Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-09-25
2003-09-23
Jones, Deborah (Department: 1775)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S697000, C428S699000, C428S702000
Reexamination Certificate
active
06623877
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to a III nitride epitaxial wafer and the usage of the same, particularly to a III nitride epitaxial wafer and the usage of the same preferably usable for a substrate of semiconductor devices such as a light-emitting diode or a high speed IC chip.
(2) Related Art Statement
III nitride films are used as semiconductor films for light-emitting diodes, and recently get attention as semiconductor films for high speed IC chips. Particularly, Al-including III nitride films get attention as field emitter materials.
Such III nitride films are formed on an epitaxial wafer, for example, which has an underfilm epitaxially grown on a given base material. The underfilm is preferably made of Al-including III nitride films in order to facilitate the epitaxial growth of the III nitride films to be formed. Moreover, such Al-including III nitride films formed between the base material and the III nitride films can enhance the efficiency of a semiconductor element because of a wider bandgap of Al-including III nitride material.
The epitaxial wafer is set on a susceptor installed in a given reactor, and heated to a predetermined temperature with a heater built in or out of the susceptor. Then, a raw material for a III metal, nitrogen and, if necessary, other elements are introduced into the reactor with carrier gases, and supplied onto the epitaxial wafer to fabricate the III nitride films by an MOCVD method.
However, the fabrication process of the epitaxial wafer is carried out in a different apparatus from the one where the above-mentioned fabrication process of the III nitride films is done, partly because the fabrication condition of the epitaxial wafer is different from the fabrication condition of the III nitride films. Therefore, the epitaxial wafer is exposed to the environmental atmosphere after the fabrication process of the epitaxial wafer. Moreover, there is a problem with damages forming at the surface of the epitaxial wafer when characterizing the epitaxial wafer.
Then, the surface of an Al-including III nitride underfilm of the epitaxial wafer is oxidized and/or comes to include some defects. As a result, the III nitride films can not have good crystal quality due to the bad condition of the epitaxial wafer surface.
From this point of view, such an attempt was made that an Al-including III nitride films as an underfilm is formed thicker on a base material, and the oxidized surface layer of the underfilm is removed. However, the oxidized surface layer including Al can not be removed by hydrogen gas or ammonia gas, which are used in the fabrication of a III nitride films, and accordingly, another etching apparatus are required. As a result, the whole fabrication process becomes complicated, and the operationality and the yield ratio are deteriorated.
SUMMARY OF THE INVENTION
It is an object of the present invention to prevent the oxidization of an under film made of an Al-including III nitride film of an epitaxial wafer, and to the usage of the epitaxial wafer having an underfilm that is not oxidized.
In order to achieve the above object, this invention relates to an epitaxial wafer comprising a base material made of a single crystal material, a III nitride underfilm including at least Al epitaxially grown on the base material, and an In
a
Ga
b
N (a+b=1) film formed on the underfilm.
This invention also relates an epitaxial wafer including a base material made of a single crystal material, a III nitride underfilm including at least more than 50 atomic percentages-Al element epitaxially grown on the base material, and an In
a
Ga
b
N (a+b=1) film formed on the underfilm.
The oxidized surface layer of the In
a
Ga
b
N film is removed through an etching process, and a III nitride film is formed on the In
a
Ga
b
N film, in which the thickness of the epitaxial wafer has been reduced subsequent to the etching process.
The inventors intensely studied ways to prevent the oxidization of the Al-including III nitride underfilm. As a result, they discovered that a protective film should be fabricated on the underfilm. However, it was required that the protective film did not obstruct the epitaxial growth of the III nitride films, and the oxidized surface layer of the protective layer needed to be easily removed. Accordingly, it is very difficult to match suitable materials to the protective film.
Then, the inventors made enormous research and development to discover suitable materials for the protective film. As a result, the inventors discovered that if the protective film is made of an In
a
Ga
b
N film (a+b=1), the epitaxial growth of the III nitride film is not obstructed and the oxidized surface layer of the protective film can be easily removed by an etching process using hydrogen gas and/or ammonia gas, which are used in the fabrication process of the III nitride films.
The In
a
Ga
b
N film functions as an underfilm for the III nitride films as well as the protective film to be formed. Therefore, the In
a
Ga
b
N film can be fabricated on the similar condition to the one of the Al-including III nitride underfilm. Therefore, both of the In
a
Ga
b
N film and the Al-including III nitride underfilm can be made by the same apparatus, so that the whole fabrication process can be simplified.
On the above-mentioned enormous research and development, the inventors found out that the In
a
Ga
b
N film is extremely suitable for the Al-including III nitride underfilm, and attained the epitaxial wafer and the usage of the substrate according to the present invention.
Herein, the Al-including III nitride underfilm is constructed, as occasion demands, of a single layer, a multi-layered structure or a composition-gradient film in which the composition of a given element is inclined in its thickness direction. Therefore, the Al content of the Al-including III nitride underfilm means the one over the underfilm structure.
The In
a
Ga
b
N film may contain inevitably, in addition to In, Ga and nitrogen, H, O, C, Al, Si, Ge, Mg, Zn, Be or the like, depending on the film-forming condition, the raw materials or the reactor materials.
Moreover, the In
a
Ga
b
N film may be entirely removed for simplifying the etching process, instead of removing the oxidized surface layer of the In
a
Ga
b
N film. The etching process for the In
a
Ga
b
N film does not influence the properties of the III nitride film to be formed on the epitaxial wafer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
This invention will be described in detail, hereinafter.
The epitaxial wafer is required to have the In
a
Ga
b
N film on the Al-including III nitride underfilm. The In
a
Ga
b
N film can be made under similar conditions and with the same apparatus used for forming the Al-including III nitride underfilm, as mentioned above. For example, trimethylgallium as a raw material for Ga and ammonia gas as a raw material for nitrogen are supplied on the base material of the epitaxial wafer heated to 1050° C. to fabricate the In
a
Ga
b
N film.
Although the thickness of the In
a
Ga
b
N film is not restricted, it may be preferably set to 50 Å or more, particularly 100 Å or more. As the result of the detailed investigation for the oxidization mechanism of the In
a
Ga
b
N film, the oxidization proceeds to a depth of about 50 Å from the surface of the In
a
Ga
b
N film at the maximum case. Therefore, if the thickness of the In
a
Ga
b
N film is set within the above-mentioned thickness range, the Al-including III nitride underfilm positioned under the In
a
Ga
b
N film is not substantially oxidized.
Although the upper limit thickness of the In
a
Ga
b
N film is not particularly restricted, it may be preferably set to about 1 &mgr;m or below. If the In
a
Ga
b
N film is fabricated thicker than 1 &mgr;m, the properties of the epitaxial wafer can not be improved, and instead, some cracks and exfoliation are created in the film due to the stress in the grown film.
The In
a
Ga
b
N film is preferably a GaN film. In this case, the protective effect fo
Nakamura Yukinori
Shibata Tomohiko
Tanaka Mitsuhiro
Burr & Brown
Jones Deborah
NGK Insulators Ltd.
Stein Stephen
LandOfFree
III nitride epitaxial wafer and usage of the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with III nitride epitaxial wafer and usage of the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and III nitride epitaxial wafer and usage of the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3103701