U.S. patent application number 12/207364 was filed with the patent office on 2009-01-01 for substrates and methods for fabricating the same.
This patent application is currently assigned to INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE. Invention is credited to Yan-Ru Lin, Song-Yeu Tsai.
Application Number | 20090004834 12/207364 |
Document ID | / |
Family ID | 39168649 |
Filed Date | 2009-01-01 |
United States Patent
Application |
20090004834 |
Kind Code |
A1 |
Lin; Yan-Ru ; et
al. |
January 1, 2009 |
SUBSTRATES AND METHODS FOR FABRICATING THE SAME
Abstract
An embodiment of the invention provides a substrate. The
substrate comprises a single crystal substrate. An epitaxial buffer
film is on the single crystal substrate. An epitaxial
ZnGa.sub.2O.sub.4 is on the epitaxial buffer film.
Inventors: |
Lin; Yan-Ru; (Taichung City,
TW) ; Tsai; Song-Yeu; (Taipei City, TW) |
Correspondence
Address: |
QUINTERO LAW OFFICE, PC
2210 MAIN STREET, SUITE 200
SANTA MONICA
CA
90405
US
|
Assignee: |
INDUSTRIAL TECHNOLOGY RESEARCH
INSTITUTE
HSINCHU
TW
|
Family ID: |
39168649 |
Appl. No.: |
12/207364 |
Filed: |
September 9, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11627219 |
Jan 25, 2007 |
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12207364 |
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Current U.S.
Class: |
438/483 ;
257/E21.462 |
Current CPC
Class: |
C09K 11/672 20130101;
C09K 11/623 20130101 |
Class at
Publication: |
438/483 ;
257/E21.462 |
International
Class: |
H01L 21/363 20060101
H01L021/363 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2006 |
TW |
TW95133453 |
Claims
1-9. (canceled)
10. A method for fabricating a substrate, comprising: providing a
single crystal substrate; epitaxially growing a buffer film on the
single crystal substrate; and epitaxially growing a
ZnGa.sub.2O.sub.4 film on the buffer film.
11. The method for fabricating the substrate as claimed in claim
10, further comprising epitaxially growing a stress buffer film
between the buffer film and the ZnGa.sub.2O.sub.4 film.
12. The method for fabricating the substrate as claimed in claim
10, wherein the buffer film comprises rock salt TiN.
13. The method for fabricating the substrate as claimed in claim
10, wherein the single crystal substrate comprises Si, MgO or
sapphire.
14. The method for fabricating the substrate as claimed in claim
11, wherein the stress buffer film comprises Zn.sub.2TiO.sub.4.
15. The method for fabricating the substrate as claimed in claim
10, wherein the epitaxial growth of the ZnGa.sub.2O.sub.4 film on
the buffer film comprises depositing an amorphous ZnGa.sub.2O.sub.4
film on the buffer film.
16. The method for fabricating the substrate as claimed in claim
10, wherein the epitaxial growth of the ZnGa.sub.2O.sub.4 film on
the buffer film comprises performing an annealing process.
17. The method for fabricating the substrate as claimed in claim
16, wherein the annealing process is performed at a temperature
ranging from 400.degree. C. to 700.degree. C.
18. The method for fabricating the substrate as claimed in claim
16, wherein the annealing process comprises a rapid thermal
annealing process.
19. The method for fabricating the substrate as claimed in claim
15, wherein the amorphous ZnGa.sub.2O.sub.4 film is deposited on
the buffer film by using DC sputtering.
20. The method for fabricating the substrate as claimed in claim
10, wherein the epitaxial growth of the buffer film on the single
substrate is performed by reactive DC sputtering or pulsed-laser
deposition.
21. The method for fabricating the substrate as claimed in claim
10, wherein the epitaxial growth of the stress buffer film between
the buffer film the ZnGa2O4 film comprises reacting the buffer film
with Zn in a furnace containing O.sub.2 and Ar gas.
22. The method for fabricating the substrate as claimed in claim
10, wherein the epitaxial growth of the ZnGa.sub.2O.sub.4 film on
the buffer film comprises heating the substrate and the buffer film
to a temperature of about 200.degree. C. to 1000.degree. C.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to substrates and methods for
fabricating the same, and more particularly to epitaxial
ZnGa.sub.2O.sub.4 substrates and methods for fabricating the
same.
[0003] 2. Description of the Related Art
[0004] Flat panel display devices, such as field emission displays
(FEDs), plasma display panels (PDPs), and thin-film
electroluminescent devices, require highly efficient phosphor
material. Oxide phosphors offer potential advantages because of
their superior stability under electron bombardment and excellent
luminescent property.
[0005] ZnGa.sub.2O.sub.4 are oxide phosphors attractive for both
cathodoluminescent and electroluminescent applications.
ZnGa.sub.2O.sub.4 possesses a cubic spinel crystal structure and
wide energy band gap of about 4.4 to 5.0 e.V. This material
exhibits an intense green luminescence when doped with Mn and blue
luminescence without doping via a transition of a self-activated
center. It has been suggested that by doping with various
activators, including Mn.sup.2+, Eu.sup.3+ and Ce.sup.3+
ZnGa.sub.2O.sub.4 phosphors can attain full color luminescence.
ZnGa.sub.2O.sub.4 is also an interesting ultraviolet-transparent
conductive oxide as moderate conductivity can be induced by
annealing under a reducing atmosphere at high temperature.
[0006] There have been several studies on ZnGa.sub.2O.sub.4. For
example, Yong Eui Lee et al. disclose "Enhanced ultraviolet
photoconductivity in semiconducting ZnGa.sub.2O.sub.4 thin films"
in JOURNAL OF APPLIED PHYSICS in volume 90, number 8. Yong Eui Lee
et al. disclose "Blue photoluminescence in ZnGa.sub.2O.sub.4 thin
film phosphors" in JOURNAL OF APPLIED PHYSICS in volume 89, number
3. Yong Eui Lee et al. disclose "Enhanced photoluminescence in
epitaxial ZnGa.sub.2O.sub.4:Mn thin film phosphors using pulsed
laser deposition" in APPLIED PHYSICS LETTER in volume 74, number
21.
[0007] Although numerous studies involve epitaxial
ZnGa.sub.2O.sub.4 film, ZnGa.sub.2O.sub.4 can currently only be
grown epitaxially on MgO substrates at high temperature.
Unfortunately, MgO substrate is not only expensive, but also easily
hydrolyzed in a moist ambient. Thus, devices and methods for
overcoming obstacles to epitaxial growth of ZnGa.sub.2O.sub.4 film
are desirable.
BRIEF SUMMARY OF THE INVENTION
[0008] A detailed description is given in the following embodiments
with reference to the accompanying drawings.
[0009] Substrates are provided. An embodiment of a substrate
comprises a single crystal substrate. An epitaxial buffer film is
on the single crystal substrate. An epitaxial ZnGa.sub.2O.sub.4
film is on the epitaxial buffer film.
[0010] Methods for fabricating substrates are provided. An
embodiment of a method for fabricating a substrate comprises
providing a single crystal substrate. A buffer film is epitaxially
grown on the single crystal substrate. A ZnGa.sub.2O.sub.4 film is
epitaxially grown on the epitaxial buffer film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The invention can be more fully understood by reading the
subsequent detailed description and examples with references made
to the accompanying drawings, wherein:
[0012] FIG. 1 is a schematic view showing a substrate with an
epitaxial ZnGa.sub.2O.sub.4 film thereon according to an embodiment
of the invention;
[0013] FIG. 2 is a schematic view showing a substrate with an
epitaxial ZnGa.sub.2O.sub.4 film thereon according to another
embodiment of the invention;
[0014] FIG. 3a-3b are diagrams showing X-ray diffraction
.theta./2.theta. of the as-deposited ZnGa.sub.2O.sub.4 film and
annealed ZnGa.sub.2O.sub.4 film according to embodiments of the
invention; and
[0015] FIG. 4 is a diagram showing Photoluminescence (PL) emission
spectra of ZnGa.sub.2O.sub.4 films with varied crystal orientations
and annealing temperatures according to an embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0016] The following description is of the best-contemplated mode
of carrying out the invention. This description is made for the
purpose of illustrating the general principles of the invention and
should not be taken in a limiting sense. The scope of the invention
is best determined by reference to the appended claims.
Embodiment 1
[0017] FIG. 1 is a schematic view showing an exemplary embodiment
of an epitaxial ZnGa.sub.2O.sub.4 substrate 10 and methods for
fabricating the same. Referring to FIG. 1, a single crystal
substrate 20 is provided. The single crystal substrate 20 may
comprise Si, sapphire, MgO or other single crystal material.
[0018] Next, a buffer film 40 is epitaxially grown on the single
crystal substrate 20. Preferably, there is little lattice
mismatching between the buffer film 40 and a sequentially formed
ZnGa.sub.2O.sub.4 film. For example, the buffer film 40 may
comprise Tin.sub.X(x.ltoreq.1), referred to as rock salt TiN.
Lattice mismatching between rock salt TiN and ZnGa.sub.2O.sub.4 is
about 1.76%. Preferably, the buffer film 40 has a thickness of
about 1 nm to about 50,000 nm. In one embodiment, the epitaxial
growth of the buffer film 40 on the single substrate 20 is
performed by reactive direct current (D.C.) sputtering or
pulsed-laser deposition (PLD). For example, epitaxial rock salt TiN
may be formed on the single crystal substrate 20 by reactive DC
sputtering, wherein during the reactive DC sputtering process, a Ti
target may be used and the single crystal substrate 20 may be
heated to a temperature of about 600.degree. C. in an ambiance
containing N.sub.2 and Ar gas.
[0019] Thereafter, a ZnGa.sub.2O.sub.4 film 60 is epitaxially grown
on the buffer film 40. The ZnGa.sub.2O.sub.4 has a spinel crystal
structure. Preferably, the ZnGa.sub.2O.sub.4 film 60 has a
thickness of about 10 nm to about 50,000 nm. The epitaxial
ZnGa.sub.2O.sub.4 film 60 may be formed on the buffer film 40 by,
for example, DC sputtering which may use ZnGa.sub.2O.sub.4 as a
target. In one embodiment, as-deposited ZnGa.sub.2O.sub.4 film is
amorphous, an annealing process is further performed to transform
the amorphous ZnGa.sub.2O.sub.4 film to an epitaxial film. The
ZnGa.sub.2O.sub.4 film may be annealed at a heating rate of
20.degree. C./second to a temperature ranging from about
200.degree. C. to 700.degree. C. for a duration of about 30
minutes. The single crystal substrate 20 with the buffer film 40
and the ZnGa.sub.2O.sub.4 film 60 formed thereon is then
furnace-cooled to room temperature which may take about 30 minutes.
Alternately, the annealing process may comprise rapid thermal
annealing performed at a heating rate of 50.degree. C./second to a
temperature ranging from about 400.degree. C. for a duration of
about 10 seconds to 1 minute. The single crystal substrate 20 with
the buffer film 40 and the ZnGa.sub.2O.sub.4 film 60 formed thereon
is then furnace-cooled to room temperature. The as-deposited
amorphous ZnGa.sub.2O.sub.4 (not shown) is transformed to the
epitaxial ZnGa.sub.2O.sub.4 film 60 by one of the above-mentioned
or another annealing process. In other embodiments, during
deposition of the ZnGa.sub.2O.sub.4 film 60 on the buffer film 40,
the single crystal substrate 20 and the buffer film 40 is
simultaneously heated to about 200.degree. C. or above, preferably
about 200.degree. C. to 1000.degree. C. Then, the epitaxial
ZnGa.sub.2O.sub.4 film 60 grown on the buffer film 40 is obtained
after the ZnGa.sub.2O.sub.4 deposition process.
Embodiment 2
[0020] FIG. 2 is a schematic view showing another exemplary
embodiment of an epitaxial ZnGa.sub.2O.sub.4 substrate 20 and
methods for fabricating the same. The inventor has found that the
epitaxial ZnGa.sub.2O.sub.4 film 60 may crack due to great stress
produced during the time the epitaxial ZnGa.sub.2O.sub.4 film 60 is
coherent with the buffer film 40. Thus, the second embodiment is
provided for sake of preventing cracks in the epitaxial
ZnGa.sub.2O.sub.4 film and/or the buffer film 40. Herein, the same
structures or materials have the same labels as FIG. 1.
[0021] A substrate 15 with an epitaxial ZnGa.sub.2O.sub.4 film 60
thereon comprises a single crystal substrate 20, a buffer film 40
epitaxially grown on the single crystal substrate 20, a stress
buffer film 50 epitaxially grown on the buffer film 40, and the
ZnGa.sub.2O.sub.4 film 60 epitaxially grown on the stress buffer
film 50. Material, thicknesses and fabrication of the single
crystal substrate 20 and the buffer film 40 in this embodiment are
approximately the same as those in the first embodiment, thus
descriptions thereof are omitted for brevity.
[0022] After the buffer film 40 is epitaxially grown on the single
crystal substrate 20, the stress buffer film 50 is epitaxially
grown on the buffer film 40. Because the sequentially formed
epitaxial ZnGa.sub.2O.sub.4 film 60 and the buffer film 40 such as
TiN are hard and brittle, the ZnGa.sub.2O.sub.4 film 60 may easily
crack. A soft material may be used as the stress buffer film 50
between the epitaxial ZnGa.sub.2O.sub.4 film 60 and the buffer film
40 to buffer stress in the ZnGa.sub.2O.sub.4 film 60 and the buffer
film 40. Preferably, the stress buffer material 50 may comprise
Zn.sub.2TiO.sub.4, and the stress buffer film 50 may have thickness
of about 1 nm to 50,000 nm. In one embodiment, after forming the
epitaxial buffer film 40 such as TiN on the single crystal
substrate 20, the single crystal substrate 20 with the epitaxial
TiN film 40 formed thereon is then disposed with ZnO in a thermal
furnace containing O.sub.2 and Ar. When the single crystal
substrate 20 is heated to a temperature of about 600.degree. C.,
the ZnGa.sub.2O.sub.4 film which functions as the stress buffer
film 50 will be formed on the epitaxial TiN film. In another
embodiment, a stress buffer film 50 may be formed on the buffer
film 40 by a deposition process, such as sputtering. After the
stress buffer film 50 is epitaxially grown on the buffer film 40,
the ZnGa.sub.2O.sub.4 film 60 is then epitaxially grown on the
stress buffer film 50. The fabrication method and thickness of the
epitaxial ZnGa.sub.2O.sub.4 film 60 in this embodiment are the same
as those in the first embodiment, thus descriptions thereof are
omitted for brevity.
X-Ray Diffraction of an Epitaxial ZnGa.sub.2O.sub.4 Film
[0023] FIGS. 3a-3b are diagrams showing X-ray diffraction
.theta./2.theta. of the as-deposited ZnGa.sub.2O.sub.4 film and
annealed ZnGa.sub.2O.sub.4 film according to the aforementioned
embodiments. FIGS. 3a-3b are diagrams demonstrating that the
epitaxial ZnGa.sub.2O.sub.4 film is successfully grown on the
buffer film by performing an annealing process. Herein, the dotted
line shows X-ray diffraction .theta./2.theta. of the as-deposited
ZnGa.sub.2O.sub.4 film, while the solid line shows X-ray
diffraction .theta./2.theta. of the annealed ZnGa.sub.2O.sub.4
film. In FIG. 3a, the (111) epitaxial TiN film is grown on the
(111) single crystal Si substrate. The ZnGa.sub.2O.sub.4 film
deposits on the (111) TiN film on the (111) single crystal Si
substrate; however the as-deposited ZnGa.sub.2O.sub.4 film is an
amorphous film. The amorphous as-deposited ZnGa.sub.2O.sub.4 film
is transformed to the epitaxial (111) and (222) ZnGa.sub.2O.sub.4
film after an annealing process. The annealing process is performed
by at a heating rate of 20.degree. C./second to a temperature of
about 400.degree. C. for a duration of about 30 minutes, and the
single crystal Si substrate with the epitaxial TiN film and the
ZnGa.sub.2O.sub.4 film formed thereon is then furnace-cooled to
room temperature. In FIG. 3b, the (200) epitaxial TiN film is grown
on the (100) single crystal Si substrate. The ZnGa.sub.2O.sub.4
film deposits on the (200) TiN film on the (100) single crystal Si
substrate; however the as-deposited ZnGa.sub.2O.sub.4 film is an
amorphous film. The amorphous as-deposited ZnGa.sub.2O.sub.4 film
is transformed to the epitaxial (400) ZnGa.sub.2O.sub.4 film after
an annealing process. The annealing process is performed by heating
at a rate of 20.degree. C./second to a temperature of about
400.degree. C. for a duration of about 30 minutes, and then the
single crystal Si substrate with the epitaxial TiN film and the
ZnGa.sub.2O.sub.4 film formed thereon is then furnace-cooled to
room temperature.
Photoluminescence (PL) Emission Spectra of ZnGa.sub.2O.sub.4
Films
[0024] FIG. 4 is a diagram showing PL emission spectra of
ZnGa.sub.2O.sub.4 films with varied crystal orientations and
annealing temperatures according to an embodiment of the invention.
In FIG. 4, line A shows a PL emission spectrum of an epitaxial
(100) ZnGa.sub.2O.sub.4 film according to an embodiment of the
invention. The epitaxial (100) ZnGa.sub.2O.sub.4 film is grown on a
TiN film which is formed on a Si substrate. The (100)
ZnGa.sub.2O.sub.4/TiN/Si is formed by performing an annealing
process at a temperature of about 400.degree. C. Line B shows a PL
emission spectrum of an epitaxial (100) ZnGa.sub.2O.sub.4 film
according to an embodiment of the invention. The epitaxial (100)
ZnGa.sub.2O.sub.4 film is grown on a TiN film which is formed on a
Si substrate. The (100) ZnGa.sub.2O.sub.4/TiN/Si is formed by
performing an annealing process at a temperature of about
700.degree. C. Line C shows a PL emission spectrum of an epitaxial
(111) ZnGa.sub.2O.sub.4 film according to an embodiment of the
invention. The epitaxial (111) ZnGa.sub.2O.sub.4 film is grown on a
TiN film which is formed on a Si substrate. The (111)
ZnGa.sub.2O.sub.4/TiN/Si is formed by performing an annealing
process at a temperature of about 400.degree. C. Line D shows a PL
emission spectrum of an epitaxial (111) ZnGa.sub.2O.sub.4 film
according to an embodiment of the invention. The epitaxial (111)
ZnGa.sub.2O.sub.4 film is grown on a TiN film which is formed on a
Si substrate. The (111) ZnGa.sub.2O.sub.4/TiN/Si is formed by
performing an annealing process at a temperature of about
700.degree. C. Line E shows a PL emission spectrum of an
conventional poly crystal ZnGa.sub.2O.sub.4 film, wherein an
amorphous ZnGa.sub.2O.sub.4 film is formed on a glass substrate. An
annealing process at a temperature of about 400.degree. C. for 30
minutes is performed to transform the amorphous ZnGa.sub.2O.sub.4
film to the poly crystal ZnGa.sub.2O.sub.4 film. As shown in FIG.
4, the epitaxial ZnGa.sub.2O.sub.4 films formed by embodiments of
the invention such as lines A, B, C and D have greater PL intensity
than a conventional poly crystal ZnGa.sub.2O.sub.4 film such as
line E. Furthermore, lines A, B, C and D have clearer peaks than
line E, thus characteristic spectra may be separated in lines A, B,
C and D.
[0025] As described, an epitaxial ZnGa.sub.2O.sub.4 film may be
grown on any single crystal substrate through the buffer film
underlying the ZnGa.sub.2O.sub.4 film. It is not necessary to grow
an epitaxial ZnGa.sub.2O.sub.4 film on a MgO substrate, thereby
reducing fabrication cost. An amorphous ZnGa.sub.2O.sub.4 film is
transformed to an epitaxial ZnGa.sub.2O.sub.4 film by performing
only an annealing process, thus the fabrication method is
simplified.
[0026] While the invention has been described by way of example and
in terms of the preferred embodiments, it is to be understood that
the invention is not limited to the disclosed embodiments. To the
contrary, it is intended to cover various modifications and similar
arrangements (as would be apparent to those skilled in the art).
Therefore, the scope of the appended claims should be accorded the
broadest interpretation so as to encompass all such modifications
and similar arrangements.
* * * * *