U.S. patent application number 15/036692 was filed with the patent office on 2017-01-12 for methods of fabricating synthetic diamond materials using microwave plasma activated chemical vapour deposition techniques and products obtained using said methods.
This patent application is currently assigned to ELEMENT SIX TECHNOLOGIES LIMITED. The applicant listed for this patent is ELEMENT SIX TECHNOLOGIES LIMITED. Invention is credited to JOHN BRANDON, STEVEN COE, IAN FRIEL, RIZWAN KHAN, MATTHEW MARKHAM, KATHARINE ROBERTSON, GEOFFREY SCARSBROOK, DANIEL TWITCHEN, JONATHAN WILMAN, CHRISTOPHER WORT.
Application Number | 20170009376 15/036692 |
Document ID | / |
Family ID | 49883764 |
Filed Date | 2017-01-12 |
United States Patent
Application |
20170009376 |
Kind Code |
A1 |
KHAN; RIZWAN ; et
al. |
January 12, 2017 |
METHODS OF FABRICATING SYNTHETIC DIAMOND MATERIALS USING MICROWAVE
PLASMA ACTIVATED CHEMICAL VAPOUR DEPOSITION TECHNIQUES AND PRODUCTS
OBTAINED USING SAID METHODS
Abstract
A method of fabricating synthetic diamond material using a
microwave plasma activated chemical vapour deposition technique is
provided which utilizes high and uniform microwave power densities
applied over large areas and for extended periods of time. Products
fabricated using such a synthesis technique are described including
a single crystal CVD diamond layer which has a large area and a low
nitrogen concentration, and a high purity, fast growth rate single
crystal CVD diamond material.
Inventors: |
KHAN; RIZWAN; (MAIDENHEAD,
GB) ; COE; STEVEN; (DIDCOT, GB) ; WILMAN;
JONATHAN; (DIDCOT, GB) ; TWITCHEN; DANIEL;
(DIDCOT, GB) ; SCARSBROOK; GEOFFREY; (DIDCOT,
GB) ; BRANDON; JOHN; (DIDCOT, GB) ; WORT;
CHRISTOPHER; (DIDCOT, GB) ; MARKHAM; MATTHEW;
(DIDCOT, GB) ; FRIEL; IAN; (DIDCOT, GB) ;
ROBERTSON; KATHARINE; (DIDCOT, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ELEMENT SIX TECHNOLOGIES LIMITED |
Didcot Oxfordshire |
|
GB |
|
|
Assignee: |
ELEMENT SIX TECHNOLOGIES
LIMITED
DIDCOT, OXFORDSHIRE
GB
|
Family ID: |
49883764 |
Appl. No.: |
15/036692 |
Filed: |
November 18, 2014 |
PCT Filed: |
November 18, 2014 |
PCT NO: |
PCT/EP2014/074864 |
371 Date: |
May 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C30B 25/105 20130101;
C30B 29/04 20130101; C23C 16/274 20130101; C23C 16/511
20130101 |
International
Class: |
C30B 25/10 20060101
C30B025/10; C23C 16/511 20060101 C23C016/511; C30B 29/04 20060101
C30B029/04; C23C 16/27 20060101 C23C016/27 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 18, 2013 |
GB |
1320304.7 |
Claims
1. A single crystal CVD diamond layer comprising: a total nitrogen
concentration as measures by secondary ion mass spectrometry of no
more than 2 ppm; and an area of at least 324 mm.sup.2.
2. A single crystal CVD diamond layer according to claim 1, wherein
the total nitrogen concentration is no more than 1.5 ppm, 1.0 ppm,
0.8 ppm, 0.5 ppm 0.1 ppm, 0.05 ppm, or 0.01 ppm.
3. A single crystal CVD diamond layer according to claim 1, wherein
the area of the single crystal CVD diamond layer is at least 361
mm.sup.2, 400 mm.sup.2, 484 mm.sup.2, 625 mm.sup.2, 900 mm.sup.2,
1600 mm.sup.2, or 2500 mm.sup.2.
4. A single crystal CVD diamond layer according to claim 1, wherein
the single crystal CVD diamond layer has a thickness of at least 30
micrometers, 60 micrometers, 100 micrometers, 150 micrometers, 200
micrometers, 250 micrometers, 300 micrometers, or 500
micrometers.
5. A single crystal CVD diamond layer according to claim 1, wherein
the single crystal CVD diamond layer is comprises a plurality of
inter-crossing dislocation lines.
6. A single crystal CVD diamond layer according to claim 1, wherein
the single crystal CVD diamond layer exhibit one or both of the
following characteristics: (i) an optical absorption coefficient at
a wavelength of 1.064 .mu.m of less than 0.09 cm.sup.-1, 0.05
cm.sup.-1, 0.02 cm.sup.-1, or 0.01 cm.sup.-1. (ii) an optical
absorption coefficient at a wavelength of 10.6 .mu.m of less than
0.04 cm.sup.-1, 0.03 cm.sup.-1, 0.02 cm.sup.-1, or 0.01
cm.sup.-1.
7. A single crystal CVD diamond layer according to claim 1, wherein
the single crystal CVD diamond layer is in the form of a
free-standing single crystal CVD diamond wafer.
8. A single crystal CVD synthetic diamond material according to
claim 1 comprising: substantially no orange luminescence from
nitrogen-vacancy defects as viewed under photoluminescent
conditions; and substantially no blue luminescence from dislocation
defects as viewed under photoluminescent conditions.
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. (canceled)
14. (canceled)
15. (canceled)
16. A method of fabricating a single crystal CVD diamond layer
according to claim 1 using a microwave plasma activated chemical
vapour deposition technique, the method comprising: introducing a
substrate into a plasma chamber; introducing process gases into the
plasma chamber, the process gases including hydrogen gas and a
carbon source gas; and introducing microwaves into the plasma
chamber to activate the process gases and form a plasma proximate
to a growth surface of the substrate wherein synthetic diamond
material is grown over the growth surface of the substrate, wherein
during growth of the synthetic diamond material a microwave power
density is maintained at a power density of at least 3 W/mm.sup.2
over a growth surface area of at least 1963 mm.sup.2 for a time
period of at least 24 hours said microwave power density being
calculated by dividing input microwave power by substrate growth
surface area.
17. A method according to claim 16, wherein the microwave power
density is at least 3.2 W/mm.sup.2, 3.4 W/mm.sup.2, or 3.6
W/mm.sup.2.
18. A method according to claim 16, wherein the microwave power
density is no more than 10 W/mm.sup.2, 8 W/mm.sup.2, 6 W/mm.sup.2,
5 W/mm.sup.2, or 4 W/mm.sup.2.
19. A method according to claim 16, wherein the microwave power
density is maintained at a target value with a variation over time
of no more than .+-.5%, .+-.3%, .+-.2%, or .+-.1% as measured by
fluctuations in total power input to the plasma chamber averaged
over 5 second measurement periods for a time period forming at
least 30%, 50%, 70%, 90%, or 95% of a total growth time period.
20. A method according to claim 16, wherein the growth surface area
is at least 2827 mm.sup.2, 3848 mm.sup.2, 5027 mm.sup.2, 6362
mm.sup.2, or 7054 mm.sup.2.
21. A method according to claim 16, wherein the growth surface area
is no more than 15394 mm.sup.2, 13273 mm.sup.2, 11310 mm.sup.2, or
9503 mm.sup.2.
22. A method according to claim 16, wherein the time period is at
least 48 hours, 72 hours, 96 hours, 120 hours, 168 hours, 216
hours, 288 hours, 360 hours, 432 hours, or 504 hours.
Description
FIELD OF INVENTION
[0001] The present invention relates to methods of fabricating
synthetic diamond materials using microwave plasma active chemical
vapour deposition techniques and products obtained using said
methods. Products comprising very high purity single crystal
synthetic diamond material are described and method of
manufacturing the same at increased growth rates while retaining
exceptional electronic, optical, thermal, and/or quantum coherence
characteristics. Such a high purity single crystal CVD diamond
material is useful in a range of applications including optical
components, electronic components, radiation detectors, and quantum
sensing and information processing devices. Certain further
implementations relate to more economic methods for fabricating
lower purity synthetic diamond products. Yet further
implementations relate to synthesis of large area synthetic diamond
wafers with improved electronic, optical, thermal, and/or quantum
coherence characteristics.
BACKGROUND OF INVENTION
[0002] By way of background, a short introduction to diamond
materials science is presented here in order to set the context for
the present invention.
[0003] Diamond materials are based on a theoretically perfect
diamond lattice. The properties that would be exhibited by this
theoretically perfect lattice are well understood. For example,
such a theoretically perfect diamond lattice would exhibit
extremely high thermal conductivity, low electrical conductivity
(very wide band gap intrinsic semi-conductor with no significant
charge carriers but with high charge carrier mobility if charge
carriers are introduced into the lattice structure), extremely low
thermal expansion coefficient, no significant optical
birefringence, and low optical absorption (no significant
absorption in the visible spectrum so there would be no
colour).
[0004] Such a theoretically perfect diamond lattice is
thermodynamically impossible to attain. In reality, it is
practically difficult to even approach a level of perfection which
would be possible to achieve in theory when taking into account
thermodynamic considerations. As such, it should be apparent that
all diamond materials contain a significant number of defects. Such
defects may come in the form of impurities. Typical impurities
which may be incorporated into a diamond lattice structure include
nitrogen, boron, silicon, phosphorous, hydrogen, and metals such as
sodium, nickel, cobalt, and chromium. Additionally, defects within
diamond materials also include crystallographic deviations from the
perfect diamond lattice structure in the form of point defects such
as vacancies and interstitials and extended defects such as various
forms of dislocation defects. Defects may also combine in various
ways. For example, vacancy defects may combine into clusters or
combine with impurity atoms to form unique vacancy structures with
their own individual properties. Examples include silicon
containing defects such as silicon-vacancy defects (Si-V), silicon
di-vacancy defects (Si-V.sub.2), silicon-vacancy-hydrogen defects
(Si-V:H), silicon di-vacancy hydrogen defects (S-V.sub.2:H) and
nitrogen containing defects such as nitrogen-vacancy defects (N-V),
di-nitrogen vacancy defects (N-V-N), and nitrogen-vacancy-hydrogen
defects (N-V-H). These defects are typically found in a neutral
charge state or in a charged state, e.g. negatively charged.
[0005] Defects within diamond materials significantly alter the
properties of the materials. On-going work in this field is
concerned with understanding the properties of the various defects
within diamond materials and their overall effect on the functional
properties of the materials. Furthermore, on-going work is
concerned with engineering diamond materials to have particular
types and distributions of defects in order to tailor diamond
materials to have particular desirable properties for particular
applications. The types and distributions of defects which are
desired will thus depend on the properties required for particular
applications.
[0006] In this regard, diamond materials may be categorized into
three main types: natural diamond materials; HPHT (high pressure
high temperature) synthetic diamond materials, and CVD (chemical
vapour deposited) synthetic diamond materials. These categories
reflect the way in which the diamond materials are formed.
Furthermore, these categories reflect the structural and functional
characteristics of the materials. This is because while natural,
HPHT synthetic, and CVD synthetic diamond materials are all based
on a theoretically perfect diamond lattice the defects in these
material are not the same. For example, CVD synthetic diamond
contains many defects unique to the process of CVD, and whilst some
defects are found in other diamond forms, their relative
concentration and contribution is very different. As such, CVD
synthetic diamond materials are different to both natural and HPHT
synthetic diamond materials.
[0007] Diamond materials may also be categorized according to their
physical form. In this regard, diamond materials may be categorized
into three main types: single crystal diamond materials;
polycrystalline diamond materials; and composite diamond materials.
Single crystal diamond materials are in the form of individual
single crystals of various sizes ranging from small "grit"
particles used in abrasive applications through to large single
crystals suitable for use in a variety of technical applications as
well for gemstones in jewellery applications. Polycrystalline
diamond materials are in the form of a plurality of small diamond
crystals bonded together by diamond-to-diamond bonding to form a
polycrystalline body of diamond material such as a polycrystalline
diamond wafer. Such polycrystalline diamond materials can be useful
in various applications including thermal management substrates,
optical windows, and mechanical applications. Composite diamond
materials are generally in the form of a plurality of small diamond
crystals bonded together by diamond-to-diamond or a non-diamond
matrix to form a body of composite material. Various diamond
composites are known including diamond containing metal matrix
composites, particularly cobalt metal matrix composites known as
PCD, and skeleton cemented diamond (ScD) which is a composite
comprising silicon, silicon carbide, and diamond particles.
[0008] It should also be appreciated that within each of the
aforementioned categories there is much scope for engineering
diamond materials to have particular concentrations and
distributions of defects in order to tailor diamond materials to
have particular desirable properties for particular applications.
In this regard, the present invention is concerned with CVD
synthetic diamond materials to which the focus of this
specification will now turn.
[0009] CVD processes for synthesis of diamond material are now well
known in the art. Useful background information relating to the
chemical vapour deposition of diamond materials may be found in a
special issue of the Journal of Physics: Condensed Matter, Vol. 21,
No. 36 (2009) which is dedicated to diamond related technology. For
example, the review article by R. S Balmer et al. gives a
comprehensive overview of CVD diamond materials, technology and
applications (see "Chemical vapour deposition synthetic diamond:
materials, technology and applications" J. Phys.: Condensed Matter,
Vol. 21, No. 36 (2009) 364221).
[0010] Being in the region where diamond is metastable compared to
graphite, synthesis of diamond under CVD conditions is driven by
surface kinetics and not bulk thermodynamics. Diamond synthesis by
CVD is normally performed using a small fraction of carbon
(typically <5%), typically in the form of methane although other
carbon containing gases may be utilized, in an excess of molecular
hydrogen. If molecular hydrogen is heated to temperatures in excess
of 2000 K, there is a significant dissociation to atomic hydrogen.
In the presence of a suitable substrate material, CVD synthetic
diamond material can be deposited. Polycrystalline CVD diamond
material may be formed on a non-diamond substrate such as a
refractory metal or silicon substrate. Single crystal CVD synthetic
diamond material may be formed by homoepitaxial growth on a single
crystal diamond substrate.
[0011] Atomic hydrogen present in the process selectively etches
off non-diamond carbon from the substrate such that diamond growth
can occur. Various methods are available for heating carbon
containing gas species and molecular hydrogen in order to generate
the reactive carbon containing radicals and atomic hydrogen
required for CVD synthetic diamond growth including arc-jet, hot
filament, DC arc, oxy-acetylene flame, and microwave plasma.
[0012] Impurities in the CVD process gases are incorporated into
the CVD synthetic diamond material during growth. As such, various
impurities may be intentionally introduced into the CVD process
gases, or intentionally excluded from the CVD process gases, in
order to engineer a CVD synthetic diamond material for a particular
application. Furthermore, the nature of the substrate material and
the growth conditions affect the type and distribution of defects
incorporated into the CVD synthetic diamond material during
growth.
[0013] For certain applications it is desirable to minimize the
number of defects, or at least certain types of defect, within the
diamond lattice structure. For example, for certain electronic
applications such as radiation detectors or semi-conductive
switching devices it is desirable to minimize the number of charge
carriers inherent in the diamond material and increase the mobility
of charge carriers intentionally introduced into the material in
use. Such a material may be engineered by fabricating a single
crystal CVD synthetic diamond material which has a low
concentration of impurities which would otherwise introduce charge
carriers into the diamond lattice structure. Patent literature
relevant to such electronic/detector grade single crystal CVD
synthetic diamond material includes WO01/096633 and
WO01/096634.
[0014] For certain optical applications it is desirable to provide
a material which has low optical absorbance and low optical
birefringence. Such a material may be engineered by fabricating a
single crystal CVD synthetic diamond material which has a low
concentration of impurities, which would otherwise increase the
optical absorbance of the material, and a low concentration of
extended defects which would otherwise introduce anisotropic strain
into the diamond lattice structure causing birefringence. Patent
literature relevant to such optical grade single crystal CVD
synthetic diamond material includes WO2004/046427 and
WO2007/066215.
[0015] High purity diamond material is also desirable to function
as a host material for quantum spin defects in certain quantum
sensing and processing applications (e.g. in measuring magnetic
fields). Diamond materials are useful in such applications as
certain quantum spin defects (e.g. the negatively charge
nitrogen-vacancy defect) disposed within the diamond lattice
structure have a long decoherence time even at room temperature
(i.e. the quantum spin defects remain in a specific quantum spin
state for a significant length of time allowing sensing and/or
quantum processing applications to be performed). Furthermore, such
quantum spin defects within the diamond lattice can be optically
addressed. However, in such applications impurities can interact
with quantum spin defects within the diamond lattice structure
reducing their decoherence time and thus reducing their sensitivity
and/or reducing the time during which quantum processing
applications can be performed. Patent literature relevant to such
high purity quantum grade single crystal CVD synthetic diamond
material includes WO 2010010344 and WO 2010010352.
[0016] In contrast to the low defect materials described above, for
certain applications it is desirable to intentionally introduce a
significant but controlled quantity, type, and distribution of
defects into the diamond lattice structure. For example,
introducing boron into the diamond lattice by providing a boron
containing gas within the CVD process gases provides an acceptor
level within the band structure of the diamond material thus
forming a p-type semi-conductor. If extremely high levels of boron
are introduced into the diamond lattice structure the material
shows full metallic conductivity. Such materials are useful as
electrodes, as electrochemical sensing electrodes, and in
electronic applications. Patent literature relevant to such boron
doped single crystal CVD synthetic diamond material includes
WO03/052174.
[0017] Another example is that of nitrogen doped single crystal CVD
synthetic diamond materials. Nitrogen is one of the most important
dopants in CVD diamond material synthesis as it has been found that
providing nitrogen in the CVD process gas increases the growth rate
of the material and can also affect the formation of
crystallographic defects such as dislocations. As such, nitrogen
doping of single crystal CVD synthetic diamond materials has been
extensively investigated and reported in the literature. Nitrogen
doped CVD synthetic diamond material tends to be brown in colour.
As such, for the previously discussed applications, such as optical
applications, it has been found to be advantageous to develop
techniques which intentionally exclude nitrogen from the CVD
process gases. However, for applications such as mechanical
applications where optical, electronic, and quantum coupling
parameters are not a concern, nitrogen doping to significant levels
can be useful in achieving growth of thick layers of CVD synthetic
diamond material. Patent literature relevant to such nitrogen doped
single crystal CVD synthetic diamond material includes
WO2003/052177 which describes a method of fabricating diamond
material using a CVD synthesis atmosphere comprising nitrogen in a
concentration range 0.5 to 500 ppm, calculated as molecular
nitrogen.
[0018] In light of the above, it will be evident that diamond
materials come in a range of different forms and can be engineered
to have a range of different properties for particular
applications. Certain embodiments of the present invention are
particularly concerned with the fabrication of low defect, high
purity single crystal CVD synthetic diamond material. In this
regard, background prior art of relevance includes the previously
discussed electronic/detector grade single crystal CVD synthetic
diamond material as described in WO01/096633 and WO01/096634, the
optical grade single crystal CVD synthetic diamond material as
described in WO2004/046427 and WO2007/066215, and the high purity
quantum grade single crystal CVD synthetic diamond material as
described in WO 2010010344 and WO 2010010352. Additional prior art
includes U.S. Pat. No. 5,908,503, JP4280896, and WO2011/146460.
[0019] A problem with synthesizing low defect, high purity single
crystal CVD synthetic diamond material is that such material has a
very low growth rate and is thus time consuming and expensive to
manufacture. Furthermore, due to the extended time periods required
to obtain a desired thickness of such material at low growth rates,
the growth process must be very precisely controlled over extended
time periods and this can be difficult to achieve in practice
resulting in reduced yields. Electronic/detector grade single
crystal CVD synthetic diamond material as described in WO01/096633
and WO01/096634 is grown using a CVD growth process in which
nitrogen is essentially excluded, at least to the extent that this
is practically possible (e.g. no more than 300 ppb, 200 ppb, 100
ppb, 50 ppb, or 20 ppb of nitrogen in the CVD synthesis
atmosphere). In contrast, optical grade single crystal CVD
synthetic diamond material as described in WO2004/046427 is grown
using a CVD growth process in which a low and controlled
concentration of nitrogen is introduced to increase growth rates
while not being so high as to unduly affect optical properties.
However, while single crystal CVD synthetic diamond material
according to this process is suitable for many optical
applications, the concentration of nitrogen incorporated into the
material is such that the material is not ideally suited for
certain high-end optical applications and certain other
applications such as electronic, radiation detector, and quantum
sensing and processing applications which require higher purity
material and a CVD growth process in which nitrogen is essentially
excluded. Furthermore, even for applications which are not
detrimentally affected by the presence of a low and controlled
concentration of nitrogen in the single crystal CVD synthetic
diamond material, it can be difficult to obtain consistent and
reproducible optical properties, such as low absorption, utilizing
a low and controlled nitrogen addition.
[0020] In relation to the above, a number of groups have
investigated CVD diamond growth parameters including microwave
power, gas pressure, and deposition area to synthesize single
crystal CVD diamond material. One type of approach involves growth
on a single substrate. In such an approach it is believed that
plasma focussing increases power density over a small growth area
and can increase vertical growth rates and crystal quality over a
small growth area. However, such a plasma focussing route is not
suitable for achieving high power densities across relatively large
growth areas to enhance volume growth rate. That is, while vertical
growth rate of single crystal CVD diamond material may be enhanced
by plasma focussing on a small growth area, the volume of single
crystal CVD diamond material which is synthesized per unit time is
relatively small as growth occurs over only a small area due to
plasma focussing, e.g. over only one single crystal diamond
substrate. An alternative approach is to grow single crystal CVD
diamond material over a plurality of single crystal diamond
substrates. Such an approach can be used to increase the volume of
single crystal CVD diamond material which is grown per unit time.
However, as the growth area is increased the power density
decreases thus decreasing the growth rate on each individual single
crystal diamond substrate. A decrease in power density also leads
to a decrease in the quality of single crystal CVD diamond material
which is synthesized. Some examples of prior art synthesis
processes are briefly summarized below.
[0021] Liang et al. (APPLIED PHYSICS LETTERS 94, 024103, 2009)
describe enhanced growth of high quality single crystal diamond by
microwave plasma assisted chemical vapour deposition at high gas
pressures. An ASTEX 5400 CVD reactor apparatus was used for the
synthesis operating at a microwave power in a range 3-5 kW and
using a chemistry comprising a nitrogen to methane ratio
(N.sub.2/CH.sub.4) in a range 0 to 2%. Three single crystal CVD
diamond growth runs are described, each of which appears to be a
single stone growth process. Power density is not quoted and there
is no evidence of deposition over significant areas. Since the
ASTEX 5400 CVD reactor apparatus is a 2.45 GHz system the
deposition area is limited. A colourless single crystal CVD diamond
product is obtained which exhibits relatively low flourescence
under room temperature photoluminescent conditions. No
spatially-dependent flourescence data is shown.
[0022] Meng et al. (Phys. Status Solidi A 209, No. 1, 101-104,
2012) describe high optical quality multi-carat single crystal
diamond produced by chemical vapour deposition. Single stone CVD
diamond growth was performed in multiple runs on a substrate of
size 9 mm.times.9 mm using a total power of 3-5 kW. Colourless
material with low nitrogen-vacancy flourescence was produced.
[0023] Grotjohn et al. (Diamond & Related Materials 14 (2005)
288-291) describe scaling behaviour of microwave reactors and
discharge size for diamond deposition. Assuming all microwave power
is absorbed in the substrate/carrier (in practice it will be some
fraction of this), a power density of up to 0.9 W/mm.sup.2 may be
derived for a 50 mm carrier, a power density of up to 0.5
W/mm.sup.2 may be derived for a 75 mm carrier, and a power density
of up to 0.4 W/mm.sup.2 may be derived for a 150 mm carrier. No
diamond synthesis data is presented.
[0024] King et al. (Diamond & Related Materials 17 (2008)
520-524) also describe the scaling behaviour of a microwave
plasma-assisted chemical vapour diamond deposition process for
150-200 mm substrates. Assuming all microwave power is absorbed in
the substrate/carrier (in practise it will be some fraction of
this), a power density of up to 0.5 W/mm.sup.2 may be derived for a
150 mm carrier and a power density of up to 0.2 W/mm.sup.2 may be
derived for a 200 mm carrier. Only polycrystalline CVD diamond
material was grown. There is no disclosure of how power density
affects single crystal CVD diamond growth.
[0025] US2009/0239078 describes a multi-substrate single crystal
CVD diamond growth process in which nitrogen gas is added to the
synthesis atmosphere to assist diamond growth. Assuming all
microwave power is absorbed in the substrate/carrier, Example II
gives a power density up to 1.4 W/mm.sup.2 for a 150 mm carrier
comprising 70 seed substrates using a power of 11 kW over a 4 to 5
inch deposition area.
[0026] One problem with prior art methodologies is how to achieve
very high purity single crystal CVD synthetic diamond material,
suitable for certain high-end optical applications and certain
other applications such as electronic, radiation detector, and
quantum sensing and processing applications, at increased volume
growth rates (e.g. over a plurality of single crystal diamond
growth substrates) while avoiding the addition of nitrogen to
enhance growth rates.
[0027] In addition, even for applications which are not
detrimentally affected by the presence of a low and controlled
concentration of nitrogen in the single crystal CVD synthetic
diamond material, it would be desirable to develop a growth process
which is capable of fabricating a single crystal CVD diamond
material which has more consistent and reproducible optical
properties while maintaining a comparable growth rate to that
achieved by a low and controlled nitrogen addition.
[0028] Further still, it would be desirable to develop a growth
process which is less sensitive to the presence of impurities in
the CVD synthesis atmosphere, particularly nitrogen, whereby
impurity uptake in the single crystal CVD diamond material is
reduced over a plurality of single crystal diamond growth
substrates. Such a growth process would allow the synthesis of high
purity single crystal CVD diamond material over a large number of
single crystal diamond substrates without the current requirement
for very high purity synthesis gases and a reactor chamber design
which is configured to alleviate problems of leakage, atmospheric
gas infiltration, and/or adsorption and desorption of impurity
species at internal surfaces of the reactor chamber. That is, such
a process would be capable of achieving synthesis of the same
quality and/or purity of single crystal CVD diamond material as
current processes at lower cost by reducing the requirements for
excluding impurities in the synthesis atmosphere. Further still,
such a process would be capable of achieving synthesis of higher
quality and/or higher purity single crystal CVD diamond material as
current processes which utilize very high purity synthesis gases
and a reactor chamber design which is configured to alleviate
problems of leakage, atmospheric gas infiltration, and/or
adsorption and desorption of impurity species at internal surfaces
of the reactor chamber.
[0029] Yet further, it has also been noted that while very high
purity single crystal CVD synthetic diamond material, such as that
described in WO01/096633 and WO01/096634, exhibits substantially no
fluorescence due to nitrogen-vacancy defects, the material does
exhibit some fluorescence as a result of dislocation defects. For
certain applications it would be desirable to fabricate a material
which comprises substantially no fluorescence either from
nitrogen-vacancy defects or from dislocation defects.
[0030] In addition to all of the above, there is an on-going need
to provide a fabrication route to achieve large area wafers of
synthetic diamond material with suitable mechanical, optical,
thermal, electronic, and/or quantum properties for end
applications. At the time of writing this specification high
quality single crystal synthetic diamond material is only available
in relatively small sizes. Polycrystalline CVD diamond wafers are
available in larger areas and are suitable for many applications.
However, due to the polycrystalline nature of such wafers their
functional properties are generally not as good as high quality
single crystal diamond materials. One approach known in the art for
increasing the area of single crystal synthetic diamond products is
to provide a tiled array of single crystal diamond substrates and
grow a single layer of single crystal diamond material over the
tiled array of substrates using a chemical vapour deposition
technique. However, it is difficult to achieve good quality single
crystal diamond growth over interface regions between the tiled
substrates and to date it has been required to introduce
significant portions of nitrogen into the synthesis atmosphere to
achieve reasonable intergrowth of single crystal diamond material
grown over tiled substrates. This results in a significant quantity
of nitrogen being incorporated into the single crystal CVD diamond
wafer grown over the tiled array of substrates detrimentally
affecting the mechanical, optical, thermal, electronic, and/or
quantum properties for end applications.
[0031] It is an aim of certain embodiments of the present invention
to solve one or more of the aforementioned problems.
SUMMARY OF INVENTION
[0032] The present applicant has previously filed a number of
patent applications directed to microwave plasma activated CVD
reactor hardware and CVD diamond synthesis methodology for
achieving high quality, thick CVD diamond growth of both single
crystal and polycrystalline CVD diamond materials over relatively
large areas and relatively high growth rates. These patent
applications include patent applications describing certain aspects
of the structure and geometry of the microwave plasma chamber (e.g.
WO2012/084661 which describes the use of a compact TM.sub.011
resonance mode plasma chamber configuration and WO2012/084657 which
describes the provision of a plasma stabilizing annulus projecting
from a side wall of the plasma chamber), certain aspects of the
microwave power coupling configuration (e.g. WO2012/084658 which
describes a microwave power delivery system for supplying microwave
power to a plurality of microwave plasma reactors and WO2012/084659
which describes a microwave coupling configuration comprising an
annular dielectric window, a coaxial waveguide, and a waveguide
plate comprising a plurality of apertures disposed in an annular
configuration for coupling microwaves towards the plasma chamber),
certain aspects of the substrate preparation, geometry, and
temperature control configurations within the microwave plasma
chamber (e.g. WO2012/084655 which describes how to prepare, locate,
and control substrate parameters within a microwave plasma reactor
to achieve desirable electric field and temperature profiles), and
certain aspects of the gas flow configuration and gas flow
parameters within a microwave plasma chamber (e.g. WO2012/084661
which describes a microwave plasma reactor with a multi-nozzle gas
inlet array having a desirable geometric configuration for
achieving uniform diamond growth over large areas and WO2012/084656
which describes the use of high gas flow rates and injection of
process gases with a desirable Reynolds number to achieving uniform
doping of synthetic diamond material over large areas).
[0033] Several of the aforementioned documents also describe that
the microwave plasma activated CVD reactor hardware and CVD diamond
synthesis methodology is capable of generating high microwave power
densities over the growth surface of the substrate. For example,
WO2012/084655 discloses a power density operating range of 0.05 to
10 W/mm.sup.2 while WO2012/084657, WO2012/08661 and WO2012/084656
disclose power densities up to and above 3.5 W/mm.sup.2.
[0034] Following on from the work described in the aforementioned
documents, the present applicant has found that using suitable
microwave plasma activated CVD reactor hardware and CVD diamond
synthesis methodology it is possible to achieve high and uniform
power densities over large substrate areas and maintain such power
densities over long operating times to achieve the fabrication of
large volumes of synthetic diamond material at high volume growth
rates and with reduced impurities.
[0035] A method of fabricating synthetic diamond material using a
microwave plasma activated chemical vapour deposition technique is
described herein, the method comprising: [0036] introducing a
substrate into a plasma chamber; [0037] introducing process gases
into the plasma chamber, the process gases including hydrogen gas
and a carbon source gas; and [0038] introducing microwaves into the
plasma chamber to activate the process gases and form a plasma
proximate to a growth surface of the substrate wherein synthetic
diamond material is grown over the growth surface of the substrate,
[0039] wherein during growth of the synthetic diamond material a
microwave power density is maintained at a power density of at
least 3 W/mm.sup.2 over a growth surface area of at least 1963
mm.sup.2 (corresponding to a 50 mm diameter substrate) for a time
period of at least 24 hours said microwave power density being
calculated by dividing input microwave power by substrate growth
surface area.
[0040] Further to the above synthesis method, a single crystal CVD
synthetic diamond material product is described herein, the single
crystal CVD synthetic diamond material comprising: substantially no
orange luminescence from nitrogen-vacancy defects as viewed under
photoluminescent conditions; and substantially no blue luminescence
from dislocation defects as viewed under photoluminescent
conditions.
[0041] In addition to the above, another product in the form of a
single crystal CVD diamond layer is described herein, the single
crystal CVD diamond layer comprising: a total nitrogen
concentration as measures by secondary ion mass spectrometry of no
more than 2 ppm; and an area of at least 324 mm.sup.2.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] For a better understanding of the present invention and to
show how the same may be carried into effect, embodiments of the
present invention will now be described by way of example only with
reference to the accompanying drawings, in which:
[0043] FIG. 1 shows a schematic diagram of a CVD reactor for
fabricating single crystal CVD diamond material;
[0044] FIG. 2 shows a DiamondView.TM. image of a single crystal CVD
diamond material;
[0045] FIG. 3 shows a DiamondView.TM. image of another single
crystal CVD diamond material; and
[0046] FIG. 4 shows current versus time plots for a single crystal
CVD diamond material.
DETAILED DESCRIPTION
[0047] As previously described in the summary of invention section,
a method of fabricating synthetic diamond material using a
microwave plasma activated chemical vapour deposition technique is
provided which utilizes high and uniform microwave power densities
applied over large areas and for extended periods of time.
[0048] The microwave power density may be maintained at a power
density of at least 3.2 W/mm.sup.2, 3.4 W/mm.sup.2, or 3.6
W/mm.sup.2 and/or no more than 10 W/mm.sup.2, 8 W/mm.sup.2, 6
W/mm.sup.2, 5 W/mm.sup.2, or 4 W/mm.sup.2. The optimal power
density within these ranges will be dependent on the precise
product which is being fabricated.
[0049] Furthermore, the microwave power density is maintained at a
target value with a variation over time of no more than .+-.5%,
.+-.3%, .+-.2%, or .+-.1% as measured by fluctuations in total
microwave power input to the plasma chamber averaged over 5 second
measurement periods for a time period forming at least 30%, 50%,
70%, 90%, or 95% of a total growth time period. For example, the
microwave power input to the plasma chamber may be continuously
measured during a growth run. The measurement data may then be
split into a plurality of 5 second measurement periods and the
microwave power averaged over each 5 second measurement period to
yield an average microwave power for each 5 second time period
during the growth run. The variations in these average values over
the growth run should then meet the aforementioned requirement that
the variation is no more than .+-.5%, .+-.3%, .+-.2%, or .+-.1% of
an average microwave power. This will equate, at least
approximately, to the percentage variation in microwave power
density over the growth surface area. Furthermore, by averaging
measurements over 5 second time periods this will allow for very
short time scale fluctuations in power which may not affect diamond
growth. The power density may thus be maintained at a target value
with a variation of no more than .+-.0.5 W/mm.sup.2, .+-.0.3
W/mm.sup.2, .+-.0.2 W/mm.sup.2, .+-.0.1 W/mm.sup.2, .+-.0.05
W/mm.sup.2, or .+-.0.03 W/mm.sup.2 as measured in this way.
Maintaining a high and uniform microwave power density over
extended time periods allows the fabrication of uniform diamond
products and alleviates problems of non-uniformities leading to
thermal stress and cracking of the diamond products.
[0050] The growth surface area over which the high and uniform
power density is maintained during diamond growth may be at least
1963 mm.sup.2, 2827 mm.sup.2, 3848 mm.sup.2, 5027 mm.sup.2, 6362
mm.sup.2, or 7054 mm.sup.2 and/or no more than 15394 mm.sup.2,
13273 mm.sup.2, 11310 mm.sup.2, or 9503 mm.sup.2 (corresponding to
substrate diameters of at least 60 mm, 70 mm, 80 mm, 90 mm, or 100
mm and/or no more than 140 mm, 130 mm, 120 mm, or 110 mm).
Furthermore, it has been found that high and uniform power density
over such growth surface areas may be maintained for extended time
periods of at least 48 hours, 72 hours, 96 hours, 120 hours, 168
hours, 216 hours, 288 hours, 360 hours, 432 hours, or 504 hours.
The optimal growth surface area and growth time within these ranges
will be dependent on the precise product which is being
fabricated.
[0051] It should be noted that the maintenance of extreme power
densities over large areas for extended periods of time during
diamond growth is not a trivial matter or simple design choice and
that precise control of operating conditions is required to
maintain a stable plasma and achieve this methodology.
[0052] The methodology as defined above may be used to achieve a
number of different desirable diamond products as described
below.
[0053] Single crystal and polycrystalline CVD diamond products
having the same specifications as currently available products can
be synthesized in a more economically viable manner. High power
densities over large growth areas which are maintainable for
extended time periods allow the growth of large volumes of diamond
material at accelerated growth rates thus reducing costs.
Furthermore, high power densities have been found to reduce the
rate of uptake of impurities from the process gases into the
growing diamond material thus negating the requirement to utilize
very high purity processes gases which are expensive.
[0054] Improved single crystal and polycrystalline CVD diamond
products having higher specifications than currently available
products can be fabricated. For example, by using high purity
process gases in combination with high power densities over large
growth areas which are maintainable for extended time periods a
reduced impurity uptake leads to higher purity diamond products.
Furthermore, the high growth rates achieved by using high power
densities over large growth areas which are maintainable for
extended time periods can subtly change the crystal structure of
the diamond material such as by changing the dislocation
distribution and reducing the concentration of blue fluorescent
dislocations under photoluminescent conditions. For example, one
product is a single crystal CVD synthetic diamond material
comprising: substantially no orange luminescence from
nitrogen-vacancy defects as viewed under photoluminescent
conditions; and substantially no blue luminescence from dislocation
defects as viewed under photoluminescent conditions.
[0055] Large area diamond wafers having specifications equivalent,
or at least approaching, those which are only currently available
in small area single crystal form may be fabricated. For example,
as described in the background section, one approach to increasing
the area of single crystal synthetic diamond products is to provide
a tiled array of single crystal diamond substrates and grow a
single layer of single crystal diamond material over the tiled
array of substrates. However, it is difficult to achieve good
quality single crystal diamond growth over interface regions
between the tiled substrates and to date it has been required to
introduce significant portions of nitrogen into the synthesis
atmosphere to achieve reasonable intergrowth of single crystal
diamond material grown over tiled substrates. This results in a
significant quantity of nitrogen being incorporated into the single
crystal CVD diamond wafer grown over the tiled array of substrates
detrimentally affecting the mechanical, optical, thermal, and/or
electronic properties for end applications. In contrast,
embodiments of the present invention propose to apply high power
densities over large growth areas which are maintainable for
extended time periods in order to encourage single crystal diamond
growth over interface regions of a tiled array of substrates to
achieve large area single crystal CVD diamond wafers with a
relatively low nitrogen content and improved mechanical, optical,
thermal, and/or electronic properties. This approach is intended to
combine the material properties of small single crystal CVD diamond
products with the area size of polycrystalline CVD diamond wafers.
For example, one product is in the form of a single crystal CVD
diamond layer comprising: a total nitrogen concentration as
measures by secondary ion mass spectrometry of no more than 2 ppm;
and an area of at least 324 mm.sup.2.
[0056] The methodolology can be used to a very high purity
synthetic diamond material suitable for high-end optical
applications and other applications such as electronic, radiation
detector, and quantum sensing and processing applications, at
increased growth rates while avoiding the addition of nitrogen to
enhance growth rates. In such applications, the concentration of
nitrogen intentionally added to the process gases in the plasma
chamber as a dopant may be less than 1 ppm, 0.8 ppm, 0.6 ppm, 0.5
ppm, 0.4 ppm, 0.3 ppm, 0.2 ppm, 0.1 ppm or zero calculated as
molecular nitrogen.
[0057] Furthermore, high purity gases may be utilized such that the
concentration of nitrogen present in the process gases in the
plasma chamber, either present as an intentionally added dopant or
as an impurity in the other process gases, is less than 1 ppm, 0.8
ppm, 0.6 ppm, 0.5 ppm, 0.4 ppm, 0.3 ppm, 0.2 ppm or 0.1 ppm
calculated as molecular nitrogen. This contrasts with the teachings
of the applicant's earlier patent application (WO2012/084656) which
discloses the use of high gas flow rates and high power densities
to produced doped diamond materials with uniform dopant. The
present applicant has found that high power densities are also
advantageous to produced high purity, undoped diamond
materials.
[0058] The methodology can be used to fabricate existing products
in a more economic manner by achieving increased volume growth
rates and less sensitivity to impurities allowing the use of less
pure process gases. In such applications the concentration of
nitrogen intentionally added to the process gases in the plasma
chamber as a dopant may be less than 1 ppm, 0.8 ppm, 0.6 ppm, 0.5
ppm, 0.4 ppm, 0.3 ppm, 0.2 ppm, 0.1 ppm or zero calculated as
molecular nitrogen as described above but the concentration of
nitrogen present as impurity in the process gases may be equal to
or higher than 0.1 ppm, 0.2 ppm, 0.3 ppm, 0.4 ppm, 0.5 ppm, 0.6
ppm, 0.8 ppm, or 1 ppm. The lower sensitivity to impurities in the
process gases can also provide a growth process which is capable of
fabricating a synthetic diamond material which has more consistent
and reproducible optical properties while maintaining a comparable
growth rate to that achieved by a low and controlled nitrogen
addition.
[0059] Advantageously, the methodology can be combined with high
gas flow rates as described in WO2012/084656. High velocity, highly
uniform gas flow, increases the efficiency at which input power is
transmitted to the substrate. Accordingly, the process gases may be
injected towards the growth surface at a total gas flow rate of at
least 1, 3, 5, or 7 standard litres per minute and/or a total gas
flow rate of no more than 30, 20, 15, or 12 standard litres per
minute. Furthermore, the process gases are injected into the plasma
chamber through one or more gas inlet nozzles with a Reynolds
number in a range 1 to 100. While WO2012/084656 discloses the use
of such synthesis conditions to produced doped diamond materials
with uniform dopant, it has been found that such synthesis
conditions are also advantageous to produced high purity, undoped
diamond materials.
[0060] As a very high power density is applied to the substrate for
prolonged periods of time using the methodology as described herein
it is desirable to select a substrate which is capable of handling
such extreme power densities. For example, the substrate may
comprise a refractory metal disk, e.g. tungsten. Polycrystalline
CVD diamond material can be fabricated directly on such a
refractory metal disk.
[0061] To fabricate single crystal diamond material, the substrate
may comprises a carrier substrate, such as the previously mentioned
refractory metal disk, on which a plurality of single crystal CVD
diamond substrates are mounted, wherein the microwave power density
is calculated by dividing input microwave power by carrier
substrate growth surface area. For example, the substrate may
comprise at least 30, 40, 50, or 60 single crystal CVD diamond
substrates. These single crystal CVD diamond substrates may be
spaced apart on the growth surface of the carrier substrate whereby
the synthetic diamond material is grown as a plurality of separate
single crystals. Alternatively, the single crystal CVD diamond
substrates may be located in contact with each other, or in close
proximity, to form a tiled array whereby the synthetic diamond
material is grown as a single continuous layer of synthetic diamond
material over the tiled array of single crystal CVD diamond
substrates. In this case, as previously described, the high power
density conditions are intended to aid overgrowth at interface
regions between the single crystal CVD diamond substrates without
the requirement to add significant quantities of nitrogen which
reduces the optical quality of the large area, tiled single crystal
diamond product.
[0062] Using the methodology as described herein the synthetic
diamond material may be grown at a volume growth rate over the
substrate of no less than 1.times.10.sup.9 micrometers.sup.3/hour,
5.times.10.sup.9 micrometers.sup.3/hr, 1.times.10.sup.10
micrometers.sup.3/hr, 3.times.10.sup.10 micrometers.sup.3/hr,
4.times.10.sup.10 micrometers.sup.3/hr, 6.times.10.sup.10
micrometers.sup.3/hr, or 8.times.10.sup.10 micrometers.sup.3/hr. In
the case where a plurality of separate spaced apart single crystal
diamond substrates are provide the volume growth rate is calculated
as the volume of single crystal diamond material grown on the
plurality of single crystal diamond substrates per unit time. In
the case where a tiled array of single crystal diamond substrates
is provided such that a single layer of single crystal diamond
material grows over the plurality of single crystal diamond
substrates then the volume growth rate is calculated as the volume
of the single layer of single crystal diamond material grown per
unit time.
[0063] Furthermore, the methodology as described herein is capable
of fabricating large volumes of synthetic diamond material at a
high volume growth rate which, if cut into a 0.5 carat round
brilliant gemstone, exhibits a colour grade of D, E, or F.
[0064] Further details of the reactor hardware, synthesis
conditions, and material products are given below.
Reactor Hardware
[0065] CVD reactor hardware has been configured so as to capable of
maintaining high and uniform power densities over large area
substrates for prolonged periods of time. The CVD reactor hardware
is also capable of generating the following combination of
synthesis conditions: [0066] high process gas flow rates oriented
towards a growth surface with a low Reynolds number gas injection
parameter; [0067] high operating pressures; [0068] high microwave
operating powers; [0069] efficient and precise thermal management;
[0070] controlled and uniform electromagnetic fields resulting in a
uniform large area plasma and a uniform power density across the
substrate growth surface; and [0071] plasma chamber design
configured to provide minimal contamination from the microwave
inlet and side walls of the plasma chamber.
[0072] In relation to the above, a suitable CVD reactor components
are described in WO2012/084661, WO2012/084657, WO2012/084658,
WO2012/084659, WO2012/084655, WO2012/084661, and WO2012/084656. An
example of a CVD reactor configuration is illustrated schematically
in FIG. 1 of the present specification.
[0073] The microwave plasma reactor comprises the following basic
components: a plasma chamber 102; a substrate holder 104 disposed
in the plasma chamber for holding a substrate 105; a microwave
generator 106 for forming a plasma 108 within the plasma chamber
102; a microwave coupling configuration 110 for feeding microwaves
from the microwave generator 106 into the plasma chamber 102 via a
coaxial waveguide and through an annular dielectric window 119; a
gas flow system 112, 122 for feeding process gases into the plasma
chamber 102 and removing them therefrom; and a substrate coolant
system 114 for controlling the temperature of a substrate 105.
[0074] The plasma chamber 102 may have a number of different
configurations suitable for supporting a standing microwave.
However, it is found that a particularly preferred configuration
utilizes a simple modal synthesis chamber, for instance the
TM.sub.011 mode is advantageous as it has been found to be the most
compact (small) mode which can be practicably used in a diamond CVD
plasma reactor. Its compactness means that the impact of gas flow
aspects on the near gas phase chemistry are maximized. The use of a
small plasma chamber having a compact microwave cavity is made
possible by the flow characteristics of the gas inlet which ensures
that process gas flows through a central portion of the plasma
chamber without undue circulation of gases within the plasma
chamber contaminating walls of the chamber which will be relatively
close to the gas flow in a compact cavity arrangement.
[0075] The gas flow system 112 comprises source gas containers 117
and a gas inlet coupled to the source gas containers and positioned
in a top portion of the plasma chamber 102 axially disposed above
the substrate holder 104 and substrate 105 for directing process
gases towards the substrate 105 in use. In the illustrated
embodiment the process gas is fed from the source gas containers
117 to the gas inlet through a central conductor of the microwave
coupling configuration 110. However, other configurations are also
possible for feeding the process gases to the gas inlet 124.
[0076] The microwave window 119 for feeding microwaves from the
microwave generator into the plasma chamber is preferably disposed
at an opposite end of the plasma chamber to the substrate holder.
Furthermore, the gas inlet is preferably disposed closer to the
substrate holder than the microwave window. Such an arrangement can
minimize the possibility of the microwave window being contaminated
with process gases while also ensuring that the process gas is
injected at a location relatively close to the substrate.
[0077] The gas inlet nozzle array 124 comprises a plurality of gas
inlet nozzles disposed opposite the substrate holder 104 for
injecting process gases towards the substrate holder 104 at high
flow rate and low Reynolds number. The gas inlet nozzle array 124
comprises a plurality of gas inlet nozzles disposed in a
substantially parallel orientation relative to the central axis of
the plasma chamber 102. The gas inlet array 124 also comprises a
housing 128 defining a cavity 130 for receiving process gases from
one or more gas inlet pipes. The housing 128 also defines the
plurality of inlet nozzles for injecting process gases from the
cavity 130 into the plasma chamber 102 and towards the substrate
holder 104. For example, the housing may comprise metallic walls in
which the inlet nozzles are integrally formed.
[0078] One or more gas outlets 122 are provided in a base of the
plasma chamber 102. The gas outlets 122 are preferably located in a
ring around the substrate holder 104 and most preferably form a
uniformly spaced array around the substrate holder 104 to enhance
continuous gas flow from the gas inlet 120 towards the substrate
105, around the substrate 105, and out of the gas outlets 122 while
minimizing turbulence and gas recirculation back up the plasma
chamber 102. In this regard, it should be noted that while the
reactor configuration functions to reduce uncontrolled gas
re-circulation within the plasma chamber, this does not preclude
the possibility of using a controlled gas re-circulation system
outside the plasma chamber for re-using process gas which is
extracted from the plasma chamber through the gas outlets.
Synthesis Conditions
[0079] WO2012/084656 describes that a CVD reactor as illustrated in
FIG. 1 can achieve CVD diamond synthesis at high gas flow rates,
high pressures, and high powers. WO2012/084656 further describes
that this is advantageous for synthesising doped CVD diamond
materials, such as boron doped CVD diamond materials, with high
dopant levels and/or more uniform dopant concentrations over larger
areas. The present applicant has found that it is possible to
maintain a high power density over large areas for extended periods
of time to achieve synthesis of large volumes of high quality CVD
diamond material at high growth rates and with less sensitivity to
impurities. In contrast to WO2012/084656, it has also been found
that high gas flow rates, high pressures, and high power densities
are advantageous for synthesising un-doped, very high purity single
crystal CVD synthetic diamond material at increased growth rates.
Previous approaches to try to increase the growth rate of very high
purity single crystal CVD diamond material involved: increasing
CH.sub.4 concentration in the synthesis atmosphere; increasing
process gas flow; and increasing substrate growth temperature. The
first two approaches led to NV incorporation while the third
approach lead to surface twinning. Only maintaining a high power
density as described herein was successful in growing very high
purity single crystal CVD diamond material with increased growth
rates.
[0080] When compared to prior art growth processes for fabricating
very high purity single crystal CVD diamond material such as that
described in WO01/096633 and WO01/096634, the present growth
process differs in that it utilizes a higher power density across
the carrier substrate, a higher pressure, a higher gas flow rate,
and a higher concentration of carbon containing process gas. In
this regard, it should be appreciated that single crystal CVD
diamond growth comprises a complex, multi-dimensional parameter
space and one embodiment involves the identification of a
combination of interrelated operating parameters within this
complex, multi-dimensional parameter space in order to achieve
fabrication of a very high purity single crystal CVD diamond
material at increased growth rates. The fabrication method
comprises: [0081] introducing process gases into a plasma chamber,
the process gases including hydrogen gas and a carbon source gas;
and [0082] introducing microwaves into the plasma chamber to
activate the process gases and form a plasma proximate to a growth
surface of a plurality of single crystal diamond substrates
disposed on a support substrate, wherein the single crystal CVD
synthetic diamond material is grown on the growth surface of each
of the plurality of single crystal diamond substrates, [0083]
wherein during growth of the single crystal CVD synthetic diamond
material the following growth conditions are utilized: [0084] a
temperature of the single crystal diamond substrates lies in a
range 750.degree. C. to 900.degree. C.; [0085] a pressure within
the plasma chamber lies in a range 175 to 225 Torr; [0086] a
hydrogen gas flow rate lies in a range 7 to 12 standard litres per
minute; [0087] a concentration of carbon source gas within the
process gas lies in a range 3.0% to 7.0%; [0088] a concentration of
nitrogen within the process gas is no more than 1 part-per-million;
and [0089] a microwave power density across the support substrate
is in a range 3 to 6 W/mm.sup.2.
[0090] Preferably, the process utilizes a microwave power of at
least 15 kW, 17 kW, 19 kW, or 22 kW. For example, the microwave
power may lie in a range 15 kW to 35 kW, 17 kW to 30 kW, 19 kW to
27 kW, or 22 kW to 25 kW. Furthermore, the support substrate may
have a diameter of at least 60 mm, 70 mm, 80 mm, 90 mm, or 100 mm
and/or no more than 140 mm, 130 mm, 120 mm, or 110 mm. For example,
the support substrate may have a diameter in a range 60 mm to 140
mm, 60 mm to 120 mm, 70 mm to 110 mm, or 80 mm to 100 mm. The
support substrate may be loaded with a plurality of single crystal
diamond substrates numbering at least 30, 40, 50 or 60.
[0091] The aforementioned process is capable of fabricating very
high purity single crystal CVD diamond material in a more
economical manner than was previously the case for such material.
Furthermore, the growth rate of the material is such that it may
also replace lower purity single crystal CVD diamond material to
the extent that it is easier to control the reproducibility of the
process when compared to a controlled nitrogen addition growth
process.
[0092] Without being bound by theory, the increase in growth rate
is attributed to an increase in flux of growth species resulting
from the higher power density, higher gas temperature, higher
carbon concentration, higher gas flow rates, and higher operating
pressures. At the same time, such operating conditions achieve
higher growth rates while also maintain very high quality single
crystal CVD diamond growth with substantially no sp2 carbon and
substantially no impurities. For example, an increase in growth
rate has been achieved without introducing NV related luminescence.
Increasing power density reduces nitrogen uptake. As such, even
when some nitrogen is present as an impurity it is still possible
to achieve very high purity single crystal CVD diamond product. It
is believed that this is due to an increase in the production of
atomic hydrogen which can prevent the uptake of impurities at the
growth surface of the diamond material. Further still, the new
material lacks dislocation luminescence which is believed to be
causally linked to the increase in growth rate in this window of
parameter space.
[0093] Certain embodiments are thus based on a single crystal CVD
diamond growth process which is substantially free of nitrogen but
which can generate growth rates over twice those achieved in prior
art growth processes which are substantially free of nitrogen such
as described in WO01/096633 and WO01/096634. Such a process can
achieve growth rates comparable to those achieved by a low and
controlled addition of nitrogen such as described in WO2004/046427.
As such, embodiments can generate a single crystal CVD diamond
material which is very high purity at increased growth rates while
avoiding the addition of nitrogen to enhance growth rates.
[0094] The single crystal CVD diamond material has many properties
comparable with those of WO01/096633 and thus has properties
suitable for certain high-end optical applications and certain
other applications such as electronic, radiation detector, and
quantum sensing and processing applications.
[0095] In addition, even for applications which are not
detrimentally affected by the presence of a low and controlled
concentration of nitrogen in the single crystal CVD synthetic
diamond material, the new growth process is capable of fabricating
a single crystal CVD diamond material which has more consistent and
reproducible optical properties while maintaining a comparable
growth rate to that achieved by a low and controlled nitrogen
addition.
[0096] Further still, the single crystal CVD diamond material
according to the present invention is distinguished over prior art
high purity single crystal CVD synthetic diamond material such as
that described in WO01/096633 and WO01/096634 in that is exhibits
substantially no fluorescence from dislocation defects in addition
to substantially no fluorescence from nitrogen-vacancy defects.
[0097] While a high purity single crystal growth process is
described above as an example of the use of the methodology
described herein, the presently described methodology is not
limited to such a high purity growth process. For example, as
previously described, it is also advantageous to apply high power
densities over large substrate areas and for extended time periods
to synthesise lower purity single crystal CVD diamond material as
high growth rates, polycrystalline CVD diamond wafers, and large
area, tiled single crystal CVD diamond products.
[0098] An example of the method steps for fabricating a large area,
tiled single crystal CVD diamond product is given below.
[0099] In step (i) a tiled array of single crystal diamond
substrates are mounted on a carrier substrate. The single crystal
diamond substrates are located in contact or close proximity.
[0100] In step (ii), a layer of single crystal CVD diamond material
is grown over the tiled array of single crystal diamond substrates.
In accordance with the present methodology synthesis is performed
by maintaining a high power density across the tiled array of
single crystal diamond substrates to aid intergrowth of diamond
material over adjacent substrates while avoiding undue nitrogen
incorporation into the layer of single crystal CVD diamond
material.
[0101] Finally, in step (iii) the layer of single crystal CVD
diamond material is optionally separated from the tiled array of
single crystal CVD diamond substrates to form a free-standing
single crystal CVD diamond wafer. One known method for achieving
release of the layer of single crystal CVD diamond material is via
implantation and chemical etching to achieve separation of the
layer of single crystal CVD diamond material from the tiled array
of single crystal CVD diamond substrates. The material product will
generally comprise a plurality of inter-crossing dislocation lines
corresponding to interfaces between individual single crystal
diamond substrates on which the layer of single crystal CVD diamond
material was grown.
Material Products
High Purity Single Crystal CVD Diamond Product
[0102] An image taken using DiamondView.TM. of a single crystal CVD
diamond material fabricated as described herein is shown in FIG. 2
while a counter example grown using the methodology as described in
WO01/096633 and WO01/096634 is shown in FIG. 3. The single crystal
CVD synthetic diamond material in FIG. 2 comprises substantially no
NV luminescence and substantially no dislocation luminescence while
the counter example shown in FIG. 3 shows significant blue
dislocation luminescence.
[0103] The orange luminescence from nitrogen-vacancy defects and
the blue luminescence from dislocation defects can be measured as
follows: [0104] (i) a DiamondView.TM. image of the single crystal
CVD synthetic diamond material is taken using an integration time
of 10 seconds with aperture and field stop settings set to 100%,
gain set to 0.00 dB, and gamma enhancement set to off; and [0105]
(ii) the DiamondView.TM. image is analysed to determine the
intensity of orange and blue luminescent components using digital
image analysis software, wherein the image analysis comprises the
following steps: [0106] (a) splitting the DiamondView.TM. image
into red, green, and blue component images, the red image
comprising the orange luminescence from nitrogen-vacancy defects
and the blue image comprising the blue luminescence from
dislocation defects; [0107] (b) converting the red and blue images
to greyscale images having an intensity range of 0 to 255 with
white corresponding to an intensity value of 255 and black
corresponding to an intensity value of 0, [0108] wherein the red
image has a mean intensity value of less than 25, 20, 15, 12, 10,
8, or 5 and [0109] wherein the blue image has a mean intensity
value of less than 25, 20, 15, 10, 8, 5, or 2.
[0110] The red image and/or the blue image may also have a mode
intensity value of less than 10, 5, or 2. Furthermore, the
DiamondView.TM. image is analysed over an area of at least 0.3
mm.sup.2, 0.6 mm.sup.2, 1.0 mm.sup.2, 2.0 mm.sup.2, 3.0 mm.sup.2,
5.0 mm.sup.2, 7.0 mm.sup.2, 10.0 mm.sup.2, 25.0 mm.sup.2, 50.0
mm.sup.2, or 100.0 mm.sup.2.
[0111] In accordance with the aforementioned methodology,
DiamondView.TM. images were analysed using the freeware Image)
program (http://rsbweb.nih.gov/ij/). It is possible to deduce a
histogram of colour values for a fluorescence image of a diamond
sample, in order to quantify its fluorescence characteristics. The
following procedure was employed to analyse the DiamondView.TM.
images of samples produced using the present synthesis methodology
and the prior art process.
[0112] For each sample, one of the {100} surfaces was analysed. A
DiamondView.TM. image was taken using an integration time of 10 s,
the aperture and field stop settings were set to 100%, the gain
value was setting to 0.00 dB (i.e. minimising noise) and the gamma
enhancement setting was set to `off` (i.e. a linear gamma curve).
The image was loaded into Image). The first stage of the analysis
involved splitting the red, green and blue components of the image
by selecting the `Split Channels` command from the `Color` submenu
under the `Image menu`.
[0113] The strength of the red/orange luminescence arising from NV
centers was quantified by analysing the red image component and
rejecting the green and blue components. The strength of the blue
luminescence arising from dislocations was quantified by analysing
the blue image component and rejecting the red and green
components. From each of the red and blue components, a selected
rectangle was taken, avoiding the sample surface, the substrate,
any twinned or included regions that could influence the
measurement, and any artefacts due to the sample holder. Note that
this rectangle should be larger than 0.3 mm.sup.2, preferably
larger than 0.6 mm.sup.2, or more preferably larger than 1.0
mm.sup.2 or more as previously described. Clicking `Analyse` and
then `Histogram` revealed the histogram and the statistical
parameters:
TABLE-US-00001 Standard RED CHANNEL Area Mean Deviation Min Max
Mode Example 1 .times. 1 mm 5.953 1.372 3 105 6 Counter Example 1
.times. 1 mm 7.641 2.832 0 63 8
TABLE-US-00002 BLUE Standard CHANNEL Area Mean Deviation Min Max
Mode Example 1 .times. 1 mm 2.845 2.201 0 93 2 Counter Example 1
.times. 1 mm 30.571 43.031 0 255 11
[0114] One can deduce the following from the above data: [0115] (i)
the red component values for the two samples are very similar,
indicating broadly comparable NV uptake in material grown using the
new process as compared to the prior art process; [0116] (ii) in
both the example and counter example, the red component of
fluorescence is very low, indicating that in both cases the
red/orange fluorescence is negligible in DiamondView.TM. images;
[0117] (iii) both the mean and the mode of the blue component
values are significantly lower for material grown using the
presently described process compared to the prior art process, as
expected from comparison of FIGS. 2 and 3; [0118] (iv) there is a
far smaller standard deviation of the blue component for material
grown using the presently described process than for the prior art
process, consistent with the blue fluorescence in the latter
arising from dislocations that have a high degree of linearity in
the DiamondView.TM. images.
[0119] From this analysis, it can be deduced that the
DiamondView.TM. images of material grown using the presently
described growth process are essentially inert. The material grown
using the new process exhibits the characteristics: [0120] (i)
negligible orange fluorescence arising from NV defects, thereby
implying a similar uptake of point defects as compared to the prior
art process; and [0121] (ii) negligible dislocation fluorescence,
unlike that of the prior art process.
[0122] For material grown using the new process, charge transport
measurements have been performed using the following procedure.
First, the samples were pre-cleaned using acid and oxygen plasma.
Then, Ti/Al mesh contacts were patterned by sputtering and
photolithography. Then, the samples were illuminated with 213 nm, 3
ns laser pulses and different bias voltages were applied to the
contacts. The total collected charge was measured by integrating
the current measured using a broadband amplifier. Fitting to Hecht
relation then gives the mobility-lifetime product and charge
collection distance. Any trapping was eliminated by illuminating
the samples with three laser pulses at zero bias between every
measurement.
[0123] Two samples grown using the new process and were measured
using this procedure. The results are shown below:
TABLE-US-00003 e- Thickness mobility h-mobility
.mu..sub.e.tau..sub.e .times. 10.sup.-6 .mu..sub.h.tau..sub.h
.times. 10.sup.-6 (.mu.m) cm.sup.2/Vs cm.sup.2/Vs cm.sup.2/V
cm.sup.2/V Sample 1 640 1350 2660 190 230 Sample 2 550 2330 2160
250 180
[0124] The current versus time plots for one of the samples (Sample
2) are shown in FIG. 4, and display clean characteristics with
little evidence of dispersion.
[0125] The material may have comparable electronic properties to
the material described in WO01/096633 and WO01/096634. For example,
the single crystal CVD synthetic diamond material may comprise one
or more of the following electronic characteristics: [0126] a
.mu..tau. product measured at 300K greater than 1.5.times.10.sup.-6
cm.sup.2V.sup.-1, 4.0.times.10.sup.-6 cm.sup.2V.sup.-1, or
6.0.times.10.sup.-6 cm.sup.2V.sup.-1, 10.times.10.sup.-6
cm.sup.2V.sup.-1, 50.times.10.sup.-6 cm.sup.2V.sup.-1,
100.times.10.sup.-6 cm.sup.2V.sup.-1, 150.times.10.sup.-6
cm.sup.2V.sup.-1, 180.times.10.sup.-6 cm.sup.2V.sup.-1,
200.times.10.sup.-6 cm.sup.2V.sup.-1, 220.times.10.sup.-6
cm.sup.2V.sup.-1, or 240.times.10.sup.-6 cm.sup.2V.sup.-1 where
.mu. is charge carrier mobility and .tau. is charge carrier
lifetime; [0127] an electron mobility (.mu..sub.e) measured at 300K
greater than 1500 cm.sup.2V.sup.-1 s.sup.-1, 2000 cm.sup.2V.sup.-1
s.sup.-1, 2400 cm.sup.2V.sup.-1 s.sup.-1, 3000 cm.sup.2V.sup.-1
s.sup.-1, or 4000 cm.sup.2V.sup.-1 s.sup.-1; [0128] a hole mobility
(.mu..sub.h) measured at 300K greater than 1500 cm.sup.2V.sup.-1
s.sup.-1, 1800 cm.sup.2V.sup.-1 s.sup.-1, 2100 cm.sup.2V.sup.-1
s.sup.-1, 2500 cm.sup.2V.sup.-1 s.sup.-1, or 3000 cm.sup.2V.sup.-1
s.sup.-1; [0129] a charge collection distance greater than 150
.mu.m, 400 .mu.m, or 600 .mu.m measured at an applied field of 1
V/.mu.m and 300 K; and [0130] a resistivity (R) greater than
1.times.10.sup.12 .OMEGA.cm, 2.times.10.sup.13 .OMEGA.cm, or
5.times.10.sup.14 .OMEGA.cm, at an applied field of 50 V.mu.m
measured at 300 K.
[0131] Furthermore, the material may have comparable optical
properties to the material described in WO01/096633 and
WO01/096634. For example, the single crystal CVD synthetic diamond
material may comprise one or more of the following characteristics:
[0132] a photoluminescence (PL) line related to the
cathodoluminescence (CL) line at 575 nm, measured at 77 K under 514
nm Ar ion laser excitation (nominally 300 mW incident beam), which
has a peak height less than 1/1000 of the diamond Raman peak at
1332 cm.sup.-1; and [0133] a free exciton (FE) emission, where the
strength of the free exciton emission excited by 193 nm ArF excimer
laser at room temperature is such that the quantum yield for free
exciton emission is at least 10.sup.-5.
[0134] Further still, the material may have some optical properties
comparable to the material described in WO2004/046427 and
WO2007/066215. For example, the single crystal CVD synthetic
diamond material may comprise one or more of the following
characteristics: [0135] an extended defect density as characterised
by X-ray topography of less than 400/cm.sup.2 over an area of
greater than 0.014 cm.sup.2; [0136] an optical isotropy of less
than 1.times.10.sup.-5 over a volume greater than 0.1 mm.sup.3;
[0137] an X-ray rocking curve for the (004) reflection has a full
width at half maximum (FWHM) of less than 10 arc seconds; [0138] a
birefringence of no more than 1.times.10.sup.-5 determined using a
light beam with a cross-sectional area greater than 0.01
mm.sup.2.
[0139] In relation to the above, in order to achieve these
characteristics it is advantageous to utilize single crystal
diamond substrates having a low concentration of surface defects
and carefully treat such substrates with an in situ plasma etch
prior to performing single crystal CVD diamond growth thereon as
described, for example, in WO01/096633 and WO01/096634.
[0140] Furthermore, according to certain embodiments the material
shares some of the quantum properties of the materials described in
WO 2010010344 and WO 2010010352. For example, the single crystal
CVD synthetic diamond material may comprise one or more of the
following characteristics: [0141] one or more NV.sup.- defects
having a decoherence time T.sub.2 at room temperature of no less
than 100 .mu.s, 300 .mu.s, 500 .mu.s, 1 ms, 2 ms, 5 ms, 10 ms, 50
ms, or 100 ms; and [0142] one or more NV.sup.- defects having a
full width half maximum intrinsic inhomogeneous zero phonon line
width of no more than 500 MHz, 300 MHz, 200 MHz, 150 MHz, 100 MHz,
80 MHz, 50 MHz, or 40 MHz wherein the full width half maximum
intrinsic inhomogeneous zero phonon line width is averaged over at
least 10, 20, 30, 50, 75, 100, 500, or 1000 seconds and/or over at
least 10, 20, 30, 50, 75, 100, 500, or 1000 spectral scans.
[0143] In order to achieve very low full width half maximum
intrinsic inhomogeneous zero phonon line widths the material may be
subjected to annealing such as a multi-stage annealing treatment
after synthesis. Furthermore, in order to achieve very high
decoherence times the material may be fabricated using isotopically
purified carbon source gas.
[0144] In terms of impurities, the single crystal CVD synthetic
diamond material may comprise one or more of: [0145] a total
nitrogen concentration, as measures by secondary ion mass
spectrometry, of no more than 100 ppb, 60 ppb 40 ppb, 20 ppb, or 10
ppb; [0146] a single substitutional nitrogen concentration, as
measured by electron paramagnetic resonance, of no more than 100
ppb, 60 ppb 40 ppb, 20 ppb, or 10 ppb; [0147] an as-grown
nitrogen-vacancy defect concentration of no more than 20 ppb, 10
ppb, 5 ppb, or 1 ppb; [0148] a concentration of boron (and/or a
concentration of uncompensated substitutional boron) of no more
than 100 ppb, 50 ppb, 20 ppb, 10 ppb, 5 ppb, 2 ppb, 1 ppb, 0.5 ppb,
0.2 ppb, or 0.1 ppb; [0149] a concentration of silicon of no more
than 100 ppb, 50 ppb, 20 ppb, 10 ppb, 5 ppb, 2 ppb, 1 ppb, 0.5 ppb,
0.2 ppb, 0.1 ppb, or 0.05 ppb; [0150] a concentration of the
silicon-vacancy (referred to as "SiV"), characterised by the
intensity of the 737 nm photoluminescence (PL) line normalised
against the intensity of the diamond Raman line at a shift of about
1332.5 cm.sup.-1, both measured at a temperature of about 77 K, of
no more than 0.5 ppb, 0.2 ppb, 0.1 ppb, 0.05 ppb, 0.02 ppb, 0.01
ppb, or 0.005 ppb; [0151] a concentration of intrinsic paramagnetic
defects (i.e. defects which have a non-zero magnetic spin) of no
more than 1 ppm, 0.5 ppm, 0.2 ppm, 0.1 ppm, 0.05 ppm, 0.02 ppm,
0.01 ppm, 0.005 ppm, or 0.001 ppm; [0152] a total concentration of
.sup.13C of 0.9% or less; [0153] a concentration of any single
non-hydrogen impurity of no more than 5 ppm, 1 ppm, or 0.5 ppm;
[0154] a total impurity content excluding hydrogen and its isotopes
of no more than 10 ppm, 5 ppm, or 2 ppm; and [0155] a concentration
of hydrogen impurities (specifically hydrogen and its isotopes) of
no more than 10.sup.18 cm.sup.-3, 10.sup.17 cm.sup.-3, 10.sup.16
cm.sup.-3, or 10.sup.15 cm.sup.-3.
Large Area, Tiled Single Crystal CVD Diamond Product
[0156] A large area single crystal CVD diamond layer can be formed
as described herein by growing over a tiled array of substrates and
using high power densities over large areas to drive growth of the
tiled substrates. Although the large area single crystal CVD
diamond layer is formed of single crystal CVD diamond material, the
material may exhibit a plurality of inter-crossing dislocation
lines corresponding to interfaces between individual single crystal
diamond substrates on which the layer of single crystal CVD diamond
material was grown. Such large area tiled single crystal CVD
diamond layers or wafers have already been described previously in
the art. The distinction here is that the large area, tiled single
crystal CVD diamond wafer comprises a low nitrogen content with
overgrowth over a tiled array of substrates being driven by use of
a high power density rather than significant quantities of nitrogen
in the process gases. As such, a single crystal CVD diamond layer
is provided comprising: [0157] a total nitrogen concentration as
measures by secondary ion mass spectrometry of no more than 2 ppm;
and [0158] an area of at least 324 mm.sup.2.
[0159] The total nitrogen concentration may be no more than 1.5
ppm, 1.0 ppm, 0.8 ppm, 0.5 ppm 0.1 ppm, 0.05 ppm, or 0.01 ppm
depending on the requirements of the end application. Furthermore,
the area of the single crystal CVD diamond wafer may be at least
361 mm.sup.2, 400 mm.sup.2, 484 mm.sup.2, 625 mm.sup.2, 900
mm.sup.2, 1600 mm.sup.2, or 2500 mm.sup.2. Further still, the
single crystal CVD diamond wafer has a thickness of at least 30
micrometers, 60 micrometers, 100 micrometers, 150 micrometers, 200
micrometers, 250 micrometers, 300 micrometers, or 500 micrometers.
The single crystal CVD diamond wafer may also exhibit one or both
of the following characteristics: [0160] (i) an optical absorption
coefficient at a wavelength of 1.064 .mu.m of less than 0.09
cm.sup.-1, 0.05 cm.sup.-1, 0.02 cm.sup.-1, or 0.01 cm.sup.-1.
[0161] (ii) an optical absorption coefficient at a wavelength of
10.6 .mu.m of less than 0.04 cm.sup.-1, 0.03 cm.sup.-1, 0.02
cm.sup.-1, or 0.01 cm.sup.-1.
[0162] Furthermore, if growth conditions are selected to fabricate
very high purity single crystal diamond material as described
previously then the single crystal CVD diamond layer or
free-standing wafer may comprise a plurality or regions formed of
single crystal CVD diamond material having one or more of the
characteristics as previous described in relation to the high
purity single crystal CVD diamond product.
Devices and Applications
[0163] The aforementioned material characteristics are advantageous
for a range of different devices and applications.
[0164] The electronic characteristics are advantageous for use in
electronic and radiation detector devices. See, for example, U.S.
Pat. No. 6,204,522, U.S. Pat. No. 6,222,141, and U.S. Pat. No.
8,053,783 which relate to high power switching device and
WO99/64892, WO01/69285, and WO2004/023160 which relate to radiation
detector devices utilizing single crystal CVD diamond material.
[0165] The thermal characteristics are advantageous for use in
thermal heat spreading applications such as in electronic and
optical devices.
[0166] The optical characteristics are advantageous for use as
optical components such as prisms for ATR spectroscopy, high power
laser windows and lenses, and Raman laser crystals. See, for
example, U.S. Pat. No. 6,507,396, U.S. Pat. No. 8,309,205,
WO2012/013687, WO2102/034926, and WO2011/086164.
[0167] The quantum characteristics are advantageous for use in
quantum sensing and information processing applications. See, for
example, WO2009/073736 and WO2009/073740 which describe diamond
based quantum magnetometers, WO2012/034924 which describes a
diamond based microfluidic NMR device, and GB2495632 which
describes a diamond based multi-photon quantum interference device
suitable for quantum information processing applications.
[0168] While this invention has been particularly shown and
described with reference to embodiments, it will be understood to
those skilled in the art that various changes in form and detail
may be made without departing from the scope of the invention as
defined by the appending claims.
* * * * *
References