U.S. patent number 3,904,505 [Application Number 05/271,014] was granted by the patent office on 1975-09-09 for apparatus for film deposition.
This patent grant is currently assigned to Space Sciences, Inc.. Invention is credited to Sol Aisenberg.
United States Patent |
3,904,505 |
Aisenberg |
September 9, 1975 |
Apparatus for film deposition
Abstract
A method and apparatus for depositing a thin film of material
upon a base substrate including a glow discharge ion source for
generating the particular ions that will be subsequently deposited
upon the base substrate, a vacuum deposition chamber wherein the
substrate material is located, and, intermediate between the glow
discharge ion source and the vacuum deposition chamber, a
constrictor electrode for isolating the deposition chamber from the
ion chamber and an anode electrode for extracting ions from the
plasma ion source and directing them toward the target substrate. A
magnetic field is also provided in the apparatus of the present
invention by the use of an externally wound magnetic coil to permit
the glow discharge ion source to operate at a lower pressure and to
constrict the flow of ions toward the substrate.
Inventors: |
Aisenberg; Sol (Natick,
MA) |
Assignee: |
Space Sciences, Inc. (Waltham,
MA)
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Family
ID: |
26694506 |
Appl.
No.: |
05/271,014 |
Filed: |
July 12, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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21282 |
Mar 20, 1970 |
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Current U.S.
Class: |
204/298.04;
219/121.15; 219/121.26; 219/121.33; 250/492.2 |
Current CPC
Class: |
H01J
37/3178 (20130101); C23C 14/221 (20130101) |
Current International
Class: |
C23C
14/22 (20060101); H01J 37/317 (20060101); C23c
015/00 (); C23c 011/00 (); B23k 015/00 () |
Field of
Search: |
;204/298 ;118/49.1,49.5
;117/93.3,93.1GD ;219/121EB |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mack; John H.
Assistant Examiner: Valentine; D. R.
Attorney, Agent or Firm: Birch; Richard J.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application is a continuation application of my previously
filed application, Ser. No. 21,282 filed Mar. 20, 1970 now
abandoned for FILM DEPOSITION.
Claims
What is claimed is:
1. A film deposition apparatus for depositing a film on a substrate
comprising:
a. a deposition chamber having means for containing the
substrate;
b. a source of deposition atoms to be deposited on the substrate,
said source of atoms being located within said deposition
chamber;
c. glow discharge ion source means for producing an energetic beam
of gaseous ions, which may be of the same material to be
deposited;
d. means disposed between said ion source and said deposition
chamber for producing a pressure differential between the ion
source and the deposition chamber; and,
e. means for directing said energetic beam of ions from the ion
source to impinge upon the substrate, further wherein said
energetic beam of ions and said source of deposition atoms are
positioned with respect to each other and with respect to the
substrate to provide for concurrent impingement of said ions and
said atoms upon the substrate.
2. A film deposition apparatus as set forth in claim 1 wherein said
source of ions includes ions of an inert gas.
3. A film deposition apparatus as set forth in claim 2 wherein said
inert gas includes argon.
4. A film deposition apparatus as set forth in claim 1 wherein said
source of deposition atoms includes silicon atoms.
5. Film deposition apparatus for depositing a film on a substrate
comprising:
a. a deposition chamber having means for containing a base
substrate;
b. a second chamber and means for maintaining at least one gas
within said second chamber;
c. at least two spaced electrodes positioned within said second
chamber with at least one of said electrodes being at least partly
formed of the material which is to be deposited;
d. means for establishing a sufficient electrical potential between
said spaced electrodes to cause a glow discharge therebetween which
releases atoms of the material which is to be deposited from said
electrode at least partly formed of said material and ionizes said
released deposition material atoms to form ions thereof;
e. means disposed between said second chamber and said deposition
chamber for producing a pressure differential between said second
chamber and said deposition chamber;
f. extraction electrode means positioned within said deposition
chamber for extracting the ions from said second chamber into said
deposition chamber and through an aperture in the extraction
electrode means;
g. accelerating means for causing at least some of said extracted
ions to impinge upon said substrate thereby depositing a film on
the substrate; and,
h. means for establishing an axial magnetic field between said
second chamber and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture.
6. The apparatus of claim 5 further characterized by means for
applying an electrical potential between at least one of said
electrodes and the base substrate contained within said base
substrate containing means.
7. The apparatus of claim 5 wherein said means for producing a
pressure differential includes means for maintaining said second
chamber at a higher pressure than said deposition chamber.
8. The apparatus of claim 5 wherein said ions are carbon ions and
said film is a film of carbon having diamond-like
characteristics.
9. The apparatus of claim 5 wherein said ions are carbon ions and
said film is a carbon film having a high index of refraction, high
electrical resistivity, transparency in the visual range, a high
dielectric constant and the ability to scratch glass.
10. The apparatus of claim 5 wherein said means for producing a
pressure differential comprises constrictor electrode means
directly separating said second chamber from said deposition
chamber and having an aperture disposed therein through which said
ions flow from said second chamber into said deposition
chamber.
11. An apparatus for depositing a relatively thin film upon a base
substrate material comprising:
a. a source of energetic ions, at least some of said ions being of
a normally solid deposition material;
b. a deposition chamber having means for containing a base
substrate;
c. constrictor electrode means positioned between said source of
ions and said deposition chamber and having an aperture disposed
therein through which said ions flow from said source of ions into
said deposition chamber;
d. extraction electrode means positioned between said constrictor
electrode means and said means for containing the base substrate
and having an aperture therein through which said ions flow; and,
means for establishing an axial magnetic field between said source
of energetic ions and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture; and
e. means for applying an electrical potential between said source
of energetic ions and the base substrate as contained within the
deposition chamber wherein said electrical potential is an AC
voltage.
12. An apparatus for depositing a relatively thin film upon a base
substrate material comprising:
a. a source of energetic ions, at least some of said ions being of
a normally solid deposition material;
b. a deposition chamber having means for containing a base
substrate;
c. constrictor electrode means positioned between said source of
ions and said deposition chamber and having an aperture disposed
therein through which said ions flow from said source of ions into
said deposition chamber wherein said constrictor electrode means
aperture is lined with a material which is the same as the
deposition material; and,
d. extraction electrode means positioned between said constrictor
electrode means and said means for containing the base substrate
and having an aperture therein through which said ions flow; and,
means for establishing an axial magnetic field between said source
of energetic ions and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture.
13. An apparatus for depositing a relatively thin film upon a base
substrate material comprising:
a. a source of energetic ions, at least some of said ions being of
a normally solid deposition material;
b. a deposition chamber having means for containing a base
substrate;
c. constrictor electrode means positioned between said source of
ions and said deposition chamber and having an aperture disposed
therein through which said ions flow from said source of ions into
said deposition chamber; and,
d. extraction electrode means positioned between said constrictor
electrode means and said means for containing the base substrate
and having an aperture therein through which said ions flow wherein
said extraction electrode means aperture is lined with a material
which is the same as the deposition material; and, means for
establishing an axial magnetic field between said source of
energetic ions and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture.
14. An apparatus for depositing a relatively thin film upon a base
substrate material comprising:
a. a source of energetic ions, at least some of said ions being of
a normally solid deposition material;
b. a deposition chamber having means for containing a base
substrate;
c. constrictor electrode means positioned between said source of
ions and said deposition chamber and having an aperture disposed
therein through which said ions flow from said source of ions into
said deposition chamber wherein said constrictor electrode means
aperture is lined with a material which, is the same as the
deposition material; and,
d. an extraction electrode means positioned between said
constrictor electrode means and said means for containing the base
substrate and having an aperture therein through which said ions
flow wherein said extraction electrode means aperture is lined with
a material which is the same as the deposition material; and, means
for establishing an axial magnetic field between said source of
energetic ions and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture.
15. Film deposition apparatus for depositing a film on a substrate
comprising:
a. a deposition chamber having means for containing a base
substrate;
b. a second chamber and means for maintaining at least one gas
within said second chamber;
c. at least two spaced electrodes positioned within said second
chamber with at least one of said electrodes being at least partly
formed of the material which is to be deposited;
d. means for establishing a sufficient electrical potential between
said spaced electrodes to cause a glow discharge therebetween which
releases atoms of the material which is to be deposited from said
electrode at least partly formed of said material and ionizes said
released deposition material atoms to form ions thereof;
e. means disposed between said second chamber and said deposition
chamber for producing a pressure differential between said second
chamber and said deposition chamber;
f. extraction electrode means for extracting the ions from said
second chamber into said deposition chamber through an aperture in
the extraction electrode means wherein said extraction electrode
means aperture is lined with a material which is the same as the
material which is to be deposited;
g. accelerating means for causing at least some of said extracted
ions to impinge upon said substrate thereby depositing a film on
the substrate; and,
h. means for establishing an axial magnetic field between said
second chamber and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture.
16. Film deposition apparatus for depositing a film on a substrate
comprising:
a. a deposition chamber having means for containing a base
substrate;
b. a second chamber and means for maintaining at least one gas
within said second chamber;
c. at least two spaced electrodes positioned within said second
chamber with at least one of said electrodes being at least partly
formed of the material which is to be deposited,
d. means for establishing a sufficient electrical potential between
said spaced electrodes to cause a glow discharge therebetween which
releases atoms of the material which is to be deposited from said
electrode at least partly formed of said material and which ionizes
said released deposition material atoms to form ions thereof;
e. means for producing a pressure differential between said second
chamber and said deposition chamber comprising constrictor
electrode means positioned between said second chamber and said
deposition chamber and having an aperture disposed therein through
which said ions flow from said second chamber into said deposition
chamber, said constrictor means aperture being lined with a
material which is the same as the material which is to be
deposited;
f. extraction electrode means for extracting the ions from said
second chamber into said deposition chamber through an aperture in
the extraction electrode means;
g. accelerating means for causing at least some of said extracted
ions to impinge upon said substrate thereby depositing a film on
the substrate; and,
h. means for establishing an axial magnetic field between said
second chamber and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture.
17. Film deposition apparatus for depositing a film on a substrate
comprising:
a. a deposition chamber having means for containing a base
substrate;
b. a second chamber and means for maintaining at least one gas
within said second chamber;
c. at least two spaced electrodes positioned within said second
chamber with at least one of said electrodes being at least partly
formed of the material which is to be deposited;
d. means for establishing a sufficient electrical potential between
said spaced electrodes to cause a glow discharge therebetween which
releases atoms of the material which is to be deposited from said
electrode at least partly formed of said material and which ionizes
said released deposition material atoms to form ions thereof;
e. means for producing a pressure differential between said second
chamber and said deposition chamber comprising constrictor
electrode means positioned between said second chamber and said
deposition chamber and having an aperture disposed therein through
which said ions flow from said second chamber into said deposition
chamber, said constrictor means aperture being lined with a
material which is the same as the material which is to be
deposited;
f. extraction electrode means for extracting the ions from said
second chamber into said deposition chamber through an aperture in
the extraction electrode means wherein said extraction electrode
means aperture is lined with a material which is the same as the
material which is to be deposited;
g. accelerating means for causing at least some of said extracted
ions to impinge upon said substrate thereby depositing a film on
the substrate; and,
h. means for establishing an axial magnetic field between said
second chamber and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture.
18. Film deposition apparatus for depositing a film on a substrate
comprising:
a. a deposition chamber having means for containing a base
substrate;
b. a second chamber and means for maintaining at least one gas
within said second chamber;
c. at least two spaced electrodes positioned within said second
chamber with at least one of said electrodes being at least partly
formed of the material which is to be deposited;
d. means for establishing a sufficient electrical potential between
said spaced electrodes to cause a glow discharge therebetween which
releases atoms of the material which is to be deposited from said
electrode at least partly formed of said material and ionizes said
released deposition material atoms to form ions thereof;
e. means disposed between said second chamber and said deposition
chamber for producing a pressure differential between said second
chamber and said deposition chamber;
f. extraction electrode means for extracting the ions from said
second chamber into said deposition chamber through an aperture in
the extraction electrode means;
g. accelerating means for causing at least some of said extracted
ions to impinge upon said substrate thereby depositing a film on
the substrate;
h. means for establishing an axial magnetic field between said
second chamber and said deposition chamber with the axis of the
magnetic field being substantially parallel to the axis of said
extraction electrode means aperture; and,
i. means for applying an electrical potential between at least one
of said electrodes and the base substrate contained within said
base substrate containing means, wherein said electrical potential
is an AC voltage.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a method and apparatus for
providing improved thin film deposition.
There have been numerous techniques employed for depositing thin
film, most of which involve the use of a substrate, which is
elevated to or maintained at a relatively high temperature. This
high substrate temperature has been considered necessary during the
deposition of the thin film for the purpose of increasing the
mobility of the atoms being deposited. However, this high
temperature substrate has certain problems associated with it. For
example, one disadvantage of vapor deposition upon a hot substrate
is that the impurities are caused to diffuse out from the substrate
and thereby affect the composition of the thin film that is being
deposited. Further, the excess temperatures cause a poor definition
at the junction between the film and the base substrate
material.
It is known that the necessary substrate atom mobility is obtained
by heating the incident ions that are to be deposited on the
substrate surface rather than the substrate itself. The apparatus
of the present invention takes this fact into account and permits
less heating of the substrate by isolating the substrate within a
separate chamber adjacent to the plasma ion source chamber.
Further, the apparatus is designed to control the energy of
impinging ions by appropriate biasing means coupled to the
substrate material.
It is an object of the present invention, therefore, to provide an
improved method and means for the deposition of thin films.
It is another object of the present invention to provide film
deposition apparatus wherein the substrate can be maintained at a
relatively low temperature.
A further object of this invention is to provide a method for
fabricating a thin film-substrate structure wherein the film can be
deposited at a high rate and in a controllable manner.
Another object of the present invention is to provide a thin film
upon a base substrate wherein there has been little or no impurity
diffusion from the substrate affecting the thin film deposited
thereon.
Still another object of the present invention is to provide a thin
film-substrate structure wherein the junction between the two
substances is well defined.
Other objects of the present invention will become apparent upon
reading the detailed description in conjunction with the drawings
and appended claims.
SUMMARY OF THE INVENTION
One embodiment of the apparatus of the present invention provides a
means by which the thin film is formed on a substrate by ionizing
and electrostatically accelerating a beam of atomic particles of a
material which is to be deposited on the substrate as a thin film.
A plasma ion source acts as a such source of atoms of the material
to be deposited. An electrical discharge occurs within this source
of ions, and the desired material is converted into a plasma form
with the ions to be deposited in a mixture with high energy
electrons. An axial magnetic field may be used to constrain the
orbits of the electrons and increase their likelihood of ionizing
atoms of the material under consideration. This magnetic field
permits the electrical discharge to operate at a lower gas pressure
than could be used without the magnetic field. Thus, in the source
discharge chamber, there is a plasma which contains a large
concentration of ions of the species that are to be subsequently
deposited.
A plasma discharge from this plasma ion source is generated into a
vacuum deposition chamber where the substrate material is located.
This can be accomplished by locating an extraction electrode in the
vacuum deposition chamber and by the use of a constrictor means
separating the higher pressure plasma ion chamber from the lower
pressure vacuum deposition chamber. The ions are extracted through
an aperture in the constrictor by means of the applied electric
field which maintains a discharge between the plasma source, which
functions as a cathode, and the extraction electrode, which is
situated in the vacuum deposition chamber. The purpose of the
constrictor means is to isolate the vacuum deposition chamber from
the higher pressures present in the plasma ion chamber while the
extractor electrode pulls the positive ions within the plasma
source toward the target substrate. It is often desirable to
surround the constrictor aperture with the same material as that to
be deposited on the substrate.
In another embodiment of the invention the accelerated beam may be
of an inert gas and the ions to be deposited may be supplied by an
auxilliary source within the deposition chamber. The beam provides
the energy necessary to deposit the ions from the source which
co-impinge with the ion beam.
BRIEF DESCRIPTION OF THE DRAWINGS
These and other objects and advantages of the present invention
will be more clearly understood when considered in conjunction with
the accompanying drawings in which:
FIG. 1 is a cross-sectional diagram of one embodiment of the
deposition system according to the invention.
FIG. 2 is a cross-sectional view of part of another embodiment of
the deposition system similar to that shown in FIG. 1.
DETAILED DESCRIPTION
As hereinbefore mentioned, the present invention permits the
deposition of improved thin films by means of an ion beam source
used in conjunction with a vacuum deposition chamber. FIG. 1 shows
an embodiment for practicing the present invention. In one
particular system, a silicon film 21 is deposited on a single
crystal silicon substrate 22. The film 21 is shown in an
exaggerated thickness in FIG. 1.
Plasma ion source 10 generally includes chamber structure 11 having
vacuum line 13 and gas input line 12 connected thereto. Vacuum line
13 connects to a vacuum pump (not shown) which controls the
pressure in source 10. Also included in ion source 10 are silicon
electrodes 14 and 15, which connect externally to power supply 34
and resistor 38. With an electrical discharge taking place within
plasma ion source 10, the material which is silicon in this
particular case, is introduced into a plasma formed by the high
energy electrons. A magnetic field set up by magnetic coil 30
influences the formation of the ions within plasma ion source 10 by
constraining the orbits of the electrons and increasaing the
likelihood of ionizing atoms of silicon. This external magnetic
field permits the electrical discharge to operate at lower gas
pressure than could be used without the magnetic field.
The generation of an ionized plasma usually can occur through a
neutral gas such as argon, hydrogen, or helium, or through a more
active gas, such as nitrogen or oxygen or a mixture thereof,
introduced via line 12. The ions produced in this source deposition
chamber in turn bombard the cathode (electrodes 14 and 15) and
sputter or vaporize atoms of material into a discharge space where
they can be ionized. Thus, in the plasma ion source 10, there is
produced a plasma which contains large concentrations of ions of
the species that one wishes to deposit upon substrate 22.
Many times it is desirous to obtain mixtures of ions, such as
aluminum and oxygen, silicon and oxygen, or silicon and nitrogen,
for the deposition of insulating layers, such as aluminum oxide,
silicon dioxide, or silicon nitride. There are generally two
different approaches. One approach is to use electrode material
fabricated of silicon or aluminum and to introduce the necessary
oxygen or nitrogen gas into the plasma by means of the appropriate
gas feed line 12 for the maintenance of this ion plasma. There may
be difficulty, however, with this approach since adjusting the
partial pressures of the oxygen or nitrogen in order to obtain the
correct film stochiometry appears to be difficult. An alternative
way, which appears to be advantageous is to fabricate the electrode
material of the necessary materials, such as silicon oxide or
nitride. One then introduces the correct mixture into the plasma
source by operating a glow discharge between the two electrodes in
the ion source chamber 10. Consideration of other types of films is
taken up later after a discussion of the operation of the
deposition chamber.
The next occurence in the operation of the apparatus is the
extraction of the plasma discharge from the plasma ion source 10
into vacuum deposition chamber 20 where the substrate 22 is
located. To facilitate this, an anode extraction electrode 24 is
located in deposition chamber 20 along with a constrictor electrode
26. The purpose of constrictor electrode 26 is basically to
separate the higher pressure sputtering source chamber 10 from the
lower pressure film deposition chamber 20. The ions are extracted
through the constrictor electrode 26 by means of the externally
applied electric field, which maintains a discharge between the
plasma source 10, operated as a cathode, and the extractor anode
24, located in deposition chamber 20. Anode supply 36 facilitates
the foregoing by biasing the anode positively with reference to the
source 10. The external electric field generated by power supply 36
is oriented along the external magnetic field caused by magnetic
coil 30 so that the plasma is extracted along magnetic field lines.
This serves to maintain the plasma in a constricted mode so that it
is able to pass through the aperture 26A in constrictor electrode
26 more efficiently. Anode electrode 24 acts to extract electrons
from the plasma source, and the electric field generated by the
extracted electron pulls the positive ions from plasma source 10
along with them. The anode 24 has an aperture 24A in it located
along the axis determined by the magnetic field produced by
magnetic coil 30, and this in turn serves to maintain the plasma
constriction and permits a large fraction of the extracted positive
ions to pass through the anode aperture, subsequently impinging on
substrate 22. The apertures in the electrodes 24 and 26 permits
differential pumping to occur, thereby maintaining a good vacuum
(about 10.sup..sup.-6 Torr) in deposition chamber 20 (provided via
vacuum line 29), while somewhat higher pressure is maintained in
plasma ion source 10. It is often desirable to surround the
apertures in electrodes 24 and 26 with the same material as that to
be deposited on the substrate. Note that the magnetic field serves
three purposes: In the plasma ion source it permits the source to
operate at lower pressures; it aids in constricting the plasma
through the constrictor electrode; and it helps to maintain the
plasma in a constricted path on its way to the substrate.
The constrictor electrode 26 may be left essentially electrically
floating through a high impedance resistor 46 to an appropriate
potential such as the one determined by the resistors 40 and 42.
For the embodiment of FIG. 1, this potential is intermediate
between the potential of the cathode in source 10 and the anode in
chamber 20. Similarly, the insulating shield 17, positioned between
electrodes 14 and 26, may be left floating. Shield 17 minimizes the
tendency of the discharge to attach other than where desired. A
focusing electrode 19 can also be used between anode 24 and
substrate 22. Electrode 19 is shown connected to anode 24, but can
be connected to a separate biasing supply if desired thereby
controlling the final path of the ion beam.
The potential on substrate 22 relative to that of plasma ion source
10 and extractor anode 24 determines in large part of the kinetic
energy with which the positive ions impinge on substrate 22.
Reference is directed to substrate supply 50 which connects via the
secondary winding of transformer 52 to substrate 22.
The combination of the DC power supply 50 with the by-pass
capacitor 51 permits a DC bias to be applied to the substrate while
maintaining the power supply at a low impedance relative to ground.
An AC or RF voltage is superimposed on the DC bias voltage by means
of oscillator 54 and transformer 52. The use of the transformer
permits the application of an additional AC voltage without
modifying the DC bias voltage provided by the DC supply 50.
As previously mentioned, the axial magnetic field helps maintain
the ion beam in a columnated mode after it is extracted through the
aperture in anode 24 and minimizes space charge spreading. In this
way, one can achieve a higher deposition rate than would otherwise
be expected in the absence of a magnetic columnating field.
There are some modifications of the deposition system of the
present invention that will enable the deposition of either
conducting films on insulating substrates or depositing insulating
films on conducting or insulating substrates. The necessity for
these modifications relates to the fact that when depositing an
insulating substrate of film it is more difficult to control the
energy of the ions impinging on the substrate 22, and therefore is
necessary to prevent the surface from building up to a positively
charged repelling condition. In the present invention, as shown in
FIG. 1, this has been remedied by using an rf power supply 54.
The AC or rf supply, which connects via transformer 52 to substrate
22, operates at a high frequency (at about 15Kc or 13 megacycles,
for example) and is used to alternately bias the substrate surface
positive and negative by using the displacement current that flow
through the insulating film or substrate. The alternating positive
and negative potential applied to the substrate is used to extract
positive ions and electrons from the plasma so that the net current
to the surface is zero; but at the same time, during portions of
the cycles, positive ions can be attracted to the surface. The rf
amplitude applied to the substrate determines the energy of the
positive ions attracted to the surface and can be used to control
the deposition energy.
FIG. 2 shows a partial view of the system of FIG. 1 which has been
adapted for practising another embodiment of the invention. A
vaporizing source 62 and associated power source 60 are added to
the configuration of FIG. 1. Source 62 is located in chamber 20
near to substrate 22. In practising this embodiment of the
invention, the introduction of energy into the surface atoms of the
vaporizing source is primarily to effect vaporization, with the
energy to effect deposition on the substrate being primarily
supplied by an energetic beam of gaseous ions. This can be
accomplished by using an argon beam, for example, generated from
the plasma source in conjunction with a source of atoms to be
deposited and located in chamber 20. Thus, an energetic beam of
gaseous ions, such as argon or another inert gas, coimpinge on the
substrate surface with atoms from source 62. Within one or two
collisions the high kinetic energy of the argon ion beam is
transferred to the lower energy neutral film atoms to be deposited
on the substrate surface and gives them the necessary mobility so
that they can nucleate and form an improved film. For example, with
the embodiment of FIG. 2 one could deposit silicon films on a
substrate by means of thermal vaporization of silicon from source
62, concurrently with impingement on the surface of a high energy
argon beam, for example. This beam should provide the necessary
kinetic energy to transfer to the silicon atoms by means of
argon-silicon collisions on the surface.
Source 62 is shown schematically but can be any one of various
types of sources of atoms. For example, source 62 may be a
sputtering source, a crucible-type vaporization source or even a
resistively heated ribbon.
There are other ways that a deposition material can be introduced
into the source plasma. One is by sputtering of material from the
electrodes 14 and 15 of FIG. 1. Thus, a silicon electrode would be
used for the deposition of silicon films, while a carbon electrode
would be used for the deposition of carbon films. Metallic
electrodes, of course, can be used for the deposition of metallic
films. An alternatively way of introducing the deposition material
into the plasma at a much faster rate is by the introduction of the
deposition material in the vapor or gaseous form or as a component
of a gaseous additive material and the subsequent decomposition of
the gaseous additive material into the appropriate ions by means of
the energy of the plasma. This is a form of plasma pyrolysis. The
use of a hydrocarbon gas, for example, in chamber 10 can permit the
deposition of carbon films on the substrate since the ions exiting
from the ion source will consist of carbon ions and of hydrogen
ions. The hydrogen ions incident on the substrate will help to
remove residual oxygen ions that may be on the substrate and thus,
enhance the subsequent deposition of the carbon ions.
The use of this ion beam deposition technique has shown, for
example, that insulating films of carbon can be deposited with
material properties very similar to that of carbon in the diamond
form. The observed points of similarity between the ion beam
deposited carbon form and a diamond-like material consists of the
following: 1) high index of refraction, 2) high electrical
resistivity, 3) transparency in the visible range, 4) high
di-electric constant, 5) ability to scratch glass. These insulating
carbon films also show a high resistance to hydrofluoric acid
etching. One advantage of insulating carbon films is that such
films are quite resistant to sodium ion diffusion through these
films which occurs at elevated temperatures. This is in agreement
with what would be expected for a densely packed diamond-like
carbon structure which has densely packed grain boundaries and
resists the motion of relatively large alkali ions. Stable
insulating and semiconductor carbon films can therefore be produced
by this technique and it is expected that the techniques of the
invention will find widespread use in the semi-conductor field.
Mixtures of gases or vapors can also be used to deposit various
film compounds. For example, tungsten and carbon mixtures or
compounds thereof can be deposited in the tungsten carbide form by
using either tungsten and carbon electrodes or, for more rapid
deposition by introducing a tungsten compound in the gaseous form
and a hydrocarbon compound in the gaseous form into the plasma ion
source region.
Apparatus similar to that shown in FIg. 1 can be used to deposit a
carbon-diamond film. The electrodes 14 and 15 may be made of
carbon, and the mixture gas may be methane for example (a
hydro-carbon gas). The carbon ions are introduced into a plasma
from ion source 10 by sputtering from the electrodes themselves or
from the gas.
By means of the acceleration potential applied to the substrate, it
is possible to have the ions come in with a moderately high kinetic
energy (about 100 electron volts for example). As a result of this
large kinetic energy of the incident ions, these ions when they
strike the deposition surface retain a very high surface mobility
and can move about to nucleate into a single crystal structure. At
the same time, the carbon atoms already on the deposition surface,
in the process of scattering the incident ions themselves, will
pick up kinetic energy and become mobile. Thus, the incident ion
and the first few surface monolayers of the deposition surface are
at a relatively high energy compared to that of the basic
substrate. These surface atoms retain enough energy so that they
can nucleate into a diamond-like single crystal structure.
Therefore, the apparatus of the present invention can be used to
deposit various types of films or different substrates and does so
by an ion beam technique, wherein the degree and uniformity of
deposition are controlled. The apparatus can be also be implemented
for use with a vapor source, which is uaually located in the
deposition chamber. Such an arrangement has also been used to
supplement the deposition from the ion beam. In other words a beam
containing silicon ions could be used with a silicon vapor source.
Another film so deposited was molybdenum.
Another feature of the invention is that relatively small layers of
diamond-like carbon can be deposited. Usually for carbon to form
into a diamond-like crystallographic structure it is necessary that
the carbon atoms be in a high temperature, high pressure,
environment for a sufficiently long time so that the
crystallization into a diamond form can occur. The technique used
herein employs an energetic ion beam that does not require high
pressures since only a small portion of the carbon is heated to a
high temperature at one time.
Having described some of the features, objects and advantages of
the invention, other modifications of and departures from the
embodiments disclosed herein will become apparent to those skilled
in the art of which are contemplated as falling within the spirit
and scope of the invention and are to be limited solely by the
appended claims.
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