WO2000048435A1

WO2000048435A1 - Method of plasma enhanced chemical vapor deposition of diamond

Info

Publication number: WO2000048435A1
Application number: PCT/US2000/003502
Authority: WO
Inventors: Yonhua Tzeng
Original assignee: Auburn University
Priority date: 1999-02-10
Filing date: 2000-02-10
Publication date: 2000-08-17
Also published as: WO2000048435A9; AU4166600A

Abstract

A plasma CVD process of forming diamond crystals or a diamond film on a substrate (11) is disclosed, wherein a liquid precursor (5) comprising methanol and at least one carbon containing compound is introduced into a reaction chamber (1) through a liquid flow controller (7), and it vaporizes to form a vapor precursor. An electromagnetic discharge is applied to dissociate the vapor precursor to generate oxidizing and etching radicals as well as carbon depositing radicals.

Description

METHOD OF PLASMA ENHANCED CHEMICAL VAPOR DEPOSITION OF

DIAMOND

This application claims benefit of U.S. Provisional Patent Application No.

60/119,771 filed February 10, 1999, incorporated herein by reference in its entirety.

The invention was made with support from the United States National Aeronautics

and Space Administration (Contract No. NASA/NCC5-165) and the United States

Department of the Navy (Contract No. Navy/N00014-98-l-0571). The Federal

Government may retain certain rights in the invention.

FIELD OF THE INVENTION

The present invention relates to a method of synthesizing diamond. In

particular, the present invention relates to a method of synthesizing diamond crystals

and diamond films using plasma enhanced chemical vapor deposition.

BACKGROUND OF THE INVENTION

Diamond synthesized by chemical vapor deposition ("CVD") has many unique

and outstanding properties that make it an ideal material a broad range of scientific

and technological applications. See Y. Tzeng et al., Application of Diamond Films

And Related Materials, Elsevier Publishers, 1991. A number of methods for diamond

CVD are reported which utilize various gas mixtures and energy sources for

dissociating the gas mixture. See P.K. Bachmann et al., Diamond and Related

Materials 1, 1, (1991). Such methods include the use of high temperature electrons in

various kinds of plasma, high solid surfaces on hot filaments, and high temperature gases in combustion flames to dissociate molecules such as hydrogen, oxygen,

halogen, hydrocarbon, and other carbon containing gases. Typically, a diamond

crystal or film is grown on a substrate, which is usually maintained at a temperature

much lower than that of electrons in the plasma, the heated surface of a hot filament,

or the combustion flame. As a result, a super equilibrium of atomic hydrogen is

developed near the diamond growing surface of the substrate.

Atomic hydrogen is believed to be crucial in the diamond CVD process. It is

theorized that atomic hydrogen is effective in stabilizing the diamond growing surface

and promoting diamond growth at a CVD temperature and pressure that otherwise

thermodynamically favors graphite growth. Consistently, the reported diamond CVD

processes involve the use of hydrogen gas or hydrogen containing molecules. The

most typical diamond CVD process utilizes a precursor comprising of methane gas

diluted by 94-99% hydrogen. With these CVD processes, the super equilibrium of

atomic hydrogen can be achieved at a varied percentage of molecular hydrogen in the

gas mixture. However, these CVD processes depend on the effectiveness of the

dissociation process in generating atomic hydrogen.

Chein et al., Proceedings of the 6th International Conference on New Diamond

Science and Technology (1998), report using a high power density microwave plasma

to deposit diamond in a precursor comprising of a mixture of methane and hydrogen

with less than 50% hydrogen. Growth of diamond from oxy-acetylene flames utilizes

a precursor comprising of acetylene and oxygen with a ratio of acetylene to oxygen

slightly greater than 1 without additional molecular hydrogen being added. Diamond

is deposited in the reducing "inner flame" where atomic hydrogen is a burn product produced by the high temperature flame. In addition to atomic hydrogen, there are

plenty of OH radicals present near the diamond growing surface inside the flame.

OH and O radicals can play another role of atomic hydrogen in the diamond

growth process. That is, preferential etching of non-diamond carbon, which results in

a net deposition of high purity diamond. Small quantity of oxygen (0.5-2%>) or water

vapor (<6%) added to the methane and hydrogen precursor is reported to improve

diamond crystallinity and lower the diamond CVD temperature. See Saito et al.,

Journal of Materials Science, 23, 842 (1988), and Kawato et al., J. Applied Physics,

26, 1429 (1987). The quantity, whether small or large, of oxygen and water in a

precursor or feedstock is a relative term depending on many other process parameters.

Diamond has also been grown in a microwave plasma of a precursor comprising of an

acetone/oxygen mixture with a molecular ratio near 1:1. See Chein et al, Proceedings

of the 6th International Conference on New Diamond Science and Technology (I

998).

Most of the diamond CVD processes involve the use of one or more

compressed gases. Typically, such CVD processes utilize a compressed gas precursor

comprising of 1 vol.% methane gas diluted by 99 vol.% hydrogen. These gases

usually must be precisely controlled by electronic mass flow controllers to ensure the

accurate composition in the gas precursor feed.

In U.S. Patent No. 5,480,686 to Rudder et al. ("Rudder") a method of diamond

growth is disclosed that utilizes a radio frequency ("RF") plasma in a precursor

comprising of a mixture of water (more than 40%) and alcohol. No compressed gases

are needed for this diamond CVD process. However, water has a low vapor pressure at room temperature, and condensation of water in the cooler part of the reactor

manifold may be a concern. Also, water has a high freezing temperature making it

easy to freeze at the orifice of a flow controller where liquid vaporizes and enters a

low pressure reactor chamber. Buck et al. ^Buck"), "Microwave CVD of diamond

using methanol-rare gas mixtures," Materials Research Society Symposium

Proceedings, Vol. 162, 97-102, 1989.) have grown clusters of diamond crystallites on

small (2-4 mm²) silicon substrates that were scratched with a diamond tip or

mechanically polished with 3 μm diamond powder by microwave plasma enhanced

CVD in pure methanol vapor. Argon gas additive was found necessary for high

quality diamond to be deposited in the methanol vapor. When it is fully dissociated

and reacted in the plasma, the pure methanol vapor plasma contains a C/O/H

composition similar to that of CO/H₂ plasma, which has been used for successful

deposition of diamond by means of electrical discharges. See Ito et al., Proceedings

of International Conference on New Diamond Science and Technology, p.2-16

(1988).

In a typical electrical discharge such as a microwave plasma, electrons with an

average temperature exceeding 10,000°C are abundant. These energetic electrons

effectively dissociate molecular species and generate a high concentration of radicals

necessary for the deposition of diamond and the preferential etching of non-diamond

deposits without needing a high temperature filament. Hot filament assisted CVD

processes employ solid surfaces at a temperature of about 2,000 C-2,500 C to

dissociate molecules and generate radicals necessary for diamond deposition. The hot

filament temperature is much lower than that of energetic electrons in a plasma. As a consequence, hot-filament CVD of diamond in CO/H₂ mixtures has not been

successful even though the same gas mixtures have been routinely used for plasma

assisted deposition of diamond films.

Nevertheless, the plasma enhanced CVD method is desirable because diamond

crystals and films can be deposited on large-area and/or irregularly shaped objects

using inexpensive equipment. Thus, there remains a need for an economic method of

synthesizing diamond utilizing plasma enhanced CVD. Further, there remains a need

for a method of diamond CVD which preferentially etch non-diamond deposits at low

substrate temperatures to provide the deposition of high quality diamond.

Additionally, there remains a need for a method of diamond CVD that does not

require the use of compressed gases or water or precision electronic mass flow

controllers. It is to the provision of a method of plasma enhanced CVD of diamond

that meets these needs that the present invention is primarily directed.

SUMMARY OF THE INVENTION

Briefly described, the present invention relates to a method of synthesizing

diamond that enables the economic growth of high quality diamond crystals and

diamond films using a liquid solution as the feedstock and an electrical discharge as

the means of dissociating and reacting the vapor of the said solution. In the method of

the present invention, a precursor comprising at least one carbon containing

compound having a carbon to oxygen ratio greater than one is fed into a deposition

chamber through a liquid flow controller such as a needle valve. The precursor

further comprises a solution of methanol and at least one carbon containing

compounds having a carbon to oxygen ratio greater than one. The solution is pre-mix

prior to entering the deposition chamber. Such carbon containing compounds include

ethanol, isopropanol, and acetone. The solution vaporizes as it enters the low pressure

deposition chamber. The vaporized precursor comprises the same composition as the

solution. When the vapor passes through an electrical discharge zone, it is dissociated

to generate OH, H, O, CH₃ and other molecules and radicals.

The substrate generally is sheet or wafer of silicon, copper, aluminum and

molybdenum. Some of the substrates are polished using 1 μm diamond paste prior to

the deposition process. Typically, the substrate is mounted on a water cooled

substrate holder. The substrate can be either in touch with the plasma or at a distance

from the plasma. In experiments using the method of the present invention, the

substrate was in touch with a microwave plasma ball generated inside a cylindrical

microwave cavity. The reactor chamber pressure generally is maintained between 1 mtorr and 250 torr. The substrate of about 25mm x 25mm was heated by the plasma

to about 300-1600°C. Diamond is deposited at a rate of 0.05-20 μm per hour

depending on the composition of the solution, the vapor pressure, the substrate

temperature, and the plasma power density.

Various other objects, features and advantages of the present invention will

become known to those skilled in the art upon reading the following specification

when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic illustration of a microwave plasma enhanced chemical

vapor deposition system made in accordance with the present invention.

Figure 2 is an optical micrograph of a free-standing diamond film deposited in

accordance with the present invention on a molybdenum substrate by a microwave

plasma in the vapor of a precursor solution comprising 4.6 grams of ethanol and 100

grams of methanol.

Figure 3 is a graphic illustration of a Raman spectrum for the diamond film of

Figure 2.

Figure 4 is an optical micrograph of a diamond film deposited in accordance

with the present invention on silicon by a microwave plasma in the vapor of a

precursor solution comprising 4 grams of isopropanol and 100 grams of methanol.

Figure 5 is a graphic illustration of a Raman spectrum for the diamond film of

Figure 4.

Figure 6 is an optical micrograph of a free-standing diamond film deposited in

accordance with the present invention on a molybdenum substrate by a microwave plasma in the vapor of a precursor solution comprising 3.5 grams of acetone and 100

grams of methanol.

Figure 7 is a graphic illustration of a Raman spectrum for the diamond film of

Figure 6.

Figure 8 is an optical micrograph of a diamond film deposited in accordance

with the present invention on an aluminum plate by a microwave plasma in the vapor

of a precursor solution comprising 15 grams of acetone and 100 grams of methanol.

Figure 9 is a graphic illustration of a Raman spectrum for the diamond film of

Figure 8.

Figure 10 is an optical micrograph of diamond crystallites grown in

accordance with the present invention on a clean and untreated silicon wafer by a

microwave plasma in the vapor of a precursor solution comprising 50 grams of

acetone and 100 grams of methanol.

Figure 11 is a graphic illustration of a Raman spectrum for a diamond

crystallite of Figure 10.

Figure 12 is an optical micrograph of a diamond film deposited in accordance

with the present invention on a clean and scratched (by diamond paste with 1 μm

diamond powder) silicon wafer by a microwave plasma in the vapor of a precursor

solution comprising 50 grams of acetone and 100 grams of methanol.

Figure 13 is a graphic illustration of a Raman spectrum for the diamond film

of Figure 12.

Figure 14 is an optical micrograph of diamond crystallites grown in

accordance with the present invention on a clean and untreated silicon wafer by a microwave plasma in the vapor of a solution comprising 100 grams of isopropanol

and 100 grams of methanol.

Figure 15 is a graphic illustration of a Raman spectrum for the diamond

crystallites of Figure 14.

Figure 16 is an optical micrograph of diamond crystallites deposited in

microwave plasma in the vapor of a precursor comprising isopropanol.

Figure 17 is a graphic illustration of a Raman spectrum for the diamond

crystallites of Figure 16.

DETAILED DESCRIPTION OF THE INVENTION

For a more complete understanding of the present invention, reference should

be made to the following detailed description taken in connection with the

accompanying figures.

The present invention relates to a method of synthesizing diamond crystals and

diamond films for a very broad range of scientific and technological applications such

as optical windows, machining tools, heat spreaders, tribological coatings, sensors and

actuators, electrochemical coatings, protective coatings, and wide-bandgap

semiconductor devices. The method of the present invention uses a premixed

methanol-based liquid solution as the feedstock. The methanol-based solution

contains 0.5-99.5% by weight of one or more carbon containing compounds with the

molar ratio of atomic carbon to atomic oxygen being greater than one. Although

water and other compounds that can be dissociated by a plasma to form O, H, F, CI,

Br, and OH radicals may be added to the methanol-based solution, it is not a requirement for the deposition of diamond crystals and diamond films by the method

of the present invention.

Figure 1 generally illustrates the plasma enhanced chemical vapor deposition

system utilized in performing the method of the present invention. As illustrated in

Fig. 1, the precursor 5 is fed from a precursor container 4 by a conduit 6, such as a

TEFLON or metal tubing, through a liquid flow controller 7, such as a needle valve,

to an inlet 2 of reactor chamber 1. The reactor chamber 1 is formed from a material

capable of withstanding the temperature generated during the CVD process. In the

present invention, the reactor chamber 1 is stainless steel and typically 8" in diameter.

When the liquid precursor 5 enters the low pressure side of the liquid flow controller

7, it vaporizes to form a vapor precursor 5 comprising a mixture with the same molar

composition as the liquid precursor 5. In addition to inlet 2, the reactor chamber 1 has

an outlet 3 connected to a mechanical vacuum pump 13 through an automatically

controlled throttle valve 14 to maintain constant pressure in the reaction chamber 1

throughout the deposition process and for circulating the vapor of the precursor 5

through the reactor chamber 1. The vapor precursor 5 is maintained at a pressure

within the vacuum chamber 1 of between 1 mtorr and 250 torr, with the pressure

being monitored by a pressure gauge (not shown).

Electromagnetic energy 8 discharged at various frequencies, for example, DC,

RF, and microwave, and also high frequency electromagnetic energy such as energy

discharged from a laser, is applied to the reactor chamber 1. A window 9 such as a

quartz window that separates the low pressure reactor from ambient pressure and

permit microwave energy to progate into the reaction chamber 1. Preferably, the electromagnetic energy 8 is microwave energy. The reactor chamber 1 is a part of the

cylindrical cavity for the microwave of 2.45 GHz. A substrate 11 is placed on a

substrate holder 12, preferably a water cooled substrate holder to control the

temperature of and cool the substrate 11. Substrate 11 temperature is monitored with

a dual color optical pyrometer (not shown). The plasma 10 dissociates the vapor

precursor 5 and releases OH, H, O, CH₃, CH₂, etc. radicals for a net deposition of

diamond on a substrate surface 15. Methanol vapor (CH₃OH) has a carbon to oxygen

ratio equal to one. In the present invention, when methanol dissociates, it forms high

concentrations of radicals that rapidly etch carbon, including diamond, resulting in

slow growth of diamond in areas where a diamond deposition rate exceeds the etching

rate. The growth rate and degree of non-uniformity also depend on the exposure of

carbon, which may be present in some reactor fixtures or previously coated on reactor

walls or the substrate holder, to the methanol plasma.

When the precursor 5 comprises a solution of methanol and a proper quantity

of one or more carbon containing compounds having a carbon to oxygen ratio greater

than one, diamond growth is substantially uniform, reproducible, and at a higher

growth rate than conventional CVD methods. For example, ethanol (CH₃CH₃OH),

isopropanol, ((CH₃)₂CHOH), and acetone (CH₃COCH₃) have respective carbon to

oxygen ratios of 2, 3, and 4. The selection of the carbon containing compound is not

limited to ethanol, isopropanol, or acetone, and may be selected from other such

carbon containing compounds having carbon to oxygen ratios greater than one. In

addition, as indicated in Example 8 below, under certain CVD conditions, it is not

required for the precursor 5 to contain methanol. However, if the precursor comprises only a carbon containing compound having carbon to oxygen ratios greater than one,

suppression of the formation of non-diamond phases can generally be maintained by

lowering the substrate temperature to below about 900° C and/or selectively neucleate

the substrate with high quality diamond particles. Also, diamond growth is as well a

function of the plasma density, reaction chamber pressure, carbon to oxygen ratio at

the substrate surface, and precursor flow rate, and these functions must be monitored

and adjusted accordingly to promote diamond growth. Further, if it is desired for the

diamond to contain a dopant, the carbon containing compound can comprises dopant

elements or moieties in addition to C, O, and H, such as boron, phosphorus, silicon,

etc. Such dopants include, but are not limited to, halides, metals, and the like. Still

further, carrier gasses, such as argon, hydrogen, and the like may be utilized to

increase the precursor flow rate into or through the reaction chamber 1.

The substrate can comprise any suitable material conventionally utilized in

CVD processes. Useful substrate materials are capable of withstanding the

temperatures generated during the plasma process. Examples of such substrates

include, but are not limited to, a sheet or wafer of silicon, copper, aluminum,

molybdenum, and alloys thereof. Further, the substrate may be either unseeded or

seeded with diamond crystallites. Seeding can be accomplished by polishing the

diamond growing surface of the substrate with diamond paste containing diamond

particles, such as 1 μm particles.

In experiments conducted using the method of the present invention, the

deposition process lasted for 2-100 hours resulting in diamond films with well faceted

diamond grains clearly visible using an optical microscope. The diamond grain sizes range from sub-micrometers to more than 500 μm.

An electromagnetic, such as microwave, plasma enhanced chemical vapor

deposition technique using a precursor comprising methanol-based solutions or a

carbon containing compound having a carbon to oxygen ratio greater than one as the

feedstock has been developed for the deposition of diamond crystals and diamond

films. The CH, H, O radicals generated by the dissociation of the precursor vapor are

shown to be sufficient in suppressing the growth of graphitic and amorphous carbon,

which results in the net deposition of diamond by the carbon containing radicals that

were dissociated from the same vapor. By the addition of carbon containing

compounds having a carbon to oxygen ratio greater than one to methanol, the

diamond growth rate increases by orders of magnitude over conventional methods.

The aforementioned precursors are less costly than the typical compressed

gases that are often used for diamond deposition. Further, the mixing of a methanol-

based solution can be performed under standard conditions without the need for an

expensive precision electronic mass flow controller.

In contrast to what was reported by Buck, who deposited clusters of diamond

crystallites in a small area of 3-4 mm² in a methanol plasma, when methanol was used

alone as the precursor feedstock for substrates of 25 mm x 25 mm in size or larger,

only the area near the edge showed acceptable diamond nucleation density in some

cases. The diamond deposition was highly non-uniform across the substrate surface.

In other cases, too much oxidizing and carbon etching radicals were generated in the

methanol piasma resulting in a very slow growth of diamond. For example, when

2,000 W microwave was applied at a pressure of 80 torr and a substrate temperature of 900 C, the methanol plasma deposited only about 2 μm diamond on a

molybdenum substrate after 40 hours of deposition. The diamond growth rate is only

0.05 μm per hour in this case. Using a solution comprising of methanol and one or

more carbon containing compounds, that have carbon to oxygen ratio being greater

than one, diamond deposition rates of more than two orders of magnitude have been

achieved in the present invention.

EXAMPLES

A. Substrate pre-treatment and cleaning.

Substrates of silicon, aluminum, and molybdenum were cleaned by acetone

and methanol before being loaded onto the substrate holder. Except those substrates

specified to be untreated, all substrates were polished with diamond paste containing 1

μm sized diamond particles.

B. Deposition parameters.

Typical deposition parameters are as follows:

Microwave power 600-3000W

Vapor pressure 1 mtorr-250 torr

Substrate temperature 300° C-l 600° C

Methanol 0.5-99.5% by weight

Ethanol, isopropanol, and acetone 0.5-99.5% by weight

C. Diamond film characterization methods.

A Normaski phase contrast optical microscope was used to examine the

crystal shapes and surface morphology of the deposited films. Diamond grains with 100 or 111 facets can clearly be seen using this optical microscope. The diamond film

thickness can also be measured by examining the cross-sectional view of such films

using the same optical microscope. A micro Raman spectrometer powered by an

Argon ion laser was used to examine the phase purity of the deposited films.

Diamond peak around 1332 cm provided convincing evidence that the deposited

carbon films were diamond.

The following examples are provided to illustrate the present invention but are

not to be construed as limiting the invention in any way.

Example 1

A liquid solution comprising 4.6 grams of ethanol and 100 grams of methanol

was used as the precursor feedstock. A molybdenum plate of 1/2 inch thick and 2

inches in diameter was polished by diamond paste containing 1 μm sized diamond

powder and cleaned by acetone and methanol. Microwave power of 2kW was applied

at the vapor pressure of 80 torr resulting in the substrate being heated to 1 ,000 C.

After 45 hours of deposition, the film separated itself from the molybdenum substrate

and was of about 45 μm in thickness. The growth rate was about 1 μm per hour.

Diamond growth rate increased with increasing quantity of ethanol in the methanol-

based solution. Figure 2 shows the optical micrograph of the flee-standing diamond

film. The diamond peak at 1332 cm in the Raman spectrum shown in Figure 3

indicates that the diamond film is of very good quality.

Example 2

N liquid solution comprising 4 grams of isopropanol and 100 grams of

methanol was used as the precursor feedstock. A molybdenum plate of 1/2 inch thick and 2 inches in diameter was polished by diamond paste containing 1 μm sized

diamond powder and cleaned by acetone and methanol. Microwave power of 2kW

was applied at the vapor pressure of 80 torr resulting in the substrate being heated to

1,000 C. Nfter 22 hours of deposition, the film separated itself from the

molybdenum substrate and was of about 44 μm in thickness. The growth rate was

about 2 μm per hour. Figure 4 shows the optical micrograph of the free-standing

diamond film. The clear diamond peak in the Raman spectrum shown in Figure 5

indicates that the diamond film is of good quality.

Example 3

A liquid solution comprising 3.5 grams of acetone and 100 grams of methanol

was used as the precursor feedstock. A silicon wafer of 1" x 1" in size was placed on

a water cooled molybdenum holder. The silicon wafer was polished by diamond paste

containing 1 μm sized diamond powder and cleaned by acetone and methanol before

loading onto the substrate holder. Microwave power of 2kW was applied at the vapor

pressure of 60 torr resulting in the substrate being heated to 1030° C. After 23 hours

of deposition, the diamond film was about 30 μm in thickness. The growth rate was

about 1.3 μm per hour. Figure 6 shows the optical micrograph of the diamond film on

silicon. The diamond peak at 1332 cm^'1 in the Raman spectrum shown in Figure 7

indicates that the diamond film is of good quality.

Example 4

A liquid solution comprising 15 grams of acetone and 100 grams of methanol

was used as the precursor feedstock. An aluminum plate of 2" diameter was placed on

a water-cooled molybdenum holder. The aluminum plate was polished by diamond paste containing 1 μm sized diamond powder and cleaned by acetone and methanol

before loading onto the substrate holder. Microwave power of 650 W was applied at a

vapor pressure of 11 torr, resulting in the substrate being heated to 535° C. After 5

hours of deposition, the microwave power was increased to 800 W, and the vapor

pressure was increased to 16 torr for another 5 hours of deposition at 613° C. A

continuous diamond film was coated onto the aluminum plate with good adhesion.

Figure 8 shows the optical micrograph of the diamond film on aluminum. The

diamond peak at 1332 cm in the Raman spectrum shown in Figure 9 indicates that

the coating was indeed a diamond film.

Example 5

A liquid solution comprising 50 grams of acetone and 100 grams of methanol

was used as the precursor feedstock. A silicon wafer of 1 " x 1 " in size was placed on

a water-cooled molybdenum holder. The silicon wafer was cleaned by acetone and

methanol but not polished by diamond paste before loading onto the substrate holder.

Microwave power of 1 , 100 W was applied at a vapor pressure of 35 torr, resulting in

the substrate being heated to 724°C. After 2 hours, diamond nucleated and grew to

the size of about 4 μm. The growth rate was about 2 μm per hour. Figure 10 shows

the optical micrograph of the diamond crystallites on the untreated silicon wafer. The

diamond peak at 1332 cm in the Raman spectrum shown in Figure 11 indicates that

the diamond crystallites are of good quality.

Example 6

A liquid solution comprising 50 grams of acetone and 100 grams of methanol

was used as the precursor feedstock. A silicon wafer of 1" x 1" in size was placed on a water-cooled molybdenum holder. The silicon wafer was polished by diamond paste

loading onto the substrate holder. Microwave power of 1,100 W was applied at a

vapor pressure of 29 torr, resulting in the substrate being heated to 800° C. After 4

hours of deposition, a diamond film was deposited. Figure 12 shows the optical

micrograph of the diamond film on silicon. The diamond peak at 1332 cm in the

Raman spectrum shown in Figure 13 indicates that the diamond film is of good

quality. In addition to the diamond peak, the Raman spectrum shows another broad

band around 1550 cm indicating the inclusion of non-diamond phases in the diamond

grains, in the grain boundaries, or in both.

Example 7

A liquid solution comprising 100 grams of isopropanol and 100 grams of

methanol was used as the precursor feedstock. A silicon wafer of 1" x 1" in size was

placed on a water-cooled molybdenum holder. The silicon wafer was cleaned by

acetone and methanol, but not polished by diamond paste, before loading onto the

substrate holder. Microwave power of lkW was applied at a vapor pressure of 36

torr, resulting in the substrate being heated to 754° C. After 2 hours and 40 minutes,

diamond nucleated and grew to the size of about 7 μm. The growth rate was about 2.7

μm per hour. Figure 14 shows the optical micrograph of the diamond crystallites on

the untreated silicon wafer. The diamond peak at 1332 cm in the Raman spectrum

shown in Figure 15 indicates that the diamond crystallites are of good quality.

Example 8

Substantially pure isopropanol was used as the precursor feedstock. N silicon wafer of 1" x 1 " in size was placed on a water-cooled molybdenum holder. The silicon

wafer was cleaned by acetone and methanol, but not polished by diamond paste,

before loading onto the substrate holder. Microwave power of 900 W was applied at a

vapor pressure of 30 torr, resulting in the substrate being heated to 740° C. After 2

hours and 14 minutes, diamond nucleated and grew to the size of about 2 μm. The

growth rate was about 1 μm per hour. Figure 16 shows the optical micrograph of the

diamond crystallites on the untreated silicon wafer. The diamond peak at 1332 cm in

the Raman spectrum shown in Figure 17 indicates that the crystallites are indeed

diamond. The much stronger background signal and the higher broad band near 1550

cm^"1 in the Raman spectrum shown in Figure 17 as compared to those shown in Figure

15 indicate that the quality of the diamond crystallites was improved by the addition

of methanol to isopropanol.

Although the invention has been described in detail for the purpose of

illustration, it is understood that such detail is solely for that purpose, and variations

can be made therein by those skilled in the art without departing from the spirit and

scope of the invention which is defined by the following claims.

Claims

WHAT IS CLAIMED IS:

1. A method of forming diamond crystals or a diamond film comprising:

disposing a substrate in a reaction chamber; and

subjecting a vaporized precursor comprising at least one carbon containing

compound having a carbon to oxygen ratio greater than one to a plasma under

conditions effective to dissociate the precursor and promote diamond growth on the

substrate.

2. The method according to claim 1, wherein the precursor comprises a

solution of methanol and the at least one compound having a carbon to oxygen ratio

greater than 1.

3. The method according to claim 2, wherein methanol is present in the

precursor in an amount between about 0.5 wt.% to about 99.5 wt. % of the precursor.

4. The method according to claim 1, wherein the precursor is selected

from the group comprising of ethanol, isopropanol, acetone, and combinations

thereof.

5. The method according to claim 1, wherein the precursor is a solution of

methanol and a compound selected from the group comprising of ethanol,

isopropanol, acetone, and combinations thereof.

6. The method according to claim 1, wherein the subjecting a vaporized

precursor step is conducted at a pressure between about lmtorr and 250 torr.

7. The method according to claim 1, wherein the substrate is heated to a

temperature between 300° C to about 1,600° C.

8. The method according to claim 1 , wherein the carbon containing compound further comprises a dopant element or moiety.

9. The method according to claim 1, wherein the substrate comprises a

sheet or wafer of silicon, copper, aluminum, molybdenum, or alloys thereof.

10. The method according to claim 1 , wherein the plasma is induced by

electromagnetic energy.

11. The method according to claim 10, wherein the electromagnetic energy

has a frequency selected from the group comprising of direct current, radio frequency,

and microwave.

12. The method according to claim 1 , wherein the plasma is induced by

microwave energy.

13. A plasma enhanced chemical vapor deposition of diamond crystals and

diamond films on surfaces of a substrate comprising:

providing an apparatus including an inlet, a dissociation zone, a deposition

zone and an outlet;

introducing a precursor comprising methanol and at least one carbon

containing compound containing a carbon to oxygen ratio greater than one into the

inlet under conditions effective to vaporize the precursor, flow the precursor through

the dissociation zone, and through the outlet;

dissociating and reacting the vaporized precursor as vaporized precursor flows

or diffuses through the dissociation zone to produce OH, H, O, and carbon containing

radicals; and

transporting the radicals to the substrate in the deposition zone to produce the

diamond crystals or diamond films on the surface of the substrate.

14. The process according to claim 13, wherein the dissociation and

reacting steps comprise:

passing the vaporized precursor through an electrical discharge zone for

dissociating the precursor in the dissociation zone.

15. The process according to claim 13, wherein the introducing step

comprises:

introducing the liquid precursor with methanol in an amount between about

0.5 wt.% and about 99.5%.

16. The process according to claim 15, further comprising:

supplementing methanol with one or more carbon containing compounds

containing carbon, hydrogen, and oxygen with the atomic ratio of carbon to oxygen

greater than one.

17. The process according to claim 16, further comprising:

selecting the supplementing compounds from the group comprising of ethanol,

isopropanol, acetone, and combinations thereof.

18. The process according to claim 13, wherein the deposition zone is

maintained at a temperature between about 200° C to 1600° C and at a pressure

between 1 mtorr and 250 torr.