U.S. patent application number 16/201293 was filed with the patent office on 2020-05-07 for method for forming hexagonal boron nitride thin film, method for forming multi-layered structure and method for manufacturing sw.
This patent application is currently assigned to KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. The applicant listed for this patent is KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY. Invention is credited to Jaikyeong KIM, Jaehyun PARK, Yumin SIM.
Application Number | 20200144390 16/201293 |
Document ID | / |
Family ID | 69626997 |
Filed Date | 2020-05-07 |
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United States Patent
Application |
20200144390 |
Kind Code |
A1 |
PARK; Jaehyun ; et
al. |
May 7, 2020 |
METHOD FOR FORMING HEXAGONAL BORON NITRIDE THIN FILM, METHOD FOR
FORMING MULTI-LAYERED STRUCTURE AND METHOD FOR MANUFACTURING
SWITCHING ELEMENT USING THE SAME
Abstract
A method for forming a hexagonal boron nitride (h-BN) thin film
is provided. According to the method, an alumina thin film
including amorphous alumina or gamma-alumina is prepared. An h-BN
thin film is synthesized at equal to or less than 750.degree. C. on
the alumina thin film. A mono-layer thickness of the h-BN film is
equal to or less than 0.40 nm.
Inventors: |
PARK; Jaehyun; (Seoul,
KR) ; SIM; Yumin; (Seoul, KR) ; KIM;
Jaikyeong; (Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF SCIENCE AND TECHNOLOGY |
Seoul |
|
KR |
|
|
Assignee: |
KOREA INSTITUTE OF SCIENCE AND
TECHNOLOGY
Seoul
KR
|
Family ID: |
69626997 |
Appl. No.: |
16/201293 |
Filed: |
November 27, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 21/02485 20130101;
H01L 21/02488 20130101; H01L 29/24 20130101; H01L 21/02444
20130101; H01L 21/0262 20130101; H01L 29/4908 20130101; H01L 29/518
20130101; H01L 29/66045 20130101; H01L 29/1606 20130101; H01L
21/02178 20130101; H01L 21/02527 20130101; H01L 21/02271 20130101;
H01L 21/02112 20130101; H01L 21/0254 20130101; H01L 29/513
20130101; H01L 29/66969 20130101; H01L 21/02502 20130101; H01L
29/778 20130101; H01L 21/02356 20130101; H01L 21/0228 20130101 |
International
Class: |
H01L 29/66 20060101
H01L029/66; H01L 29/16 20060101 H01L029/16; H01L 29/49 20060101
H01L029/49; H01L 29/51 20060101 H01L029/51; H01L 21/02 20060101
H01L021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 6, 2018 |
KR |
10-2018-0134962 |
Claims
1. A method for forming a hexagonal boron nitride (h-BN) thin film,
the method comprising: preparing an alumina thin film including
amorphous alumina or gamma-alumina; and synthesizing an h-BN thin
film at equal to or less than 750.degree. C. on the alumina thin
film, wherein a mono-layer thickness of the h-BN film is equal to
or less than 0.40 nm.
2. The method of claim 1, wherein amorphous alumina in the alumina
thin film is crystallized and changed to gamma-alumina when the
h-BN thin film is synthesized.
3. The method of claim 1, wherein the alumina thin film includes
gamma-alumina, and has a thickness equal to or less than 100 nm,
wherein (110) plane is more than 50% at an upper surface of the
alumina thin film, and a root mean square roughness of the alumina
thin film is equal to or less than 0.2 nm.
4. The method of claim 1, further comprising: physically adhering a
masking block to a portion of an upper surface of the gamma-alumina
thin film before the h-BN thin film is synthesized, wherein the
h-BN thin film is selectively formed on an exposed upper surface of
the gamma-alumina thin film.
5. The method of claim 1, wherein nitrogen atoms in the h-BN thin
film are partially replaced by carbon atoms.
6. A method for forming a stacked structure, the method comprising:
preparing an alumina thin film including amorphous alumina or
gamma-alumina; synthesizing an h-BN thin film on the alumina thin
film, wherein a mono-layer thickness of the h-BN film is equal to
or less than 0.40 nm; and synthesizing a graphene thin film at an
interface between the h-BN film and the alumina thin film.
7. The method of claim 6, wherein the alumina thin film includes
gamma-alumina, and has a thickness equal to or less than 100 nm,
wherein (110) plane is more than 50% at an upper surface of the
alumina thin film, and a root mean square roughness of the alumina
thin film is equal to or less than 0.2 nm.
8. The method of claim 6, wherein the graphene thin film is
synthesized at equal to or less than 800.degree. C., wherein a
process gas provided for synthesizing the graphene thin film
includes hydrocarbon gas.
9. The method of claim 8, wherein the process gas further includes
an oxygen-containing gas as a growth inhibitor.
10. The method of claim 6, further comprising: physically adhering
a catalyst block including a catalyst material to an upper surface
of the h-BN thin film before the graphene thin film is synthesized,
wherein the graphene thin film includes a lower graphene thin film
synthesized at the interface between the h-BN film and the alumina
thin film, and un upper graphene thin film synthesized at the
interface between the h-BN film and the catalyst block.
11. A method for manufacturing a switching element, the method
comprising: forming a gate electrode on a substrate; forming an
alumina thin film including amorphous alumina or gamma-alumina on
the gate electrode; synthesizing an h-BN thin film on the alumina
thin film, wherein a mono-layer thickness of the h-BN film is equal
to or less than 0.40 nm; forming a channel layer including a
two-dimensional active material on the h-BN thin film; and forming
an electrode contacting the channel layer.
12. The method of claim 11, wherein the channel layer include
graphene or transitional metal dichalcogenide.
13. The method of claim 11, wherein the thickness of the alumina
thin film is equal to or less than 100 nm, and the thickness of the
h-BN thin film is equal to or more than 2 nm
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority under 35 U.S.C. .sctn. 119
to Korean Patent Application No. 10-2018-0134962, filed on Nov. 6,
2018, and all the benefits accruing therefrom, the content of which
is herein incorporated by reference in its entirety.
BACKGROUND
1. Field
[0002] Exemplary embodiments relate to a method for forming a
hexagonal boron nitride thin film. More particularly, exemplary
embodiments relate to a method for forming a hexagonal boron
nitride thin film, a method for forming a multi-layered structure
and a method for manufacturing a switching element.
2. Description of the Related Art
[0003] Hexagonal boron nitride (h-BN) is a two-dimensional material
not having surface dangling bonds. Thus, h-BN does not cause
adsorbate doping to a material disposed thereon. Thus, intrinsic
performance of the material disposed on h-BN may be achieved.
[0004] Furthermore, h-BN has a small lattice mismatch with
graphene, and does not cause strain because of its flexibility.
Thus, h-BN is an important material to achieve the intrinsic
performance of graphene. Therefore, technologies capable of forming
h-BN having a high quality is necessary.
SUMMARY
[0005] Exemplary embodiments provide a method for forming a
hexagonal boron nitride thin film having a high quality.
[0006] Exemplary embodiments provide a method for forming a
multiple-layered structure including a hexagonal boron nitride thin
film.
[0007] Exemplary embodiments provide a method for manufacturing a
switching element including a hexagonal boron nitride thin
film.
[0008] According to an exemplary embodiment, a method for forming a
hexagonal boron nitride (h-BN) thin film is provided. According to
the method, an alumina thin film including amorphous alumina or
gamma-alumina is prepared. An h-BN thin film is synthesized at
equal to or less than 750.degree. C. on the alumina thin film. A
mono-layer thickness of the h-BN film is equal to or less than 0.40
nm.
[0009] According to an exemplary embodiment, a method for forming a
stacked structure is provided. According to the method, an alumina
thin film including amorphous alumina or gamma-alumina is prepared.
An h-BN thin film is synthesized on the alumina thin film. A
mono-layer thickness of the h-BN film is equal to or less than 0.40
nm. A graphene thin film is synthesized at an interface between the
h-BN film and the alumina thin film.
[0010] According to an exemplary embodiment, a method for
manufacturing a switching element is provided. According to the
method, a gate electrode is formed on a substrate. An alumina thin
film including amorphous alumina or gamma-alumina is formed on the
gate electrode. An h-BN thin film is synthesized on the alumina
thin film. A mono-layer thickness of the h-BN film is equal to or
less than 0.40 nm. A channel layer including a two-dimensional
active material is formed on the h-BN thin film. An electrode is
formed to contact the channel layer.
[0011] According to the exemplary embodiments, an h-BN thin film
having a high quality, which may not be obtained by conventional
methods, may be formed at a low temperature.
[0012] Furthermore, a graphene thin film pattern and/or an h-BN
thin film pattern may be formed by using a catalyst block and/or a
masking block without an individual pattering process. Thus,
contamination or damage of the thin films due to a patterning
process such as transferring, etching or the like may be prevented,
and manufacturing efficiencies may be improved.
[0013] Furthermore, combination of a gamma-alumina thin film and an
h-BN thin film may provide a gate dielectric layer having superior
characteristics thereby forming a switching element achieving a
high performance with a low power consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] The above and other features and advantages will become more
apparent by describing exemplary embodiments thereof with reference
to the accompanying drawings, in which:
[0015] FIGS. 1A to 1B are cross-sectional views illustrating a
method for forming a hexagonal boron nitride thin film according to
an exemplary embodiment.
[0016] FIGS. 2A to 2C are cross-sectional views illustrating a
method for forming a stacked structure of an h-BN thin film and a
graphene thin film according to an exemplary embodiment.
[0017] FIGS. 3A to 3C are cross-sectional views illustrating a
method for forming a stacked structure of an h-BN thin film and a
graphene thin film according to another exemplary embodiment.
[0018] FIGS. 4A to 4E are cross-sectional views illustrating a
method for forming a stacked structure of an h-BN thin film and a
graphene thin film according to another exemplary embodiment.
[0019] FIGS. 5A to 5E are cross-sectional views illustrating a
method for manufacturing a switching element according to an
exemplary embodiment.
[0020] FIG. 6 is an XRD analysis graph of the thin films obtained
by Example 1.
[0021] FIG. 7A are XPS analysis graphs of the thin films obtained
by Example 1 and Comparative Example 1.
[0022] FIG. 7B are XPS analysis graphs of the thin films obtained
by Example 1 and Example 2.
DETAILED DESCRIPTION
[0023] Example embodiments are described more fully hereinafter
with reference to the accompanying drawings. The inventive concept
may, however, be embodied in many different forms and should not be
construed as limited to the example embodiments set forth herein.
In the drawings, the sizes and relative sizes of layers and regions
may be exaggerated for clarity. It will be understood that,
although the terms first, second, third etc. may be used herein to
describe various elements, components, regions, layers, patterns
and/or sections, these elements, components, regions, layers,
patterns and/or sections should not be limited by these terms.
These terms are only used to distinguish one element, component,
region, layer pattern or section from another region, layer,
pattern or section. Thus, a first element, component, region, layer
or section discussed below could be termed a second element,
component, region, layer or section without departing from the
teachings of example embodiments.
[0024] Example embodiments are described herein with reference to
cross sectional illustrations that are schematic illustrations of
illustratively idealized example embodiments (and intermediate
structures) of the inventive concept. As such, variations from the
shapes of the illustrations as a result, for example, of
manufacturing techniques and/or tolerances, are to be expected.
Thus, example embodiments should not be construed as limited to the
particular shapes of regions illustrated herein but are to include
deviations in shapes that result, for example, from manufacturing.
The regions illustrated in the figures are schematic in nature and
their shapes are not intended to illustrate the actual shape of a
region of a device and are not intended to limit the scope of the
inventive concept.
[0025] The terminology used herein is for the purpose of describing
particular example embodiments only and is not intended to be
limiting of the invention. As used herein, the singular forms "a,"
"an" and "the" are intended to include the plural forms as well,
unless the context clearly indicates otherwise. It will be further
understood that the terms "comprises" and/or "comprising," when
used in this specification, specify the presence of stated
features, integers, steps, operations, elements, and/or components,
but do not preclude the presence or addition of one or more other
features, integers, steps, operations, elements, components, and/or
groups thereof.
[0026] Unless otherwise defined, all terms (including technical and
scientific terms) used herein have the same meaning as commonly
understood by one of ordinary skill in the art to which this
inventive concept belongs. It will be further understood that
terms, such as those defined in commonly used dictionaries, should
be interpreted as having a meaning that is consistent with their
meaning in the context of the relevant art and will not be
interpreted in an idealized or overly formal sense unless expressly
so defined herein.
[0027] Method for Forming a Hexagonal Boron Nitride Thin Film
[0028] FIGS. 1A to 1B are cross-sectional views illustrating a
method for forming a hexagonal boron nitride thin film according to
an exemplary embodiment.
[0029] Referring to FIG. 1A, a catalyst substrate including an
alumina thin film is prepared. The alumina thin film may include
amorphous alumina or gamma-alumina (.gamma.-Al.sub.2O.sub.3). In an
exemplary embodiment, the catalyst substrate may include a
gamma-alumina thin film 20 disposed on a base substrate 10. For
example, the base substrate 10 may include silicon, silicon oxide,
glass or the like.
[0030] The gamma-alumina thin film 20 may have a single-crystalline
phase or a poly-crystalline phase.
[0031] Gamma-alumina has a defect spinel structure at a surface
thereof. The defect spinel structure of gamma-alumina includes an
aluminum tri-coordination (Al.sub.III) site. The aluminum
tri-coordination site is not stable. Thus, when a precursor such as
borazine is adsorbed on a surface of gamma-alumina, the aluminum
tri-coordination site reduces an activation barrier for
dehydrogenation thereby functioning as a catalyst.
[0032] Furthermore, gamma-alumina may inhibit decomposition of the
precursor thereby forming an h-BN thin film of a mono-layer or a
bi-layer through surface limited growth.
[0033] Furthermore, gamma-alumina has a small lattice mismatch to
h-BN. Thus, defects caused by a lattice mismatch or strain
therefrom may be effectively inhibited. Thus, an h-BN thin film may
be formed through epitaxial-like growth. Therefore, an h-BN thin
film having a high quality with inhibited defects may be
formed.
[0034] In an exemplary embodiment, (110) plane may be dominant at
an upper surface of the gamma-alumina thin film 20. For example,
(110) plane may be more than 50% at an upper surface of the
gamma-alumina thin film 20. For example, sum of (110) plane and
(111) plane may be equal to or more than 99%.
[0035] Furthermore, a surface of the gamma-alumina thin film 20 has
a fine 3-dimensional convexo-concave structure. Such
convexo-concave structure may reduce strain due to lattice
mismatch. Thus, defects may be inhibited when the h-BN film is
formed on the gamma-alumina thin film 20.
[0036] For example, the root mean square roughness of the
gamma-alumina thin film 20 may be equal to or less than 2 nm, and
may be preferably equal to or less than 0.2 nm. When the root mean
square roughness of the gamma-alumina thin film 20 is excessively
large, defects may be increased in the h-BN thin film formed on the
gamma-alumina thin film 20.
[0037] For example, the thickness of the gamma-alumina thin film 20
may be equal to or less than 100 nm, preferably equal to or less
than 50 nm and more preferably equal to or less than 10 nm. When
the thickness of the gamma-alumina thin film 20 is excessively
large, defects such as wrinkles may be formed in the h-BN thin film
due to difference between thermal expansion efficiencies of the
gamma-alumina thin film 20 and the h-BN thin film formed on the
gamma-alumina thin film 20. Furthermore, less thickness may be
advantageous for forming gamma phase of alumina.
[0038] In an exemplary embodiment, the gamma-alumina thin film 20
may be formed by a deposition method. For example, the
gamma-alumina thin film 20 may be formed by chemical vaporization
deposition (CVD) including atomic layer deposition (ALD), molecular
beam epitaxy (MBE) growth or the like.
[0039] For example, an amorphous alumina thin film may be formed by
ALD, and the amorphous alumina thin film may be changed to the
gamma-alumina thin film 20 through a heat treatment.
[0040] For example, an aluminum precursor and an oxygen precursor
may be provided in an ALD process to form the amorphous alumina
thin film. For example, the aluminum precursor may include
trimethyl aluminium ((CH.sub.3).sub.3Al, TMA), aluminum isoproxide,
([Al(OC.sub.3H.sub.7).sub.3], IPA), methyl-pyrolidine-tri-methyl
aluminum (MPTMA), ethyl-pyridinetriethyl-aluminum (EPPTEA)
ethyl-pyridine-dimethyl-aluminumhydridge, EPPDMAH, AlCH.sub.3 or a
combination thereof.
[0041] For example, a crystallization process using a heat
treatment may be performed at about 100.degree. C. to 1,450.degree.
C. for 1 to 30 minutes.
[0042] The crystallization process using a heat treatment may be
omitted. For example, a deposition temperature in a CVD process and
an ALD process may be controlled, or an MBE growth may be performed
to form a gamma-alumina thin film without an individual heat
treatment process.
[0043] Referring to FIG. 1B, an h-BN thin film 30 is formed on the
gamma-alumina thin film 20.
[0044] For example, the h-BN thin film 30 may be formed by
deposition. For example, the h-BN thin film 30 may be formed by
various deposition methods including CVD.
[0045] In an exemplary embodiment, a growth temperature of the h-BN
thin film 30 may be equal to or less than about 1,200.degree. C.
Preferably, the growth temperature of the h-BN thin film 30 may be
equal to or less than about 750.degree. C. The h-BN thin film 30
having a structure of a mono-layer or bi-layer may be formed
through surface limited growth at equal to or less than about
750.degree. C.
[0046] For example, the growth temperature of the h-BN thin film 30
may be about 100.degree. C. to 750.degree. C. When the growth
temperature is excessively low, a growth rate of the h-BN thin film
30 may be excessively reduced, or defects in h-BN thin film 30 may
be increased. Furthermore, when formed on the gamma-alumina thin
film 20, the h-BN thin film 30 may be synthesized at a temperature
lower than when formed on an amorphous alumina thin film.
[0047] For example, borazine (N.sub.3B.sub.3H.sub.6) may be used as
a source for forming the h-BN thin film 30. Borazine may be
dehydrogenated thereby forming h-BN. In another exemplary
embodiment, a nitrogen source and a boron source may be separately
provided. For example, borane such as BH.sub.3 may be used as a
boron source, and ammonia may be used as a nitrogen source.
Furthermore, hydrogen gas (H.sub.2) may be added for adjusting flux
of the source gas or for reducing the growth temperature. An inert
gas such as argon may be used as a carrier gas.
[0048] The h-BN thin film 30 may have extremely inhibited defects
such as sp3 bonds, C--N bonds, B--O bonds or the like thereby
having a high quality. Thus, the h-BN thin film 30 may have a small
thickness close to an ideal thickness. For example, the thickness
of a mono-layer in the h-BN thin film 30 may be equal or less than
0.40 nm, and the thickness of a bi-layer in the h-BN thin film 30
may be equal or less than 0.80 nm. In an exemplary embodiment, the
thickness of a mono-layer in the h-BN thin film 30 may be equal or
less than 0.36 nm, and the thickness of a bi-layer in the h-BN thin
film 30 may be equal or less than 0.72 nm.
[0049] In an exemplary embodiment, the h-BN thin film 30 may have a
thickness of a mono-layer or a bi-layer. However, exemplary
embodiments are not limited thereto, and the thickness of the h-BN
thin film 30 may be increased as desired. For example, the CVD
process for forming the h-BN thin film 30 may be performed at more
than 750.degree. C. in order to increase the thickness of the h-BN
thin film 30 to be equal to or more than a triple-layer.
[0050] In another exemplary embodiment, the h-BN thin film 30 may
be formed on an amorphous alumina thin film. The amorphous alumina
thin film may be crystallized by heat in the CVD process for
forming the h-BN thin film 30 thereby forming the gamma-alumina
thin film 20.
[0051] In another exemplary embodiment, the h-BN thin film 30 may
include hexagonal boron nitride carbide (h-BNC) in which nitrogen
atoms are partially replaced by carbon atoms. The h-BNC may be used
for a sensor, a switching element, a light-emitting element, a
tunable resistor by adjusting a band gap thereof. For example, the
h-BNC may be formed by adding a carbon source to a source gas. The
carbon source may include various materials such as methane,
ethane, carbon dioxide or the like.
[0052] In an exemplary embodiment, the h-BN thin film 30 having a
high quality, which may not be obtained by conventional methods,
may be formed at a low temperature. The h-BN thin film 30 may be
used for synthesis of graphene having a high quality, an
electro-optical element, a doping barrier or the like.
[0053] Since the h-BN thin film 30 does not have dangling bonds at
a surface thereof, an adhesion energy between the h-BN thin film 30
and the gamma-alumina thin film 20 is low. Thus, the h-BN thin film
30 may be easily separated from the gamma-alumina thin film 20 by
an external force as desired. The catalyst substrate including the
gamma-alumina thin film 20 may be reused for forming another h-BN
thin film.
[0054] Method for Forming a Stacked Structure
[0055] FIGS. 2A to 2C are cross-sectional views illustrating a
method for forming a stacked structure of an h-BN thin film and a
graphene thin film according to an exemplary embodiment.
[0056] Referring to FIG. 2A, a catalyst substrate including an
alumina thin film is prepared. The alumina thin film may include
amorphous alumina or gamma-alumina. In an exemplary embodiment, the
alumina thin film may include gamma-alumina crystallized by heat
treatment. When the alumina thin film includes amorphous alumina,
the amorphous alumina may be crystallized in a following CVD
process or the like thereby forming gamma-alumina.
[0057] For example, a gamma-alumina thin film 120 may be formed as
a pattern on a base substrate 100. For example, the gamma-alumina
thin film 120 may be patterned after or before crystallized.
[0058] Referring to FIG. 2B, an h-BN thin film 130 is formed on the
gamma-alumina thin film 120. Processes for forming the h-BN thin
film 130 and the gamma-alumina thin film 120 may be substantially
same as the previously explained exemplary embodiment. Thus, any
duplicated explanation may be omitted.
[0059] The h-BN thin film 130 may be formed according to surface
limited growth using the gamma-alumina thin film 120 as a catalyst.
Thus, the h-BN thin film 130 may be formed as a pattern on the
gamma-alumina thin film 120.
[0060] Referring to FIG. 2c, a graphene thin film 130 is formed
between the h-BN thin film 130 and the gamma-alumina thin film
120.
[0061] The h-BN thin film 130 does not have dangling bonds at a
surface thereof. Thus, the h-BN thin film 130 is not chemically
bonded to the gamma-alumina thin film 120, but is physically
adhered to the gamma-alumina thin film 120 thereby forming an
interface.
[0062] For example, the substrate including the stacked structure
of the h-BN thin film 130 and the gamma-alumina thin film 120 may
be disposed in a chamber, and a CVD process may be performed for
synthesizing graphene. Hydrocarbons such as methane, ethane or the
like may be provided as a carbon source for synthesizing graphene.
In an exemplary embodiment, methane gas may be used for a carbon
source.
[0063] The carbon source may be dehydrogenated on an exposed
surface of the gamma-alumina thin film 120 by catalyst activation
thereby generating source atoms such as carbon atoms. The carbon
atoms generated from the carbon source may be diffused at the
interface between the h-BN thin film 130 and the gamma-alumina thin
film 120. Thus, the graphene thin film 140 may be synthesized
between the h-BN thin film 130 and the gamma-alumina thin film
120.
[0064] For example, the graphene thin film 140 may be formed at
150.degree. C. to 1,200.degree. C. In an exemplary embodiment, the
graphene thin film 140 may be synthesized at a relatively low
temperature by catalyst activation of the gamma-alumina thin film
120. Preferably, the graphene thin film 140 may be synthesized at a
lower temperature compared with other methods for synthesizing
graphene, for example, at 150.degree. C. to 800.degree. C.
[0065] In an exemplary embodiment, synthesis of the graphene thin
film 140 may be performed under a process condition including a
carbon source and a growth inhibitor. Thus, an atmosphere in which
the graphene thin film 140 is synthesized may include at least the
carbon source and the growth inhibitor. The growth inhibitor may
include an oxygen-containing material such as an oxygen gas,
hydrogen oxide or the like.
[0066] Accordingly, graphene is not synthesized in an exposed area
excluding the interface, because combustion reaction of the carbon
atoms with the growth inhibitor or oxygen atoms from the growth
inhibitor is predominant to graphitization reaction. Thus, the
graphene thin film 140 is selectively formed between the h-BN thin
film 130 and the gamma-alumina thin film 120 to form a graphene
pattern.
[0067] For example, a concentration of the growth inhibitor, which
is a volume ratio to the carbon source, may be equal to or more
than 1/10.sup.6 so that combustion reaction may be predominant at
an area excluding the interface. The concentration of the growth
inhibitor, which satisfies the condition, may be varied depending
on a process temperature. For example, the concentration of the
growth inhibitor to the carbon source may be equal to or more than
1/10.sup.5 at 800.degree. C. to 1,200.degree. C. In an exemplary
embodiment, the concentration of the growth inhibitor to the carbon
source may be equal to or more than 1/10.sup.4 to further promote
the combustion reaction in an exposed area excluding the interface.
The concentration of the growth inhibitor may be a concentration of
molecules, and a concentration of oxygen atoms generated from the
growth inhibitor to the carbon atoms from the carbon source may be
different from the concentration of molecules. For example, the
concentration of the oxygen atoms to the carbon atoms may be equal
to or more than 1/10.sup.3, may be preferably equal to or more than
1/10.sup.2.
[0068] A thickness of the graphene thin film 140 may be controlled.
For example, the graphene thin film 140 may have a thickness of a
mono-layer or a bi-layer as well as a thickness equal to or more
than a triple-layer. For example, a thickness of the graphene thin
film 140 may be at least 0.33 nm, and may be increased depending on
a process condition.
[0069] The graphene thin film 140 may have extremely inhibited
defects thereby having a high quality.
[0070] In the CVD process, impurities causing defects of graphene
may enter a process chamber. When the graphene thin film 140 is
formed at the interface between the h-BN thin film 130 and the
gamma-alumina thin film 120 as an exemplary embodiment, affection
of impurities in the process chamber may be minimized. Atoms or
molecules are diffused according to interfacial diffusion between
the h-BN thin film 130 and the gamma-alumina thin film 120.
Diffusivity of the atoms or the molecules according to interfacial
diffusion may be varied drastically depending kinds of the atoms
and the molecules. For example, diffusivity according to
interfacial diffusion may be calculated as the following:
D .apprxeq. v 0 exp ( - E d k B T ) ##EQU00001##
[0071] .nu..sub.0: n-th order vibrational frequency, (mostly
10.sup.13/s)
[0072] E.sub.d: interfacial diffusion barrier
[0073] k.sub.B: Boltzmann constant (8.62.times.10.sup.-5 eV/K)
[0074] T: absolute temperature (K)
[0075] According to the above, a ratio of diffusivities of carbon
atoms and oxygen molecules is at least 20,000. Thus, affection of
impurities such as oxygen molecules may be minimized in the process
of synthesizing graphene. Therefore, graphene having inhibited
defects may be obtained.
[0076] In an exemplary embodiment, a graphene thin film pattern may
be formed without an individual pattering process. Furthermore,
h-BN is a two-dimensional material having a similar structure to
graphene, and may provide a template, of which lattice mismatch is
minimized to graphene, for synthesizing graphene. Thus, strain and
defects of the graphene thin film may be reduced and/or minimized
so that the graphene thin film has a high quality.
[0077] In an exemplary embodiment, a stacked structure of an h-BN
thin film and a graphene thin film may be obtained, and the stacked
structure may be formed as a pattern by using a patterned catalyst
thin film without an individual pattering process.
[0078] FIGS. 3A to 3C are cross-sectional views illustrating a
method for forming a stacked structure of an h-BN thin film and a
graphene thin film according to another exemplary embodiment.
[0079] Referring to FIG. 3A, a catalyst substrate is prepared. The
catalyst substrate includes a gamma-alumina thin film 120 disposed
on a base substrate 100, and an h-BN thin film 130 disposed on the
gamma-alumina thin film 120. Processes for forming the h-BN thin
film 130 and the gamma-alumina thin film 120 may be substantially
same as the previously explained exemplary embodiment. Thus, any
duplicated explanation may be omitted.
[0080] Thereafter, a catalyst block 200 is physically adhered to
the h-BN thin film 130. In an exemplary embodiment, the catalyst
block 200 may include a body 210 and a catalyst layer 220 covering
a surface of the body 210. The catalyst layer 220 may cover at
least a lower surface of the body 210, and may contact an upper
surface of the h-BN thin film 130. For example, the body 210 may
include silicon, silicon oxide, metals, metal oxides or a
combination thereof.
[0081] In another exemplary embodiment, the catalyst layer 220 may
further cover a side surface of the body 210 to increase a contact
area with a carbon source.
[0082] The catalyst block 200 may function as a catalyst to form a
graphene thin film on the upper surface of the h-BN thin film 130.
Furthermore, the catalyst block 200 is physically adhered to the
upper surface of the h-BN thin film 130 thereby forming an
interfacial diffusion barrier for a growth inhibitor between the
catalyst block 200 and the h-BN thin film 130. For example, a
distance between the catalyst block 200 and the h-BN thin film 130
may be equal to or less than 2 nm.
[0083] In order to physically adhere the catalyst block 200 to the
h-BN thin film 130, a contact surface of the catalyst block 200 may
be cleaned.
[0084] For example, cleaning the contact surface of the catalyst
block 200 may include steps of chemical cleaning, physical cleaning
and drying.
[0085] In an exemplary embodiment, Piranha solution may be used for
the chemical cleaning. The Piranha solution may be obtained by
mixing sulfuric acid with hydrogen peroxide. For example, the
contact surface of the catalyst block 200 may be dipped in the
Piranha solution for the chemical cleaning.
[0086] In an exemplary embodiment, supersonic wave and water may be
used for the physical cleaning. For example, a process such as
Megasonic cleaning may be used for generating an acoustic field
thereby removing particles on the contact surface of the catalyst
block 200.
[0087] In an exemplary embodiment, nitrogen gas or the like may be
provided for drying.
[0088] Furthermore, a contact surface of the h-BN thin film 130 may
be cleaned by same processes as the above.
[0089] After the cleaning process, the catalyst block 200 and the
h-BN thin film 130 are disposed to contact each other such that the
contact surface of the catalyst block 200 is parallel with an upper
surface of the h-BN thin film 130. Accordingly, the catalyst block
200 is physically adhered to the h-BN thin film 130 thereby forming
the interfacial diffusion barrier to the growth inhibitor between
the catalyst block 200 and the h-BN thin film 130.
[0090] Referring to FIG. 3B, a lower graphene thin film 140a is
formed between the h-BN thin film 130 and the gamma-alumina thin
film 120, and an upper graphene thin film 140b is formed between
the h-BN thin film 130 and the catalyst block 200.
[0091] For example, graphene thin films may be formed through a CVD
process. The graphene thin films may be synthesized in an
atmosphere including a carbon source and a growth inhibitor.
[0092] As previously explained in the above, a carbon source such
as methane may be dehydrogenated by the gamma-alumina thin film 120
and the catalyst block 200 to provide carbon atoms. The carbon
atoms may be diffused at an interface between the h-BN thin film
130 and the gamma-alumina thin film 120 and at an interface between
the h-BN thin film 130 and the catalyst block 200. Furthermore,
diffusion of the growth inhibitor at the interfaces is extremely
inhibited. Furthermore, graphene is not synthesized in an exposed
area excluding the interfaces because of combustion reaction of the
carbon atoms and the growth inhibitor. Thus, the graphene thin
films may be selectively formed between the h-BN thin film 130 and
the gamma-alumina thin film 120 and between the h-BN thin film 130
and the catalyst block 200.
[0093] Referring to FIG. 3C, the catalyst block 200 is separated
from the upper graphene thin film 140b. An adhesion energy between
the upper graphene thin film 140b and the h-BN thin film 130 is
larger than an adhesion energy between the upper graphene thin film
140b and the catalyst layer 220 including gamma-alumina. Thus, when
an external force is applied to the catalyst block 200, the
catalyst block 200 may be easily separated from the upper graphene
thin film 140b.
[0094] Generally, it may be difficult to separate members that are
physically adhered to each other through chemical and physical
cleaning. However, according to an exemplary embodiment, the upper
graphene thin film 140b is formed between the h-BN thin film 130
and the catalyst block 200, and an adhesion energy between the
upper graphene thin film 140b and the catalyst layer 220 including
gamma-alumina is relatively low. Thus, the catalyst block 200 may
be easily separated. The catalyst bock 200 may be reused for
another process for synthesizing graphene.
[0095] According to an exemplary embodiment, graphene thin films
may be formed on both surfaces of the h-BN thin film through a
single deposition process. A stacked structure of graphene thin
film/h-BN thin film/graphene thin film may be used for various
elements including a capacitor. Furthermore, the stacked structure
may have various shapes by using the catalyst block.
[0096] FIGS. 4A to 4E are cross-sectional views illustrating a
method for forming a stacked structure of an h-BN thin film and a
graphene thin film according to another exemplary embodiment.
[0097] Referring to FIG. 4A, a catalyst substrate is prepared. The
catalyst substrate includes an alumina thin film disposed on a base
substrate 100. In an exemplary embodiment, the alumina thin film
may be a gamma-alumina thin film 122. When the alumina thin film
includes amorphous alumina, the alumina thin film may be changed
into a gamma-alumina thin film in the process of forming an h-BN
thin film.
[0098] Thereafter, a masking block 202 is physically adhered to the
gamma-alumina thin film 122. The masking block 202 may cover a
portion of an upper surface of the gamma-alumina thin film 122.
Thus, the upper surface of the gamma-alumina thin film 122 is
partially exposed.
[0099] In an exemplary embodiment, the masking block 202 may
include a catalyst material such as gamma-alumina. However,
exemplary embodiments are not limited thereto, and the masking
block 202 may not include a catalyst material in another exemplary
embodiment.
[0100] Referring to FIG. 4B, an h-BN thin film 132 is formed on an
exposed upper surface of the gamma-alumina thin film 122. For
example, the h-BN thin film 132 may be formed through a CVD
process.
[0101] As previously explained in the above, borazine may be used
as a source gas for forming the h-BN thin film 132. The
gamma-alumina thin film 122 is physically adhered to the masking
block 202 thereby forming a diffusion barrier for the source gas.
Thus, the source gas is not provided between the gamma-alumina thin
film 122 and the masking block 202. Thus, the h-BN thin film 132 is
selectively formed on the exposed upper surface of the
gamma-alumina thin film 122.
[0102] Referring to FIG. 4C, a graphene thin film 142 is formed
between the gamma-alumina thin film 122 and the masking block 202
and between the gamma-alumina thin film 122 and the h-BN thin film
132.
[0103] The graphene thin film 142 may be synthesized in an
atmosphere including a carbon source and a growth inhibitor.
[0104] The carbon atoms generated from the carbon source may be
diffused at an interface between the h-BN thin film 132 and the
gamma-alumina thin film 122 and at an interface between the masking
block 202 and the gamma-alumina thin film 122. Furthermore,
diffusion of the growth inhibitor at the interfaces is extremely
inhibited. Furthermore, graphene is not synthesized in an exposed
area excluding the interfaces because of combustion reaction of the
carbon atoms and the growth inhibitor. Thus, the graphene thin film
142 having a high quality may be selectively formed at the
interfaces.
[0105] Referring to FIG. 4D, the masking block 202 is removed from
the graphene thin film 142. Thus, the h-BN thin film 132 may be
formed as a pattern having an opening or a gap, which correspond to
a contact surface of the masking block 202.
[0106] Accordingly, the patterned h-BN thin film 132 may be formed
on the graphene thin film 142 without an individual patterning
process.
[0107] In another exemplary embodiment, the masking block 202 may
be removed before the graphene thin film 142 is formed. When
graphene is synthesized without the masking block 202, a graphene
thin film 142 is formed between the h-BN thin film 132 and the
gamma-alumina thin film 122 without covering an exposed surface of
the gamma-alumina thin film 122. Thus, as illustrated in FIG. 4E,
stacked structures of h-BN/graphene, which are spaced apart from
each other, may be formed.
[0108] Method for Manufacturing a Switching Element
[0109] FIGS. 5A to 5E are cross-sectional views illustrating a
method for manufacturing a switching element according to an
exemplary embodiment.
[0110] Referring to FIG. 5A, an alumina thin film is formed on a
base substrate 100 including a gate electrode 110 formed thereon.
In an exemplary embodiment, the alumina thin film may include
gamma-alumina crystallized through a heat treatment. When the
alumina thin film include amorphous alumina, the amorphous alumina
may be crystallized in a following CVD process or the like thereby
forming gamma-alumina.
[0111] In an exemplary embodiment, the base substrate 100 may have
a trench recessed from an upper surface of the base substrate 100,
and the gate electrode 110 may be disposed in the trench. However,
exemplary embodiments are not limited thereto. For example, the
gate electrode 110 may be formed on a flat upper surface of the
base substrate 100 to have an exposed side surface, and a
gamma-alumina thin film 124 may be formed to be conformal on an
upper surface and a side surface of the gate electrode 110 and on
the upper surface of the base substrate 100.
[0112] For example, the gate electrode 110 may include a metal. For
example, the gate electrode 110 may include titanium, aluminum,
tungsten, copper, molybdenum, gold, silver, nickel, an alloy
thereof, a conductive nitride thereof or the like.
[0113] In an exemplary embodiment, the gamma-alumina thin film 124
is formed on the gate electrode 110. The gamma-alumina thin film
124 may be formed as a pattern covering an upper surface of the
gate electrode 120 and a portion of an upper surface of the base
substrate 100.
[0114] Referring to FIG. 5B, an h-BN thin film 134 is formed on the
gamma-alumina thin film 124. In an exemplary embodiment, the h-BN
thin film 134 may continuously cover an upper surface and a side
surface of the gamma-alumina thin film 124 and an exposed upper
surface of the base substrate 100.
[0115] In an exemplary embodiment, the h-BN thin film 134 may be
formed on the upper surface of the gamma-alumina thin film 124
through surface limited growth by a catalyst at a low temperature
to have a structure of a mono-layer or a bi-layer. Thereafter, the
h-BN thin film 134 may further grow at a high temperature to cover
the side surface of the gamma-alumina thin film 124 and the exposed
upper surface of the base substrate 100.
[0116] In another exemplary embodiment, the h-BN thin film 134 may
continuously grow at a high temperature.
[0117] Referring to FIG. 5C, a channel layer 144 is formed on the
h-BN thin film 134. At least a portion of the channel layer 144 may
overlap the gate electrode 110.
[0118] For example, the channel layer 144 may include a
two-dimensional active material. For example, the two-dimensional
active material may include graphene, a transitional metal
dichalcogenide or the like. For example, the transitional metal
dichalcogenide may include molybdenum sulfide, molybdenum selenide,
tungsten sulfide, tungsten selenide, titanium selenide or the
like.
[0119] In an exemplary embodiment, the channel layer 144 may be
formed as a pattern partially covering an upper surface of the h-BN
thin film 134, or as a continuous layer entirely covering the upper
surface of the h-BN thin film 134.
[0120] Referring to FIG. 5D, a first electrode 152 and a second
electrode 154 are formed to contact the channel layer 144. The
first electrode 152 and the second electrode 154 may be spaced
apart from each other, and may function as a source electrode and a
drain electrode, respectively. The first electrode 152 and the
second electrode 154 may be formed of various conductive materials
including metals.
[0121] In an exemplary embodiment, the h-BN thin film 134 may
continuously cover the upper surface of the gamma-alumina thin film
124 and the upper surface of the base substrate 100. However,
exemplary embodiments are not limited thereto. For example, an h-BN
thin film 134 may be formed selectively on the gamma-alumina thin
film 124 as illustrated in FIG. 5E.
[0122] According to an exemplary embodiment, a combination of the
gamma-alumina thin film 124 and the h-BN thin film 134 is provided
for a gate dielectric layer of a switching element. The combination
may provide advantages as the gate dielectric layer. For example,
since the h-BN thin film 134 does not have dangling bonds, doping
of an active material contacting the h-BN thin film 134 may be
prevented. Furthermore, since gamma-alumina has a high
permittivity, the combination may provide a gate dielectric layer
having superior dielectric properties and surface properties.
[0123] Furthermore, if defects exist in the h-BN thin film 134, the
defects may form dipole when an electric field is applied thereto.
Thus, transmitting the electric field may be hindered, and an h-BN
thin film having many defects may be easily broke down. However,
according to an exemplary embodiment, defects in the h-BN thin film
134 may be inhibited. Thus, break-down by an electric field may be
prevented. Therefore, a total thickness of the gate dielectric
layer may be reduced. Furthermore, since a strong electric field
may be formed by a small voltage, a switching element may be driven
by lower power consumption.
[0124] Furthermore, since the h-BN thin film 134 includes a
two-dimensional insulation material and has few defects, the
two-dimensional active material formed thereon may have a high
quality.
[0125] A thickness of the gamma-alumina thin film 124 and the h-BN
thin film 134 may be designed according to desired permittivity or
the like.
[0126] For example, the thickness of the gamma-alumina thin film
124 may be equal to or less than 100 nm. When the thickness of the
gamma-alumina thin film 124 is excessively large, the quality of
the h-BN thin film 134 may be deteriorated by wrinkle. When the
thickness of the gamma-alumina thin film 124 is excessively small,
permittivity may be reduced. For example, the thickness of the h-BN
thin film 134 may be equal to or more than 2 nm, and preferably 2
nm to 20 nm so that the combination of the gamma-alumina thin film
124 and the h-BN thin film 134 may have appropriate characteristic
as the gate dielectric layer.
[0127] Hereinafter, effects of exemplary embodiments will be
explained with reference to particular examples and experiments
[0128] Experiment 1--Evaluation of Catalyst Characteristics of
Gamma-Alumina
Synthetic Example 1--Forming Amorphous Alumina Thin Film
[0129] An alumina (Al.sub.2O.sub.3) thin film was formed on a base
substrate at 150.degree. C. in an atomic layer deposition (ALD)
reactor. The base substrate included SiO.sub.2/Si having a
thickness of 300 nm. Trimethylaluminum and deionized water were
used for a precursor of an ALD process. A pressure was 1 torr, and
pulse-maintaining time was 1 second with providing high-purity
nitrogen gas (99.99%) for 60 seconds with 200 sccm in the ALD
reactor. Under the above condition, 500 cycles were performed to
form an amorphous alumina thin film having a thickness of 50
nm.
Synthetic Example 2--Forming Gamma-Alumina Thin Film
[0130] The amorphous alumina thin film of Synthetic Example 1 was
disposed on a reaction furnace and heat-treated at 1,050.degree. C.
for 30 minutes with vacuum condition to form a gamma-alumina thin
film.
Example 1--CVD for Forming h-BN Thin Film
[0131] With maintaining a temperature of borazine canister as
10.degree. C., under 2 atm, with providing 20 sccm of Ar/borazine
mixture gas and 1,000 sccm of hydrogen gas by MFC, a source gas was
guided to the reaction furnace, on which the amorphous alumina thin
film of Synthetic Example 1 was disposed. The above was performed
at 1,050.degree. C., 850.degree. C., 700.degree. C., 600.degree. C.
and 500.degree. C., respectively.
Example 2--CVD for Forming h-BN Thin Film
[0132] Under the same condition as Example 1, a source gas was
guided to a reaction furnace, on which the gamma-alumina thin film
of Synthetic Example 2 was disposed. The above was performed at
700.degree. C., 600.degree. C. and 500.degree. C.,
respectively.
Comparative Example 1--CVD for Forming h-BN Thin Film
[0133] Under the same condition as Example 1, a source gas was
guided to a reaction furnace, on which an SiO.sub.2/Si substrate
having a thickness of 300 nm was disposed. The above was performed
at 1,050.degree. C., 850.degree. C., 700.degree. C., 600.degree. C.
and 500.degree. C., respectively.
[0134] FIG. 6 is an XRD analysis graph of the thin films obtained
by Example 1. FIG. 7A are XPS analysis graphs of the thin films
obtained by Example 1 and Comparative Example 1. FIG. 7B are XPS
analysis graphs of the thin films obtained by Example 1 and Example
2.
[0135] Referring to FIG. 6, (110), (220), (400) and (440) peaks
have endemic positions of gamma-alumina, which do not overlap other
crystal phase. Thus, it can be noted that the amorphous alumina
thin film was changed to the gamma-alumina thin film. Especially,
(440) and (400) peaks are crystal directions due to a defect spinel
structure of gamma-alumina, which may be proof of aluminum
tri-coordination (Al.sub.III) site.
[0136] Referring to FIG. 6, a peak corresponding to h-BN appears at
1,050.degree. C., and does not appear at 700.degree. C. However,
referring to FIG. 7A, sp2 peak of N1s corresponding to h-BN appears
with single Gaussian shape at 700.degree. C. When considering that
XRD cannot analyze a thickness less than a tri-layer, it can be
noted that an h-BN film having a thickness equal to or less than a
bi-layer was formed at 700.degree. C.
[0137] Referring to FIG. 7A, sp2 peak of N1s appears with single
Gaussian shape at 600.degree. C. in Example 1. Thus, an h-BN film
having a high quality was formed in Example 1.
[0138] However, when the SiO.sub.2/Si substrate was used as
Comparative Example 1, a peak of B1s as well as sp2 peak of N1s
does not appear at equal to or less than 700.degree. C.
[0139] Thus, it can be noted that gamma-alumina formed from
amorphous alumina through crystallization by heat may function as a
catalyst for synthesizing h-BN and that an-h-BN thin film having a
high quality may be formed at a low temperature.
[0140] Referring to FIG. 7B, when the h-BN thin film was formed on
the gamma-alumina thin film as Example 2, sp2 peak of N1s appears
at 500.degree. C. Thus, it can be noted that synthesizing h-BN on a
gamma-alumina thin film may reduce a process temperature than
synthesizing h-BN on an amorphous alumina thin film.
[0141] Exemplary embodiments of the present invention may be used
for forming an insulation layer, a dielectric layer, a doping
barrier for various elements, and for manufacturing various
electronic elements including an electro-optical modulator, a
switching element, a transistor, optical device or the like.
[0142] The foregoing is illustrative and is not to be construed as
limiting thereof. Although a few exemplary embodiments have been
described, those skilled in the art will readily appreciate that
many modifications are possible in the exemplary embodiments
without materially departing from the novel teachings, aspects, and
advantages of the invention. Accordingly, all such modifications
are intended to be included within the scope of this
disclosure.
* * * * *