U.S. patent application number 12/188214 was filed with the patent office on 2008-12-04 for group iii-v crystal.
This patent application is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD.. Invention is credited to Ryu Hirota, Seiji Nakahata, Koji Uematsu.
Application Number | 20080299748 12/188214 |
Document ID | / |
Family ID | 33432087 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080299748 |
Kind Code |
A1 |
Nakahata; Seiji ; et
al. |
December 4, 2008 |
Group III-V Crystal
Abstract
Favorable-quality III-V crystals are easily obtained at low cost
without causing cracks, even when using a variety of substrates.
The III-V crystals are obtained by manufacturing method
characterized in including: a step of depositing a metal film (2)
on a substrate (1); a step of heat-treating the metal film (2) in
an atmosphere in which a patterning compound is present; and a step
of growing a group III-V crystal (4) on the metal film after the
heat treatment. Alternatively, the III-V crystal manufacturing
method is characterized in including: a step of growing a group
III-V compound buffer film on the metal film after the heat
treatment; and a step of growing a group III-V crystal on the group
III-V compound buffer film.
Inventors: |
Nakahata; Seiji; (Itami-shi,
JP) ; Uematsu; Koji; (Itami-shi, JP) ; Hirota;
Ryu; (Itami-shi, JP) |
Correspondence
Address: |
Judge Patent Associates
Dojima Building, 5th Floor, 6-8 Nishitemma 2-Chome, Kita-ku
Osaka-Shi
530-0047
JP
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD.
Osaka-shi
JP
|
Family ID: |
33432087 |
Appl. No.: |
12/188214 |
Filed: |
August 8, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11871162 |
Oct 12, 2007 |
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12188214 |
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10521060 |
Dec 30, 2004 |
7297625 |
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11871162 |
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Current U.S.
Class: |
438/503 ;
257/E21.131; 257/E21.132 |
Current CPC
Class: |
C30B 29/403 20130101;
C30B 29/406 20130101; H01L 21/02642 20130101; C30B 25/18 20130101;
H01L 21/02378 20130101; H01L 21/02381 20130101; C30B 25/02
20130101; H01L 21/0242 20130101; C30B 29/40 20130101; H01L 21/02538
20130101; Y10T 428/12674 20150115; H01S 5/323 20130101; Y10T
428/12681 20150115 |
Class at
Publication: |
438/503 ;
257/E21.132 |
International
Class: |
H01L 21/20 20060101
H01L021/20 |
Foreign Application Data
Date |
Code |
Application Number |
May 8, 2003 |
JP |
JP-2003-129829 |
Claims
1. A method of manufacturing a crystal of a group III-V compound,
the method comprising: a physical vapor deposition step of
depositing a metal film on a substrate by either evaporation or
sputtering; a heat-treatment step of heat-treating the metal film
under an atmosphere in which a metal-film patterning compound is
present so that the metal film becomes patterned with a plurality
of grooves having an indefinite shape, the grooves having an
average width of 2 nm to 5000 nm, the metal film having an aperture
fraction of 5% to 80%, the aperture fraction being the percentage
of the surface area that the grooves occupy with respect to the
substrate total surface area; and a growth step of growing a group
III-V crystal on the post-heat-treated metal film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to crystals of group III-V
compounds and to methods of their manufacture, and more
particularly relates to methods of manufacturing good-quality group
III-V crystals without producing cracks, even with the use of a
variety of substrates.
[0003] 2. Description of the Related Art
[0004] Growing a crystal of a group III-V compound, such as GaN
crystal, on a substrate of a different material from the crystal
material, such as a sapphire substrate or a silicon (Si) substrate,
causes stress between the crystal and the substrate due to
differences in properties such as their crystal lattice constants
and thermal expansion coefficients, leading to warps and cracks;
thus, the process does not yield group III-V crystals of good
quality.
[0005] In view of this problem, a method has been carried out for
alleviating the stress between the crystals and the substrate by
depositing a film of a silicon oxide (such as SiO.sub.2) on a
sapphire substrate; patterning the silicon oxide film is by a
technique such as photolithography, and thereafter growing a group
III-V crystal onto the patterned substrate. Such a method, however,
is problematic in that it requires the patterning of the silicon
oxide film, which means the manufacturing cost is high.
[0006] Another technique that has been proposed is one in which a
GaN layer is grown on a substrate such as sapphire by a metal
organic chemical vapor deposition (MOCVD) technique, followed by
the depositing of a metal film thereon and performance of a heat
treatment to form voids in the GaN layer; thereafter, a GaN crystal
is grown. (See Japanese Unexamined Pat. App. Pub. No. 2002-343728,
for example.) Nevertheless, a problem arises with such a method
because growing a GaN layer by MOCVD leads to extremely high
manufacturing costs.
[0007] Still another technique that has been proposed is one in
which a metal film is deposited on a sapphire or like substrate and
thereafter a GaN crystal is grown. (See Japanese Unexamined Pat.
App. Pub. Nos. 2002-284600, for example.) Such a method, however,
is problematic in that the qualities of the resulting GaN crystal
are compromised because the GaN crystal is grown on a metal film
that has a different lattice constant from that of the GaN
crystal.
BRIEF SUMMARY OF THE INVENTION
[0008] An object of the present invention, brought about to resolve
the foregoing problems, is to make available good-quality group
III-V crystal that is obtained by a simple, low-cost manufacturing
method.
[0009] A group III-V compound crystal structure according to the
present invention comprises a substrate; a metal film patterned
with holes or grooves having an average width of 2 nm to 5000 nm,
at an aperture fraction of 5% to 80% with respect to the substrate
total surface area; and III-V compound grown on the metal film. The
III-V crystal in the structure may be a GaAlInN composition. The
substrate may be composed of silicon, sapphire, SiC, ZrB.sub.2, or
a Group III-V compound, and the metal film may be deposited on the
substrate and contain at least titanium or vanadium. A III-V
compound crystal structure of the present invention can exhibit a
full width at half-maximum (FWHM), by X-ray diffraction (XRD), of
150 arcsec or less.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0010] FIG. 1 illustrates one method of manufacturing a group III-V
crystal according to the present invention;
[0011] FIG. 2 illustrates another method of manufacturing a group
III-V crystal according to the present invention; and
[0012] FIG. 3A is a schematic diagram illustrating one
representative configuration of holes or grooves formed in a metal
film, and FIG. 3B is a schematic diagram illustrating another
representative configuration of holes or grooves formed in a metal
film.
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
[0013] Referring to FIG. 1, one method of manufacturing a group
III-V crystal according to the present invention is characterized
in comprising a step of depositing a metal film 2 on a substrate 1
as illustrated in FIG. 1A; a step, as represented in FIG. 1B, of
heat-treating the metal film 2 under an atmosphere in which a
patterning compound is present; and a step, as represented in FIG.
1C, of growing a group III-V crystal 4 on the metal film after the
heat treatment.
[0014] Specifically, referring to FIGS. 1 and 3, a method of
manufacturing a group III-V crystal according to the present
invention is carried out through the following steps. First, as
illustrated in FIG. 1A, a metal film 2 is deposited on a substrate
1 using a physical vapor deposition technique such as evaporation
or sputtering. Next, the metal film 2 is heat-treated under an
atmosphere in which a patterning compound is present, whereby the
metal film 2 becomes patterned in indefinite shapes as illustrated
in FIG. 1B, forming holes or grooves 12 in a worm-eaten pattern, as
illustrated in FIGS. 3A as well as 3 B, exposing the substrate 1 at
the bottoms of the holes or grooves 12. Subsequently, as
illustrated in FIG. 1C, a group III-V crystal 4 is grown, using a
technique such as a hydride vapor phase epitaxy (HVPE), onto the
metal film 2 in which the holes or grooves 12 in a worm-eaten
pattern have been formed following the heat treatment.
[0015] Herein, each of FIGS. 3A and 3B schematically illustrates a
representative configuration of holes or grooves in a worm-eaten
pattern that are formed in the metal film 2 by heat-treating the
metal film 2 under an atmosphere in which a patterning compound is
present. When the number of holes or grooves is small, a
configuration such as that of FIG. 3A tends to form, and as the
number of holes or grooves increases, a configuration such as that
of FIG. 3B tends to form.
[0016] By means of such a manufacturing method, a good-quality
group III-V crystal 4 is grown because, as will be seen from FIG.
1, the group III-V crystal 4 can pick up information from the
substrate 1 such as its crystal lattice constant. Moreover, the
formation in the metal film of the pattern of holes or grooves 12
in worm-eaten contours alleviates the stress between the group
III-V crystal 4 and the metal film 2, preventing the group III-V
crystal 4 from forming cracks. Furthermore, the manufacturing cost
is reduced because the group III-V crystal can be produced by a
vapor phase epitaxy (VPE) technique such as the HVPE technique
mentioned above, rather than by the high-cost MOCVD technique.
[0017] Referring to FIGS. 1 and 3, in the group III-V crystal
manufacturing method according to the present invention, it is
preferable that the holes or grooves formed in the metal film by
heat-treating the metal film under an atmosphere in which a
patterning compound is present have an average width W of 2 nm to
5000 nm and that the aperture fraction, which is the surface area
that holes or grooves occupy, be 5% to 80% of the total area of the
substrate. If the average width W of the holes or grooves is less
than 2 nm, the holes or grooves as formed do not reach the
substrate, making it difficult to read information from (that is,
take on the characteristics of) the substrate. If on the other hand
the average width W of the holes or grooves exceeds 5000 nm, it
becomes difficult to alleviate stress between the group III-V
crystal and the substrate. Given these perspectives, it is further
preferable that the average width W of the holes or grooves be from
5 nm to 1000 nm. Further, if the aperture fraction is less than 5%
of the total area of the substrate, the smallness of the surface
area in which the group III-V crystal is in contact with the
substrate would be prohibitive of the growing III-V crystal reading
information from the substrate. If on the other hand the aperture
fraction exceeds 80%, the excessively large extent to which the
metal film is absent would be prohibitive of alleviating stress
between the group III-V crystal and the substrate. Given these
perspectives, it is further preferable that the aperture fraction
be 10% to 50% of the total area of the substrate. Herein, aperture
fraction is defined as the percentage of surface area that the
holes or grooves occupy with respect to the total area of the
substrate, according to the following equation (1):
Aperture fraction ( % ) = ( holes or grooves occupying area ) (
substrate total surface area ) .times. 100 ( 1 ) ##EQU00001##
[0018] As for the substrate herein, a wide variety of substrates
may be used, whether the same kind as or a different kind from the
group III-V crystal to be grown, as long as its use does not
conflict with the object of the present invention. For example,
silicon, sapphire, SiC, ZrB.sub.2, or group III-V compounds are
preferable because the lattice constants of crystals of these
compounds are similar to the lattice constant of the group III-V
crystals, and thus, good-quality crystals are readily produced. It
should be noted that the group III-V compound used for the
substrate need not be the same compound as the group III-V crystal
that is to be grown thereon.
[0019] Although there are no restrictions on the metal film, a
metal film containing titanium (Ti) or vanadium (V), including such
metals and alloys as Ti, Ti--Al, V, and V--Al, is preferable from
the viewpoint of readiness for patterning.
[0020] Although not particularly limited, the thickness of the
metal film is preferably 10 nm to 1000 nm. A film thickness of less
than 10 nm is prohibitive of causing the metal film to stay in the
patterning operation, while the thickness exceeding 1000 nm is
prohibitive of exposing the substrate in the patterning operation.
In light of these factors, it is preferable that the thickness of
the metal film be 30 nm to 500 nm.
[0021] A compound that patterns the metal film means a compound,
preferable examples of which include ammonia (NH.sub.3) and
nitrogen (N.sub.2), that when a metal film is heat-treated under an
atmosphere in which the compound is present patterns into
indefinite shapes holes or grooves in worm-eaten contours in the
metal film.
[0022] Preferable heat-treating conditions for heat-treating of
metal film in an atmosphere in which a patterning compound is
present are temperatures of 800.degree. C. to 1200.degree. C. for a
duration of 0.5 minutes to 20 minutes. If the heat-treatment
temperature is less than 800.degree. C. or the heat-treatment time
is less than 0.5 minutes, insufficient patterning of the metal film
results; if the heat-treatment temperature exceeds 1200.degree. C.
or the heat-treatment time exceeds 20 minutes, the metal film is
patterned excessively. In light of these factors, it is preferable
that the heat-treatment temperature be 900.degree. C. to
1100.degree. C. and the heat-treatment time 0.5 minutes to 10
minutes.
[0023] The simple and low-cost manufacturing method described above
yields good-quality group III-V crystals. Furthermore, in cases in
which the III-V crystals in the foregoing are
Ga.sub.xAl.sub.yIn.sub.1-x-y (0.ltoreq.x.ltoreq.1 and
0.ltoreq.y.ltoreq.1), because at present there is no other
particularly serviceable manufacturing method for such crystals,
the method proves to be an invaluable manufacturing technique.
Embodiment 2
[0024] Referring to FIG. 2, another method of manufacturing a group
III-V crystal according to the present invention is characterized
in comprising: a step of depositing a metal film 2 on a substrate 1
as illustrated in FIG. 2A; a step, as represented in FIG. 2B, of
heat-treating the metal film in an atmosphere in which a patterning
compound is present; a step, as represented in FIG. 2C, of growing
a group III-V compound buffer film 3 on the metal film 2 after the
heat treatment; and a step, as represented in FIG. 2D, of growing a
group III-V crystal 4 on the group III-V compound buffer film
3.
[0025] Specifically, referring to FIGS. 2 and 3, another method of
manufacturing a group III-V crystal according to the present
invention is carried out through the following steps. First, as
illustrated in FIG. 2A, a metal film 2 is deposited on a substrate
1 using a physical vapor deposition technique such as evaporation
or sputtering. Next, the metal film 2 is heat-treated in an
atmosphere in which a patterning compound is present, whereby the
metal film 2 is patterned in indefinite shapes as illustrated in
FIG. 2B, forming holes or grooves 12 in worm-eaten contours, as
illustrated in FIG. 3A as well as 3B, so that the substrate 1 is
exposed in the bottoms of the holes or grooves 12.
[0026] Next, using, for example, an HVPE technique a group III-V
compound buffer film 3 as illustrated in FIG. 2C is grown onto the
post-heat-treated metal film 2 in which the holes or grooves 12 in
worm-eaten contours are formed. Herein, the term "a group III-V
compound buffer film" 3 refers to an amorphous film of the group
III-V compound that is grown at a lower temperature than that for
growing the crystal. Subsequently, as illustrated in FIG. 2D, a
group III-V crystal 4 is grown on the group III-V compound buffer
film 3, using, for example, an HVPE technique.
[0027] In Embodiment 2, described above, the formation onto the
metal film 2 in which holes or grooves in a worm-eaten pattern have
been formed makes it possible to alleviate the stress between the
substrate 1 and the group III-V crystal 4 that is later formed on
the group III-V compound buffer film 3. Moreover, because the group
III-V crystal 4 in growing picks up information not from the
substrate 1 but from the amorphous III-V film, even better-quality
III-V crystal--crystal that has not taken in unnecessary
crystalline information--is produced.
EXAMPLES
[0028] Embodiments 1 and 2 described above are further detailed
based on specific examples.
Example 1
[0029] Reference is made to FIG. 1. Based on Embodiment 1, by an
evaporation technique a 30 nm-thick metallic Ti film was deposited
as a metal film 2 on a substrate 1, as illustrated in FIG. 1A,
using a sapphire base as the substrate 1. Next, as represented in
FIG. 1B the metal film 2 was heat-treated within a NH.sub.3
atmosphere at 1000.degree. C. for 0.5 minutes. The surface of the
metal film 2 after its temperature was lowered was observed with a
scanning electron microscope (SEM). Holes or grooves in a
worm-eaten pattern as shown in FIG. 3A were found; the average
width W of the holes or grooves was 8 nm and the aperture fraction
was 12%. In addition, a group III-V crystal 4 as illustrated in
FIG. 1C was grown at 1000.degree. C. for a 5-hour duration by an
HVPE technique using Ga and NH.sub.3 as source materials, resulting
in a crystal free of cracks. The resulting crystal was found to be
a good-quality GaN crystal by an XRD measurement, with its full
width at half-maximum (FWHM) in the XRD being 120 arcsec. The
results are set forth in Table I.
Examples 2 to 12
[0030] With the test conditions set out in Table I, group III-V
crystals were grown by the same procedure as in Example 1. The
results are summarized in Table I.
TABLE-US-00001 TABLE I Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Ex. 7
Substrate type Sapphire Sapphire GaAs Sapphire Si AlN ZrB.sub.2
Metal Class Ti Ti Ti Ti Ti Ti Ti film (Composition: mole %) Film
thickness (nm) 30 200 200 200 200 500 200 Heat Atmosphere NH.sub.3
NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 N.sub.2 NH.sub.3 (40) treatment
(Composition: mole %) H.sub.2 (60) Temp. (.degree. C.) 1000 800
1000 1000 1100 1200 1000 Duration (min.) 0.5 10 6 3 3 10 3
Hole/groove width (nm) 8 10 110 31 280 900 32 Aperture fraction (%)
12 25 34 22 45 75 22 Crystal Source material 1 Ga Ga Ga Ga Ga Ga Ga
growth (Composition: mole %) Source material 2 NH.sub.3 NH.sub.3
NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 (Composition: mole %)
Temp. (.degree. C.) 1000 1100 1000 1000 1100 1000 1000 Duration
(hrs.) 5 5 5 5 5 5 5 Cracking incidents None None None None None
None None Crystal composition GaN GaN GaN GaN GaN GaN GaN
(XRD-identified) XRD FWHM 120 120 103 110 105 108 118 (arcsec) Ex.
8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Substrate type GaN SiC Sapphire
Sapphire Si Metal Class Ti (90) V V Ti Ti film (Composition: mole
%) Al (10) Film thickness (nm) 300 200 200 200 200 Heat Atmosphere
NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 treatment
(Composition: mole %) Temp. (.degree. C.) 1000 1000 1000 1000 1100
Duration (min.) 3 3 2 3 3 Hole/groove width (nm) 26 29 18 31 280
Aperture fraction (%) 18 11 8 22 38 Crystal Source material 1 Ga Ga
Ga (80) Al Ga (70) growth (Composition: mole %) Al (10) Al (30) In
(10) Source material 2 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3
(Composition: mole %) Temp. (.degree. C.) 1000 1100 1000 1000 1100
Duration (hrs.) 5 5 5 5 5 Cracking incidents None None None None
None Crystal composition GaN GaN Ga.sub.0.8Al.sub.0.1In.sub.0.1N
AlN Ga.sub.0.7Al.sub.0.3N (XRD-identified) XRD FWHM 135 138 150 115
97 (arcsec)
Example 13
[0031] Reference is made to FIG. 2. Based on Embodiment 2, by an
evaporation technique a 200 nm-thick metallic Ti film was deposited
as a metal film 2 on a substrate 1, as illustrated in FIG. 2A,
using a sapphire base as the substrate 1. Next, as represented in
FIG. 2B the metal film 2 was heat-treated in a NH.sub.3 atmosphere
at 1000.degree. C. for 3 minutes. The surface of the metal film 2
after its temperature was lowered was observed with an SEM. Holes
or grooves in a worm-eaten pattern as shown in FIG. 3A were found;
the average width W of the holes or grooves was 31 nm and the
aperture fraction was 22%. Next, a group III-V compound buffer film
3 as illustrated in FIG. 2C was grown at 500.degree. C. for a
0.5-hour duration. Then, a group III-V crystal 4 as illustrated in
FIG. 2D was grown at 1000.degree. C. for a 5-hour duration by an
HVPE technique using Ga and NH.sub.3 as source materials, resulting
in a crystal free of cracks. The resulting crystal was found to be
a good-quality GaN crystal by an XRD measurement, with its FWHM in
the XRD being 80 arcsec. The results are set forth in Table I.
Examples 14 to 20
[0032] With the test conditions set out in Table II, group III-V
crystals were grown in the same procedure as in Example 13. The
results are summarized in Table II.
TABLE-US-00002 TABLE II Ex. 13 Ex. 14 Ex. 15 Ex. 16 Ex. 17 Ex. 18
Ex. 19 Ex. 20 Substrate type Sapphire Si GaAs AlN GaN SiC Sapphire
Si Metal Class Ti Ti Ti Ti Ti (90) V Ti Ti film (Comp.: mole %) Al
(10) Film thickness (nm) 200 200 200 500 300 200 200 200 Heat
Atmosphere NH.sub.3 NH.sub.3 NH.sub.3 N.sub.2 NH.sub.3 NH.sub.3
NH.sub.3 NH.sub.3 treatment (Comp.: mole %) Temp. (.degree. C.)
1000 1100 1000 1200 1000 1000 1000 1100 Duration (min.) 3 3 6 10 3
3 3 3 Hole/groove width (nm) 31 280 110 900 26 29 31 280 Aperture
fraction (%) 22 45 34 75 18 11 22 38 Buffer film growth Source
material 1 Ga Ga Al Ga Ga Ga Al Ga (70) (Comp.: mole %) Al (30)
Source material 2 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3
NH.sub.3 NH.sub.3 NH.sub.3 (Comp.: mole %) Temp. (.degree. C.) 500
500 500 500 500 500 500 500 Duration (hrs.) 0.5 0.5 0.5 0.5 0.5 0.5
0.5 0.5 Crystal growth Source material 1 Ga Ga Ga Ga Ga Ga Al Ga
(70) (Comp.: mole %) Al (30) Source material 2 NH.sub.3 NH.sub.3
NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 NH.sub.3 (Comp.: mole
%) Temp. (.degree. C.) 1000 1100 1000 1000 1000 1000 1000 1100
Duration (hrs.) 5 5 5 5 5 5 5 5 Cracking incidents None None None
None None None None None Crystal composition GaN GaN GaN GaN GaN
GaN AlN Ga.sub.0.7Al.sub.0.3N (XRD-identified) XRD FWHM 80 65 72 85
88 92 90 78 (arcsec)
[0033] As is evident from Tables I and II, good-quality group III-V
crystals that are free from cracks were obtained in all of the
examples. Furthermore, it will be understood from comparisons, for
example, between Examples 4 and 13, and between Examples 11 and 19,
that the FWHMs of the crystals in the XRD analysis were reduced
from 110 arcsec to 80 arcsec and from 115 arcsec to 90 arcsec,
respectively, and that growing the buffer film prior to growing a
group III-V crystal improved the quality of the crystals
further.
[0034] It should be understood that the presently disclosed
embodiments and examples are in all respects illustrative and not
limiting. The scope of the present invention is set forth not by
the foregoing description but by the scope of the patent claims,
and is intended to include meanings equivalent to the scope of the
patent claims and all modifications within the scope.
INDUSTRIAL APPLICABILITY
[0035] As described in the foregoing, in accordance with the
present invention, the provision of a step of depositing a metal
film on a substrate, a step of heat-treating the metal film in an
atmosphere in which a patterning compound is present, and a step of
growing a group III-V crystal on the metal film after the heat
treatment, yields good-quality group III-V crystals without causing
cracks, using a simple and low-cost manufacturing method.
* * * * *