Process for production of high-hardness boron nitride film

In a process for the production of a high-hardness boron nitride film by vacuum-depositing a boron component on a substrate from a boron-containing vacuum deposition source and simultaneously irradiating the substrate with an ion seed comprising at least nitrogen from an ion-generating source, if the atomic ratio (B/N) between boron and nitrogen supplied from the vacuum deposition source and the ion seed is adjusted within a range of from 4 to 25, the ion acceleration energy of the ion seed is adjusted to 5 to 100 KeV per atom of the ion seed and vacuum deposition and irradiation are carried out in an atmosphere of a nitrogen atom or nitrogen compound activated at an energy level lower than that of the ion seed, the hardness and quality of the film are highly improved. Furthermore, if a negative bias voltage is applied to the substrate at the vacuum deposition and irradiation with the seed ion, the film-forming speed can be increased and the hardness and quality of the film are further improved.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
The present invention relates to a process for the production of a 
high-hardness boron nitride film. More particularly, the present invention 
relates to a process for preparing a high-hardness boron nitride film by 
the vacuum deposition method and ion irradiation method (boron nitride 
will be referred to as "BN" hereinafter). 
(2) Description of the Prior Art 
BN includes crystal structures of cubic boron nitride (hereinafter referred 
to as "CBN"), hexagonal closest packing boron nitride (hereinafter 
referred to as "WBN") and hexagonal boron nitride (hereinafter referred to 
as "HBN"). Of these crystal structures, CBN and WBN are excellent in the 
heat shock resistance, heat conductivity, hardness and abrasion resistance 
and also in resistance to a metal of the iron group at high temperatures. 
Accordingly, application of CBN and WBN to various uses has attracted 
attention and investigations have been made concerning the production of 
high-hardness boron nitride composed mainly of CBN or WBN which has a high 
quality. 
As one conventional production technique, a method exists in which 
synthesis of high-hardness boron nitride is carried out under such high 
pressure and temperature conditions as scores of thousands of atmospheres 
and one thousand and several hundreds of .degree.C. by using an expensive 
apparatus. Recently, studies have been made on a method in which a film of 
high-hardness boron nitride composed mainly CBN or WBN is formed on the 
surface of a substrate at a high efficiency by the gas phase growth 
process. 
The film-forming techniques are roughly divided into the chemical 
deposition method and the physical deposition methods. In the field of the 
production of BN films, the physical deposition methods using ions are 
mainly investigated. These physical deposition methods include an ion beam 
deposition method in which an ionized atom is accelerated and is then 
decelerated and deposited on a substrate, a cluster ion plating method in 
which a cluster ion is accelerated and caused to impinge against a 
substrate and a large quantiy of atoms are deposited on the substrate at a 
time, and an in beam sputtering method in which an ionized and accelerated 
atom sputtered by a rare-gas or the like is deposited on a substrate. In 
this lost method, the kinetic energy of the ion is several eV to several 
hundreds of eV and the seed is barely implanted into the interior of the 
substrate, and therefore, the adhesion between the film and substrate is 
insufficient. 
As another known method of producing high-hardness boron nitride, there 
exists an ion mixing method. According to this method, a certain substance 
is vacuum-depositioned on a substrate and the deposited film is irradiated 
with an ion seed such as a rare-gas with a kinetic energy of at least 
several hundreds of KeV. By such irradiation the atom of the 
vacuum-deposited substance is bounced by impingment of the ion seed and is 
caused to intrude into the interior of the substrate and a new film 
composed of components of both the substrate. Thereby the vacuum-deposited 
layer is formed between the substrate and the vacuum-deposited layer. 
Then, the remaining vacuum-deposited film is removed by chemical means to 
form a new film on the surface of the substrate. In this method, even if 
the energy of the ion seed becomes large, the ion current need not be 
increased, and large quantities of different atoms can be implanted in the 
vicinity of the surface of the substrate. However, this method is still 
insufficient in that it is difficult to maintain a constant mixing ratio 
between the implanted ions and the constituent atoms of the substrate. 
As is seen from the foregoing description, even according to the 
above-mentioned film-forming techniques using ions, films of high-hardness 
boron nitride composed mainly of CBN or WBN have not been synthesized. 
SUMMARY OF THE INVENTION 
Proceeding from the above-mentioned background, research was performed, and 
as a result, it was found that when vacuum deposition and ion irradiation 
are carried out on a substrate by using a boron-containing vacuum 
deposition source and an ion-generating source for generating an ion seed 
comprising at least nitrogen, then a film of high-hardness boron nitride 
composed mainly of CBN or WBN, which has a good quality, can be obtained. 
The present invention is based on this finding. 
It is therefore a primary object of the present invention to provide a 
novel process for the production of a high-hardness BN film. Particularly, 
a high-quality film of high-hardness boron nitride composed mainly of CBN 
or WBN is formed on a substrate. 
Another object of the present invention is to provide a process in which a 
high-quality film of high-hardness boron nitride composed mainly of CBN or 
WBN is formed on a substrate at a high film-forming speed. 
Still another object of the present invention is to provide a process in 
which a high-quality boron nitride film is formed on a substrate at a high 
energy efficiency. 
In accordance with one fundamental aspect of the present invention, there 
is provided a process for the production of a high-hardness boron nitride 
film. This process comprises vacuum-depositing a boron component on a 
substrate from a boron-containing vacuum deposition source and 
simultaneously irradiating the substrate with an ion seed comprising at 
least nitrogen from an ion-generating source for generating said ion seed 
in order to therein form boron nitride on the substrate. The atomic ratio 
(B/N) between boron and nitrogen supplied from the vacuum deposition 
source and the ion seed is adjusted within a range of from 4 to 25, the 
ion acceleration energy of the ion seed is adjusted to 5 to 100 KeV per 
atom of the ion seed, and vacuum deposition and irradiation are carried 
out in an atmosphere of a nitrogen atom or nitrogen compound activated at 
an energy level lower than that of the ion seed. 
In accordance with the present invention, there is further provided a 
process as set forth above, wherein activated boron is vacuum-deposited on 
the substrate by (i) supplying a boron-containing gas to an arc discharge 
region and/or (ii) forming an arc discharge region by using a 
boron-containing substance as an arc discharge electrode material. 
In accordance with another fundamental aspect of the present invention, 
there is provided a variant process for the production of a high-hardness 
BN film. This variant process comprises vacuum-depositing a boron 
component on a substrate form a boron-containing vacuum deposition source 
and simultaneously irradiating the substrate with an ion seed comprising 
at least nitrogen from an ion-generating source for generating said in 
seed, therein forming BN on the substrate. The ion acceleration energy of 
the ion seed is adjusted to 5 to 100 KeV per atom of the ion seed, the 
deposition and irradiation are carried out in an atmosphere of a nitrogen 
atom or nitrogen compound activated at an energy level lower than that of 
the ion seed, and simultaneously, a negative bias voltage is applied to 
the substrate. 
Moreover, in accordance with the present invention, there is provided a 
process as set forth above, wherein the total concentration of the oxygen 
and carbon atoms in the atmosphere adopted for vacuum deposition and 
irradiation is controlled below 100 ppm.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
In the present invention, high-hardness boron nitride composed mainly of 
CBN or WBN is synthesized by vacuum-depositing a boron component on a 
substrate from a boron-containing vacuum deposition source, and by 
simultaneously irradiating the substrate with an ion seed comprising at 
least nitrogen from an ion-generating source for generating said ion seed. 
Furthermore, the thickness of the high-hardness BN film can be increased 
by first vacuum-depositing the boron component on the substrate and by 
then irradiating the substrate with the above-mentioned ion seed to form 
high-hardness boron nitride composed mainly of CBN or WBN, and by 
repeating formation of the vacuum deposition film and irradiation with the 
ion seed alternately. 
According to the present invention, simultaneously with or after formation 
of the vacuum-deposited boron film--because of the implantation and recoil 
effect of the implanted nitrogen atom and the thermal effect of the energy 
generated when the ion becomes stationary in the film--a highly exciting 
state resembling the state produced by scores of thousands of atmospheres 
and one thousand and several hundreds of .degree.C. is produced 
instantaneously and locally, and SP.sup.3 hybrid orbits of boron and 
nitrogen atoms, indispensable for formation of CBN or WBN, are formed. 
Based on this phenomenon, SP.sup.3 coupling is caused between these boron 
and nitrogen atoms and they act as crystal nuclei for CBN or WBN, and 
high-hardness boron nitride composed mainly of CBN or WBN is thus formed. 
As the boron-containing vacuum deposition source, there can be used at 
least one member selected from metallic boron and boron compounds such as 
boron sulfide, phosphorus boride, hydrogen boride, aluminum-containing or 
magnesium-containing metal borides and transition metal borides. 
Any of ion seeds having a predetermined ion acceleration energy and being 
capable of reacting with a boron-containing vacuum deposition source to 
form a film of high-hardness boron nitride composed mainly of CBN or WBN 
can be used as the ion seed. More specifically, at least one member 
selected from a nitrogen atom ion (N.sup.+), a nitrogen molecule ion 
(N.sub.2.sup.+), a nitrogen compound ion such as an ammonium ion 
(NH.sub.3.sup.+), a boron compound ion such as a boron nitride ion 
(BN.sup.+) and an inert gas ion such as Ar.sup.+ is preferably used as the 
ion seed. Furthermore, B.sub.3 N.sub.3 H.sub.6 or Al.sub.2 B.sub.2 N.sub.4 
may be ionized and used as the ion seed. Moreover, an ion seed such as a 
boron ion (B.sup.+) or a hydrogen boride ion (B.sub.2 H.sub.6.sup.+) may 
be used in combination with the above-mentioned nitrogen-containing ion 
seed. 
An ion seed as described above is produced by an apparatus described below, 
is magnetically selected by using a magnetron for the mass analysis 
according to need and is then supplied to the surface of the substrate. 
The material of the substrate is not particularly critical, and ceramics, 
cemented carbides, cermets, and various metals and alloys may be used. 
However, if the substrate is formed of an electrically insulating 
material, the properties of the vacuum-deposited film differ between a 
charged part and a non-charged part, and deviation of the characteristics 
is readily caused. Accordingly, it is preferred that an electric conductor 
be used as the substrate. Of course, however, an electrically insulating 
substrate may be used if a film of an electric conductor is formed on the 
surface according to a customary method. 
In one embodiment of the present invention, it is important that the atomic 
ratio (B/N) in the boron and nitrogen atoms supplied from the vacuum 
deposition source and ion seed should be adjusted within a range of from 4 
to 25 and the ion acceleration energy of the ion seed should be 5 to 100 
KeV per atom of the ion seed. 
If this atomic ratio B/N is lower than 4, BN in the amorphous state is 
readily formed, and if the atomic ratio B/N exceeds 25, boron becomes 
excessive and boron in the amorphous state is readily formed in the film. 
From the results of experiments made by us, it has been confirmed that best 
results can be obtained if the atomic ratio B/N is within a range of from 
5 to 18. 
If the ion acceleration energy of the ion seed is smaller than 5 KeV, the 
amount of the ion seed implanted in the vacuum-deposited film is decreased 
and the sputtering phenomenon becomes dominant, and if the ion 
acceleration energy of the ion seed exceeds 100 KeV, since the ion seed is 
implanted deeply beyond the vacuum-deposited layer formed on the surface 
of the substrate, high-hardness BN composed mainly of CBN or WBN is hardly 
formed and moreover, since the temperature of the vacuum-deposited layer 
becomes too high, formation of HBN becomes dominant while high-hardness BN 
composed mainly of CBN or WBN is hardly formed. 
In the present invention, sicne the atomic ratio B/N is 4 to 25 and boron 
is extremely excessive, it also is important that the vacuum deposition 
and ion seed irradiation treatments should be carried out in an atmosphere 
of a nitrogen atom or nitrogen compound activated at an energy level lower 
than that of the ion seed. Namely, the present invention is based on the 
novel finding that under conditions where a boron-containing vacuum 
evaporation source and a high-energy nitrogen-containing ion seed are 
copresent, even a nitrogen atom activated at a level lower than that of 
the ion seed participates in formation of high-hardness boron nitride 
composed mainly of CBN and/or WBN. 
As pointed out hereinbefore, the ion seed used in the ion and vapor 
deposition process (IVD method) of the present invention has such a high 
energy as 5 to 100 KeV per atom of the ion seed. On the other hand, the 
kinetic energy of the ion used in the conventional film-forming technique 
such as the ion beam deposition method, the cluster ion plating method or 
the ion beam sputtering method is much lower than in the ion and vapor 
deposition method and is in the order of several eV to several hundreds of 
eV. 
In the present invention, by making a nitrogen atom or nitrogen compound, 
which is excited at a low level, present in the ion and vapor deposition 
atmosphere, the state where the nitrogen atom is extremely defined in the 
vacuum deposition source and ion seed is compensated and a BN film having 
a good quality is obtained. 
Moreover, according to the present invention, as is apparent from the 
results of Examples given hereinafter, by adjusting the atomic ratio B/N 
within a range of from 4 to 25, a BN film having a very high quality can 
be obtained, and by supplement of the nitrogen atom from the atmosphere, 
the film-forming speed per unit time is extremely increased, as shown in 
Examples given hereinafter. Furthermore, by utilizing the ion seed 
irradiation mainly for attainment of the implantation and recoil effect 
and the thermal effect and supplying the reactants as an atmosphere 
excited at a low energy level, the energy efficiency for formation of the 
film is prominently improved. 
Various means may be adopted for forming a nitrogen or nitrogen compound 
atmosphere excited at a low energy level in the vicinity of the surface of 
the substrate in the present invention. Simplest means comprises supplying 
a nitrogen atom or nitrogen compound activated at a low energy level to 
the surface of the substrate together with a high-energy ion seed form the 
above-mentioned ion-generating source. Another means comprises causing arc 
discharge in a current of a nitrogen gas or nitrogen compound to form a 
nitrogen atom or nitrogen compound activated at a low energy level and 
introducing the nitrogen atom or nitrogen compound into the vacuum 
deposition and irradiation zone. 
In the present invention, it also is important that the ion acceleration 
energy should be set within the above-mentioned predetermined range and 
simultaneously, the dose rate (the ion current per unit area) of the ion 
seed should be set so that the quantity of heat generated in the substrate 
by irradiation with the ion seed is 0.01 to 20 W per unit area (cm.sup.2). 
If this heat quantity exceeds 20 W/cm.sup.2, the temperature of the boron 
vacuum-deposited layer becomes too high, formation of HBN becomes dominant 
while high-hardness BN composed mainly of CBN or WBN is hardly formed. If 
the quantity of heat is smaller than 0.01 W/cm.sup.2, the implantation and 
recoil effect or thermal effect cannot be attained by the ion seed and 
high-hardness boron nitride composed mainly of CBN or WBN is hardly 
synthesized. 
In the present invention, it is preferred that the temperature of the 
substrate be set at -200.degree. to 700.degree. C. 
If the substrate temperature is set at -200.degree. to 700.degree. C., the 
highly excited state formed locally and instantaneously can be easily 
maintained, and formed CBN or WBN can be frozen so that it is not 
converted to HBN. If the substrate temperature is lower than -200.degree. 
C., the BN film formed on the surface of the substrate is readily peeled, 
and if the substrate temperature exceeds 700.degree. C., conversion of 
formed CBN or WBN to HBN is readily caused. From the results of 
experiments made by us, it has been confirmed that best results can be 
obtained when the substrate temperature is 0.degree. to 400.degree. C. 
An apparatus for the production of a high-hardness BN film according to the 
present invention will now be described with reference to FIG. 1. 
A gas to be ionized, for example, N.sub.2, is introduced into an ion source 
2 through a leak valve 1, and the gas is ionized in the ion source 2 and 
is accelerated by an accelerator 3 to impart a predetermined ion 
acceleration energy. The ion is then introduced into an analyzing magnet 
4, and only the necessary ion seed is magnetically selected in the 
analyzing magnet 4 and is supplied to a reaction chamber 5. 
A high vacuum less than 10.sup.-4 Torr is maintained in the reaction 
chamber 5 by a vacuum pump 6 (for example, a turbo molecule pump). A 
substrate 7 is secured to a substrate holder 8 and irradiated with the 
above-mentioned ion seed. In order to uniformly irradiate the substrate 
with the ion seed, the ion seed is passed through a convergent lens 9. 
A vacuum deposition device 10 is arranged below the substrate 7, and an 
appropriate heating method such as electron beam heating or laser heating 
may be adopted in this device 10. A boron-containing vacuum deposition 
source is contained in the device 10. The vacuum-deposited amount and 
vacuum deposition speed of the boron-containing vacuum deposition source 
may be measured by, for example, an oscillating type film thickness meter 
11 using a quartz plate, which is arranged beside the substrate holder 8. 
The number of atoms of the ion seed, that is, the ion current, can be 
measured precisely by a current integrating meter 13 provided with a 
secondary electron emission electrode 12. 
In order to form an atmosphere of a nitrogen atom activated at a low energy 
level, an arc discharge chamber 14 is diposed, N.sub.2 gas is supplied in 
this discharge chamber and nitrogen atoms excited by differential 
evacuation are introduced into the reaction chamber 5. 
In the above-mentioned apparatus, the substrate 7 is set at a predetermined 
position and a predetermined vacuum degree is maintained in the reaction 
chamber 5, and the vacuum deposition device 10 is actuated to a 
predetermined amount vacuum deposition from the boron-containing vacuum 
deposition source on the substrate 7. If the substrate 7 is irradiated 
with the predetermined ion seed at a predetermined ion acceleration 
energy, a film of high-hardness BN composed mainly of CBN and WBN is 
formed on the surface of the substrate 7. 
Incidentally, since either vacuum deposition of the boron-containing vacuum 
deposition source or irradiation with the ion source is effected only from 
one direction of the substrate, in the case where a high-hardness BN film 
composed mainly of CBN and WBN is formed on the entire surface of the 
substrate, it is necessary to give such a motion as rotation or swinging 
to the substrate. 
Second Embodiment 
According to the second embodiment of the present invention, in the 
above-mentioned film production process, activated boron is 
vacuum-deposited by supplying a boron-containing gas to an arc discharge 
region and/or forming an arc discharge region by using an arc discharge 
electrode. 
It is considered that according to this embodiment of the present 
invention, the ion seed of nitrogen will be relatively easily activated to 
a high energy level of SP.sup.3 hybrid orbits on the substrate. 
Accordingly, the other atom, that is, boron, is activated by supplying a 
boron-containing gas or substance to an arc discharge region. More 
specifically, at this arc discharge, the boron atom is sputtered by an 
electron and an ion and a part of boron is ionized. This boron ion gains 
an activated energy state and is vacuum-deposited on the substrate, and 
therefore, SP.sup.3 coupling is readily caused with the nitrogen atom. 
In the present invention, when a nitrogen gas or nitrogen compound gas is 
supplied into the arc discharge region, a nitrogen ion is generated by the 
discharge and causes chemical reaction with a boron-containing gas or 
sputters boron of the arc discharge electrode. Accordingly, an 
intermediate product composed of boron and nitrogen can be 
vacuum-deposited on the substrate. From the results of experiments made by 
us, it has been confirmed that the speed of formation of a BN film can be 
prominently increased by formation of this intermediate product. 
Furthermore, if an apparatus of FIG. 2, described hereinafter, is employed, 
since the arc discharge region is located at a portion through which the 
ion seed of nitrogen passes, the above-mentioned intermediate product of 
boron and nitrogen is easily formed and the speed of formation of a BN 
film is prominently increased. 
Moreover, as described hereinafter, the nitrogen ion generated by the arc 
discharge can be used for formation of a nitrogen atmosphere activated at 
a low energy level. 
As the boron-containing gas, there can be used, for example, B.sub.2 
H.sub.6, B.sub.10 H.sub.14 and borazol. 
As the boron-containing substance, there can be used at least one member 
selected from metallic boron and boron compounds such as boron sulfide, 
phophorus boride, hydrogen boride, aluminum-containing and 
magnesium-containing metal borides and transition metal borides. 
Other conditions are substantially the same as those of the first 
embodiment. 
The second embodiment of the present invention will now be described with 
reference to FIG. 2. The apparatus shown in FIG. 2 is the same as the 
apparatus shown in FIG. 1 except the apparatus of FIG. 2 is provided with 
an arc discharge mechanism, and common members and parts are indicated by 
the same reference numerals as used in FIG. 1. 
Referring to FIG. 2, reference numeral 15 represents a double electrode 
composed of a linear boron-containing substance would by a reel (not 
shown). The double electrode 15 is located at a predetermined position by 
a roll 16. This roll 16 is connected to an arc discharge power source 17. 
A jet opening of an introduction tube 18 is located in the vicinity of the 
top end of the arc discharge double electrode 15 to introduce a nitrogen 
gas into an arc discharge region. 
In the above-mentioned apparatus, the substrate 7 is set at a predetermined 
position and a predetermined vacuum degree is maintained in the reaction 
chamber 5, and a nitrogen gas is introduced through the introduction tube 
and arc discharge is caused between the double electrodes 15, 15 by the 
arc discharge power source 17 to form a nitrogen-cotaining boron ion. A 
predetermined amount of this ion is vacuum-deposited on the substrate 7. 
If the substrate is irradiated in this state with a predetermined ion seed 
at a predetermined ion acceleration energy, a film of high-hardness BN 
composed mainly of CBN and WBN is formed on the surface of the substrate. 
According to this production process of the present invention, since boron 
is vacuum-deposited on the substrate by the arc discharge, the hourly 
supply rate of boron can be controlled by controlling the arc discharge 
power source or adjusting the distance between the double electrodes 15, 
15. Accordingly, a desired film-forming speed can be obtained by adjusting 
the supply rate of boron while adjusting the irradiation quantity of the 
nitrogen ion. 
Moreover, since the linear arc discharge electrode material acting as the 
boron supply source is wound by the reel, even if the top end portion of 
the electrode is consumed by the arc discharge, the electrode can be 
supplied in succession and a high-quality BN film can be continuously 
formed on the substrate over a long period. Moreover, vacuum deposition on 
a substrate having a large area to be covered can be conveniently 
accomplished and the film thickness can be increased. 
In the apparatus shown in FIG. 2, an arc discharge electrode is disposed as 
the boron supply source. Instead of this method, there may be adopted a 
method in which a boron-containing gas such as B.sub.2 H.sub.6, B.sub.5 
H.sub.9, B.sub.10 H.sub.14 or borazol gas is supplied as the boron supply 
source into the arc discharge region through the introduction tube 18. 
These methods may be adopted singly or in combination. 
Third Embodiment 
According to the third embodiment of the present invention, the 
above-mentioned vacuum deposition and irradiation are carried out in a 
state where a negative bias voltage is applied to the substrate. 
This embodiment is based on the novel finding that an atmosphere of a 
nitrogen atom or nitrogen compound activated at a low energy level is 
positively charged as a whole. As is shown in Examples given hereinafter, 
if a negative bias voltage is applied to the substrate, the positively 
charged atmosphere is attracted to the substrate and the nitrogen 
component is positively implanted in the surface of the substrate. Thus, 
the atmosphere makes an effective contribution to formation of a BN film. 
A component to be ionized at the vacuum deposition and ion irradiation is 
produced in the boron component emitted from the vacuum deposition source 
by application of the negative bias voltage, and this component is 
accelerated and attracted to the surface of the substrate to effectively 
promote formation of a BN film. 
Moreover, since the ion seed generated from the ion-generating source is 
scattered by the ion irradiation, and a part of the scattered ion seed 
becomes extinct without participating in formation of a BN film, but 
according to the present invention, the scattered ion seed is attracted to 
the substrate and fruitless ion irradiation can be avoided. 
From the results of experiments made by us, it has been confirmed that best 
results are obtained when the bias voltage to be applied to the substrate 
is set at -100 V to -10 V, though the optimum bias voltage changes to some 
extent according to the ion acceleration energy of the negative ion seed. 
By this application of the bias voltage, supplement of the nitrogen atom 
from the atmosphere can be advanced more effectively, and the film-forming 
speed per unit time can be further increased. Moreover, by efficiently 
supplying reactants as an atmosphere excited at a low energy level by 
mainly utilizing the implantation and recoil effect and the thermal effect 
for irradiation with the ion seed, the energy efficiency for formation of 
the film can be prominently improved. Attainment of these advantages has 
been experimentally confirmed. 
In this third embodiment of the present invention, if the atomic ratio 
(B/N) in boron and nitrogen atoms supplied from the vacuum deposition 
source and the ion seed is adjusted within a range of from 0.2 to 10, 
formation of a high-hardness BN film can be greatly facilitated. 
If the atomic ratio B/N is lower than 0.2, amorphous BN is readily formed, 
and if the atomic ratio B/N exceeds 10, amorphous boron is readily formed 
in the film. From the results of experiments made by us, it has been 
confirmed that best results can be obtained when the atomic ratio B/N is 
adjusted within a range of from 0.5 to 5. 
Other conditions in the third embodiment are substantially the same as in 
the first embodiment. 
An apparatus for use in carrying out this embodiment will now be described 
with reference to FIG. 3. The apparatus of FIG. 3 is the same as the 
apparatus shown in FIG. 1 except that mechanism for apply a bias voltage 
to the substrate is disposed in the apparatus of FIG. 3. 
In the apparatus shown in FIG. 3, a voltage-adjustable bias power source 19 
is connected between a substrate 7 and a secondary electron emission 
electrode 12 so that a negative bias voltage is applied to the substrate 
7. 
In this apparatus, the substrate 7 is set at a predetermined position, a 
predetermined vacuum degree is maintained in a reaction chamber, a vacuum 
deposition device 10 is actuated to a predetermined amount vacuum 
deposition from a boron-containing vacuum deposition source, the substrate 
is irradiated with a predetermined ion seed at a predetermined ion 
acceleration energy, and simultaneously, a predetermined negative bias 
voltage is applied to the substrate 7 from the power source 19, whereby a 
film of high-hardness BN composed mainly of CBN and WBN is formed on the 
surface of the substrate. 
Fourth Embodiment 
According to the fourth embodiment, in each of the above-mentioned 
processes, the total concentration of oxygen and carbon atoms in the 
atmosphere for the vacuum deposition and irradiation is controlled below 
100 ppm. 
In the present invention, as pointed out hereinbefore, the vacuum 
deposition and ion seed irradiation treatments are carried out in an 
atmosphere of a nitrogen atom or nitrogen compound activated to a lower 
energy level than the ion seed. It is preferred that the amount of oxygen 
or carbon atoms considered to be inevitably present in this atmosphere be 
controlled. Namely, the fourth embodiment of the present invention is 
based on the novel finding that in the system of reaction of forming CBN 
or WBN, an oxygen or carbon atom acts as an inhibitor factor. 
Reaction is caused very easily between a boron atom and an oxygen atom, and 
if an oxygen atom is present in the reaction system of the ion and vapor 
deposition process of the present invention, a part of the boron atom 
couples with the oxygen atom to form boron oxide, which inhibits the gas 
phase growth of CBN or WBN or promotes inclusion of boron oxide in the 
grain boundary of CBN or WBN, with the result that the stability of the 
film is generated and a high-quality film cannot be obtained. 
Similarly, a carbon atom is very liable to react with a boron atom and 
inhibits the gas phase growth of CBN or WBN, and the carbon atom is 
included as boron carbide to render the production of a high-quality film 
impossible. 
In the present invention, if the atomic ratio B/N in the boron and nitrogen 
atoms supplied from the vacuum deposition source and ion seed is adjusted 
to 4 to 25 when a negative bias voltage is not applied or to 0.2 to 10 
when a negative bias voltage is applied, a high-hardness BN film can be 
easily formed. 
In order to control the concentration of the oxygen and carbon atoms in the 
reaction chamber to the above-mentioned level, there may be adopted means 
of using refined starting boron and nitrogen materials in which the amount 
of incorporated oxygen or carbon atoms is extremely small and increasing 
the vacuum degree in the reaction chamber. 
The present invention will now be described in detail with reference to the 
following examples that by no means limit the scope of the invention. 
EXAMPLE 1 
High-purity N.sub.2 gas was introduced into a PIG type ion source 2 from a 
leak valve 1 in the apparatus shown in FIG. 1. 
Various acceleration energies were given to generated ions by an 
accelerator 3, and the ion beams were subjected to the mass analysis in an 
analyzing magnet 4 to magnetically select N.sub.2.sup.+ alone. 
A silicon plate was used as the substrate and was set on a substrate holder 
8, and a reaction chamber 5 was evacuated by a turbo molecule pump having 
a capacity of 650 l/sec. 
An electron beam vacuum deposition device 10 in which metallic boron was 
contained was actuated to evapolate metallic boron, and boron was 
vacuum-deposited on the silicon plate 7 while simultaneously irradiating 
the substrate 7 with N.sub.2.sup.+ ions. When the gas in the reaction 
chamber 5 was analyzed, it was found that an activated nitrogen gas 
atmosphere was produced in the reaction chamber 5. 
The vacuum-deposited amount and vacuum deposition speed of B were measured 
by an oscilating type thickness meter 11 and the number of N.sub.2.sup.+ 
ions was measured by a current integrating meter 13, and the atomic ratio 
B/N was calculated. Formation of the film was carried out by changing the 
amount deposited of B by changing the ion acceleration energy for 
N.sub.2.sup.+ ions. 
A BN film having a thickness of 2 .mu.m was formed by continuing the 
operation for 2 hours under such conditions that the N.sub.2.sup.+ ion 
acceleration energy was 35 KeV (corresponding to the acceleration energy 
of 17.5 KeV per atom of the ion seed), the atomic ratio B/N was 10 and the 
vacuum degree was 0.8.times.10.sup.-5 Torr. 
When the obtained BN film was analyzed by X-ray diffractometry, peaks 
attributed to CBN (111) and WBN (002) were observed, and the presence of 
CBN and WBN was confirmed. 
EXAMPLE 2 
BN films were prepared in the same manner as described in Example 1 except 
that the atomic ratio B/N and the dose rate were changed as indicated in 
Table 1. The obtained results are shown in Table 1. 
From the results shown in Table 1, it is seen that if the atomic ratio B/N 
exceeds 25, the electric resistance and hardness are reduced, and that if 
the atomic ratio B/N is lower than 4, formation of HBN becomes conspicuous 
and the hardness is reduced. 
Moreover, from the results of Runs Nos. 8 through 11, it is seen that there 
is an optimum range for the dose rate (W/cm.sup.2), and that if the dose 
rate is too low and below this range, no substantial efect is attained by 
the ion irradiation and if the dose rate is too high, the quantity of 
generated heat is increased and formation of HBN becomes conspicuous to 
reduce the hardness. It also is seen that by adjusting the atomic ratio 
B/N to 4 or higher the film-forming speed is extremely increased. 
TABLE 1 
__________________________________________________________________________ 
N.sub.2 + Accelera- 
Generated Heat 
Film-Forming 
Electric 
Hardness 
Run tion Voltage 
Ion Current 
Quantity 
Speed Resistance 
Hv 
No. 
B/N 
V(KV) I(.mu.A/cm.sup.2) 
V .times. I(W/cm.sup. 2) 
.ANG./min 
.OMEGA. .multidot. cm 
kg/mm.sup.2 
__________________________________________________________________________ 
1 28 35 15 0.525 251 3.2 .times. 10.sup.5 
3200 
2 22 35 15 0.525 182 1.0 .times. 10.sup.9 
3850 
3 15 35 15 0.525 135 1.8 .times. 10.sup.10 
4650 
4 10 35 15 0.525 99 2.1 .times. 10.sup.10 
4850 
5 5 35 15 0.525 75 1.9 .times. 10.sup.10 
4000 
6 1 35 15 0.525 14 2.8 .times. 10.sup.13 
3000 
7 0.3 
35 15 0.525 4 1.7 .times. 10.sup.14 
2700 
8 10 5 1 0.005 8 3.0 .times. 10.sup.13 
2650 
9 10 30 10 0.300 92 2.2 .times. 10.sup.10 
4750 
10 10 40 21 0.820 171 1.8 .times. 10.sup.10 
4900 
11 10 100 230 23.000 1,424 1.1 .times. 10.sup.10 
2900 
__________________________________________________________________________ 
EXAMPLE 3 
BN films were prepared in the same manner as described in Example 1 except 
that cermet of the TiC-TiN type was used as the substrate, the ion seed 
acceleration voltage was changed to 35 KeV (corresponding to the 
acceleration energy of 17.5 KeV per atom of the ion seed), the atomic 
ratio B/N was adjusted to 10 and the substrate temperature was changed as 
shown in Table 2. 
With respect to each of the formed films, the identification of the crystal 
was performed by X-ray diffractometry and the hardness was measured. 
The obtained results are shown in table 2. 
TABLE 2 
______________________________________ 
Substrate 
Temperature 
Presence or Absence of Crystal 
Hardness 
(.degree.C.) 
CBN WBN HBN Amorphous 
(Hv) 
______________________________________ 
-150 O O X O 3300 
-100 O O X O 3450 
-50 O O X O 3540 
0 O O X O 3950 
50 O O X X 4150 
100 O O X X 4950 
200 O O X X 4770 
400 O O O X 4150 
800 X O O X 3100 
1000 X X O X 2600 
______________________________________ 
Note 
O: present 
X: absent 
EXAMPLE 4 
This Example is to prove the presence of the nitrogen atom excited at a low 
energy level in the atmosphere in the process of the present invention. 
As shown in FIG. 4, a metal plate 20 was located at a position not 
irradiated with N.sub.2.sup.+ ions, and the current was measured by a 
.mu..mu.A meter 21. The obtained results are shown in Table 3. 
TABLE 3 
______________________________________ 
Current of 
Current of 
Acceleration Substrate Metal Plate 20 
Voltage KV .mu.A/cm.sup.2 
.mu.A/cm.sup.2 
______________________________________ 
30 14 0.033 
32 15 0.040 
34 16 0.047 
36 17 0.057 
38 20 0.067 
40 20 0.077 
______________________________________ 
From the results of the analysis of the residual gas in the reaction 
chamber, it was confirmed that a nitrogen gas atmosphere was produced in 
the reaction chamber, and from the above results, it was confirmed that an 
atmosphere containing activated nitrogen atoms was produced around the 
substrate. 
EXAMPLE 5 
High-purity N.sub.2 was introduced into a PIG ion source 2 from a gas 
introduction opening 1 in the apparatus shown in FIG. 2. Various 
acceleration energies were given to the generated ions. The ion beams were 
subjected to the mass analysis in an analyzing magnet 4 to magnetically 
select N.sub.2.sup.+ ions alone. 
A silicon plate was used as the substrate and was secured to a substrate 
holder 8, and a reaction chamber 5 was evacuated by a turbo molecule pump 
having a capacity of 650 l/sec. 
Then, nitrogen gas was supplied from an introduction pipe 18 and an arc 
discharge region was produced by an arc discharge power source 17, whereby 
boron ions were mainly formed while a boron-nitrogen intermediate product 
was partially formed. These ions and intermediate product were 
vacuum-deposited on the substrate 7 simultaneously with irradiation with 
N.sub.2.sup.+ ions. When the gas in the reaction chamber 5 was analyzed at 
this step, it was found that an activated nitrogen gas atmosphere was 
produced. 
The vacuum-deposited amount and vacuum deposition speed of boron were 
measured by an oscillating type thickness meter 11 and the number of the 
N.sub.2.sup.+ ions was measured by a current integrating meter 13, and the 
atomic ratio B/N was calculated. 
Thus, films were prepared by changing the ion acceleration energy for 
N.sub.2.sup.+ ions and the vacuum-deposited amount. 
A BN film having a thickness of 2.5 .mu.m was prepared by continuing the 
operation for 2 hours under such conditions that the N.sub.2.sup.+ ion 
acceleration voltage was 35 KV (corresponding to the acceleration energy 
of 17.5 KeV per atom of the ion seed), the atomic ratio B/N was 10, the 
substrate temperature was 200.degree. C. and the vacuum degree was 
0.8.times.10.sup.-5 Torr. 
When the obtained BN film was analyzed by X-ray diffractometry, as shown in 
FIG. 5, peaks of CBN and WBN corresponding to lattice constants d thereof 
were observed and the relative intensity could be known. When the Vickers 
hardness of the BN film was measured, such a large value as 7000 
Kg/mm.sup.2 was obtained. 
Comparative Example 1 
The film-forming operation was carried out for 2 hours in the same manner 
as described in Example 5 except that a boron-containing vacuum deposition 
source was arranged instead of the boron arc discharge mechanism, the 
atomic ratio B/N in the boron and nitrogen atoms supplied from the vacuum 
deposition source and ion seed was adjusted to 10 and boron was 
vacuum-deposited by electron beam heating, whereby a BN film having a 
thickness of 2 .mu.m was obtained. 
When the so-obtained BN film was analyzed by X-ray diffractometry, peaks 
attributed to CBN (111) and WBN (002) were observed. When the Vickers 
hardness was measured, a value of 5000 Kg/mm.sup.2 was obtained. 
As is seen from the foregoing description, the hardness of the film 
obtained in Example 5 is much higher than that of the film obtained in 
Comparative Example 1, and the activating effect by the boron arc 
discharge is obvious and prominent. 
EXAMPLE 6 
BN films were prepared in the same manner as in Example 5 except that the 
atomic ratio B/N, the N.sub.2.sup.+ acceleration voltage and the dose rate 
were changed as shown in Table 4. 
The obtained results are shown in Table 4. 
TABLE 4 
__________________________________________________________________________ 
Quantity of 
Generated 
Film-Forming 
Electric 
Run 
Atomic Ratio 
N.sub.2.sup.+ Acceleration 
Ion Current 
Heat Speed Resistance 
Hardness 
No. 
B/N Voltage V(KV) 
(.mu.A/cm.sup.2) 
V .times. I(W/cm.sup.2) 
(.ANG./min) 
(.OMEGA. .multidot. cm) 
HV(kg/mm.sup.2) 
__________________________________________________________________________ 
1 30 35 6.0 0.21 350 4.1 .times. 10.sup.5 
3050 
2 20 35 5.8 0.20 320 1.8 .times. 10.sup.9 
3500 
3 15 35 6.4 0.22 250 1.6 .times. 10.sup.10 
5100 
4 13 35 9.3 0.33 210 2.3 .times. 10.sup.10 
6200 
5 9 35 8.7 0.30 100 2.3 .times. 10.sup.10 
6900 
6 5 35 9.1 0.32 50 5.9 .times. 10.sup.10 
5900 
7 3 35 9.4 0.33 15 2.0 .times. 10.sup.11 
3100 
8 1.5 35 9.9 0.35 5 7.0 .times. 10.sup.13 
3000 
9 10 35 0.2 0.007 10 3.0 .times. 10.sup.12 
3300 
10 9 50 450.0 22.0 900 measurement 
measurement 
impossible 
impossible 
11 8 8 37.5 0.30 800 3.9 .times. 10.sup.12 
3000 
12 11 210 1.4 0.28 10 measurement 
measurement 
impossible 
impossible 
__________________________________________________________________________ 
In Table 4, the N.sub.2.sup.+ acceleration voltage V (KV) corresponds to 2 
times the acceleration energy (KeV) per atom of the ion seed. 
From the results shown in Table 4, it is seen that in Runs Nos. 2 through 6 
and 9, since the N.sub.2.sup.+ acceleration voltage and the atomic ratio 
B/N are within the ranges specified in the present invention, films 
excellent in the hardness are obtained, and films obtained in Runs Nos. 3 
through 6 have an especially excellent hardness. 
In Runs Nos. 9 and 10, even though the N.sub.2.sup.+ acceleration voltage 
and the atomic ratio B/N are within the ranges specified in the present 
invention, the quantity of heat generated in the substrate by the ion seed 
irradiation is outside the range specified in the present invention. 
Accordingly, though the hardness is somewhat improved in Run No. 9, the 
film obtained in Run No. 10 is rendered porous since the quantity of 
generated heat is extremely large and evaporation is caused. Therefore, 
the measurement of the electric resistance or hardness is impossible in 
this sample. 
In Runs Nos. 11 and 12, since the N.sub.2.sup.+ acceleration voltage is 
outside the range specified in the present invention, an excellent 
hardness is not obtained in Run No. 11, and swelling is caused in Run No. 
12 because of an excessive acceleration voltage and the film is rendered 
porous, with the result that the measurement of the electric resistance or 
the hardness is impossible. In Runs Nos. 1, 7 and 8 even though an 
improvement of the hardness is expected by implantation of ions, since the 
atomic ratio B/N is outside the range specified in the present invention, 
an excellent hardness cannot be obtained. 
EXAMPLE 7 
This Example is to illustrate the relation between the atomic ratio B/N 
calculated from the preparation conditions and the actual atomic ratio B/N 
in the formed film. 
BN films were formed on an Au foil having a thickness of 8000 .ANG. while 
changing the atomic ratio B/N within a range of from 2.5 to 11, and with 
respect to each of the obtained BN films, the atomic ratio B/N was 
determined by the quantitative analysis using high-speed ions. The 
obtained results are shown in FIG. 6. 
In the analysis of the atomic ratio B/N in the BN film, the hydrogen ion 
acceleration energy was 2 MeV, the angle of a semiconductor detector was 
165.degree. and the gain was 300, and the atomic ratio was determined from 
the formation spectrum of back-scattered ions. In this formation spectrum, 
the composition ratio of B and N was determined from the peak ratio of 
B.sub.11 and N.sub.14 (11 and 14 indicate the atom numbers). 
In FIG. 6, the actual atomic ratio B/N of the BN film determined from the 
peak ratio in the formation spectrum is plotted by marks relatively to the 
atomic ratio B/N calculated from the preparation conditions in the case 
where no bias voltage was applied, and the actual atomic ratio B/N of the 
BN film determined from the peak ratio in the formation spectrum is 
plotted by marks O relatively to the atomic ratio B/N calculated from the 
preparation conditions in the case where a bias voltage of -0.5 KV was 
applied. 
From the results shown in FIG. 6, it is seen that it is when the atomic 
ratio B/N calculated from the preparation conditions is about 10 that the 
atomic ratio B/N in the film is ideally 1, and this supports that the 
nitrogen component is supplementarily supplied from the nitrogen gas of a 
low energy level present around the substrate. 
It also is seen that when a negative bias voltage is applied, nitrogen ions 
of a low energy level present around the substrate are attracted to the 
substrate, the effects of the present invention are enhanced. 
As is apparent from the foregoing description, according to the process of 
the present invention, by vacuum-depositing boron activated by the arc 
discharge on the substrate, the film-forming speed can be optionally 
controlled, and a high-quality BN film composed mainly of CBN and WBN can 
be continuously prepared at a high speed. 
EXAMPLE 8 
High-purity N.sub.2 gas was introduced into a PIG in source 2 from a leak 
valve 1 in the apparatus shown in FIG. 3. 
Various acceleration energy were given to generated ions by an accelerator 
3. The ion beams were subjected to the mass analysis by an analyzing 
magnet 4 to magnetically select N.sub.2.sup.+ ions alone. 
A silicon plate was used as the substrate and was secured to a substrate 
holder 8, and a reaction chamber 5 was evacuated by a turbo molecule pump 
having a capacity of 650 l/sec. 
A negative bias voltage was applied to the substrate 7 from a bias power 
source 19, and an electron beam vacuum deposition device 10 containing 
metallic boron therein was actuated to evaporate metallic boron and the 
vapor of boron was deposited on the substrate 7 while simultaneously 
irradiating the substrate 7 with N.sub.2.sup.+ ions. The gas in the 
reaction chamber 5 at this step was analyzed, and it was found that an 
activated nitrogen gas atmosphere was produced in the reaction chamber 5. 
The vacuum deposited quantity and vacuum deposition speed of B were 
measured by an oscillating type thickness meter 11 and the number of 
N.sub.2.sup.+ ions was measured by a current integrating meter 13, and the 
atomic ratio B/N was calculated. 
Films were prepared by changing the amount deposited of B by changing the 
ion acceleration energy for N.sub.2.sup.+ ions while changing the bias 
voltage. 
A BN film having a thickness of 2.5 .mu.m was prepared by continuing the 
operation for 2 hours under such conditions that the N.sub.2.sup.+ ion 
acceleration energy was 35 KeV, the atomic ratio B/N was 1.5, the bias 
voltage was -1 KV, the substrate temperature was 200.degree. C. and the 
vacuum degree was 0.8.times.10.sup.-5 Torr. 
When the obtained BN film was analyzed by X-ray diffractometry, it was 
found that peaks attributed to CBN (111) and WBN (002) appeared, and the 
presence of CBN and WBN was confirmed. When the Vickers hardness of the BN 
film was measured, such a large value as 6900 kg/mm.sup.2 was obtained. 
Comparative Example 2 
A BN film having a thickness of 2 .mu.m was prepared by continuing the 
operation for 2 hours in the same manner as described in Example 8 except 
that no bias voltage was applied to the substrate and the atomic ratio B/N 
was set at 10. 
When the obtained BN film was analyzed by X-ray diffractometry, peaks 
attributed to CBN (111) and WBN (002) were observed. When the Vickers 
hardness was measured, a value of 4850 kg/mm.sup.2 was obtained. 
In this Comparative Example, no amount of the nitrogen component supplied 
from the atmosphere was included in calculating the atomic ratio B/N but 
only the amount of the nitrogen component supplied from the irradiated 
ions was taken in calculating the atomic ratio B/N. On the other hand in 
Example 8, the ion seed activated to a low energy level in the atmosphere 
was added to the amount of irradiated ions, and therefore, the ion current 
was 5 to 6 times the ion current in Comparative Example 2 and the amount 
of the nitrogen component participating actually in the reaction was 
increased. Accordingly, even though a BN film composed mainly of CBN or 
WBN is similarly prepared by the same reaction in Example 8 and 
Comparative Example 2, the parameter of the atomic ratio B/N is 1.5 in the 
former while this parameter is 10 in the latter. This difference indicates 
that according to the process of the present invention, an atmosphere 
activated to a low energy level is caused to participate positively in 
formation of a BN film, whereby the quality and hardness of the BN film 
can be highly improved. 
EXAMPLE 9 
In this Example, the influences of the atomic ratio B/N were examined by 
changing this atomic ratio (a bias voltage of -1.0 KV was applied). 
More specifically, in Runs Nos. 1 through 8, BN films were prepared in the 
same manner as described in Example 8 except that the atomic ratio BV/N 
was changed as shown in Table 5. 
The obtained results are shown in Table 5. 
TABLE 5 
__________________________________________________________________________ 
N.sub.2.sup.+ Acceleration 
Ion Current 
Film-Forming 
Electric 
Run Voltage I Speed Resistance 
Hardness 
No. 
B/N 
V(KV) (.mu.A/cm.sup.2) 
.ANG./min 
.OMEGA. .multidot. cm 
HV(Kg/cmm.sup.2) 
__________________________________________________________________________ 
1 12 35 62 340 4.0 .times. 10.sup.5 
3150 
2 8 35 57 310 1.9 .times. 10.sup.9 
3400 
3 4 35 63 250 1.7 .times. 10.sup.10 
5050 
4 2 35 92 200 2.1 .times. 10.sup.10 
6100 
5 1 35 87 90 2.3 .times. 10.sup.10 
6800 
6 0.7 
35 91 20 5.6 .times. 10.sup.10 
6300 
7 0.5 
35 93 8 1.7 .times. 10.sup.14 
4800 
8 0.1 
35 98 5 2.1 .times. 10.sup.14 
3000 
__________________________________________________________________________ 
From the results shown in Table 5, it is seen that if the atomic ratio B/N 
exceeds 10, the electric resistance and hardness are reduced and that if 
the atomic ratio B/N is lower than 0.2, formation of HBN becomes 
conspicuous and the hardness is reduced. 
EXAMPLE 10 
In this Example, influences of application of a bias voltage on the ion 
current were examined. 
Changes of the ion current were examined by changing the N.sub.2.sup.+ ion 
acceleration voltage within a range of 25 to 40 KV while applying no bias 
voltage in Runs Nos. 1 through 4 or applying a bias voltage of -1.0 KV in 
runs Nos. 5 through 8. The obtained results are shown in Table 6. 
From the results shown in Table 6, it is seen that if a negative bias 
voltage is applied, the ion current is increased to a level about 5 times 
the iron current obtained when no bias voltage is applied. Accordingly, it 
is seen that the film-forming speed is increased by applying a negative 
bias voltage. 
TABLE 6 
______________________________________ 
Run N.sub.2.sup.+ Acceleration 
Ion Current 
Bias Voltage 
No. Voltage V(KV) I(.mu.A/cm.sup.2) 
VB(KV) 
______________________________________ 
1 25 10 0 
2 30 15 0 
3 35 18 0 
4 40 22 0 
5 25 49 -1.0 
6 30 55 -1.0 
7 35 90 -1.0 
8 40 120 -1.0 
______________________________________ 
EXAMPLE 11 
In this Example, influences of the temperature were examined. 
BN films were prepared in the same manner as described in Example 8 except 
that cermet of the TiC-TiN type was used as the substrate, the ion seed 
acceleration energy was adjusted to 35 KeV, the bias voltage was set at 
-1.0 KV, the atomic ratio B/N was adjusted 1.5 and the substrate 
temperature was changed as indicated in Table 7. The obtained results are 
shown in Table 7. 
TABLE 7 
______________________________________ 
Substrate Hardness 
Temperature 
Presence or Absence of Crystal 
Hv 
.degree.C. 
CBN WBN HBN amorphous 
(kg/mm.sup.2) 
______________________________________ 
-150 O O X O 3400 
-100 O O X O 3550 
-50 O O X O 3940 
0 O O X O 5000 
50 O O X O 5350 
100 O O X O 6450 
200 O O X X 6800 
400 O O O X 5100 
800 X O O X 3200 
1000 X X O X 2900 
______________________________________ 
Note 
O: present 
X: absent 
EXAMPLE 12 
A BN film was prepared in the same manner as described in Example 8 except 
that high-purity H.sub.2 gas having a purity of 99.995%, an oxygen 
concentration lower than 1 ppm and a carbon gas concentration of 2 ppm was 
used as the starting N.sub.2 gas and metallic boron having a purity of 
99.995% was used as the starting metallic boron and the vacuum degree at 
the film-forming operation was adjusted to 4.times.10.sup.-6 Torr. 
During formation of the BN film, the oxygen concentration and carbon 
concentration were measured by a mass analyzer. It was found that the 
oxygen concentration was 2 ppm and carbon was not substantially detected. 
When the obtained BN film was analyzed by X-ray diffractometry, the peaks 
attributed to CBN (111) and WBN (002) were observed and the presence of 
CBN and WBN was confirmed. When the Vickers hardness of the film was 
measured, such a large value as 7200 kg/mm.sup.2 was obtained. 
The above procedures were repeated in the same manner except that the 
vacuum degree and the purities of the starting N.sub.2 gas and B were 
changed as shown in Table 8. 
The obtained results are shown in table 8. 
TABLE 8 
__________________________________________________________________________ 
Concentration in 
Run 
Vacuum Degree 
Purity of 
Purity of B 
Atmosphere (ppm) 
Hardness 
No. 
(Torr) N.sub.2 Gas (%) 
(%) oxygen atom 
carbon atom 
Hv(kg/mm.sup.2) 
__________________________________________________________________________ 
1 4 .times. 10.sup.-6 
99.9995 
99.999 
5 1 7200 
2 0.8 .times. 10.sup.-5 
99.995 99.99 40 30 6400 
3 0.8 .times. 10.sup.-5 
99.995 99.999 
50 20 6300 
4 0.8 .times. 10.sup.-5 
99.9995 
99.999 
30 20 6500 
5 0.8 .times. 10.sup.-5 
99.99 99.99 80 40 5000 
__________________________________________________________________________ 
EXAMPLE 13 
In forming BN films in the same manner as described in Example 12, the 
amounts of oxygen and nitrogen atoms contained in the reaction chamber 
were set as shown in Table 9 by making oxygen gas, carbon monoxide or 
carbon dioxide gas present in the reaction chamber. Incidentally, the gas 
concentrations were calculated from the partial pressures of the gases 
present in the reaction chamber. 
In each of the obtained BN films, the presence or absence of CBN or WBN was 
checked by X-ray diffractometry, and the Vickers hardness of each film was 
measured. 
The obtained results are shown in Table 9. 
TABLE 9 
______________________________________ 
Carbon 
Oxygen Con- 
Concentra- 
Presence of 
Vickers 
Run centration tion Absence of 
Hardness 
No. (ppm) (ppm) CBN or WBN 
Hv(kg/mm.sup.2) 
______________________________________ 
1 5 0 O 6800 
2 10 0 O 6600 
3 4 12 O 6400 
4 10 20 O 6300 
5 23 23 O 6200 
6 81 0 O 5000 
7 54 54 .DELTA. 4400 
8 138 0 .DELTA. 3800 
9 64 128 .DELTA. 3100 
10 410 0 X 2200 
11 220 220 X 2000 
______________________________________ 
Note 
O: presence of CBN and WBN was confirmed but HBN was not present and 
amorphous phase was partially included 
.DELTA.: HBN was formed together with CBN and WBN 
X: CBN or WBN was not formed 
From the results shown in Table 9, it is seen that according to Runs Nos. 1 
through 6 of the present invention, HBN is not formed and high-quality BN 
films composed mainly of CBN and WBN are obtained. It also is seen that 
the hardness is reduced with increase of the oxygen and carbon 
concentrations.