U.S. patent application number 12/253287 was filed with the patent office on 2009-02-12 for apparatus and method for diamond production.
Invention is credited to Russell J. Hemley, Ho-Kwang Mao, Yogesh K. Vohra, Chih-shiue Yan.
Application Number | 20090038934 12/253287 |
Document ID | / |
Family ID | 23292514 |
Filed Date | 2009-02-12 |
United States Patent
Application |
20090038934 |
Kind Code |
A1 |
Hemley; Russell J. ; et
al. |
February 12, 2009 |
APPARATUS AND METHOD FOR DIAMOND PRODUCTION
Abstract
An apparatus for producing diamond in a deposition chamber
including a heat-sinking holder for holding a diamond and for
making thermal contact with a side surface of the diamond adjacent
to an edge of a growth surface of the diamond, a noncontact
temperature measurement device positioned to measure temperature of
the diamond across the growth surface of the diamond and a main
process controller for receiving a temperature measurement from the
noncontact temperature measurement device and controlling
temperature of the growth surface such that all temperature
gradients across the growth surface are less than 20.degree. C. The
method for producing diamond includes positioning diamond in a
holder such that a thermal contact is made with a side surface of
the diamond adjacent to an edge of a growth surface of the diamond,
measuring temperature of the growth surface of the diamond to
generate temperature measurements, controlling temperature of the
growth surface based upon the temperature measurements, and growing
single-crystal diamond by microwave plasma chemical vapor
deposition on the growth surface, wherein a growth rate of the
diamond is greater than 1 micrometer per hour.
Inventors: |
Hemley; Russell J.; (Chevy
Chase, MD) ; Mao; Ho-Kwang; (Washington, DC) ;
Yan; Chih-shiue; (Washington, DC) ; Vohra; Yogesh
K.; (Birmingham, AL) |
Correspondence
Address: |
MORGAN LEWIS & BOCKIUS LLP
1111 PENNSYLVANIA AVENUE NW
WASHINGTON
DC
20004
US
|
Family ID: |
23292514 |
Appl. No.: |
12/253287 |
Filed: |
October 17, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11785996 |
Apr 23, 2007 |
7452420 |
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12253287 |
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11043062 |
Jan 27, 2005 |
7235130 |
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11785996 |
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10288499 |
Nov 6, 2002 |
6858078 |
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11043062 |
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60331073 |
Nov 7, 2001 |
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Current U.S.
Class: |
204/173 |
Current CPC
Class: |
C30B 25/105 20130101;
C30B 25/12 20130101; C30B 29/04 20130101; Y10T 117/1004 20150115;
Y10T 117/1008 20150115; Y10T 117/108 20150115; Y10T 117/1016
20150115 |
Class at
Publication: |
204/173 |
International
Class: |
C01B 31/06 20060101
C01B031/06 |
Goverment Interests
STATEMENT OF GOVERNMENT INTEREST
[0002] This invention was made with Government support under Grant
Nos. EAR-8929239 and DMR-9972750 awarded by the National Science
Foundation. The Government has certain rights in this invention.
Claims
1.-64. (canceled)
65. In a method for diamond production, comprising controlling
temperature of a growth surface of the diamond such that all
temperature gradients across the growth surface are less than
20.degree. C.; and growing single-crystal diamond by microwave
plasma chemical vapor deposition on the growth surface at a
temperature of 900-1400.degree. C. in a deposition chamber having
an atmosphere with a pressure of at least 130 torr, the
modification wherein said atmosphere includes oxygen.
66. The method of claim 1, wherein said atmosphere further includes
hydrogen and Methane.
67. The method of claim 2, wherein said atmosphere further includes
nitrogen.
68. The method of claim 3, wherein said atmosphere includes 1-5%
nitrogen per unit of hydrogen and 6-12% methane per unit of
hydrogen.
69. The method of claim 4, wherein said atmosphere includes 1-3%
oxygen per unit of hydrogen.
Description
[0001] The present invention claims the benefit of Provisional
Application No. 60/331,073 filed on November 7, 2001, which is
hereby incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to an apparatus and a method
for producing diamond, and more particularly, for growing diamond
using Microwave Plasma Chemical Vapor Deposition (MPCVD) within a
deposition chamber.
[0005] 2. Description of Related Art
[0006] Large-scale production of synthetic diamond has long been an
objective of both research and industry. Diamond, in addition to
its gem properties, is the hardest known material, has the highest
known thermal conductivity, and is transparent to a wide variety of
electromagnetic radiation. Therefore, it is valuable because of its
wide range of applications in a number of industries, in addition
to its value as a gemstone.
[0007] For at least the last twenty years, a process of producing
small quantities of diamond by chemical vapor deposition (CVD) has
been available. As reported by B. V. Spitsyn et al. in "Vapor
Growth of Diamond on Diamond and Other Surfaces," Journal of
Crystal Growth, vol 52, pp. 219-226, the process involves CVD of
diamond on a substrate by using a combination of methane, or
another simple hydrocarbon gas, and hydrogen gas at reduced
pressures and temperatures of 800-1200.degree. C. The inclusion of
hydrogen gas prevents the formation of graphite as the diamond
nucleates and grows. Growth rates of up to 1 .mu.m/hour have been
reported with this technique.
[0008] Subsequent work, for example, that of Kamo et al. as
reported in "Diamond Synthesis from Gas Phase in Microwave Plasma,"
Journal of Crystal Growth, vol. 62, pp. 642-644, demonstrated the
use of Microwave Plasma Chemical Vapor Deposition (MPCVD) to
produce diamond at pressures of 1-8 Kpa in temperatures of
800-1000.degree. C. with microwave power of 300-700 W at a
frequency of 2.45 GHz. A concentration of 1-3% methane gas was used
in the process of Kamo et al. Maximum growth rates of 3 .mu.m/hour
have been reported using this MPCVD process.
[0009] In the above-described processes, and in a number of more
recently reported processes, the growth rates are limited to only a
few micrometers per hour. Known higher-growth rate processes only
produce or grow polycrystalline forms of diamond. Typically,
attempts to produce single-crystal diamond at grown rates higher
than about one micrometer per hour result in heavily twinned single
crystal diamonds, polycrystalline diamond, or no diamond at all.
Further, known processes for growing diamond usually require low
pressures of less than 100 torr.
SUMMARY OF THE INVENTION
[0010] Accordingly, the present invention is directed to a an
apparatus and a method for producing diamond that substantially
obviates one or more of the problems due to limitations and
disadvantages of the related art.
[0011] An object of the present invention relates to an apparatus
and method for producing diamond in a microwave plasma chemical
vapor deposition system at a high growth rate and at moderate
pressures.
[0012] Additional features and advantages of the invention will be
set forth in the description which follows, and in part will be
apparent from the description, or may be learned by practice of the
invention. The objectives and other advantages of the invention
will be realized and attained by the structure particularly pointed
out in the written description and claims hereof as well as the
appended drawings.
[0013] To achieve these and other advantages and in accordance with
the purpose of the present invention, as embodied and broadly
described, an embodiment of the apparatus for producing diamond in
a deposition chamber includes a heat-sinking holder for holding a
diamond and for making thermal contact with a side surface of the
diamond adjacent to an edge of a growth surface of the diamond, a
noncontact temperature measurement device positioned to measure
temperature of the diamond across the growth surface of the diamond
and a main process controller for receiving a temperature
measurement from the noncontact temperature measurement device and
controlling temperature of the growth surface such that all
temperature gradients across the growth surface are less than
20.degree. C.
[0014] In another embodiment, a specimen holder assembly for
producing diamond includes a diamond, a heat-sinking holder making
thermal contact with a side surface of the diamond adjacent to an
edge of a growth surface of the diamond, wherein the diamond is
slidably mounted within the heat-sinking holder, a stage for
receiving thermal energy from the heat-sinking holder, and a first
actuator member that can translate along an axis substantially
perpendicular to the growth surface for repositioning the diamond
within the heat-sinking holder.
[0015] In another embodiment, a specimen holder assembly for
producing diamond includes a diamond, a heat-sinking holder making
thermal contact with a side surface of the diamond adjacent to an
edge of a growth surface of the diamond, a thermal mass for
receiving thermal energy from the heat-sinking holder, wherein the
diamond is retained in the heat-sinking holder by pressure applied
through the thermal mass, and a stage for receiving thermal energy
from the heat-sinking holder via the thermal mass.
[0016] In accordance with another embodiment of the present
invention, a method for producing diamond includes positioning
diamond in a holder such that a thermal contact is made with a side
surface of the diamond adjacent to an edge of a growth surface of
the diamond, measuring temperature of the growth surface of the
diamond to generate temperature measurements, controlling
temperature of the growth surface based upon the temperature
measurements, and growing single-crystal diamond by microwave
plasma chemical vapor deposition on the growth surface, wherein a
growth rate of the diamond is greater than 1 micrometer per
hour.
[0017] In accordance with another embodiment of the present
invention, a method for producing diamond includes positioning
diamond in a holder, measuring temperature of a growth surface of
the diamond to generate temperature measurements, controlling
temperature of the growth surface with a main process controller
using the temperature measurements such that all temperature
gradients across the growth surface are less than 20.degree. C.,
growing diamond on the growth surface and repositioning the diamond
in the holder.
[0018] In accordance with another embodiment of the present
invention, a method for producing diamond includes controlling
temperature of a growth surface of the diamond such that all
temperature gradients across the growth surface are less than
20.degree. C. and growing single-crystal diamond by microwave
plasma chemical vapor deposition on the growth surface at a growth
temperature in a deposition chamber having an atmosphere with a
pressure of at least 130 torr.
[0019] In accordance with another embodiment of the present
invention, a method for producing diamond includes controlling
temperature of a growth surface of the diamond such that all
temperature gradients across the growth surface are less than
20.degree. C.; and growing single-crystal diamond by microwave
plasma chemical vapor deposition on the growth surface at a
temperature of 900-1400.degree. C.
[0020] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are intended to provide Per explanation of the
invention as claimed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The accompanying drawings, which are included to provide a
further understanding of the invention and are incorporated in and
constitute a part of this specification, illustrate embodiments of
the invention and together with the description serve to explain
the principles of the invention.
[0022] FIG. 1 is a diagram of a diamond production apparatus
according to an embodiment of the present invention in which a
cross-section of deposition apparatus with a specimen holder
assembly for holding the diamond stationary during a diamond growth
process is depicted.
[0023] FIG. 2a is a perspective view of the deposition apparatus
shown in FIG. 1.
[0024] FIG. 2b is a perspective view of the diamond and sheath
shown in FIG. 1.
[0025] FIG. 3 is a diagram of a diamond production apparatus
according to an embodiment of the present invention in which a
cross-section of a deposition apparatus with a specimen holder
assembly for moving the diamond during the diamond growth process
is depicted.
[0026] FIGS. 4a-4c depict cross-sectional views of holders or
thermal masses that can be used in accordance with the present
invention.
[0027] FIG. 5 is a diagram of a diamond production apparatus
according to another embodiment of the present invention in which a
cross-section of a deposition apparatus with a specimen holder
assembly for moving the diamond during the diamond growth process
is depicted.
[0028] FIG. 6 is a flow diagram illustrating a process 600 in
accordance with embodiments of the present invention that can be
used with the specimen holder assembly shown in FIG. 1.
[0029] FIG. 7 is a flow diagram illustrating a process 700 in
accordance with embodiments of the present invention that can be
used with the specimen holder assembly shown in FIG. 3 or with the
specimen holder assembly shown in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Reference will now be made in detail to the preferred
embodiments of the present invention, examples of which are
illustrated in the accompanying drawings. FIG. 1 is a diagram of a
diamond production system 100, according to an embodiment of the
present invention, in which a deposition apparatus 102 is depicted
in cross-section. The diamond production system 100 includes a
Microwave Plasma Chemical Vapor Deposition (MPCVD) system 104 that
contains a deposition apparatus 102 as well as reactant and plasma
controls 106. For example, the MPCVD system 104 can be a WAVEMAT
MPDR 330 313 EHP made by Wavemat, Inc. Such a MPCVD system is
capable of producing a 6-kilowatt power output at a frequency of
2.45 GHz, and has a chamber volume of approximately 5,000 cubic
centimeters. However, the MPCVD system specifications can vary with
the scale of a deposition process in terms of size of the
deposition area and/or rate of deposition.
[0031] The MPCVD system 104 includes a chamber within the
deposition apparatus 102 that is at least in part defined by a bell
jar 108, which is used in sealing the chamber. Prior to MPCVD
operations, the air within the chamber is withdrawn. For example, a
first mechanical type of vacuum pump is used to draw down the
chamber and then a second high vacuum type of vacuum pump, such as
a turbopump or cryopump, further draws out the air inside the
chamber. Plasma is generated within the chamber by a set of plasma
electrodes spaced apart within the chamber. Neither the pumps nor
the plasma electrodes are illustrated in FIG. 1.
[0032] The deposition apparatus 102 also includes a specimen holder
assembly 120 installed within the chamber of the MPCVD system 104.
Typically, a specimen holder assembly is positioned in the center
of the deposition chamber floor 122 of the deposition apparatus
102, as shown in FIG. 1. The specimen holder assembly 120 shown in
FIG. 1 is illustrated in cross-section. The specimen holder
assembly 120 can include a stage 124 installed in the floor of the
deposition apparatus 102.
[0033] As shown in FIG. 1, the stage 120 can be attached to the
deposition chamber floor 122 using bolts 126a and 126c. The stage
124 can be molybdenum or any other type of material having a high
thermal conductivity. In addition, the stage 124 can be cooled
during the process of growing diamond by a coolant passing through
a coolant pipe 128 within the stage 124. The coolant can be water,
a refrigerant or other types of fluid with sufficient heat carrying
capacity to cool the stage. Although the coolant pipe is shown as
having a U-shaped path through the stage 124 in FIG. 1, the coolant
pipe 128 can have a helically shaped path or other types of paths
within the stage 124 to more efficiently cool the stage 124.
[0034] Positioned on the stage 124 of the specimen holder assembly
120, as shown in FIG. 1, is a set ring 130 having set screws, such
as screws 131a and 131c, for tightening collets 132a and 132b
around a sheath 134 that holds diamond 136. The sheath 134 is a
holder, which makes a thermal contact with a side surface of the
diamond 136 adjacent to an edge of a top surface of the diamond
136. Because collets 132a and 132b are tightened onto the sheath
134 by screws 131, the sheath 134 holds the diamond 136 in a
stationary position and acts as a heat-sink to prevent the
formation of twins or polycrystalline diamond along the edges of
the growth surface of the diamond 136.
[0035] The diamond 136 can include a diamond seed portion 138 and a
grown diamond portion 140. The diamond seed portion 138 can be a
manufactured diamond or a natural diamond. As shown in FIG. 1, the
top surface or growth surface of the diamond 136 is positioned
within a region of the plasma 141 having a resonant power at a
height H above the deposition chamber floor 122. The resonant power
can be the maximum resonant power within the plasma 141 or a degree
thereof. The top surface or growth surface of the diamond 136 is
initially the diamond seed portion 138 and is then the grown
diamond portion 140 as the diamond grows.
[0036] As shown in FIG. 1, the top edge of the sheath 134 is at a
distance D just below the top surface or top edges of the diamond
136. The distance D should be sufficiently large enough to expose
the edges of the growth surface of the diamond 136 to the plasma
141. However, the distance D can not be so large as to prevent the
heat-sinking effect of the sheath 134 that prevents the formation
of twins or polycrystalline diamond along the edges of the growth
surface of the diamond 136. Thus, D should be within a specified
distance range, such as 0-1.5 mm. The distance D and the height H,
as shown in FIG. 1, are manually set using the screws 131 of the
set ring 130 by positioning the diamond 136 in the sheath,
positioning the sheath in the collets 132a and 132b, and then
tightening the screws 131.
[0037] FIG. 2 is a perspective view of the deposition apparatus
shown in FIG. 1. In the center of the deposition chamber floor 122
of FIG. 2 is a circular stage 124 with a central recess 125. As
shown in FIG. 2, the stage 124 is held in position by bolts
126a-126d. The stage 124 can be formed of molybdenum or other
materials having a high thermal conductivity. A set ring 130 with
four screws 131a-131b is positioned within the recess 125 of the
stage 124 along with collets 132a-132b. In the alternative, the set
ring 130 can be bolted to the stage 124 to increase thermal
conductance between the stage and the set ring.
[0038] As shown in FIG. 2a, a rectangular sheath 134, which can
either be a short length of rectangular tubing or a sheet folded
into a rectangle, is positioned in the collets 132a and 132b with a
diamond 136 therein. The sheath 124 can be molybdenum or any other
type of material having a high thermal conductivity. The screws
131a-131d are tightened on the collets 132a-132b such that the
sheath 134 is tightened onto the diamond 136 such that the sheath
134 acts as a heat sink on the four side surfaces of the diamond
136. As shown in FIG. 1, the sheath 134 also makes thermal contact
to the stage 124. The collets 132a-132b make thermal contact with
the stage 124 and serve as thermal masses for transferring heat
from the sheath 134 into the stage 124. The tightening of the
sheath 134 onto the diamond 136 increases the quality of the
thermal contact between the diamond and the sheath. As shown in
FIG. 1, the sheath 134 can also make thermal contact to the stage
124. Although a rectangular shape is shown in FIG. 2a for both the
sheath and the diamond, the sheath and the diamond can have any
geometric shape such as elliptical, circular or polygonal. The
shape of the sheath or holder should be substantially the same as
the diamond.
[0039] In the exemplary embodiment of the invention shown in FIGS.
1 and 2a, the stage 124 can have a diameter of approximately 10.1
cm. and the sheath 134 can be approximately 2.5 cm wide. Regardless
of the dimensions selected for the stage and the sheath 134, the
thermal mass of the stage 122, molybdenum sheath 124, and collets
132 can be adjusted to provide an optimal heat sink for the diamond
136. Additionally, the path and extent of the coolant pipes 128 can
be modified for greater cooling effect, especially if a
particularly large diamond is to be produced. Further, a
refrigerant or other low temperature fluids can be used as a
coolant.
[0040] Molybdenum is only one potential material used in the stage
124, set ring 130, collets 132, sheath 134 and other components.
Molybdenum is suitable for these components because it has a high
melting point, which is 2617.degree. C., and a high thermal
conductivity. In addition, a large graphite build-up does not tend
to form on molybdenum. Other materials, such as molybdenum-tungsten
alloys or engineered ceramics, having high melting points above the
process temperature and a thermal conductivity comparable to that
of molybdenum, can alternatively be used instead of molybdenum.
[0041] Returning to FIG. 1, another component of the diamond
production system 100 is an noncontact measurement device, such as
an infrared pyrometer 142, which is used to monitor the temperature
of the diamond seed 138 and later the grown diamond 140 during the
growth process without contacting the diamond 136. The infrared
pyrometer 142 can be, for example, a MMRON M77/78 two color
infrared pyrometer from Mikron Instruments, Inc. of Oakland, N.J.
The infrared pyrometer 142 is focused on the diamond seed 138 or
later on the grown diamond 140 with a target area measure of 2 mm.
By using the infrared pyrometer 142, the temperature of the growth
surface of the diamond 136 is measured to within 1.degree. C.
[0042] The diamond production system 100 of FIG. 1 also includes an
MPCVD process controller 144. The MPCVD process controller 144 is
typically provided as a component of the MPCVD system 104. As is
well-known in the art, the MPCVD process controller 144 exercises
feedback control over a number of MPCVD parameters, including, but
not limited to, the process temperature, gas mass flow, plasma
parameters, and reactant flow rates by using the reactant and
plasma controls 106. The MPCVD process controller 144 operates in
cooperation with a main process controller 146. The main process
controller 146 takes input from the MPCVD controller 144, the
infrared pyrometer 142, and from other measuring devices of other
components in the diamond production system 100 and carries out
executive-level control over the process. For example, the main
process controller 146 can measure and control coolant temperatures
and/or flow rates of the coolant in the stage using a coolant
controller 148.
[0043] The main process controller 146 can be a general purpose
computer, a special purpose computing system, such as an ASIC, or
any other known type of computing system for controlling MPCVD
processes. Depending on the type of main process controller 146,
the MPCVD process controller 144 can be integrated into the main
process controller so as to consolidate the functions of the two
components. For example, the main process controller 146 can be a
general purpose computer equipped with the LabVIEW programming
language from National Instruments, Inc. of Austin, Tex. and the
LabVIEW program such that the general purpose computer is equipped
to control, record, and report all of the process parameters.
[0044] The main process controller 146 in FIG. 1 controls the
temperatures of the growth surface such that all the temperature
gradients across the growth surface of the diamond are less than or
equal to 20.degree. C. Precise control over growth surface
temperatures and growth surface temperature gradients prevents the
formation of polycrystalline diamond or twins such that a large
single crystal diamond can be grown. The ability to control all of
the temperature gradients across the growth surface of the diamond
136 is influenced by several factors, including the heat sinking
capability of the stage 124, the positioning of the top surface of
the diamond in the plasma 141, the uniformity of the plasma 141
that the growth surface of the diamond is subjected to, the quality
of thermal transfer from edges of the diamond via the holder or
sheath 134 to the stage 124, the controllability of the microwave
power, coolant flow rate, coolant temperature, gas flow rates,
reactant flow rate and the detection capabilities of the infrared
pyrometer 142. Based upon temperature measurements from the
pyrometer 142, the main process controller 146 controls the
temperature of the growth surface such that all temperature
gradients across the growth surface are less than 20.degree. C. by
adjusting at least one of microwave power to the plasma 141, the
coolant flow rate, coolant temperature, gas flow rates and reactant
flow rate.
[0045] FIG. 2b is a perspective view of the diamond 136 shown in
FIG. 1 depicting exemplary points P1, P2, P3 and P4 along the
growth surface 137 of the diamond 136. FIG. 2b also depicts the
distance D between the growth surface 137 or top edges 139 of the
diamond 136 and an edge 135 of the sheath 134. Typically, large
temperature variations, in terms of temperature differences across
the growth surface, occur between the edges and the middle of the
growth surface of the diamond. For example, larger temperature
gradients occur between the points P1 and P2 than occur between the
points P1 and P3. In another example, larger temperature gradients
occur between the points P4 and P2 than occur between the points P4
and P3. Thus, controlling temperature of the growth surface of the
diamond such that all temperature gradients across the growth
surface are less than 20.degree. C. should at least take into
account a temperature measurement between the middle and an edge
139 of the growth surface 137. For example, the main controller 146
may control the temperature of the growth surface such that the
temperature gradient between points P1 and P2 is less than
20.degree. C.
[0046] The spot size of the infrared pyrometer can affect the
ability to monitor temperature gradients across the top surface of
the diamond and thus the growth rate of the diamond. For example,
if the size of the diamond is large in comparison to the spot size
of the infrared pyrometer, the temperature at each of the edges of
the growth surface of the diamond can be outside of the field of
view of the infrared pyrometer. Thus, multiple infrared pyrometers
should be used for a diamond with a large growing area. Each of the
multiple pyrometers should be focused on different edges about the
surface of the diamond and preferably near the corners, if any.
Thus, the main process controller 146, as shown in FIG. 1, should
be programmed to integrate overlapping fields of view from the
multiple pyrometers to produce a contiguous "map" of the
temperatures across the diamond's surface or interpolate between
non-overlapping fields of view to a produce an interpreted "map" of
the temperatures across the diamond's growth surface. In the
alternative, the temperature gradient between a single edge or
corner point with respect to the middle of the growth surface can
be monitored as indicative of the maximum temperature gradient that
exists across the growth surface of the diamond.
[0047] In addition to the infrared pyrometer 142 for temperature
control, other process control instrumentation may be included in
the diamond production system 100. Additional process control
instrumentation can include equipment for determining the type and
quality of the diamond 136 while the growth process is underway.
Examples of such equipment include visible, infrared, and Raman
spectrometers, which are optical in nature and can be focused on
the same point as the infrared pyrometer 142 to obtain data on the
structure and quality of the diamond while growth is underway. If
additional equipment is provided, it can be connected to the main
process controller 146 such that the main process controller 146
controls the instrumentation and presents the results of the
analytical methods along with other status information. Additional
process control instrumentation may be particularly useful in
experimental settings, in "scaling up" a process to produce larger
diamonds, and in quality control efforts for an existing diamond
production system 100 and corresponding process.
[0048] As the diamond 136 grows, both the distance D and the height
H increase. As the distance D increases, the heat-sinking capacity
of the sheath 134 for the top edges 139 of the growth surface of
the diamond 136 reduces. In addition, characteristics of the
plasma, such as temperature and/or consistency, change as the
growth surface of the diamond 136 extends into the plasma 141. In
the diamond production system 100, the growth process is
periodically halted so that the position of the diamond 136 can be
adjusted downward with respect to the sheath 134 to reduce the
distance D, and both the diamond 136 and the sheath 134 can be
adjusted downward with respect to the deposition chamber floor 122
to reduce the height H. This repositioning allows the diamond
growth of on the growth surface of the diamond 136 to occur within
a desired region of resonant power within the plasma 141, allows
the infrared pyrometer 142 and any additional instruments to remain
focused on the growth surface of the diamond 136, and has the
effect of maintaining an efficient thermal contact for sinking heat
from the edges of the growth surface of the diamond 136. However,
repeatedly halting the growth process can be inconvenient for
large-scale production, and increases the chance of introducing
contamination into the process if not carefully performed.
[0049] FIG. 3 is a diagram of a diamond production apparatus 300
according to an embodiment of the present invention in which a
cross-section of deposition apparatus 304 with a specimen holder
assembly 320 for moving the diamond 136 during the diamond growth
process is depicted. Some of the components of diamond production
apparatus 300 are substantially the same as those of diamond
production system 100, and thus, the discussion above with regard
to FIG. 1 will suffice to describe those components likewise
numbered in FIG. 3. For example, the pyrometer 142, deposition
chamber floor 122, coolant pipe 128 and bell jar 108 in FIG. 3 are
substantially the same as those described in FIG. 1.
[0050] As show in FIG. 3, the diamond 136 is mounted on a diamond
actuator member 360 within the sheath 134 of the specimen holder
assembly 320. The diamond 136 is slidably mounted within the sheath
134 on a diamond actuator member 360 that translates along an axis
substantially perpendicular to the growth surface. The diamond
actuator member 360 protrudes through a stage 324 and is controlled
from underneath the stage 324 with a diamond control, which is
shown as a part of the coolant and diamond/holder controls 329 in
FIG. 3. The diamond actuator member 360 is or setting the height H
between the growth surface of Me diamond 136 and the deposition
chamber floor 122. Although the diamond actuator member 360 in FIG.
3 is shown as a threaded rod, the diamond actuator member can be of
any geometric shape that enables positioning of the diamond 136 at
height or position above the deposition chamber floor. Those
skilled in the art will realize that components placed within the
bell jar, such as the diamond actuator member 360, should be vacuum
compatible so as to avoid problems in maintaining the desired
atmosphere.
[0051] The actuator (not shown) for the diamond actuator member 360
is a motor (not shown). However, the actuator can be any one of a
number of known types of actuator, depending on the size of diamond
that is to be grown, the growth rate, and the level of movement
precision required. For example, if the diamond 136 is small in
size, a piezoelectric actuator may be used. If the diamond 136 is
relatively large or can be grown relatively large, a motorized
computer-controllable actuator is preferred. Regardless of the
particular actuator employed, the main process controller 346
controls the movement of the diamond actuator member 360 so that
the diamond 136 can be automatically moved downward as diamond
growth progresses.
[0052] In addition, a holder actuator member 362 protrudes through
the stage 324 and is controlled from underneath the stage 324 with
holder control, which is shown as a part of the coolant and
diamond/holder controls 329 in FIG. 3. The holder actuator member
362 translates along an axis substantially perpendicular to the
growth surface and is for maintaining the distance D between an
edge of the growth surface of the diamond 136 and a top edge of the
holder or sheath 134. A diamond production system can have a
diamond actuator member, a holder actuator member, or a combination
of both.
[0053] The holder actuator member 362 in FIG. 3 is threaded into
the stage 324 and the diamond actuator member 360 is threaded into
the holder actuator member 362. By this arrangement, the diamond
and holder controls of the coolant and diamond/holder controls 329
shown in FIG. 3 can move the diamond 136, the sheath 134, or both
the sheath 134 and the diamond 136. Although the holder actuator
member 362 in FIG. 3 is shown as a threaded cylinder with threading
on the inside for the diamond actuator member 360 and threads on
the outside for threading into the stage 324, the holder actuator
member can be of any geometric shape that enables maintaining a
specified distance range between an edge of the growth surface of
the diamond 136 and the top edge of the holder or sheath 134. Those
skilled in the art will realize that components placed within the
bell jar, such as the holder actuator member 362 or a combination
of both the holder actuator member and the diamond actuator member,
should be vacuum compatible so as to avoid problems in maintaining
the desired atmosphere.
[0054] As shown in FIG. 3, a thermal mass 364 is positioned within
a recess of the stage 324. The holder or sheath 134 is slidably
positioned within thermal mass 364 such that thermal energy is
transferred from the sheath 134 to the stage 324. The top surface
of the thermal mass 364 can be contoured such that heat can be
transferred from the sheath 134 while minimizing the electrical
effect of the thermal mass 364 on the plasma 341. Thermal masses
466a, 466b and 466c in FIGS. 4a-4c, respectively, are examples of
other contoured thermal masses with different cross-sectional
shapes, which in the alternative, can be used in lieu of the
thermal mass 364 shown in FIG. 3. A thermal mass can be made of
molybdenum. Other materials, such as molybdenum-tungsten alloys or
engineered ceramics, having high melting points above the process
temperature and a thermal conductivity comparable to that of
molybdenum can be used as a thermal mass for transferring heat from
a side of the diamond to a stage.
[0055] By minimizing the electrical effect of thermal mass 364 on
the plasma 341, the region within the plasma 341 in which the
diamond is grown will be more uniform. In addition, higher pressure
can be used in growing diamond, which will increase the growth rate
of single-crystal diamond. For example, pressures can vary from 130
to 400 torr and single-crystal growth rates can be from 50 to 150
microns per hour. Using a higher pressure, such as 400 torr, is
possible because the uniformity, shape and/or position of the
plasma 341 are not as readily affected by thermal mass 364, which
is contoured to remove heat from the edges of the growth surface of
the diamond and minimizes the electrical effect of the thermal mass
364 on the plasma 341. In addition, less microwave power, such as
1-2 kW, is needed to maintain the plasma 341. Otherwise, a lower
pressure and/or increased microwave power would have to be used to
maintain the uniformity, shape and/or position of the plasma
341.
[0056] As the diamond 136 grows, both the distance D and the height
H increase. As the distance D increases, the heat-sinking capacity
of the sheath 134 for the top edges of the growth surface of the
diamond 136 decreases. In addition, characteristics of the plasma,
such as temperature, change as the growth surface of the diamond
136 extends into the plasma 341. In the diamond production system
300, the growth process is halted when the diamond 136 reaches a
predetermined thickness since the distance D and the height H can
be controlled by the main process controller 346, via the coolant
and diamond/holder controls 329, using the holder actuator member
362 and diamond actuator member 360 during the diamond growing
process. This repositioning, either manually or automatically under
control of the controller 144, allows the diamond growth on the
growth surface of the diamond 136 to occur within a desired region
of resonant power within the plasma 341. Further, repositioning
allows the infrared pyrometer 142 and any additional instruments to
remain focused on the growth surface of the diamond 136, and can
maintain an efficient sinking of heat from the edges of the growth
surface of the diamond 136.
[0057] FIG. 5 is a diagram of a diamond production apparatus 500
according to an embodiment of the present invention in which a
cross-section of deposition apparatus 504 with a specimen holder
assembly 520 for moving the diamond 136 during the diamond growth
process is depicted. Some of the components of diamond production
apparatus 500 are substantially the same as those of diamond
production system 100 and 300, and thus, the discussion above the
regard to FIG. 1 and FIG. 3 will suffice to describe those
components likewise numbered in FIG. 5. For example, the pyrometer
142, deposition chamber floor 122, coolant pipe 128 and bell jar
108 in FIG. 5 are substantially the same as those described in FIG.
1. In another example, the coolant and diamond/holder controller
329 and diamond actuator member 360 in FIG. 5 are substantially the
same as those in FIG. 3.
[0058] As shown in FIG. 5, the diamond 136 is mounted on the
diamond actuator member 360 and within a contoured thermal mass
566, which acts as a holder. By placing the diamond 136 directly
within the contoured thermal mass 566, thermal efficiencies for
heat-sinking the diamond 136 are increased. However, the plasma 541
may be more easily affected since the whole contoured thermal mass
is moved by the holder actuator 562 in the stage 524 with a diamond
holder control, which is shown as a part of the coolant and
diamond/holder controls 329 in FIG. 3. Thus, the main process
controller 546 should take into account such a factors for
appropriately controlling the plasma and/or other parameters of the
growth process. In the alternative, the convex thermal mass 364
shown in FIG. 3, the slant-sided thermal mass 466b in FIG. 4b, a
slant-sided/cylindrical apex thermal mass 466c in FIG. 4c or other
geometric configurations can be used m lieu of the concave thermal
mass 566, in FIG. 5.
[0059] FIG. 6 is a flow diagram illustrating a process 600 in
accordance with embodiments of the present invention that can be
used with specimen holder assembly shown in FIG. 1. The process 600
begins with step S670 in which an appropriate seed diamond or a
diamond in the process of being grown is positioned in a holder. In
the specimen holder assembly 120 of FIG. 1 for example, the diamond
seed portion 138 is placed in a sheath 134 and the screws 131a-131d
are tightened by an operator. Other mechanisms can be used to
maintain both the sheath and diamond in position, such as spring
loaded collets, hydraulics or other mechanisms can be used in
exerting a force against the holder or sheath.
[0060] As referred to in step S672, the temperature of the growth
surface of the diamond, either the diamond seed or grown diamond,
is measured. For example, the pyrometer 142 in FIG. 1 takes a
measurement of the growth surface, which is the top surface of the
growing diamond portion 140, and provides the measurement to the
main process controller 146. The measurement is taken such that a
thermal gradient across the growth surface of the diamond 136 can
be determined by the main process controller or at least the
temperature of an edge of the growth surface of the diamond are
inputted into the main process controller.
[0061] The main process controller, such as main process controller
146 shown in FIG. 1, is used in controlling the temperature of the
growth surface, as referred to in S674 in FIG. 6. The main process
controller controls the temperature by maintaining thermal
gradients of less than 20.degree. C. across the growth surface.
While controlling the temperature of the growth surface, a
determination is made to whether the diamond should be repositioned
in the holder, as shown in step S675 of FIG. 6. If the main
controller can not control the temperature of the growth surface of
the diamond such that all temperature gradients across the growth
surface are less than 20.degree. C. by controlling the plasma, gas
flows and coolant flows, then the growth process is suspended so
that the diamond can be repositioned in the holder, as shown in
step S678 of FIG. 6, for better heat-sinking of the diamond and/or
better positioning of the diamond within the plasma. If the main
controller can maintain all of the thermal gradients across the
growth surface of the diamond to be less than 20.degree. C., then
the growing of the diamond on the growth surface occurs as shown in
step S676 of FIG. 6.
[0062] Measuring the temperature of a growth surface of the
diamond, controlling temperature of the growth surface and growing
diamond on the growth surface occurs until it is determined that
the diamond should be repositioned, as shown in FIG. 6. Although
measuring, controlling, growing and the acts of determining are
shown and described as steps, they are not necessarily sequential
and can be concurrent with one another For example, the step of
growing diamond on the growth surface can occur while measuring the
temperature of a growth surface of the diamond and controlling
temperature of the growth surface are occurring.
[0063] The repositioning of the diamond, as referred to in step
S678, can be done manually or with a robotic mechanism. In
addition, a determination can be made of whether the diamond has
reached a predetermined or desired thickness, as shown in step S673
of FIG. 6. The determination can be based on an actual measurement
via mechanical or optical devices. In another example, the
determination can be based on the length of processing time in view
of known growth rates for the process. If the diamond has reached
the predetermined thickness, then the growing process is complete,
as referred to by step 680 in FIG. 6. If the diamond has not
reached the predetermined thickness, then the growth process is
started again and continues with measuring the temperature of a
growth surface of the diamond, controlling temperature of the
growth surface and growing diamond on the growth surface until it
is determined that the diamond needs to be repositioned, as shown
in FIG. 6.
[0064] FIG. 7 is a flow diagram illustrating a process 700 in
accordance with embodiments of the present invention that can be
used with specimen holder assembly shown in FIG. 3 and FIG. 5. The
process 700 begins with step S770 in which an appropriate seed
diamond, which can be a grown diamond, manufactured diamond,
natural diamond or combination thereof, is positioned in a holder.
In the specimen holder assembly 320 of FIG. 3 for example, the
diamond seed portion 138 is placed with in sheath 134 on the
diamond actuator member 360, as shown in FIG. 3. In another example
of a specimen holder assembly, the diamond seed portion 138 is
placed within a contoured thermal mass 566 on the diamond actuator
360, as shown in FIG. 5.
[0065] As referred to in step S772, the temperature of the growth
surface of the diamond, either the diamond seed or a newly grown
diamond portion on the diamond seed, is measured For example, the
pyrometer 142 in FIG. 3 takes a measurement of the growth surface,
which is the top surface of the growing diamond portion 140, and
provides the measurement to the main process controller 346. In
another example, the pyrometer 142 in FIG. 5 takes a measurement of
the growth surface, which is the top surface of the seed diamond
portion 138, and provides the measurement to the main process
controller 546. The measurement is taken such that thermal gradient
across the growth surface of the diamond can be determined by the
main process controller or at least the temperatures of an edge and
the middle of the growth surface are inputted into the main process
controller.
[0066] A main process controller, such as main process controller
346 or 546, is used in controlling the temperature of the growth
surface, as referred to in S774 in FIG. 7. The main process
controller controls the temperature of the growth surface of the
diamond such that all temperature gradients across the growth
surface are less than 20.degree. C. while controlling the
temperature of the growth surface, a determination is made to
whether the diamond needs to be repositioned in the holder, as
shown in step S775 of FIG. 7. If the main controller can not
maintain the temperature of the growth surface of the diamond such
that all temperature gradients across the growth surface are less
than 20.degree. C. by controlling the plasma, gas flows and coolant
flows, then the diamond is repositioned while the diamond is
growing as shown in FIG. 7 with the "YES" path from step S775 to
both of steps S776 and S778. By repositioning the diamond within
the holder, the heat-sinking of the edges of the growth surface is
improved. In addition, the growth surface can be positioned within
an optimal region of the plasma having a consistency for
maintaining all of the thermal gradients across the growth surface
of the diamond to be less than 20.degree. C. If the main controller
can maintain all of the thermal gradients across the growth surface
of the diamond to be less than 20.degree. C., then the growing of
the diamond on the growth surface occurs without repositioning as
shown in the "NO" path from step S775 to step S776 of FIG. 7.
[0067] Measuring the temperature of a growth surface of the
diamond, controlling temperature of the growth surface, growing
diamond on the growth surface and repositioning the diamond in the
holder occurs until it is determined that the diamond has reached a
predetermined thickness. As referred to in step S773 of FIG. 7, if
a determination is made of whether the diamond has reached a
predetermined or desired thickness. The determination can be based
on an actual measurement via mechanical or optical devices. For
example, a tracking program which records the depth or the amount
in terms of distance that the diamond had to be repositioned during
the growth process. In another example, the determination can be
based on the length of processing time in view of known growth
rates for the growth process. If the diamond has reached the
predetermined thickness, then the growing process is complete, as
referred to by step 780 in FIG. 7. If the diamond has not reached
the predetermined thickness, then the growth process continues with
measuring the temperature of a growth surface of the diamond,
controlling temperature of the growth surface, growing diamond on
the growth surface and repositioning the diamond in the holder
until it is determined that the diamond needs to be repositioned,
as show in the "NO" path from S773 to within S774 of FIG. 7.
[0068] When implementing processes 600 and 700, diamond growth is
usually continued as long as a "step growth" condition can be
maintained. In general, the "step growth" condition refers to
growth in which diamond is grown on the growth surface of the
diamond 136 such that the diamond 136 is smooth in nature, without
isolated "outcroppings" or twins. The "step growth" condition may
be verified visually. Alternatively, a laser could be used to scan
the growth surface of the diamond 136. A change in laser
reflectance would indicate the formation of "outcroppings" or
twins. Such a laser reflectance could be programmed into the main
process controller as a condition for stopping the growth process.
For example, in addition to determining if the diamond is a
predetermined thickness, a determination can also be made of
whether a laser reflectance is being received.
[0069] In general, the methods in accordance with exemplary
embodiments of the present invention are designed to create large,
high-quality diamonds with increased [100] growth rates. The
process temperature may be selected from a range of about
900-1400.degree. C.; depending on the particular type of
single-crystal diamond that is desired or if oxygen is used.
Polycrystalline diamond may be produced at higher temperatures, and
diamond-like carbon may be produced at lower temperatures. During
the growth process, a pressure of about 130-400 torr is used, with
a methane concentration in the range of 6-12% methane. A
hydrocarbon concentration greater than 15% may cause excessive
deposition of graphite inside the MPCVD chamber. A 1-5%
N.sub.2/CH.sub.4 added to the reactant mix creates more available
growth sites, enhances the growth rate, and promotes {100} face
growth. Other aspects of the invention can be understood in greater
detail from the following examples.
EXAMPLE 1
[0070] A diamond growth process was conducted in the
above-described MPCVD chamber in FIG. 1. First, a commercial
3.5.times.3.5.times.1.6 mm high pressure high temperature (UPHT)
synthetic type Ib diamond seed was positioned in the deposition
chamber. The diamond seed has polished, smooth surfaces that were
ultrasonically cleaned with acetone. The deposition surface was
within two degrees of the {100} surface of the diamond seed.
[0071] Then, the deposition chamber was evacuated to a base
pressure of 10.sup.-3 torr. The infrared pyrometer 142 was focused
though a quartz window at an incident angle of 65 degrees on the
growth surface of the diamond and had a minimum 2 mm.sup.2 diameter
spot size. Diamond growth was performed at 160 torr pressure using
gas concentrations of 3% N.sub.2/CH.sub.4, and 12%
CH.sub.4/H.sub.2. The process temperature was 1220.degree. C., and
gas flow rates were 500 sccm H.sub.2, 60 sccm CH.sub.4, and 1.8
sccm N.sub.2. Deposition was allowed to continue for 12 hours.
[0072] The resulting diamond was 4.2.times.4.2.times.2.3 mm.sup.3
unpolished, and represented about 0.7 mm of growth on the seed
crystal that was grown at a growth rate 5 microns per hour. The
growth morphology indicated that the <100> side growth rate
was faster than the <111> comer growth rate. The growth
parameter, .alpha., was estimated at 2.5-3.0.
[0073] The deposited diamond was characterized using x-ray
diffraction (XRD), Raman spectroscopy, photoluminescence (PL)
spectroscopy and electron paramagnetic resonance (EPR). The X-ray
diffraction study of the resulting diamond conformed that it was a
single crystal, with a small degree of polycrystallinity localized
at the top edges of the diamond. Visible/near infrared transmission
spectra of the MPCVD grown diamond and seed diamonds confirm that
nitrogen is incorporated effectively into the crystal structure.
Raman spectroscopy demonstrates that the top face of the MPCVD
grown diamond has different optical characteristics than the seed
diamond but has the same internal stress.
[0074] A number of MPCVD diamonds were produced according to the
guidelines of Example 1 while varying the described process
temperature. These experiments demonstrate the process temperature
ranges for producing various types of diamond in the growth process
according embodiments of the present invention. Table 1 sets forth
the results of these additional experiments.
TABLE-US-00001 TABLE 1 Process temperatures for various types of
diamond Temperature Range Type of Diamond Produced <1000.degree.
C. Spherical, black diamond-like carbon (DLC) 1000-1100.degree. C.
Smooth dark brown 1100-1200.degree. C. Brown 1200-1220.degree. C.
Smooth, yellow tint growth 1220-1400.degree. C. Step-flow type with
pyramid like octahedra tinted yellow >1300.degree. C. Twinned or
polycrystalline diamond
EXAMPLE 2
[0075] A high-quality, pure CVD single crystal diamond over 0.6 mm
in thickness was created substantially in accordance with the
procedure of Example 1 above by adding a small amount (1-3%) of
oxygen and lowering the growth temperature to 900 degrees Celsius.
The added oxygen allows a lower growth temperature, which removes
the nitrogen-related impurities and reduces the silicon and
hydrogen impurity levels. The growth rate using this process is
approximately 10 m/hr, less than that of Example 1 but still
greater than; conventional processes.
[0076] The colors of diamond formed by the methods discussed above
be changed by annealing. For example, a yellow of brown diamond can
be annealed into a green diamond. Additional information with
regard to the diamond produced in the examples described above is
in a paper by the inventors entitled "Very High Growth Rate
Chemical Vapor Deposition of Single-Crystal Diamond" Proceedings of
the National Academy of the Sciences, October 1, 2002, volume 99,
no. 20., pages 12523-12525, which is hereby incorporated by
reference in its entirety. Diamond produced by the above methods
and apparatus will be sufficiently large, defect free and
translucent so as to be useful as windows in high power laser
applications or as anvils in high pressure apparatuses.
[0077] As the present invention may be embodied in several forms
without departing from the spirit or essential characteristics
thereof, it should also be understood that the above-described
embodiments are not limited by any of the details of the foregoing
description, unless otherwise specified, but rather should be
construed broadly within its spirit and scope as defined in the
appended claims, and therefore all changes and modifications that
fall within the metes and bounds of the claims, or equivalence of
such metes and bounds are therefore intended to be embraced by the
appended claims.
* * * * *