A method for forming thin films of cubic boron nitride on substrates at low pressures and temperatures. A substrate is first coated with polycrystalline diamond to provide a uniform surface upon which cubic boron nitride can be deposited by chemical vapor deposition. The cubic boron nitride film is useful as a substitute for diamond coatings for a variety of applications in which diamond is not suitable. any tetragonal or hexagonal boron nitride. The cubic boron nitride produced in accordance with the preceding example is particularly well-suited for use as a coating for ultra hard tool bits and abrasives, especially those intended to use in cutting or otherwise fabricating iron

Ong, Tiong P.

Shing, Yuh-Han

NASA Technical Reports Server

United States Patent 1191 1111 Patent Number: 5,639,55 1 
Ong et al. 1451 Date of Patent: Jun. 17,1997 
LOW PRESSURE GROWTH OF CUBIC 
BORON NITRIDE FILMS 
Inventors: Tiong P. Ong, Austin, Tex.; Yuh-Han 
Shing, Hsinchu, Taiwan 
Assignee: California Institute of Technology, 
Pasadena. Calif. 
Appl. No.: 538,458 
Filed Oct. 3,1995 
Related U.S. Application Data 
Division of Ser. No. 338,281, Nov. 14, 1994, abandoned, 
which is a continuation of Ser. No. 180,534, Jan. 12, 1994, 
abandoned, whichis a continuation of Ser. No. 16,132, Feb. 
10,1993, abandoned. 
Int. C1.6 ....................................................... GO36 5102 
U.S. C1. .......................... 4281408; 428l336; 428/446; 
4281698; 428/704; 4281216; 51/295; 511307; 
5 11309 
Field of Search ..................................... 428/704, 408, 
428/698, 336, 323,216,446; 51/295, 307, 
309 
4,297,387 
4,734,339 
4,988,421 
5,015,528 
5,043,219 
5,082,359 
5,104,420 
5,117,267 
5,162,886 
5,164,051 
References Cited 
U.S. PAI’ENT DOCUMENTS 
10/1981 Beale ........................................ 427/38 
3/1988 Schachuer et al. ........... 428/698 
1/1991 Drawl et al. ......................... 204/192.3 
5/1991 Pinneo .................................... 428/403 
8/1991 Yoshida et al. ......................... 428/408 
111992 Kirkpatrick ............................. 359/642 
4/1992 Yoshida et al. ........................... 51L293 
5/1992 Kimoto et al. ............................ 357/16 
11/1992 Nishibayashi et al. ................. 257/421 
1111992 Komaki et al. .......... 204/129.43 
5,264,296 11/1993 Doll et al. ............................... 428/698 
5,373,171 12/1994 Imai et al. ................................ 257tl7 
FOREIGN PMENT DOCUMENTS 
5795881 6/1989 Japan. 
1-252303 10/1989 Japan. 
2-173264 7/1990 Japan. 
3-257176 1111991 Japan. 
6-148908 91994 Japan. 
OTHER PUBLICATIONS 
Paisley, M.J., et al., “Cubic Boron Nitride Thin Film Syn- 
thesis By Microwave ECR Plasma Chemical Vapor Depo- 
sition,’’ Kobe Engineering Reports, Sep. 20. 1991. 
Santhanam, A.T. et al., “Cemented Carbides”, pp.95&977. 
Matsumoto, S. et al., “Vapor Deposition of Diamond Par- 
ticles from Methane”, Japanese Journal of Applied Physics, 
vol. 21, No. 4, Apr. 1982, pp. L183-Ll85. 
Primary Examiner-Archene Turner 
Attorney, Agent, or Fimz-Oppenheher Poms Smith 
[571 ABSTRACT 
A method for forming thin films of cubic boron nitride on 
substrates at low pressures and temperatures. A substrate is 
first coated with polycrystalline diamond to provide a uni- 
form surface upon which cubic boron nitride can be depos- 
ited by chemical vapor deposition. 
The cubic boron nitride film is useful as a substitute for 
diamond coatings for a variety of applications in which 
diamond is not suitable. any tetragonal or hexagonal boron 
nitride. 
The cubic boron nitride produced in accordance with the 
preceding example is particulrnly well-suited for use as a 
coating for ultra hard tool bits and abrasives, especially 
those intended to use in cutting or otherwise fabricating iron. 
16 Claims, 1 Drawing Sheet 
14 
16 
5U BSTRATE 
to’ 
https://ntrs.nasa.gov/search.jsp?R=20080004815 2019-08-30T02:41:03+00:00Z
U.S. Patent Jun. 17,1997 5,639,551 
5 u BST RATE 
i 
5,639,55 1 
1 
LOW PRESSURE GROWTH OF CUBIC 
BORON NITRIDE FILMS 
ORIGIN OF INVENTION 
The invention described herein was made in the perfor- 
mance of work under a NASA contract, and is subject to the 
provisions of Public Law 960517 (35 USC 202) in which the 
Contractor has elected to retain title. 
This is a divisional of application Ser. No. 08/338.281 
filed on Nov. 14, 1994 now abandoned which is a continu- 
ation of Ser.  No. 08/180,534 filed on Jan. 12. 1994 now 
abandoned which is a continuation of Ser. No. 08/016,132 
filed Feb. 10, 1993, now abandoned. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates generally to the formation of 
cubic boron nitride (c-BN) films on substrates such as 
cutting tools. More particularly, the present invention relates 
to the formation of such films at low pressure and relatively 
low temperature. 
2. Description of Related Art 
C-BN is a very important technological material. It has 
properties similar to those of diamond it is chemically inert, 
thermally highly conducting. and electrically insulating. The 
material is also known to be the hardest material after 
diamond. Consequently, c-BN has found uses in many 
industrial applications ranging from high precision cutting 
and grinding of ferrous materials to high temperature elec- 
tronic devices. 
Boron nitride is known to have two crystallographic 
structures in addition to c-BN. These two structures are 
tetragonal boron nitride (t-BN) and hexagonal boron nitride 
(h-BN). C-BN is much harder than either of the two alternate 
crystal structures and therefore is the preferred coating 
material for ultra hard tools. At present. cubic boron nitride 
is deposited on various substrates using high pressure 
(approximately 45-55 kbar) and high temperature 
(140O0-170O0 C.) conditions. In order for c-BN to be used 
in a wide variety of applications, it is necessary that pro- 
cesses be developed wherein thin films of c-BN can be 
formed onto a variety of substrates without requiring high 
pressures and high temperatures. 
Attempts to deposit c-BN films at low pressures have not 
been successful. For example, present low pressure methods 
2 
cubic boron nitride at low pressures and relatively low 
temperatures utilizing chemical vapor deposition. As a fea- 
ture of the present invention, a layer of diamond is deposited 
on the substrate prior to vapor deposition of the cubic boron 
5 nitride layer. The chemistries between diamond and cubic 
boron nitride are compatible and it is possible to deposit a 
layer consisting substantially of cubic boron nitride onto the 
diamond interlayer under low temperature and low pressure 
conditions. 
The cubic boron nitride films of the present invention are 
especially well-suited for use as coatings for ultra hard 
cutting tools wherein diamond-like hardness is required. An 
additional advantage provided by the present invention is 
that cubic boron nitride is resistant to attack by iron at the 
15 high temperatures generated during cutting and grinding 
operations. 
The method of the present invention involves the steps of 
depositing diamond onto a substrate utilizing chemical 
vapor deposition to form a substantially continuous diamond 
2o interlayer which covers the substrate. Cubic boron nitride is 
then applied to the diamond interlayer utilizing low 
temperaturelow pressure chemical vapor deposition. The 
vapor deposition may be assisted utilizing low energy ion 
bombardment such as direct current (dc) or radio frequency 
25 (RE) biasing. The resulting boron nitride film deposited on 
the diamond interlayer is composed substantially of cubic 
boron nitride. 
The above discussed and many other features and atten- 
3o dant advantages of the present invention will become better 
understood by reference to the following detailed descrip- 
tion when taken in conjunction with the accompanying 
drawing. 
BIUEF DESCRIPTION OF THE DRAWING 
The drawing is a partially schematic cross-sectional rep- 
resentation of a preferred exemplary embodiment of the 
present invention wherein polycrystalline cubic boron 
nitride is formed on a substrate which has been previously 
10 
35 
40 coated with polycrystalline diamond. 
DESCRETION OF THE PREFERRED 
EXEMPLARY EMBODIMENTS 
The present invention has wide application to the forma- 
45 tion of cubic boron nitride (c-BN) films on a wide variety of 
have only been able to produce films containing up to 10% substrates. Suitable substrates onto which the c-BN film-can 
c-BN. Accordingly. there is a present need to develop simple be deposited include metals and metal alloys, Silicon, quartz, 
and efficient methods for depositing films of cubic boron alumina and any other substrate upon which diamond can be 
nitride onto a wide variety of substrates at low pressure and deposited. A preferred substrate is tungsten carbide. Tung- 
relatively low temperature. 50 sten carbide is used in a wide variety of ultra hard tool 
Diamond has also been widely used as a coating material materials and super abrasives in which diamond is bonded Or 
for hard tools and abrasives. ~ ~ t h d ~  have been otherwise imbedded into the tungsten carbide. Details 
developed for growing diamond films at reduced tempera- regarding the use Of tungsten carbide and diamond Coatings 
tures and pressures. However, diamond films are not well- as tool bit materids is discussed in “Metals Handbook,” 9th 
s i ted for cutting or abrading iron. Diamond is reactive with 55 Edition, VOlUIlle 3, Propel63 Selection: StaillleSS steel 
iron at the high temperatures generated during cutting opera- Tools and TOO1 Material7 Special m o s e  Metals-ASM. 
tions. Cubic boron nitride is well-suikd as a Referring to the drawing, an article in accordance With the 
substitute for diamond in such cutting operations since cubic present invention is shown schematically at 10. The article 
boron nitride is not attacked by iron. Accordingly, it would 10 includes a Substrate 12, Polycrystalline cubic boron 
be desirable to provide a method for coating tool bits made 60 nitride layer 14 and a polycrystalline diamond interlayer 16. 
from tungsten and other hard cubic The article 10 is preferably a tool bit wherein the substrate 
boron nitride to provide ultra hard tools which are s&ible 12 is tungsten carbide. Although the preferred exemplary 
for use in cutting iron. embodiment is a cutting tool for use in fabricating iron 
wherein cubic boron nitride is deposited on a diamond- 
SUMMARY OF THE INVENTION 65 treated tungsten carbide substrate, it wiU be recognized by 
In accordance with the present invention, a method is those skilled in the art that the present invention has wide 
provided for coating a variety of substrates with films of application to the formation of cubic boron nitride films on 
5,639,SS 1 
3 4 
any substrate upon which diamond can be deposited as a 
polycrystalline interlayer or primer coating. 
The Polycrystalline diamond film 16 is applied to the 
substrate using of the known Vapor deposition tech- 
niques for depositing thin films of diamond Suitable vapor 
&position processes include microwave plasma or hot 
filament-assisted CVD techniques* An CVD 
technique is set forth in "Vapor Deposition of Diamond 
Particles from Methane", S. Matsumoto, et al.. Japanese 
Examples of practice are as follows: 
A polycrystalline diamond film is deposited onto a tung- 
sten carbide substrate utilizing microwave ECR plasma 
chemical vapor deposition as described by M. J. Paisley, et 
al. in "Cubic Boron Nitride Thin Film Synthesis By Micro- 
wave ECR Plasma Chemical vapor Deposition; Kobe 
Engineering Reports, Sep. 20, 1991. The basic system and 
procedure is followed except that a methanehy*ogen reac- 
10 tive gas is introduced into the vapor deposition zone instead 
amount of methanehydrogen in the deposition zone being 
The particular CVD process which is utilized to deposit maintained at between 0.5-2% with flow rates of the gas 
the Pob'crys*e dhmond film is not ParticUlar1Y critical being maintained between 100-500 sccm. Deposition tem- 
provided that the technique is capable of depositing thin 15 peratures range from 6OO0-1o0O0 C. and the pressure within 
Journal Of &plied vol' 21. No* 4, 19829 PP' of borozene. The diamond deposition is out with the 
L183-L185. 
films Of p o l y ~ s m n e  diamond On a Of substrates' 
The polyqsmne diamond layer l6 shown in the drawing 
is a 
the CVD chamber is maintained at 40-100 Torr. Although 
RF-biasing can be used to enhance diamond deposition, it is 
preferred that hot filament-assisted growth be conducted representation Only so that the thickness of the polycrystalline diamond interlayer with 
respect to the substrate shown in the drawing is not to scale. with the filament temperature being maintained at about 
preferably, the polycrysmne diamond layer will be as thin 2o 2ooo 
as possible while still providing substantially continuous 
The microwave power is Preferably 400-700 
with the microwave frequency being 2.45 GHz' 
coverage of the surface area ofthe substrate- QPicdYj layer As is well known. tungsten carbide includes cobalt as a 
thickness W i l l  range about to l o  microns. binder for the tungsten particles. Cobalt has the tendency to 
The thickness Of the diamond layer will vary depending 25 catalyze the hydrocarbon gas present in the reactive atmo- 
upon the sphere into soot. Accordingly, it is preferred that the sub- surface characteristics* The PolYcrys- 
talline layer thickness does not have to be uniforrm~ but strate be etched away prior to diamond growth. Nitric acid 
should be thick so that little if Of the is a preferred agent. The use of nitric add to etch 
underlYing is exposed' In the diamond to re&ce soot generation during CVD growth is 
known. In addition to etching, the substrate surface is layer perform the function of a primer coating which is 30 utilized to impart desirable surface characteristics to the 
substrate in order to enhance formation of cubic boron 
nitride during subsequent deposition procedures. 
Preferably Illbbed with sub-micron diamond Powders to 
promote diamond nucleation during the WD process. If 
~ ~ ~ ~ d i n ~ l ~ ,  it is preferred that the layer be as 
possible 
substrate surface. 
includes crystal sizes ranging from 1-10 microns. The 
particular c rys ta l  size for the crystals in the diamond layer 
may be varied depending upon the surface characteristics of 40 
the underlying substrate and the particular crystal size of 
cubic boron nitride being deposited. 
layer also is preferably formed using chemical vapor depo- 45 deposition are 
sition techniques. In accordance with the present invention, 
it was discovered that the pretreatment of the substrate to 
as desired, a thin i.e. 0.02 micron buffer layer, such as amor- 
providing continuing coverage of the 35 phous silicon, can be deposited onto the substrate to further 
enhance diamond adhesion. The microwave ECR plasma 
chemical vapor deposition process is carried out for a 
which is substantially continuous, i.e. no voids or open 
areas, which cover the substrate surface area. 
After deposition Of the diamond interlayer, a layer of 
cubic boron nitride is then applied to the treated substrate 
also utilizing microwave ECR plasma chemical vapor depo- 
to the diamond or B2Hm, depo- 
sition except that a B,HdN2 reactive atmospheres is utilized 
wherein the percentage of B2HdN,or B,Hm, is main- 
c-BN onto the substrate. The same CVD techniques utilized 5o between about 50-100 Seem and the temperature in the 
able CVD processes include electron cyclotron residence GHz microwave is applied again at 4oo-700 w. The deP- 
other reactive vapor deposition techniques utilized for 55 layer of cubic boron nitride which is free of voids and 
enhanced CVD is the preferred deposition technique. In 
general, temperatures in the CVD chamber will range from The cubic boron nitride produced in accordance with the 
4oOo-10000 C. with pressures ranging up to 100 Torr. This preceding example is particularly well-suited for use as a 
of low temperature and low pressure CVD system is coating for ultra hard tool bits and abrasives, especially 
known to those skilled in the art and the various parameters those intended to use in cutting or otherwise fabricating iron. 
used to deposit both diamond and cubic boron nitride films Having thus described exewlw embodiments of the 
can be established by routine experimentation. present invention, it will be understood by those skilled in 
The polycrystalline cubic boron nitride layer 14 may be the art that the preceding description is exemplary only and 
varied in thickness depending upon the particular applica- 65 that various other alternatives, adaptations and variations 
tion. In general. layer thicknesses on the order of 5-20 may be made within the scope of the present invention. The 
microns are preferred. present invention is only limited by the following claims. 
The diamond layer 16 is preferably polycrystalline and sufficient time to apply a 5 micron thick diamond layer 
with respect t' the polycrystalline c-BN layer 14, this sition. The process conditions for the cubic boron nitride 
a diamond interlayer thereon allows the Of low tained at bemeen about 0.5 to 1.5%. n e  flow rate of 
reactive gases into the reaction vessel is maintained at pressure and low CVD processes to 
for gowing the diamond interlayer l6 may for 
forming the polycrystalline cubic boron nitride layer* suit- 
be reaction vessel is between 4000-7000 C. The pressure in the 
vessel is controlled to be within 0.5-10 mTorr and the 2.45 
@CR) plasma enhanced techniques Or Of the sition process is -ed out for a sufficient h e  to deposit a 
depositing diamond ECR microwave plasma includes little if any tetragonal or hexagonal boron nitride. 
5,63935 1 
5 6 
We claim: 
1. An article comprising: 
a substrate having a surface area treated with amorphous 
silicon; 
a substantially continuous polycrystalline diamond inter- 
layer covering said surface area treated with amoqhous 
silicon; and 
a layer of cubic boron nitride covering said diamond 
interlayer to form a film of cubic boron nitride covering 1o 
said substrate. 
10. An article according to claim 9 wherein said article is 
a cutting tool and said substrate comprises a metal cutting 
surface. 
11. An article according to claim 9 wherein said article is 
a cutting tool and said substrate comprises a tungsten 
c h i d e  cutting surface. 
12. A tool, comprising: 
a metal cutting surface treated with amorphous silicon; 
a substantially continuous polycrystalline diamond inter- 
2. An article according to claim 1 wherein said substrate layer covering the cutting surface treated with amor- 
phous silicon; and 
3. An article according to claim 2 wherein said substrate 
a polycrystalline layer consisting essentially of cubic 
boron nitride covering the diamond interlayer to form 4. An article according to claim 3 wherein said article is 
a film of cubic boron nitride covering the cutting 
5. An article according to claim 1 wherein said cubic surface. 
13. A tool as claimed in claim 12, wherein the metal 
6- An article according to Claim 1 wherein said diamond 20 cutting surface comprises a tungsten carbide cutting surface. 
is a metal, ceramic or alloys thereof. 
is tungsten carbide. 
a cutting tool. 
boron nitride film is 5-20 microns thick. 
l5 
interlayer “qrises diamond crystals having crystal sizes Of 14. At001 as claimed in claim 12, wherein the cubic boron 
nitride film is 5-20 microns thick. between about 1 to 10 microns. 7. An article according to claim 1 wherein said cubic 
boron nitride interlayer comprises cubic boron nitride crys- 15. A tool as claimed in claim 12, wherein the cubic boron 
tals having crystal sizes of between about 1 to 10 microns. nitride film comprises cubic boron crystals having 
8. An article according to 6 wherein cubic 25 crystal sizes of between about 1 to 10 microns. 
boron nitride interlayer comprises cubic boron nitride crys- 16. A tool as Claimed in Claim 12, wherein the diamond 
tals having crystal sizes of between about 1 to 10 microns. 
9. An article according to claim 1 wherein said cubic 
boron nitride layer comprises polycrystalline cubic boron 
nitride. * * * * *  
interlayer comprises diamond crystals having crystal sizes of 
between about 1 to 10 microns. 


Low pressure growth of cubic boron nitride films

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