U.S. patent application number 12/938766 was filed with the patent office on 2011-03-03 for diamond medical devices.
This patent application is currently assigned to Apollo Diamond, Inc. Invention is credited to John M. Abrahams, Patrick J. Doering, William W. Dromeshauser, Alfred R. Genis, Bryant Linares, Robert C. Linares, Michael Murray, Alicia E. Novak.
Application Number | 20110054450 12/938766 |
Document ID | / |
Family ID | 37109027 |
Filed Date | 2011-03-03 |
United States Patent
Application |
20110054450 |
Kind Code |
A1 |
Linares; Robert C. ; et
al. |
March 3, 2011 |
DIAMOND MEDICAL DEVICES
Abstract
Masked and controlled ion implants, coupled with annealing or
etching are used in CVD formed single crystal diamond to create
structures for both optical applications, nanoelectromechanical
device formation, and medical device formation. Ion implantation is
employed to deliver one or more atomic species into and beneath the
diamond growth surface in order to form an implanted layer with a
peak concentration of atoms at a predetermined depth beneath the
diamond growth surface. The composition is heated in a
non-oxidizing environment under suitable conditions to cause
separation of the diamond proximate the implanted layer. Further
ion implants may be used in released structures to straighten or
curve them as desired. Boron doping may also be utilized to create
conductive diamond structures.
Inventors: |
Linares; Robert C.;
(Sherborn, MA) ; Doering; Patrick J.; (Holliston,
MA) ; Linares; Bryant; (Sherborn, MA) ; Genis;
Alfred R.; (East Douglas, MA) ; Dromeshauser; William
W.; (Norwell, MA) ; Murray; Michael; (Mountain
View, CA) ; Novak; Alicia E.; (Denver, CO) ;
Abrahams; John M.; (Scarsdale, NY) |
Assignee: |
Apollo Diamond, Inc
Framingham
MA
|
Family ID: |
37109027 |
Appl. No.: |
12/938766 |
Filed: |
November 3, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11329959 |
Jan 11, 2006 |
7829377 |
|
|
12938766 |
|
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|
60643390 |
Jan 11, 2005 |
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Current U.S.
Class: |
606/1 ; 623/1.24;
623/27 |
Current CPC
Class: |
H01L 21/0405 20130101;
B81C 1/00634 20130101 |
Class at
Publication: |
606/1 ; 623/1.24;
623/27 |
International
Class: |
A61B 17/00 20060101
A61B017/00; A61F 2/06 20060101 A61F002/06; A61F 2/64 20060101
A61F002/64 |
Claims
1. An apparatus, comprising: a medical device comprising at least a
portion configured to come into contact with human tissue in use,
the at least a portion of the medical device coated in
monocrystalline synthetic diamond formed by chemical vapor
deposition.
2. The apparatus of claim 1, wherein the device comprises an
implantable medical device.
3. The apparatus of claim 1, wherein the device comprises a
cardiovascular device.
4. The apparatus of claim 3, wherein the cardiovascular device
comprises a valve or a stent.
5. The apparatus of claim 1, wherein the device comprises an
orthopedic device.
6. The apparatus of claim 5, wherein the device comprises at least
a portion of a knee joint, an elbow joint, or a hip joint.
7. The apparatus of claim 1, wherein the device comprises a medical
delivery device.
8. The apparatus of claim 7, wherein the device comprises at least
one of a catheter, a pump, a porous diamond membrane, and a
capillary.
9. The apparatus of claim 7, wherein the device comprises a
capillary operable through electrical actuation to act as at least
one of a switch or pump.
10. The apparatus of claim 1, wherein the device comprises a
surgical instrument.
11. The apparatus of claim 10, wherein the device comprises a
scalpel or a drill bit.
12. A method of forming a medical device, comprising: coated at
least a portion of a medical device in monocrystalline synthetic
diamond formed by chemical vapor deposition, the coated portion of
the medical device comprising at least a portion configured to come
into contact with human tissue in use.
13. The method of forming a medical device of claim 12, wherein the
device comprises an implantable medical device.
14. The method of forming a medical device of claim 12, wherein the
device comprises a cardiovascular device.
15. The method of forming a medical device of claim 14, wherein the
cardiovascular device comprises a valve or a stent.
16. The method of forming a medical device of claim 12, wherein the
device comprises an orthopedic device.
17. The method of forming a medical device of claim 16, wherein the
device comprises at least a portion of a knee joint, an elbow
joint, or a hip joint.
18. The method of forming a medical device of claim 12, wherein the
device comprises a medical delivery device.
19. The method of forming a medical device of claim 18, wherein the
device comprises at least one of a catheter, a pump, a porous
diamond membrane, and a capillary.
20. The method of forming a medical device of claim 18, wherein the
device comprises a capillary operable through electrical actuation
to act as at least one of a switch or pump.
21. The method of forming a medical device of claim 12, wherein the
device comprises a surgical instrument.
22. The method of forming a medical device of claim 21, wherein the
device comprises a scalpel or a drill bit.
Description
RELATED APPLICATION
[0001] This application is a continuation of and claims the benefit
of priority under 35 U.S.C. .sctn.120 to U.S. patent application
Ser. No. 11/329,959, filed Jan. 11, 2006, titled "Diamond Medical
Devices," which claims the benefit of U.S. Provisional Application
Ser. No. 60/643,390 filed Jan. 11, 2005, titled "Diamond Medical
Devices," both of which are incorporated herein by reference in
their entirety. U.S. application Ser. No. 11/329,959 also claims
priority to U.S. patent application Ser. No. 11/178,623 filed Jul.
11, 2005, titled "Structures Formed in Diamond," which is
incorporated herein by reference. U.S. application Ser. No.
11/329,959 also claims priority to U.S. patent application Ser. No.
11/056,338 filed Feb. 11, 2005, titled "Diamond Structure
Separation," which is incorporated herein by reference.
BACKGROUND
[0002] Diamond appears to be highly biocompatible with living
tissue. Currently, diamond does not appear to exhibit
carcinogenetic or toxicity for in situ applications, and it appears
to be biologically inert in bulk form. Diamond may be synthesized
in a variety of ways. However, it is a difficult material to work
with, and new techniques may be required for forming structures for
handling biological materials.
[0003] Modern semiconductors are typically based on silicon, with
various elements doped to change their electrical properties. For
example, doping silicon with phosphorous creates a surplus of
electrons resulting in n-type semiconductor material due to the
fifth valence electron not present in silicon, which has only four
valence electrons. Similarly, doping silicon with boron creates
p-type silicon having a surplus of Aholes@, or an absence of
electrons, because boron has only three valence electrons which is
one fewer than silicon.
[0004] When n-type and p-type silicon are in contact with one
another, electricity flows in one direction across the junction
more easily than in the other direction. More complex
configurations of n-type and p-type material can be assembled to
form various types of transistors, integrated circuits, and other
such devices.
[0005] But, the performance of certain semiconductor devices is
limited by the properties inherent in the semiconductor materials
used. For example, a processors speed is limited by the amount of
power that can be dissipated in the transistors and other devices
that make up the processor integrated circuit, which can literally
melt if operated too fast. Reduction in size is also limited,
because as more transistors dissipating a certain amount of power
are packed into a smaller area, the amount of heat dissipated in a
certain area increases. Even simple devices such as diodes used in
high-frequency, high-power applications suffer from power
limitations, since the physical size of an individual transistor or
diode is typically very small.
[0006] Semiconductor devices enabling greater power dissipation and
higher semiconductor device densities are desirable to provide
higher performance, smaller electrical devices.
SUMMARY
[0007] Masked and controlled ion implants, coupled with annealing
or etching are used in CVD formed single crystal diamond to create
structures for both optical applications, nanoelectromechanical
device formation, and medical device formation. Ion implantation is
employed to deliver one or more atomic species into and beneath the
diamond growth surface in order to form an implanted layer with a
peak concentration of atoms at a predetermined depth beneath the
diamond growth surface. The composition is heated in a
non-oxidizing environment under suitable conditions to cause
separation of the diamond proximate the implanted layer. Further
ion implants may be used in released structures to straighten or
curve them as desired. Boron doping may also be utilized to create
conductive diamond structures.
[0008] In one embodiment, a nanochannel is formed by implanting
ions in a diamond at a point where the nanochannel is desired.
Masks may be used to control a width and length of the implant, and
selected implant power levels can be utilized to control the depth
of the implant. Heating the diamond causes a separation to occur at
or about the implant. Such separation may be used as a nanochannel
for conveying fluids, or as a low refractive index portion of a
waveguide.
[0009] Further implants may be sized and shaped to form an etalon,
optical filter, or optical deflector when heated to cause
separation. An approximately 500 nm circular shape is used in one
embodiment. Using a progression of masks and implant depths can
provide for formation of many different mechanical structures, such
as those that may be formed in silicon. Further layers of synthetic
diamond of one or more diamond layers may be grown following the
implants.
[0010] In still further embodiments, device formed of materials
other than diamond, such as silicon or germanium based devices are
coated with CVD diamond, providing a highly biocompatible device
protected from oxidation.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a block representation of a diamond having a
Nv-center according to an example embodiment.
[0012] FIG. 2 is a side view cross sectional representation of a
diamond illustrating a masked ion implant process according to an
example embodiment.
[0013] FIG. 3 is a top view of the diamond of FIG. 2, illustrating
the mask for ion implantation according to an example
embodiment.
[0014] FIG. 4 is a side view cross sectional representation of the
diamond of FIG. 2 following the ion implant and heating according
to an example embodiment.
[0015] FIG. 5 is a side view cross sectional representation of a
diamond illustrating a masked ion implant process for forming a
cantilever according to an example embodiment.
[0016] FIG. 6 is a top view representation of an ion implantation
mask used to form a cantilever according to an example
embodiment.
[0017] FIG. 7 is a side view cross sectional representation of a
released cantilever according to an example embodiment.
[0018] FIG. 8 is a side view cross sectional representation of a
masked diamond for forming optical structures according to an
example embodiment.
[0019] FIG. 9 is a top cross sectional view of the diamond of FIG.
8 illustrating optical structures formed according to an example
embodiment.
[0020] FIG. 10 is a top view representation of a drug pump
according to an example embodiment.
[0021] FIG. 11 is a side cross section view of a multilevel
capillary system according to an example embodiment.
[0022] FIG. 12 is a block cross section view of a CVD diamond
coated optical device according to an example embodiment.
[0023] FIG. 13 is a top view of a porous CVD diamond membrane
according to an example embodiment.
[0024] FIG. 14 is a block diagram representation of a structure
coated with CVD diamond.
[0025] FIG. 15 shows a boron-doped diamond seed crystal with a
hydrogen ion implant layer, consistent with an example embodiment
of the present invention.
[0026] FIG. 16 shows a boron-doped diamond seed crystal with grown
boron-doped diamond, consistent with an example embodiment of the
present invention.
[0027] FIG. 17 shows a boron-doped diamond seed crystal with grown
diamond separated at a hydrogen implant level, consistent with an
example embodiment of the present invention.
[0028] FIG. 18 shows a Schottky diode formed from the boron-doped
diamond seed crystal with grown boron-doped diamond, consistent
with an example embodiment of the present invention.
[0029] FIG. 19 shows a method of forming a boron-doped diamond
semiconductor, consistent with an example embodiment of the present
invention.
[0030] FIG. 20 shows an integrated circuit having first and second
boron-doped diamond semiconductor regions, consistent with an
example embodiment of the present invention.
[0031] FIG. 21 shows an electronic device utilizing a boron-doped
diamond semiconductor, consistent with an example embodiment of the
present invention.
DETAILED DESCRIPTION
[0032] In the following description, reference is made to the
accompanying drawings that form a part hereof, and in which is
shown by way of illustration specific embodiments which may be
practiced. These embodiments are described in sufficient detail to
enable those skilled in the art to practice the invention, and it
is to be understood that other embodiments may be utilized and that
structural, logical and electrical changes may be made without
departing from the scope of the present invention. The following
description is, therefore, not to be taken in a limited sense, and
the scope of the present invention is defined by the appended
claims.
[0033] A first section of the application describes the ability to
create N-V centers in single crystal diamond in a controlled
manner. Various ion implant processes are described that allow the
creation of structures in single crystal diamond. These processes
may then be used to create structures in other contexts, as
described in a medical devices section. Further description is
provided with respect to doping of single crystal diamond to obtain
various semiconductor and conducting properties, which may be used
in conjunction with nano and micromechanical devices formed in the
diamond.
[0034] N-V centers in diamond can be created in a controlled
manner. In one embodiment, a single crystal diamond is formed using
a CVD process with nitrogen included in the growth process, and
then annealed to remove N-V centers. A thin layer of single crystal
diamond is then formed with a controlled number of N-V centers. The
N-V centers form Qubits for use in electronic circuits.
[0035] Qubit devices are formed in diamond having highly controlled
purity. A highly controlled number of N-V centers can be produced,
and the N-V centers are isolated from each other and from other
elements having a magnetic spin such as N-V0, Ns and 13C (carbon
13). In one embodiment, single, isolated N-V centers are used to
obtain information from individual atoms rather than from clusters.
In further embodiments, it may be desirable to have N-V adjacent to
13C. In still further embodiments, the diamond has high crystal
perfection since imperfections lead to shorter spin lifetimes and
nitrogen tends to segregate at imperfections such as dislocations
giving the effect of a higher concentration and the attendant
interaction between adjacent spins and reduction of lifetime.
[0036] In one embodiment, light is able to enter and leave the
diamond host material in a controlled manner. When a Qubit emits
light, the light will be emitted over a spherical surface and the
light intensity at any point will be very low and difficult to
detect. The Qubit is contained within an optical waveguide which
traps and directs the light in a minimum number of directions.
Diamond is ideal for such a waveguide since it has a very high
index of refraction (2.4 in the visible range). A thin layer of
diamond in contact with air or vacuum on both sides provides such a
waveguide. Diamond has a significantly higher index of refraction
than air, such that a light beam propagating down the waveguide is
internally reflected by the walls of the diamond waveguide and be
confined to the diamond waveguide. With the Qubit within the
diamond waveguide, most of the light emitted by the Qubit will be
transmitted down the waveguide and be readily collected and
detected. Other forms of transmission may also be utilized, such as
by means of a plasma waveguide or slot waveguide. In still further
embodiments, small metal wires are utilized to draw light from a
Qubit. The light propagates on the outside of the wire within a
diamond cladding.
[0037] One method for building a Qubit device involves growing
single crystals by the HPHT method, incorporating a desired amount
of nitrogen atoms which will all be Ns, irradiating the diamond to
generate carbon vacancies and annealing to diffuse the carbon
vacancies to the nitrogen atoms thereby causing N-V centers. This
method may result in irradiation causing a significant level of
crystal damage which decreases Qubit lifetime.
[0038] Another method of producing N-V centers in HPHT diamond
involves growing the diamond with a titanium or aluminum getter to
remove all of the nitrogen from the diamond and put nitrogen into
the diamond later by ion implantation into selected spots. This
method may not lend itself well to production of large size diamond
wafers which would be suitable for device production.
[0039] FIG. 1 is a block representation of a diamond crystal
lattice 100 having an N-V.sup.- center 110 according to an example
embodiment. Center 110 is also representative of N-V centers with
different charge states. As described above, an N-V.sup.- center
110 is nitrogen 115 in a substitutional site in diamond which is
adjacent to a carbon vacancy 120. In FIG. 1, the N-V.sup.- center
110 is isolated from other N-V centers such that spins of other
centers and other structures do not interfere with the isolated
N-V.sup.- center, thus forming a Qubit.
[0040] The N-V-center 110 in diamond has several attributes which
make it desirable for Qubit based devices. It is easily pumped
using low power microwaves. It is also easily detected (emission at
675 nanometers wavelength). Such N-V.sup.- centers in diamond have
long lifetimes (60 to 500 microseconds) and room temperature
operation. Diamond also has a high degree of optical transparency
and a high optical index of refraction, enabling construction of
optical waveguides and other optical structures.
[0041] One method of producing N-V centers involves the use of CVD
grown diamond. CVD diamond can be grown in large sizes with highly
controlled purity as seen in (see U.S. Pat. No. 6,582,513) and with
layers of controlled purity, thickness and properties. CVD diamond
may be grown with high or low nitrogen concentrations, thin layers
with or without 13C. N-V center formation may be controlled by
several means.
[0042] CVD diamond grows under conditions where N-V.sup.-,
N-V.sup.o and Ns are all stable. Furthermore the ratios of these
states can be varied by the growth conditions, the concentration
and by heat treatment after growth. Moreover, it is possible to
grow a substrate which is essentially free of all states of
nitrogen and then grow a film of diamond which has only the desired
level of nitrogen. Since the number of atoms of nitrogen in the
film will be a function of concentration and thickness, N-V.sup.-
centers may be isolated from all other centers. In other words,
given a known concentration of N-V centers that will be formed in a
given volume of CVD grown diamond, making the diamond layer very
thin assures that very few N-V centers are formed, and are thus
isolated from each other.
[0043] In further embodiments, a carbon source for the CVD growth
of the film has a desired level of 13C carbon by either depleting
the 13C in the source gas or by enriching the 13C level. In one
embodiment, a separation of about 2 microns is desired for non
interaction between a N-V.sup.- and other N centers. This is
estimated at about 10 ppb which has already been demonstrated.
Additionally, a diamond layer of only nominal purity may be grown
and then annealed at high temperature to convert all N-V centers to
Ns. This removes any extraneous signal from stray N-V atoms since
Ns does not have an optical signal at the N-V.sup.- wavelength. It
can also be appreciated that a number of layers can be grown which
are alternating between high purity and specific numbers of N-V
centers to obtain a three dimensional structure having isolated N-V
in adjacent layers. Each layer may be designed as a waveguide as
described below, and have multiple and separated functions.
[0044] In each of the above embodiments, N-V centers may be
randomly placed in the volume of the crystal, but can be readily
found and marked for detection during the operation of the
device.
[0045] In further embodiments, different types of diamond may be
used, such as natural, mined diamonds, high pressure, high
temperature manufactured diamonds, CVD formed diamonds or others.
Such diamond may then be annealed to destroy N-V centers, followed
by implantation to create desired densities of N-V centers, and
further implantation to form waveguides.
[0046] An alternate method utilizes very pure bulk crystal with or
without the film of desired isotopic purity, heat treat to destroy
all residual N-V centers and then implant single, isolated, N-V
centers at desired locations. A capping layer of highly pure
diamond may then be grown on the layer.
[0047] Waveguides may be formed proximate the N-V centers and
optically coupled to them. In one embodiment, Hydrogen is implanted
in the diamond in stripes, followed by heat treating the structure
to create a cavity which separates the strip of diamond from the
underlying diamond. The strip of diamond is essentially surrounded
by air and is used as an optical waveguide for bringing signals
into and out of the diamond structure. It provides a highly
isolated optical signal in and out and allows for multiple channels
for optical in and out on a single diamond chip. Furthermore
multiple functions may be provided, such as amplifiers, storage and
computing all on one optical chip. Implant of multiple energies may
provide multiple strips with separation layers from each other, in
depth, allowing production of three dimensional, optically isolated
Qubit structures. Such structures may significantly decrease the
size of such devices since much of the volume could be utilized.
Slot waveguides may also be formed.
[0048] It should also be noted that in the case of separated
channel waveguides, that the waveguide can be altered in its
properties by causing the waveguide to rise or fall in spots or
along its length by application of heat or voltage cycling. This is
in essence a fully attached device. This can be used as a switch to
turn off or on the light or as a switch to move the light to
another channel. In one embodiment, Qubits, optical switching and
MEMS technology are combined into the same chip with its attendant
applications. The use of masked or otherwise patterned implantation
and lift-off technology permits the building of a range of
waveguide structures such as sheets, plates, wires, disks and
multiples of these shapes all with the possibility of modulation
and switching as in optoelectronic and MEMS devices. It is also
possible to build either normally open or normally closed switches
and mixers by design of the proximity and shape of such
waveguides.
[0049] Diamond Qubits may also be formed in conjunction with other
semiconductors. Diamond may be bonded to other semiconductors such
as silicon, gallium arsenide, gallium nitride, silicon carbide or
III-IV alloys. The semiconductors can also be grown onto the
diamond substrate. The attachment of diamond to other
semiconductors will permit optoelectronic devices such as lasers,
detectors and associated circuitry to be directly integrated with
the diamond QBIT to provide input and output to and from
conventional sources, devices and systems. This will provide the
basis for optical busses for higher speed interconnects in
conventional computers and future QBIT based computers. In fact a
whole new family of integrated Qubit-Semiconductor devices (QSD)
will be possible by combining the technologies and methods
discussed.
[0050] FIG. 2 is a side view cross sectional representation of a
diamond illustrating a masked ion implant process according to an
example embodiment in order to form a waveguide in proximity to a
Qubit formed as above. In one embodiment, the Qubit is an isolated
Qubit, and the location of the Qubit is used as a guide for forming
the waveguide, such that the Qubit is located within the waveguide.
In further embodiments, the Qubit is formed in an already formed
waveguide.
[0051] A diamond substrate 210 is covered with a mask 215 in one
embodiment. The mask 215 is formed of a material sufficient to
screen out ions 220 being implanted at desired energy levels. The
mask may take many different shapes, but one such shape is shown in
top view FIG. 3 at 310. In this embodiment, the mask is in the
shape of a long, thin rectangle, resulting in a long thin implant
225 at a desired depth.
[0052] FIG. 4 is a side view cross sectional representation of the
diamond 210 of FIG. 2 following the ion implant and heating to form
an open space 410 within the diamond 210. Open space 410 provides a
low refractive index region on one side of a strip of diamond
indicated at 420. The other side of the strip 420 is essentially
the top of the diamond 210, which may be exposed to air, also
having a low refractive index compared to the index of refraction
of the diamond strip 420. Thus, the diamond strip 420 forms a
waveguide. A Qubit 430 is formed within the strip 420, and the
strip provides a mechanism to capture and provide light to the
Qubit to both detect and effect changes in the Qubit. It is evident
that the strip 420 may be formed in different shapes, in order to
conduct the light to a desired light source 440 and a light
detector 450 which may each be further connected to processing
circuitry, formed either, within, on, or off of the diamond
substrate. The source 440 and light detector 450 may also be
within, on, or off the diamond substrate in various embodiments.
Optical fiber connections or optical couplers may be formed to
conduct light to and from the waveguide strip 420.
[0053] In one embodiment, patterned ion implantation is employed to
deliver one or more atomic species into and beneath the diamond
growth surface in order to form an implanted layer with a peak
concentration of atoms at a predetermined depth beneath the diamond
growth surface. The composition is heated in a non-oxidizing
environment under suitable conditions to cause separation of the
synthetic diamond structure.
[0054] Such a non-oxidizing atmosphere generally includes any
atmosphere not containing a sufficient concentration of oxygen so
as to be reactive through oxidation. Examples of such atmospheres
include inert (e.g., helium, neon, argon, etc.) and other
non-oxygen containing gases (e.g., hydrogen, nitrogen, etc.).
Environments used to provide such atmospheres can include plasmas,
vacuums, and the like.
[0055] In certain embodiments of the invention, various initial
steps can be performed prior to or concurrent with the ion
implantation stage. One such step involves choosing a substrate.
When growing single crystalline CVD diamond, for instance, such
substrate may be a single crystalline diamond.
[0056] Upon selection of the substrate, at least one major surface
of the substrate can be identified, and optionally prepared, for
ion implantation. Preparation of the diamond surface can include
any suitable means for affecting the chemical and/or physical
make-up of the surface, for instance, by polishing using
conventional polishing methods. Preparation of this sort can be
accomplished in advance of the ion implantation. Typically, ions
are implanted in a manner at a set distance and even flux across
the diamond growth surface, such that the configuration of the
implanted species layer will itself replicate the surface profile
of the substrate. In turn, any defects on an implanted surface of
the substrate will typically have a corresponding influence on the
implant profile, including on the configuration of the
predetermined peak atomic layer. Thus, such structures may actually
be substantially polished if the surface of the diamond is
polished. Preparation of the substrate can be important to
initially remove such defects. In addition, in certain embodiments,
surfaces are thoroughly cleaned for ion implanting, for instance,
using solvents or other suitable methods known in the art,
including plasma etching, gas phase etching and the like. Polishing
damage may result in creation of undesired N-V centers. The surface
of the polished diamond may be further etched to remove such damage
and N-V centers.
[0057] Ion implantation is generally conducted under conditions of
high vacuum, high voltage, and relatively low beam currents. As is
known in the art, ion implantation typically involves the process
of ionizing a species of atoms, subsequently accelerating the
species in an electric field, and directing the accelerated,
ionized species toward a substrate. With its rate of motion being
accelerated, the species generally penetrates an outer surface of
the substrate and come to rest within a zone in the substrate as
indicated at 225 in FIG. 2.
[0058] The zone is within an implanted layer of the substrate. In
one embodiment, the species is accelerated toward the substrate at
an angle generally normal or vertical to the surface. However, the
species can also be accelerated toward the substrate at a wide
variety of angles as well. For a given species, the depth of
implantation is generally accomplished with adjustments made to the
electric field. Typically, as one increases the voltage of the
electric field, the energy of the species is increased, which
ultimately results in a deeper implantation by the species into the
substrate. It is fully contemplated that the substrate may be any
of a variety of crystalline shapes. For example, the substrate may
be of any predetermined geometry including a cube, cone, prism,
pyramid, wedge, or other geometries, as well as frustums of
each.
[0059] The species generally penetrates the upper surface of the
substrate until reaching a zone, such as zone 225 within the
substrate. A peak concentration of the species is at a certain
depth generally known as the end of range depth. While the species
is only shown at the one depth (the end of range depth), it should
be appreciated that this is done for simplicity. Following ion
implantation, the species is generally distributed throughout the
zone at and proximate to the end of range depth.
[0060] Before ion implantation is started, the species to be
implanted must be selected. Many variables are considered in
selecting a species, such as cost and availability, as well as
concern for how much damage the species is expected to cause to the
substrate lattice, as described below.
[0061] During ion implantation, by directing the species (of
ionized atoms) into the crystal lattice of the substrate, the
implanted portion of the lattice generally dilates or expands.
Excessive dilation of the lattice in this manner generally leads to
strain within the implanted layer. Consequently, excessive strain
can cause damage to the implanted layer. This damage is generally
represented by dislocations, or cracking, within the implanted
layer. These dislocations can generally create an unfavorable outer
substrate surface for growing quality synthetic diamond (e.g.,
producing diamond via CVD having no defects or dislocations, or
insignificant amounts thereof). However, the manner in which
lattice dilation can be controlled in a number of ways, and in
fact, relied upon.
[0062] One way involves selecting an appropriate species for
implanting. In certain embodiments of the invention, hydrogen ions
are implanted within a diamond substrate using the conventional
techniques of ion implantation. Since the covalent radius of
hydrogen is small, only a small amount of lattice dilation occurs
within the implanted layer. Consequently, there is little strain
(and little damage) within the implanted layer. Generally, as the
covalent radius of the implanted species increases, the potential
for creating such a favorable surface (e.g., having limited defects
or dislocations) decreases.
[0063] Generally, any species can be used for ion implanting in the
inventive process so long as the species is suitable for
subsequently enabling separation of a portion of the implanted
layer from the substrate. As such, the species is selected so as to
allow for suitable implantation within the substrate. Examples of
such species include most, if not all, atomic elements. In certain
embodiments of the invention, the substrate is also used for
growing a synthetic diamond thereon. As such, the species
preferably allows for suitable implantation within the substrate to
enable separation, and allows for suitable formation of a favorable
growth surface on the substrate from which a quality synthetic
diamond can be grown. Therefore, the species is selected so as to
allow for suitable implantation within the substrate without
undesirably damaging the substrate. Small- to medium-sized species
(having small- to medium-sized covalent radiuses) are generally
preferred. Examples include atomic species such as helium, lithium,
boron, carbon, oxygen, phosphorous, and sulfur. However,
embodiments of the process can also involve large-sized species
(having large-sized covalent radiuses). In such embodiments, other
parameters affecting the implant of the species, such as species
dose quantity and species energy level, are considered so as to
limit the amount of damage to the substrate lattice upon
implantation of the larger-sized species.
[0064] The extent of lattice damage to the implanted portion can be
limited by the dose quantity of the species implanted, with the
dose being defined as the area density of atoms (atoms/cm.sup.2)
which are implanted into the substrate. For example, if the species
is implanted using a high dose, the species will generally cause
more damage to the substrate upon implantation than if a species
were implanted using a lower dose. As the species (of ionized
atoms) travels through the substrate, the damage to the substrate
lattice is generally maximized near the end of the species range
into the substrate (generally referred to as "end of range
damage").
[0065] In turn, the degree of damage at the end of range is a
function of the total dose at that level. However, the ability to
cause separation within the diamond crystal is also a function of
the total dose. At dose levels that are too low, there will be no
separation, while at levels that are too high for a particular
embodiment, there can be excessive damage and poor diamond growth.
In some embodiments, the dose quantity is set in the range from
about 1.times.10e.sup.14 atoms/cm.sup.2 to about 1.times.10e.sup.20
atoms/cm.sup.2, and even more preferably, is set in the range from
about 1.times.10e.sup.15 atoms/cm.sup.2 to about 1.times.10e.sup.18
atoms/cm.sup.2. When implanting species of large sizes, in order to
limit lattice damage, it is generally preferable to choose a dose
quantity on the lower end of the range. Conversely, when implanting
species of small to medium sizes, any dose quantity within the
range is generally suitable.
[0066] In addition, the extent of lattice damage to the diamond
growth surface can be controlled by modifying the voltage of the
electric field used in ion implantation. As one increases the
voltage of the electric field, the energy of the species increases
as well, ultimately resulting in a deeper implantation by the
species into the substrate. In turn, the energy level can be
selected for a specific species so as to implant a peak
concentration of the species at about a certain implantation depth
within the substrate (the end of range depth). This depth may range
anywhere from about 500 angstroms to about 20,000 angstroms. While
the end of range depth for the species can be limited by decreasing
the species energy, one ought not limit the energy too
severely.
[0067] In some embodiments of the invention, the energy level is
set in the range from about 10 KeV to about 10,000 KeV, and in
another embodiment, is set in the range from about 50 KeV to about
500 KeV. When implanting species of large sizes, in order to limit
lattice damage of the substrate, it may be desired to select the
species energy on the higher end of this range. As such, the large
size species are implanted further from the diamond growth surface,
thereby attempting to isolate any lattice damage from the diamond
growth surface. Conversely, when implanting species of small to
medium sizes, the method provides more freedom in selecting the
species energy.
[0068] The species dose rate may affect the temperature of the
substrate during the implant. If the dose rate is too high,
unwanted graphitization of the zone of the implanted layer may
occur. In some embodiments of this invention, the dose rate is set
in the range from about 0.05 microamps/cm.sup.2 to about 100
milliamps/cm.sup.2, and in others, is set in the range from about
0.1 microamps/cm.sup.2 to about 500 microamps/cm.sup.2.
[0069] In one embodiment, implants at multiple levels, followed by
heating are performed to create gaps at different levels of the
substrate. One example provides three such gaps by implanting
H.sub.2 at energy levels of 150, 155 and 160 KeV. This can provide
three levels of structures, such as waveguides, with potential
corresponding isolated N-V centers.
[0070] Given the present description, those skilled in the art will
appreciate the manner in which the end of range depth of the
species can be determined, given specifics regarding the species
implanted and the energy used. Such calculations are generally
known as TRIM (Transport of Ions in Matter) calculations. See J. P.
Biersack et al., A Monte Carlo Computer Program for the Transport
of Energetic Ions in Amorphous Targets, Nucl. Instr. Meth., pp.
174:257 (1980), the teachings of which are incorporated herein by
reference. See also generally J. F. Ziegler et al., In the Stopping
and Range of Ions in Matter, Pergamon Press, N.Y., vol. 1 (1985),
the teachings of which are incorporated herein by reference. Table
1 lists the approximate end of range depths for various species at
various energy levels, given a diamond seed being used as the
substrate. Regardless of whether the diamond seed is HPHT, CVD, or
natural diamond, the end of range depths for the species generally
remain the same. As illustrated, as the energy level is increased
for a species such as hydrogen, its end of range depth is also
increased. Calculations were run at an energy level of about 200
keV for species including boron and carbon to demonstrate that as
the atom diameter of the species increased, the corresponding end
of range depth decreased. In addition, it should be noted that in
order to achieve similar end of range depths (e.g., 1900 angstroms
to 2000 angstroms), energy levels would have to be increased by a
factor of four when using carbon as the implant species as opposed
to hydrogen.
TABLE-US-00001 TABLE 1 Implant Depths as a Function of Atom
Implanted and Implant Energy Implanted Implant Energy Ion/atom 50
keV 100 keV 200 keV 1,000 keV Hydrogen 1900 .ANG. 3700 .ANG. 7200
.ANG. 63500 .ANG. Boron 2800 .ANG. Carbon 2000 .ANG.
[0071] Heat treatments are provided on the diamond composition in
the non-oxidizing atmospheres. Such treatments can be provided by
any suitable method, including radiation, conduction, or convection
sources, all generally known in the art. Generally, the temperature
range of the heat treatments is preferably set in the range from
about 1100.degree. C. to about 1800.degree. C. and, more
preferably, about 1100.degree. C. to about 1500.degree. C. The
combination of the appropriate atmosphere and the temperature
levels provides an ideal environment to cause spontaneous
separation of the synthetic diamond and the implanted layer
portion.
[0072] FIG. 5 is a side view cross sectional representation of a
diamond illustrating a masked ion implant process for forming a
cantilever according to an example embodiment. In this embodiment,
a first mask is used to form a generally rectangular area which
will end up defining the size of a cavity in which the cantilever
will be released to be free to move. As can be seen, shapes other
than rectangular may be used. Depending on the size of elements
desired, the implantation depth may be varied, such that a
sufficient density of ions are implanted in the entire area beneath
the cantilever and to the sides of the cantilever to allow
sufficient motion once the cantilever is released to move. Thus,
the mask extends at least slightly beyond the edges and released
end of the cantilever.
[0073] Following ion implantation to form the base of the cavity, a
new mask is used as shown in FIG. 6, which is a top view
representation of an ion implantation mask 600 used to form a
cantilever according to an example embodiment. This mask allows
implantation to the sides and past the released end of the
cantilever, while defining the shape of the cantilever itself with
projection 610. The energy levels of implantation used with this
mask are designed to implant a sufficient density of ions to the
sides and released end of the cantilever. This implant may vary the
depth of implant from the surface of the diamond substrate to the
cavity defined below the cantilever. Thus, heating in a
non-oxidizing environment released the cantilever as shown in FIG.
7, which is a side view cross sectional representation of a
released cantilever beam 710 according to an example embodiment.
Alternatively, releasing may be performed using a carbon implant at
the edges and etching by oxidation via heat, electrolysis or
oxidizing acid.
[0074] In one embodiment, cantilever beam 710 tends to curve upward
when released. Further implants in the upper levels may be provided
either prior to or after release of the cantilever beam. Such
implants, depending on depth and density, will begin to straighten
the cantilever by putting the surface in compression, and if
continued, may actually cause the cantilever beam to curve
downward.
[0075] As can be seen from the formation of the cantilever beam
710, many other three dimensional structures may be created with
the use of one or more masks, and varying the depths of multiple
implants to remove desired materials. Such structures may also be
further cleaned in acid solutions to remove undesired residual
implanted diamond material. The structures may be used for many
different applications, including NEMs and MEMs devices have
general applications. Such devices may be useful as sensors and
other mechanical devices having a wide variety of applications
beyond Qubit devices, such as medical devices.
[0076] FIG. 8 is a side view cross sectional representation of a
masked diamond for forming optical structures according to an
example embodiment. In one embodiment, the mask 800 comprises an
array of one or more multiple round openings 810. The resulting
implants at a desired depth followed by heating, forms an array of
disk like voids 910, as shown in FIG. 9, which is a top cross
sectional view of the diamond of FIG. 8. The disk like voids 910
may behave as a pump, or optical deflector in one embodiment. When
formed near the surface of the diamond, the surface of the diamond
bubbles up slightly. These bubbles can result in optical fringe
effects, including color changes. In one embodiment, the disks are
approximately 500 nm in diameter. Other shapes and sizes may easily
be formed.
[0077] In one embodiment, further masks and implants may be used to
fully release the diamond above each of the disk like voids, to
create small lens like structures. Such structures may be of
desired thicknesses tied to the implant levels.
[0078] In one embodiment, the lenses are approximately 50 um thick,
forming an etalon or optical filter. It should be noted that lasers
and other method of releasing the lenses may be utilized in
addition to varying depth implants and heat to release the lenses.
In some embodiments, thicknesses of less than 1 um are utilized.
The thickness may also be a function of the desired wavelength of
operation of the optical device including such structures.
[0079] Medical Applications
[0080] Diamond appears to be highly biocompatible with living
tissue. Currently, diamond does not appear to exhibit
carcinogenetic or toxicity for in situ applications, and it appears
to be biologically inert in bulk form. Thus, it is a very desirable
material to incorporate on medical devices, orthopedics,
instruments, tools, sensors and other structures for use within
living creatures, including humans. Such medical structures may be
formed from CVD diamond directly, using the above identified
processes, or from materials that are currently used, and then
coated with CVD diamond to provide enhanced biocompatibility. The
coating may be applied by coating desired surfaces, or the entire
structures with nanocrystalline diamond, and the growing a thin
layer of CVD diamond on such surfaces. Such a diamond layer may be
made conductive by including desired dopants, or may be
non-conductive if desired.
[0081] In one embodiment, a 50 nm coating of CVD diamond is
sufficient to provide desired characteristics. Such characteristics
include biocompatibility, as well as the ability to inhibit
oxidation of the structures they are coating. In one method,
nanocrystalline diamond is used to seed the structure where
desired. The nanocrystalline diamond is commercially available, and
may be suspended in alcohol for application to the structure. The
structure may be dipped in the alcohol, and the alcohol allowed to
evaporate, leaving a desired amount of diamond seed on the
structure. An adhesive carrier for the diamond seed may also be
used, such as photoresist, which may then be evaporated. The CVD
diamond layer may be formed from the seed, such as growing from the
seeds at various process temperatures, such as between 500 to
1000.degree. C., or approximately 200.degree. C. depending on the
thermal budget of the structures, or their tolerance to heat. The
CVD diamond is grown on the seeds sufficient to cover desired
portions of the structure with CVD diamond. Multiple such coatings
may be performed to cover the entire structure.
[0082] Some applications include surgical scalpels and drill bits.
The CVD diamond coating provides increased durability. For drill
bits, such as dental, neuro, or orthopedic type drill bits, the CVD
diamond structure or coating may provide increased durability, and
in addition, can permit a desired level of sharpness without
increased erosion of the drill bit. A duller drill bit may have a
desired property of providing increased control of drill rates.
[0083] In further applications, orthopedic devices may have
improved performance. Ball and socket or cub mechanisms forming
artificial knee, hip, shoulder and elbow joints may be selectively
coated with CVD diamond, or in some embodiments, entirely created
from CVD diamond. Further devices, such as spinal disc
replacements, screws, plates, nodes, etc may be formed of diamond,
or coated with CVD diamond.
[0084] Cardiovascular applications for CVD diamond formed or coated
devices include catheter systems, such as rotator blades for
cleaning arteries, stents, and heat valves may all have increased
lives because of associated reduction in wear and tear rates.
[0085] Nano medical applications include the use of CVD diamond to
encase devices that deliver proteins, recombinant protein, and/or
retrovirus, endovirus, and plasmid technologies.
[0086] The above masked implantation processes may be used to form
many different medical related devices. Using the above described
implant techniques, drug delivery devices can be formed, which may
be implanted within a living creature. One example of such a device
is shown in a simplified block diagram in FIG. 10 at 1000. A
reservoir 1010 containing a drug, is formed in diamond, silicon, or
other substrate material using methods suitable for the
corresponding materials. When formed of silicon, many basic
photolithographic techniques may be used to form structures.
Sacrificial layers may be used to form the reservoir 1010, and a
first tube or conduit 1015 to a pump 1020, which is a small,
bubble-like structure having the ability to have its volume
controlled by desired actuation. The pump 1020 is further connected
to an output tube or conduit 1025, for injecting fluids.
[0087] Pump 1020 may be actuated by application of voltage, or
mechanically by use of piezoelectric material to cause the bubble
to controllably collapse and reform. This results in a nanofluidic
switch or pump. The silicon device 1000 may then be coated with CVD
diamond as described above. Two applications of CVD diamond may be
used, with the device turned over for the second application to
coat a bottom of the device.
[0088] When device 1000 is formed of diamond, such as CVD diamond,
different forms of ion implant and annealing may be utilized to
form the structures. Smaller structures, such as tubes 1015 and
1025 may be formed by hydrogen ion implant and anneal. In further
embodiments, larger structures, such as reservoir 1010 and pump
structure 1020 may be formed by implant of a larger ion species,
such as carbon, with multiple energy levels if desired. Such an
implant may form graphite in the diamond, which can then be etched
by use of oxidation and using sulfuric nitric acid, which attacks
the graphitic layer. The acid may be introduced through the tubes
1015 and 1025. In one embodiment, tubes 1015 and 1025 are formed as
a single continuous tube, providing access for subsequent etching
of reservoir 1010. Such a process of forming larger openings
conserves thermal budgets over hydrogen implant and anneal
processes.
[0089] In further embodiments, a masked carbon ion implant of
various energy levels may be used to create a via from the
reservoir 1010 to the surface of the device 1000. This provide
access for easier etching, and also for quicker loading of the
device with desired drugs. Circuitry may also be provided to supply
controlled voltages or suitable pressure to surfaces of the pump
1020, to provide actuation of the pump. In still further
embodiments, an additional pump or bubble 1030 may be formed such
that there are two pumps between the reservoir and exit conduit.
When operated in the proper sequence, they ensure that fluid is
pumped in the desired direction. While the shape of device 1000 is
shown as rectangular, the actual shape may be varied as desired for
compatibility with in situ applications. The sizes of tubes and
reservoirs may also be varied to achieve desired operating
parameters.
[0090] In one embodiment, capillaries and other fluidic structures
may be formed in multiple levels in a diamond using the above
techniques. Single crystalline diamond, nanocrystal on single
crystal and polycrystalline on top of single crystal diamond may be
used for structures. In one embodiment, such as a device 1100 in
FIG. 11 may be formed with interconnects between levels. A first
level capillary 1110 is formed using a first masked implant at a
low voltage. A second level capillary 1120 is formed at a lower
level in the device 1100 using a higher energy masked implant. An
interconnect or via 1130 is formed between the two capillaries 1110
and 1120 by using one or more implants of the same or a different
species.
[0091] Multiple implants at varying energy levels may be used to
form the via. An anneal is used to open the capillaries, and may
also serve to open the via. If the via is formed using a carbon ion
implant, etching as described above may be used to open the via.
The etchant may be provided through the open capillaries if
desired. Electrolysis with water and a current applied between ends
of the capillaries may also be used to remove the graphitic
material.
[0092] Multiple capillaries and vias may be formed in and between
multiple levels in various embodiments to form complex fluidic
structures. The above bubbles may be integrated into the
capillaries and operate as switches or pumps between intersecting
capillaries or channels. Reservoirs and other desired structures
may be added, including diaphragms, cantilever beams and beams
supported on both ends may also be formed to provide multiple
different functions. Since the devices are formed of diamond, or
may be coated with CVD diamond, they are highly biocompatible for
in situ applications.
[0093] The capillaries may be formed with varying dimensions, such
as from 5 to 10 nm wide to millimeter range widths. They may also
be formed as long as desired. Both dimensions are controlled by
masking the implantations used to form them.
[0094] In one embodiment, capillary 1110 is formed with a portion
of the capillary doped to make it conductive. The doping may be
provided during formation of the diamond device 1100 such that the
top of capillary 1110 is conductive, with the remainder of the tube
having insulative properties of undoped CVD diamond. Electrical
pulses may be used to close off the capillary or open it, thus
operating as a switch. In a further embodiment, electrodes may be
placed on either end of the conductive portions of the capillary to
measure conductivity of fluid within the capillary.
[0095] In still further embodiments, optical sensors and emitters
may be embedded in a diamond, or coated with CVD diamond as shown
in block diagram in FIG. 12. A silicon substrate 1205 has an
optical emitter 1210 coupled to an optical detector 1220 by a
waveguide 1230. A CVD diamond coating 1235 is used to encapsulate
the silicon structures. The diamond coating 1235 serves to protect
the silicon structures and prevent oxidation of them. Thus, they
may be used implanted into living beings and be biocompatible. In
one embodiment, a conductive input path 1240 extends from optical
detector 1210 through the diamond layer, such as by doping both the
silicon and diamond layer to form a contact in the diamond layer. A
conductive output path is formed at 1245, and extends from the
optical detector 1220 to the outside of the diamond coating 1235.
The input and output may be used as a neural conductor in some
embodiments. In further embodiments, various combinations of
silicon and diamond may be constructed as described below with
respect to boron doping of diamond semiconductor. Various other
optical and electrical detectors formed of silicon or gallium
arsenide or other semiconductor materials may also be encased or
selectively coated with CVD diamond. In some embodiments, the
diamond conductive portion extends from one end of the diamond to
the other, providing a diamond based neural connector.
[0096] In a further embodiment, as shown in FIG. 13, a sheet of
diamond 1300 of desired thickness may be used to create a porous
membrane. 10 nm to micron size or larger pores 1310 may be created,
such as an array of pores to create membranes with desired
filtering properties. The pores may be creased by masked ion
implantation and annealing or etching as described above. Since
diamond is highly biocompatible, many in situ applications are
possible. The membranes may be significantly varied in thickness in
some embodiments depending on application and surface area. The
sizes and arrangement of the pores may be varied beyond these
specified limits.
[0097] FIG. 14 is a representation of a structure 1410, such as one
of the structures described above, including prosthetic devices,
implantable medical devices, tools, etc. selectively coated with
CVD diamond 1420. It is in block diagram form, since many of such
structures are well known. While the entire structure 1410 is shown
as coated, only a portion need be coated with CVD diamond. The CVD
diamond 1420 may be single crystalline, nano-crystalline or poly
crystalline depending on application.
Boron Doping of Single Crystal CVD Diamond and Circuitry
Creation
[0098] One example embodiment provides first and second synthetic
diamond regions doped with boron. The second synthetic diamond
region is doped with boron to a greater degree than the first
synthetic diamond region, and in physical contact with the first
synthetic diamond region. In a further example embodiment, the
first and second synthetic diamond regions form a diamond
semiconductor, such as a Schottky diode.
[0099] FIGS. 15-18 illustrate a method of producing a
monocrystalline synthetic diamond Schottky diode, which is one
example of a diamond semiconductor device such as can be produced
using the present invention. FIG. 15 illustrates a diamond seed
crystal that is heavily doped with boron, which has only three
valence electrons relative to carbon=s four valence electrons,
making the diamond a strongly p-type semiconductor material. The
absence of electrons in sites in the diamond that contain boron
leaves a Ahole@ that is receptive to electrons, making what is in
effect a mobile positive charge. The negatively charged boron atom
is fixed in the diamond lattice, meaning that the boron atoms
cannot move but contribute holes as electron receptors to the
electrical conduction process.
[0100] In some examples, the boron is grown into the diamond as the
diamond is formed by chemical vapor deposition, or is incorporated
by another process, while other examples use diffusion or ion
implantation to implant boron into diamond, whether the diamond is
synthetic or naturally occurring. The diamond contains boron doping
through at least a top region of the seed diamond 101 extending a
half micron to a few microns, such that a top layer has a
relatively uniform distribution of boron atoms distributed to a
desired density.
[0101] The seed 101 is polished to have a flat top surface, and the
edges of the seed are trimmed such as with a laser or cutting tool,
and are cleaned, etched, and polished. Hydrogen atoms are then
implanted to a desired depth, as is shown in FIG. 15 at 102. The
hydrogen atoms are implanted under various conditions in various
examples, but in one example are implanted at an angle of ten
degrees relative to the diamond surface, and at a dose rate of
approximately one microamp per square centimeter. The electrons are
implanted with an energy of approximately 200 KeV, until the total
dose of approximately ten to the seventeenth atoms per square
centimeter are implanted into the diamond 101. Varying the
parameters of the hydrogen implant will vary the depth and density
of the resulting hydrogen implant layer. The hydrogen implant layer
is shown as the dotted layer 102 of FIG. 15.
[0102] Once the hydrogen implantation into the boron-doped diamond
seed is completed, more diamond is grown on the seed, such as via a
chemical vapor deposition plasma reactor. Various technologies that
can be employed for diamond formation in other examples, including
microwave plasma reactors, DC plasma reactors, RF plasma reactors,
hot filament reactors, and other such technologies. The formation
of synthetic diamond can be achieved through a variety of methods
and apparatus, such as that described in U.S. Pat. No. 6,582,513,
titled ASystem and Method for Producing Synthetic Diamond@, which
is incorporated by reference.
[0103] The diamond grown in one example is a monocrystalline
synthetic diamond uses a stream of gas, such as methane or other
gas, to provide the precursor material for the plasma reactor to
produce a plasma that precipitates to form diamond. The gas in some
examples or in some layers of the diamond contains various
impurities, such as boron dopants or various isotopes of carbon.
For example, diamonds having a greater than average purity of
carbon-12 and a corresponding reduced concentration of carbon-13
isotopes are known as isotopically enhanced, and are particularly
thermally conductive. This makes them well-suited for applications
such as semiconductor device fabrication, enabling higher power and
higher density than can otherwise be achieved. Isotopic enhancement
of the diamond CVD precursor gases with carbon-12 can result in a
diamond having significantly less than the typical 1.1% carbon-13
concentration, resulting in thermal conductivity as high as 3300
W/mK. Other examples of methods of producing synthetic diamond with
high thermal conductivity include growing diamond in a low nitrogen
environment, growing synthetic diamond in an environment rich in
hydrogen, and using boron doping resulting in an increase in
thermal conductivity.
[0104] In some embodiments, diamond regions having boron or other
dopants implanted will have somewhat larger or smaller lattice
structures than undoped diamond as a result of placement of the
dopant within the diamond crystal structure. The lattice mismatch
between diamonds having different doping concentrations or between
doped and undoped diamonds is controlled in some embodiments by
implantation of ions selected to give the desired lattice
structure. For example, a lightly boron-doped diamond region will
have a lattice structure somewhat expanded relative to undoped
diamond made from primarily carbon-12. Adding carbon-13 to the
boron-doped diamond shrinks the lattice structure, and is used in
some embodiments to eliminate the lattice mismatch between diamond
layers or to control the lattice mismatch or strain between diamond
layers.
[0105] In a more detailed embodiment, a first lightly boron-doped
region is grown in contact with a second more heavily boron-doped
region, in a diamond structure comprising approximately 99%
carbon-12 and 1% carbon-13. Addition of more carbon 13 to the
second more heavily boron-doped region enables matching the lattice
structures of the more heavily boron-doped and less heavily
boron-doped diamond regions to one another, reducing or eliminating
lattice strain at the boundary between diamond layers.
[0106] FIG. 16 shows the see diamond of FIG. 15 with a hydrogen
implant layer 201 that has another synthetic diamond layer 202 that
is boron-doped grown on the surface that was implanted with
hydrogen. In some examples, the seed 201 is polished flat before
hydrogen implantation or at some other point before growth of the
second synthetic diamond region 202, and is trimmed to a desired
size or shape such as by laser cutting before or after growth of
the second synthetic diamond region. The top layer is grown to a
desired thickness, such as 100 microns in one example, and is then
polished and cut to form the diamond assembly shown in FIG. 16.
[0107] The assembly of FIG. 16 is then heated to a temperature
sufficient to cause separation of the first diamond region 101 at
the hydrogen implant level, resulting in a portion of the seed
diamond region 101's becoming detached with the grown synthetic
diamond region 202. This operation results in a seed diamond 301
that is somewhat smaller than the original seed diamond 101, due to
the more heavily boron-doped diamond portion 302 that is removed
with the more lightly boron-doped portion 303. The resulting
structure of 302 and 303 in FIG. 17 forms the semiconductor portion
of a Schottky diode, which is able to operate at particularly high
voltage and power levels due to the characteristics of diamond when
compared to other semiconductor materials such as silicon. In other
examples, the grown region will be more heavily doped with boron
than the seed region, the thicknesses of the diamond regions will
differ, and other structural and design changes will be made.
[0108] FIG. 18 shows the diamond assembly formed by 302 and 303 in
FIG. 17 that was lifted off the diamond seed region at 401, with
electrical leads attached at 402 and 403. The metal attached is
selected based on the metal=s work function or fermi function and
the desired characteristics of the Schottky diode, and will
typically be a metal or metal alloy containing metals such as
aluminum, platinum, gold, titanium, or nickel. This forms a
completed Schottky diode, which is similar to other types of diode
in its ability to rectify some signals, or to pass current in only
one direction under certain circumstances. Looking at the Schottky
diode of FIG. 18, the terminal 403 is known as the anode, and
terminal 402 is known as the cathode. When the anode is at a
potential that is higher than that of the cathode by a certain
voltage level, current will flow through the diode, but when the
anode is lower in potential or voltage than the cathode current
doesn't flow through the diode. This property makes a diode useful
for a wide variety of electronic applications, including detection,
filtering, and shaping electrical signals.
[0109] The rectifying portion of the Schottky diode is actually the
metal-to diamond semiconductor contact, rather than the interface
between semiconductor materials as is the case in most other types
of diodes such as p-n semiconductor diodes. The theory of Schottky
diode operation is well-understood but relatively complex, and
results in a number of significant advantages over regular
semiconductor diodes for many applications. The forward voltage
drop across a Schottky diode is typically much less than across a
typical p-n junction semiconductor diode, with typical values of
0.2 Volts drop across a Schottky diode and 0.6-0.7 Volts drop
across a silicon p-n junction diode. The capacitance across a
Schottky diode is also significantly lower, and the carrier
recombination at the metal interface forming the Schottky diode
barrier region is significantly faster than in p-n semiconductor
junctions, on the order of ten picoseconds. This makes Schottky
diodes particularly well-suited for applications such as
high-frequency detection, mixing, and other such applications. The
low noise characteristics of Schottky diodes relative to
semiconductor p-n junction diodes further makes them desirable for
use in low-level detection applications, such as radar or other
radio detection.
[0110] FIG. 19 is a flowchart of a method of making a boron-doped
diamond semiconductor device such as that of FIG. 18. At 501, a
boron-doped seed diamond is created. This can be achieved by ion
implantation into a natural or synthetic diamond, by growing a
synthetic diamond in an environment that is rich in boron, or by
any other suitable method. Grown diamond can be produced by high
pressure high temperature (HPHT) methods, by chemical vapor
deposition, or by any other suitable method. The boron-doped seed
diamond surface is polished at 502, to prepare a flat diamond
crystal surface of a desired crystal orientation. For example, the
diamond may be polished in the 100 plane, tilted two degrees toward
the 110 plane, to produce a polished surface slightly off the 100
plane of the diamond. The edges of the seed may be cut and various
other facets are polished or shaped in various examples, and the
surfaces are cleaned with an acid wash, water rinse, and solvent
dry.
[0111] Next, an implantation angle, energy, and dose are selected,
and hydrogen ion implantation is performed at 503. The implantation
parameters are configured to implant a selected density of hydrogen
atoms at a selected depth in the seed diamond, as shown and
described in FIG. 15. After hydrogen implantation, the implanted
seed diamond is used as a seed for growing additional diamond, such
as by chemical vapor deposition. The grown diamond in some examples
includes either a higher or lower boron concentration than the seed
diamond, as shown and described in FIG. 16. The diamond is grown
until a desired thickness is reached, such as 500 microns
thickness, or between 10 and 15,000 microns thick.
[0112] Once the growth process is complete, the diamond assembly is
removed from the grower, and edges are trimmed with a laser cutter
at 505. In other examples, the edges are trimmed using other
methods, and may be polished or ground. The edges of the seed are
thereby also trimmed to desired dimensions, such as back to the
original seed dimensions before growth on top of the seed diamond
region.
[0113] The resulting diamond assembly is heated in a non-oxidizing
environment, such as in hydrogen or an inert gas, to an elevated
temperature designed to cause the seed diamond region of the
diamond assembly to separate at the area of hydrogen implantation.
This separation occurs in one example at about 1200 degrees
Celsius, while in other examples occurs within a range of 1100 to
2400 degrees Celsius. Once the seed and the grown diamond-seed
diamond assembly separate, the grown diamond-see diamond assembly
remains, as is shown in FIG. 17, with a portion of the seed diamond
above the hydrogen implant layer attached to the grown diamond. The
separation occurs spontaneously at elevated temperatures in some
examples, but is cause by application of pressure across the
hydrogen implant layer in other examples.
[0114] The result is a boron-doped semiconductor device that can be
trimmed and polished further at 507, and that can be attached to
wire leads and packaged for use as a semiconductor device as is
shown at 509.
[0115] Other embodiments of semiconductor devices consistent with
various embodiments of the present invention include forming an
integrated circuit, as is shown in FIG. 20. This figure shows
generally a diamond semiconductor substrate at 601, which has at
least a region or portion 602 that is boron-doped. A second region
603 is grown, implanted, or otherwise formed in contact with the
diamond region 602, but with a different boron doping density. This
forms the semiconductor portion of a Schottky diode, but similar
processes can be used to form transistors and various other
components. The elements 602 and 603 are coupled to a circuit using
metallic wire having an appropriate work function, and in further
examples are connected using polysilicon or other conductor or
semiconductor elements to other portions of the integrated
circuit.
[0116] FIG. 21 illustrates an example of an electronic device that
may be constructed, consistent with some example embodiments of the
present invention. A radar apparatus 701 uses Schottky diodes for
low-level, high-frequency radio detection, and for mixing in
further example applications such as Doppler radar. The electronic
device benefits from the increased performance possible with
boron-doped diamond semiconductors, such as improved power
handling, higher density, and higher performance relative to
traditional semiconductors such as silicon.
[0117] Boron-doped diamond is also distinct from silicon-based
semiconductors in that it is largely transparent, with a bluish
tint. This makes boron-doped diamonds particularly well-suited for
applications such as blue LED or laser semiconductor devices in
configurations where light is emitted from other than an external
surface of a semiconductor junction, in addition to other
applications such as traditional LED or laser diodes. Because
boron-doped diamond conducts electricity to some extent, it is also
used in a variety of applications where conductivity is desired,
such as in electrodes, in an electrically conductive cutting tool
where the condition or other characteristics of the cutting tool
can be electrically monitored, in conductive heat sinks or heat
spreaders, and in optical windows that can be heated or that have
an index of refraction that can be altered by current flow.
[0118] Schottky barrier junctions are further usable in a variety
of applications other than Schottky diodes, including in use in
bipolar junction transistors where a Schottky junction is located
between the base and collector of the transistor. This prevents the
transistor from saturating too deeply, resulting in faster
switching times for the transistor. Metal-semiconductor field
effect transistors (MESFETs) also use a reverse-biased Schottky
barrier to provide the depletion region in the transistor, and
works similarly to a JFET. Still other devices, including high
electron mobility transistors (HEMTs) use Schottky barriers in a
heterojunction device to provide extremely high conductance in a
transistor.
[0119] It is anticipated that the methods and devices described
here will apply not only to Schottky diodes and related devices,
but to other semiconductors, integrated circuits, and electronic
devices. Although specific embodiments have been illustrated and
described herein, those of ordinary skill in the art will
appreciate that a variety of arrangements which are calculated to
achieve the same purpose may be substituted for the specific
embodiments shown. This application is intended to cover any
adaptations or variations of the invention. It is intended that
this invention be limited only by the claims, and the full scope of
equivalents thereof.
[0120] The Abstract is provided to comply with 37 C.F.R.
.sctn.1.72(b) to allow the reader to quickly ascertain the nature
and gist of the technical disclosure. The Abstract is submitted
with the understanding that it will not be used to interpret or
limit the scope or meaning of the claims.
* * * * *