CA1329791C

CA1329791C - Process for making diamond, doped diamond, diamond-cubic boron nitride composite films

Info

Publication number: CA1329791C
Application number: CA000575141A
Authority: CA
Inventors: Chandra V. Desphandey; Rointan F. Bunshah; Hans J. Doerr
Original assignee: University of California
Current assignee: University of California
Priority date: 1987-08-19
Filing date: 1988-08-18
Publication date: 1994-05-24
Anticipated expiration: 2011-05-24
Also published as: KR890003982A; JPS6472993A; US4816291A; ZA885917B; IL87406A0; BR8804197A; EP0304201A1

Abstract

PROCESS FOR MAKING DIAMOND, DOPED DIAMOND, DIAMOND-CUBIC BORON NITRIDE COMPOSITE FILMS

ABSTRACT OF THE INVENTION
A process and apparatus that may be used for the production of diamond and doped diamond films at high rates by activated reactive vapor deposition. Carbon is evaporated in a vacuum chamber in the presence of atomic hydrogen containing plasma to form diamond precursors which then deposit on a substrate located within the vacuum chamber.

Description

~L3297~1 PROCESS FOR MAKING DIAMOND, DOPED DIAMOND, DIAMOND-CUBIC BORON NITRIDE COMPOSITE FILMS
BACKGROUND OF THE INVENTION
1. Field of tne Invention This lnventlon relates to the process of deposlting diamond, doped dlamond and cublc boron nltride-diamond composlte fllms. ~ore speclflcally it relates to deposltlon of these fllms at hlgh rates over large areas, based on Activated Reactive Evaporation (ARE) as flrst descrlbed ln U.S. Patent No. 3,791,852.

2. DescriPtion of the Backqround Art For convenience, the reference materials are numerically referenced and grouped ln the appended blbliography.
Techniques used ln recen~ years to deposlt films of - dlamond-llke carbon (l-Ct, diamond and boron nltride onto sub-strates have included chemical vapor deposition ~CVD) and plasma assisted chemical vapor deposltlon (PACV~) lnvolvlng pla~ma de-composltlorl of hydrocarbon/boron corltalnlng gases. Ion beam asslsted/enhanced deposltlon has also been used.
Diamond mlcrocrystals were prepared uslng chemical vapor deposltlon and related techniques, at low pressures for the first tlme by Der~aguin and co-workers~l) by a chemlcal transport method. Subsequently Angus et al.(2~ reported deposltlon of dlamond onto natural dlamond powder from methane gas at 1050C and 0.3 torr pressure. They also proposed a qualitatlve model explalning the klnetlcs of diamond growth from the vapor phase.
More recently Matsumoto et al.(3,4), have reported synthesls of dlamond microcrystals by chemical .~ 1 . ,. , . ,, . ~ . ,., . i , . . . . . ~, . ..

Docket No. 66-l~
7 ~ 1 vapor deposition from a mixture of methane and hydrogen gas in open flow systems. They have shown that the growth of diamond films can be enhanced if a heated tungsten filament is used in the CVD set up. Spitsyn et al.(5) in their paper have discussed the kinetics of diamond growth from CH4 + X2 gas mixtures. They have argued that atomic hydrogen plays a unique role in the growth of diamond from vapor phase.
Whitmell et al.(6) were the first to report the use ; 10 of plasma decomposition techniques in the deposition of amorphous carbon-like films onto a negatively biased d.c. electrode using methane gas. However, the growth of filrns in their earlier experiment was thickness limited. This was believed to be due to the formation of an insulating film (i-C) on the surface of the d.c.
biased electrode which after a critical thickness was reached, prevented the bombardment of the growing film with energetic ions from the plasma. Following that report, Holland (7) proposecl a modification where an r.f. potential was applied to the electrode to achieve a constant film bombardment during growth. Using this technique Holland e~ al.(8,9) successfully deposited diamond-like carbon films on a variety of substrates.
over the years, many researchers have used similax processes (i.e. r.f. decomposition of hydrocarbon gas) to prepare diamond-like carbon films.(10,11) Similar techniques have been used to deposit BN films, where boron containing gases are used instead of hydrocarbon gases.
The remote plasma deposition technique developed by Lucovsky et al.(12) also falls under the category of a PACVD type process. In this process a mixture of reactive and inert gas is dissociated using r.f.
excitation. The activated species, e.g., oxygen, from the plasma react down stream with the process gas such as SiH4 (for sio2 deposition) to form complexes such as 13~97~1 H3Si-o-SiH3 in the gas phase which subsequently condense on the substrate. Bombardment by energetic neutrals dissociate the complex to produce the compound films.
This technique has been successfully used by Richard et al.(13) to prepare sio2, Si3N4 at low deposition temperatures. They have proposed to extend this technique to the deposition of diamond by using CH4 as a process gas and H2 or a H2 + He gas mixture for activa-tion.
.
Aisenberg and Chabot~14) were the first to report deposition of diamond-like carbon films by ion-beam deposition of carbon. Attempts to deposit similar films using magnetron sputtering and r.f. sputtering were only i partially successful. It is likely that negligible substrate bombardment in the case of magnetron sputter-ing and substrate overheating in case of r.f. sputtering may have restricted the formation of i-C films in the above two techniques.
However, the dual ion beam technique used by ~ 20 Weissmantel(15,16) has proved to be quit~ successful in i synthesis of diamond-like carbon films. He used a .7 primary beam to deposit carbon with the growing film being simultaneously bombarded by Ar+ ions generated ~ from the second ion source. Weissmantel has success-`~ 25 fully used this technique to deposit i-C, i-BN as well as i-C/i-BN composite coatings.
In plasma decomposition techniques, the rate of i depositian of the carbon films critically depends on the rate of dissociation of the hydrocarbon gas. To increase the dissociation rate, one has to increase the gas pressure and/or the r.f. power used to excite the plasma. However, the increase in r.f. power also increases the energy of the bombardlng species.
, Moreover, increased dissociation of hydrocarbon gas , 35 produces a greater amount of hydrogen that can be - trapped into the growing films - thereby producing ~!
:

, . ,, . ~

13~7~

excessive stress in the film.
A modification has been suggested where independent ; sources are used, one to dissociate the hydrocarbon gas, and the other for film bombardment. One such modifica-tion is due to Nyaiesh et al.(17) who have used separate r.f. sources, one to dissociate the hydrocarbon gas and the other for substrate biasing which in turn controls the bombardment of growing film. Though this technique has shown some improvement in deposition rate, the - 10 authors note that the substrate bias was affected by the power applied to the r.f. oven. Moreover, they report that input power to the r.f. oven was limited due to deposits formed by polymerization onto the chamber walls, which reduced the deposition rate.
Another approach is proposed by Kamo et al.(18), ~ Saito et al.(19), and also by Doi et al.(20,21), where a 3 microwave discharge is used to decompose the hydrogen gas and an independent r.f. source is used for substrate biasing. These authors have reported deposition of i-C, diamond and boron doped diamond films using this technique. However, this technique does not appear to be much different than that of Nyaiesh et al.(17) and would therefore suffer from similar limitations. In fact, the optimum deposition rate reported by Doi et al.(21) is about 1 um/hr. which seems to be very low.
~;~ Moreover, even with the above-proposed modifications, it .:;
~;, is not possible to control the hydrogen content of the `~ films independently of the other process variables.
Although the ion beam technique provides advantages as regards independent control of substrate bombardment, deposition rate and hydrogen content, it suffers from ~J the following two major limitations: 1) low deposition rates due to the low sputtering yield of c~rbon; and 2) limitations for large area deposition due to limitations in the available sizes of the ion sources.
Strel'nitskii et al.(23) have reported deposition , - . , ~
. ~ . ~ , ,, . ~ , ... :

132~731 of l-C films uslng energetlc C~ lons from an arc source.
As ls apparent from the above background, there presently ls a contlnulng need to provlde lmproved processes for deposltlng diamond and diamond-like fllms on substrates. Such lmproved processes should be able to provlde control over the rate of generatlon of reactlon vapors e.g. C, B, etc. lndependently o~
other process parameters. The process should also provlde control over the plasma volume chemlstry lndependent of th~ other process varlables and provlde control over the fllm bombardment lndependent of the other process variables. These attrlbutes ln such a process wlll make lt posslble to deposlt dlamond, doped dlamond and cublc boron nltrlde-dlamond fllms at hlgher rates and over large areas.
SUMMARY OF THE INVENTION
Thl~ lnventlon provldes an lmproved method of synthesls of dlamond fllms on a suitable substrate uslng plasma asslsted physical vapor deposltlon technlques. The method ls based on controlllng the plasma chemlstry ln ~he reactlon zone between the source of carbon and the substrate.
Accordln~ to the present lnventlon there 19 provlded a process for deposltlng fllms comprlslng dlamond on a substrate, ~aid proces~ comprlslng the steps of:
supporting a substrate ln a vacuum;
evaporating a source of carbon to produce a carbon vapor ln a zone between the source of carbon and the substrate;
lntroduclng a hydrogen contalnlng gas lnto sald zone;

:, ~
.

, acceleratlng electrons from an electron source into sald zone to lonlze sald carbon vapor and hydrogen contalnlng gas to form carbon-hydrogen complex precursor molecules ln sald zone, deposltlng sald precursor molecules from sald zone onto sald substrate~ and malntainlng sald substrate at a temperature sufficlent to dlssociate sald deposlted precursor molecules to form sald fllm comprlslng dlamond.
Graphite or other materlal used as a source for carbon is vaporized in the vacuum chamber uslng an electron beam, or cathodlc arc to provlde carbon vapors ln the reactlon zone.
Hydrogen contalnlng gas is lntroduced into the reactlon zone. Gas activatlon as well as carbon vapor actlvatlon ls achleved uslng a ~ilament/anode geometry, where electrons emltted thermlonlcally ~rom a heated tungsten fllament are accelerated towards a posltlvely biaqed electrode. It 19 belleved that the atomic hydrogen produc~d by electron colllslon wlth molecular hydrogen plays a crucial role in synthesls of the dlamond. Atomlc hydrogen thus produced enhances the evaporatlon rate o~

;

~ 5a '"'''' -,, . . ~ : . , :, : , ~ . . , . : . . -: ~ . ~ , :

~32~7~1 carbon by producing volatile carbon-hydrogen complexes at the surface of the carbon evaporation source. This reaction is stimulated by the electrons bombarding or near to the carbon source. Collision between atomic hydrogen and the evaporated carbon and/or carbon-; hydrogen molecules is believed to producP molecular precursors which are responsible f~r the synthesis and depositing of diamond films on the substrate.
The microstructure of the diamond deposit and therefore its physical and mechanical properties can be .~
varied by changing substrate temperature and substrate bombarclment. An important advantage of the above process results from its ability to control the plasma volume chemistry independent of the source and substrate ; 15 reactions. This makes it possible to obtain high ', deposition rates and also better control over the film ?I properties.
:! The above-discussed and many other features and attendant advantages of the present invention will ¦ 20 become apparent as the invention becomes better under-stood by reference to the following detailed description when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING
~; The single figure of the drawing is a schematic vertical sectional view of a vacuum chamber and associated equipment suitable for performing the process of the invention and incorporating the presently preferred embodiment of the apparatus of the invention.
:, DESCRIPTION OF THE PREFERRED EMBODIMENTS
~, The preferred apparatus for carrying out the process of the present invention is a modification of the apparatus disclosed in U.S. Patent No. 3,791,852, for carrying out Activated Reactive Evaporation (ARE) ., ,' " , ~ .'.' ! ' , ' ~. ' ' , . , . :
.' ' . ' ' , '. .. .
' . ' ~' . . ., , ' , , ' " .
' ',, ', , , .' ' ' . ,, 13297~1 621g6-510 and the apparatus descrlbed by Chopra et al.(22) for carrylng out Actlvated Dissoclatlon Reductlon Reactlon processes. The appar atus includes a vacuum chamber whlch may comprlse a conventlonal cover or dome 10 restlng on a base 11 wlth a seallng gasket 12 at the lower rlm of the cover 10. A support and feed unit 13 for a source carbon rod used for evaporatlon 14 may be mounted ln the base 11. The unlt 13 lncludes a mechanlsm (not shown) for movlng the carbon rod 14 upward at a controlled rate. Coollng colls 15 may be mounted ln the unlt 13 and supplled wlth cooling water from a coollng water source, 16. An electron gun 20 is mounted ln unit 13 and provides an electron beam along the path 21 to the upper surface of the carbon rod 14, with the electron gun being ener-gized from a power supply 22.
A substrate 24 on which the diamond film is to be de-poslted, is supported ln a frame 25 on a rod 26 pro~ectlng upward from the base 10. The substrate 24 may be heated by an electrlc reslstance heater 27 supported on a bracket 28. Energy for the heater 27 ls provlded from a power æupply 29 via a cable 30. The temperature of the substrate 24 is maintalned at a desired value ~Y:
by means of a thermocouple 32 ln contact wlth the upper surface of the substrate 24, wlth the thermocouple connected to a controller 33 by line 34, wlth the controller output slgnal regulatlng the power from the supply 29 to the heater 27.
The deslred low pressure is maintained within the vacuum chamber by a vacuum pump 36 connected to the interior of the chamber via a line 37. Gas from a gas supply 39 ls lntroduced lnto the zone between the carbon rod 14 and substrate 24 via a line 40 and nozzle 41. A shutter 43 is mounted on a rod 44 which is manually rotatable to move the shutter into and out of position between the carbon rod 14 and substrate 24.
~, ~ ; 7 ;, ~.~'~i', ~' :, .. . . .

13~7~
, A tungsten filament 46 is supported from the base 11 in the reaction zone between the source 14 and the substrate 24. The filament 46 is thermionically heated using a supply 47 via line 48. An anode, typically a metal plate 49, is supported from base 11 opposite to the filament 46. An electric potential is provided for the anode 49 from a voltage supply 50 via line 51.
Various components utilized in the apparatus , described above are conventional. The evaporation l 10 chamber lO is preferably a 24 inch diameter and 35 inch ; high water cooled stainless steel bell jar. The vacuum pump is preferably a lO inch diameter fractionating diffusion pump, with an anti-migration type liquid ;~i nitrogen trap. The source carbon unit 13 is preferably 1 inch diameter rod fed electron beam gun, self-accelerated 270 deflection type, such as Airco Temescal Model RIH-270. The power supply 22 is preferably an , ~ Airco Temescal Model CV30 3OkW unit which may be operated at a constant voltage such as 10 kilovolts, with a variable emission current.
Z Various sizes and shapes of substrates can be Z utilized. Various substrates such as stainless steel, molybdenum, glass, quartz, silicon etc. have been used.
~ In a preferred embodimentl the substrate is based about Z 25 8" above the surface of the carbon source 14. The ~j heater 27 may be a 4 kilowatt tungsten resistance heater ;Z providing for heating the substrate to 700C and higher.
Temperatures in the range of 600 to 1000C are preferr-l ed. The reactions that produce molecular precursors required for synthesis of diamond film take place primarily in the vapor phase in the reaction zone and/or on the surface of the carbon evaporation source. These reactions are independent of suhstrate temperature.
^~Z However, as discussed below the properties and structure of the film is dependent on substrate temperature and bombardment.
., :
,, ~; rrc, Je -i~ Q~` k , ., .

' :`~ , : ' ' ' : ` ' ~' ' . ': ' ,, . ~' :

~ ~2~791 The source of carbon may be a solid rod or billet.
For the feed unit mentioned above, the rod is 0.975 inches diameter and 6" long. Appropriate alloys can be used to obtain p or n type doping in the films. An arc source can also be used to provide carbon vapors.
i Hydrogen gas which dissociates to form atomic hydrogen is introduced via a series of needle valves.
The preferred range of pressure is 2 x 10-4 to 20 x 10-3 torr. In addition to hydrogen, hydrocarbon gases such as methane, ethane, etc. can be used to provide atomic hydrogen and the molecular fragments necessary for diamond growth. Mixtures of the above gases with hydrogen are also used. Additionally, argon has also been used with hydrogen and/or hydrocarbon gases to , 15 enhance the plasma volume chemistry in the region between the source and the substrate and to increase the ' density of precursors necessary for the growth of diamond films.
The filament 46 provides electrons for dissociating and ionizing the gases and the evaporated carbon vapor.
The filament 46 is thermionically heated using a d.c.
supply 47. A.C. can also be used for heating the filament. The electrons emitted from the heated filament 46 are accelerated to an anode 49, to which a d.c. potential is applied from a d.c. supply 50. The usual potential is in the range of about 80 volts, however higher voltages may be used if desired, by using a R.F. plasma Therm d.c. power supply. An a.c. poten-tial as well as r.f. excitation with effective d.c. bias in similar voltage range has also been used.
As examples diamond films can be produced by using the above apparatus utilizing carbon evaporation in H2, CH4, H2 + CH4, H2 + Ar, H2 + Ar + CH4 gases and gas mixtures.
Doped diamond films are also possible. Boron is an excellent p-type dopant for diamond. For n-type doping _9_ : ., . : .

.

13~7~1 Al and Li can be used. Boron doped films can be prepared by evaporating carbon in a plasma of Ar + CH4 (or Ar + CH4 + H2 or any other hydrocarbon gas preferab-ly with SP3 bonding) and boron containing gas such as B2H6. For aluminum doping, metal-organic compounds such as trimethyl aluminum vapors can be used. For lithium doping, Li can be co-evaporated with carbon in Ar + CH4 - plasma~ Cubic boron nitride (CBN)-diamond composite films can be prepared by co-evaporating Boric acid/boric oxide and carbon in CH4 + N2/CH4 ~H2 plasma. The possible reactions leading to the formation of the CBN-diamond composite films are:

; B02 + C ----? B + CO
CH4---~ C + CHX + H
H + BO2 r B + H
~, B + N -- BN
C + C -~ H----~C - C ~ H
CHX + CHX + H ~ C - C + H
~ 20 :J The above are a few of the likely reactions. In addition, a variety of other reactions can take place depending on the energy, concentration and nature of the reactive species ~excited, ionized, etc.) in the plasma volume. Glow discharge optical spectroscopy can be used to study the plasma chemistry and optimize plasma conditions to obtain CBN-diamond films.
An example of practice is as follows. The vacuum chamber was initially pumped down to 10-6 torr pressure and then purged with inert gas to 10-4 torr for a few times. The chamber was again pumped down to 10-6 torr.
This procedure was used to minimize the presence of ex-traneous gases.
When pressure in the chamber was again down to 10-6 i 35 torr, the filament 46 was slowly heated to the desired , temperature of about 1000C. One of the above gases was , - 1 0 -', ,. ~ . ,., ~ ,,,, . ...... "

',', ' ,, '' ' . ' ~

~ 3~7~

then introduced in the vacuum chamber at a controlled rate to obtain a desired pressure. Pressure ranged from 2 x 10-2 torr to about 1 x 10-3 torr. Anode potential was then applied to obtain required anode current. The electron beam was turned on to heat the upper end of the carbon rod 14. The shutter 43 was in position blocking the substrate 24. When steady state conditions were obtained, the shutter 43 was moved to one side and films were deposited on the substrate 24. The process was continued until the desired thickness of film ,was , obtained after which the shutter 43 was moved to theblocking position and the various supplies were turned off.
The gas pressure within the chamber, the anode ,, 15 potential and electron beam current required to produce the diamond films are interrelated and may be varied over a substantial range. With higher electron beam currents it is required to increase the partial pressure of hydrogen gas and the anode potential to obtain desired films. For example, successful formation of diamond films can be achieved in the range of 600 ~atts - 1.5 kw with gas partial pressure in the range of 10-3 to 2 x 10-2 torr.
H2, C~4, H2 ~ CH4, Ar -~ CH4, Ar + H2 ~ CH4 gases have been used. Use of hydrocarbon gas such as CH4 and its mixture with H2 and/or Ar enhance the electron-molecular reactions producing appropriate precursors necessary for growth of diamond films.
The acts of precursor formation and deposit growth , 30 are separate steps in this process. The character of ` the deposit changes with substrate temperature and bombardment. For given conditions the deposit trans-forms from transparent/insulating type to absorbent/con-ducting type back to transparent/insulating type with increasing substrate temperature. The above transforma-~, tion corresponds to the formation of diamond-like i-C

, ,: , .' ;. . : .

, ' ' ' : , ~3~791 films, graphitic films, diamond films, respectively. At low substrate temperature, the film growth is essen-tially controlled by the reaction occurring in the region between the source and the substrate.
As the temperature of the substrate increases beyond a critical value, substrate reactions also comes into play. At this temperature the condensing species tend to nucleate into graphitic structure. When the temperature is further increased a point is reached beyond which transparent diamond films can be formed.
It is believed that the condensation of the graphitic phase in this temperature range is prevented by the competitive process of etching of graphite by atomic hydrogen since the etching rate increases with tempera-ture.
It has been found that the film properti~s can be controlled by changing the partial pressure of reactive gas, evaporation rate and substrate temperature/bombard-ment. As an example, with a carbon evaporation rate of 0.2 gms/min and a hydrogen partial pressure of 10 millitorr, transparent and insulating films of diamond are deposited at a ate of 3 um/hr at source-to-substrate distance of 8". Higher deposition rates could be achieved by adjusting the electron beam current and H2 partial pressure appropriately or decreasing the source to substrate distance. Higher or lower rates may be obtained by varying the process parameters of the system. The carbon evaporation rate may be controlled by varying output of electron gun 20 and gas pressure may be controlled by adjusting a valve 59 in the gas line 40.
Having thus described exemplary embodiments of the - present invention, it should be noted by those skilled in the art that the within disclosures are exemplary ' 35 only and that various other alternatives, adaptations and modifications may be made within the scope of the .j ., . -., . , .- . .. , , . ~ . . -, -: :

~ 32~
.,i . I
: ", present invention. Accordingly, the present invention ~i is not limited to the specific embodiments as -' illustrated herein, but is only limited by the following claims.
~j 5 :.~

.
~`

:,, ,~
. :;j ;, :

~! .
~, ~ -13~
; ~, ", , : . :

~ 1329791 . BIBLIOGRAPHY
~` 1. B. V. Derjaguin, D. V. Fedoseev, V. M.
Lykualiovich, B. V. Spitsyn, V. A. Ryanov and A. v.
Lavreutyev, J. Cryst. Growth 2, 380, 1968.
2. J. C. Angus, H. A. Will and W. S. Steinko, J.
Apl. Phys. 39(6), 2915, 1968.
f~. S. Matsumoto, Y. Saito, M. Kano and N. Setaka, Jap. J. Appl. Phys., 21, L163, 1982.
. S. Matsumoto, Y. 5aito, M. Tsutsumi and N.
Setaka, Jour. Mater. Sci~ 17, 3106, 1982.
. . .

5. B. V. Spitsyn, B. V. Derjaguin, L. L. Builov, A. A. Klochkov, A. E. Gorodetskii and A. V.
Smoi'yanihov, Sov. Phys. Dokl, 21 676, 1976.

6. D. S. Whitmell and R. W. Williamson, Thin Solid Films, 35, 255, 1976.

7. L. Holland, U. K. Patent No. 1582231, Aug. 76.

8. L. Holland and S. M. Ojha, Thin Solid Films, ~' 38, L17, 1976.

9. L. Holland and S. M. Ojha, Thin Solid Films, 48, L21, 1978. Also L. Holland and S. M. Ojha, Thin, Solid Films, 58, 107, 1979.

10. H. Vora and T. J. Moravac, J. Appl. Phys., 52, 6151, 1981.
~ 11. L. P. Anderson, S. Berg, H. Norstrom and S.
;~ 25 Towa, Thin Solid Films, 63, 155, 1978.
12. G. Lucovsky, P. D. Richards and R. J. Markura, paper presented at workshop of Dielectric Systems for III-V Semiconductors, San Diego, CA, May 26-27, 1984.
~3. P. D. Richard, R. J¢ Markura, G. Lucovsky, G.
G. Fountain, A. N. Mansour and D. V. Tsu, J. Vac. Sci.
Technology, J. VacO Sci. Technol. A3~3), 867, 1985.
~4. S. Ainsberg and R. Chabot, J. Appl. Phys. 42, 2953, 1971.
15. C. Weissmantel, Thin Solid Films, 35, 255, 1976.

16. C. Weissmantel, K. Breuer and B. Winde, Thin ~;

~;
1~297 ;

Solid Films, 100, 383, 1983.
~` 17. A. R. Nyaiesh, Ro E. Kirby, F. K. Xing and E.
L. Garwin, J~ Vac. Sci. Technol. A3(3), 610, 19850 ~18. Mo Xamo, Y. Saito, M. Matsumoto and N. Setaka, J. Cryst. Growth, 62, 642, 1983.
19. Y. Saito, S. Matsuda and S. Nogita, Mat. Sci.
Letter, 3, 565, 1986.
20. A. Doi, N. Fujimon and T. Yoshioka, Proc.
Intt. Ion Eneryy Congress. p. 1137, Institute of 10Electronic Engineering of Japan, Tokyo, 1983.
~1. N. Fujimon, T. Imei and A. Doi, Vacuum 36, 99, 1986.
~2. K. ~. Chopra, V. Agarwa, V. D. Vankar, C. V.
Deshpandey and R. Fo Bunshah, Thin Solid Films, 126, 15307, 1985.
~3. V. E. Strel'nitskii, V. G. Padalka and S. I.
Vakula, Sov. Phys. Tech. Phys. 23(2), 222, 1978.

:, ~, .~

~!

. .

',~
., .

;~

f ' ~'1" , , . ': . ' ,

Claims

1. A process for depositing a film comprising diamond on a substrate, said process comprising the steps of:
supporting a substrate in a vacuum;
evaporating a source of carbon to produce a carbon vapor in a zone between the source of carbon and the substrate;
introducing a hydrogen-containing gas into said zone;
accelerating electrons from an electron source into said zone to ionize said carbon vapor and hydrogen-containing gas to form carbon-hydrogen complex precursor molecules in said zone, depositing said precursor molecules from said zone onto said substrate; and maintaining said substrate at a temperature sufficient to dissociate said deposited precursor molecules to form said film comprising diamond.

2. A diamond deposition process according to claim 1 wherein said source of carbon is graphite.

3. A diamond deposition process according to claim 2 wherein said graphite is evaporated by an electron beam.

4. A diamond deposition process according to claim 1 wherein said hydrogen-containing gas is hydrogen and a hydrocarbon gas.

5. A diamond deposition process according to claim 1 wherein said hydrogen-containing gas is hydrogen and methane or ethane.

6. A diamond deposition process according to claim 1 wherein said hydrogen-containing gas is a mixture of hydrogen and a hydrocarbon gas or a mixture of hydrogen and argon or a mixture of hydrogen, argon and a hydrocarbon gas.

7. A diamond deposition process according to claim 1 wherein said substrate is selected from the group consisting of stainless steel, molybdenum, glass, quartz, silicon and aluminum.

8. A diamond deposition process according to claim 1 wherein the temperature of said substrate 18 maintained at a temperature of between about 600°C and 1000°C.

9. A diamond deposition process according to claim 1 wherein the partial pressure of said hydrogen-containing gas is between about 2 x 10-4 torr and 20 x 10-3 torr.

10. A diamond deposition process according to claim 9 wherein said hydrogen-containing gas is hydrogen.

11. A diamond deposition process according to claim 1 wherein the electrons which are accelerated into said zone are produced by a heated filament.

12. A diamond deposition process according to claim 11 wherein said filament is tungsten, tantalum, nolybdenum or carbon.

13. A diamond deposition process according to claim 1 wherein said electrons are deflected into said zone by accelerating said electrons toward an anode.

14. A diamond deposition process according to claim 11 wherein the electrons generated by said filament are accelerated through said zone toward an anode.

15. A diamond deposition process according to claim 13 wherein the potential at said anode is about 80 volts.

16. A diamond deposition process according to claim 1 wherein said film is doped with p and n type dopants.

17. A diamond deposition process according to claim 1 wherein said film is doped with aluminum, lithium or boron.

18. A deposition process according to claim 1 wherein the film is a diamond-cubic boron nitride film.

19. A diamond deposition process according to claim 16 wherein a boron-containing gas is introduced into said zone to form a film comprising boron doped diamond.

20. A diamond deposition process according to claim 16 wherein a vapor of a metal organic compound is introduced into said zone to form a film comprising metal doped diamond.

21. A diamond deposition process according to claim 16 wherein trimethyl aluminum vapor is introduced into said zone to form a film comprising aluminum doped diamond.

22. A diamond deposition process according to claim 1 wherein said hydrogen-containing gas contains CH4, nitrogen and hydrogen and boric acid/boric oxide is co-evaporated with said carbon to thereby form a film comprising cubic boron nitride doped diamond.