U.S. patent application number 13/037015 was filed with the patent office on 2011-06-23 for group iii nitride crystal and method for surface treatment thereof, group iii nitride stack and manufacturing method thereof, and group iii nitride semiconductor device and manufacturing method thereof.
This patent application is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD. Invention is credited to Masato IRIKURA, Keiji ISHIBASHI, Naoki MATSUMOTO.
Application Number | 20110146565 13/037015 |
Document ID | / |
Family ID | 40790645 |
Filed Date | 2011-06-23 |
United States Patent
Application |
20110146565 |
Kind Code |
A1 |
ISHIBASHI; Keiji ; et
al. |
June 23, 2011 |
GROUP III NITRIDE CRYSTAL AND METHOD FOR SURFACE TREATMENT THEREOF,
GROUP III NITRIDE STACK AND MANUFACTURING METHOD THEREOF, AND GROUP
III NITRIDE SEMICONDUCTOR DEVICE AND MANUFACTURING METHOD
THEREOF
Abstract
A method for surface treatment of a group III nitride crystal
includes the steps of lapping a surface of a group III nitride
crystal using a hard abrasive grain with a Mohs hardness higher
than 7, and abrasive-grain-free polishing the lapped surface of the
group III nitride crystal using a polishing solution without
containing abrasive grain, and the polishing solution without
containing abrasive grain has a pH of not less than 1 and not more
than 6, or not less than 8.5 and not more than 14. Accordingly, the
method for surface treatment of a group III nitride crystal can be
provided according to which hard abrasive grains remaining at the
lapped crystal can be removed to reduce impurities at the crystal
surface.
Inventors: |
ISHIBASHI; Keiji;
(Itami-shi, JP) ; MATSUMOTO; Naoki; (Itami-shi,
JP) ; IRIKURA; Masato; (Itami-shi, JP) |
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD
|
Family ID: |
40790645 |
Appl. No.: |
13/037015 |
Filed: |
February 28, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12432105 |
Apr 29, 2009 |
7919343 |
|
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13037015 |
|
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Current U.S.
Class: |
117/54 ; 117/84;
117/88 |
Current CPC
Class: |
C30B 29/403 20130101;
H01L 2224/48247 20130101; H01L 2224/73265 20130101; H01L 2924/12041
20130101; H01L 24/32 20130101; H01L 2224/73265 20130101; C30B 33/00
20130101; H01L 2224/32245 20130101; H01L 21/02024 20130101; H01L
2224/48091 20130101; H01L 2924/12041 20130101; H01L 2924/00014
20130101; H01L 2224/32245 20130101; H01L 2924/00 20130101; H01L
2224/48247 20130101; H01L 21/02013 20130101; H01L 2224/48091
20130101; H01L 2924/00 20130101 |
Class at
Publication: |
117/54 ; 117/84;
117/88 |
International
Class: |
C30B 19/00 20060101
C30B019/00; C30B 23/02 20060101 C30B023/02; C30B 25/02 20060101
C30B025/02 |
Foreign Application Data
Date |
Code |
Application Number |
May 1, 2008 |
JP |
2008-119835 (P) |
Claims
1-13. (canceled)
14. A method for surface treatment of a group III nitride crystal,
comprising the steps of: growing a group III nitride crystal by a
gas phase method or a liquid phase method; soft-abrasive-grain
polishing for polishing said group III nitride crystal using a
polishing solution containing a soft abrasive grain with a Mohs
hardness of not more than 7; and abrasive-grain-free polishing for
polishing said group III nitride crystal using a polishing solution
without containing abrasive grain.
15. The method for surface treatment of a group III nitride crystal
according to claim 14, wherein said gas phase method is a hydride
vapor phase epitaxy method or a sublimation method.
16. The method for surface treatment of a group III nitride crystal
according to claim 14, wherein said soft abrasive grain contains
one of ZrO.sub.2, SiO.sub.2, CeO.sub.2, MnO.sub.2, Fe.sub.2O.sub.3,
Fe.sub.3O.sub.4, NiO, ZnO, CoO, CO.sub.3O.sub.4, GeO.sub.2,
Ga.sub.2O.sub.3 and In.sub.2O.sub.3.
17. The method for surface treatment of a group III nitride crystal
according to claim 14, wherein said polishing solution without
containing abrasive grain has a pH of not less than 1 and not more
than 6, or not less than 8.5 and not more than 14.
18. The method for surface treatment of a group III nitride crystal
according to claim 14, wherein said polishing solution without
containing abrasive grain has a pH of not less than 2 and not more
than 4, or not less than 10 and not more than 12.
19. The method for surface treatment of a group III nitride crystal
according to claim 14, further comprising the step of water
cleaning, after said step of abrasive-grain-free polishing.
20. The method for surface treatment of a group III nitride crystal
according to claim 14, further comprising the step of lapping said
group III nitride crystal using a hard abrasive grain with a Mohs
hardness higher than 7, or the step of grinding said group III
nitride crystal, after said step of growing said group III nitride
crystal and before said step of soft-abrasive-grain polishing.
21. The method for surface treatment of a group III nitride crystal
according to claim 20, wherein in said step of lapping said group
III nitride crystal using said hard abrasive grain, said hard
abrasive grain contains one of diamond, SiC, BN, Si.sub.3N.sub.4,
Al.sub.2O.sub.3, Cr.sub.2O.sub.3 and ZrO.sub.2.
22. The method for surface treatment of a group III nitride crystal
according to claim 20, wherein in said step of lapping said group
III nitride crystal using said hard abrasive grain, a multi-step
lapping from the step using said hard abrasive grain of larger size
to the step using said hard abrasive grain of smaller size is
performed.
23. The method for surface treatment of a group III nitride crystal
according to claim 14, wherein said group III nitride crystal in a
GaN crystal.
24. A method for manufacturing a group III nitride semiconductor
device using the group III nitride crystal as recited in claim 14,
comprising the steps of: preparing said group III nitride crystal;
and epitaxially growing at least one group III nitride layer on
said group III nitride crystal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for surface
treatment of a group III nitride crystal that is suitably used, for
example, as a material for a substrate of a semiconductor
device.
[0003] 2. Description of the Background Art
[0004] The surface of a grown group III nitride crystal to be used
for example as a material for a substrate of a semiconductor device
is preferably treated so that the surface is as flat as possible
and as low as possible in impurity concentration. U.S. Pat. No.
6,399,500 accordingly discloses that the surface of a
Ga.sub.1-X-YAl.sub.XIn.sub.YN crystal is polished with a basic
polishing solution that does not contain abrasive grains and
thereafter polished with pure water.
[0005] The group III nitride crystal, however, is chemically stable
and thus the polishing efficiency is still low when polished with
the basic polishing solution without containing abrasive grains as
described above.
SUMMARY OF THE INVENTION
[0006] In order to efficiently treat the surface of the chemically
stable group III nitride crystal, it is therefore necessary to
perform lapping or polishing with abrasive grains. In particular,
the group III nitride crystal is preferably lapped with hard
abrasive grains having a Mohs hardness higher than that of the
group III nitride crystal, for example, a Mohs hardness higher than
7.
[0007] When the group III nitride crystal is lapped, however, the
hard abrasive grains bite the surface of the crystal to
mechanically remove the surface layer. Thus, some hard abrasive
grains caught in the surface of the crystal remain after the
lapping. Since the group III nitride crystal is chemically stable,
the surface of the crystal is not effectively etched with a
chemical solution. Thus, washing with a chemical solution cannot
sufficiently remove the hard abrasive grains remaining at the
crystal surface. A resultant problem is the contamination due to
the abrasive grains remaining at the crystal surface, in a
post-process such as formation of an epitaxial layer on the
crystal.
[0008] An object of the present invention is therefore to provide a
method for surface treatment of a group III nitride crystal
according to which hard abrasive grains remaining at the crystal
surface after lapped can be removed to reduce impurities at the
crystal surface.
[0009] Here, the lapping may be followed by polishing with soft
abrasive grains having a Mohs hardness of 7 or less to remove the
hard abrasive grains remaining at the crystal surface after lapped.
Soft abrasive grains, however, remain at the crystal surface after
polished with soft abrasive grains. Further, regarding a group III
nitride crystal including a high dislocation density region and a
low dislocation density region, there is a problem that the high
dislocation density region and its peripheral region are removed to
a relatively larger extent, so that the outermost or edge region
has an outwardly and downwardly sloping shape to reduce the
effective area.
[0010] Another object of the present invention is therefore to
provide a method for surface treatment of a group III nitride
crystal, according to which, when polishing with soft abrasive
grains is performed after lapping, excessive removal of the surface
in a high dislocation density region and its peripheral region can
be restrained to prevent the outermost or edge region from having
an outwardly and downwardly sloping shape, and soft abrasive grains
remaining at the crystal surface can be removed to reduce
impurities at the crystal surface.
[0011] The present invention is a method for surface treatment of a
group III nitride crystal, including the steps of: lapping a
surface of a group III nitride crystal using a hard abrasive grain
with a Mohs hardness higher than 7; and abrasive-grain-free
polishing for polishing the lapped surface of the group III nitride
crystal using a polishing solution without containing abrasive
grain, and the polishing solution without containing abrasive grain
has a pH of not less than 1 and not more than 6, or not less than
8.5 and not more than 14.
[0012] Regarding the method for surface treatment of a group III
nitride crystal according to the present invention, in the step of
abrasive-grain-free polishing, polishing may be performed using a
polishing pad with a compressibility of not less than 1.5% and not
more than 20% and at a polishing pressure of not less than 0.98 kPa
(10 gf/cm.sup.2) and not more than 58.8 kPa (600 gf/cm.sup.2).
[0013] The method for surface treatment of a group III nitride
crystal according to the present invention may further include the
step of soft abrasive grain polishing for polishing the lapped
surface of the group III nitride crystal using a polishing solution
containing a soft abrasive grain with a Mohs hardness of not more
than 7, after the step of lapping and before the step of
abrasive-grain-free polishing. In the step of soft abrasive grain
polishing, polishing may be performed using a polishing pad with a
compressibility of not less than 0.8% and not more than 5% and at a
polishing pressure of not less than 4.9 kPa (50 gf/cm.sup.2) and
not more than 98 kPa (1000 gf/cm.sup.2).
[0014] Further, the present invention is a group III nitride
crystal produced through the surface treatment as described above.
Through the above-described surface treatment, surface roughness Ra
of the group III nitride crystal may be made not more than 2 nm. A
work-affected layer may have a thickness of not more than 50 nm.
The group III nitride crystal may include a low dislocation density
region and a high dislocation density region, and a difference in
level between a surface of the low dislocation density region and a
surface of the high dislocation density region may be not more than
3 .mu.m. Here, in the group III nitride crystal including the low
dislocation density region and the high dislocation density region,
a flat surface region of the low dislocation density region may
have an area of not less than 40% of the whole surface of the low
dislocation density region.
[0015] Further, the present invention is a group III nitride stack
including the group III nitride crystal as described above and at
least one group III nitride layer epitaxially grown on a surface of
the group III nitride crystal. Further, the present invention is a
method for manufacturing a group III nitride stack using the group
III nitride crystal as described above, and the method includes the
steps of: preparing the group III nitride crystal; and epitaxially
growing at least one group III nitride layer on a surface of the
group III nitride crystal.
[0016] Further, the present invention is a group III nitride
semiconductor device including: the group III nitride crystal as
described above; at least one group III nitride layer epitaxially
grown on a surface of the group III nitride crystal; and an
electrode formed on at least one of a surface of an outermost layer
of the group III nitride layer and a surface of the group III
nitride crystal. Further, the present invention is a method for
manufacturing a group III nitride semiconductor device using the
group III nitride crystal as described above, and the method
includes the steps of: preparing the group III nitride crystal;
epitaxially growing at least one group III nitride layer on a
surface of the group III nitride crystal; and forming an electrode
on at least one of a surface of an outermost layer of the group III
nitride layer and a surface of the group III nitride crystal.
[0017] In accordance with the present invention, a method for
surface treatment of a group III nitride crystal can be provided
according to which hard abrasive grains remaining at the crystal
surface after lapped are removed by abrasive-grain-free polishing
so that impurities at the crystal surface can be reduced. A method
for surface treatment of a group III nitride crystal can also be
provided according to which the crystal surface is lapped and
thereafter polished with soft abrasive grains. Hard abrasive grains
remaining at the crystal surface after lapped are removed by the
soft abrasive grain polishing and soft abrasive grains remaining at
the crystal surface after polished with soft abrasive grains are
further removed, so that impurities at the crystal surface can be
reduced.
[0018] "Polishing solution" of the present invention includes those
containing abrasive grains as well as those without containing
abrasive grains.
[0019] 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
[0020] FIG. 1 is a schematic cross section showing a lapping step
in a method for surface treatment of a group III nitride crystal
according to the present invention.
[0021] FIG. 2 is a schematic cross section showing an
abrasive-grain-free polishing step in a method for surface
treatment of a group III nitride crystal according to the present
invention.
[0022] FIG. 3 is a schematic cross section showing a soft abrasive
grain polishing step in a method for surface treatment of a group
III nitride crystal according to the present invention.
[0023] FIG. 4A is a schematic plan view showing a group III nitride
crystal including a high dislocation density region and a low
dislocation density region after the soft abrasive grain polishing
step.
[0024] FIG. 4B is a schematic cross section showing the group III
nitride crystal including the high dislocation density region and
the low dislocation density region after the soft abrasive grain
polishing step.
[0025] FIG. 5 is a schematic cross section showing a group III
nitride stack according to the present invention.
[0026] FIG. 6 is a schematic cross section showing a group III
nitride semiconductor device according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0027] Referring to FIGS. 1 and 2, an embodiment of a method for
surface treatment of a group III nitride crystal of the present
invention includes the step of lapping a surface of a group III
nitride crystal 1 using hard abrasive grains 16 with a Mohs
hardness higher than 7, and the abrasive-grain-free polishing step
for polishing the lapped surface of group III nitride crystal 1
using a polishing solution 27 that does not contain abrasive
grains, and polishing solution 27 without containing abrasive
grains has a pH of not less than 1 and not more than 6, or not less
than 8.5 and not more than 14. The method for surface treatment of
a group III nitride crystal in the present embodiment can remove
hard abrasive grains remaining at the crystal surface after the
lapping step using hard abrasive grains, so as to reduce impurities
at the crystal surface, by means of the abrasive-grain-free
polishing step using the polishing solution without containing
abrasive grains and having a pH of not less than 1 and not more
than 6, or not less than 8.5 and not more than 14.
[0028] Referring to FIG. 1, the method for surface treatment of a
group III nitride crystal in the present embodiment thus includes
the step of lapping a surface of group III nitride crystal 1 using
hard abrasive grains 16 with a Mohs hardness higher than 7. This
lapping step can be used to efficiently lap the surface of the
group III nitride crystal.
[0029] The lapping step in the present embodiment refers to the
step of mechanically smoothing the surface of group III nitride
crystal 1 using hard abrasive grains 16 with a Mohs hardness higher
than 7. For example, with reference to FIG. 1, the surface of group
III nitride crystal 1 can be lapped by rotating a surface plate 15
about a rotational axis 15c while feeding hard abrasive grains 16
from an abrasive grain feed port 19 onto surface plate 15, and
rotating about a rotational axis 11c a crystal holder 11 to which
group III nitride crystal 1 is secured and on which a weight 14 is
placed while pressing group III nitride crystal 1 against surface
plate 15 fed with hard abrasive grains 16.
[0030] Surface plate 15 is not particularly limited to a specific
one as long as surface plate 15 can be used to smoothly perform the
lapping. Preferably, a surface plate containing at least one of
metallic materials such as Sn (tin), Sn--Bi (tin-bismuth) alloy,
Sn--Sb (tin-antimony) alloy, Sn--Pb (tin-lead) alloy, Cu (copper),
inorganic materials such as Al.sub.2O.sub.3 (aluminum oxide),
SiO.sub.2 (silicon dioxide), CeO.sub.2 (cerium oxide), and organic
materials such as phenol resin, urethane resin, amide resin, imide
resin, or a surface plate containing any combination of them is
used. Further, a pad (not shown) may be secured on surface plate 15
and hard abrasive grains 16 may be scattered on the pad to perform
the lapping in a similar manner to the above-described one.
[0031] Hard abrasive grains 16 are not particularly limited to a
specific one as long as hard abrasive grains 16 have a Mohs
hardness higher than 7. Abrasive grains containing a material such
as diamond, SiC, BN, Si.sub.3N.sub.4, Al.sub.2O.sub.3,
Cr.sub.2O.sub.3, ZrO.sub.2 are preferably used. The type and size
of these abrasive grains are selected in consideration of the
mechanical lapping function of the abrasive grains. In order to
increase the lapping speed, abrasive grains of high hardness and
large size are used. In order to decrease surface roughness Ra and
surface roughness Ry so as to smooth the surface and/or make a
work-affected layer smaller, abrasive grains of low hardness and
small size are used. In order to shorten the polishing time and
obtain a smooth surface, a multi-step lapping from the step using
abrasive grains of larger size to the step using abrasive grains of
smaller size is performed.
[0032] Here, surface roughness Ra refers to a value determined in
the following way. A reference area is sampled. In the sampled
area, the distance from a mean plane to a point on a roughness
profile (absolute value of the deviation) is measured. The sum of
the measured distances is calculated. The average distance in the
reference area is surface roughness Ra. Surface roughness Ry is
determined in the following way. A reference area is sampled. In
the sampled area, the sum of the height from a mean plane to the
highest peak of a roughness profile and the depth from the mean
plane to the lowest valley of the roughness profile is surface
roughness Ry. Surface roughness Ra and surface roughness Ry can be
identified through observation by means of an AFM (Atomic Force
Microscope). Further, the work-affected layer refers to a layer in
which a crystal lattice formed in the surface side region of the
crystal is disordered due to grinding or polishing of the crystal
surface. The presence and the thickness of the work-affected layer
can be identified through observation by means of a TEM
(Transmission Electron Microscope) or CL (cathode
luminescence).
[0033] In order to mechanically smooth the surface of group III
nitride crystal 1, grinding may be used instead of the lapping. For
the grinding, a grindstone containing hard abrasive grains fixed by
a binder is used. The grinding can remove the surface of a group
III nitride crystal to smooth the surface faster than the
lapping.
[0034] Referring to FIG. 2, the method for surface treatment of the
group III nitride crystal in the present embodiment includes the
abrasive-grain-free polishing step for polishing the lapped surface
of group III nitride crystal 1 using polishing solution 27 without
containing abrasive grains. The abrasive-grain-free polishing step
can be used to remove hard abrasive grains remaining at the crystal
surface to reduce impurities at the crystal surface.
[0035] The abrasive-grain-free polishing step of the present
embodiment refers to the step of chemically smoothing the surface
of group III nitride crystal 1 using a polishing solution without
containing abrasive grains. For example, referring to FIG. 2, a
polishing pad 28 secured on a surface plate 25 is rotated about a
rotational axis 25c while polishing solution 27 that does not
contain abrasive grains is fed onto polishing pad 28 from a
polishing solution feed port 29, and a crystal holder 21 on which
group III nitride crystal 1 is secured and on which a weight 24 is
placed is rotated about its rotational axis 21c while group III
nitride crystal 1 is pressed against polishing pad 28. In this way,
impurities such as abrasive grains remaining at the surface of
group III nitride crystal 1 can be efficiently removed.
[0036] Here, surface plate 25 is not particularly limited to a
specific one as long as surface plate 25 can be used to smoothly
perform the abrasive-grain-free polishing. Preferably, a surface
plate containing at least one of metallic materials such as
stainless, aluminum (Al), inorganic materials such as aluminum
oxide (Al.sub.2O.sub.3), magnesium oxide (MgO), aluminum nitride
(AlN), silicon carbide (SiC), and organic materials such as phenol
resin, urethane resin, amide resin, imide resin, or a surface plate
containing any combination of them is used.
[0037] The polishing solution without containing abrasive grains
used in the abrasive-grain-free polishing step has a pH of not less
than 1 and not more than 6 or a pH of not less than 8.5 and not
more than 14. In the case where pH is lower than 1 or higher than
14, surface roughness Ra and surface roughness Ry of the crystal
are larger. In the case where pH is higher than 6.5 and lower than
8.5, the effect of removing impurities from the crystal surface is
insufficient. For a similar reason, pH is more preferably not less
than 2 and not more than 4, or not less than 10 and not more than
12.
[0038] Here, for adjusting the pH of the polishing solution without
containing abrasive grains, an inorganic acid such as hydrochloric
acid, nitric acid, sulfuric acid, phosphoric acid, an organic acid
such as formic acid, acetic acid, citric acid, malic acid, tartaric
acid, succinic acid, phthalic acid, maleic acid, fumaric acid, an
inorganic alkali such as KOH, NaOH, an organic alkali such as
NH.sub.4OH, amine, an inorganic salt such as sulfate, nitrate,
phosphate, and an organic salt such as citrate, malate, may be
used. Of these pH adjusters, the organic acid and the organic
alkali that do not contain a metal element are more preferable
rather than the inorganic acid and the inorganic alkali for
enhancing the effect of removing impurities from the crystal
surface. Of the organic acids, a polycarboxylic acid containing two
or more carboxyl groups is preferred. Further, an oxidizer
described below may be added to adjust the pH as well.
[0039] Preferably, the polishing solution without containing
abrasive grains contains an oxidizer. The polishing solution
without containing abrasive grains has an increased ORP
(oxidation-reduction potential) by containing an oxidizer, so that
the effect of removing impurities such as abrasive grains remaining
at the crystal surface is enhanced. While the oxidizer is not
particularly limited to a specific one, it is preferable to use,
for increasing the ORP, any of hypochlorous acid, chlorinated
isocyanuric acid such as trichloroisocyanuric acid, chlorinated
isocyanurate such as sodium dichloroisocyanurate, permanganate such
as potassium permanganate, dichromate such as potassium dichromate,
bromate such as potassium bromate, thiosulfate such as sodium
thiosulfate, persulfate such as ammonium persulfate and potassium
persulfate, nitric acid, hydrogen peroxide solution, and ozon for
example.
[0040] In order to enhance the effect of removing impurities such
as abrasive grains remaining at the crystal surface, it is
preferable that the polishing solution without containing abrasive
grains satisfies the following relation between pH value x and ORP
value y (mV). Specifically, under the acid condition
1.ltoreq.x.ltoreq.6, the relation
-50x+1000<y<-50x+1800 (1)
is preferably satisfied and, under the alkaline condition
8.5.ltoreq.x.ltoreq.14, the relation
-50x+800<y<-50x+1500 (2)
is preferably satisfied.
[0041] In order to enhance the effect of removing impurities, a
surface active agent may be further added to the polishing solution
without containing abrasive grains. The surface active agent to be
added to the polishing solution without containing abrasive grains
is not particularly limited to a specific one. Anionic agent,
cationic agent or nonionic agent may be used as the surface active
agent. Anionic or cationic surface active agent, however, is
preferably used because it has a high impurity removal effect.
[0042] Here, the group III nitride crystal is grown by any of
various gas phase methods such as HYPE (hydride vapor phase
epitaxy), sublimation, and various liquid phase methods such as
solution method (including flux method). For growth of the group
III nitride crystal, in order to decrease the dislocation density
in the crystal, a mask layer of SiO.sub.2 for example that has an
opening may be formed on an underlying substrate and a group III
nitride crystal may be facet-grown on the mask (see for example
Japanese Patent Laying-Open Nos. 2003-165799 and 2003-183100).
[0043] Referring to FIGS. 4A and 4B, group III nitride crystal 1
that is facet-grown as described above includes a high dislocation
density region 1h where dislocations in the crystal concentrate and
a low dislocation density region 1k where the number of
dislocations is smaller. Here, the group III nitride crystal
including high dislocation density region 1h and low dislocation
density region 1k has, for example, a structure where high
dislocation density regions are arranged like stripes with respect
to low dislocation density regions (stripe structure, see FIGS. 4A
and 4B) or a structure where high dislocation density regions are
arranged like dots with respect to the low dislocation density
regions (dot structure, not shown). High dislocation density region
1h and low dislocation density region 1k in group III nitride
crystal 1 can be observed by means of CL (S-4300 manufactured by
Hitachi Corporation) for example.
[0044] In the facet-grown group III nitride crystal as described
above, the surface of low dislocation density region 1k is a Ga
atomic surface, while the surface of high dislocation density
region 1h is an N atomic surface. Therefore, the surface of high
dislocation density region 1h is chemically polished at a higher
rate than the surface of low dislocation density region 1k.
Therefore, referring to FIGS. 4A and 4B, if the surface of group
III nitride crystal 1 including high dislocation density region 1h
and low dislocation density region 1k is treated by chemical
polishing such as abrasive-grain-free polishing, the surface of
high dislocation density region 1h depresses relative to the
surface of low dislocation density region 1k.
[0045] Accordingly, it is preferable to use, in the
abrasive-grain-free polishing step in the present embodiment,
polishing pad 28 having a compressibility of not less than 1.5% and
not more than 20%. If the compressibility of polishing pad 28 is
lower than 1.5%, surface roughness Ra and surface roughness Ry of
the crystal after polished without abrasive grains are larger. If
the compressibility of polishing pad 28 is higher than 20%, the
effect of removing impurities is lessened, the depth of the
depression of the surface of high dislocation density region 1h of
the group III nitride crystal is larger and a flat surface region
1ps of the surface of low dislocation density region 1k is smaller.
In view of this, the compressibility of the polishing pad used in
the abrasive-grain-free polishing step is preferably not less than
3% and not more than 10%.
[0046] In view of this, it is preferable that polishing pad 28 is
made of polyurethane or the like and has the form of suede,
non-woven fabric, elastomer, foam or the like.
[0047] The compressibility of the polishing pad in the present
application is defined by the following expression:
compressibility (%)=(T.sub.1-T.sub.2)/T.sub.2.times.100 (A)
where T.sub.1 is the thickness of the pad after one minute from the
time when the pad is loaded with initial load W.sub.1, and T.sub.2
is the thickness of the pad after one minute from the time when the
load on the pad is increased to W.sub.2. Here, for the calculation
of the compressibility, initial load W.sub.1 of 100 g and load
W.sub.2 of 1600 g are used.
[0048] Preferably, the polishing pressure in the
abrasive-grain-free polishing step is not less than 0.98 kPa (10
gf/cm.sup.2) and not more than 58.8 kPa (600 gf/cm.sup.2). If the
polishing pressure is lower than 0.98 kPa (10 gf/cm.sup.2), the
effect of removing impurities such as hard abrasive grains
remaining at the crystal surface is smaller and the effect of
smoothing the whole crystal surface is also smaller. If the
polishing pressure is higher than 58.8 kPa (600 gf/cm.sup.2),
surface roughness Ra and surface roughness Ry of the crystal are
larger and flat surface region 1ps of the surface of low
dislocation density region 1k is smaller. In view of this, the
polishing pressure in the abrasive-grain-free polishing step is
more preferably not less than 4.9 kPa (50 gf/cm.sup.2) and not more
than 39.2 kPa (400 gf/cm.sup.2).
[0049] In order to further remove hard abrasive grains, a water
cleaning step may be performed after the above-described
abrasive-grain-free polishing step. The cleaning method is not
particularly limited to a specific one, and ultrasonic cleaning,
scrub cleaning or the like may be used. In order to enhance the
effect of removing hard abrasive grains, scrub cleaning is
preferred. The scrub cleaning is preferably performed before the
crystal surface dries after polished. The scrub cleaning can
effectively remove not only impurities of the main surface of the
crystal but also impurities of the side surface thereof.
[0050] For the surface of group III nitride crystal 1 that has been
ground using a grindstone containing hard abrasive grains fixed by
a binder as well, the surface can be polished using polishing
solution 27 without containing abrasive grains. This
abrasive-grain-free polishing step can be used to remove hard
abrasive grains remaining at the crystal surface to reduce
impurities at the crystal surface.
Second Embodiment
[0051] Referring to FIGS. 1 to 3, another embodiment of the method
for surface treatment of a group III nitride crystal of the present
invention further includes a soft abrasive grain polishing step
(FIG. 3), after the lapping step (FIG. 1) and before the
abrasive-grain-free polishing step (FIG. 2) of the surface
treatment method in the first embodiment, for polishing the lapped
surface using a polishing solution 37 containing soft abrasive
grains 36 with a Mohs hardness of not more than 7. The soft
abrasive grain polishing step can be used to remove hard abrasive
grains remaining at the crystal surface. Further, soft abrasive
grains remaining at the crystal surface due to the soft abrasive
grain polishing step are removed by the subsequent
abrasive-grain-free polishing step.
[0052] Namely, the method for surface treatment of a group III
nitride crystal in the present embodiment includes the step of
lapping a surface of a group III nitride crystal using hard
abrasive grains with a Mohs hardness higher than 7 (FIG. 1), the
soft abrasive grain polishing step of polishing the lapped surface
of the group III nitride crystal using polishing solution 37
containing soft abrasive grains 36 with a Mohs hardness of not more
than 7 (FIG. 3), and the abrasive-grain-free polishing step of
polishing the soft-abrasive-grain-polished surface of the group III
nitride crystal using a polishing solution containing no abrasive
grain and having a pH of not less than 1 and not more than 6 or a
pH of not less than 8.5 and not more than 14 (FIG. 2).
[0053] The lapping step of the present embodiment is similar to the
lapping step of the first embodiment.
[0054] The soft abrasive grain polishing step of the present
embodiment refers to the step of chemically and mechanically
smoothing the surface of group III nitride crystal 1. For example,
referring to FIG. 3, a polishing pad 38 secured on a surface plate
35 is rotated about a rotational axis 35c while polishing solution
37 containing soft abrasive grains 36 is supplied from a polishing
solution feed port 39 onto polishing pad 38, and a crystal holder
31 to which group III nitride crystal 1 is secured and on which a
weight 34 is placed is rotated about its rotational axis 31c while
group III nitride crystal 1 is pressed against polishing pad 38. In
this way, the surface of group III nitride crystal 1 can be
chemically and mechanically polished. The soft abrasive grain
polishing step can be used to remove hard abrasive grains remaining
at the crystal surface.
[0055] Here, surface plate 35 is not particularly limited to a
specific one as long as surface plate 35 can be used to smoothly
perform the soft abrasive grain polishing. Preferably, a surface
plate containing at least one of inorganic materials such as
stainless, aluminum (Al), aluminum oxide (Al.sub.2O.sub.3),
magnesium oxide (MgO), aluminum nitride (MN), silicon carbide
(SiC), and organic materials such as phenol resin, urethane resin,
amide resin, imide resin, or a surface plate containing any
combination of them is used.
[0056] The soft abrasive grains used for the soft abrasive grain
polishing step are not particularly limited to a specific one as
long as the abrasive grains have a Mohs hardness of not more than
7. Preferably, abrasive grains containing a material such as
ZrO.sub.2, SiO.sub.2, CeO.sub.2, MnO.sub.2, Fe.sub.2O.sub.3,
Fe.sub.3O.sub.4, NiO, ZnO, CoO, Co.sub.3O.sub.4, GeO.sub.2,
Ga.sub.2O.sub.3, In.sub.2O.sub.3 are used. In order to promote
removal of soft abrasive grains in the subsequent
abrasive-grain-free polishing step, a metallic element for the soft
abrasive grains having a higher ionization tendency is preferred.
Further, in order to promote removal of soft abrasive grains as
well in the subsequent cleaning step as described below, a metallic
element for the soft abrasive grains having a higher ionization
tendency than H (hydrogen) is preferred.
[0057] Polishing solution 37 containing soft abrasive grains 36 is
not particularly limited to a specific one. In order to enhance the
effect of removing impurities such as hard abrasive grains
remaining at the crystal surface, the polishing solution preferably
has a pH comparable to that of the polishing solution without
containing abrasive grains. Specifically, the pH of polishing
solution 37 containing soft abrasive grains 36 is preferably not
less than 1 and not more than 6 or not less than 8.5 and not more
than 14, and more preferably not less than 2 and not more than 4 or
not less than 10 and not more than 12. For adjustment of the pH of
the polishing solution containing soft abrasive grains, the
inorganic acids, organic acids, inorganic alkalis, organic alkalis,
inorganic salts, organic salts and oxidizers similar to those for
the polishing solution without containing abrasive grains may be
used. In order to enhance the effect of removing impurities at the
crystal surface, the organic acids and organic alkalis without
containing metallic element are more preferable than the inorganic
acids and inorganic salts, among these pH adjusters. Further, of
the organic acids, polycarboxylic acid containing two or more
carboxyl groups is preferred.
[0058] In order to enhance the effect of removing impurities such
as hard abrasive grains remaining at the crystal surface, it is
preferable that the polishing solution containing soft abrasive
grains, like the polishing solution without containing abrasive
grains, satisfies the following relation between pH value x and ORP
value y (mV). Specifically, under the acid condition
1.ltoreq.x.ltoreq.6, the relation:
-50x+1000<y<-50x+1800 (3)
is preferably satisfied and, under the alkaline condition
8.5.ltoreq.x.ltoreq.14, the relation
-50x+800<y<-50x+1500 (4)
is preferably satisfied.
[0059] The group III nitride crystal is grown by any of various gas
phase methods such as HYPE (hydride vapor phase epitaxy),
sublimation, and various liquid phase methods such as solution
method (including flux method). For growth of the group III nitride
crystal, in order to decrease the dislocation density in the
crystal, a mask layer of SiO.sub.2 for example that has an opening
may be formed on an underlying substrate and the group III nitride
crystal may be facet-grown on the mask layer (see for example
Japanese Patent Laying-Open Nos. 2003-165799 and 2003-183100).
Referring to FIGS. 4A and 4B, group III nitride crystal 1 that is
facet-grown as described above includes a high dislocation density
region 1h where dislocations in the crystal concentrate and a low
dislocation density region 1k where the number of dislocations is
smaller. Here, the group III nitride crystal including high
dislocation density region 1h and low dislocation density region 1k
has, for example, a structure where high dislocation density
regions are arranged like stripes with respect to low dislocation
density regions (stripe structure, see FIGS. 4A and 4B) or a
structure where high dislocation density regions are arranged like
dots with respect to the low dislocation density regions (dot
structure, not shown). High dislocation density region 1h and low
dislocation density region 1k in group III nitride crystal 1 can be
observed by means of CL (S-4300 manufactured by Hitachi
Corporation) for example.
[0060] In the facet-grown group III nitride crystal as described
above, the surface of low dislocation density region 1k is a Ga
atomic surface, while the surface of high dislocation density
region 1h is an N atomic surface. Therefore, the surface of high
dislocation density region 1h is chemically and mechanically
polished at a higher rate than the surface of low dislocation
density region 1k. Therefore, referring to FIGS. 4A and 4B, if the
surface of group III nitride crystal 1 including high dislocation
density region 1h and low dislocation density region 1k is treated
by chemical mechanical polishing such as polishing with a polishing
solution containing soft abrasive grains, the surface of high
dislocation density region 1h depresses relative to the surface of
low dislocation density region 1k.
[0061] Accordingly, it is preferable that, in the step of polishing
with soft abrasive grains in the present embodiment, polishing is
performed with a polishing pad 38 having a compressibility of not
less than 0.8% and not more than 5% and at a polishing pressure of
not less than 4.9 kPa (50 gf/cm.sup.2) and not more than 98 kPa
(1000 gf/cm.sup.2). In view of this, it is preferable that
polishing pad 38 is made of polyurethane or the like and has the
form of suede, non-woven fabric, elastomer, foam or the like.
[0062] If the compressibility of polishing pad 38 is lower than
0.8%, surface roughness Ra and surface roughness Ry of the crystal
after polished with soft abrasive grains are larger. If the
compressibility of polishing pad 38 is higher than 5%, the depth of
the depression of the surface of high dislocation density region 1h
of the group III nitride crystal is larger, and a flat surface
region 1ps of the surface of low dislocation density region 1k is
smaller. In view of this, the compressibility of polishing pad 38
is preferably not less than 1% and not more than 3%.
[0063] If the polishing pressure is lower than 4.9 kPa (50
gf/cm.sup.2), the effect of removing impurities such as hard
abrasive grains remaining at the crystal surface is smaller and the
effect of smoothing the whole crystal surface is also smaller. If
the polishing pressure is higher than 98.1 kPa (1000 gf/cm.sup.2),
surface roughness Ra and surface roughness Ry of the crystal are
larger, the depth of the depression of the surface of the high
dislocation density region is larger and flat surface region 1ps of
the surface of low dislocation density region 1k is smaller. In
view of this, preferably the polishing pressure is not less than
9.8 kPa (100 gf/cm.sup.2) and not more than 68.6 kPa (700
gf/cm.sup.2).
[0064] The abrasive-grain-free polishing step of the present
embodiment is similar to the abrasive-grain-free polishing step of
the first embodiment except that the surface of the group III
nitride crystal having been polished with soft abrasive grains is
polished instead of the lapped surface of the group III nitride
crystal. Through this abrasive-grain-free polishing step,
impurities such as soft abrasive grains remaining at the crystal
surface are removed.
[0065] In order to further remove soft abrasive grains, the
abrasive-grain-free polishing step may be followed by the water
cleaning step. The method for cleaning is not particularly limited
to a specific one, and ultrasonic cleaning, scrub cleaning for
example may be used. In order to enhance the effect of removing
soft abrasive grains, scrub cleaning is preferred. The scrub
cleaning is preferably performed before the surface of the crystal
dries after being polished. The scrub cleaning can effectively
remove not only the impurities of the main surface of the crystal
but also the impurities of the side surface thereof.
Third Embodiment
[0066] Referring to FIG. 2, an embodiment of the group III nitride
crystal of the present invention relates to group III nitride
crystal 1 obtained through the surface treatment of the first
embodiment or second embodiment. Since the group III nitride
crystal of the present embodiment is surface-treated according to
the first embodiment or second embodiment, impurities such as hard
abrasive grains and soft abrasive grains remaining at the crystal
surface are removed. Therefore, one or more group III nitride
layers can be epitaxially grown on the surface of the group III
nitride crystal of the present embodiment to produce a
semiconductor device having excellent characteristics with high
yield.
[0067] In order to produce a semiconductor device having excellent
characteristics with high yield by epitaxially growing one or more
group III nitride layers on the surface of group III nitride
crystal 1 of the present embodiment, surface roughness Ra is
preferably not more than 2 nm and more preferably not more than 1
nm. For like purpose, surface roughness Ry is preferably not more
than 20 nm and more preferably not more than 10 nm. Further, for
like purpose, the thickness of a work-affected layer of the group
III nitride crystal is preferably not more than 50 nm and more
preferably not more than 30 nm.
[0068] The group III nitride crystal of the present embodiment may
be a crystal where the dislocation density in the crystal surface
is uniform, or may be a crystal where the dislocation density in
the crystal surface is not uniform. An example of the crystal where
the dislocation density in the crystal surface is not uniform is
the crystal as shown in FIGS. 4A and 4B including low dislocation
density region 1k and high dislocation density region 1h.
[0069] Referring to FIGS. 4A and 4B, it is preferable that, in the
group III nitride crystal of the present embodiment, level
difference D between the surface of low dislocation density region
1k and that of high dislocation density region 1h is not more than
3 .mu.m. One or more group III nitride layers can be epitaxially
grown on the surface of group III nitride crystal 1 where level
difference D between the surface of low dislocation density region
1k and that of high dislocation density region 1h is not more than
3 .mu.m to produce a semiconductor device having excellent
characteristics with high yield.
[0070] Further, referring to FIGS. 4A and 4B, it is preferable
that, in the group III nitride crystal of the present embodiment,
flat surface region 1ps of low dislocation density region 1k has an
area of at least 40% relative to the whole surface 1ks of low
dislocation density region 1k. Here, flat surface region 1ps of low
dislocation density region 1k is defined as follows. From the
uppermost point P.sub.0 or uppermost line L.sub.0 of the surface of
low dislocation density region 1k toward the outer periphery of the
low dislocation density region, points P.sub.1, P.sub.2, . . . ,
P.sub.k-1, P.sub.k are plotted at regular intervals of 10 .mu.m
(where k is a positive integer). The angle of inclination .theta.
refers to the angle formed between the straight line including
points P.sub.k-1 and P.sub.k and a reference plane Q abutting on
the surface (a curved surface close to flat surface) of low
dislocation density region 1k at uppermost point P.sub.0 or
uppermost line L.sub.0. Then, the flat surface region is defined as
a surface region where arbitrary points P.sub.k having an angle of
inclination .theta. of less than 0.1.degree. are present. This flat
surface region 1ps continues from the central portion of the
surface of low dislocation density region 1k toward the outer
periphery. Since high dislocation density region 1h is more likely
to be removed in the polishing step, the outer peripheral portion
of low dislocation density region 1k that is located near high
dislocation density region 1h is removed first relative to the
central portion of low dislocation density region 1k, so that the
outermost or edge region has an outwardly and downwardly sloping
shape. Consequently, inclination angle .theta. as described above
is larger and a region where the angle is 0.1.degree. or more is
generated. It is further supposed here that the ratio (percentage)
of the area of flat surface region 1ps in low dislocation density
region 1k with respect to the area of the whole surface 1ks in low
dislocation density region 1k is defined as flat surface region
ratio (%).
[0071] On the surface of the group III nitride crystal where flat
surface region 1ps of low dislocation density region 1k has an area
of 40% or more with respect to the whole surface 1ks of low
dislocation density region 1k (namely the group III nitride crystal
having a flat surface region ratio of 40% or more), one or more
group III nitride layers can be epitaxially grown to produce a
group III nitride semiconductor device having excellent
characteristics with high yield. In view of this, the flat surface
region ratio is preferably not less than 60% and more preferably
not less than 80%.
Fourth Embodiment
[0072] Referring to FIG. 5, a group III nitride stack of the
present invention includes group III nitride crystal 1 of the third
embodiment and at least one group III nitride layer 650 that is
epitaxially grown on a surface of group III nitride crystal 1.
Group III nitride stack 500 of the present embodiment thus includes
at least one group III nitride layer 650 that is epitaxially grown
on a surface of the group III nitride crystal of the third
embodiment, and therefore, the intensity (PL intensity) of the
light emitted by means of the PL (photoluminescence) method is
high.
[0073] More specifically, referring to FIG. 5, the group III
nitride stack of the present embodiment includes at least one
epitaxially-grown group III nitride layer on one main surface of an
n-type GaN crystal substrate (group III nitride crystal 1). The at
least one group III nitride layer includes an n-type semiconductor
layer 620, a light emitting layer 640 and a p-type semiconductor
layer 630. N-type semiconductor layer 620 includes an n-type GaN
layer 621 of 1 .mu.m in thickness and an n-type
Al.sub.0.1Ga.sub.0.9N layer 622 of 150 nm in thickness, and p-type
semiconductor layer 630 includes a p-type Al.sub.0.2Ga.sub.0.8N
layer 631 of 20 nm in thickness and p-type GaN layer 632 of 150 nm
in thickness. These layers are laid in order on each other. Here,
light emitting layer 640 has a multiple quantum well structure in
which four barrier layers made up of GaN layers each having a
thickness of 10 nm and three well layers made up of
Ga.sub.0.85In.sub.0.15N layers each having a thickness of 3 nm are
alternately stacked on each other.
Fifth Embodiment
[0074] Referring to FIG. 5, a method for manufacturing a group III
nitride stack of the present invention is specifically a method for
manufacturing group III nitride stack 500 using group III nitride
crystal 1 of the third embodiment, including the steps of preparing
group III nitride crystal 1, and epitaxially growing at least one
group III nitride layer 650 on a surface of group III nitride
crystal 1. Thus, on a surface of the group III nitride crystal, one
or more group III nitride layers can be epitaxially grown to
produce a group III nitride stack having a high intensity (PL
intensity) of the light emitted by means of the PL method.
[0075] Referring to FIG. 5, according to the method for
manufacturing a group III nitride stack of the present embodiment,
an n-type GaN crystal substrate (group III nitride crystal 1) is
disposed in an MOCVD apparatus for example. Then, on one main
surface of the n-type GaN crystal substrate (group III nitride
crystal 1), the MOCVD (Metal Organic Chemical Vapor Deposition)
method is used to epitaxially grow at least one group III nitride
layer 650. Specifically, Group III nitride layer 650 includes
n-type semiconductor layer 620, light emitting layer 640 and p-type
semiconductor layer 630. N-type semiconductor layer 620 includes
n-type GaN layer 621 of 1 .mu.m in thickness and n-type
Al.sub.0.1Ga.sub.0.9N layer 622 of 150 nm in thickness, and p-type
semiconductor layer 630 includes p-type Al.sub.0.2Ga.sub.0.8N layer
631 of 20 nm in thickness and p-type GaN layer 632 of 150 nm in
thickness. These layers are epitaxially grown in order. Here, light
emitting layer 640 has a multiple quantum well structure in which
four barrier layers made up of GaN layers each having a thickness
of 10 nm and three well layers made up of Ga.sub.0.85In.sub.0.15N
layers each having a thickness of 3 nm are alternately stacked on
each other.
Sixth Embodiment
[0076] Referring to FIG. 6, a group III nitride semiconductor
device of the present invention includes group III nitride crystal
1 of the third embodiment, at least one group III nitride layer 650
that is epitaxially grown on a surface of group III nitride crystal
1, and electrodes 661, 662 formed on at least one of a surface of
the outermost layer of group III nitride layer 650 and a surface of
group III nitride crystal 1. Since group III nitride semiconductor
device 600 of the present embodiment includes at least one group
III nitride layer 650 that is epitaxially grown on the surface of
the group III nitride crystal of the third embodiment, the
semiconductor device has a high emission intensity.
[0077] More specifically, referring to FIG. 6, a group III nitride
semiconductor device of the present embodiment includes at least
one group III nitride layer 650 that is epitaxially grown on one
main surface of an n-type GaN crystal substrate (group III nitride
crystal 1). Group III nitride layer 650 includes n-type
semiconductor layer 620, light emitting layer 640 and p-type
semiconductor layer 630. N-type semiconductor layer 620 includes
n-type GaN layer 621 of 1 .mu.n in thickness and n-type
Al.sub.0.1Ga.sub.0.9N layer 622 of 150 nm in thickness, and p-type
semiconductor layer 630 includes p-type Al.sub.0.2Ga.sub.0.8N layer
631 of 20 nm in thickness and p-type GaN layer 632 of 150 nm in
thickness. These layers are laid in order on each other. Here,
light emitting layer 640 has a multiple quantum well structure in
which four barrier layers made up of GaN layers each having a
thickness of 10 nm and three well layers made up of
Ga.sub.0.85In.sub.0.15N layers each having a thickness of 3 nm are
alternately stacked on each other.
[0078] Further, the group III nitride semiconductor device of the
present embodiment includes a second electrode 662 (p side
electrode) on p-type GaN layer 632 that is the outermost layer of
group III nitride layer 650 and a first electrode 661 (n side
electrode) on the other main surface of the n-type GaN crystal
substrate (group III nitride crystal 1), as the electrodes formed
on at least one of a surface of the outermost layer of group III
nitride layer 650 and a surface of group III nitride crystal 1.
[0079] In a semiconductor device 700 including an LED (light
emitting diode) as group III nitride semiconductor device 600 as
described above, the second electrode (p side electrode) of group
III nitride semiconductor device 600 is bonded to a conductor 682
with a solder layer 670 and the first electrode (n side electrode)
is bonded to a conductor 681 with a wire 690.
Seventh Embodiment
[0080] A method for manufacturing a group III nitride semiconductor
device of the present invention is a method for manufacturing a
semiconductor device using the group III nitride crystal of the
third embodiment, and includes the steps of preparing group III
nitride crystal 1, epitaxially growing at least one group III
nitride layer 650 on a surface of group III nitride crystal 1, and
forming electrodes 661, 662 on at least one of a surface of the
outermost layer of group III nitride layer 650 and a surface of
group III nitride crystal 1. The group III nitride semiconductor
device can be produced with high yield by epitaxially growing one
or more group III nitride layers on a surface of the group III
nitride crystal.
[0081] Referring to FIG. 6, according to the method for
manufacturing a group III nitride semiconductor device of the
present embodiment, an n-type GaN crystal substrate (group III
nitride crystal 1) is disposed in an MOCVD apparatus for example.
Then, on one main surface of the n-type GaN crystal substrate
(group III nitride crystal 1), the MOCVD (Metal Organic Chemical
Vapor Deposition) method is used to epitaxially grow at least one
group III nitride layer 650 in order. Specifically, group III
nitride layer 650 includes n-type semiconductor layer 620, light
emitting layer 640 and p-type semiconductor layer 630. N-type
semiconductor layer 620 includes n-type GaN layer 621 of 1 .mu.m in
thickness and n-type Al.sub.0.1Ga.sub.0.9N layer 622 of 150 nm in
thickness, and p-type semiconductor layer 630 includes p-type
Al.sub.0.2Ga.sub.0.8N layer 631 of 20 nm in thickness and p-type
GaN layer 632 of 150 nm in thickness. Here, light emitting layer
640 has a multiple quantum well structure in which four barrier
layers made up of GaN layers each having a thickness of 10 nm and
three well layers made up of Ga.sub.0.85In.sub.0.15N layers each
having a thickness of 3 nm are alternately stacked on each
other.
[0082] Subsequently, on the other main surface of the n-type GaN
crystal substrate (group III nitride crystal 1), an n side
electrode with a diameter of 100 .mu.m is formed as first electrode
661. On p-type GaN layer 632, a p side electrode is formed as
second electrode 662. The above described stack is formed into a
chip of 400 .mu.m.times.400 .mu.m to produce an LED (light emitting
diode) as group III nitride semiconductor device 600.
[0083] After this, the p side electrode is bonded to conductor 682
with solder layer 670 while the n side electrode and conductor 681
are bonded together with wire 690 to produce semiconductor device
700 including the LED.
Examples A1-A7, Comparative Examples AR1, AR2
1. Lapping Step
[0084] An n-type GaN crystal grown by the HVPE method was sliced
along a plane parallel to a {0001} plane to obtain an n-type GaN
crystal substrate (group III nitride crystal 1) of 50 mm
(diameter).times.0.5 mm (thickness). Referring to FIG. 1, the rear
surface (N atomic surface that is (000-1) plane)) of the n-type GaN
crystal substrate (group III nitride crystal 1) was attached to
crystal holder 11 of a ceramic material with a wax. Surface plate
15 of 300 mm in diameter was placed in a lapping apparatus (not
shown). Diamond abrasive grains (hard abrasive grains 16) with a
grain size of 2 .mu.m were sprayed from abrasive grain feed port 19
to surface plate 15 made of Sn (tin), while surface plate 15 was
rotated about its rotational axis 15c. Further, weight 14 was put
on crystal holder 11 to press the n-type GaN crystal substrate
(group III nitride crystal 1) against surface plate 15, while the
n-type GaN crystal substrate (group III nitride crystal 1) was
rotated about rotational axis 11c of crystal holder 11. In this
way, the surface (Ga atomic surface that is (0001) plane) of the
n-type GaN crystal was lapped. The diamond abrasive grains have a
Mohs hardness of 10.
[0085] Here, the lapping pressure was 29.4 kPa (300 gf/cm.sup.2),
the number of rotations of the n-type GaN crystal substrate (group
III nitride crystal 1) and that of surface plate 15 were both 30
rpm (rotations/min) to 100 rpm (rotations/min), and the lapping
time was 30 minutes. Through the lapping, the surface of the n-type
GaN crystal substrate was made specular. After the lapping, the
n-type GaN crystal substrate had a surface roughness Ry of 30 nm
and a surface roughness Ra of 3.0 nm.
2. Abrasive-Grain-Free Polishing Step
[0086] Referring next to FIGS. 1 and 2, the n-type GaN crystal
substrate (group III nitride crystal 1) having been lapped and
remained secured to crystal holder 11 (corresponding to crystal
holder 21 in FIG. 2) was polished without abrasive grains. On
surface plate 25 with a diameter of 380 mm that was placed in a
polishing apparatus (not shown), polishing pad 28 was disposed.
Polishing solution 27 without containing abrasive grains was fed
from polishing solution feed port 29 to polishing pad 28, while
polishing pad 28 was rotated about rotational axis 25c. Further,
weight 24 was put on crystal holder 21 to press the lapped n-type
GaN crystal substrate (group III nitride crystal 1) secured to
crystal holder 21 against polishing pad 28, while the n-type GaN
crystal substrate (group III nitride crystal 1) was rotated about
rotational axis 21c of crystal holder 21. In this way, the surface
(Ga atomic surface) of the n-type GaN crystal substrate (group III
nitride crystal 1) was polished.
[0087] Here, as polishing solution 27 without containing abrasive
grains, a solution containing an acid and an oxidizer as shown in
Table 1 and having a pH and an ORP shown in Table 1 was used. In
Table 1, TCIA represents trichloroisocyanuric acid, and DCIA-Na
represents sodium dichloroisocyanurate. As polishing pad 28, a
non-woven pad made of polyurethane and having a compressibility
shown in Table 1 was used. As surface plate 25, a stainless surface
plate was used. As to the polishing conditions, the polishing
pressure was 29.4 kPa (300 gf/cm.sup.2), the number of rotations of
the n-type GaN crystal substrate (group III nitride crystal 1) and
that of polishing pad 28 were both 30 rpm (rotations/min) to 100
rpm (rotations/min), and the polishing time was 30 minutes.
[0088] Through the above-described steps, respective crystals of
Examples A1 to A7 and Comparative Examples AR1 and AR2 shown in
Table 1 were surface-treated. The impurity concentration, surface
roughness Ra and surface roughness Ry of the crystal surface after
treated were measured. Here, the concentration of impurity C
(carbon) was measured by means of AES (Auger Electron
Spectroscopy). C is considered to be originated from the diamond
abrasive grains. Surface roughness Ra and surface roughness Ry were
calculated through AFM (Atomic Force Microscope) observation in the
range of a square of 10 .mu.m.times.10 .mu.m of the crystal
surface. The results are summarized in Table 1.
TABLE-US-00001 TABLE 1 Example A .cndot. Comparative Example AR
Comparative Comparative Example Example Example Example Example
Example Example Example Example AR1 A1 A2 A3 A4 AR2 A5 A6 A7
lapping abrasive material diamond diamond diamond diamond diamond
diamond diamond diamond diamond grain grain size 2 2 2 2 2 2 2 2 2
(.mu.m) surface material Sn Sn Sn Sn Sn Sn Sn Sn Sn plate abrasive-
polishing acid HCl HCl HCl citric acid citric acid -- HCl HCl
citric acid grain-free solution oxidizer TCIA TCIA DCIA-Na DCIA-Na
DCIA-Na -- -- -- -- polishing pH 0.5 1 2 4 6 7 1 2 4 ORP (mV) 1600
1550 1500 1350 1200 800 1100 1000 850 compressibility of 3 3 3 3 3
3 3 3 3 polishing pad (%) polishing pressure 29.4 29.4 29.4 29.4
29.4 29.4 29.4 29.4 29.4 (kPa) evaluation impurity C (mass %) 3.9
4.2 4.6 5.3 8.6 15.2 4.4 4.9 5.8 of crystal surface roughness 52 33
26 24 19 19 31 23 21 surface Ry (nm) surface roughness 4.5 3.2 2.2
2.2 2 1.8 3 2 1.9 Ra (nm)
[0089] Referring to Table 1, as seen from Examples A1 to A7,
through the surface treatment including the lapping step using hard
abrasive grains with a Mohs hardness higher than 7 (diamond
abrasive grains with a Mohs hardness of 10 for example), and the
abrasive-grain-free polishing step using a polishing solution
without containing abrasive grains and having a pH of not less than
1 and not more than 6 as well as a polishing pad having a
compressibility of not less than 1.5% and not more than 20%,
performed under the condition that the polishing pressure was not
less than 0.98 kPa and not more than 58.8 kPa, a crystal surface
with low impurity concentration and small surface roughness Ra and
small surface roughness Ry was obtained. As for Comparative Example
AR1, because of the fact that the polishing solution without
containing abrasive grains had a pH of 0.5 which is lower than 1,
surface roughness Ra and surface roughness Ry were larger. As for
Comparative Example AR2, because of the pH of 7 which is higher
than 6, the concentration of impurity C (carbon) remaining at the
crystal surface was higher.
Examples B1-B5, Comparative Example BR1
1. Lapping Step
[0090] A surface (Ga atomic surface) of an n-type GaN crystal
substrate (group III nitride crystal 1) was lapped in a similar
manner to Example A1 except that diamond abrasive grains with a
grain size of 3 .mu.m were used as hard abrasive grains 16 and a
surface plate made of a Sn--Bi (Bi content: 2% by mass) alloy was
used as surface plate 15. Through the lapping, the surface of the
n-type GaN crystal substrate was made specular. After the lapping,
the n-type GaN crystal substrate had a surface roughness Ry of 58
nm and a surface roughness Ra of 5.1 nm.
2. Abrasive-Grain-Free Polishing Step
[0091] Subsequently, the surface (Ga atomic surface) of the n-type
GaN crystal substrate (group III nitride crystal 1) was polished
without abrasive grains in a similar manner to Example A1, except
that a solution containing an alkali and an oxidizer shown in Table
2 and having a pH and an ORP shown in Table 2 was used as polishing
solution 27 without containing abrasive grains, a suede pad made of
polyurethane having a compressibility shown in Table 2 was used as
polishing pad 28, a stainless surface plate was used as surface
plate 25, and the polishing pressure was 19.6 kPa (200
gf/cm.sup.2). Here, TCIA represents trichloroisocyanuric acid, and
DCIA-Na represents sodium dichloroisocyanurate.
[0092] Through the above-described steps, respective crystals of
Examples B1 to B7 and Comparative Example BR1 shown in Table 2 were
surface-treated. The impurity concentration, surface roughness Ry
and surface roughness Ra of the crystal surface after treated were
measured. The concentration of impurity C (carbon), surface
roughness Ry and surface roughness Ra were determined in a similar
manner to Example A1. The results are summarized in Table 2.
TABLE-US-00002 TABLE 2 Example B .cndot. Comparative Example BR
Comparative Example Example Example Example Example Example BR1 B1
B2 B3 B4 B5 lapping abrasive material diamond diamond diamond
diamond diamond diamond grain grain size 3 3 3 3 3 3 (.mu.m)
surface material Sn--Bi Sn--Bi Sn--Bi Sn--Bi Sn--Bi Sn--Bi plate
abrasive- polishing alkali, -- sodium KOH KOH KOH sodium grain-free
solution salt carbonate carbonate polishing oxidizer -- -- -- -- --
DCIA-Na pH 7 8.5 10 12 14 10 ORP (mV) 650 600 500 400 250 1050
compressibility of 6 6 6 6 6 6 polishing pad (%) polishing pressure
(kPa) 19.6 19.6 19.6 19.6 19.6 19.6 evaluation impurity C (mass %)
19.2 9.2 5.6 4.3 3.6 4.1 of crystal surface roughness Ry (nm) 30 33
35 48 78 42 surface surface roughness Ra (nm) 2.9 2.9 3 4.5 6.2
3.5
[0093] Referring to Table 2, as seen from Examples B1 to B5,
through the surface treatment including the lapping step using hard
abrasive grains with a Mohs hardness higher than 7 (for example,
diamond abrasive grains with a Mohs hardness of 10), and the
abrasive-grain-free polishing step using a polishing solution
without containing abrasive grains and having a pH of not less than
8.5 and not more than 14 as well as a polishing pad having a
compressibility of not less than 1.5% and not more than 20%,
performed under the condition that the polishing pressure was not
less than 0.98 kPa and not more than 58.8 kPa, a crystal surface
with low impurity concentration, small surface roughness Ra and
small surface roughness Ry was obtained. As for Comparative Example
BR1, because of the pH of 7 which is higher than 6, the
concentration of impurity C (carbon) remaining at the crystal
surface was higher.
Examples C1-C13
1. Lapping Step
[0094] A surface (Ga atomic surface in a low dislocation density
region and N atomic surface in a high dislocation density region,
the surface is (0001) plane) of an n-type GaN crystal substrate
(group III nitride crystal 1) was lapped in a similar manner to
Example A1, except that an n-type GaN crystal substrate grown by
the HYPE method to have facets as formed and including a high
dislocation density region and a low dislocation density region was
used as group III nitride crystal 1, SiC abrasive grains (Mohs
hardness: 9.5) with a grain size of 3 .mu.m were used as hard
abrasive grains 16, and a stainless surface plate to which a
non-woven pad made of polyurethane was attached was used as surface
plate 15. Through the lapping, the surface of the n-type GaN
crystal substrate was made specular. After the lapping, the n-type
GaN crystal substrate had a surface roughness Ry of 30 nm and a
surface roughness Ra of 3.2 nm.
2. Abrasive-Grain-Free Polishing Step
[0095] Subsequently, the Ga atomic surface ((0001) plane) of the
n-type GaN crystal substrate (group III nitride crystal 1) was
polished without abrasive grains, in a similar manner to Example
A1, except that a solution containing an alkali shown in Table 3
and having a pH and an ORP shown in Table 3 was used as polishing
solution 27 without containing abrasive grains, a polyurethane foam
pad having a compressibility shown in Table 3 was used as polishing
pad 28, an aluminum surface plate was used as surface plate 25, and
a polishing pressure shown in Table 3 was used.
[0096] Through the above-described steps, surface treatment was
performed on Examples C1 to C13 shown in Table 3. For the crystal
surface after treated, the impurity concentration, the depth of the
depression in the high dislocation density region (namely level
difference D shown in FIG. 4 between the surface of low dislocation
density region 1k and the surface of high dislocation density
region 1h), the flat surface region ratio (namely the ratio
(percentage) of the area of flat surface region 1ps of low
dislocation density region 1k to the area of the whole surface 1ks
of low dislocation density region 1k), and surface roughness Ry and
surface roughness Ra were measured. Here, the concentration of
impurity Si (silicon) was measured by the TXRF (total reflection
x-ray fluorescence) method. This Si is considered to be originated
from the SiC abrasive grains. The depth of the depression in the
high dislocation density region was measured using an
interferometry profilometer. The flat surface region ratio was
calculated from surface profile data obtained using the
interferometry profilometer. Surface roughness Ry and surface
roughness Ra were determined similarly to Example A1. The results
are summarized in Table 3.
TABLE-US-00003 TABLE 3 Example C Example C1 Example C2 Example C3
Example C4 Example C5 Example C6 Example C7 lapping abrasive
material SiC SiC SiC SiC SiC SiC SiC grain grain size 3 3 3 3 3 3 3
(.mu.m) pad on material, polyurethane polyurethane polyurethane
polyurethane polyurethane polyurethane polyurethane surface form
non-woven non-woven non-woven non-woven non-woven non-woven
non-woven plate abrasive- polishing alkali KOH KOH KOH KOH KOH KOH
KOH grain-free solution oxidizer -- -- -- -- -- -- -- polishing pH
13 13 13 13 13 13 13 ORP (mV) 350 350 350 350 350 350 350
compressibility of 1 1.5 3 7 10 20 25 polishing pad (%) polishing
pressure (kPa) 19.6 19.6 19.6 19.6 19.6 19.6 19.6 evaluation
impurity Si (.times.10.sup.10 1100 630 580 720 480 390 320 of
crystal cm.sup.-2) surface depression depth of high 400 500 700
1200 2100 3000 4200 dislocation density region (nm) flat surface
region ratio (%) 95 90 85 80 80 75 70 surface roughness Ry (nm) 42
31 29 24 23 25 28 surface roughness Ra (nm) 4.5 3.3 3 2.6 2.4 2.7
2.9 Example C Example C8 Example C9 Example C10 Example C11 Example
C12 Example C13 lapping abrasive material SiC SiC SiC SiC SiC SiC
grain grain size 3 3 3 3 3 3 (.mu.m) pad on material, polyurethane
polyurethane polyurethane polyurethane polyurethane polyurethane
surface form non-woven non-woven non-woven non-woven non-woven
non-woven plate abrasive- polishing alkali KOH KOH KOH KOH KOH KOH
grain-free solution oxidizer -- -- -- -- -- -- polishing pH 13 13
13 13 13 13 ORP (mV) 350 350 350 350 350 350 compressibility of 7 7
7 7 7 7 polishing pad (%) polishing pressure (kPa) 0.49 0.98 4.9
39.2 58.8 78.5 evaluation impurity Si (.times.10.sup.10 8200 2900
950 570 240 120 of crystal cm.sup.-2) surface depression depth of
high 350 450 600 1900 3000 4100 dislocation density region (nm)
flat surface region ratio (%) 100 95 90 80 75 70 surface roughness
Ry (nm) 23 22 24 32 35 47 surface roughness Ra (nm) 2.1 2 2.2 2.8
3.4 4.3
[0097] Referring to Table 3, as seen from Examples C1 to C13,
through the surface treatment including the lapping step using hard
abrasive grains with a Mohs hardness higher than 7 (SiC abrasive
grains with a Mohs hardness of 9.5 for example), and the
abrasive-grain-free polishing step using a polishing solution
containing no abrasive grains and having a pH of not less than 1
and not more than 6.5 as well as a polishing pad with a
compressibility of not less than 1.5% and not more than 20%,
performed under the condition that the polishing pressure was not
less than 0.98 kPa and not more than 58.8 kPa, a crystal surface
where the impurity concentration was low, the depth of the
depression in the high dislocation density region was small, the
flat surface region ratio was high, and surface roughness Ry and
surface roughness Ra were small, was obtained. As for Example C1,
the low compressibility of the polishing pad increased surface
roughness Ry and surface roughness Ra. As for Example C7, the high
compressibility of the polishing pad increased the depth of the
depression in the high dislocation density region. As for Example
C8, the low polishing pressure increased the impurity
concentration. As for Example C13, the high polishing pressure
increased the depth of the depression in the high dislocation
density region.
Examples D1-D7
1. Lapping Step
[0098] A surface (Ga atomic surface in a low dislocation density
region and N atomic surface in a high dislocation density region,
the surface is (0001) plane) of an n-type GaN crystal substrate
(group III nitride crystal 1) was lapped in a similar manner to
Example A1, except that an n-type GaN crystal substrate grown by
the HVPE method to have facets as formed and including a high
dislocation density region and a low dislocation density region was
used as group III nitride crystal 1, Al.sub.2O.sub.3 abrasive
grains (Mohs hardness: 9) with a grain size of 4 .mu.m were used as
hard abrasive grains 16, a stainless surface plate to which a
non-woven pad made of polyurethane was attached was used as surface
plate 15, and the lapping pressure was 29.4 kPa (300 gf/cm.sup.2).
Through the lapping, the surface of the n-type GaN crystal
substrate was made specular. After the lapping, the n-type GaN
crystal substrate had a surface roughness Ry of 26 nm and a surface
roughness Ra of 2.4 nm.
2. Abrasive-Grain-Free Polishing Step
[0099] Subsequently, the Ga atomic surface ((0001) plane) of the
n-type GaN crystal substrate (group III nitride crystal 1) was
polished without abrasive grains in a similar manner to Example A1,
except that a solution containing an acid and an oxidizer shown in
Table 4 and having a pH and an ORP shown in Table 4 was used as
polishing solution 27 without containing abrasive grains, a
polyurethane foam pad having a compressibility shown in Table 4 was
used as polishing pad 28, a stainless surface plate was used as
surface plate 25, and the polishing pressure was 39.2 kPa (400
gf/cm.sup.2). Here, TCIA in Table 4 represents trichloroisocyanuric
acid.
[0100] Through the above-described steps, surface treatment was
performed on Examples D1 to D7 shown in Table 4. For the crystal
surface after treated, the impurity concentration, the depth of the
depression in the high dislocation density region (namely level
difference D shown in FIGS. 4A and 4B between the surface of low
dislocation density region 1k and the surface of high dislocation
density region 1h), the flat surface region ratio (namely the ratio
(percentage) of the area of flat surface region 1ps in low
dislocation density region 1k to the area of the whole surface 1ks
of low dislocation density region 1k), and surface roughness Ry and
surface roughness Ra were measured. Here, the concentration of
impurity Al (aluminum) was measured by the TXRF (total reflection
x-ray fluorescence) method. This Al is considered to be originated
from the Al.sub.2O.sub.3 abrasive grains. The depth of the
depression in the high dislocation density region was measured
using an interferometry profilometer. The flat surface region ratio
was calculated from surface profile data obtained using the
interferometry profilometer. Surface roughness Ry and surface
roughness Ra were determined similarly to Example A1. The results
are summarized in Table 4.
TABLE-US-00004 TABLE 4 Example D Example D1 Example D2 Example D3
Example D4 Example D5 Example D6 Example D7 lapping abrasive
material Al.sub.2O.sub.3 Al.sub.2O.sub.3 Al.sub.2O.sub.3
Al.sub.2O.sub.3 Al.sub.2O.sub.3 Al.sub.2O.sub.3 Al.sub.2O.sub.3
grain grain size 4 4 4 4 4 4 4 (.mu.m) pad on material,
polyurethane polyurethane polyurethane polyurethane polyurethane
polyurethane polyurethane surface form non-woven non-woven
non-woven non-woven non-woven non-woven non-woven plate abrasive-
polishing acid malic acid malic acid malic acid malic acid malic
acid malic acid malic acid grain-free solution oxidizer TCIA TCIA
TCIA TCIA TCIA TCIA TCIA polishing pH 2 2 2 2 2 2 2 ORP (mV) 1450
1450 1450 1450 1450 1450 1450 compressibility of 1 1.5 3 7 10 20 25
polishing pad (%) polishing pressure (kPa) 39.2 39.2 39.2 39.2 39.2
39.2 39.2 evaluation impurity Al (.times.10.sup.10 1400 740 630 850
520 440 390 of crystal cm.sup.-2) surface depression depth of high
400 600 800 1400 2200 3000 4800 dislocation density region (nm)
flat surface region ratio (%) 95 90 80 75 70 70 60 surface
roughness Ry (nm) 38 27 25 21 18 24 27 surface roughness Ra (nm)
3.5 2.4 2.2 1.8 1.4 2.1 2.5
[0101] Referring to Table 4, as seen from Examples D1 to D7,
through the surface treatment including the lapping step using hard
abrasive grains with a Mohs hardness higher than 7 (Al.sub.2O.sub.3
abrasive grains with a Mohs hardness of 9 for example), and the
abrasive-grain-free polishing step using a polishing solution
without containing abrasive grains and having a pH of not less than
1 and not more than 6.5 and a polishing pad with a compressibility
of not less than 1.5% and not more than 20%, performed under the
condition that the polishing pressure was not less than 0.98 kPa
and not more than 58.8 kPa, the crystal surface having a low
impurity concentration, a small depth of the depression in the high
dislocation density region, a high flat surface region ratio, and
small surface roughness Ry and small surface roughness Ra was
obtained. As for Example D1, the low compressibility of the
polishing pad increased surface roughness Ry and surface roughness
Ra. As for Example D7, the high compressibility of the polishing
pad increased the depth of the depression in the high dislocation
density region.
Examples E1-E12
1. Lapping Step
[0102] A surface (Ga atomic surface that is (0001) plane) of an
n-type GaN crystal substrate (group III nitride crystal 1) was
lapped in a similar manner to Example A1, except that diamond
abrasive grains (Mohs hardness: 10) with a grain size of 2 .mu.m
were used as hard abrasive grains 16, a stainless surface plate to
which a non-woven pad made of polyurethane was attached was used as
surface plate 15, and the lapping pressure was 29.4 kPa (300
gf/cm.sup.2). Through the lapping, the surface of the n-type GaN
crystal substrate was made specular. After the lapping, the n-type
GaN crystal substrate had a surface roughness Ry of 25 nm and a
surface roughness Ra of 2.3 nm.
2. Soft Abrasive Grain Polishing Step
[0103] Subsequently, referring to FIGS. 1 and 3, the lapped n-type
GaN crystal substrate (group III nitride crystal 1) remained
secured to crystal holder 11 (corresponding to crystal holder 31 in
FIG. 3) was polished with soft abrasive grains in the following
manner. On surface plate 35 with a diameter of 300 mm placed in a
polishing apparatus (not shown), polishing pad 38 was disposed. The
surface (Ga atomic surface) of the n-type GaN crystal substrate
(group III nitride crystal 1) was polished by supplying polishing
solution 37 containing soft abrasive grains 36 from polishing
solution feed port 39 to polishing pad 38 while rotating polishing
pad 38 about rotational axis 35c, and pressing the n-type GaN
crystal substrate (group III nitride crystal 1) secured to crystal
holder 31 against polishing pad 38 by putting weight 34 on crystal
holder 31 while rotating the n-type GaN crystal substrate (group
III nitride crystal 1) about rotational axis 31c of crystal holder
31.
[0104] Here, Fe.sub.2O.sub.3 abrasive grains (Mohs hardness: 6)
with a grain size of 0.5 .mu.m were used as soft abrasive grains
36. A solution containing HCl (hydrochloric acid) as acid and
H.sub.2O.sub.2 as oxidizer and having a pH of 2 and an ORP of 700
mV was used as polishing solution 37 containing soft abrasive
grains 36. A foam pad of polyurethane having a compressibility
shown in Table 5 was used as polishing pad 38. An aluminum surface
plate was used as surface plate 35. The polishing was performed
under the conditions that the polishing pressure was the one shown
in Table 5, the number of rotations of the n-type GaN crystal
substrate (group III nitride crystal 1) and that of polishing pad
38 were both 30 rpm (rotations/min) to 100 rpm (rotations/min), and
the polishing time was 60 minutes.
3. Abrasive-Grain-Free Polishing Step
[0105] The surface (Ga atomic surface) of the n-type GaN crystal
substrate (group III nitride crystal 1) was polished without
abrasive grains in a similar manner to Example A1, except that a
solution containing HCl (hydrochloric acid) as acid and
H.sub.2O.sub.2 as oxidizer and having a pH of 2 and an ORP of 700
mV was used as polishing solution 27 without containing abrasive
grains, a suede pad of polyurethane having a compressibility shown
in Table 5 was used as polishing pad 28, a stainless surface plate
was used as surface plate 25, and the polishing pressure was 39.2
kPa (400 gf/cm.sup.2).
[0106] Through the above-described steps, surface treatment was
performed on Examples E1 to E12 shown in Table 5. For the crystal
surface after treated, the impurity concentration, the depth of the
depression in the high dislocation density region (namely the
difference in level between the surface of the low dislocation
density region and the surface of the high dislocation density
region), the flat surface region ratio (namely the ratio
(percentage) of the area of flat surface region 1ps of low
dislocation density region 1k to the area of the whole surface 1ks
of low dislocation density region 1k), surface roughness Ry and
surface roughness Ra, and the thickness of the work-affected layer
were measured. Here, the concentration of impurity C (carbon) was
measured using the AES (Auger Electron Spectroscopy) method. C is
considered to be originated from the diamond abrasive grains that
are hard abrasive grains. The concentration of impurity Fe (iron)
was measured using the TXRF (total reflection x-ray fluorescence)
method. Fe is considered to be originated from soft abrasive grains
Fe.sub.2O.sub.3. Surface roughness Ra and surface roughness Ry were
determined similarly to Example A1. The results are summarized in
Table 5.
4. Process of Manufacturing Group III Nitride Stack
[0107] Subsequently, referring to FIG. 5, the n-type GaN crystal
substrate (group III nitride crystal 1) polished without abrasive
grains for each of Examples E1 to E12 as described above was placed
in an MOCVD apparatus. On one main surface (Ga atomic surface) of
the n-type GaN crystal substrate (group III nitride crystal 1),
n-type semiconductor layer 620 including n-type GaN layer 621
(dopant: Si) of 1 .mu.m in thickness and n-type
Al.sub.0.1Ga.sub.0.9N layer 622 (dopant: Si) of 150 nm in
thickness, light emitting layer 640, and p-type semiconductor layer
630 including p-type Al.sub.0.2Ga.sub.0.8N layer 631 (dopant: Mg)
of 20 nm in thickness and p-type GaN layer 632 (dopant: Mg) of 150
nm in thickness were formed successively by the MOCVD method to
produce group III nitride stack 500. Here, light emitting layer 640
has a multiple quantum well structure in which four barrier layers
made up of GaN layers each having a thickness of 10 nm and three
well layers made up of Ga.sub.0.85In.sub.0.15N layers each having a
thickness of 3 nm are alternately stacked on each other.
[0108] The PL (photoluminescence) method was used to cause thus
obtained group III nitride stack 500 to emit light, and the
intensity (PL intensity) of the light was measured. The results are
summarized in Table 5.
5. Process of Manufacturing Group III Nitride Semiconductor
Device
[0109] Further, referring to FIG. 6, on the other main surface (N
atomic surface) of the n-type GaN crystal substrate (group III
nitride crystal 1) of group III nitride stack 500 for each of
Examples E1 to E12 as described above, a stack structure made up of
a Ti layer of 200 nm in thickness, an Al layer of 1000 nm in
thickness, a Ti layer of 200 nm in thickness, and an Au layer of
2000 nm in thickness was formed and then heated in a nitrogen
atmosphere to form an n side electrode of 100 .mu.m in diameter as
first electrode 661. On p-type GaN layer 632 of group III nitride
stack 500, a stack structure made up of an Ni layer of 4 nm in
thickness and an Au layer of 4 nm in thickness was formed and then
heated in an inert gas atmosphere to form a p side electrode as
second electrode 662. The above-described stack was formed into a
chip of 400 .mu.m.times.400 .mu.m in size to produce an LED (light
emitting diode) as group III nitride semiconductor device 600.
[0110] Subsequently, the p side electrode (second electrode 662)
was bonded to conductor 682 with solder layer 670 while the n side
electrode (first electrode 661) and conductor 681 were bonded
together with wire 690 to produce semiconductor device 700
including the LED.
[0111] For each of the Examples, 200 semiconductor devices 700
including respective group III nitride semiconductor devices 600 as
described above were manufactured to examine the properties of the
devices. Of the manufactured devices, those having predetermined
properties were extracted as effective products. The manufacturing
yield (%) is shown in Table 5.
TABLE-US-00005 TABLE 5 Example E Example E1 Example E2 Example E3
Example E4 Example E5 Example E6 Example E7 lapping abrasive
material diamond diamond diamond diamond diamond diamond diamond
grain grain size 2 2 2 2 2 2 2 (.mu.m) pad on material,
polyurethane polyurethane polyurethane polyurethane polyurethane
polyurethane polyurethane surface form non-woven non-woven
non-woven non-woven non-woven non-woven non-woven plate soft
abrasive abrasive material Fe.sub.2O.sub.3 Fe.sub.2O.sub.3
Fe.sub.2O.sub.3 Fe.sub.2O.sub.3 Fe.sub.2O.sub.3 Fe.sub.2O.sub.3
Fe.sub.2O.sub.3 grain polishing grain grain size 0.5 0.5 0.5 0.5
0.5 0.5 0.5 (.mu.m) polishing acid HCl HCl HCl HCl HCl HCl HCl
solution oxidizer H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2
H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2 pH 2 2
2 2 2 2 2 ORP (mV) 700 700 700 700 700 700 700 compressibility of
0.5 0.8 2 5 10 2 2 polishing pad (%) polishing pressure (kPa) 58.8
58.8 58.8 58.8 58.8 2.9 4.9 abrasive-grain- polishing acid HCl HCl
HCl HCl HCl HCl HCl free polishing solution oxidizer H.sub.2O.sub.2
H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2
H.sub.2O.sub.2 H.sub.2O.sub.2 pH 2 2 2 2 2 2 2 ORP (mV) 700 700 700
700 700 700 700 compressibility of 8 8 8 8 8 8 8 polishing pad (%)
polishing pressure (kPa) 39.2 39.2 39.2 39.2 39.2 39.2 39.2
evaluation of impurity C (mass %) 8.9 7.2 5.5 4.8 3.2 14 7.5
crystal surface Fe (.times.10.sup.10 300 120 60 30 20 0 10
cm.sup.-2) surface roughness Ry (nm) 32 20 14 8 6.1 25 20 surface
roughness Ra (nm) 3.1 2 1.2 0.81 0.62 2.4 1.9 work-affected layer
(nm) 240 30 0 30 50 320 50 stack PL intensity (AU) 35 65 100 82 75
29 55 characteristic device yield (%) 42 71 91 85 79 36 61
characteristic Example E Example E8 Example E9 Example E10 Example
E11 Example E12 lapping abrasive material diamond diamond diamond
diamond diamond grain grain size 2 2 2 2 2 (.mu.m) pad on material,
polyurethane polyurethane polyurethane polyurethane polyurethane
surface form non-woven non-woven non-woven non-woven non-woven
plate soft abrasive abrasive material Fe.sub.2O.sub.3
Fe.sub.2O.sub.3 Fe.sub.2O.sub.3 Fe.sub.2O.sub.3 Fe.sub.2O.sub.3
grain polishing grain grain size 0.5 0.5 0.5 0.5 0.5 (.mu.m)
polishing acid HCl HCl HCl HCl HCl solution oxidizer H.sub.2O.sub.2
H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2 pH 2 2
2 2 2 ORP (mV) 700 700 700 700 700 compressibility of 2 2 2 2 2
polishing pad (%) polishing pressure (kPa) 9.8 19.6 68.6 98.1 118
abrasive-grain- polishing acid HCl HCl HCl HCl HCl free polishing
solution oxidizer H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2
H.sub.2O.sub.2 H.sub.2O.sub.2 pH 2 2 2 2 2 ORP (mV) 700 700 700 700
700 compressibility of 8 8 8 8 8 polishing pad (%) polishing
pressure (kPa) 39.2 39.2 39.2 39.2 39.2 evaluation of impurity C
(mass %) 6.1 4.9 3.8 3.2 2.8 crystal surface Fe (.times.10.sup.10
20 50 60 110 320 cm.sup.-2) surface roughness Ry (nm) 9.1 46 34 33
11 surface roughness Ra (nm) 0.82 0.45 0.31 0.37 0.91 work-affected
layer (nm) 20 0 0 30 50 stack PL intensity (AU) 72 95 98 88 65
characteristic device yield (%) 82 88 92 80 76 characteristic
[0112] Referring to Table 5, as seen from Examples E1 to E12,
through the surface treatment including the lapping step using hard
abrasive grains with a Mohs hardness higher than 7 (diamond
abrasive grains with a Mohs hardness of 10 for example), the soft
abrasive grain polishing step using a polishing solution containing
soft abrasive grains with a Mohs hardness of not more than 7
(Fe.sub.2O.sub.3 abrasive grains with a Mohs hardness of 6 for
example) and using a polishing pad with a compressibility of not
less than 0.8% and not more than 5%, performed under the condition
that the polishing pressure was not less than 4.9 kPa and not more
than 98 kPa, and the abrasive-grain-free polishing step using a
polishing solution without containing abrasive grains and having a
pH of not less than 1 and not more than 6.5 and using a polishing
pad with a compressibility of not less than 1.5% and not more than
20%, performed under the condition that the polishing pressure was
not less than 0.98 kPa and not more than 58.8 kPa, the crystal
surface having a low impurity concentration, a small depth of
depression in the high dislocation density region, a high flat
surface region ratio, and a small surface roughness Ry and a small
surface roughness Ra was obtained.
[0113] As for Example E1, the low compressibility of the polishing
pad used in the soft abrasive grain polishing step increased
surface roughness Ry and surface roughness Ra. As for Example E6,
the low polishing pressure in the soft abrasive grain polishing
step increased the concentration of impurity (C) originated from
the hard abrasive grains. As for Example E12, the high polishing
pressure in the soft abrasive grain polishing step increased the
concentration of impurity (Fe) originated from the soft abrasive
grains.
[0114] As for Examples E2 to E5 and E7 to E12, the low impurity
concentration, the small surface roughness Ra and small surface
roughness Ry, and the small thickness of the work-affected layer of
the crystal surface increased the PL intensity of the group III
nitride stack. Thus, the group III nitride semiconductor device was
produced with high yield. In contrast, as for Example E1, the high
impurity concentration and the large thickness of the work-affected
layer decreased the PL intensity of the group III nitride stack and
accordingly decreased the yield of the group III nitride
semiconductor device. As for Example E6, the high impurity
concentration and the large thickness of the work-affected layer of
the crystal surface decreased the PL intensity of the group III
nitride stack and accordingly decreased the yield of the group III
nitride semiconductor device.
Examples F1-F12
1. Lapping Step
[0115] A surface (Ga atomic surface of a low dislocation density
region and N atomic surface of a high dislocation density region)
of an n-type GaN crystal substrate (group III nitride crystal 1)
was lapped in a similar manner to Example A1, except that an n-type
GaN crystal substrate grown by the HVPE method to have facets as
formed and including a high dislocation density region and a low
dislocation density region was used as group III nitride crystal 1,
SiC abrasive grains (Mohs hardness: 9.5) with a grain size of 4
.mu.m were used as hard abrasive grains 16, and a surface plate
made of phenol resin was used as surface plate 15. Through the
lapping, the surface of the n-type GaN crystal substrate was made
specular. After the lapping, the n-type GaN crystal substrate had a
surface roughness Ry of 32 nm and a surface roughness Ra of 3.4
nm.
2. Soft Abrasive Grain Polishing Step
[0116] Subsequently, referring to FIGS. 1 and 3, the lapped n-type
GaN crystal substrate (group III nitride crystal 1) remained
secured to crystal holder 11 (corresponding to crystal holder 31 in
FIG. 3) was polished with soft abrasive grains in the following
manner. On surface plate 35 with a diameter of 300 mm placed in a
polishing apparatus (not shown), polishing pad 38 was disposed. The
surface (Ga atomic surface of the low dislocation density region
and N atomic surface of the high dislocation density region) of the
n-type GaN crystal substrate (group III nitride crystal 1) was
polished by supplying polishing solution 37 containing soft
abrasive grains 36 from polishing solution feed port 39 to
polishing pad 38 while rotating polishing pad 38 about rotational
axis 35c, and pressing the n-type GaN crystal substrate (group III
nitride crystal 1) secured to crystal holder 31 against polishing
pad 38 by putting weight 34 on crystal holder 31 while rotating the
n-type GaN crystal substrate (group III nitride crystal 1) about
rotational axis 31c of crystal holder 31.
[0117] Here, SiO.sub.2 abrasive grains (Mohs hardness: 7) with a
grain size of 0.1 .mu.m were used as soft abrasive grains 36. A
solution containing malic acid as acid and H.sub.2O.sub.2 as
oxidizer and having a pH of 2 and an ORP of 700 mV was used as
polishing solution 37 containing soft abrasive grains 36. A foam
pad of polyurethane having a compressibility shown in Table 6 was
used as polishing pad 38. An aluminum surface plate was used as
surface plate 35. The polishing was performed under the conditions
that the polishing pressure was the one shown in Table 6, the
number of rotations of the n-type GaN crystal substrate (group III
nitride crystal 1) and that of polishing pad 38 were both 30 rpm
(rotations/min) to 100 rpm (rotations/min), and the polishing time
was 60 minutes.
3. Abrasive-Grain-Free Polishing Step
[0118] The surface (Ga atomic surface of the low dislocation
density region and N atomic surface of the high dislocation density
region) of the n-type GaN crystal substrate (group III nitride
crystal 1) was polished without abrasive grains, in a similar
manner to Example A1, except that a solution containing malic acid
as acid and TICA (trichloroisocyanuric acid) as oxidizer and having
a pH of 2 and an ORP of 700 mV was used as polishing solution 27
without containing abrasive grains, a suede pad of polyurethane
having a compressibility shown in Table 6 was used as polishing pad
28, a stainless surface plate was used as surface plate 25, and the
polishing pressure was 19.6 kPa (200 gf/cm.sup.2).
[0119] Through the above-described steps, surface treatment was
performed on Examples F1 to F12 as shown in Table 6. For the
crystal surface after treated, the impurity concentration, the
depth of the depression in the high dislocation density region
(namely the difference in level between the surface of the low
dislocation density region and the surface of the high dislocation
density region), the flat surface region ratio (namely the ratio
(percentage) of the area of flat surface region 1ps of low
dislocation density region 1k to the area of the whole surface 1ks
of low dislocation density region 1k), surface roughness Ry and
surface roughness Ra, and the thickness of the work-affected layer
were measured. Here, the concentration of impurity Si (silicon),
the depth of the depression in the high dislocation density region,
the flat surface region ratio, and surface roughness Ry and surface
roughness Ra were determined similarly to Example C1. Si is
considered to be originated from the hard abrasive grains, namely
SiC abrasive grains. The thickness of the work-affected layer was
measured through observation by means of the TEM (transmission
electron microscope) of a cross section appearing by cutting the
crystal along a cleavage plane. The results are summarized in Table
6. TCIA in Table 6 represents trichloroisocyanuric acid.
4. Process of Manufacturing Group III Nitride Stack
[0120] Subsequently, referring to FIG. 5, the n-type GaN crystal
substrate (group III nitride crystal 1) polished without abrasive
grains for each of Examples F1 to F12 as described above was placed
in an MOCVD apparatus. On one main surface (Ga atomic surface of
the low dislocation density region and N atomic surface of the high
dislocation density region) of the n-type GaN crystal substrate
(group III nitride crystal 1), n-type semiconductor layer 620
including n-type GaN layer 621 (dopant: Si) of 1 .mu.m in thickness
and n-type Al.sub.0.1Ga.sub.0.9N layer 622 (dopant: Si) of 150 nm
in thickness, light emitting layer 640, and p-type semiconductor
layer 630 including p-type Al.sub.0.2Ga.sub.0.8N layer 631 (dopant:
Mg) of 20 nm in thickness and p-type GaN layer 632 (dopant: Mg) of
150 nm in thickness were formed successively by the MOCVD method to
produce group III nitride stack 500. Here, light emitting layer 640
has a multiple quantum well structure in which four barrier layers
made up of GaN layers each having a thickness of 10 nm and three
well layers made up of Ga.sub.0.85In.sub.0.15N layers each having a
thickness of 3 nm are alternately stacked on each other.
[0121] The PL (photoluminescence) method was used to cause thus
obtained group III nitride stack 500 to emit light, and the
intensity (PL intensity) of the light was measured. The results are
summarized in Table 6.
5. Process of Manufacturing Group III Nitride Semiconductor
Device
[0122] Further, referring to FIG. 6, on the other main surface (N
atomic surface of the low dislocation density region and Ga atomic
surface of the high dislocation density region) of the n-type GaN
crystal substrate (group III nitride crystal 1) of group III
nitride stack 500 for each of Examples F1 to F12 as described
above, a stack structure made up of a Ti layer of 200 nm in
thickness, an Al layer of 1000 nm in thickness, a Ti layer of 200
nm in thickness, and an Au layer of 2000 nm in thickness was formed
and then heated in a nitrogen atmosphere to form an n side
electrode of 100 .mu.m in diameter as first electrode 661. On
p-type GaN layer 632 of group III nitride stack 500, a stack
structure made up of an Ni layer of 4 nm in thickness and an Au
layer of 4 nm in thickness was formed and then heated in an inert
gas atmosphere to form a p side electrode as second electrode 662.
The above-described stack was formed into a chip of 400
.mu.m.times.400 .mu.m in size to produce an LED (light emitting
diode) as group III nitride semiconductor device 600.
[0123] Subsequently, the p side electrode (second electrode 662)
was bonded to conductor 682 with solder layer 670 while the n side
electrode (first electrode 661) and conductor 681 were bonded
together with wire 690 to produce semiconductor device 700
including the LED.
[0124] For each of the Examples, 200 semiconductor devices 700
including respective group 111 nitride semiconductor devices 600 as
described above were manufactured to examine the properties of the
devices. Of the manufactured devices, those having predetermined
properties were extracted as effective products. The manufacturing
yield (%) is shown in Table 6.
TABLE-US-00006 TABLE 6 Example F Example F1 Example F2 Example F3
Example F4 Example F5 Example F6 lapping abrasive material SiC SiC
SiC SiC SiC SiC grain grain size 4 4 4 4 4 4 (.mu.m) surface
material resin resin resin resin resin resin plate soft abrasive
abrasive material SiO.sub.2 SiO.sub.2 SiO.sub.2 SiO.sub.2 SiO.sub.2
SiO.sub.2 grain polishing grain grain size 0.1 0.1 0.1 0.1 0.1 0.1
(.mu.m) polishing acid malic acid malic acid malic acid malic acid
malic acid malic acid solution oxidizer H.sub.2O.sub.2
H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2
H.sub.2O.sub.2 pH 2 2 2 2 2 2 ORP (mV) 700 700 700 700 700 700
compressibility of 0.5 0.8 2 5 10 2 polishing pad (%) polishing
pressure (kPa) 39.2 39.2 39.2 39.2 39.2 2.9 abrasive- polishing
acid malic acid malic acid malic acid malic acid malic acid malic
acid grain-free solution oxidizer TCIA TCIA TCIA TCIA TCIA TCIA
polishing pH 2 2 2 2 2 2 ORP (mV) 1450 1450 1450 1450 1450 1450
compressibility of 8 8 8 8 8 8 polishing pad (%) polishing pressure
(kPa) 19.6 19.6 19.6 19.6 19.6 19.6 evaluation of impurity Si
(.times.10.sup.10 1200 510 270 210 170 2500 crystal surface
cm.sup.-2) depression depth of high 0.8 1.0 1.2 3.0 4.5 0.7
dislocation density region (.mu.m) flat surface region ratio (%) 90
80 60 40 30 95 surface roughness Ry (nm) 62 18 33 25 46 30 surface
roughness Ra (nm) 5.5 1.9 3.3 2.5 4.6 3.3 work-affected layer (nm)
300 30 0 50 50 500 stack PL intensify (AU) 28 68 100 53 18 22
characteristic device yield (%) 26 58 82 46 14 21 characteristic
Example F Example F7 Example F8 Example F9 Example F10 Example F11
Example F12 lapping abrasive material SiC SiC SiC SiC SiC SiC grain
grain size 4 4 4 4 4 4 (.mu.m) surface material resin resin resin
resin resin resin plate soft abrasive abrasive material SiO.sub.2
SiO.sub.2 SiO.sub.2 SiO.sub.2 SiO.sub.2 SiO.sub.2 grain polishing
grain grain size 0.1 0.1 0.1 0.1 0.1 0.1 (.mu.m) polishing acid
malic acid malic acid malic acid malic acid malic acid malic acid
solution oxidizer H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2
H.sub.2O.sub.2 H.sub.2O.sub.2 H.sub.2O.sub.2 pH 2 2 2 2 2 2 ORP
(mV) 700 700 700 700 700 700 compressibility of 2 2 2 2 2 2
polishing pad (%) polishing pressure (kPa) 4.9 9.8 19.6 68.6 98.1
118 abrasive- polishing acid malic acid malic acid malic acid malic
acid malic acid malic acid grain-free solution oxidizer TCIA TCIA
TCIA TCIA TCIA TCIA polishing pH 2 2 2 2 2 2 ORP (mV) 1450 1450
1450 1450 1450 1450 compressibility of 8 8 8 8 8 8 polishing pad
(%) polishing pressure (kPa) 19.6 19.6 19.6 19.6 19.6 19.6
evaluation of impurity Si (.times.10.sup.10 710 620 460 220 90 40
crystal surface cm.sup.-2) depression depth of high 0.75 0.8 0.85
1.8 2.6 4.2 dislocation density region (.mu.m) flat surface region
ratio (%) 90 80 75 55 45 35 surface roughness Ry (nm) 19 5.2 4 4.1
8.4 15 surface roughness Ra (nm) 2.1 0.63 0.42 0.33 0.59 0.82
work-affected layer (nm) 50 20 0 0 30 30 stack PL intensify (AU) 50
71 92 95 46 15 characteristic device yield (%) 45 60 71 75 40 12
characteristic
[0125] Referring to Table 6, as seen from Examples F1 to F12,
through the surface treatment including the lapping step using hard
abrasive grains with a Mohs hardness higher than 7 (SiC abrasive
grains with a Mohs hardness of 9.5 for example), the soft abrasive
grain polishing step using a polishing solution containing soft
abrasive grains with a Mohs hardness of not more than 7 (SiO.sub.2
abrasive grains with a Mohs hardness of 7 for example) and using a
polishing pad with a compressibility of not less than 0.8% and not
more than 5%, performed under the condition that the polishing
pressure was not less than 4.9 kPa and not more than 98 kPa, and
the abrasive-grain-free polishing step using a polishing solution
without containing abrasive grains and having a pH of not less than
1 and not more than 6.5 and using a polishing pad with a
compressibility of not less than 1.5% and not more than 20%,
performed under the condition that the polishing pressure was not
less than 0.98 kPa and not more than 58.8 kPa, the crystal surface
having a low impurity concentration, a small depth of the
depression in the high dislocation density region, a high flat
surface region ratio, and small surface roughness Ry and small
surface roughness Ra was obtained.
[0126] As for Example F1, the low compressibility of the polishing
pad used in the soft abrasive grain polishing step increased
surface roughness Ry and surface roughness Ra. As for Example F5,
the high compressibility of the polishing pad used in the soft
abrasive grain polishing step increased the depth of the depression
in the high dislocation density region. As for Example F6, the low
polishing pressure in the soft abrasive grain polishing step
increased the concentration of impurity (Si) originated from the
hard abrasive grains. As for Example F12, the high polishing
pressure in the soft abrasive grain polishing step increased the
depth of the depression in the high dislocation density region.
[0127] As for Examples F2 to F4 and F7 to F11, since the crystal
surface had a low impurity concentration, a depth of the depression
in the high dislocation density region of not more than 3 and a
flat surface region ratio of not less than 40%, the group III
nitride stack had a high PL intensity, and accordingly the group
III nitride semiconductor device was produced with high yield. In
contrast, as for Example F1, the large surface roughness Ry and
large surface roughness Ra as well as the large thickness of the
work-affected layer decreased the PL intensity of the group III
nitride stack, and accordingly the yield of the group III nitride
semiconductor device was deteriorated. As for Example F6, the high
impurity concentration of the crystal surface decreased the PL
intensity of the group III nitride stack, and accordingly the yield
of the group III nitride semiconductor device was deteriorated. As
for Examples F5 and F12, the depth of the depression in the high
dislocation density region that is larger than 3 .mu.m and the flat
surface region ratio of less than 40% decreased the PL intensity of
the group III nitride stack, and accordingly the yield of the group
III nitride semiconductor device was deteriorated.
[0128] 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 scope of the present invention being interpreted
by the terms of the appended claims.
* * * * *