U.S. patent application number 12/884926 was filed with the patent office on 2011-04-14 for base material for growing single crystal diamond and method for producing single crystal diamond substrate.
This patent application is currently assigned to SHIN-ETSU CHEMICAL CO., LTD.. Invention is credited to Hitoshi NOGUCHI.
Application Number | 20110084285 12/884926 |
Document ID | / |
Family ID | 43854127 |
Filed Date | 2011-04-14 |
United States Patent
Application |
20110084285 |
Kind Code |
A1 |
NOGUCHI; Hitoshi |
April 14, 2011 |
BASE MATERIAL FOR GROWING SINGLE CRYSTAL DIAMOND AND METHOD FOR
PRODUCING SINGLE CRYSTAL DIAMOND SUBSTRATE
Abstract
The present invention is a base material for growing a single
crystal diamond comprising: at least a single crystal SiC
substrate; and an iridium film or a rhodium film heteroepitaxially
grown on a side of the single crystal SiC substrate where the
single crystal diamond is to be grown. As a result, there is
provided a base material for growing a single crystal diamond and a
method for producing a single crystal diamond substrate which can
grow the single crystal diamond having a large area and good
crystallinity and produce a high quality single crystal diamond
substrate at low cost.
Inventors: |
NOGUCHI; Hitoshi; (Annaka,
JP) |
Assignee: |
SHIN-ETSU CHEMICAL CO.,
LTD.
Tokyo
JP
|
Family ID: |
43854127 |
Appl. No.: |
12/884926 |
Filed: |
September 17, 2010 |
Current U.S.
Class: |
257/77 ;
257/E21.041; 257/E29.082; 438/105 |
Current CPC
Class: |
C30B 29/36 20130101;
C30B 29/04 20130101; C30B 29/16 20130101; C30B 29/02 20130101; C30B
25/18 20130101; C30B 33/08 20130101; C30B 25/06 20130101; C30B
25/183 20130101 |
Class at
Publication: |
257/77 ; 438/105;
257/E29.082; 257/E21.041 |
International
Class: |
H01L 29/16 20060101
H01L029/16; H01L 21/04 20060101 H01L021/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 13, 2009 |
JP |
2009-235992 |
Claims
1. A base material for growing a single crystal diamond comprising:
at least a single crystal SiC substrate; and an iridium film or a
rhodium film heteroepitaxially grown on a side of the single
crystal SiC substrate where the single crystal diamond is to be
grown.
2. The base material for growing a single crystal diamond according
to claim 1, wherein crystal structure of the single crystal SiC
substrate is cubic .beta.-SiC.
3. The base material for growing a single crystal diamond according
to claim 1, wherein a thickness of the single crystal SiC substrate
is 0.03 mm to 20.00 mm.
4. The base material for growing a single crystal diamond according
to claim 2, wherein a thickness of the single crystal SiC substrate
is 0.03 mm to 20.00 mm.
5. The base material for growing a single crystal diamond according
to claim 1, wherein the iridium film or the rhodium film is
heteroepitaxially grown by a sputtering method.
6. The base material for growing a single crystal diamond according
to claim 1, wherein a thickness of the iridium film or the rhodium
film is 5 .ANG. to 100 .mu.m.
7. The base material for growing a single crystal diamond according
to claim 2, wherein a thickness of the iridium film or the rhodium
film is 5 .ANG. to 100 .mu.m.
8. The base material for growing a single crystal diamond according
to claim 3, wherein a thickness of the iridium film or the rhodium
film is 5 .ANG. to 100 .mu.m.
9. The base material for growing a single crystal diamond according
to claim 4, wherein a thickness of the iridium film or the rhodium
film is 5 .ANG. to 100 .mu.m.
10. The base material for growing a single crystal diamond
according to claim 5, wherein a thickness of the iridium film or
the rhodium film is 5 .ANG. to 100 .mu.m.
11. The base material for growing a single crystal diamond
according to claim 1, wherein a surface of the iridium film or the
rhodium film is subjected to a bias treatment.
12. The base material for growing a single crystal diamond
according to claim 1, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
13. The base material for growing a single crystal diamond
according to claim 2, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
14. The base material for growing a single crystal diamond
according to claim 3, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
15. The base material for growing a single crystal diamond
according to claim 4, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
16. The base material for growing a single crystal diamond
according to claim 5, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
17. The base material for growing a single crystal diamond
according to claim 6, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
18. The base material for growing a single crystal diamond
according to claim 7, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
19. The base material for growing a single crystal diamond
according to claim 8, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
20. The base material for growing a single crystal diamond
according to claim 9, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
21. The base material for growing a single crystal diamond
according to claim 10, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
22. The base material for growing a single crystal diamond
according to claim 11, further comprises a MgO film
heteroepitaxially grown between the single crystal SiC substrate
and the iridium film or the rhodium film.
23. The base material for growing a single crystal diamond
according to claim 12, wherein the MgO film is heteroepitaxially
grown on the single crystal SiC substrate by a sputtering method or
an electron beam evaporation method.
24. The base material for growing a single crystal diamond
according to claim 12, wherein a thickness of the MgO film is 5
.ANG. to 100 .mu.m.
25. A method for producing a single crystal diamond substrate
comprising at least the steps of: preparing a single crystal SiC
substrate; heteroepitaxially growing an iridium film or a rhodium
film over the prepared single crystal SiC substrate;
heteroepitaxially growing a single crystal diamond on the iridium
film or the rhodium film heteroepitaxially grown; and separating
the single crystal diamond heteroepitaxially grown to obtain the
single crystal diamond substrate.
26. The method for producing a single crystal diamond substrate
according to claim 25, wherein the step of heteroepitaxially
growing a MgO film on the single crystal SIC substrate is performed
before the step of heteroepitaxially growing the iridium film or
the rhodium film and the iridium film or the rhodium film is
heteroepitaxially grown on the MgO film.
27. The method for producing a single crystal diamond substrate
according to claim 25, wherein before the step of heteroepitaxially
growing the single crystal diamond, a bias treatment is
preliminarily performed on a surface of the iridium film or the
rhodium film.
28. The method for producing a single crystal diamond substrate
according to claim 26, wherein before the step of heteroepitaxially
growing the single crystal diamond, a bias treatment is
preliminarily performed on a surface of the iridium film or the
rhodium film.
29. The method for producing a single crystal diamond substrate
according to claim 25, wherein the single crystal diamond is
heteroepitaxially grown by a microwave CVD method or a
direct-current plasma CVD method in the step of heteroepitaxially
growing the single crystal diamond.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a base material for growing
a single crystal diamond and a method for producing a single
crystal diamond substrate.
[0003] 2. Description of the Related Art
[0004] Diamond has a wide band gap of 5.47 eV and a very high
dielectric breakdown electric field intensity of 10 MV/cm, and it
has the highest thermal conductivity in materials. Therefore, if
this is used for an electronic device, the device is advantageous
as a high output power device.
[0005] Furthermore, the diamond has a high drift mobility and is
the most advantageous as a high speed power device among
semiconductors in comparison of Johnson performance index.
[0006] The diamond is thus said to be the ultimate semiconductor
suitable for high frequency/high power electronic devices, and
accordingly studies of various kinds of electronic devices using a
single crystal diamond as a substrate have progressed.
[0007] Now, a single crystal diamond for producing a diamond
semiconductor is, in many cases, the diamond referred to as an Ib
type formed by a high-pressure-high-temperature method (HPHT) or an
IIa type of which purity is enhanced.
[0008] However, it is difficult to grow in size, while the HPHT
single crystal diamond having high crystallinity can be obtained.
In addition, a price of the diamond becomes extremely high when its
size becomes big and consequently, it is difficult to put it into
practical use as the substrate for the devices.
[0009] In view of this, a CVD single crystal diamond formed by a
vapor deposition method has been also studied to provide a low-cost
single crystal diamond substrate having a large area.
[0010] Recently, there was reported a homoepitaxial CVD single
crystal diamond that is homoepitaxially grown directly on the HPHT
single crystal diamond base material (a seed base material) by the
vapor deposition method (the 20th diamond symposium lecture summary
(2006), pp. 6-7).
[0011] However, in this method, since the base material and the
single crystal diamond grown are composed of the same material, it
is difficult to separate these, and there are cost problems that
the base material needs implanting ions in advance, a lengthy wet
etching separation treatment after the growth and the like. There
is also another problem that crystallinity of the single crystal
diamond to be obtained deteriorates to a certain degree due to the
ion implantation of the base material.
[0012] As an alternative, there was reported a CVD single crystal
diamond heteroepitaxially grown by a CVD method on a single crystal
iridium (Ir) film heteroepitaxially grown on a single crystal MgO
base material (the seed base material) (Jpn. J. Appl. Phys. Vol. 35
(1996), pp. L1072-L1074).
[0013] However, in this method, there is a problem that the base
material and the single crystal diamond grown are finely broken due
to stress generated between the single crystal MgO substrate and
the single crystal diamond grown via the single crystal Ir film
(sum of internal stress and heat stress). Moreover, the
crystallinity of the single crystal diamond to be obtained does not
achieve a satisfactory level since crystallinity of an available
single crystal MgO that is the seed base material is not
sufficient.
SUMMARY OF THE INVENTION
[0014] The present invention was accomplished in view of the
aforementioned problems, and it is an object of the present
invention to provide a base material for growing a single crystal
diamond and a method for producing a single crystal diamond
substrate which can grow the single crystal diamond having a large
area and good crystallinity and produce a high quality single
crystal diamond substrate at low cost.
[0015] In order to accomplish the above object, the present
invention provides a base material for growing a single crystal
diamond comprising: at least a single crystal SiC substrate; and an
iridium film or a rhodium film heteroepitaxially grown on a side of
the single crystal SiC substrate where the single crystal diamond
is to be grown.
[0016] In case of the single crystal SiC substrate as described
above, since the single crystal. SiC substrate having good
crystallinity can be obtained at relatively low cost, a good
epitaxial growth can be performed on the substrate surface and
crystallinity of the iridium film or the rhodium film becomes good
by growing it directly or through other layers. The single crystal
diamond having high crystallinity can be thereby obtained by
growing the single crystal diamond on the base material having good
crystallinity. Moreover, in case of the single crystal SiC
substrate, since the thermal expansion coefficient of SiC is
relatively near to that of diamond, the stress generated due to
thermal expansion is small during the growth of the single crystal
diamond, and the single crystal diamond and the base material are
scarcely broken. When the base material has the iridium film or the
rhodium film on the single crystal SiC substrate, it functions as a
good buffer layer during the growth of the single crystal
diamond.
[0017] As described above, the base material for growing a single
crystal diamond according to the present invention can grow the
single crystal diamond having a large area and high crystallinity
at low cost.
[0018] In this case, crystal structure of the single crystal SiC
substrate is preferably cubic .beta.-SiC.
[0019] In this manner, when the crystal structure of the single
crystal SiC substrate is cubic .beta.-SiC, the base material can
grow the single crystal diamond having higher crystallinity.
[0020] In this case, a thickness of the single crystal SiC
substrate is preferably 0.03 mm to 20.00 mm.
[0021] The single crystal SiC substrate having the thickness as
described above enables handling to make easy, and when the
thickness is 20.00 mm or less, a double-side polishing and the like
can be performed well and cost is not excessive.
[0022] In this case, the iridium film or the rhodium film can be
heteroepitaxially grown by a sputtering method.
[0023] In this manner, the iridium film or the rhodium film of the
base material according to the present invention can be
heteroepitaxially grown by the sputtering method.
[0024] In this case, a thickness of the iridium film or the rhodium
film is preferably 5 .ANG.to 100 .mu.m.
[0025] In this manner, when the thickness of the iridium film or
the rhodium film is 5 .ANG.or more, film thickness uniformity and
the crystallinity is sufficiently high. When the thickness is 100
.mu.m or less, the stress generated between the base material and
the single crystal diamond is small, thereby the single crystal
diamond can be surely grown and moreover the base material becomes
low-cost.
[0026] In this case, a surface of the iridium film or the rhodium
film is preferably subjected to a bias treatment.
[0027] In this manner, the base material subjected to the bias
treatment forms a diamond nucleus on its surface and can thereby
grow the single crystal diamond with good crystallinity at a
sufficient growth rate.
[0028] In this case, the base material preferably comprises a MgO
film heteroepitaxially grown between the single crystal SiC
substrate and the iridium film or the rhodium film.
[0029] In this manner, when the base material according to the
present invention comprises the MgO film, the iridium film or the
rhodium film can be formed thereon with better crystallinity. In
addition, in the case of separating the grown single crystal
diamond, the MgO film can be used as a good separation layer, and
thereby the base material can be easily separated to provide a
single crystal diamond substrate.
[0030] In this case, the MgO film can be heteroepitaxially grown on
the single crystal SiC substrate by a sputtering method or an
electron beam evaporation method.
[0031] In this manner, the MgO film of the base material according
to the present invention can be grown by the sputtering method or
the electron beam evaporation method.
[0032] In this case, a thickness of the MgO film is preferably 5
.ANG. to 100 .mu.m.
[0033] In this manner, when the thickness of the MgO film is 5
.ANG.or more, film thickness uniformity and the crystallinity
become higher. When the thickness is 100 .mu.m or less, the stress
generated between the base material and the single crystal diamond
is small, thereby the single crystal diamond can be surely grown
and moreover the base material becomes low-cost.
[0034] Furthermore, the present invention provides a method for
producing a single crystal diamond substrate comprising at least
the steps of: preparing a single crystal SiC substrate;
heteroepitaxially growing an iridium film or a rhodium film over
the prepared single crystal SiC substrate; heteroepitaxially
growing a single crystal diamond on the iridium film or the rhodium
film heteroepitaxially grown; and separating the single crystal
diamond heteroepitaxially grown to obtain the single crystal
diamond substrate.
[0035] In case of the single crystal SiC substrate as described
above, the substrate having good crystallinity can be prepared at
low cost, the iridium film or the rhodium film can be grown over
the single crystal SiC substrate with good crystallinity, and the
single crystal diamond having high crystallinity can be grown on
the iridium film or rhodium film having good crystallinity.
Moreover, in case of the single crystal SiC substrate, since the
stress due to thermal expansion generated during the growth of the
single crystal diamond is small, both of the single crystal SiC
substrate and the single crystal diamond are scarcely broken.
[0036] As described above, the method for producing according to
the present invention can efficiently produce the single crystal
diamond substrate having high crystallinity at low cost.
[0037] In this case, it is preferable that the step of
heteroepitaxially growing a MgO film on the single crystal SiC
substrate is performed before the step of heteroepitaxially growing
the iridium film or the rhodium film and the iridium film or the
rhodium film is heteroepitaxially grown on the MgO film.
[0038] In this manner, when the MgO film is grown before the
iridium film or the rhodium film is grown, the iridium film or the
rhodium film can be grown thereon with better crystallinity. In
addition, the single crystal diamond can be easily separated by
using the MgO film as a separation layer in the step of the
separation.
[0039] In this case, before the step of heteroepitaxially growing
the single crystal diamond, a bias treatment is preferably
preliminarily performed on a surface of the iridium film or the
rhodium film.
[0040] In this manner, when the bias treatment is preliminarily
performed, a diamond nucleus is formed on the surface and the
single crystal diamond can be grown with good crystallinity at a
sufficient growth rate.
[0041] In this case, the single crystal diamond can be
heteroepitaxially grown by a microwave CVD method or a
direct-current plasma CVD method in the step of heteroepitaxially
growing the single crystal diamond.
[0042] In this manner, the single crystal diamond can be
heteroepitaxially grown by the microwave CVD method or the
direct-current plasma CVD method in the method for producing
according to the present invention.
[0043] As described above, the base material for growing a single
crystal diamond and the method for producing a single crystal
diamond substrate according to the present invention can grow the
single crystal diamond having a large area and high crystallinity
at low cost and produce a high quality single crystal diamond
substrate at good productivity.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 are schematic views showing an example of embodiments
of the base material for growing a single crystal diamond according
to the present invention; and
[0045] FIG. 2 are flow charts showing an example of embodiments of
the method for producing a single crystal diamond substrate
according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Conventionally, in an attempt to obtain the single crystal
diamond by a cost-advantageous CVD method, there are problems that
a portion of the single crystal diamond grown cannot be easily
separated without damage and it is difficult to grow the single
crystal diamond having high crystallinity and a large area.
Accordingly, the present inventor repeatedly keenly conducted
studies on a type and structure of the base material and a method
for producing a single crystal.
[0047] As a result, the present inventor found that when the single
crystal SiC substrate, in which the difference in a linear
expansion coefficient from the diamond is relatively small, is used
as the seed base material, which mainly generates the stress at an
interface between a single crystal diamond layer and the base
material, the stress generated due to thermal expansion is smaller
in comparison with the case of using a conventional MgO seed base
material and that a break of all of them can be consequently
prevented (the linear expansion coefficient diamond:
1.1.times.10.sup.-6/K, SiC:6.6.times.10.sup.-6/K,
MgO:13.8.times.10.sup.-6/K).
[0048] In addition, the single crystal SiC substrate having higher
crystallinity in comparison with the conventional MgO seed base
material can be relatively easily obtained, and when the single
crystal SiC substrate is used as the seed base material, the single
crystal Ir (iridium) film or the single crystal Rh (rhodium) film
can be heteroepitaxially grown over the substrate with good
crystallinity. The present inventor also found that when these high
crystallinity materials are used for the base material and the
single crystal diamond is heteroepitaxially grown thereon by the
CVD method, the single crystal diamond having high crystallinity
can be obtained. The present inventor further confirmed that the
single crystal diamond grown on this base material can be also
separated by a wet etching method and a mechanical polishing
method, and brought the present invention to completion.
[0049] Hereinafter, an example of embodiments of the present
invention will be explained in detail with reference to the
drawings. However the present invention is not restricted
thereto.
[0050] FIG. 1 are schematic views showing an example of embodiments
of the base material for growing a single crystal diamond according
to the present invention.
[0051] FIG. 2 are flow charts showing an example of embodiments of
the method for producing a single crystal diamond substrate
according to the present invention.
[0052] The base material for growing a single crystal diamond 10
according to the present invention as shown in FIG. 1(a) comprises
the single crystal SiC substrate 11, the iridium film or the
rhodium film 12 heteroepitaxially grown on the side of the single
crystal SiC substrate 11 where the single crystal diamond is to be
grown.
[0053] In the event that the seed base material is the single
crystal SiC substrate as described above, since the single crystal
SiC substrate having good crystallinity can be obtained at low
cost, the iridium film or the rhodium film grown directly or
through other layers on the substrate surface having good
crystallinity has good crystallinity. The single crystal diamond
having high crystallinity can be obtained by growing the single
crystal diamond on the base material. Moreover, in case of the
single crystal SiC substrate, since the thermal expansion
coefficient of SiC is relatively near to that of diamond, the
single crystal diamond and the base material itself are scarcely
broken by the stress due to thermal expansion during the growth of
the single crystal diamond and the like. When the base material has
the iridium film or the rhodium film on the single crystal SiC
substrate, it functions as a good buffer layer during the growth of
the single crystal diamond.
[0054] On the other hand, the base material for growing a single
crystal diamond 10' according to the present invention as shown in
FIG. 1(b) comprises the MgO film 13 heteroepitaxially grown between
the single crystal SiC substrate 11 and the iridium film or the
rhodium film 12.
[0055] As described above, when the base material according to the
present invention has the MgO film, the iridium film or the rhodium
film can be formed thereon with better crystallinity. In addition,
in the case of separating the grown single crystal diamond, the MgO
film can be used as a good separation layer, and thereby the base
material can be easily separated to provide the single crystal
diamond substrate.
[0056] Hereinafter, an example of a method of fabricating the base
material for growing a single crystal diamond as described above
and the method for producing a single crystal diamond substrate
according to the present invention will be explained with reference
to FIG. 2.
[0057] First, as shown in FIG. 2(a), the single crystal SiC
substrate 11 is prepared in the present invention. As described
above, when the single crystal. SiC substrate is used as the seed
base material, the single crystal SiC substrate having higher
crystallinity in comparison with the conventional MgO seed base
material can be relatively easily obtained, and thereby a good
epitaxial growth can be performed on the substrate surface.
[0058] In this case, the single crystal SiC substrate 11 to be
prepared is not restricted in particular, but its crystal structure
is preferably cubic .beta.-SiC.
[0059] As described above, when the crystal structure of the single
crystal SiC substrate is cubic .beta.-SiC, the base material can
grow the single crystal diamond having better crystallinity.
[0060] Next, as shown in FIG. 2(b), the MgO film 13 is preferably
heteroepitaxially grown on the single crystal SiC substrate 11, for
example, by the sputtering method or the electron beam evaporation
method.
[0061] As described above, when the MgO film is formed, the iridium
film or the rhodium film can be grown thereon with better
crystallinity. In addition, at the time of separating the single
crystal diamond in a subsequent step, the MgO film, which has
relatively low chemical resistance, can be used as the separation
layer, and the single crystal diamond can be easily separated by
etching of the MgO film portion. Although the linear expansion
coefficient of the MgO is greatly different from that of the
diamond, the MgO is a form of a film in the present invention and
can thereby absorb the stress, and it does not particularly become
issue with regard to the growth of the single crystal diamond.
[0062] Growth conditions and the like are not restricted in
particular, but the thickness of the MgO film 13 is preferably 5
.ANG. to 100 .mu.m.
[0063] As described above, when the thickness of the MgO film is 5
.ANG. or more, the film thickness uniformity and the crystallinity
can be made high. When the thickness is 100 .mu.m or less, the
stress generated between the seed base material portion and the
single crystal diamond is small, thereby the single crystal diamond
can be more surely grown, and moreover the base material becomes
cost-advantageous and low-cost.
[0064] However, it is not necessarily to form the MgO film in the
present invention.
[0065] Next, as shown in FIG. 2(c), the iridium film or the rhodium
film 12 is heteroepitaxially grown, for example, by the sputtering
method.
[0066] In this case, the growth conditions and the like are not
restricted in particular. For example, it can be grown at a
sufficient growth rate by the R. F. magnetron sputtering method. In
the event that the MgO film 13 is not formed in a previous step,
the iridium film or the rhodium film 12 can be also directly grown
on a surface of the single crystal SiC substrate 11. Since the
single crystal SiC substrate that is the seed base material has
good crystallinity, the iridium film or the rhodium film 12 grown
as described above can be easily grown directly on the substrate
surface or through the MgO film with good crystallinity.
[0067] The thickness of the iridium film or the rhodium film 12 is
preferably 5 .ANG. to 100 .mu.m.
[0068] As described above, when the thickness of the iridium film
or the rhodium film is grown up to 5 .ANG. or more, the film
thickness uniformity and the crystallinity can be made higher. When
the thickness is 100 .mu.m or less, the stress generated between
the base material and the single crystal diamond is small, thereby
the single crystal diamond can be more surely grown and moreover
the cost can be reduced.
[0069] The base material for growing a single crystal diamond 10'
according to the present invention in the case of growing the MgO
film 13 can be fabricated by the foregoing way.
[0070] Here, before the growth of the single crystal diamond in a
subsequent step, the bias treatment is preferably performed on the
surface of the iridium film or the rhodium film 12 of the base
material for growing a single crystal diamond 10'.
[0071] This bias treatment first performs a pretreatment for
forming the diamond nucleus by a direct-current discharge in which
an electrode of the base material side is set at a cathode in
advance so that the diamond nucleus having a uniform crystal
orientation on the surface of the iridium film or the rhodium film
is formed, for example, by the method as described in Japanese
Patent Laid-open (Kokai) No. 2007-238377. Accordingly, the single
crystal diamond can be grown with good crystallinity at a
sufficient growth rate in a subsequent step.
[0072] Next, as shown in FIG. 2(d), the single crystal diamond 14
is heteroepitaxially grown, for example, by the microwave CVD
method or the direct-current plasma CVD method.
[0073] As described above, in the case of growing the single
crystal diamond on the base material according to the present
invention, since the single crystal SiC substrate is used as the
seed base material, which is the thickest among the base material
and is apt to generate the stress due to thermal expansion, the
stress is hard to generate during the growth of the single crystal
diamond and the break can be prevented. In addition, since the
iridium film or the rhodium film has good crystallinity, the single
crystal diamond having high crystallinity can be grown.
[0074] Next, as shown in FIG. 2(e), the single crystal diamond
substrate 15 is obtained by separating the single crystal diamond
14.
[0075] The method of separating it is not restricted in particular.
For example, after dividing it into the single crystal diamond/the
iridium film or the rhodium film and the MgO film/the single
crystal SiC substrate by immersing it into the wet etching solution
such as phosphoric acid solution, hot mixed acid or the like, the
single crystal diamond substrate can be obtained by removing the
remaining iridium film or the rhodium film by the mechanical
polishing method. As described above, the single crystal diamond
can be easily separated by using the MgO film as the separation
layer. In the case of not growing the MgO film, since the single
crystal SiC substrate, the iridium film and the rhodium film are
composed of high chemical resistance materials, it is difficult to
separate the single crystal diamond by etching. In this case, the
iridium film/the single crystal SiC substrate may be removed by a
mechanical polishing method at once or it may be cut with laser at
the vicinity of the interfaces between the single crystal diamond
and the iridium film or the rhodium film, without immersing it into
the wet etching solution. The method of the separation by the
polishing or the laser can be also applied in the case of forming
the MgO film.
[0076] In the present invention, when the MgO film 13 is used as
the separation layer or the cutting with the laser is performed in
the step of the separation, the single crystal SiC substrate 11
after the separation can be reused as the seed base material by
performing polishing until its surface is approximately exposed.
This enables production cost of the single crystal diamond
substrate to be more reduced.
[0077] Using the base material for growing a single crystal diamond
and the method for producing a single crystal diamond substrate
according to the present invention as described above enables the
single crystal diamond substrate having a large area and high
crystallinity, which is usable for device application, to be
produced at low cost.
EXAMPLES
[0078] Hereinafter, the present invention will be more specifically
explained by showing Examples and Comparative Examples. However,
the present invention is not restricted thereto.
Example 1
[0079] As the seed base material, there was prepared a
double-side-polished single crystal .beta.-SiC substrate having a
diameter of 20.0 mm, a thickness of 0.25 mm and an orientation
(100). The MgO film having a thickness of 0.1 .mu.m was epitaxially
grown, by the electron beam evaporation method, on the side of the
seed base material where the single crystal diamond was to be grown
in a vacuum under the conditions of a substrate temperature of
800.degree. C.
[0080] Next, the iridium (Ir) film was heteroepitaxially grown on
the single crystal MgO film. The film-forming was completed by
performing the sputtering with the R. F. magnetron sputtering
method in which an target was Ir under the conditions of an Ar gas
of 8 Pa (6.times.10.sup.-2 Torr) and a substrate temperature of
700.degree. C., until a thickness of the single crystal Ir film
became 1.5 .mu.m.
[0081] For the sake of electrical continuity in the bias treatment
and the direct-current plasma CVD, the Ir film having a thickness
of 1.5 .mu.m was also grown on a back surface under the same
conditions except for making the base material temperature 100
C.degree..
[0082] Next, the bias treatment was performed for forming the
diamond nucleus on the surface of the single crystal Ir film of the
base material.
[0083] First, the base material was placed on a negative
voltage-applying electrode (cathode) of a bias treatment apparatus,
and then vacuum exhaust was performed. Next, after the base
material was heated to 600 C.degree., a hydrogen-diluted methane
gas of 3 vol. % was introduced so that pressure became 160 hPa (120
Torr). Then, the bias treatment was performed. That is, DC voltage
was applied to both the electrodes to apply a prescribed DC
electricity.
[0084] Finally, the single crystal diamond was heteroepitaxially
grown on the base material subjected to the bias treatment at 900
C..degree. for 30 hours by the direct-current plasma CVD
method.
[0085] After finishing the growth, a product taken out from a bell
jar was a laminated structure of the diamond/Ir/MgO/SiC without the
break. It was divided into the diamond/Ir and the MgO/SiC by the
wet etching with hot mixed acid. Then, the Ir film was removed by
the mechanical polishing method to get self-standing structure of
the single crystal diamond (the single crystal diamond substrate).
The surface was also subjected to a final polishing so that it was
finished so as to have surface roughness of a usable level for
device application.
[0086] It was confirmed that the obtained single crystal diamond
substrate had sufficient crystallinity as a result of evaluation by
raman spectroscopy, XRD rocking curve, X-sectional TEM and
cathodoluminescence (CL).
[0087] On the other hand, the base material after the separation
was polished until a clean surface of the single crystal SiC was
approximately exposed so that it was able to be reused as the
single crystal SiC substrate of the seed base material.
Example 2
[0088] Except for heteroepitaxially growing the It film directly
without forming the MgO film on the .beta.-SiC substrate that was
the seed base material, the single crystal diamond was
heteroepitaxially grown as with Example 1.
[0089] A product taken out from the bell jar was a laminated
structure of the diamond/Ir/SiC without the break. In this case,
since the product was composed of only high chemical resistance
materials and was not able to separate by the wet etching with hot
mixed acid, it was cut with laser at the vicinity of the interfaces
between the diamond and the Ir to get self-standing structure of
the single crystal diamond (the single crystal diamond substrate).
The surface was also subjected to a final polishing so that it was
finished so as to have surface roughness of a usable level for
device application.
[0090] It was confirmed that the obtained single crystal diamond
substrate had sufficient crystallinity as a result of evaluation by
raman spectroscopy, XRD rocking curve, X-sectional TEM and
cathodoluminescence (CL).
[0091] On the other hand, the base material after the separation
was polished until a clean surface of the single crystal SiC was
approximately exposed so that it was able to be reused as the
single crystal SiC substrate of the seed base material.
Comparative Example 1
[0092] Except for using a double-side-polished single crystal MgO
substrate having a 5.0 mm square, a thickness of 0.5 mm and an
orientation (100) as the seed base material, there was prepared the
base material by the Ir growth and the bias treatment, and the
single crystal diamond was heteroepitaxially grown thereon by the
direct-current plasma CVD method as with Example 1.
[0093] Then, the bell jar was opened to observe the product in the
chamber. As a result, both of the base material and a portion of
the single crystal diamond were broken into fine pieces having an
approximate 1.0 mm square. One of the pieces was taken out and its
crystallinity was evaluated. As a result, it was observed that
raman full width at half maximum was wide, a lot of dislocation
defects existed in X-sectional TEM and the like and thus the
crystallinity was an insufficient level for device application.
Comparative Example 2
[0094] Except for using a double-side-polished single crystal MgO
substrate having a 5.0 mm square, a thickness of 120 .mu.m and an
orientation (100) as the seed base material, there was prepared the
base material by the Ir growth and the bias treatment, and the
single crystal diamond was heteroepitaxially grown thereon by the
direct-current plasma CVD method as with Example 1.
[0095] Then, the bell jar was opened to observe the product in the
chamber. As a result, both of the base material and a portion of
the single crystal diamond were broken into fine pieces having an
approximate 1.0 mm square.
[0096] It is to be noted that the present invention is not
restricted to the foregoing embodiment. The embodiment is just an
exemplification, and any examples that have substantially the same
feature and demonstrate the same functions and effects as those in
the technical concept described in claims of the present invention
are included in the technical scope of the present invention.
* * * * *