond-based film 20 formed thereon is small.

  In the method for manufacturing a diamond-based film according to the present embodiment, after the step of forming the diamond-based film 20 (FIG. 2B), the step of removing the support substrate 11 by dissolving it in an acid (FIG. 2C). ). After the diamond-based film 20 is formed on the main surface 13m of the single crystal film 13 disposed on the main surface 11m side of the support substrate 11 of the composite substrate 10, the support substrate 11 is dissolved in an acid and removed. The diamond-based film 20 having a large principal surface area, small warpage, few cracks, and good crystallinity can be efficiently taken out.

(Support substrate removal process)
Referring to FIG. 2C, the method for manufacturing a diamond-based film according to the present embodiment can include a step of removing the support substrate 11 by dissolving it in an acid.

  The composite substrate 10 prepared in the composite substrate preparation step is dissolved on the acid so that the support substrate 11 is dissolved in the acid, and the support substrate 11 is removed by dissolving the support substrate 11 on the main surface 13 m of the single crystal film 13. The diamond-based film 20 having a large area of the main surface 20m thus formed and a small warpage and good crystallinity is taken out. Here, when the single crystal film 13 is formed of a diamond-based single crystal film such as a diamond single-crystal film, a diamond-based film formed entirely of a diamond-based material is obtained.

Example 1
1. Measurement of Thermal Expansion Coefficient of Diamond Crystal A sample for evaluation having a size of 4 mm × 4 mm × 20 mm was cut out from a diamond single crystal crystallized by a high pressure synthesis method. Here, since the diamond single crystal has no direction specificity with respect to the thermal expansion coefficient, the cutting direction was arbitrary.

About said sample for evaluation, the average thermal expansion coefficient when it heated up from room temperature (25 degreeC) to 800 degreeC was measured by TMA (thermomechanical analysis). Specifically, the thermal expansion coefficient of the evaluation sample was measured in a nitrogen gas flow atmosphere by a differential expansion method using TMA8310 manufactured by Rigaku Corporation. The average thermal expansion coefficient α _D at 25 ° C. to 800 ° C. of the diamond crystal obtained by such measurement was 2.30 × 10 ⁻⁶ / ° C.

2. Preparation Step of Composite Substrate (1) Sub-Step of Preparing Support Substrate Referring to FIG. 3 (A), a mixture of SiO ₂ , Al ₂ O ₃ and MgO in a predetermined molar ratio is used as a material for support substrate 11. Eight types of SiO ₂ —Al ₂ O ₃ —MgO-based sintered bodies A to H were prepared by sintering at 1700 ° C. for 1 hour under a pressure of 50 MPa in a uniaxial direction under an argon gas atmosphere. The obtained eight types of SiO ₂ —Al ₂ O ₃ —MgO-based sintered bodies A to H were confirmed by X-ray diffraction, and all of them were SiO ₂ , Al ₂ O ₃ , mullite (3Al ₂ O _{3 · 2SiO 2 ~2Al 2 O 3 ·} SiO 2 or Al ₆ O ₁₃ Si ₂₎ and MgO were present. Each of the eight types of SiO ₂ —Al ₂ O ₃ —MgO-based sintered bodies has a size of 4 mm × 4 mm × 20 mm (the longitudinal direction is substantially parallel to the main surface of the support substrate cut out from the sintered body). Direction) measurement sample was cut out. Here, since the SiO ₂ —Al ₂ O ₃ —MgO-based sintered body has no direction specificity with respect to the thermal expansion coefficient, the cutting direction was arbitrary. For these measurement samples, the average thermal expansion coefficient α _S at the time of temperature increase from room temperature (25 ° C.) to 800 ° C. was measured in the same manner as described above.

The SiO ₂ —Al ₂ O ₃ —MgO-based sintered body A has a mixing molar ratio of SiO ₂ , Al ₂ O ₃ and MgO (hereinafter referred to as a mixing molar ratio SiO ₂ : Al ₂ O ₃ : MgO) of 65: The average thermal expansion coefficient α _S (hereinafter simply referred to as the average thermal expansion coefficient α _S ) from 25 ° C. to 800 ° C. is 1.70 × 10 ⁻⁶ / ° C., and the average thermal expansion of the diamond crystal is 30: 5. The ratio of the thermal expansion coefficient α _S of the sintered body to the coefficient α _D (hereinafter referred to as α _S / α _D ratio) was 0.739. In the SiO ₂ —Al ₂ O ₃ —MgO-based sintered body B, the mixing molar ratio SiO ₂ : Al ₂ O ₃ : MgO is 60: 35: 5, and the average thermal expansion coefficient α _S is 1.92 × 10 ^{− 6} / ° C. and the α _S / α _D ratio was 0.835. The SiO ₂ —Al ₂ O ₃ —MgO-based sintered body C has a mixing molar ratio of SiO ₂ : Al ₂ O ₃ : MgO of 55: 40: 5 and an average thermal expansion coefficient α _S of 2.14 × 10 ^{−. 6} / ° C. and the α _S / α _D ratio was 0.930. The SiO ₂ —Al ₂ O ₃ —MgO-based sintered body D has a mixed molar ratio of SiO ₂ : Al ₂ O ₃ : MgO of 52: 43: 5 and an average thermal expansion coefficient α _S of 2.27 × 10 ^{−. 6} / ° C. and the α _S / α _D ratio was 0.987. The SiO ₂ —Al ₂ O ₃ —MgO-based sintered body E has a mixed molar ratio of SiO ₂ : Al ₂ O ₃ : MgO of 50: 45: 5 and an average thermal expansion coefficient α _S of 2.34 × 10 ^{− 6} / ° C., and the α _S / α _D ratio was 1.017. SiO ₂ -Al ₂ O ₃ -MgO based sintered body F, the mixing molar ratio of _{SiO 2: Al 2 O 3:} MgO is 46: 49: 5, average thermal expansion coefficient alpha _S is 2.52 × 10 ^{- 6} / ° C. and the α _S / α _D ratio was 1.096. The SiO ₂ —Al ₂ O ₃ —MgO-based sintered body G has a mixed molar ratio of SiO ₂ : Al ₂ O ₃ : MgO of 45: 50: 5 and an average coefficient of thermal expansion α _S of 2.57 × 10 ^{− 6} / ° C. and the α _S / α _D ratio was 1.117. The SiO ₂ —Al ₂ O ₃ —MgO-based sintered body H has a mixed molar ratio of SiO ₂ : Al ₂ O ₃ : MgO of 40: 55: 5 and an average thermal expansion coefficient α _S of 2.79 × 10 ^{−. 6} / ° C. and the α _S / α _D ratio was 1.213.

From the SiO ₂ —Al ₂ O ₃ —MgO-based sintered bodies A to H, a support substrate having a diameter of 4 inches (101.6 mm) and a thickness of 1 mm is cut out, and both main surfaces of each support substrate are mirror surfaces. To support substrates A to H. That is, the average thermal expansion coefficients of the supporting substrates A to H from 25 ° C. to 1000 ° C. are the average thermal expansion coefficients of the SiO ₂ —Al ₂ O ₃ —MgO-based sintered bodies A to H from 25 ° C. to 800 ° C., respectively. be equivalent to. The results are summarized in Table 1.

(2) Sub-Process for Forming Single Crystal Film on Base Substrate With reference to FIG. 3B, the base substrate 30 has a main surface 30n of (001) surface polished to a mirror surface and has a diameter of 5 inches ( 127 mm) and a 0.5 mm thick Si substrate was prepared.

A diamond film having a thickness of 0.4 μm was formed as the single crystal film 13 on the main surface 30n of the Si substrate (underlying substrate 30) by a CVD (chemical vapor deposition) method. The film forming conditions were such that CH ₄ (methane) gas was used as the source gas, H ₂ (hydrogen) gas was used as the carrier gas, the film forming temperature (substrate temperature) was 800 ° C., and the film forming pressure was 1 atm. The main surface 13m of the diamond film (single crystal film 13) thus obtained has a plane orientation with an off angle within ± 1 ° from the (001) plane, and is measured using an AFM (atomic force microscope). The RMS (root mean square) roughness (referred to the root mean square roughness Rq defined in JIS B0601: 2001, hereinafter the same) in a 10 μm × 10 μm square area was a mirror surface of 1 nm or less.

(3) Sub-process for bonding support substrate and single crystal film Referring to (C1) in FIG. 3 (C), each of the main substrates A to H (support substrate 11) in FIG. A SiO ₂ film having a thickness of 2 μm was formed on the surface 11 m by the CVD method. Next, the SiO ₂ film having a thickness of 2 μm on each main surface 11 m of each of the support substrates A to H (support substrate 11) is polished with CeO ₂ slurry, so that only the SiO ₂ layer having a thickness of 0.2 μm is obtained. The adhesive layer 12a was made to remain. Thus, the gap is filled in each of the main surfaces 11m of the supporting substrate A to H (the supporting substrate 11), SiO ₂ layer having a thickness of 0.2μm having a flat main surface 12am (adhesive layer 12a) was obtained .

Further, referring to (C2) in FIG. 3C, on the main surface 13n of the diamond film (single crystal film 13) formed on the Si substrate (underlying substrate 30) in FIG. 3B. A SiO ₂ film having a thickness of 2 μm was formed by a CVD method. Next, this SiO ₂ film having a thickness of 2 μm was polished using a CeO ₂ slurry, so that only the SiO ₂ layer having a thickness of 0.2 μm was left to form an adhesive layer 12b.

Next, referring to (C3) in FIG. 3C, the main surface 12am of the SiO ₂ layer (adhesive layer 12a) formed on each of the support substrates A to H (support substrate 11) and the Si substrate (underlayer) The main surface 12bn of the SiO ₂ layer (adhesive layer 12b) formed on the diamond film (single crystal film 13) formed on the substrate 30) is cleaned and activated by argon plasma, and then the SiO ₂ layer The main surface 12am of the (adhesive layer 12a) and the main surface 12bn of the SiO ₂ layer (adhesive layer 12b) were bonded together and heat-treated at 300 ° C. for 2 hours in a nitrogen atmosphere.

(4) Sub-process for removing base substrate Referring to FIG. 3D, the main surface and side surfaces of the back side (side where single crystal film 13 is not bonded) of support substrates A to H (support substrate 11) are After covering and protecting with wax 40, the Si substrate (underlying substrate 30) was removed by etching using a mixed acid aqueous solution containing 10% by mass of hydrofluoric acid and 3% by mass of nitric acid. Thus, composite substrates A to H in which the diamond film (single crystal film 13) was arranged on the main surface 11m side of each of the support substrates A to H (support substrate 11) were obtained.

3. Step of Forming Diamond Film Referring to FIG. 2B, the main surface 13m of the diamond film (single crystal film 13) of composite substrate A to H (composite substrate 10) (the main surface is the (001) surface). A diamond film (diamond-based film 20) was formed by CVD. In the film formation of the diamond film (diamond-based film 20), the film formation conditions are such that CH ₄ (methane) gas is used as the source gas and H ₂ (hydrogen) gas is used as the carrier gas, and the film formation temperature (substrate) (Temperature) A diamond single crystal layer (diamond-based single crystal layer 23) having a thickness of 5 μm was grown at 800 ° C. and a film forming pressure of 1 atm. Here, the growth rate of the diamond single crystal layer was 1 μm / hr. Thereafter, the wafers A to H on which the diamond films were formed on the composite substrates A to H were cooled to room temperature (25 ° C.) at a rate of 10 ° C./min.

  For wafers A to H taken out from the film forming apparatus after cooling to room temperature, the warpage of the wafer, the number of cracks in the diamond film, and the dislocation density were measured. Here, the shape and amount of warpage of the wafer were measured by optical interference fringes observed on the main surface on the diamond film side using FM200EWafer manufactured by Corning Tropel. Here, the amount of warpage of the wafer was evaluated as “very small” when less than 3 μm, “small” when 3 μm or more but less than 10 μm, and “large” when 10 μm or more. The number density of cracks in the diamond film is determined by measuring the number of cracks per unit length using a Nomarski microscope. The book / mm or more and less than 10 / mm was evaluated as “many”, and the book / mm or more was evaluated as “very many”. The dislocation density of the diamond film was measured by the number of dark spots per unit area by CL (cathode luminescence). In this example, cracks generated in the diamond film were minute ones that did not penetrate the film.

The wafer A warped in a concave shape on the diamond film side, the warpage amount was 13 μm, the diamond film had a large number of cracks, and the dislocation density of the diamond film was 9 × 10 ⁵ cm ⁻² . Wafer B warped in a concave shape on the diamond film side, the warpage amount was 7 μm, the number of cracks in the diamond film was small, and the dislocation density of the diamond film was 7 × 10 ⁵ cm ⁻² . The wafer C warped in a concave shape on the diamond film side, the warpage amount was 4 μm, the crack number density of the diamond film was small, and the dislocation density of the diamond film was 3 × 10 ⁵ cm ⁻² . The wafer D was warped convexly on the diamond film side, the warpage amount was 2 μm, the crack number density of the diamond film was extremely small, and the dislocation density of the diamond film was 1 × 10 ⁵ cm ⁻² . The wafer E was warped convexly on the diamond film side, the warpage amount was 3 μm, the crack number density of the diamond film was extremely small, and the dislocation density of the diamond film was 2 × 10 ⁵ cm ⁻² . The wafer F was warped convexly on the diamond film side, the warpage amount was 6 μm, the crack number density of the diamond film was small, and the dislocation density of the diamond film was 5 × 10 ⁵ cm ⁻² . The wafer G was warped in a convex shape on the diamond film side, the warpage amount was 9 μm, the crack number density of the diamond film was small, and the dislocation density of the diamond film was 8 × 10 ⁵ cm ⁻² . The wafer H was warped convexly on the diamond film side, the warpage amount was 14 μm, the crack number density of the diamond film was large, and the dislocation density of the diamond film was 10 × 10 ⁵ cm ⁻² .

4). Step of removing support substrate Referring to FIG. 2C, wafers A to H obtained above are immersed in a 10% by mass hydrofluoric acid aqueous solution, thereby supporting substrates A to H (support substrate 11). ) And the SiO ₂ layer (adhesive layer 12) are dissolved and dissolved, and the diamond films A to H (diamond-based film 20) formed on the main surface 13m of the diamond single crystal film (single crystal film 13). was gotten. It should be noted that warpage is also observed in the diamond films A to H (diamond-based film 20) from which the supporting substrates A to H and the SiO ₂ layer are removed from the wafers A to H due to optical interference fringes observed using the Corning Tropel FM200EWafer It was recognized by the measurement, and the magnitude relationship of the warpage of the wafers A to H was maintained as the magnitude relationship of the warpage of the diamond films A to H.

Referring to Table 1, the thermal expansion coefficient (average thermal expansion coefficient α _S ) in the main surface of the support substrate is greater than 0.8 times the thermal expansion coefficient (average thermal expansion coefficient α _D ) of the diamond crystal and is 1.2. By using a composite substrate having a support substrate smaller than twice (ie, 0.8 <(α _S / α _D ratio) <1.2) (wafers B to G), warpage is small, cracks are generated, and dislocation density is small. A diamond film having low crystallinity and good crystallinity could be formed. From the viewpoint of further reducing the warpage and dislocation density of the diamond film, the thermal expansion coefficient (average thermal expansion coefficient α _S ) in the main surface of the support substrate of the composite substrate is the thermal expansion coefficient (average thermal expansion coefficient) of the diamond crystal. α _D ) is preferably larger than 0.9 times and smaller than 1.1 times (that is, 0.9 <(α _S / α _D ratio) <1.1) (wafers C to F). It is more preferable that the expansion coefficient α _D is larger than 0.98 times and smaller than 1.02 times (that is, 0.98 <(α _S / α _D ratio) <1.02) (wafers _{D to} E).

  In the above embodiment, an example is shown in which an undoped diamond film is formed on a composite substrate. However, when a diamond film to which n-type or p-type conductivity is imparted by doping is formed, doping is performed. Even when a diamond film having a higher specific resistance was formed, the same result as in the above example was obtained.

  In addition, when a diamond-based film such as a diamond-like carbon (DLC) film was formed instead of the diamond film, the same result as in the above example was obtained.

  In the practice of the present invention, a known dislocation reduction technique such as an ELO (Epitaxial Lateral Overgrowth) technique can be applied when forming a diamond-based film.

  Further, after removing the diamond-based film on the composite substrate, the diamond-based film may be transferred to another support substrate when the support substrate of the composite substrate is removed.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  DESCRIPTION OF SYMBOLS 10 Composite substrate, 11 Support substrate, 11m, 12m, 12am, 12bn, 13m, 13n, 20m, 21m, 23m, 30n Main surface, 12, 12a, 12b Adhesive layer, 13 Single crystal film, 20 Diamond system film, 21 Diamond System buffer layer, 23 diamond single crystal layer, 30 base substrate, 40 wax.

Claims (6)

A support substrate that dissolves in an acid, and a single crystal film disposed on a main surface side of the support substrate,
Thermal expansion coefficient of the main surface of the supporting substrate, as compared to the thermal expansion coefficient of diamond crystals, rather less than the 1.2 times greater than 0.8 times,
The single crystal film is a composite substrate that is any one of a Si film whose principal surface is a (001) plane, a diamond film whose principal surface is a (001) plane, and a GaAs film whose principal surface is a (001) plane. .   The composite substrate according to claim 1, wherein the support substrate includes a composite oxide containing silicon. A support substrate that dissolves in an acid, and a single crystal film that is disposed on a main surface side of the support substrate, and a thermal expansion coefficient in the main surface of the support substrate is larger than that of a diamond crystal. , rather less than the 1.2 times greater than 0.8 times, the single crystal film, Si film is major surface (001) plane, the diamond film is major surface (001) plane, main surface (001 ) Preparing a composite substrate that is one of the GaAs films that are surfaces ;
Forming a diamond-based film on the main surface of the single crystal film disposed on the main surface side of the support substrate.   The method for producing a diamond-based film according to claim 3, further comprising a step of removing the support substrate by dissolving the support substrate in an acid after the step of forming the diamond-based film. The method for producing a diamond-based film according to claim 3 or 4, wherein an area of a main surface of the single crystal film of the support substrate is 5 cm ² or more.   The step of forming the diamond-based film includes a sub-step of forming a diamond-based buffer layer on the main surface of the single-crystal film and a sub-step of forming a diamond-based single crystal layer on the main surface of the diamond-based buffer layer. A method for producing a diamond-based film according to any one of claims 3 to 5, comprising a step.

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