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EP-4741542-A1 - PRODUCTION METHOD FOR GAN EPITAXIAL FILM AND PRODUCTION METHOD FOR SEMICONDUCTOR DEVICE

EP4741542A1EP 4741542 A1EP4741542 A1EP 4741542A1EP-4741542-A1

Abstract

The present invention is a method for producing a GaN epitaxial film, the method including the steps of providing a support substrate having a diameter of 150 mm or more and a thickness of less than 1 mm, in which the support substrate includes a core composed of nitride ceramic enclosed by an encapsulating layer, producing a substrate in which a planarization layer and a seed crystal layer composed of SiC single crystal are sequentially laminated on the support substrate to obtain a substrate for epitaxial growth, and epitaxially growing a GaN epitaxial film having a thickness of 7 µm or more on the substrate for epitaxial growth, by which the GaN epitaxial film having a dislocation density of 1.0×10 6 / cm 2 or less is produced. This provides the method for producing a thick GaN film having a dislocation density of 1.0×10 6 / cm 2 or less, in which the film has a large diameter without warping and cracking at low cost using a simple process.

Inventors

  • HAGIMOTO KAZUNORI
  • YAMADA MASATO

Assignees

  • Shin-Etsu Handotai Co., Ltd.

Dates

Publication Date
20260513
Application Date
20240618

Claims (5)

  1. A method for producing a GaN epitaxial film, the method comprising the steps of: providing a support substrate having a diameter of 150 mm or more and a thickness of less than 1 mm, in which the support substrate comprises a core composed of nitride ceramic enclosed by an encapsulating layer; producing a substrate in which a planarization layer and a seed crystal layer composed of SiC single crystal are sequentially laminated on the support substrate to obtain a substrate for epitaxial growth; and epitaxially growing a GaN epitaxial film having a thickness of 7 µm or more on the substrate for epitaxial growth, by which the GaN epitaxial film having a dislocation density of 1.0×10 6 / cm 2 or less is produced.
  2. The method for producing a GaN epitaxial film according to claim 1, wherein in the step of epitaxially growing, a forming step for forming a SiN layer in an island shape and an ELO step for growing a GaN layer using the SiN layer as a mask are performed, and a growth step is subsequently performed to grow the GaN epitaxial film on the uppermost SiN layer or the uppermost GaN layer.
  3. The method for producing a GaN epitaxial film according to claim 2, wherein in the step of epitaxially growing, the forming step and the ELO step are alternately performed.
  4. The method for producing a GaN epitaxial film according to claim 1, wherein the SiC single crystal has an off-angle of 0° to 4°.
  5. A method for producing a semiconductor device, the method comprising: forming a device on the GaN epitaxial film produced by the method for producing a GaN epitaxial film according to any one of claims 1 to 4; and subsequently, etching the planarization layer to separate the device from the support substrate.

Description

TECHNICAL FIELD The present invention relates to a method for producing a GaN epitaxial film and a method for producing a semiconductor device. BACKGROUND ART With regard to substrates on which GaN epitaxial films are formed, bulk substrates such as Si, GaAs, or Sap (sapphire) are promising due to the availability of large-diameter substrates at low cost. However, in an attempt to reduce dislocation density in the epitaxial films by increasing thickness, problems such as substrate warping or cracking may arise. Moreover, attempts to overcome these problems lead to significantly complex buffer steps, and this results in degraded productivity. In contrast, GaN bulk substrate systems and those of AlN, having a close coefficient of thermal expansion as well as a similar lattice constant, are promising in terms of material properties. However, the substrates having a diameter of 150 mm or more have not yet been mass-produced and are therefore expensive. Although Patent Document 1 discloses a method in which a GaN film having low dislocation density is formed on a substrate of a different kind using a VAS (Void-Assisted Separation) method, and is used as a substrate, it remains unclear whether an increase in diameter is achievable, and the steps in the method are complex. In addition, although Non Patent Document 1 discloses an example in which a defect density on a GaN on Si substrate is high and is therefore improved with GaN on GaN, it is unclear whether a diameter enlargement is achievable. As disclosed in Patent Documents 2 and 3, when substrates having ceramic cores are used, which have substantially the same coefficient of thermal expansion compared with that of crystals to be formed, thick films can be formed. However, a difference in lattice constants between seed crystals, such as Si, and the crystals to be formed makes it difficult to achieve a dislocation density of 1.0×106 / cm2 or less in the crystals. Note that when a substrate having a ceramic core is used, Patent Document 4 discloses a method to separate a support substrate including a ceramic core by ion implantation, thereby producing a vertical transistor. Moreover, Patent Document 5 discloses another method to separate a support substrate including a ceramic core by etching a planarization layer (SiO2 layer), thereby providing a device for ultraviolet light emission. Further, Patent Documents 4 and 6 disclose that SiC, AlN, AlGaN, and Al2O3, in addition to Si, can be employed as a single crystal layer on a support substrate including a ceramic core, and the materials having lattice constants close to the ceramic core are preferable. However, no disclosure is provided on whether dislocation density can be lowered or not. In addition, ELO (Epitaxial Lateral Overgrowth) is also known as a means to reduce dislocation density. For example, Patent Documents 7 and 8 disclose ELO growth on support substrates of Patent Document 2, using island-shaped SiN. Moreover, Patent Documents 9 and 10 disclose a concept in which GaN is grown in a two-step island shape on a Si-containing film that includes island-shaped SiN to perform ELO growth, thereby reducing dislocation density. The disclosure includes that the Si (doping) concentration in the two-step island-shaped growth portion is 1.0×1017 to 1020 / cm3. Patent Document 11 discloses that island-shaped GaN is formed under growth conditions, and ELO is grown to reduce dislocation density without using masks, such as SiN. This document also discloses that a GaN film having a TD (threading dislocation) density of 5.0×106 / cm2 can be obtained through one process, and the GaN film having 5.0×105 / cm2 can be obtained through three processes. However, these techniques are used to form ELO on Si, and the reduction of dislocation density is required to perform a plurality of ELOs. As a method for reducing dislocation density, a method is known to prevent a growth of a plane (0001) prone to propagate dislocation from underneath intact, as a base layer, and instead to form a film composed of an inclined surface, resulting in a reduction of dislocation. Such a growth of the inclined surface film is realized either by using masks, such as island-shaped SiN (Patent Documents 1, 12, and 13), or by controlling growth conditions without pattern processing, such as mask layers (Patent Documents 14 to 17). Note that substrates used herein are freestanding GaN substrates produced once by a VAS method on substrates composed of Si, GaAs, Sap, or the like. However, it is unclear whether enlargement of a diameter can be achieved or not. CITATION LIST PATENT LITERATURE Patent Document 1: JP 2020-070229 APatent Document 2: JP 2013-177285 APatent Document 3: JP 2019-523994 APatent Document 4: WO 2021/230148 A1Patent Document 5: JP 2022-056492 APatent Document 6: JP 2022-012558 APatent Document 7: JP 2022-165964 APatent Document 8: JP 2020-505767 APatent Document 9: JP 2018-88528 APatent Document 10: JP 2015-29042 APatent Document