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Crystalline film, semiconductor device including crystalline film, and method for producing crystalline film

Foreign code F200010118
File No. 5926
Posted date May 18, 2020
Country United States of America
Application number 201816106753
Gazette No. 10460934
Date of filing Aug 21, 2018
Gazette Date Oct 29, 2019
Priority data
  • P2017-158306 (Aug 21, 2017) JP
  • P2018-050516 (Mar 19, 2018) JP
  • P2018-120457 (Jun 26, 2018) JP
Title Crystalline film, semiconductor device including crystalline film, and method for producing crystalline film
Abstract According to an aspect of a present inventive subject matter, a crystalline film includes a crystalline metal oxide as a major component, the crystalline film includes a corundum structure, a surface area that is 9 μm2 or more, and a dislocation density that is less than 5×106 cm-2.
Outline of related art and contending technology BACKGROUND OF THE INVENTION
Field of the Invention
The present disclosure relates to a crystalline film. Also, the present disclosure relates to a semiconductor device including a crystalline film. Furthermore, the present disclosure relates to a method for producing a crystalline film.
Description of the Related Art
As a background, gallium oxide (Ga2O3) is known to possess five different polymorphs including α-, β-, γ-, δ-, and ε-phases (for reference, see NPL1: Rustum Roy et al, “Polymorphism of Ga2O3 and the System Ga2O3-H2O”).
Among these five polymorphs, β-Ga2O3 is believed to be thermodynamically the most stable, and α-Ga2O3 is believed to be metastable. Gallium oxide (Ga2O3) exhibits wide band gap and attracts more attention as a potential semiconductor material for semiconductor devices.
According to NPL 2, it is suggested that a band gap of gallium oxide (Ga2O3) is able to be controlled by forming mixed crystal with indium and/or aluminum (for reference, see NPL 2: Kentaro KANEKO, “Fabrication and physical properties of corundum-structured alloys based on gallium oxide”, Dissertation, Kyoto Univ., issued in March 2013, summary and contents were open to the public on Jan. 31, 2014). Among them, InAlGaO based semiconductors represented by InXAlYGaZO3 (0≤X≤2, 0≤Y≤2, 0≤Z≤2, X+Y+Z=1.5 to 2.5) are extremely attractive materials (for reference, see PCT international publication No. WO2014/050793A1).
However, since β-phase is the most stable phase of gallium oxide, it is difficult to form a metastable corundum-structured crystalline film of gallium oxide without using a suitable film-formation method. Also, bulk substrates obtained from melt-growth are not available for α-Ga2O3 that is corundum-structured and metastable. Accordingly, sapphire substrates having a same structure as the corundum structure α-Ga2O3 has are used to form α-Ga2O3 on the sapphire substrates, however, lattice mismatch of sapphire and α-Ga2O3 is not small (Δa/a˜4.5%, Δc/c˜3.3%) and thus, α-Ga2O3 crystalline film hetero-epitaxially grown on a sapphire substrate tends to include a high density of dislocations. Furthermore, there are further challenges to accelerate film-formation speed, to enhance quality of a crystalline film of α-phase gallium oxide and/or a crystalline film of mixed crystal of α-phase gallium oxide, to suppress crystal defects including occurrence of cracks, abnormal growth, crystal twinning, and/or curves of crystalline film. Under such circumstances, researches of corundum-structured crystalline semiconductor films are ongoing.
It is open to the public that a crystalline film of oxide is produced by a mist chemical vapor deposition (CVD) method using bromide or iodide of gallium and/or indium (see Japanese patent publication No. 5397794). Also, it is open in public that a multilayer structure includes a corundum-structured semiconductor layer on a corundum-structured base substrate, and a corundum-structured insulating layer (see Japanese patent publications No. 5343224 and No. 5397795 and unexamined Japanese patent publication No. JP2014-72533). Furthermore, film-formation by a mist CVD method using ELO substrates and void formation is disclosed (see unexamined Japanese patent publications No. 2016-100592, No. 2016-98166, No. 2016-100593, and No. 2016-155714). Also, it is open to the public that a corundum-structured gallium oxide film is formed by a halide vapor phase epitaxy (HYPE) method. However, there is a room for improvement in the rate or speed for forming a film, and a method for producing a crystalline film with a sufficient speed has been desired.
Also, considering that α-Ga2O3 is metastable, α-Ga2O3 films and crystalline films of crystalline metal oxide containing gallium and one or more metals are more difficult to form with suppressed defect density, compared to the case of stable β-Ga2O3 , and thus, there are still various challenges to cope with for obtaining α-Ga2O3 films and crystalline films of crystalline metal oxide containing gallium and one or more metals.
Scope of claims [claim1]
1. A crystalline film comprising:
a crystalline metal oxide as a major component;
the crystalline film comprising a corundum structure, a surface area that is 9 μm2 or more, and a dislocation density that is less than 5×106 cm-2.

[claim2]
2. The crystalline film of claim 1, wherein
the surface area that is 9 μm2 or more comprises an epitaxial lateral overgrowth layer of the crystalline metal oxide.

[claim3]
3. The crystalline film of claim 1, wherein
the crystalline film comprises an epitaxial lateral overgrowth of the crystalline metal oxide grown in at least a direction perpendicular to a (1014) plane.

[claim4]
4. The crystalline film of claim 1, wherein
the crystalline film comprises a dopant.

[claim5]
5. A crystalline film comprising:
a crystalline metal oxide as a major component; and
an epitaxial lateral overgrowth of the crystalline metal oxide grown in at least a direction perpendicular to a (1014) plane.

[claim6]
6. The crystalline film of claim 5, wherein
the crystalline metal oxide comprises gallium, a surface area that is 9 μm2 or more, and a dislocation density that is less than 5×106 cm-2.

[claim7]
7. The crystalline film of claim 6, wherein
the crystalline metal oxide further comprises at least one metal selected from among aluminum, indium, iron, chromium, vanadium, titanium, rhodium, nickel, cobalt, and iridium.

[claim8]
8. The crystalline film of claim 6, wherein
the crystalline film comprises a dopant.

[claim9]
9. A semiconductor device comprising:
the crystalline film of claim 4;
a first electrode electrically connected to the crystalline film; and
a second electrode electrically connected to the crystalline film.

[claim10]
10. A semiconductor device comprising:
the crystalline film of claim 5.

[claim11]
11. A method for producing a crystalline film comprising:
gasifying a metal source to turn the metal source into a metal-containing raw-material gas;
supplying the metal-containing raw-material gas and an oxygen-containing raw-material gas into a reaction chamber onto a substrate on that an uneven portion comprising at least one mask and/or at least one opening is arranged; and
supplying a reactive gas into the reaction chamber onto the substrate to grow at least one island of crystalline metal oxide vertically, laterally and/or radially at the at least one opening of the uneven portion on the substrate under a gas flow of the reactive gas such that the at least one island of crystalline metal oxide forms an epitaxial lateral overgrowth layer of crystalline metal oxide.

[claim12]
12. The method of claim 11, wherein
the reactive gas is an etching gas.

[claim13]
13. The method of claim 11, wherein
the reactive gas comprises at least one selected from among hydrogen halide and groups comprising halogen and hydrogen.

[claim14]
14. The method of claim 11,
wherein the at least one mask of the uneven portion comprises a sheet-shaped mask with the at least one opening comprising two or more openings arranged on a surface of the substrate, and
wherein the two or more openings of the sheet-shaped mask on the substrate are regularly arranged on the surface of the substrate.

[claim15]
15. The method of claim 11, wherein
the substrate is heated at a temperature that is in a range of 400° C. to 700° C.

[claim16]
16. The method of claim 11,
wherein the metal source comprises a gallium source, and
wherein the metal-containing raw-material gas comprises a gallium-containing raw-material gas.

[claim17]
17. The method of claim 11, wherein
the gasifying the metal source is done by halogenating the metal source.

[claim18]
18. The method of claim 11, wherein
the oxygen-containing raw-material gas comprises at least one selected from among oxygen (O2), water (H2O) and nitrous oxide (N2O).

[claim19]
19. The method of claim 11, wherein
the substrate comprises a corundum structure, and the crystalline film comprises a corundum structure.

[claim20]
20. The method of claim 11,
wherein the substrate further comprises a buffer layer formed by use of a mist chemical vapor deposition (CVD) method on at least a surface of the substrate, and
wherein the uneven portion on the substrate is positioned on the buffer layer.

[claim21]
21. The method of claim 11, wherein
the forming the crystalline film of metal oxide under the gas flow of the reactive gas is done by use of a halide vapor phase epitaxy (HVPE) method.

[claim22]
22. The method of claim 11, wherein
the forming the crystalline film of metal oxide is done at a growth rate that is 5 μm/h or more.

[claim23]
23. The method of claim 22, wherein
the forming the uneven portion on the surface of the first crystalline film is done by arranging at least one mask comprising two or more metals, a metal compound, and/or a nonmetallic compound on the surface of the first crystalline film.

[claim24]
24. The method of claim 11, wherein
the at least one mask of the uneven portion comprises two or more elongated masks arranged in parallel with the at least one opening positioned between adjacently arranged two of the elongated masks.

[claim25]
25. The method of claim 24,
wherein the first crystalline film comprises a crystalline gallium oxide as a major component or a mixed crystal as a major component comprising gallium and one or more metals, and
wherein the second crystalline film comprises a crystalline gallium oxide as a major component or a mixed crystal as a major component comprising gallium and one or more metals.

[claim26]
26. The method of claim 11, wherein
the at least one mask of the uneven portion comprises dot-patterned masks that are arranged at a regular interval that is in a range of 3 μm or more to 100 μm or less.

[claim27]
27. The method of claim 26,
wherein the first crystalline film comprises a crystalline gallium oxide as a major component or a mixed crystal as a major component comprising gallium and one or more metals, and
wherein the second crystalline film comprises a crystalline gallium oxide as a major component or a mixed crystal as a major component comprising gallium and one or more metals.

[claim28]
28. The method of claim 11 further comprising:
forming an uneven portion on a surface of the crystalline film that is a first crystalline film of the crystalline oxide; and
forming a second crystalline film on the uneven portion on the surface of the first crystalline film of the crystalline oxide.

[claim29]
29. The method of claim 28, wherein
the first crystalline film is formed as a sacrificial layer that is to be peel-off such that the second crystalline film is separable from the uneven portion on the surface of the first crystalline film.
  • Inventor, and Inventor/Applicant
  • OSHIMA Yuichi
  • FUJITA Shizuo
  • KANEKO Kentaro
  • KASU Makoto
  • KAWARA Katsuaki
  • SHINOHE Takashi
  • MATSUDA Tokiyoshi
  • HITORA Toshimi
  • FLOSFIA INC.
  • NATIONAL INSTITUTE FOR MATERIALS SCIENCE
  • KYOTO UNIVERSITY
  • SAGA UNIVERSITY
IPC(International Patent Classification)
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