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JP-7856077-B2 - Seed crystal substrate and graphite susceptor with seed crystal substrate

JP7856077B2JP 7856077 B2JP7856077 B2JP 7856077B2JP-7856077-B2

Inventors

  • 中村 大輔
  • 伊藤 健治

Assignees

  • 株式会社豊田中央研究所

Dates

Publication Date
20260511
Application Date
20231005

Claims (10)

  1. A substrate having GaN seed crystals on its surface, An adhesion layer formed on the back surface of the substrate, The adhesive layer comprises a carbon film covering the aforementioned adhesion layer, The substrate consists of a GaN single crystal substrate or a GaN film-coated sapphire substrate. The aforementioned adhesion layer is made of Si. Seed crystal substrate.
  2. The seed crystal substrate according to claim 1, wherein the adhesion layer has a thickness of 10 nm or more and 200 nm or less.
  3. The seed crystal substrate according to claim 1, wherein the carbon film has a thickness of 5 nm or more and 100 nm or less.
  4. An expanded graphite sheet is disposed on the back side of the carbon film , The seed crystal substrate according to any one of claims 1 to 3, further comprising a bonding layer that bonds the carbon film and the expanded graphite sheet.
  5. The aforementioned bonding layer is Graphite particles and, The seed crystal substrate according to claim 4, further comprising a carbon layer interposed between the graphite particles.
  6. A seed crystal substrate according to any one of claims 1 to 3, A graphite susceptor is disposed on the back side of the seed crystal substrate, The seed crystal substrate is fixed to the graphite susceptor, and the rest of the substrate is fixed to the graphite susceptor. A graphite susceptor with a seed crystal substrate, wherein the absolute value of the difference in average thermal expansion coefficients between the substrate and the graphite susceptor is 0.5 × 10⁻⁶ K⁻¹ or less.
  7. The aforementioned fixed layer is Graphite particles and, A graphite susceptor with a seed crystal substrate according to claim 6, further comprising a carbon layer interposed between the graphite particles.
  8. The seed crystal substrate according to claim 4, A graphite susceptor is disposed on the back side of the seed crystal substrate, A graphite susceptor with a seed crystal substrate, comprising a fixed layer for fixing the seed crystal substrate to the graphite susceptor.
  9. The graphite susceptor with a seed crystal substrate according to claim 8, wherein the absolute value of the difference in the average thermal expansion coefficients between the substrate and the graphite susceptor is 0.5 × 10⁻⁶ K⁻¹ or less.
  10. The aforementioned fixed layer is Graphite particles and, A graphite susceptor with a seed crystal substrate according to claim 8, further comprising a carbon layer interposed between the graphite particles.

Description

This invention relates to a seed crystal substrate and a graphite susceptor with a seed crystal substrate, and more particularly, to a seed crystal substrate having a GaN seed crystal on its surface and a graphite susceptor with a seed crystal substrate having a GaN seed crystal on its surface. Gallium nitride (GaN) has traditionally been widely used, primarily in optical devices such as LEDs and lasers. Furthermore, GaN is a wide-bandgap semiconductor (bandgap: 3.39 eV), possessing high dielectric breakdown strength. This allows for thinner drift layers and reduced on-resistance, making it promising for applications not only in optical devices but also in power devices. Several methods are known for growing GaN crystals. For example, molecular beam epitaxy (MBE) and metal-organic vapor deposition (MOVPE) are used for growing crystals with relatively thin film thicknesses of a few micrometers. On the other hand, hydride vapor deposition (HVPE) is used for growing crystals on self-supporting substrates with film thicknesses exceeding 10 micrometers. The HVPE method, with its high crystal growth rate (approximately 100 μm/h), is suitable for creating self-supporting substrates. However, autodoping from the quartz reaction vessel inevitably introduces oxygen (O) impurities into the grown crystals. Since O impurities act as donors in GaN crystals, this posed a problem for the quality of the GaN single crystals. Therefore, the halogen-free vapor phase growth (HF-VPE) method described in Non-Patent Document 1 has been proposed as a crystal growth method for producing high-quality, large-diameter, and low-cost GaN self-supporting substrates. Non-patent document 1 contains: (1) A crucible that holds molten Ga and is kept at a high temperature, (2) NH3 gas supply source, (3) A configuration is disclosed comprising a seed crystal substrate having a GaN seed crystal on its surface and facing the crucible. Reference 1 discloses that the HF-VPE method exhibits a high crystal growth rate (>100 μm/h) and high stability of the crystal growth rate. However, in the HF-VPE method described in Non-Patent Document 1, crystal growth is performed under low-pressure conditions (<10 kPa), making it impossible to rely on gas thermal conduction, which sometimes hinders heat dissipation from the substrate. This is due to the significantly low infrared emissivity ε on the back side of the substrate (ε = 0.2 to 0.4) when using a GaN single-crystal substrate or a GaN-coated sapphire substrate. In other words, under conditions where heat dissipation from the substrate must rely on radiation, the low infrared emissivity ε of the above-mentioned substrates makes them prone to excessive heat buildup. As a result, the circuit board would overheat, and the surface temperature of the circuit board would not stabilize. Therefore, one possible solution is to bring the seed crystal substrate into contact with other components such as a graphite susceptor and dissipate heat by conducting heat to those components. However, under low-pressure conditions, simply bringing it into contact with other components is not sufficient to achieve adequate heat dissipation. Since fluctuations in substrate surface temperature impede the crystal growth rate and its stability, further improvements are needed in controlling the substrate surface temperature. Therefore, various proposals have been made, as shown below. Patent Document 1 contains, (1) A SiC substrate having a seed crystal on its surface, (2) A carbon film formed on the back surface of the SiC substrate, (3) A seed crystal substrate support is disclosed, comprising a carbon film and a carbon immobilization layer derived from a carbon-based adhesive, which is interposed between the carbon film and a support portion located on the back side of the carbon film to fix the SiC substrate to the support portion. Patent Document 2 contains: (1) A SiC substrate having a seed crystal on its surface, (2) A support part with a seed crystal substrate is disclosed, which comprises a SiC fixing layer derived from a polycarbonosilane adhesive that is interposed between the back surface of the SiC substrate and the support part to fix the SiC substrate to the support part. At this point, some might argue that the heat dissipation of the substrate can be improved by joining the substrate described in Non-Patent Document 1 to other components using the carbon-based adhesive described in Patent Document 1. However, substrates having GaN seed crystals on their surface generally include sapphire substrates or GaN single-crystal substrates, both of which exhibit very poor adhesion to carbon films. This is also true for carbon-based adhesives, making it difficult to join sapphire substrates and GaN single-crystal substrates to other components using carbon-based adhesives. On the other hand, it is possible to join sapphire substrates and GaN single crystal substrates to other components by using the polycarbonate adhesive des