Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-10-16
2003-11-18
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
Reexamination Certificate
active
06649288
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the invention:
This invention relates to a III nitride film, particularly to an Al-including III nitride film which is suitable for a light-emitting diode or a high speed IC chip.
(2) Related Art Statement:
Al-including III nitride films are used as semiconductor films for light-emitting diodes, and recently get attention as semiconductor films for high speed IC chips of cellular phones.
Conventionally, such an Al-including film is fabricated by a MOCVD method in which trimethyl aluminum (TMA) and triethyl aluminum (TEA) are employed as an Al supply source, and ammonia (NH
3
) is employed as a nitrogen supply source.
In this case, a substrate on which the III nitride film is formed is set on a susceptor installed in a reactor and is heated to around 1000° C. by a heater provided in or out of the reactor. Then, the Al supply source, the nitrogen supply source and another supply source including another additive element, with given carrier gases, are introduced into the reactor and supplied onto the substrate.
Just then, the supply sources thermochemically react on the substrate, and the thus decomposed constituent elements chemically react to deposit a desired Al-including III nitride film on the substrate.
However, when the Al-including III nitride film is formed directly on a single crystal substrate made of C-faced sapphire single crystal, C-faced SiC single crystal or the like or an epitaxial substrate constructed of the same single crystal and an underfilm made of III nitride, some cracks may be created in the film, irrespective of the composition, depending on the film-forming condition and the film-forming apparatus condition such as the reactor configuration and size.
Therefore, the yield ratio of elements constructed of such single crystal substrates or epitaxial substrates and the Al-including III nitride films formed on the substrates is degraded.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an Al-including III nitride film without cracks when it is formed directly on a single crystal substrate or an epitaxial substrate.
In order to achieve the above object, this invention relates to a III nitride film including at least Al element and having hexagonal crystal system which is directly grown on a crystalline substrate along the C-axis, the lattice constant “c” of the main axis of the III nitride film and the lattice constant “a” of the crystal face perpendicular to the main surface of the substrate satisfying the relation of “c>2.636a-3.232”. Here, “along the C-axis” includes subtle tilt of the C-axis originated form deviation of growth conditions, subtle off-angle value of crystalline substrate and so forth.
In a preferred embodiment of the present invention, the lattice constant “c” and the lattice constant “a” satisfy the relation of “c>2.636a-3.221”. In this case, even though the III nitride film is thermally shocked, no cracks are created in the film.
The inventors intensely studied to obtain an Al-including III nitride film without cracks when the III nitride film is formed directly on a crystalline substrate. Since the cracks in the III nitride film occurred, irrespective of the composition, depending on the film-forming condition and the film-forming apparatus condition, the inventors intensely investigated the physical properties of the film and substrate which influence the creation of cracks.
As a result, the inventors discovered that the crack creation in the III nitride film directly formed on the crystalline substrate relates to the sizes of lattice constants of the crystal lattice of the III nitride film. That is, in the hexagonal crystal lattice of the III nitride film, if the lattice constant “c” of the main axis and the lattice constant “a” of the crystal face perpendicular to the main axis satisfy the above relation, the crack creation can be inhibited even though the III nitride film is formed directly on the crystalline substrate. This invention results from the above enormous research and development.
FIG. 1
is a graph showing the correlation between the lattice constants and the crack creation in a III nitride film having a composition of AlxGayInzN (x+y+z=1, x>0). As is apparent from
FIG. 1
, if the relation of “c>2.636a-3.232” is satisfied, cracks are not created in the film. On the other hand, if the relation is not satisfied, some cracks are created in the film.
Herein, in
FIG. 1
, ∘ plots designate that cracks are not created and x plots designate that cracks are created.
REFERENCES:
patent: 5729029 (1998-03-01), Rudaz
patent: 6326638 (2001-12-01), Kamiyama et al.
patent: 6429465 (2002-08-01), Yagi et al.
patent: 2002/0020850 (2002-02-01), Shibata et al.
patent: 0497350 (1992-08-01), None
U.S. copending application 10/102,545, Tomohiko Shibata et al., filed Mar. 20, 2002.
U.S. copending application 10/163,256, Tomohiko Shibata et al., filed Jun. 5, 2002.
U.S. copending application 10/074,589, Tomohiko Shibata et al., filed Feb. 13, 2002.
“Biaxial strain in AlxGa1-xN/GaN layers deposited on 6H-SiC,” Perry et al.,Thin Solid Films, Elsevier (pub.), 324(1998) pp. 107-114, No Month.
“Structural characterization of Al1-xInxN lattice-matched to GaN,” Kariya et al.,Journalof Crystal Growth, Elsevier (pub.), 209(2000) pp. 419-423, No Month.
“Biaxial strain in AlxGa1-xN/GaN layers deposited on 6H-SiC,”, Perry et al.,Thin Solid Films, Elsevier (pub.), 324(1998) pp. 107-114.
“Structural characterization of Al1-xInxN lattice-matched to GaN,” Kariya et al.,Journal of Crystal Growth, Elsevier (pub.), 209(2000) pp. 419-423.
Nakamura Yukinori
Shibata Tomohiko
Tanaka Mitsuhiro
Blackwell-Rudasill G.
Burr & Brown
Jones Deborah
NGK Insulators Ltd.
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