U.S. patent application number 13/777547 was filed with the patent office on 2013-09-19 for fabrication method and fabrication apparatus of group iii nitride crystal substance.
This patent application is currently assigned to Sumitomo Electric Industries, Ltd.. The applicant listed for this patent is SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Shunsuke Fujita, Ryu Hirota, Hideyuki Ijiri, Hitoshi KASAI, Naoki Matsumoto, Kensaku Motoki, Seiji Nakahata, Takuji Okahisa, Fumitaka Sato, Koji Uematsu.
Application Number | 20130244406 13/777547 |
Document ID | / |
Family ID | 37808103 |
Filed Date | 2013-09-19 |
United States Patent
Application |
20130244406 |
Kind Code |
A1 |
KASAI; Hitoshi ; et
al. |
September 19, 2013 |
FABRICATION METHOD AND FABRICATION APPARATUS OF GROUP III NITRIDE
CRYSTAL SUBSTANCE
Abstract
A fabrication method of a group III nitride crystal substance
includes the steps of cleaning the interior of a reaction chamber
by introducing HCl gas into the reaction chamber, and vapor
deposition of a group III nitride crystal substance in the cleaned
reaction chamber. A fabrication apparatus of a group III nitride
crystal substance includes a configuration to introduce HCl gas
into the reaction chamber, and a configuration to grow a group III
nitride crystal substance by HVPE. Thus, a fabrication method of a
group III nitride crystal substance including the method of
effectively cleaning deposits adhering inside the reaction chamber
during crystal growth, and a fabrication apparatus employed in the
fabrication method are provided.
Inventors: |
KASAI; Hitoshi; (Itami-shi,
JP) ; Okahisa; Takuji; (Itami-shi, JP) ;
Fujita; Shunsuke; (Itami-shi, JP) ; Matsumoto;
Naoki; (Itami-shi, JP) ; Ijiri; Hideyuki;
(Itami-shi, JP) ; Sato; Fumitaka; (Itami-shi,
JP) ; Motoki; Kensaku; (Itami-shi, JP) ;
Nakahata; Seiji; (Itami-shi, JP) ; Uematsu; Koji;
(Itami-shi, JP) ; Hirota; Ryu; (Itami-shi,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC INDUSTRIES, LTD. |
Osaka |
|
JP |
|
|
Assignee: |
Sumitomo Electric Industries,
Ltd.
Osaka
JP
|
Family ID: |
37808103 |
Appl. No.: |
13/777547 |
Filed: |
February 26, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12949268 |
Nov 18, 2010 |
8404569 |
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13777547 |
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12540492 |
Aug 13, 2009 |
7858502 |
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12949268 |
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11643675 |
Dec 22, 2006 |
7589000 |
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12540492 |
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Current U.S.
Class: |
438/478 |
Current CPC
Class: |
C23C 16/303 20130101;
C23C 16/4488 20130101; C30B 29/403 20130101; C30B 23/02 20130101;
H01L 21/02617 20130101; C30B 25/02 20130101; C23C 16/4405
20130101 |
Class at
Publication: |
438/478 |
International
Class: |
H01L 21/02 20060101
H01L021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2005 |
JP |
2005-379917 |
Aug 10, 2006 |
JP |
2006-218475 |
Claims
1-5. (canceled)
6. A fabrication method of a group III nitride crystal substance,
comprising the step of cleaning an interior of a reaction chamber
by introducing HCl gas into said reaction chamber, and the step of
vapor deposition of a group III nitride crystal substance with
trapping ammonium chloride powder generated as a by-product in a
trap device attached on said cleaned reaction chamber.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a fabrication method and
fabrication apparatus of a group III nitride crystal substance
extensively employed in substrates and the like of various
semiconductor devices. More particularly, the present invention
relates to a fabrication method of a group III nitride crystal
substance including a method for effectively cleaning deposits
adhering in a reaction chamber during growth of a group III nitride
crystal substance, and a fabrication apparatus employed in this
fabrication method.
[0003] 2. Description of the Background Art
[0004] Group III nitride crystal substances such as GaN crystal
substances and AlN crystal substances are extremely useful for the
substrate of various semiconductor devices such as a light emitting
element, electronic element, semiconductor sensor, and the like.
The fabrication method of a group III nitride crystal substance
includes various types of vapor deposition such as hydride vapor
phase epitaxy (hereinafter, also referred to as HVPE),
metal-organic chloride vapor phase epitaxy (hereinafter, also
referred to as MOC), metal-organic chemical vapor deposition
(hereinafter, also referred to as MOCVD), and the like (for
example, refer to the pamphlet of International Publication No.
WO99/23693).
[0005] All of the aforementioned vapor deposition methods cause
deposits formed of polycrystalline group III nitride to adhere to
the interior of the reaction chamber, particularly at the crystal
growth zone and the raw material introduction zone, when a group
III nitride crystal substance is grown on the underlying substrate
in the reaction chamber. Such deposits must be removed since they
may prevent stable supply of raw material, and/or be mixed into the
group III nitride crystal substance that is to be grown
subsequently.
[0006] In order to remove such deposits, the reactor tube
constituting the reaction chamber was discarded after one use, or
the interior of the reaction chamber had to be rinsed with solution
such as phosphoric acid, sulfuric acid, sodium hydroxide, potassium
hydroxide, and the like. Usage of a disposable reaction tube is
disadvantageous since the reaction tube is expensive and a
pre-baking step (a heating process of the reaction chamber prior to
crystal growth; the same applies hereinafter) is required, leading
to degradation in fabrication efficiency and increase in
fabrication cost. If the interior of the reaction chamber is rinsed
with solution such as phosphoric acid, sulfuric acid, sodium
hydroxide, potassium hydroxide, and the like, the atoms of at least
any of phosphorus, sulfur, sodium, potassium, and oxygen included
in the solution will remain in the reaction chamber to be mixed in
the crystal to be grown subsequently.
SUMMARY OF THE INVENTION
[0007] In view of the foregoing, an object of the present invention
is to provide a fabrication method of a group III nitride crystal
substance including a method for effectively cleaning deposits
adhering to the interior of the reaction chamber during crystal
growth, and a fabrication apparatus employed in such a fabrication
method.
[0008] The present invention corresponds to a fabrication method of
a group III nitride crystal substance including the steps of
cleaning the interior of a reaction chamber by introducing HCl gas
into the reaction chamber, and vapor deposition of a group III
nitride crystal substance in the cleaned reaction chamber.
[0009] In the group III nitride crystal substance fabrication
method of the present invention, the step of cleaning the interior
of the reaction chamber can be carried out under the conditions
that the HCl gas partial pressure is at least 1.013 hPa and not
more than 1013 hPa (at least 0.001 atm and not more than 1 atm),
and the temperature in the reaction chamber is at least 650.degree.
C. and not more than 1200.degree. C.
[0010] A fabrication apparatus of a group III nitride crystal
substance employed in the fabrication method set forth above of the
present invention includes a reaction chamber formed in a reactor
tube, a group III element raw material gas generation chamber, an
HCl gas introduction pipe to introduce HCl gas into the reaction
chamber, an HCl gas introduction pipe to introduce HCl gas to the
group III element raw material gas generation chamber, a group III
element raw material gas introduction pipe to introduce the group
III raw material gas generated at the group III element raw
material gas generation chamber into the reaction chamber, a
nitrogen raw material gas introduction pipe to introduce nitrogen
raw material gas into the reaction chamber, a gas exhaust pipe to
discharge gas from the reaction chamber, and a substrate holder to
dispose an underlying substrate to grow a group III nitride crystal
substance in the reaction chamber.
[0011] In the group III nitride crystal substance fabrication
apparatus of the present invention, the reaction chamber includes a
crystal growth zone that is the region in close proximity to
substrate holder 119. A protection member of the reaction chamber
can be disposed on the inner wall of the reaction chamber at this
crystal growth zone. Further, a device to trap ammonium chloride
can be attached at the inlet and/or outlet of the gas exhaust
pipe.
[0012] In accordance with the present invention, a fabrication
method of a group III nitride crystal substance including a method
for effectively cleaning deposits adhering to the interior of the
reaction chamber during crystal growth, and a fabrication apparatus
employed in the fabrication method can be provided.
[0013] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a schematic sectional view representing an
embodiment of a fabrication method and fabrication apparatus of a
group III nitride crystal substance of the present invention,
wherein (a) corresponds to the step of cleaning the interior of the
reaction chamber by introducing HCl gas into the reaction chamber,
and (b) corresponds to the step of vapor deposition of a group III
nitride crystal substance in the cleaned reaction chamber.
[0015] FIG. 2 is a schematic sectional view of a group III nitride
crystal substance fabrication apparatus according to another
embodiment of the present invention.
[0016] FIG. 3 is a schematic sectional view of a group III nitride
crystal substance fabrication method according to a further
embodiment of the present invention.
[0017] FIG. 4 is a schematic sectional view of a general group III
nitride crystal substance fabrication apparatus.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0018] Referring to FIG. 1, an embodiment of a fabrication method
of a group III nitride crystal substance of the present invention
includes the step of cleaning the interior of a reaction chamber
110 by introducing HCl gas 1 into reaction chamber 110, as shown in
(a), and the step of vapor deposition of a group III nitride
crystal substance 11 in the cleaned reaction chamber 110, as shown
in (b).
[0019] Referring to (a) and (b) in FIG. 1, the inventors found that
deposits 9 formed of polycrystalline group III nitride accumulated
inside reaction chamber 110 during growth of a group III nitride
crystal substance 11 (specifically, at the inner wall of a reactor
tube 101 constituting reaction chamber 110, and at the ends of
group III element raw material gas introduction pipe 123, nitrogen
raw material gas introduction pipe 113, HCl gas introduction pipe
111, and the like) are etched away by HCl gas 1. The inventors used
HCl gas 1 for cleaning the interior of reaction chamber 110 to
complete the present invention.
[0020] For example, GaN identified as group III nitride reacts with
HCl gas, as set forth in the following equations of (1)-(3):
GaN(s)+HCl(g).fwdarw.GaCl(g)+(1/2)N.sub.2(g)+(1/2)H.sub.2(g)
(1)
GaN(s)+2HCl(g).fwdarw.GaCl.sub.2(g)+(1/2)N.sub.2(g)+H.sub.2(g)
(2)
GaN(s)+3HCl(g).fwdarw.GaCl.sub.3(g)+(1/2)N.sub.2(g)+(3/2)H.sub.2(g)
(3)
and is converted into GaCl gas, GaCl.sub.2 gas or GaCl.sub.3 gas to
be removed. The same can be said for group III nitride crystal
substances other than GaN such as AlN.
[0021] Referring to FIG. 1(b), during growth of a group III nitride
crystal substance, deposits 9 formed of polycrystalline group III
nitride adhere to the interior of reaction chamber 110,
particularly to the ends of group III element raw material gas
introduction pipe 123, nitrogen raw material gas introduction pipe
113, and HCl gas introduction pipe 111, and also to the inner wall
of reactor tube 101 at the crystal growth zone (the zone in the
proximity to substrate holder 119 for crystal growth, mainly the
zone heated by a heater 133; the same implies hereinafter).
[0022] In the step of cleaning the interior of a reaction chamber
110 by introducing HCl gas 1 into reaction chamber 110
corresponding to FIG. 1(a), HCl gas 1 is introduced into reaction
chamber 110 contaminated with adhering deposits 9 via HCl gas
introduction pipe 111. At this stage, carrier gas is additionally
used to deliver the HCl gas efficiently, and/or to adjust the
partial pressure of HCl gas. H.sub.2 gas, N.sub.2 gas, Ar gas, He
gas and the like can be enumerated as carrier gas. From the
standpoint of facilitating removal of deposits 9 formed of
polycrystalline group III nitride and the economic aspect, H.sub.2
gas is preferable for the carrier gas. Deposits 9 react with HCl
gas 1 to generate group III element chloride gas, N.sub.2 gas and
H.sub.2 gas. Such group III element chloride gas, N.sub.2 gas and
H.sub.2 gas are discharged via gas exhaust pipe 115 from reaction
chamber 110 to be output as exhaust gas 5, whereby the interior of
reaction chamber 110 is cleaned. The opening of HCl gas
introduction pipe 111 is preferably located at the leading end of
nitrogen raw material gas introduction pipe 113 and group III
element raw material gas introduction pipe 123, i.e. upstream of
the region where deposits 9 adhere.
[0023] With reference to FIG. 1(b), the step of vapor deposition of
a group III nitride crystal substance 11 in cleaned reaction
chamber 110 is carried out as set forth below. HCl gas 1 is
introduced into group III element raw material gas generation
chamber 120 via an HCl gas introduction pipe 122. A group III
element boat 121 with group III element 2 placed therein is
disposed in group III element raw material gas generation chamber
120. Group III element 2 reacts with HCl gas 1 to generate group
III element chloride gas qualified as group III element raw
material gas 3.
[0024] Group III element raw material gas 3 is introduced from
group III element raw material gas generation chamber 120 into
reaction chamber 110 via group III element raw material gas
introduction pipe 123. NH.sub.3 gas qualified as nitrogen raw
material gas 4 is introduced into reaction chamber 110 via a
nitrogen raw material gas introduction pipe 113. In reaction
chamber 110, group III element raw material gas 3 and nitrogen raw
material gas 4 react, whereby a group III nitride crystal substance
11 is grown on underlying substrate 10 disposed on substrate holder
119 at the crystal growth zone. Excessive gas is discharged from
reaction chamber 110 via gas exhaust pipe 115, as exhaust gas 5. At
this stage, carrier gas is additionally used to efficiently deliver
the group III element raw material gas and nitrogen raw material
gas, and/or to adjust the partial pressure of each raw material
gas. H.sub.2 gas, N.sub.2 gas, and the like can be enumerated for
the carrier gas.
[0025] Deposits 9 formed of polycrystalline group III nitride
adhere to the interior of reaction chamber 110. Attachment of
deposits 9 at the leading end portions of group III element raw
material gas introduction pipe 123, nitrogen raw material gas
introduction pipe 113, and HCl gas introduction pipe 111 in
reaction chamber 110 will impede supply of raw material gas. It
will therefore become difficult to obtain a crystal substance of
stable quality, and conduct growth for a long period of time to
obtain a thick crystal substance.
[0026] By repeating the step of introducing HCl gas into the
reaction chamber to clean the interior of the reaction chamber
effectively and the step of vapor deposition of a group III nitride
crystal substance in the cleaned reaction chamber, cleaning the
interior of the reaction chamber and growing a group III nitride
crystal substance in vapor phase can be conducted efficiently.
Thus, a group III nitride crystal substance of favorable
crystallinity can be obtained efficiently.
[0027] In the fabrication method of a group III nitride crystal
substance of the present embodiment, the step of cleaning the
interior of the reaction chamber is preferably carried out under
the conditions that the HCl gas pressure is at least 1.013 hPa and
not more than 1013 hPa (at least 0.001 atm and not more than 1
atm), and the temperature in the reaction chamber is at least
650.degree. C. and not more than 1200.degree. C. If the HCl gas
partial pressure is lower than 1.013 hPa, the removal effect of
deposits 9 is degraded. If the partial pressure is higher than 1013
hPa, it will be difficult to discharge the introduced HCl gas from
the reaction chamber. Further, if the temperature in the reaction
chamber is lower than 650.degree. C., the removal effect of
deposits 9 is degraded. If the temperature is higher than
1200.degree. C., the reactor tube constituting the reaction chamber
will be deteriorated and/or damaged. In view of the foregoing, the
temperature in the reaction chamber is preferably at least
800.degree. C. and more preferably at least 900.degree. C.
[0028] In the fabrication method of a group III nitride crystal
substance of the present embodiment, the oxygen atom concentration
and silicon atom concentration in the group III nitride crystal
substance can be adjusted by regulating the temperature at the raw
material introduction zone in the reaction chamber in the step of
vapor deposition of a group III nitride crystal substance in the
cleaned reaction chamber.
[0029] In the case where the reactor tube is formed of
oxygen-containing material such as quartz, the oxygen atoms and
silicon atoms contained in the reactor tube will be mixed into the
group III nitride crystal substance during growth thereof. Upon a
thermodynamic calculation for the pyrolysis of quartz in a system
where NH.sub.3(g) and H.sub.2(g) are brought into contact with
quartz SiO.sub.2(s) when the mole ratio of
SiO.sub.2(s):NH.sub.3(g):H.sub.2(g) is 1:10:40 and the total
pressure of NH.sub.3(g) and H.sub.2(g) is 1013 hPa (1 atm), for
example, it was found that moisture (H.sub.2O(g)) and Si type gas
(for example, Si.sub.2N.sub.2O(g)) were generated as the
temperature in the reaction chamber rises. The partial pressure of
the generated H.sub.2O(g) and Si type gas increases as the
temperature in the reaction chamber rises, i.e. the partial
pressure is 0.41 Pa (4.times.10.sup.-6 atm and 0.10 Pa
(1.times.10.sup.-6 atm), respectively, at 600.degree. C., and 2.43
Pa (2.4.times.10.sup.-5 atm) and 0.61 Pa (6.times.10.sup.-6 atm),
respectively, at 1000.degree. C. The oxygen atoms in the moisture
and the silicon atoms in the Si type gas enter the group III
nitride crystal substance as impurities.
[0030] The temperature in the reaction chamber (hereinafter, also
referred to as in-reaction chamber temperature) is adjusted by
regulating the temperature at the raw material introduction zone
and crystal growth zone. From the standpoint of stably growing a
group III nitride crystal substance of favorable crystallinity, the
crystal growth zone is preferably maintained at approximately
1000.degree. C.-1200.degree. C. Therefore, adjustment of the
in-reaction chamber temperature to control the oxygen atom
concentration and silicon atom concentration can be conducted in
practice mainly by adjusting the temperature at the raw material
introduction zone (the zone in proximity to the ends of group III
element raw material gas introduction pipe 123, nitrogen raw
material gas introduction pipe 113 and HCl gas introduction pipe
111; mainly the region heated by heater 132; the same apply
hereinafter), instead of adjusting the temperature at the crystal
growth zone, or by disposing a quartz component in the reaction
chamber and heating the same. The crystal growth zone refers to the
region where a group III nitride crystal substance is to be grown,
and the region heated by heater 133 in reaction chamber 110 in FIG.
1.
[0031] When a GaN crystal substance is to be grown as a group III
nitride crystal substance, the temperature in group III element raw
material gas generation chamber 120 and the raw material
introduction zone is preferably adjusted in the range of at least
650.degree. C. and not more than 1200.degree. C. If the temperature
in group III element raw material gas generation chamber 120 is
lower than 650.degree. C., reaction between HCl gas 1 and metal Ga
(group III element 2) is degraded, such that introduction of GaCl
gas (group III element raw material gas 3) into reaction chamber
110 is impeded. If the temperature at the raw material introduction
zone is higher than 1200.degree. C., degradation and/or damage of
the quartz component and the like will readily occur,
Second Embodiment
[0032] Referring to FIG. 1, an embodiment of a fabrication
apparatus of a group III nitride crystal substance (fabrication
apparatus 100) of the present invention includes a reaction chamber
110 formed in a reactor tube 101, a group III element raw material
gas generation chamber 120, an HCl gas introduction pipe 111 to
introduce HCl gas 1 into reaction chamber 110, an HCl gas
introduction pipe 122 to introduce HCl gas 1 into group III element
raw material gas generation chamber 120, a group III element raw
material gas introduction pipe 123 to introduce group III raw
material gas 3 generated at group III element raw material gas
generation chamber 120 to reaction chamber 110, a nitrogen raw
material gas introduction pipe 113 to introduce nitrogen raw
material gas 4 into reaction chamber 110, a gas exhaust pipe 115 to
discharge gas from reaction chamber 110, and a substrate holder 119
to dispose an underlying substrate 10 to grow a group III nitride
crystal substance 11 in reaction chamber 110. By the provision of
HCl gas introduction pipe 111 to introduce HCl gas 1 into reaction
chamber 110, HCl gas can be directly introduced into reaction
chamber 110 without the passage of another chamber when a group III
nitride crystal substance 11 is to be grown. Therefore, deposits 9
formed of polycrystalline group III nitride adhering to the
interior of reaction chamber 110 can be removed efficiently in
vapor phase.
[0033] In fabrication apparatus 100 of the present embodiment, HCl
gas introduction pipe 111 to introduce HCl gas 1 into reaction
chamber 110 corresponds to the configuration of introducing HCl gas
1 into reaction chamber 110, and components other than HCl gas
introduction pipe 111 to introduce HCl gas 1 into reaction chamber
1 correspond to the configuration of growing a group III nitride
crystal substance 11 by HVPE. In other words, fabrication apparatus
100 of the present embodiment includes a configuration of
introducing HCl gas into the reaction chamber, and a configuration
of growing a group III nitride crystal substance by HVPE. As used
herein, HVPE refers to the method of growing a group III nitride
crystal substance in vapor phase based on the reaction between
group III element chlorine gas qualified as the group III element
raw material gas, and NH.sub.3 gas qualified as the nitrogen raw
material gas. The apparatus to grow a crystal substance by HVPE is
referred to as the "HVPE apparatus".
[0034] Referring to FIG. 1, for example, group III nitride crystal
substance fabrication apparatus 100 of the present embodiment
includes reaction chamber 110, group III element raw material gas
generation chamber 120, and heaters 131, 132 and 133 to heat
reaction chamber 110 and group III element raw material gas
generation chamber 120. Reaction chamber 110 and group III element
raw material gas generation chamber 120 have HCl gas introduction
pipe 122 arranged to introduce HCl gas 1 into group III element raw
material gas generation chamber 120. In group III element raw
material gas generation chamber 120, a group III element boat 121
in which group III element 2 is placed is disposed therein. Group
III element raw material gas generation chamber 120 has a group III
element raw material gas introduction pipe 123 arranged to deliver
the generated group III element raw material gas 3 into reaction
chamber 110. Reaction chamber 110 is provided with nitrogen raw
material gas introduction pipe 113 to introduce nitrogen raw
material gas 4 into reaction chamber 110, and gas exhaust pipe 115
to discharge gas 5 from reaction chamber 110. Substrate holder 119
to dispose an underlying substrate 10 for growth of a group III
nitride crystal substance 11 is arranged in reaction chamber 110.
From the standpoint of readily producing a large reactor tube,
reactor tube 101 constituting reaction chamber 110 is preferably,
but not particularly limited to, a quartz reactor tube.
[0035] During the step of growing a crystal substance or cleaning
the interior of the reaction chamber, ammonium chloride
(NH.sub.4Cl) powder is generated as a by-product. Since the powder
may block gas exhaust pipe 115 to impede continuous crystal growth
of long duration, i.e. impede growth of a thick crystal substance,
it is preferable to attach a device 116 that traps ammonium
chloride (hereinafter, also referred to as trap device 116) at an
inlet 115a and/or an outlet 115b of gas exhaust pipe 115. Ammonium
chloride is generated when HCl and NH.sub.3 are present at the
temperature of below approximately 340.degree. C. The form thereof
is powder. It is preferable to cool the interior of trap device
116. Although this may be conducted by air-cooling or
water-cooling, the air-cooling approach is preferable from the
standpoint of maintenance. A filter 116f may be installed in trap
device 116. Trap device 116 is configured to obviate clogging at
the inlet and outlet of gas exhaust pipe 115. For example, trap
device 116 is preferably configured such that the gas inlet and
outlet is located at the upper portion of trap device 116, and the
lower portion of trap device 116 corresponds to a deep concave for
accumulation of ammonium chloride powder.
Third Embodiment
[0036] Referring to FIG. 2, another embodiment of a group III
nitride crystal substance fabrication apparatus (fabrication
apparatus 200) of the present invention has a protection member 112
for the reaction chamber arranged on the inner wall of reactor tube
101 at the crystal growth zone located in proximity to substrate
holder 119 in reaction chamber 110 corresponding to fabrication
apparatus 100 of a group III nitride crystal substance of the
second embodiment shown in FIG. 1. Protection member 117 may be
brought into intimate contact with the inner wall of reactor tube
101, as shown in FIG. 2, or disposed apart from the inner wall of
reactor tube 101.
[0037] At the crystal growth zone of reaction chamber 110, the
temperature becomes as high as appropriately 1000.degree.
C.-1200.degree. C. during crystal growth. The inner wall of reactor
tube 101 in the proximity of the crystal growth zone in reaction
chamber 110 attains a temperature equal to that of the crystal
growth zone, corresponding to an environment of facilitating
crystal generation. Therefore, a large amount of polycrystalline
group III nitride (for example, polycrystalline GaN when GaN
crystal substance is grown; polycrystalline AlN when AlN crystal
substance is grown) adheres to the inner wall of reactor tube 101
in the proximity of the crystal growth zone. In the case where
reactor tube 101 is formed of oxygen-containing material such as
quartz, the reactor tube reacts with the NH.sub.3 gas qualified as
the nitrogen raw material gas and/or H.sub.2 gas qualified as the
carrier gas to generate moisture. As a result, oxygen atoms will be
mixed into the group III nitride crystal substance to degrade and
damage reactor tube 101.
[0038] The provision of protection member 117 for reactor tube 101
at the inner wall of reactor tube 101 at the crystal growth zone of
reaction chamber 110 suppresses the contact between the quartz of
reactor tube 101 and the raw material gas and/or hydrogen gas at
the crystal growth zone. Therefore, adherence of polycrystalline
group III nitride deposits onto the inner wall of reactor tube 101
at the crystal growth zone as well as the degradation and damage of
reactor tube 101 can be suppressed. Even if the quartz (SiO.sub.2)
of reactor tube 101 is decomposed at the crystal growth zone, gas
including oxygen atoms and silicon atoms will not reach the crystal
growth zone since the group III nitride crystal growth zone is
separated from the SiO.sub.2 decomposition region by protection
member 117. Thus, introduction of oxygen atoms and silicon atoms
into a group III nitride crystal substance 11 as well as
degradation and damage of reactor tube 101 can be suppressed. From
the standpoint of suppressing introduction of oxygen atoms into the
group III nitride crystal substance as well as degradation and
damage of reactor tube 101, protection member 117 is preferably
formed of, but not limited to, a substance other than oxide such as
pBN (pyrolitic boron nitride), carbon, SiC, WC, TaC, and the like.
Likewise the second embodiment, a device 116 to trap ammonia
chloride is preferably provided at inlet 115a and/or outlet 115b of
gas exhaust pipe 115. Further, trap device 116 may be provided with
filter 116f, likewise the second embodiment.
Fourth Embodiment
[0039] Referring to FIG. 3, another embodiment of a group III
nitride crystal substance fabrication method of the present
invention is directed to the step of cleaning the interior of
reaction chamber 110 by introducing HCl gas into reaction chamber
110 via HCL gas introduction pipe 122 after group III element raw
material gas generation chamber 120 and group III element raw
material gas introduction pipe 123 are removed from reaction
chamber 110 in fabrication apparatus 300. The removed group III
element raw material gas generation chamber 120 and group III
element raw material gas introduction pipe 123 are cleaned
separately by vapor phase etching using HCl gas or by liquid phase
etching using phosphoric acid, sulfuric acid, and the like.
[0040] The cleaned group III element raw material gas generation
chamber 120 and group III element raw material gas introduction
pipe 123 are attached again to the cleaned reaction chamber 110.
Then, a group III nitride crystal substance is grown in the cleaned
reaction chamber 110.
[0041] In accordance with the step of cleaning the interior of the
reaction chamber according to the fourth embodiment, HCl gas 1 can
be introduced into reaction chamber 110 by means of HCl gas
introduction pipe 122 introducing HCl gas into the group III
element raw material gas reaction chamber in the step of growing a
group III nitride crystal substance. Therefore, HCl gas
introduction pipe 111 to introduce HCl gas 1 into reaction chamber
110 as in fabrication apparatus 100 of FIG. 1 is dispensable.
However, group III element raw material gas generation chamber 120
and group III element raw material gas introduction pipe 123 must
be cleaned otherwise. In fabrication apparatus 300 of the present
embodiment, a device 116 to trap ammonia chloride is preferably
provided at inlet 115a and/or outlet 115b of gas exhaust pipe 115.
Further, trap device 116 may be provided with filter 116f, likewise
the second embodiment.
[0042] The first to fourth embodiments were described based on
HVPE. The present invention is preferably applicable to vapor
deposition methods other than HVPE such as MOC or MOCVD. The MOC
method includes the step of effecting reaction between organic
metal compound gas of a group III element and HCl gas to generate
group III element chloride gas, qualified as group III element raw
material gas, and then effecting reaction between the group III
element chloride gas and NH.sub.3 gas qualified as nitrogen raw
material gas to grow a group III nitride crystal substance with
vapor phase. The MOCVD method includes the step of effecting
reaction between organic metal compound gas of a group III element
and NH.sub.3 gas qualified as nitrogen raw material gas to grow a
group III nitride crystal substance with vapor phase.
COMPARATIVE EXAMPLE 1
[0043] A GaN crystal substance was grown using a general
fabrication apparatus 400 of a group III nitride crystal substance
shown in FIG. 4. Crystal growth was conducted by fabrication
apparatus 400, absent of a device for trapping ammonia chloride
(trap device) at gas exhaust pipe 115. First, a new quartz reactor
tube 101 constituting reaction chamber 110 was set in fabrication
apparatus 400. In order to remove any impurities such as moisture
adhered to quartz reactor tube 101, pre-baking was conducted for 50
hours at 1050.degree. C. while supplying a flow of N.sub.2 gas in
reaction chamber 110.
[0044] Then, a (0001) sapphire substrate (a sapphire substrate with
the (0001) plane as the crystal growing plane; the same applies
hereinafter) of 50.8 mm in diameter was set as underlying substrate
10 in reaction chamber 110. A GaN crystal substance (group III
nitride crystal substance 11) was grown on underlying substrate 10
for 15 hours under the conditions of 850.degree. C. for the
temperature in group III element raw material gas generation
chamber 120 and the raw material introduction zone and 1030.degree.
C. for the temperature at the crystal growth zone in reaction
chamber 110, and 20.26 hPa (0.02 atm) for the HCl gas partial
pressure (GaCl gas partial pressure) and 303.9 hPa (0.3 atm) for
the NH.sub.3 gas partial pressure (first crystal growth). Crystal
growth was conducted using a substrate of 50.8 mm in diameter in
the comparative examples and examples of the present invention set
forth below. The obtained GaN crystal substance exhibiting an
uneven surface was approximately 1.7 mm in thickness with brown
transparency. The periphery of the obtained GaN crystal substance
had polycrystalline GaN adhered thereto.
[0045] After the polycrystalline GaN at the periphery of the GaN
crystal substance was removed by peripheral grinding, the surface
was ground and polished to be smooth. No cracks were observed
during the process of peripheral grinding, surface grinding, and
polishing. The smoothed surface of the GaN crystal substance was
observing with visible light using a fluorescent microscope. A
light domain and a dark domain were observed. The dark domain
indicates the region where the crystal grows at the facet of the
(11-22) plane and the like (hereinafter, referred to as the facet
growth domain). The light domain indicates the region where the
crystal grows at the (0001) plane (hereinafter, referred to as the
C-plane growth domain). By the presence of both the facet growth
domain and C-plane growth domain in crystal growth, dislocations
can be gathered at the region extending from the vertex of the
concave pit formed of a plurality of facets perpendicularly inward
of the crystal with respect to the C-plane. The dislocation density
at a region other than this dislocation gathering region can be
reduced. Formation of such a facet growth domain is facilitated as
the crystal growth temperature becomes lower, or as the ratio of
the partial pressure of group III element raw material gas to the
partial pressure of the nitrogen raw material gas becomes
lower.
[0046] The impurity concentration at the facet growth domain of the
GaN crystal substance was measured by SIMS (Secondary Ion Mass
Spectroscopy). H atoms, C atoms, Si atoms, and O atoms were
observed as impurities. The concentration of the H atoms, C atoms,
and Si atoms were all below 1.0.times.10.sup.17 cm.sup.-3. The
concentration of O atoms was 1.2.times.10.sup.19 cm.sup.-3. With
regards to the impurity concentration at the C-plane growth domain
of the GaN crystal substance, the impurity concentration was below
1.0.times.10.sup.17 cm.sup.-3 for the O, H, and C atoms, and
1.0.times.10.sup.18 cm.sup.-3 for the Si atoms.
[0047] In reaction chamber 110 subsequent to this GaN crystal
substance growth, particularly at the inner wall of quartz reactor
tube 101 at the crystal growth zone and at the ends of group III
element raw material gas introduction pipe 123 and nitrogen raw
material gas introduction pipe 113 at the raw material introduction
zone, attachment of deposits 9 formed of polycrystalline GaN,
approximately 0.3-0.7 mm in thickness, was observed. Further,
ammonium chloride was deposited on the inner wall of gas exhaust
pipe 115 to a thickness of approximately 2-4 mm.
[0048] Using this quartz reactor tube 101 as reaction chamber 110,
a GaN crystal substance was grown again (second crystal growth)
under conditions identical to those of the first crystal growth.
The obtained GaN crystal substance exhibiting an uneven surface was
approximately 1 mm in thickness with brown transparency, thinner
than the first grown GaN crystal substance. The periphery of the
obtained GaN crystal substance had polycrystalline GaN adhered
thereto. The concentration of O atoms and Si atoms at the facet
growth domain of this GaN crystal substance was 1.2.times.10.sup.19
cm.sup.-3 and below 1.0.times.10.sup.17 cm.sup.-3, respectively.
The concentration of the O atoms and Si atoms at the C-plane growth
domain was below 1.0.times.10.sup.17 cm.sup.-3 and
1.1.times.10.sup.18 cm.sup.-3, respectively. In the assessment, the
same process as set forth above was applied. However, no
cracks-were observed.
[0049] The thickness of deposits 9 formed inside reaction chamber
110 subsequent to the second crystal growth, particularly at the
inner wall of quartz reactor tube 101 at the crystal growth zone
and the ends of group III element raw material gas introduction
pipe 123 and nitrogen raw material gas introduction pipe 113 at the
raw material introduction zone was 1.1-2.4 mm. It is assumed that
deposits at least two times the thickness of the first crystal
growth were accumulated at the second crystal growth. Further,
ammonium chloride was deposited on the inner wall of gas exhaust
pipe 115 to a thickness of at least two times that of the first
crystal growth during the second crystal growth. It was found that,
in the second crystal growth, more Ga material and nitrogen
material became deposits 9, and the growth rate of the GaN crystal
substance was degraded by the clogging at gas exhaust pipe 115, as
compared to the first crystal growth.
COMPARATIVE EXAMPLE 2
[0050] Deposits 9 of approximately 1.1-2.4 mm in thickness were
attached inside reaction chamber 110, and ammonium chloride of
approximately 5-10 mm in thickness was attached at the inner wall
of gas exhaust pipe 115, subsequent to the second crystal growth in
Comparative Example 1. This quartz reactor tube 101 contaminated
with deposits 9 was removed from fabrication apparatus 400 and
dipped in a mixed solution of phosphoric acid and sulfuric acid
under the mole ratio of 1:1 (solution temperature 180.degree. C.)
to be etched for 24 hours to be cleaned (cleaning of quartz reactor
tube by liquid phase etching). The remaining deposits were reduced
to the thickness of 1.0 mm by etching relative to the thickness of
2.4 mm prior to etching. In this context, the etching rate of the
deposits can be estimated as approximately 60 .mu.m/hr. This quartz
reactor tube 101 with deposits still remaining was further
subjected to etching for 24 hours under the same conditions to
remove the remaining deposits. Additionally, gas exhaust pipe 115
contaminated with ammonium chloride was cleaned with water to
remove the adhering ammonium chloride.
[0051] Quartz rector tube 101 cleaned as set forth above was set in
fabrication apparatus 400 as reaction chamber 110, and then
subjected to pre-baking for 50 hours at 1050.degree. C. while
supplying a flow of N.sub.2 gas into reaction chamber 110 to remove
moisture adhering to the inner wall of quartz reactor tube 101.
[0052] Then, a (0001) sapphire substrate was set in reaction
chamber 110 as underlying substrate 10. A GaN crystal substance
(group III nitride crystal substance 11) was grown on underlying
substrate 10 for 15 hours under the conditions of 850.degree. C.
for the temperature in group III element raw material gas
generation chamber 120 and the raw material introduction zone and
1030.degree. C. for the temperature at the crystal growth zone in
reaction chamber 110, and 20.26 hPa (0.02 atm) for the HCl gas
partial pressure (GaCl gas partial pressure) and 303.9 hPa (0.3
atm) for the NH.sub.3 gas partial pressure.
[0053] The obtained GaN crystal substance exhibiting an uneven
surface was approximately 1.7 mm in thickness with darker brown
transparency as compared with the GaN crystal substance grown at
Comparison Example 1. The periphery of the obtained GaN crystal
substance had polycrystalline GaN adhered thereto. A crack of
approximately several ten to several hundred .mu.m in length was
observed at the interface between the polycrystalline portion and
the single crystal portion. For oxygen concentration analysis, a
process similar to that of Comparative Example 1 was conducted. The
crystal substance subjected to this process had small cracks of
approximately several ten to several hundred .mu.m in length in
addition to the crack identified prior to the process. The impurity
concentration of the GaN crystal substance was evaluated avoiding
the region of the small cracks. The GaN crystal substance had a
facet growth domain and a C-plane growth domain. The concentration
of O atoms and Si atoms at the facet growth domain was
3.5.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 2.0.times.10.sup.18 cm.sup.-3, respectively. Since
the concentration of oxygen atoms identified as impurities in the
GaN crystal substance was higher than that of the GaN crystal
substance grown in Comparative Example 1, it is assumed that
pre-baking of approximately 50 hours at 1050.degree. C. is not
sufficient in the case of cleaning by liquid phase etching as in
the present comparative example. The generation of cracks not
observed in Comparative Example 1 indicates that the crystal
substance has become brittle by the hardening due to impurities
corresponding to the higher oxygen concentration.
EXAMPLE 1
[0054] A GaN crystal substance was grown using a group III nitride
crystal substance fabrication apparatus 100 according to the
present invention shown in FIG. 1. Crystal growth was conducted
without providing a device to trap ammonium chloride (trap device
116) in fabrication apparatus 100. First, a new quartz reactor tube
101 constituting reaction chamber 110 was set in fabrication
apparatus 100. In order to remove impurities such as moisture in
quartz reactor tube 101, pre-baking was conducted for 50 hours at
the temperature of 1050.degree. C. in the reaction chamber while
supplying a flow of N.sub.2 gas in reaction chamber 110. Then, a
(0001) sapphire substrate of 50.8 mm in diameter was set as
underlying substrate 10 in reaction chamber 110. A GaN crystal
substance (group III nitride crystal substance 11) was grown on
underlying substrate 10 for 15 hours under the conditions of
850.degree. C. for the temperature in group III element raw
material gas generation chamber 120 and the raw material
introduction zone and 1030.degree. C. for the temperature at the
crystal growth zone in reaction chamber 110, and 20.26 hPa (0.02
atm) for the HCl gas partial pressure (GaCl gas partial pressure)
and 303.9 hPa (0.3 atm) for the NH.sub.3 gas partial pressure. The
obtained GaN crystal substance had a facet growth domain and a
C-plane growth domain. The concentration of O atoms and Si atoms at
the facet growth domain was 1.2.times.10.sup.19 cm.sup.-3 and below
1.0.times.10.sup.17 cm.sup.-3, respectively. The concentration of O
atoms and Si atoms at the C-plane growth domain was below
1.0.times.10.sup.17 cm.sup.-3 and 1.0.times.10.sup.18 cm.sup.-3,
respectively.
[0055] In reaction chamber 110 subsequent to this GaN crystal
growth, particularly at the inner wall of quartz reactor tube 101
at the crystal growth zone and at the ends of group III element raw
material gas introduction pipe 123, nitrogen raw material gas
introduction pipe 113, and HCl gas introduction pipe 111 at the raw
material introduction zone, attachment of deposits 9 formed of
polycrystalline GaN, approximately 0.3-0.7 mm in thickness, was
observed. Further, ammonium chloride was deposited on the inner
wall of gas exhaust pipe 115 to a thickness of approximately 2-4
mm.
[0056] HCl gas 1 and H.sub.2 gas (carrier gas) were introduced via
HCl gas introduction pipe 111 into reaction chamber 110
contaminated with deposits 9 to conduct etching for 5 hours at the
temperature of 1000.degree. C. in the reaction chamber, whereby the
interior of reaction chamber 110 was cleaned (cleaning by vapor
phase etching). At this stage, the partial pressure of HCl gas 1
was 50.65 hPa (0.05 atm). As a result, deposits 9 in reaction
chamber 110 were completely removed by the vapor phase etching.
From an additional vapor phase etching experiment, it was estimated
that the etching rate of deposits 9 under the present conditions
was approximately 500 .mu.m/hr. Ammonium chloride adhered to gas
exhaust pipe 115.
[0057] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. A GaN crystal substance
(group III nitride crystal substance 11) was grown on underlying
substrate 10 for 15 hours under the conditions of 850.degree. C.
for the temperature in group III element raw material gas
generation chamber 120 and the raw material introduction zone and
1030.degree. C. for the temperature at the crystal growth zone in
reaction chamber 110, and 20.26 hPa (0.02 atm) for the HCl gas
partial pressure (GaCl gas partial pressure) and 303.9 hPa (0.3
atm) for the NH.sub.3 gas partial pressure.
[0058] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with lighter
brown transparency than the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the concentration of O atoms and Si atoms at the facet growth
domain of the GaN crystal substance was 6.6.times.10.sup.18
cm.sup.-3 and below 1.0.times.10.sup.17 cm.sup.-3, respectively.
The concentration of O atoms and Si atoms at the C-plane growth
domain was below 1.0.times.10.sup.17 cm.sup.-3 and
6.5.times.10.sup.17 cm.sup.-3, respectively. No cracks were
observed after the growing stage and processing stage.
EXAMPLE 2
[0059] Inside reaction chamber 110 subsequent to the GaN crystal
growth of Example 1, deposits 9 of approximately 0.3-0.7 mm in
thickness, formed of polycrystalline GaN, were observed. The
interior of reaction chamber 110 contaminated with deposits 9 was
cleaned by vapor phase etching for 5 hours at the in-chamber
temperature of 1000.degree. C. with 50.65 hPa (0.05 atm) for the
HCl gas partial pressure and employing N.sub.2 gas as the carrier
gas. As a result, deposits 9 were completely removed. From an
additional vapor phase etching experiment, it was estimated that
the etching rate of deposits 9 under the present conditions was
approximately 200 .mu.m/hr. The reason why the etching rate is
reduced as compared to Example 1 may be due to the fact that the
nitrogen gas partial pressure has risen by using N.sub.2 gas as the
carrier gas to suppress escape and decomposition of nitrogen from
the polycrystalline GaN constituting deposits 9.
[0060] Then, a device for trapping ammonium chloride (trap device
116) was attached at inlet 115a of gas exhaust pipe 115. The
attached trap device 116 is a SUS-made container, designed to trap
ammonium chloride in the container. Then, a (0001) sapphire
substrate was set as underlying substrate 10 in reaction chamber
110. A GaN crystal substance (group III nitride crystal substance
11) was grown on underlying substrate 10 for 15 hours under the
conditions of 850.degree. C. for the temperature in group III
element raw material gas generation chamber 120 and the raw
material introduction zone and 1030.degree. C. for the temperature
at the crystal growth zone in reaction chamber 110, and 20.26 hPa
(0.02 atm) for the HCl gas partial pressure (GaCl gas partial
pressure) and 303.9 hPa (0.3 atm) for the NH.sub.3 gas partial
pressure.
[0061] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with lighter
brown transparency than the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain was 6.2.times.10.sup.18 cm.sup.-3 and below
1.0.times.10.sup.17 cm.sup.-3, respectively. The concentration of O
atoms and Si atoms at the C-plane growth domain was below
1.0.times.10.sup.17 cm.sup.-3 and 6.3.times.10.sup.17 cm.sup.-3,
respectively. No cracks were observed after the growing stage and
processing stage. Upon removing and examining trap device 116,
ammonium chloride was accumulated in trap device 116, and there was
only a thin layer (approximately 0.1-0.2 mm in thickness) of
ammonium chloride at gas exhaust pipe 115. Gas exhaust pipe 115 was
completely free from clogging.
EXAMPLE 3
[0062] Inside reaction chamber 110 subsequent to the GaN crystal
growth of Example 2, deposits 9 of approximately 0.3-0.7 mm in
thickness formed of polycrystalline GaN were observed. The interior
of reaction chamber 110 contaminated with deposits 9 was cleaned by
vapor phase etching for 8 hours at the in-chamber temperature of
850.degree. C. with 50.65 hPa (0.05 atm) for the HCl gas partial
pressure and employing H.sub.2 gas as the carrier gas. As a result,
deposits 9 were completely removed. From an additional vapor phase
etching experiment, it was estimated that the etching rate of
deposits 9 under the present conditions was approximately 100
.mu.m/hr.
[0063] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. A GaN crystal substance
(group III nitride crystal substance 11) was grown on underlying
substrate 10 for 15 hours under the conditions of 850.degree. C.
for the temperature in group III element raw material gas
generation chamber 120 and the raw material introduction zone and
1030.degree. C. for the temperature at the crystal growth zone in
reaction chamber 110, and 20.26 hPa (0.02 atm) for the HCl gas
partial pressure (GaCl gas partial pressure) and 303.9 hPa (0.3
atm) for the NH.sub.3 gas partial pressure.
[0064] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with lighter
brown transparency than the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain of the GaN crystal substance was
6.0.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 6.2.times.10.sup.17 cm.sup.-3, respectively. No
cracks were observed after the growing stage and processing
stage.
[0065] There was a tendency for slight reduction in the
concentration of oxygen atoms identified as impurities in the GaN
crystal substance in proportion to the increased times of crystal
growth, as shown in Examples 1, 2 and 3 set forth above. This is
probably because of the fact that impurities including oxygen atoms
such as H.sub.2O or CO in the used quartz reactor tube 101 are
gradually reduced. Another possible reason is that the inner wall
of the quartz reactor tube with uneveness at the surface at the
start of usage corresponds to a larger area of reaction with the
nitrogen raw material gas such as NH.sub.3, which is reduced as a
result of the surface of the inner wall rendered smooth by the
etching and/or high temperature atmosphere during usage.
[0066] Hall measurement was conducted at room temperature
(25.degree. C.) for the GaN crystal substances obtained at Examples
1, 2 and 3. The oxygen concentration obtained by SIMS and the
carrier concentration identified by Hall measurement substantially
matched each other. It was identified that the carrier in the GaN
crystal substances relate to the oxygen atoms that are impurities
in the crystal substance.
EXAMPLE 4
[0067] A GaN crystal substance was grown using group III nitride
crystal substance fabrication apparatus 100 according to the
present invention shown in FIG. 1. First, a new quartz reactor tube
101 constituting reaction chamber 110 was set in fabrication
apparatus 100. In order to remove impurities such as moisture in
quartz reactor tube 101, pre-baking was conducted for 50 hours at
the temperature of 1050.degree. C. while supplying a flow of
N.sub.2 gas in reaction chamber 110. Then, a (0001) sapphire
substrate was set as underlying substrate 10 in reaction chamber
110. A GaN crystal substance (group III nitride crystal substance
11) was grown on underlying substrate 10 for 15 hours under the
conditions of 850.degree. C. for the temperature in group III
element raw material gas generation chamber 120 and the raw
material introduction zone and 1030.degree. C. for the temperature
at the crystal growth zone in reaction chamber 110, and 20.26 hPa
(0.02 atm) for the HCl gas partial pressure (GaCl gas partial
pressure) and 303.9 hPa (0.3 atm) for the NH.sub.3 gas partial
pressure. The obtained GaN crystal substance had a facet growth
domain and a C-plane growth domain. The concentration of O atoms
and Si atoms at the facet growth domain was 1.2.times.10.sup.19
cm.sup.-3 and below 1.0.times.10.sup.17 cm.sup.-3, respectively.
The concentration of O atoms and Si atoms at the C-plane growth
domain was below 1.0.times.10.sup.17 cm.sup.-3 and
6.9.times.10.sup.17 cm.sup.-3, respectively.
[0068] In reaction chamber 110 subsequent to this GaN crystal
growth, particularly at the inner wall of quartz reactor tube 101
at the crystal growth zone and at the ends of group III element raw
material gas introduction pipe 123, nitrogen raw material gas
introduction pipe 113, and HCl gas introduction pipe 111 at the raw
material introduction zone, attachment of deposits 9 formed of
polycrystalline GaN, approximately 0.3-0.7 mm in thickness, was
observed.
[0069] HCl gas 1 and H.sub.2 gas (carrier gas) were introduced via
HCl gas introduction pipe 111 into reaction chamber 110
contaminated with deposits 9 to conduct etching for 10 hours at the
temperature of 800.degree. C. in the reaction chamber, where by the
interior of reaction chamber 110 was cleaned (cleaning by vapor
phase etching). At this stage, the partial pressure of HCl gas 1
was 50.65 hPa (0.05 atm). As a result, deposits 9 in reaction
chamber 110 were completely removed by the vapor phase etching.
From an additional vapor phase etching experiment, it was estimated
that the etching rate of deposits 9 under the present conditions
was approximately 80 .mu.m/hr.
[0070] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. A GaN crystal substance
(group III nitride crystal substance 11) was grown on underlying
substrate 10 for 15 hours under the conditions of 650.degree. C.
for the temperature in group III element raw material gas
generation chamber 120 and the raw material introduction zone and
1030.degree. C. for the temperature at the crystal growth zone in
reaction chamber 110, and 20.26 hPa (0.02 atm) for the HCl gas
partial pressure (GaCl gas partial pressure) and 303.9 hPa (0.3
atm) for the NH.sub.3 gas partial pressure.
[0071] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.5 mm with lighter
brown transparency than the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain of the GaN crystal substance was
5.3.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 6.7.times.10.sup.17 cm.sup.-3, respectively. No
cracks were observed after the growing stage and processing stage.
The reason why the GaN crystal substance obtained in the present
example is thin is probably due to the fact that the generation
efficiency of GaCl gas is reduced by setting the temperature at the
group III element raw material gas generation chamber to
650.degree. C. This induces no problem in connection with crystal
quality and fabrication.
EXAMPLE 5
[0072] Inside reaction chamber 110 subsequent to the GaN crystal
growth of Example 4, deposits 9 of approximately 0.3-0.7 mm in
thickness formed of polycrystalline GaN were observed. The interior
of reaction chamber 110 contaminated with deposits 9 was cleaned by
vapor phase etching for 15 hours at the in-chamber temperature of
700.degree. C. with 50.65 hPa (0.05 atm) for the HCl gas and
employing H.sub.2 gas as the carrier gas. As a result, deposits 9
were completely removed. From an additional vapor phase etching
experiment, it was estimated that the etching rate of deposits 9
under the present conditions was approximately 50 .mu.m/hr.
[0073] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. A GaN crystal substance
(group III nitride crystal substance 11) was grown on underlying
substrate 10 for 15 hours under the conditions of 750.degree. C.
for the temperature in group III element raw material gas
generation chamber 120 and the raw material introduction zone and
1030.degree. C. for the temperature at the crystal growth zone in
reaction chamber 110, and 20.26 hPa (0.02 atm) for the HCl gas
partial pressure (GaCl gas partial pressure) and 303.9 hPa (0.3
atm) for the NH.sub.3 gas partial pressure.
[0074] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with lighter
brown transparency than the GaN crystal substances grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain of the GaN crystal substance was
5.7.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 4.2.times.10.sup.17 cm.sup.-3, respectively. No
cracks were observed after the growing stage and processing stage.
Since the thickness of the GaN crystal substance obtained in the
present example was approximately 1.7 mm, equal to those of
Examples 1-3, it was identified that the generation efficiency of
GaCl gas can be maintained at a high level by setting the
temperature at group III element raw material gas generation
chamber 120 to at least 750.degree. C.
EXAMPLE 6
[0075] Inside reaction chamber 110 subsequent to the GaN crystal
growth of Example 5, deposits 9 of approximately 0.3-0.7 mm in
thickness formed of polycrystalline GaN were observed. The interior
of reaction chamber 110 contaminated with deposits 9 was cleaned by
vapor phase etching for 5 hours at the in-chamber temperature of
900.degree. C. with 50.65 hPa (0.05 atm) for the HCl gas and
employing H.sub.2 gas as the carrier gas. As a result, deposits 9
were completely removed. From an additional vapor phase etching
experiment, it was estimated that the etching rate of deposits 9
under the present conditions was approximately 200 .mu.m/hr.
[0076] By comparing the etching rates of Examples 1, 3, 4, 5 and 6,
it was identified that the etching rate becomes higher in
proportion to a higher etching temperature (the temperature in the
reaction chamber during etching; the same applies hereinafter).
This is probably because the reaction rate between HCl and GaN, or
the decomposition rate of GaN itself becomes higher.
[0077] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. A GaN crystal substance
(group III nitride crystal substance 11) was grown on underlying
substrate 10 for 15 hours under the conditions of 1000.degree. C.
for the temperature in group III element raw material gas
generation chamber 120 and the raw material introduction zone and
1030.degree. C. for the temperature at the crystal growth zone in
reaction chamber 110, and 20.26 hPa (0.02 atm) for the HCl gas
partial pressure (GaCl gas partial pressure) and 303.9 hPa (0.3
atm) for the NH.sub.3 gas partial pressure.
[0078] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with dark brown
transparency similar to that of the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain of the GaN crystal substance was
7.8.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 6.5.times.10.sup.17 cm.sup.-3, respectively. No
cracks were observed after the growing stage and processing
stage.
[0079] From Examples 4-6, it was identified that the concentration
of oxygen atoms that are impurities in the GaN crystal substance
becomes higher when the temperature in reaction chamber 110 other
than the crystal growth zone (for example, the temperature at the
Ga raw material introduction zone) is raised. This is probably
because the amount of moisture generated by the reaction between
the quartz of quartz reactor tube 101 constituting reaction chamber
110 and NH.sub.3 and H.sub.2 gases increases so that more oxygen
atoms in the moisture enter the GaN crystal substance. Vapor phase
etching was conducted under conditions similar to those of Examples
4-6, with the exception that Ar gas and He gas were employed as the
carrier gas. It was identified that an etching rate of similar
level to Examples 4-6 was obtained based on H.sub.2 gas as the
carrier gas.
EXAMPLE 7
[0080] Inside reaction chamber 110 subsequent to the GaN crystal
growth of Example 6, deposits 9 of approximately 0.3-0.7 mm in
thickness formed of polycrystalline GaN were observed. The interior
of reaction chamber 110 contaminated with deposits 9 was cleaned by
vapor phase etching for 15 hours at the in-chamber temperature of
1000.degree. C. with 6.078 hPa (0.006 atm) for the HCl gas partial
pressure and employing H.sub.2 gas as the carrier gas. As a result,
deposits 9 were completely removed. From an additional vapor phase
etching experiment, it was estimated that the etching rate of
deposits 9 under the present conditions was approximately 50
.mu.m/hr.
[0081] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. In order to prevent
attachment of deposits 9 on the inner wall of quartz reactor tube
101 at the crystal growth zone of reaction chamber 110, a pBN-made
protection drum was inserted as protection member 117 between
quartz reactor tube 101 and underlying substrate 10, as shown in
FIG. 2. A GaN crystal substance (group III nitride crystal
substance 11) was grown on underlying substrate 10 for 15 hours
under the conditions of 1000.degree. C. for the temperature in
group III element raw material gas generation chamber 120 and the
raw material introduction zone and 1030.degree. C. for the
temperature at the crystal growth zone in reaction chamber 110, and
20.26 hPa (0.02 atm) for the HCl gas partial pressure (GaCl gas
partial pressure) and 303.9 hPa (0.3 atm) for the NH.sub.3 gas
partial pressure.
[0082] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with lighter
brown transparency than that of the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain of the GaN crystal substance was
4.7.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 6.5.times.10.sup.17 cm.sup.-3, respectively. No
cracks were observed after the growing stage and processing
stage.
EXAMPLE 8
[0083] Inside reaction chamber 110 subsequent to the GaN crystal
growth of Example 7, deposits 9 of approximately 0.3-0.7 mm in
thickness formed of polycrystalline GaN were observed. The interior
of reaction chamber 110 contaminated with deposits 9 was cleaned by
vapor phase etching for 10 hours at the in-chamber temperature of
1000.degree. C. with 2.156 hPa (0.012 atm) for the HCl gas and
employing H.sub.2 gas as the carrier gas. As a result, deposits 9
were completely removed. From an additional vapor phase etching
experiment, it was estimated that the etching rate of deposits 9
under the present conditions was approximately 100 .mu.m/hr.
[0084] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. In order to prevent
attachment of deposits 9 on the inner wall of quartz reactor tube
101 at the crystal growth zone of reaction chamber 110, carbon-made
protection drum was inserted as protection member 117 between
quartz reactor tube 101 and underlying substrate 10, as shown in
FIG. 2. A GaN crystal substance (group III nitride crystal
substance 11) was grown on underlying substrate 10 for 15 hours
under the conditions of 1000.degree. C. for the temperature in
group III element raw material gas generation chamber 120 and the
raw material introduction zone and 1030.degree. C. for the
temperature at the crystal growth zone in reaction chamber 110, and
20.26 hPa (0.02 atm) for the HCl gas partial pressure (GaCl gas
partial pressure) and 303.9 hPa (0.3 atm) for the NH.sub.3 gas
partial pressure.
[0085] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with lighter
brown transparency than the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain of the GaN crystal substance was
4.1.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 6.4.times.10.sup.17 cm.sup.-3, respectively. As a
result of analyzing the concentration of C atoms by the same method
of measurement, the concentration was 2.times.10.sup.17 cm.sup.-3,
higher than that of Comparative Example 1. It is assumed that the C
atoms generated from the carbon protection drum were included in
the crystal substance. No cracks were observed after the growing
stage and processing stage.
EXAMPLE 9
[0086] Inside reaction chamber 110 subsequent to the GaN crystal
growth of Example 8, deposits 9 of approximately 0.3-0.7 mm in
thickness formed of polycrystalline GaN were observed. The interior
of reaction chamber 110 contaminated with deposits 9 was cleaned by
vapor phase etching for 5 hours at the in-chamber temperature of
1000.degree. C. with 202.6 hPa (0.2 atm) for the HCl gas partial
pressure and employing H.sub.2 gas as the carrier gas. As a result,
deposits 9 were completely removed. From an additional vapor phase
etching experiment, it was estimated that the etching rate of
deposits 9 under the present conditions was approximately 600
.mu.m/hr.
[0087] Then, a (0001) sapphire substrate was set as underlying
substrate 10 in reaction chamber 110. In order to prevent
attachment of deposits 9 on the inner wall of quartz reactor tube
101 at the crystal growth zone of reaction chamber 110, an SiC-made
protection drum was inserted as protection member 117 between
quartz reactor tube 101 and underlying substrate 10, corresponding
to FIG. 2. A GaN crystal substance (group III nitride crystal
substance 11) was grown on underlying substrate 10 for 15 hours
under the conditions of 1000.degree. C. for the temperature in
group III element raw material gas generation chamber 120 and the
raw material introduction zone and 1030.degree. C. for the
temperature at the crystal growth zone in reaction chamber 110, and
20.26 hPa (0.02 atm) for the HCl gas partial pressure (GaCl gas
partial pressure) and 303.9 hPa (0.3 atm) for the NH.sub.3 gas
partial pressure.
[0088] The obtained GaN crystal substance exhibiting an uneven
surface had the thickness of approximately 1.7 mm with lighter
brown transparency than that of the GaN crystal substance grown in
Comparative Examples 1 and 2. The periphery of the obtained GaN
crystal substance had polycrystalline GaN adhered thereto, likewise
Comparative Examples 1 and 2. As a result of conducting the process
and measurement similar to those of Comparative Examples 1 and 2,
the GaN crystal substance had a facet growth domain and a C-plane
growth domain. The concentration of O atoms and Si atoms at the
facet growth domain of the GaN crystal substance was
4.1.times.10.sup.18 cm.sup.-3 and below 1.0.times.10.sup.17
cm.sup.-3, respectively. The concentration of O atoms and Si atoms
at the C-plane growth domain was below 1.0.times.10.sup.17
cm.sup.-3 and 7.1.times.10.sup.17 cm.sup.-3, respectively. The
reason why the concentration of Si atoms at the C-plane growth
domain in the present example is higher than that of Example 8 may
be due to the Si atoms generated from the SiC employed as
protection member 117 entering the GaN crystal substance. No cracks
were observed after the growing stage and processing stage.
[0089] From the results of Examples 7-9, it was found that a GaN
crystal substance of low oxygen concentration was obtained by
disposing protection member 117 at the high temperature region in
reaction chamber 110, around the crystal growth zone. This is
probably due to the fact that, even if the quartz (SiO.sub.2) at
the crystal growth zone of quartz reactor tube 101 is decomposed,
gas including oxygen will not reach the crystal growth zone since
the GaN crystal growth zone and SiO.sub.2 decomposition region are
separated by protection member 117. The gas including oxygen will
be exhausted outside from gas exhaust pipe 115, such that the
mixture of oxygen atoms into the crystal substance is reduced.
Crystal growth was conducted under similar conditions to those of
Examples 7-9 with the exception of using a protection member made
of WC, TaC, and the like. Effects similar to those of Examples 7-9
were obtained.
COMPARATIVE EXAMPLE 3
[0090] An AlN crystal substance was grown using group III nitride
crystal substance fabrication apparatus 200 shown in FIG. 2. First,
a new quartz reactor tube 101 constituting reaction chamber 110 was
set in fabrication apparatus 200. In order to remove any impurities
such as moisture adhered to the inner wall of quartz reactor tube
101, pre-baking was conducted for 50 hours at 1050.degree. C. while
supplying a flow of N.sub.2 gas in reaction chamber 110.
[0091] Then, a (0001) sapphire substrate of 50.8 mm in diameter was
set as an underlying substrate 10 in reaction chamber 110. A
pBN-made protection drum was inserted as protection member 117
between quartz reactor tube 101 and underlying substrate 10. An AlN
crystal substance (group III nitride crystal substance 11) was
grown on underlying substrate 10 for 10 hours under the conditions
of 1000.degree. C. for the temperature in group III element raw
material gas generation chamber 120 and the raw material
introduction zone and 1100.degree. C. for the temperature at the
crystal growth zone in reaction chamber 110, and 5.065 hPa (0.005
atm) for the AlCl.sub.3 gas partial pressure and 506.5 hPa (0.5
atm) for the NH.sub.3 gas partial pressure. Instead of placing
group III element 2 in group III element boat 121 of group III
element raw material gas generation chamber 120 as in Comparative
Examples 1 and 2 and Examples 1-9, AlCl.sub.3 gas obtained by
sublimation of solid AlCl.sub.3 outside reaction chamber 110 was
introduced into reaction chamber 110 via HCl gas introduction pipe
122, group III element raw material gas generation chamber 120 and
group III element raw material gas introduction pipe 123.
[0092] The obtained AlN crystal substance exhibiting a flat surface
with no unevenness had a thickness of approximately 0.9 mm with
brown transparency, and had the periphery covered with
polycrystalline AlN. As a result of observing the surface of the
AlN crystal substance by XRD (X-ray diffraction), the surface was a
(0001) plane. In other words, the AlN crystal substance was formed
at a region grown with the C-plane (C-plane growth domain).
[0093] Upon conducting peripheral grinding on the obtained AlN
crystal substance to remove the polycrystalline AlN on the
periphery, numerous cracks were generated from the periphery
inwardly to impede analysis by SIMS. This peripheral grinding was
conducted using a diamond cup wheel as the grindstone. This process
was carried out under the conditions of 0.5-1.0 mm/min for the
table feed rate, 10.+-.2 rpm for the work rotation speed, and 490
kPa (5 kgf/cm.sup.2) for the crystal clamp pressure.
[0094] An AlN crystal substance was grown again to a thickness of
approximately 0.9 mm under the conditions of the present
comparative example. The obtained AlN crystal substance was divided
into a single crystal portion of 45 mm in diameter, and an AlN
polycrystalline portion of the periphery using a cylindrical
grinding apparatus with a cylindrical grinding blade. No cracks
were generated. Here, cylindrical grinding was conducted using a
diamond electrodeposition drill with a water-soluble coolant. The
crystal substance was secured to a holder by wax, and subjected to
grinding with 5000-8000 rpm as the rotation speed of the grindstone
and 0.5-30 mm/min as the working rate. Then, the surface of the AlN
crystal substance was ground and polished to be smooth. At this
stage, small cracks of several ten to several hundred microns in
length were generated in the AlN crystal substance. The impurity
concentration in the AlN crystal substance was measured by SIMS at
a region absent of a crack. H atoms, C atoms, Si atoms and O atoms
were observed as the impurities in the AlN crystal substance. The
concentration of the H atoms and C atoms were both below
1.0.times.10.sup.17 cm.sup.-3. The concentration of the O atoms and
Si atoms was 6.2.times.10.sup.19 cm.sup.-3 and 3.0.times.10.sup.17
cm.sup.-3, respectively.
[0095] The reason why cracks were generated when peripheral
grinding was applied on the previously grown AlN crystal substance
may be due to the increased amount of impurities in the crystal
substance to render the crystal brittle, as well as the local load
caused by polycrystalline AlN dropped during grinding to be located
between the AlN crystal substance and grindstone. In contrast, the
polycrystalline portion will not be ground by cylindrical grinding
applied on the AlN crystal substance later grown. No local load was
generated, resulting in a crystal substance absent of a crack.
[0096] The thickness of AlN polycrystalline deposits 9 formed
inside reaction chamber 110 subsequent to the AlN crystal growth,
particularly on the inner wall of quartz reactor tube 101 at the
crystal growth zone and the ends of group III element raw material
gas introduction pipe 123, nitrogen raw material gas introduction
pipe 113, and HCl gas introduction pipe 111 at the raw material
introduction zone was approximately 0.1-0.5 mm. This quartz reactor
tube 101 contaminated with deposits 9 was removed from the
fabrication apparatus and dipped in a mixed solution of phosphoric
acid and sulfuric acid under the mole ratio of 1:1 (solution
temperature 180.degree. C.) to be etched for 24 hours to be
cleaned. Deposits 9 on the inner wall of quartz reactor tube 101
were removed (cleaning of quartz reactor tube by liquid phase
etching).
[0097] Then, an AlN crystal substance was grown to the thickness of
approximately 0.9 mm based on conditions identical to those set
forth above. It was observed that the obtained AlN crystal
substance had polycrystalline AlN attached at the periphery, and
exhibited small cracks. In order to suppress development of the
cracks, a 10 mm.times.10 mm square AlN crystal substance sample for
evaluation was cut with polycrystalline AlN still located at the
periphery. This sample was ground and polished, and then subjected
to SIMS analysis based on a region with no cracks. The
concentration of O atoms and Si atoms in this AlN crystal substance
sample was 8.5.times.10.sup.19 cm.sup.-3 and 3.0.times.10.sup.17
cm.sup.-3, respectively.
EXAMPLE 10
[0098] Likewise Comparative Example 3, a new quartz reactor tube
101 constituting reaction chamber 110 was set at fabrication
apparatus 200, followed by pre-baking of quartz reactor tube 101.
Following this pre-baking, an AlN crystal substance was grown,
likewise Comparative Example 3. H atoms, C atoms, Si atoms and O
atoms were observed as the impurities in the AlN crystal substance.
The concentration of the H atoms and C atoms were both below
1.0.times.10.sup.17 cm.sup.-3. The concentration of the O atoms and
Si atoms was 6.2.times.10.sup.19 cm.sup.-3 and 3.0.times.10.sup.17
cm.sup.-3, respectively.
[0099] The interior of reaction chamber 110 subsequent to AlN
crystal growth was observed. Deposits 9 formed of polycrystalline
AlN, approximately 0.1-0.5 mm in thickness, adhered to the inner
wall of quartz reactor tube 101 at the crystal growth zone and the
ends of group III element raw material gas introduction pipe 123,
nitrogen raw material introduction pipe 113 and HCl gas
introduction pipe 111 at the raw material introduction zone.
[0100] HCl gas 1 and H.sub.2 gas (carrier gas) were introduced via
HCl gas introduction pipe 111 into reaction chamber 110
contaminated with deposits 9 to conduct etching for 5 hours at the
in-chamber temperature of 1000.degree. C., whereby the interior of
reaction chamber 110 was cleaned (cleaning by vapor phase etching).
At this stage, the partial pressure of HCl gas 1 was 50.65 hPa
(0.05 atm). As a result, deposits 9 in reaction chamber 110 were
completely removed by the vapor phase etching. From an additional
vapor phase etching experiment, it was estimated that the etching
rate of deposits 9 under the present conditions was approximately
340 .mu.m/hr.
[0101] Then, as in Comparative Example 3, a (0001) sapphire
substrate (underlying substrate 10) and a pBN-made protection drum
(protection member 117) were arranged in reaction chamber 110. An
AlN crystal substance was grown under conditions similar to those
of Comparative Example 3. The obtained AlN crystal substance had
higher transparency and no cracks, as compared to the two AlN
crystal substances grown in Comparative Example 3. Peripheral
grinding was applied on the AlN crystal substance, leading to the
generation of several cracks inwardly from the periphery. A crystal
substance of a large size could not be obtained. Peripheral
grinding was conducted using a diamond cup wheel as the grindstone.
This process was carried out under the conditions of 0.5-1.0 mm/min
for the table feed rate, 10.+-.2 rpm for the work rotation speed,
and 490 kPa (5 kgf/cm.sup.2) for the crystal clamp pressure.
[0102] An AlN crystal substance was grown again to a thickness of
approximately 0.9 mm under the conditions of the present example
(that is, Comparative Example 3). The obtained AlN crystal
substance was divided into a single crystal portion of 45 mm in
diameter, and an AlN polycrystalline portion of the periphery using
a cylindrical grinding apparatus with a cylindrical grinding blade.
No cracks were generated. Here, cylindrical grinding was conducted
using a diamond electrodeposition drill with a water-soluble
coolant. The crystal substance was secured to a holder by wax, and
subjected to grinding with 5000-8000 rpm as the rotation speed of
the grindstone and 0.5-30 mm/min as the working rate. Then, the
surface of the single crystal portion was ground and polished to be
smooth. An AlN crystal substance of 45 mm in diameter was obtained,
absent of cracks. Here, a (0001) sapphire substrate of 50.8 mm in
diameter was used as the underlying substrate for growth, and
cylindrical grinding was conducted. Therefore, an AlN crystal
substance smaller than 50.8 mm in diameter (i.e. 45 mm in diameter)
was obtained. It is needless to say that an AlN crystal substance
having a diameter larger than 50.8 mm subsequent to cylindrical
grinding can be obtained by using an underlying substrate having a
diameter greater than 50.8 mm (for example, a substrate of 76.2 mm
in diameter).
[0103] The impurity concentration in the AlN crystal substance
subjected to the cylindrical grinding, surface grinding, and
polishing set forth above was measured by SIMS. H atoms, C atoms,
Si atoms and O atoms were observed as the impurities in the AlN
crystal substance. The concentration of the H atoms and C atoms
were both below 1.0.times.10.sup.17 cm.sup.-3. The concentration of
the O atoms and Si atoms was 6.3.times.10.sup.18 cm.sup.-3and
1.0.times.10.sup.17 cm.sup.-3, respectively.
EXAMPLE 11
[0104] In reaction chamber 110 subsequent to the AlN crystal growth
of Example 10, attachment of deposits 9, approximately 0.1-0.5 mm
in thickness, formed of AlN polycrystalline on the internal wall of
the protection drum and the ends of group III element raw material
gas introduction pipe 123, nitrogen raw material gas introduction
pipe 113, and HCl gas introduction pipe 111 at the raw material
introduction zone was observed. This quartz reactor tube 101
contaminated with deposits 9 was cleaned by vapor phase etching,
likewise Example 10.
[0105] Then, a (0001) sapphire substrate (underlying substrate 10)
and a pBN protection drum (protection member 117) were arranged in
reaction chamber 110, likewise Example 10. An AlN crystal substance
(group III nitride crystal substance 11) was grown on underlying
substrate 10 for ten hours under the conditions of 1000.degree. C.
for the temperature in group III element raw material gas
generation chamber 120, 700.degree. C. for the temperature at the
raw material introduction zone, 1100.degree. C. for the temperature
at the crystal growth zone in reaction chamber 110, 50.65 hPa (0.05
atm) for the AlCl.sub.3 gas partial pressure, and 506.5 hPa (0.5
atm) for the NH.sub.3 gas partial pressure.
[0106] The concentrations of O atoms and Si atoms in the obtained
AlN crystal substance was 5.8.times.10.sup.18 cm.sup.-3 and below
1.0.times.10.sup.17 cm.sup.-3, respectively. No cracks were
observed in this AlN crystal substance subsequent to peripheral
grinding, surface grinding, and polishing. The interior of reaction
chamber 110 subsequent to the AlN crystal growth was observed.
Although deposits of approximately 0.1-0.5 mm in thickness formed
of polycrystalline AlN adhered to the inner wall of quartz reactor
tube 101, likewise Example 10, the thickness of the deposits
adhering to the ends of group III element raw material gas
introduction pipe 123 and nitrogen raw material gas introduction
pipe 113 were reduced to 0.1 mm or smaller. This is probably due to
the growth of polycrystalline AlN being degraded by reducing the
temperature at the ends of group III element raw material gas
introduction pipe 123 and nitrogen raw material gas introduction
pipe 113, i.e. the region where the raw material are mixed with
each other.
EXAMPLE 12
[0107] A GaN crystal substance was grown using group III nitride
crystal substance fabrication apparatus 100 shown in FIG. 1
according to the present invention. Crystal growth was conducted
without providing a device to trap ammonium chloride (trap device
116) in fabrication apparatus 100. First, a new quartz reactor tube
101 constituting reaction chamber 110 was set in fabrication
apparatus 100. In order to remove impurities such as moisture in
quartz reactor tube 101, pre-baking was conducted for 50 hours at
the temperature of 1050.degree. C. in the reaction chamber while
supplying a flow of N.sub.2 gas in reaction chamber 110. Then, a
(0001) sapphire substrate of 50.8 mm in diameter was set as
underlying substrate 10 in reaction chamber 110. A GaN crystal
substance (group III nitride crystal substance 11) was grown on
underlying substrate 10 for 15 hours under the conditions of
1000.degree. C. for the temperature at group III element raw
material gas generation chamber 120 and the raw material
introduction zone and 1100.degree. C. for the temperature at the
crystal growth zone in reaction chamber 110, and 5.065 hPa (0.005
atm) for the HCl gas partial pressure (GaCl gas partial pressure)
and 303.9 hPa (0.3 atm) for the NH.sub.3 gas partial pressure.
[0108] The obtained GaN crystal substance had a flat surface with
polycrystalline GaN adhering to the periphery. The surface of the
GaN crystal substance subjected to XRD (X-ray diffraction) was a
(0001) plane. In other words, the GaN crystal substance was formed
at the region growing at the C-plane (C-plane growth domain). The
GaN crystal substance had the thickness of 2.6 mm, and no cracks
were observed. By grinding the GaN crystal substance with a
peripheral grinder, a GaN crystal disk of 50 mm in diameter was
obtained. Then, the surface of the GaN crystal substance was ground
and polished, and then subjected to SIMS analysis. The
concentration of O atoms and Si atoms of the GaN crystal substance
was below 1.0.times.10.sup.17 cm.sup.-3 and 6.8.times.10.sup.17
cm.sup.-3, respectively. The carrier concentration of the GaN
crystal substance was measured using a Hall measurement apparatus.
The carrier concentration was 6.6.times.10.sup.17 cm.sup.-3,
substantially matching the Si atom concentration.
EXAMPLE 13
[0109] In the case where a GaN crystal substrate is to be employed
as a conductive substrate for an LED (Light Emitting Diode), LD
(laser diode), and the like, at least 0.8.times.10.sup.18
cm.sup.-3, preferably at least 1.0.times.10.sup.18 cm.sup.-3, is
required for the carrier concentration of the GaN crystal
substrate. To this end, a GaN crystal substance was grown under
conditions similar to those of Example 12 provided that, in
addition to the Si atoms generated from quartz reactor tube 101, Si
atoms were doped using SiH.sub.4 gas at the partial pressure of
4.559.times.10.sup.-3 Pa (4.5.times.10.sup.-8 atm) such that the
carrier concentration of the crystal substance attains
1.0.times.10.sup.18 cm.sup.-3. As a result, a GaN crystal substance
having the carrier concentration of 1.2.times.10.sup.18 cm.sup.-3,
substantially as designed, could be obtained.
EXAMPLE 14
[0110] By growing a GaN crystal substance for 550 hours under the
crystal growing conditions of Example 13, the crystal carrier
concentration became lower than 0.8.times.10.sup.18 cm.sup.-3, even
though Si atoms are doped to the GaN crystal substance using
SiH.sub.4 gas with the partial pressure of 4.559.times.10.sup.-3 Pa
(4.5.times.10.sup.-8 atm). Supply of SiH.sub.4 gas was ceased, and
a GaN crystal substance was grown under conditions similar to those
of Example 12. The obtained crystal substance was ground by a
cylindrical grinder to obtain a GaN crystal disk of 48 mm in
diameter. After grinding and polishing the surface of the GaN
crystal disk at both sides, no cracks were observed using a
microscope. The concentration of Si atoms in the GaN crystal
substance was as low as 1.3.times.10.sup.17 cm.sup.-3 by SIMS
analysis. Here, a GaN crystal substance was grown under conditions
similar to those of Example 12, provided that Si was doped by the
SiH.sub.4 gas partial pressure of 1.013.times.10.sup.-2 Pa
(1.0.times.10.sup.-7 atm) such that the crystal carrier
concentration attains 1.0.times.10.sup.-18 cm.sup.-3. As a result,
a GaN crystal substance having a carrier concentration of
1.2.times.10.sup.18 cm.sup.-3, substantially as designed, could be
obtained.
EXAMPLE 15
[0111] By growing a GaN crystal substance further for 550 hours
under the crystal growing conditions of Example 14, the crystal
carrier concentration became lower than 0.8.times.10.sup.18
cm.sup.-3 even though Si atoms are doped into the GaN crystal
substance using the SiH.sub.4 gas with the partial pressure of
1.013.times.10.sup.-2 Pa (1.0.times.10.sup.-7 atm). Therefore,
supply of SiH.sub.4 gas was ceased to grow a GaN crystal substance
under conditions similar to those of Example 12. Likewise Example
14, the obtained crystal substance was subjected to cylindrical
grinding, had both sides ground and polished, and then subjected to
SIMS analysis. The Si atom concentration of the GaN crystal
substance became as low as 0.9.times.10.sup.17 cm.sup.-3. Here, a
GaN crystal substance was grown under the conditions similar to
those of Example 12, provided that Si atoms were doped with the
partial pressure of the SiH.sub.4 gas at 1.216.times.10.sup.-3 Pa
(1.2.times.10.sup.-8 atm) such that the crystal carrier
concentration attains the level of 1.0.times.10.sup.18 cm.sup.-3.
As a result, a GaN crystal substance having the carrier
concentration of 1.2.times.10.sup.18 cm.sup.-3, substantially as
designed, could be obtained.
[0112] From Examples 13-15, it is identified that the concentration
of the doping gas must be modified in accordance with the duration
of using quartz reactor tube 101 when Si atoms are to be doped into
the GaN crystal substance. Examples 13-15 were based on the usage
of SiH.sub.4 gas as the doping gas. Since the change in the Si
concentration in the crystal substance in association with the
usage duration of the quartz reactor tube is caused by the change
in the amount of the Si type gas generated from quartz reaction
tube 101 instead of the amount of doping gas, the same result can
be obtained even if SiH.sub.2Cl.sub.2 gas, SiCl.sub.4 gas, or the
like is employed as the doping gas.
[0113] With regards to controlling the concentration of O atoms in
the facet growth domain of the GaN crystal substances in Examples
1-9, it was confirmed that the concentration of O atoms becomes
lower in proportion to the duration of using quartz reactor tube
101 when growth of a GaN crystal substance is continued under the
crystal growing conditions such as of Example 9. It was also
confirmed that the concentration of O atoms can be increased by
raising the temperature at the raw material introduction zone, as
shown in Examples 4-6. Further, it was confirmed that the moisture
(H.sub.2O gas) or O.sub.2 gas can be used as dopant gas.
[0114] Although Examples 1-15 are based on the case where a
sapphire substrate is employed as the underlying substrate, it was
confirmed that the same effect can be obtained by using a (111)
GaAs substrate (GaAs substrate with (111) plane as the crystal
growing plane), a (0001) SiC substrate (SiC substrate with (0001)
plane as the crystal growth plane), an LiAlGaO substrate, or a GaN
substrate.
[0115] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *