U.S. patent application number 10/210672 was filed with the patent office on 2003-02-27 for group iii nitride compound semiconductor thin film and deposition method thereof, and semiconductor device and manufacturing method thereof.
Invention is credited to Mitamura, Satoshi.
Application Number | 20030039866 10/210672 |
Document ID | / |
Family ID | 16503339 |
Filed Date | 2003-02-27 |
United States Patent
Application |
20030039866 |
Kind Code |
A1 |
Mitamura, Satoshi |
February 27, 2003 |
Group III nitride compound semiconductor thin film and deposition
method thereof, and semiconductor device and manufacturing method
thereof
Abstract
A Group III nitride compound semiconductor thin film which can
be deposited on any given substrate to have uniform film quality
and excellent crystalline, and a deposition method thereof. A
semiconductor device and a manufacturing method thereof. A
poly-crystalline Group III nitride compound thin film is deposited
on a substrate by sputtering at a deposition rate of 15 to 200
nm/hour using a Group III nitride compound target in a plazma
atmosphere of gas comprising 10 mole % or more nitrogen. Then, the
poly-crystalline Group III nitride compound semiconductor thin film
deposited on the substrate is irradiated with an excimer pulsed
laser with an energy density of about 200 mJ/cm.sup.2, in an
atmosphere of gas with an oxygen content of 2 mole % or less.
Thereby, lattice defects such as grain boundaries or dislocations
which occur in the thin film are removed.
Inventors: |
Mitamura, Satoshi; (Saitama,
JP) |
Correspondence
Address: |
SONNENSCHEIN NATH & ROSENTHAL
SEARS TOWER
WACKER DRIVE STATION
P.O. BOX #061080
CHICAGO
IL
60606-6404
US
|
Family ID: |
16503339 |
Appl. No.: |
10/210672 |
Filed: |
July 31, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10210672 |
Jul 31, 2002 |
|
|
|
09616688 |
Jul 14, 2000 |
|
|
|
6475923 |
|
|
|
|
Current U.S.
Class: |
428/698 ;
204/192.25 |
Current CPC
Class: |
H01L 21/0237 20130101;
H01L 21/02458 20130101; H01L 21/02576 20130101; H01L 21/0254
20130101; H01L 33/007 20130101; H01L 21/0262 20130101; H01L 21/0242
20130101; H01L 21/02631 20130101; C23C 14/0617 20130101 |
Class at
Publication: |
428/698 ;
204/192.25 |
International
Class: |
B32B 009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 19, 1999 |
JP |
P11-205216 |
Claims
What is claimed is:
1. A deposition method of a Group III nitride compound
semiconductor thin film, for depositing a Group III nitride
compound semiconductor thin film comprising at least one Group III
element and nitrogen (N), wherein a poly-crystalline Group III
nitride compound semiconductor thin film is deposited on a
substrate by sputtering using a target comprised of a Group III
nitride compound in a plazma atmosphere of gas comprising at least
nitrogen.
2. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 1, wherein a Group III
nitride compound semiconductor thin film is deposited at a
deposition rate ranging from 15 nm/hour to 200 nm/hour, both
inclusive.
3. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 1, wherein a Group III
nitride compound semiconductor thin film is deposited in a plazma
atmosphere of gas comprising 10 mole % or more nitrogen (N).
4. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 1, wherein the target
is comprised of a Group III nitride compound comprising at least
one element from the group consisting of aluminum (Al), gallium
(Ga), indium (In) and boron (B).
5. A deposition method of a Group III nitride compound
semiconductor thin film, the method comprising steps of:
depositing, on a substrate, a poly-crystalline Group III nitride
compound semiconductor thin film comprising at least one Group III
element and nitrogen (N); and removing a lattice defect which
occurs in the poly-crystalline Group III nitride compound
semiconductor thin film, by irradiating the poly-crystalline Group
III nitride compound semiconductor thin film deposited on the
substrate with a pulsed laser.
6. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 5, wherein irradiation
with a pulsed laser is performed in an atmosphere of gas with an
oxygen (O) content of 2 mole % or less.
7. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 5, wherein the
poly-crystalline Group III nitride compound semiconductor thin film
is deposited by sputtering in a plazma atmosphere of gas comprising
at least nitrogen.
8. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 5, wherein the Group
III element is at least one element from the group consisting of
aluminum (Al), gallium (Ga), indium (In) and boron (B).
9. A deposition method of a Group III nitride compound
semiconductor thin film, the method comprising steps of:
depositing, on a substrate, a single-crystal Group III nitride
compound semiconductor thin film comprising at least one Group III
element and nitrogen (N); and removing a lattice defect which
occurs in the single-crystal Group III nitride compound
semiconductor thin film, by irradiating the single-crystal Group
III nitride compound semiconductor thin film deposited on the
substrate with a pulsed laser.
10. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 9, wherein irradiation
with a pulsed laser is performed in an atmosphere of gas with a
nitrogen content of 95 mole % or more.
11. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 9, wherein the Group
III nitride compound semiconductor thin film is deposited by
epitaxial growth.
12. A deposition method of a Group III nitride compound
semiconductor thin film as claimed in claim 9, wherein the Group
III element is at least one element from the group consisting of
aluminum (Al), gallium (Ga), indium (In) and boron (B).
13. A Group III nitride compound semiconductor thin film comprising
at least one Group III element and nitrogen (N), wherein the Group
III nitride compound semiconductor thin film is deposited by
sputtering using a target comprised of a Group III nitride compound
in a plazma atmosphere of gas comprising at least nitrogen, and has
a poly-crystalline structure.
14. A Group III nitride compound semiconductor thin film as claimed
in claim 13, with an oxygen content of 2 mole % or less.
15. A manufacturing method of a semiconductor device comprising a
Group III nitride compound semiconductor layer comprising at least
one Group III element and nitrogen (N), wherein a poly-crystalline
Group III nitride compound semiconductor layer is deposited on a
substrate by sputtering using a target comprised of a Group III
nitride compound in a plazma atmosphere of gas comprising at least
nitrogen.
16. A manufacturing method of a semiconductor device comprising a
Group III nitride compound semiconductor layer comprising at least
one Group III element and nitrogen (N), the method comprising steps
of: depositing, on a substrate, a poly-crystalline Group III
nitride compound semiconductor layer comprising at least one Group
III element and nitrogen; and removing a lattice defect which
occurs in the poly-crystalline Group III nitride compound
semiconductor layer, by irradiating the poly-crystalline Group III
nitride compound semiconductor layer deposited on the substrate
with a pulsed laser.
17. A manufacturing method of a semiconductor device comprising a
Group III nitride compound semiconductor layer comprising at least
one Group III element and nitrogen (N), the method comprising steps
of: depositing, on a substrate, a single-crystal Group III nitride
compound semiconductor layer comprising at least one Group III
element and nitrogen; and removing a lattice defect which occurs in
the single-crystal Group III nitride compound semiconductor layer,
by irradiating the single-crystal Group III nitride compound
semiconductor layer deposited on the substrate with a pulsed
laser.
18. A semiconductor device comprising a Group III nitride compound
semiconductor layer comprising at least one Group III element and
nitrogen (N), wherein the Group III nitride compound semiconductor
layer is deposited by sputtering using a target comprised of a
Group III nitride compound in a plazma atmosphere of gas comprising
at least nitrogen, and has a poly-crystalline structure.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a Group III nitride
compound semiconductor thin film comprising a Group III element
such as aluminum (Al), gallium (Ga), indium (In) or boron (B), and
nitrogen (N), and a deposition method thereof. The present
invention also relates to a semiconductor device comprising such a
Group III nitride compound semiconductor thin film, and a
manufacturing method thereof
[0003] 2. Description of the Related Art
[0004] GaN (gallium nitride), InGaN (indium gallium nitride)
compound crystal, GaAlN (gallium aluminum nitride) compound crystal
and InAlGaN (indium aluminum gallium nitride) compound crystal are
typical Group III nitride compound semiconductors. Group III
nitride compound semiconductors are attractive as practical
semiconductor materials applicable to light emitting devices such
as a light emitting diode (LED) that emits blue light or a laser
diode (LD) that emits blue light. Active exercise of research and
development thereof is still going on.
[0005] In the related art practice, a Group III nitride compound
semiconductor is grown on a substrate by MOCVD (Metal Organic
Chemical Vapor Deposition), which is also called MOVPE (Metal
Organic Vapor Phase Epitaxy), or by MBE (Molecular Beam Epitaxy) to
be formed into a single-crystal thin film.
[0006] In MOCVD, a Group III nitride compound semiconductor is
obtained through chemical reactions between material gases of a
Group III element and nitrogen, and is heteroepitaxially grown on a
substrate. MOCVD has an advantage that a single-crystal thin film
having a uniform composition can be deposited on a substrate. MOCVD
also allows the substrate temperature (growth temperature) to be
set high. This contributes to another advantage of relative
easiness of depositing a single-crystal thin film of excellent
crystalline, or a single-crystal thin film having few lattice
defects such as dislocations.
[0007] On the other hand, in MBE, a substrate is irradiated with
particle beams of a Group III element and nitrogen, which are
evaporated from a Knudsen cell, to grow a crystal thereon. Thus,
MBE has a difficulty in forming a thin film of uniform composition
and film thickness. In addition, MBE requires a low substrate
temperature (growth temperature) in order to suppress desorption of
nitrogen from the surface of a thin film at the time of crystal
growth. This makes it difficult to form a single-crystal thin film
of excellent crystalline. Since the light emission efficiency of a
light emitting device is said to depend largely on the crystalline
of a thin film, MOCVD, which is practically effective, is
frequently used with the current state of the art.
[0008] MOCVD, however, has a problem of the limited material and
size of a substrate used. That is, a substrate used in MOCVD has to
have a lattice constant substantially equal to that of a Group III
nitride compound semiconductor to be grown thereon. Moreover, a
substrate used in MOCVD has to have high heat resistance.
[0009] Present practice followed in growing a Group III nitride
compound semiconductor is to use a crystalline sapphire
(.alpha.-Al.sub.2O.sub.3) substrate. Sapphire of this type has a
lattice constant approximately equal to those of Group III nitride
compound semiconductors, especially GaN. The sapphire also has
excellent heat resistance. For these reasons, the sapphire is
suitable for a material of substrates used in MOCVD.
[0010] The use of sapphire substrates, however, involves the growth
on c surfaces. Thus, sapphire substrates have a problem in
workability or formability, resulting in high materials cost.
[0011] Another problem with sapphire substrates is low production
efficiency. Since it is difficult to deposit a thin film of uniform
film thickness over the entire surface of a substrate, a substrate
of large surface area cannot be used (with the current state of
art, the maximum size is about 8 inches).
[0012] Furthermore, a single-crystal Group III nitride compound
semiconductor thin film manufactured by MOCVD includes lattice
defects such as dislocations at a rate of about 10.sup.10
cm.sup.-2. The use of such a single-crystal Group III nitride
compound semiconductor thin film as a luminescent material in an
LED causes an increase in non-radiative recombination probability
in which electrons recombine with holes without emitting radiation,
resulting in a problem of deterioration in light emission
efficiency.
SUMMARY OF THE INVENTION
[0013] The present invention has been achieved to overcome the
above-described problems. A first object of the invention is to
provide a Group III nitride compound semiconductor thin film which
can be deposited on any given substrate and a deposition method
thereof and a semiconductor device using such a Group III nitride
compound semiconductor and a manufacturing method thereof.
[0014] A second object of the invention is to provide a Group III
nitride compound semiconductor thin film of uniform film quality
and excellent crystalline and a deposition method thereof, and a
semiconductor device using such a Group III nitride compound
semiconductor and a manufacturing method thereof.
[0015] A deposition method of a Group III nitride compound
semiconductor thin film according to the invention is a method for
depositing a Group III nitride compound semiconductor thin film
comprising at least one Group III element and nitrogen, wherein a
poly-crystalline Group III nitride compound semiconductor thin film
is deposited on a substrate by sputtering using a target comprised
of a Group III nitride compound in a plazma atmosphere of gas
comprising at least nitrogen.
[0016] Another deposition method of a Group III nitride compound
semiconductor thin film according to the invention comprises steps
of: depositing, on a substrate, a poly-crystalline Group III
nitride compound semiconductor thin film comprising at least one
Group III element and nitrogen; and removing a lattice defect which
occurs in the poly-crystalline Group III nitride compound
semiconductor thin film, by irradiating the poly-crystalline Group
III nitride compound semiconductor thin film deposited on the
substrate with a pulsed laser.
[0017] Still another deposition method of a Group III nitride
compound semiconductor thin film according to the invention
comprises steps of: depositing, on a substrate, a single-crystal
Group III nitride compound semiconductor thin film comprising at
least one Group III element and nitrogen; and removing a lattice
defect which occurs in the single-crystal Group III nitride
compound semiconductor thin film, by irradiating the single-crystal
Group III nitride compound semiconductor thin film deposited on the
substrate with a pulsed laser.
[0018] A Group III nitride compound semiconductor thin film
according to the invention is a Group III nitride compound
semiconductor thin film comprising at least one Group III element
and nitrogen, wherein the Group III nitride compound semiconductor
thin film is deposited by sputtering using a target comprised of a
Group III nitride compound in a plazma atmosphere of gas comprising
at least nitrogen, and has a poly-crystalline structure.
[0019] A manufacturing method of a semiconductor device according
to the invention is a manufacturing method of a semiconductor
device comprising a Group III nitride compound semiconductor layer
comprising at least one Group III element and nitrogen, wherein a
poly-crystalline Group III nitride compound semiconductor layer is
deposited on a substrate by sputtering using a target comprised of
a Group III nitride compound in a plazma atmosphere of gas
comprising at least nitrogen.
[0020] Another manufacturing method of a semiconductor device
according to the invention is a manufacturing method of a
semiconductor device comprising a Group III nitride compound
semiconductor layer comprising at least one Group III element and
nitrogen, the method comprising steps of: depositing, on a
substrate, a poly-crystalline Group III nitride compound
semiconductor layer comprising at least one Group III element and
nitrogen; and removing a lattice defect which occurs in the
poly-crystalline Group III nitride compound semiconductor layer, by
irradiating the poly-crystalline Group III nitride compound
semiconductor layer deposited on the substrate with a pulsed
laser.
[0021] Still another manufacturing method of a semiconductor device
according to the invention is a manufacturing method of a
semiconductor device comprising a Group III nitride compound
semiconductor layer comprising at least one Group III element and
nitrogen, the method comprising steps of: depositing, on a
substrate, a single-crystal Group III nitride compound
semiconductor layer comprising at least one Group III element and
nitrogen; and removing a lattice defect which occurs in the
single-crystal Group III nitride compound semiconductor layer, by
irradiating the single-crystal Group III nitride compound
semiconductor layer deposited on the substrate with a pulsed
laser.
[0022] A semiconductor device according to the invention is a
semiconductor device comprising a Group III nitride compound
semiconductor layer comprising at least one Group III element and
nitrogen, wherein the Group III nitride compound semiconductor
layer is deposited by sputtering using a target comprised of a
Group III nitride compound in a plazma atmosphere of gas comprising
at least nitrogen, and has a poly-crystalline structure.
[0023] In a deposition method of a Group III nitride compound
semiconductor thin film according to the invention, a
poly-crystalline Group III nitride compound semiconductor thin film
is deposited by sputtering using a Group III nitride compound
target in a plazma atmosphere of gas comprising at least nitrogen.
Thus, a Group III nitride compound semiconductor thin film of the
invention is obtained.
[0024] In another deposition method of a Group III nitride compound
semiconductor thin film according to the invention, a
poly-crystalline Group III nitride compound semiconductor thin film
is deposited, and then the poly-crystalline Group III nitride
compound semiconductor thin film is irradiated with a pulsed
laser.
[0025] In still another deposition method of a Group III nitride
compound semiconductor thin film according to the invention, a
single-crystal Group III nitride compound semiconductor thin film
is deposited, and then the single-crystal Group III nitride
compound semiconductor thin film is irradiated with a pulsed
laser.
[0026] In a manufacturing method of a semiconductor device
according to the invention, a poly-crystalline Group III nitride
compound semiconductor layer is deposited by the deposition method
of a Group III nitride compound semiconductor thin film. Thus, a
semiconductor device of the invention is obtained.
[0027] In another manufacturing method of a semiconductor device
according to the invention, a poly-crystalline Group III nitride
compound semiconductor layer is deposited by, for example,
sputtering, and then the poly-crystalline Group III nitride
compound semiconductor layer is irradiated with a pulsed laser.
[0028] In still another manufacturing method of a semiconductor
device according to the invention, a single-crystal Group III
nitride compound semiconductor layer is deposited by, for example,
epitaxial growth, and then the single-crystal Group III nitride
compound semiconductor layer is irradiated with a pulsed laser.
[0029] Other and further objects, features and advantages of the
invention will appear more fully from the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a schematic cross section for illustrating a
construction of a sputtering system used in a deposition method of
a Group III nitride compound semiconductor thin film according to a
first embodiment of the invention.
[0031] FIG. 2 is a cross section for illustrating a step of the
deposition method of a Group III nitride compound semiconductor
thin film according to the first embodiment of the invention.
[0032] FIG. 3A is a plan view illustrating a configuration of an
LED manufactured by the deposition method of a Group III nitride
compound semiconductor thin film according to the first embodiment
of the invention.
[0033] FIG. 3B is a cross section taken along line X-X of FIG.
3A.
[0034] FIG. 4 is a characteristic figure showing a CL emission
spectrum of a Group III nitride compound semiconductor thin film
according to Example 1 of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Embodiments of the invention will now be described in detail
below by referring to the drawings.
[0036] (First Embodiment)
[0037] A deposition method of a Group III nitride compound
semiconductor thin film according to the first embodiment of the
invention involves the deposition of a poly-crystalline Group III
nitride compound semiconductor thin film comprising, for example,
at least one Group III element from the group consisting of
aluminum, gallium, indium and boron, and nitrogen. Examples of such
Group III nitride compound semiconductors are GaN, InN, AlN, BN,
InGaN compound crystal, GaAlN compound crystal and InAlGaN compound
crystal. The Group III nitride compound semiconductors may comprise
n-type impurities such as silicon (Si) or p-type impurities such as
magnesium (Mg) as necessary. The Group III nitride compound
semiconductor thin film according to the present embodiment is
embodied by the deposition method of the present embodiment and
will be incorporated in the description given below.
[0038] FIG. 1 illustrates a schematic construction of a sputtering
system used in a deposition method of a Group III nitride compound
semiconductor thin film according to the embodiment. The sputtering
system comprises, for example, a vacuum chamber 13 made of
stainless steel. A gas supply pipe 11 and a gas exhaust pipe 12 is
connected to the vacuum chamber 13. Inside the vacuum chamber 13, a
substrate holder 15 for mounting a substrate 14 and a target
mounting plate 17 for mounting a target 16 are arranged to face
each other. The sputtering system is shown provided with one target
mounting plate 17, but the sputtering system may be also provided
with a plurality of target mounting plates 17. A voltage can be
applied to the target 16 by an RF power source, although not shown,
which is provided outside the vacuum chamber 13. A heating means
such as a heater, although not shown, is provided inside the vacuum
chamber 13, and the substrate 14 is heated by the heating means.
The vacuum chamber 13 is further provided therein with an excimer
laser, which will be described later in detail. In the sputtering
system, gas in the vacuum chamber is exhausted via the gas exhaust
pipe 12, and thereby the pressure in the vacuum chamber is reduced
to a vacuum condition of, for example, about 5.0.times.10.sup.-7
Torr. Then, predetermined gas is supplied via the gas supply pipe
11, and thus the atmosphere in the chamber becomes an atmosphere of
the gas supplied.
[0039] In the embodiment, the sputtering system as described above
is used in RF (Radio Frequency) sputtering to deposit a
poly-crystalline Group III nitride compound semiconductor thin film
as follows.
[0040] First, the substate 14 of any given size, shape and
thickness suitable for its application is mounted on a mounting
surface of the substrate holder 15. The substrate 14 may be, for
example, a glass substrate, a ceramic substrate, a gallium nitride
substrate, a silicon substrate, a silicon carbide substrate, a
resin substrate made of for example, polycarbonate resin, a poly
(ethylene terephthalate) resin, a polyester resin, an epoxy resin,
an acrylic resin or an ABS (Acrylonitrile-Butadiene-Styrene
copolymer) resin, or an appropriate metal substrate.
[0041] Then, a predetermined Group III nitride compound target such
as GaN is mounted on the target mounting plate 17. In addition to a
Group III nitride compound target as mentioned above, a single
substance target of a Group III element may be possible. However, a
Group III nitride compound target is preferred for several reasons.
First, the use of a Group III nitride compound target enables the
formation of a Group III nitride compound semiconductor of
stoichiometric composition or of nearly stoichiometric composition
with stability, as compared with the case with the use of a single
substance target of a Group III element. Secondly, when producing a
Group III nitride compound semiconductor comprising gallium as a
Group III element, the use of a gallium metal target as a single
substance target causes a problem that gallium sputtered from the
target becomes attached to and diffused into the inside surfaces of
the vacuum chamber 13 to cause corrosion of the vacuum chamber 13.
Moreover, since the melting point of gallium is as low as
29.78.degree. C., a gallium metal target is in liquid state at the
time of sputtering. Therefore, the use of a gallium metal target
requires a device for preventing liquid leaks.
[0042] Next, the gas in the vacuum chamber 13 is exhausted via the
gas exhaust pipe 12, and thereby the pressure in the vacuum chamber
13 is reduced to a predetermined pressure of, for example,
5.0.times.10.sup.-7 Torr. Subsequently, the substrate 14 is heated
to a prescribed temperature lower than, for example, 900.degree.
C., and then gas comprising at least nitrogen is introduced via the
gas supply pipe 11 into the vacuum chamber 13 to reach a prescribed
pressure of, for example, 17 mTorr. Preferably, the gas comprises
10 mole % or more nitrogen in a plazma condition inside the vacuum
chamber 13.
[0043] After that, a voltage is applied to the target 16 with a
power of, for example, 10 W from the RF power source. Thereby, the
atmosphere inside the vacuum chamber 13 is made a plazma atmosphere
of gas comprising nitrogen, while sputtering is initiated. Thus, a
Group III nitride compound semiconductor is deposited over the
substrate to a prescribed thickness.
[0044] In this case, preferably, the deposition rate is in the
range of 15 to 200 nm/hour and more preferably 15 to 70 nm/hour. If
the deposition rate is smaller than 15 nm/hour, RF power is too
small and the plazma becomes unstable. This causes deterioration in
reproducibility of the composition of the poly-crystalline Group
III nitride compound semiconductor thin film thus obtained. On the
other hand, if the deposition rate is greater than 200 nm/hour,
there occurs more lattice defects such as grain boundaries or
dislocations per unit volume of the poly-crystalline Group III
nitride compound semiconductor thin film thus obtained. This
results in deterioration in the crystalline of the poly-crystalline
Group III nitride compound semiconductor thin film.
[0045] Preferably, the plazma of the gas comprising nitrogen
comprises 10 mole % or more nitrogen and more preferably 80 mole %
or more nitrogen. If the nitrogen content is smaller than 10 mole
%, the Group III nitride compound semiconductor becomes deficient
in nitrogen, and therefore, an essential semiconductor property of
the Group III nitride compound semiconductor does not become
manifest. By sputtering in a plazma atmosphere comprising 10 mole %
or more nitrogen, obtained is a clear thin film of nearly
stoichiometric composition. On the other hand, by sputtering in a
plazma atmosphere of 100% argon gas, obtained is a black thin film
in which a composition ratio of gallium is extremely larger than a
stoichiometric composition. This thin film has a resistivity of
about 10.sup.-4 .OMEGA.cm and exhibits high electrical
conductivity. This thin film is so fragile that it is crushed in
the scratch test.
[0046] After depositing the poly-crystalline Group III nitride
compound semiconductor thin film, as shown in FIG. 2, the
poly-crystalline Group III nitride compound semiconductor thin film
18 deposited over the substrate 14 is irradiated with a pulsed
laser L using, for example, an excimer laser, although not shown,
provided in the vacuum chamber 13, and thus the poly-crystalline
Group III nitride compound semiconductor thin film 18 is heated.
Specifically, the poly-crystalline Group III nitride compound
semiconductor thin film 18 is irradiated with an energy density of
about 200 mJ/cm.sup.2 in an atmosphere of gas with an oxygen
content of 2 mole % or less and preferably 0.5 mole % or less.
Thereby, part or all of grain boundaries, dislocations and other
lattice defects are removed and the number of lattice defects is
reduced. This contributes to an improvement in the crystalline of
the poly-crystalline Group III nitride compound semiconductor thin
film 18.
[0047] The reason for laser irradiation in an atmosphere of gas
with an oxygen content of 2 mole % or less is given as follows. In
a gaseous atmosphere with a high oxygen content, laser irradiation
turns the poly-crystalline Group III nitride compound semiconductor
thin film 18 into a compound crystal Group III nitride compound
semiconductor thin film comprising an oxide microcrystal. Thus, an
essential semiconductor property of a Group III nitride compound
semiconductor does not become manifest. It is therefore preferable
that an oxygen content in the thin film be smaller than or equal to
2 mole %. Moreover, setting the irradiation energy density at about
200 mJ/cm.sup.2 prevents nitrogen from being struck out of the
surface of the thin film.
[0048] The excimer laser may be an excimer pulsed laser of
wavelengths in the ultraviolet region such as XeCl of a wavelength
of 308 nm, XeF of a wavelength of 351 nm, XeBr of a wavelength of
282 nm, KrF of a wavelength of 248 nm or KrCl of a wavelength of
222 nm.
[0049] The deposition method of a Group III nitride compound
semiconductor according to the embodiment is utilized in a
manufacturing method of a semiconductor device as described
below.
[0050] FIGS. 3A and 3B illustrate a configuration of an LED as a
semiconductor device manufactured by the deposition method
according to the embodiment. FIG. 3A is a plan view seen from the
electrode side and FIG. 3B is a cross section taken along line X-X
of FIG. 3A.
[0051] First, a clear substrate 21 made of, for example, quartz is
mounted on the mounting surface of the substrate holder 15. Then,
an AlN target, a GaN target with silicon mixed therein as n-type
impurities and a GaN target with, for example, a high content of
magnesium mixed therein as p-type impurities are mounted on the
target mounting plate 17.
[0052] Next, the gas in the vacuum chamber 13 is exhausted via the
gas exhaust pipe 12, and thereby the pressure in the vacuum chamber
13 is reduced to a pressure of, for example, 5.0.times.10.sup.-7
Torr. Subsequently, the clear substrate 21 is heated using a
heating means such as a heater to, for example, 700 to 850.degree.
C., and then gas comprising, for example, 10 mole % or more
nitrogen is introduced via the gas supply pipe 11 into the vacuum
chamber 13 to reach a pressure of, for example, 17 mTorr.
[0053] After that, a voltage is applied to the AlN target with a
power of, for example, 50 W from the RF power source. Thereby,
inside the vacuum chamber 13, the above-described gas turns into
plazma condition to become a plazma atmosphere of gas comprising
nitrogen, while sputtering is initiated. Thus, a buffer layer 22
comprised of poly-crystalline AlN having a thickness of, for
example, 30 nm is deposited on the clear substrate 21.
[0054] Next, the buffer layer 22 is subjected to excimer pulsed
laser irradiation using, for example, an excimer laser, although
not shown, provided in the vacuum chamber 13, and thus the buffer
layer 22 is heated. Specifically, laser irradiation is performed
with an energy density of about 200 mJ/cm.sup.2 in an atmosphere of
gas with an oxygen content of 2 mole % or less and preferably 0.5
mole % or less. Thereby, grain boundaries dislocations and other
lattice defects are suppressed. This contributes to an improvement
in the crystalline of poly-crystalline AlN.
[0055] After laser irradiation of the buffer layer 22, a voltage is
applied to the GaN target having n-type impurities mixed therein,
and a poly-crystalline n-type GaN layer 23 having a thickness of,
for example 2 .mu.m is deposited on the buffer layer 22. Then, the
poly-crystalline n-type GaN layer 23 is subjected to laser
irradiation as in the case of, for example, the buffer layer
22.
[0056] Furthermore, a voltage is applied to the GaN target having
p-type impurities mixed therein, and a poly-crystalline p-type GaN
layer 24 having a thickness of, for example, 100 nm is deposited on
the poly-crystalline n-type GaN layer 23. Then, the
poly-crystalline p-type GaN layer 24 is subjected to laser
irradiation. As described above, the poly-crystalline p-type GaN
layer 24 is deposited using the GaN target with a high content of
p-type impurities mixed therein as described above, and therefore
exhibits high resistivity.
[0057] Next, on the poly-crystalline p-type GaN layer 24, a resist
pattern in stripes, although not shown, is formed in correspondence
with the position where an n-side electrode 25 is to be formed.
After that, the poly-crystalline p-type GaN layer 24 is selectively
removed with the resist pattern as a mask by, for example, RIE
(Reactive Ion Etching). Thus, the poly-crystalline n-type GaN layer
is exposed.
[0058] Then the resist pattern is removed off. On the
poly-crystalline p-type GaN layer 24, for example, a nickel (Ni)
layer, a platinum (Pt) layer and a gold (Au) layer is deposited in
the order named, and a p-side electrode 26 is formed nearly over
the entire surface of the poly-crystalline p-type GaN layer 24.
Since the p-side electrode 26 is formed nearly over the entire
surface of the poly-crystalline p-type GaN layer 24, the
poly-crystalline p-type GaN layer 24 and the p-side electrode 26
are in contact with each other in a broad area. As a result, a
forward voltage at the time of energization of the electrode is
reduced, and light emission is attained nearly throughout the
entire surface of the poly-crystalline p-type GaN layer 24.
Furthermore, on the poly-crystalline n-type GaN layer 23 thus
exposed, for example, a titanium (Ti) layer, an aluminum (Al)
layer, a platinum layer and a gold layer are deposited in the order
named, and thus the n-side electrode 25 is formed. After that,
through heat treatments, the n-side electrode 25 and the p-side
electrode 26 are alloyed. Thus, an LED as shown in FIGS. 3A and 3B
is completed.
[0059] In an LED thus manufactured, if a prescribed voltage is
applied between the n-side electrode 25 and the p-side electrode
26, a current is fed to the poly-crystalline p-type GaN layer 24,
and light emission is achieved through electron-hole recombination.
Since the poly-crystalline n-type GaN layer 23 and the
poly-crystalline p-type GaN layer 24 have high crystalline, the
layers 23 and 24 have high carrier mobility and small resistivity.
This contributes to high light emission efficiency.
[0060] As described above, according to the deposition method of a
Group III nitride compound semiconductor thin film of the
embodiment, a poly-crystalline Group III nitride compound
semiconductor thin film is deposited by sputtering. This enables
the deposition of a poly-crystalline Group III nitride compound
semiconductor thin film excellent in uniformity in film thickness
and composition (that is, film quality). Moreover, since the
temperature at the time of the deposition of a thin film can be set
at 30 to 700.degree. C., it becomes unnecessary to use a substrate
having high heat resistance, as distinct from the deposition of a
thin film by epitaxial growth. This makes it possible to deposit a
thin film on a substrate of any given material and of large surface
area, which contributes to cost reduction.
[0061] Furthermore, according to the deposition method of a Group
III nitride compound semiconductor thin film of the embodiment, a
poly-crystalline Group III nitride compound semiconductor thin film
is irradiated with a pulsed laser, and thereby lattice defects
which occur in the thin film are removed. This enables the
deposition of a thin film of improved crystalline. As a result, the
resistivity is reduced and the carrier mobility is increased.
[0062] The application of the poly-crystalline Group III nitride
compound semiconductor thin film of the embodiment to a
semiconductor light emitting device such as an LED enables a
reduction in the probability of non-radiative recombination where
electrons recombine with holes without emitting radiation due to
lattice defects or others. Therefore, the semiconductor light
emitting device can expect an improved light emission efficiency.
The semiconductor light emitting device can also expect a long life
and a great light emission intensity.
[0063] (Second Embodiment)
[0064] A deposition method of a Group III nitride compound
semiconductor thin film according to a second embodiment of the
invention involves the deposition of a single-crystal Group III
nitride compound semiconductor thin film comprising at least one
Group III element from the group consisting of aluminum, gallium,
indium and boron, and nitrogen, by MOVPE as heteroepitaxial growth.
Description given below relates to the case of a single-crystal
n-type GaN thin film as an example of a single-crystal Group III
nitride compound semiconductor thin film.
[0065] In the embodiment, first, a clear substrate comprised of,
for example, cleaned c-surfaced sapphire is carried into an MOVPE
system. The sapphire substrate is dry etched at the substrate
temperature of 1050.degree. C. while hydrogen (H.sub.2) gas is
supplied into the system at the rate of 2 liters per minute at
atmospheric pressure. Thereby, an oxide layer of low crystalline,
which forms the top surface of the clear substrate, is removed.
This enables epitaxial growth of high quality thereon.
[0066] Then, the temperature of the clear substrate is set at, for
example, 400.degree. C. After that, hydrogen gas as carrier gas,
ammonia (NH.sub.3) gas for deriving nitrogen therefrom and
trimethylaluminum ((CH.sub.3).sub.3Al) for deriving aluminum
therefrom are introduced into the MOVPE system at the rate of, for
example, 20 liters per minute, 10 liters per minute, and
1.8.times.10.sup.-5 mole per minute, respectively. Thus, a buffer
layer comprised of single-crystal AlN having a thickness of, for
example, 0.05 .mu.m is deposited on the clear substrate.
[0067] Subsequently, the temperature of the clear substrate is set
at, for example, 1000.degree. C. After that, while the substrate
temperature is maintained there, hydrogen gas, ammonia gas,
trimethylgallium ((CH.sub.3).sub.3Ga) for deriving gallium
therefrom and silane (SiH.sub.4) gas diluted to 0.88 ppm with
hydrogen gas, for deriving n-type impurities therefrom, are
introduced into the system for 30 minutes at the rate of, for
example, 20 liters per minute, 10 liters per minute, and
1.8.times.10.sup.-4 mole per minute, and 200 milliliters per
minute, respectively. Thus, on the buffer layer, deposited is a
single-crystal n-type GaN thin film having a film thickness of, for
example, 2.2 .mu.m and a carrier density of, for example,
7.8.times.10.sup.18 cm.sup.-3.
[0068] The single-crystal n-type GaN thin film thus obtained is
subjected to laser irradiation using, for example, an excimer
laser, and thus the thin film is heated. Specifically, laser
irradiation is carried out with an energy density of 100
mJ/cm.sup.2 in an atmosphere of gas with a nitrogen content of 95
mole % or more and preferably 99 mole % or more. Thereby, part or
all of dislocations and other lattice defects are removed, and the
number of lattice defects is reduced. This contributes to an
improvement in the crystalline of the single-crystal n-type GaN
thin film. The reason for laser irradiation in an atmosphere of gas
with a nitrogen content of 95 mole % or more is as follows. If a
nitrogen content in the thin film is low, the thin film becomes
deficient in nitrogen in the neighborhood of its surface, and the
crystalline of the thin film deteriorates while the resistivity of
the thin film rapidly increases. Setting the energy density at
about 100 mJ/cm.sup.2 prevents nitrogen from being struck out of
the surface of the thin film.
[0069] Research of light emission characteristics of the
single-crystal n-type GaN thin film thus completed and the
single-crystal n-type GaN thin film before subjected to excimer
laser irradiation shows that the thin film after subjected to laser
irradiation has greater light emission intensity than the thin film
before subjected to irradiation. The possible reason is a reduction
in lattice defects which occur in the thin film and a reduction in
energy traps which may serve as centers of non-radiative
recombination due to lattice defects.
[0070] The deposition method of a Group III nitride compound
semiconductor thin film according to the embodiment is applicable
to a manufacturing method of a semiconductor device such as an LED,
as in the first embodiment.
[0071] As described above, according to the deposition method of a
Group III nitride compound semiconductor thin film of the
embodiment, the single-crystal Group III nitride compound
semiconductor thin film is irradiated with a laser, and thereby
lattice defects which occur in the thin film are removed. This
enables the deposition of a thin film of high crystalline,
resulting in a reduction in resistivity and an increase in carrier
mobility.
[0072] The application of the single-crystal Group III nitride
compound semiconductor thin film of the embodiment to the
manufacture of a semiconductor light emitting device as an LED
enables a reduction in the probability of non-radiative
recombination where electrons recombine with holes without emitting
radiation due to lattice defects or others. This further achieves
enhancement of light emission efficiency a longer life of a
semiconductor light emitting device and an increase in light
emission intensity.
EXAMPLE
[0073] Description now moves to the details of specific examples of
the present invention.
Example 1
[0074] First, a clear substrate made of cultured quartz having
translucency was prepared. The dimensions of the clear substrate,
i.e., length, width and height, were 125 mm, 125 mm and 1 mm,
respectively. The clear substrate was cleaned with a neutral
detergent, washed in water, and then subjected to ultrasonic
cleaning with an organic solvent.
[0075] Then, the clear substrate was mounted on the substrate
holder 15 of a sputtering system similar to the sputtering system
shown in FIG. 1. Subsequently, a GaN target, i.e., the target 16,
in the form of disk 3 inches in diameter and 5 mm in thickness was
prepared. The GaN target was mounted on the target mounting plate
17. The distance between the clear substrate and the GaN target was
set at 150 mm.
[0076] Next, the gas in the vacuum chamber 13 was exhausted via the
gas exhaust pipe 12, and thereby the pressure in the vacuum chamber
13 was reduced to a pressure of 5.0.times.10.sup.-7 Torr.
Subsequently, the clear substrate was heated to 850.degree. C., and
then nitrogen gas, i.e., gas with a nitrogen content of 100 mole %,
was introduced via the gas supply pipe 11 into the vacuum chamber
13 at a rate of 100 sccm to a pressure of 17 mTorr.
[0077] After that, a voltage was applied to the GaN target with a
power of 10 W from the RF power source. Thereby, the atmosphere
inside the vacuum chamber 13 was made a plazma atmosphere of
nitrogen gas, while sputtering was initiated. Sputtering was
carried out for 390 minutes, and a GaN thin film having a film
thickness of 0.1 .mu.m was obtained. The deposition rate was
therefore 15.4 nm/hour. The substrate temperature was maintained at
850.degree. C. throughout sputtering.
Example 2
[0078] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that the RF power was 20 W and
sputtering time was 180 minutes. The deposition rate was therefore
33.3 nm/hour.
Example 3
[0079] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that the RF power was 30 W and
sputtering time was 120 minutes. The deposition rate was therefore
50 nm/hour.
Example 4
[0080] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that the RF power was 50 W and
sputtering time was 60 minutes. The deposition rate was therefore
100 nm/hour.
Example 5
[0081] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 2 except that the substrate temperature at
the time of sputtering was 750.degree. C.
Example 6
[0082] A poly-crystalline GaN thin film having a film thickness of
0.1 .mu.m was obtained as in Example 2 except that the substrate
temperature at the time of sputtering was 600.degree. C.
Example 7
[0083] An InGaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except for the use of an InGaN target
instead of the GaN target. The InGaN target had a gallium to indium
content ratio by mole of 9 to 1.
Example 8
[0084] A GaAlN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except for the use of a GaAlN target
instead of the GaN target. The GaAlN target had a gallium to
aluminum content ratio by mole of 9 to 1.
Example 9
[0085] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that nitrogen-argon (Ar) mixed gas
with a nitrogen content of 10 mole % was introduced into the vacuum
chamber, instead of nitrogen gas.
Example 10
[0086] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that nitrogen-argon mixed gas with
a nitrogen content of 50 mole % was introduced into the vacuum
chamber, instead of nitrogen gas.
[0087] The following Comparative Examples 1 to 4 were carried out
with respect to Examples 1 to 4 above.
Comparative Example 1
[0088] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that the RF power was 100 W and
sputtering time was 30 minutes. The deposition rate was therefore
200 nm/hour.
Comparative Example 2
[0089] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that the RF power was 200 W and
sputtering time was 15 minutes. The deposition rate was therefore
400 nm/hour.
Comparative Example 3
[0090] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that reactive sputtering was
conducted using a gallium metal target instead of the GaN
target.
Comparative Example 4
[0091] A GaN thin film having a film thickness of 0.1 .mu.m was
obtained as in Example 1 except that argon gas, i.e., gas with an
argon content of 100 mole %, was introduced into the vacuum
chamber, instead of nitrogen gas.
[0092] Each thin film obtained in Examples 1 to 10 and Comparative
Examples 1 to 4 was subjected to composition analysis by RBS
(Rutherford Back Scattering), an evaluation of light emission
characteristics by CL (Cathodoluminescnece) measurements and an
evaluation of electrical characteristics by Hall effect
measurements.
[0093] The RBS measurements were made by irradiating each thin film
with He.sup.++ accelerated to 2.275 MeV. The conditions of the
measurements were as follows: the incident angle of the beam was
0.degree.; the vertical detector was set at an angle of
160.degree.; and the inclined detector was set at an angle of about
110.degree. or about 100.degree.. The results are summarized in
Table 1 below.
1 TABLE 1 CL emission peak Carrier Composition of wavelength
Resistivity density thin film (nm) (.OMEGA.cm) (cm.sup.-3) Example
1 Ga.sub.0 46N.sub.0 54 380 14.7 -9.9 .times. 10.sup.17 Example 2
Ga.sub.0 458N.sub.0 542 381 10.6 -5.8 .times. 10.sup.17 Example 3
Ga.sub.0 46N.sub.0 54 380 24.0 -8.3 .times. 10.sup.17 Example 4
Ga.sub.0 458N.sub.0 542 380 16.8 -9.4 .times. 10.sup.17 Example 5
Ga.sub.0 458N.sub.0 542 381 21.2 -8.9 .times. 10.sup.17 Example 6
Ga.sub.0 46N.sub.0 54 no emission beyond below measuring detection
range range Example 7 Ga.sub.0 43In.sub.0 08 N.sub.0 49 431 11.3
-6.3 .times. 10.sup.17 Example 8 Ga.sub.0 469Al.sub.0 06N.sub.0 471
380 13.6 -7.7 .times. 10.sup.17 Example 9 Ga.sub.0 46N.sub.0 54 no
emission beyond below measuring detection range range Example 10
Ga.sub.0 461N.sub.0.539 no emission beyond below measuring
detection range range Comparative Ga.sub.0 457N.sub.0 503O.sub.0.04
no emission beyond below Example 1 measuring detection range range
Comparative Ga.sub.0 459N.sub.0 501, O.sub.0 04 no emission beyond
below Example 2 measuring detection range range Comparative
Ga.sub.0.64N.sub.0.30O.sub.0.06 no emission beyond below Example 3
measuring detection range range Comparative Ga.sub.0 91, N.sub.0 09
no emission 8 .times. 10.sup.-3 -8.1 .times. Example 4
10.sup.20
[0094] As understood from Table 1, it was confirmed that the GaN
thin films of Examples 1 to 6, 9 and 10 did not comprise oxygen but
gallium and nitrogen. XRD (X-ray Diffraction) measurements of the
thin films and microscope observation of the thin films using a TEM
(Transmission Electron Microscope) revealed that the thin films had
poly-crystalline structures. It was also confirmed that the Example
7 InGaN thin film did not comprise oxygen but gallium, indium and
nitrogen, and had a poly-crystalline structure. It was further
confirmed that the Example 8 GaAlN thin film did not comprise
oxygen but gallium, aluminum and nitrogen, and had a
poly-crystalline structure. On the other hand, it was confirmed
that the thin films of Comparative Examples 1 to 3 had
poly-crystalline structures, but comprised 4 to 6 mole % oxygen and
had oxides or others mixed therein. With respect to Comparative
Example 4, it was confirmed that GaN was produced but comprised
only 9 mole % nitrogen. Furthermore, XRD measurements of the
Comparative Example 4 thin film revealed that the main component of
the thin film was gallium metal.
[0095] The conditions of CL measurements were as follows: an
electron beam was accelerated at an acceleration voltage (anode
voltage) of 4 kV; the spectrum sampling time was 1 sec. The optical
detector used was a photodiode array. The anode current was 5
.mu.A. The CL emission spectrum with respect to the Example 1
poly-crystalline GaN thin film is shown in FIG. 4, wherein the
vertical axis denotes light emission intensity and the abscissa
axis denotes wavelength in the unit nm. The peak wavelength in the
CL emission spectrum obtained in each thin film of Examples and
Comparative Examples is also summarized in Table 1.
[0096] As seen from FIG. 4, with respect to the Example 1
poly-crystalline GaN thin film, the peak of the CL light emission
intensity was found at a wavelength of about 380 nm, which was
probably because of forbidden transition light emission. It was
thus confirmed that this poly-crystalline GaN thin film had a
property as a luminescent material. As also understood from Table
1, with respect to the poly-crystalline GaN thin films of Examples
2 to 5 and the poly-crystalline AlGaN thin film of Example 8, the
peak of the CL light emission intensity was found at a wavelength
of 380 nm or 381 nm. Further, with respect to the Example 7
poly-crystalline GaInN thin film, the peak of the CL light emission
intensity was found at a wavelength of 431 nm, which was probably
an superposed spectrum of forbidden transition light emission of
GaN and InN. It was thus confirmed that the Example 7
poly-crystalline GaInN thin film had a property as a luminescent
material. On the other hand, with respect to the poly-crystalline
GaN thin films of Examples 6, 9 and 10, no peak of the CL light
emission intensity was found. Thus, these thin films were found to
lack a property as a luminescent material. With respect to the thin
films of Comparative Examples 1 to 4, no CL light emission spectrum
was found. Thus, these thin film were also found to lack a property
as a luminescent material.
[0097] The measuring instrument used in the Hall effect
measurements was HL5500C manufactured by Nippon Bio-Rad
Laboratories KK. The results obtained are also summarized in Table
1. In Table 1, the measured values of the carrier density are
prefixed with either a + sign or a - sign, thereby clearly
disclosing the kind of the carrier, i.e., a hole or an electron,
respectively.
[0098] As understood from Table 1, the poly-crystalline GaN thin
films of Examples 1 to 5 had the resistivity in the range of 10 to
25 .OMEGA.cm and the carrier density of the order of
-1.0.times.10.sup.17 cm.sup.-3, and were found to have n-type
semiconductor characteristics. The Example 7 poly-crystalline InGaN
thin film and the Example 8 poly-crystalline AlGaN thin film also
had the resistivity in the range of 10 to 25 .OMEGA.cm and the
carrier density of the order of -1.0.times.10.sup.17 cm.sup.-3, and
were found to have n-type semiconductor characteristics. On the
other hand, with respect to the poly-crystalline GaN thin films of
Examples 6, 9 and 10, the resistivity was beyond the measuring
range while the carrier density was below the detection range.
Thus, it was found that these thin films had a high insulating
characteristic and did not exhibit semiconductor characteristics.
With respect to the thin films of Comparative Examples 1 to 4, the
resistivity was also beyond the measuring range while the carrier
density was below the detection range. Thus, it was found that
these thin films had a high insulating characteristic and did not
exhibit semiconductor characteristics.
Example 11
[0099] A poly-crystalline GaN thin film was deposited as in Example
6 except for the use of a non alkaline glass substrate having
translucency instead of the clear substrate made of cultured
quartz. The poly-crystalline GaN thin film thus obtained was
irradiated with a pulsed laser with an energy density of 200
mJ/cm.sup.2 using a XeCl excimer laser, although not shown,
provided inside the vacuum chamber 13. The conditions of
irradiation were as follows. Inside the vacuum chamber 13, the
pressure was adjusted to 760 Torr and the atmosphere inside was an
atmosphere of nitrogen gas. The pulsed laser beam was produced with
an energy of 670 mJ at a frequency of 200 Hz with a pulse length of
25 ns, beam size of 150.times.0.35 mm.sup.2 and an overlap area
length of 0.035 mm. The temperature of the clear substrate was set
at 25.degree. C.
Comparative Examples 5 and 6
[0100] Comparative Examples 5 and 6 were carried out with respect
to Example 11. In Comparative Example 5, laser irradiation was
conducted as in Example 11 except for the use of a He--Ne laser of
a wavelength of 633 nm, instead of a XeCl excimer laser. In
Comparative Example 6, ultraviolet irradiation was performed as in
Example 11 except for the use of a Hg--Xe ultraviolet lamp of main
peak of 360 nm, instead of a XeCl excimer laser.
[0101] With respect to the thin films thus obtained in Example 11,
and Comparative Examples 5 and 6, an evaluation of light emission
characteristics by CL measurements and an evaluation of electrical
characteristics by Hall effect measurements were carried out. These
evaluations were also made on the Example 11 thin film before
subjected to laser irradiation. The results are summarized in Table
2.
2 TABLE 2 CL emission peak Carrier Carrier wavelength Resistivity
mobility density (nm) (.OMEGA.cm) (cm.sup.2/V .multidot. S)
(cm.sup.-3) Example 11 no emission beyond below below before laser
measuring detection detection irradiation range range range Example
11 380 1.3 10 -6.8 .times. 10.sup.17 after laser irradiation
Comparative no emission beyond below below Example 5 measuring
detection detection range range range Comparative no emission
beyond below below Example 6 measuring detection detection range
range range
[0102] As seen from Table 2, with respect to the Example 11 thin
film after subjected to laser irradiation, the peak of the CL
emission spectrum was found at a wavelength of about 380 nm. Thus
the Example 11 thin film after subjected to laser irradiation was
found to have a property as a luminescent material. Further, the
resistivity was 1.3 .OMEGA.cm, the carrier mobility was 10
cm.sup.2V.sup.-1s.sup.-1, and the carrier density was
-6.8.times.10.sup.17 cm.sup.-3. It was thus confirmed that the
Example 11 thin film after subjected to laser irradiation had
n-type semiconductor characteristics. On the other hand, with
respect to the Example 11 thin film before subjected to excimer
laser irradiation, and the thin films of Comparative Examples 5 and
6, the resistivity, the carrier mobility and the carrier density
were all beyond the measuring range. As understood from these
results, excimer laser irradiation of a poly-crystalline GaN thin
film which lacks semiconductor characteristics before subjected to
irradiation causes the thin film to exhibit semiconductor
characteristics, and some thin films become applicable to the
manufacture of semiconductor light emitting devices such as an
LED.
Example 12
[0103] In the present Example, a sapphire substrate with its
crystal lattice c surface exposed was prepared. The dimensions of
the sapphire substrate, i.e., length, width and height, were 20 mm,
20 mm and 1 mm, respectively. The sapphire substrate was cleaned
with a neutral detergent, washed in water, and then subjected to
ultrasonic cleaning with an organic solvent.
[0104] Then, the sapphire substrate thus washed was carried into an
MOVPE system. The sapphire substrate was dry etched at the
substrate temperature of 1050.degree. C. while hydrogen was
supplied into the system at the rate of 2 liters per minute at
atmospheric pressure.
[0105] Then, the temperature of the sapphire substrate was set at
400.degree. C. After that, hydrogen gas, ammonia gas and
trimethylaluminum were introduced into the system at the rate of 20
liters per minute, 10 liters per minute, and 1.8.times.10.sup.-5
mole per minute, respectively. Thus, a buffer layer comprised of
single-crystal AlN having a thickness of 0.05 .mu.m was deposited
on the sapphire substrate.
[0106] Subsequently, the temperature of the sapphire substrate was
set at 1000.degree. C. After that, while the substrate temperature
was maintained there, hydrogen gas, ammonia gas, trimethylgallium
and silane gas diluted to 0.88 ppm with hydrogen gas were
introduced into the system for 30 minutes at the rate of 20 liters
per minute, 10 liters per minute, 1.8.times.10.sup.-4 mole per
minute, and 200 milliliters per minute, respectively. Thus, on the
buffer layer, deposited was a single-crystal n-type GaN thin film
having a film thickness of 2.2 .mu.m and carrier density of
7.8.times.10.sup.18 cm.sup.-3.
[0107] The single-crystal n-type GaN thin film thus obtained was
irradiated with a pulsed laser beam using a XeCl excimer laser
provided inside the MOVPE system. The conditions of irradiation
were the same as in Example 11.
Comparative Examples 7 and 8
[0108] Comparative Examples 7 and 8 were carried out with respect
to Example 12. In Comparative Example 7, a single-crystal n-type
GaN thin film was deposited and subjected to laser irradiation as
in Example 12 except for the use of a He--Ne laser, instead of a
XeCl excimer laser. In Comparative Example 8, a single-crystal
n-type GaN thin film was deposited and subjected to ultraviolet
irradiation as in Example 12 except for the use of a Hg--Xe
ultraviolet lamp, instead of a XeCl excimer laser.
[0109] With respect to the thin films thus obtained in Example 12,
and Comparative Examples 7 and 8, an evaluation of light emission
characteristics by CL measurements and an evaluation of electrical
characteristics by Hall effect measurements were carried out. These
evaluations were also made on the Example 12 thin film before
subjected to laser irradiation. The results are summarized in Table
3.
3 TABLE 3 CL emission peak Relative Carrier Carrier wavelength
light emission mobility density (nm) intensity ratio (cm.sup.2/V
.multidot. S) (cm.sup.-3) Example 12 367 1.0 115 -7.8 .times.
10.sup.18 before laser (reference) irradiation Example 12 367 1.8
275 -1.8 .times. 10.sup.18 after laser irradiation Comparative 367
1.0 115 -7.8 .times. 10.sup.18 Example 7 Comparative 367 1.0 115
-7.8 .times. 10.sup.18 Example 8
[0110] As understood from Table 3, with respect to the Example 12
thin film before subjected to excimer laser irradiation, the
Example 12 thin film after subjected to excimer laser irradiation,
and the thin films of Comparative Examples 7 and 8, the peak of the
CL emission spectrum was found at a wavelength of about 367 nm.
Thus these thin films were found to have a property as a
luminescent material. Especially, with respect to the Example 12
thin film after subjected to excimer laser irradiation, the light
emission intensity was 1.8 times greater than before subjected to
irradiation. A probable reason may be that excimer laser
irradiation caused a reduction in lattice defects which occurred in
the thin film and a reduction in energy traps which might serve as
centers of non-radiative recombination due to lattice defects.
Excimer laser irradiation also more than doubled the carrier
mobility and reduced the carrier density to about one quarter.
These results of an evaluation of electrical characteristics also
suggested a reduction in lattice defects such as nitrogen deletion.
It was thus confirmed that the thin film came to have excellent
n-type semiconductor characteristics. As understood from these
results, excimer laser irradiation of a single-crystal GaN thin
film caused the thin film to exhibit excellent semiconductor
characteristics, and some thin films become applicable to the
manufacture of semiconductor light emitting devices such as an
LED.
[0111] Although the invention has been described by referring to
the embodiments and examples, the invention is not limited to the
embodiments and examples but can be variously modified. For
example, in the first embodiment above, a poly-crystalline Group
III nitride compound semiconductor thin film was deposited by RF
sputtering, but various sputtering methods can be also adopted.
Examples include RF magnetron sputtering, focusing target
sputtering, electron cyclotron resonance sputtering, DC (Direct
Current) sputtering and DC magnetron sputtering.
[0112] The second embodiment above relates to the case of a
single-crystal n-type GaN thin film, as an example of a deposition
method of a single-crystal Group III nitride compound
semiconductor. The invention, however, is also applicable to the
deposition of other single-crystal Group III nitride compound
semiconductors such as InN, BN, InGaN compound crystal, GaAlN
compound crystal and InAlGaN compound crystal. The invention is
also applicable to the case where p-type impurities such as
magnesium are added. Indium can be derived from, for example,
trimethylindium ((CH.sub.3).sub.3In), and boron from, for example,
triethylboron ((C.sub.2H.sub.5).sub.3B). When adding, for example,
magnesium as p-type impurities, magnesium can be derived from
bis=cyclopentadienyl magnesium ((C.sub.2H.sub.5).sub.2Mg).
[0113] The description given above with respect to the embodiments
relates to a manufacturing method of a specific LED as an example
of a semiconductor device. However, the invention is applicable
with equal utility to the manufacture of an LED of other
configurations. The invention has a broad range of applications
including the manufacture of other semiconductor light emitting
devices such as a laser diode, and the manufacture of semiconductor
devices such as transistors except for semiconductor light emitting
devices.
[0114] As described above, according to the deposition method of a
Group III nitride compound semiconductor thin film, the Group III
nitride compound semiconductor thin film, a manufacturing method of
a semiconductor device or a semiconductor device of the invention,
a poly-crystalline Group III nitride compound semiconductor thin
film (poly-crystalline Group III nitride compound semiconductor
layer) is deposited by sputtering. Thus, the thin film deposited
becomes a thin film of uniform film thickness. Moreover, since the
temperature at the time of deposition of a thin film can be
lowered, it becomes unnecessary to use a substrate having high heat
resistance, as distinct from the case where a thin film is
deposited by epitaxial growth. This enables the use of any given
substrate without limitation of material, shape and size of the
substrate, and contributes to reduction in the manufacturing
cost.
[0115] According to the deposition method of a Group III nitride
compound semiconductor thin film of the invention, a Group III
nitride compound semiconductor thin film is irradiated with a
pulsed laser, and thereby lattice defects which occur in the thin
film are removed. This enables an improvement in the crystalline of
the Group III nitride compound semiconductor thin film.
[0116] Furthermore, the manufacturing method of a semiconductor
device of the invention involves the use of the deposition method
of a Group III nitride compound semiconductor thin film of the
invention. This enables an improvement in the crystalline of the
Group III nitride compound semiconductor thin film and enhancement
of the performance of a semiconductor device.
[0117] Obviously many modifications and variations of the present
invention are possible in the light of the above teachings. It is
therefore to be understood that within the scope of the appended
claims the invention may be practiced otherwise than as
specifically described.
* * * * *