U.S. patent number 3,906,892 [Application Number 05/417,842] was granted by the patent office on 1975-09-23 for plasma deposition of thin layers of substrated or the like.
This patent grant is currently assigned to Compagnie Industrielle des Telecommunications Cit-Alcatel. Invention is credited to Jean L. Van Cakenberghe.
United States Patent |
3,906,892 |
Van Cakenberghe |
September 23, 1975 |
Plasma deposition of thin layers of substrated or the like
Abstract
Device for producing thin layers of mineral substances
comprising a vacuum container and a cavity whose walls consist of
the substance to be deposited, and having an opening in one of its
faces. An electromagnetic field is generated in the cavity to form
a plasma.
Inventors: |
Van Cakenberghe; Jean L. (Mons,
BE) |
Assignee: |
Compagnie Industrielle des
Telecommunications Cit-Alcatel (Paris, FR)
|
Family
ID: |
25647552 |
Appl.
No.: |
05/417,842 |
Filed: |
November 21, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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246019 |
Apr 20, 1972 |
3801355 |
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Foreign Application Priority Data
Current U.S.
Class: |
118/723VE;
118/726; 118/723IR; 313/231.31; 219/651 |
Current CPC
Class: |
H01J
37/342 (20130101); C23C 14/3471 (20130101); H01J
37/34 (20130101); H01J 37/32009 (20130101); C23C
14/228 (20130101) |
Current International
Class: |
H01J
37/32 (20060101); H01J 37/34 (20060101); C23C
14/34 (20060101); C23C 013/12 () |
Field of
Search: |
;118/49.1,49.5
;117/93.1R,93.1GD,93.1PF ;219/10.49,121P ;313/231.3,362 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Kaplan; Morris
Attorney, Agent or Firm: Sughrue, Rothwell, Mion, Zinn and
Macpeak
Parent Case Text
This is a division of application Ser. No. 246,019, filed Apr. 20,
1972 now U.S. Pat. No. 3,801,355.
Claims
What is claimed is:
1. A plasma deposition device comprising:
a vacuum container formed of an insulating material,
means for maintaining said container at high vacuum,
a substrate support within said container,
a substrate carried thereby,
means defining a cavity lined on its inside with the substance to
be deposited and having an opening therein adjacent to the
substrate, the wall of said cavity being formed of an insulating
material,
a high-frequency excitation means for generating an electromagnetic
field within said cavity, and
means for injecting into said cavity a gas at a pre-determined
pressure for promoting the formation of a plasma in the cavity in
the presence of the electromagnetic field.
2. The device according to claim 1, wherein: said cavity is of
generally cylindrical shape and defined by the cylindrical wall
provided on its inside with longitudinal ribs.
3. The device according to claim 1, further comprising: an
electrode in the cavity; said electrode being connected to an
electrical potential supply producing a spark to promote the
starting up of the plasma.
4. The device according to claim 2, wherein: said high-frequency
excitation means comprises an induction winding surrounding the
insulating container at the level of the cavity and means
connecting said induction winding to a high-frequency voltage
supply.
5. The device according to claim 3 wherein: said high-frequency
excitation means comprises an induction winding within the vacuum
container and surrounding said cavity which is lined on its inside
with the substance to be deposited.
Description
BACKGROUND OF THE INVENTION
1. field of the Invention
The present invention concerns a method enabling thin layers of
mineral substances to be deposited, as well as the device for
implementing the method.
2. Description of the Prior Art
Thin layers are usually produced by evaporation in a vacuum or by a
method called reactive projection. The first method can be used
only in cases where the substance to be deposited decomposes when
it is brought to a high temperature in a vacuum, into elements
having very different vapor pressures and the most volatile of
which can have a vapor pressure which can be measured at the
depositing temperature. Such is the case, more particularly, with
the majority of oxides, certain sulphides as well as of gallum
arsenide and gallium phosphide.
The second method mentioned above consists in causing the
evaporation of the material to be deposited in an electrical
discharge at low pressure, between two electrodes one of which
consists of the material to be deposited or the metallic component
of that material, the other component then being contained in
gaseous phase. The material to be deposited is deposited in the
form of a thin layer on a substrate, arranged at a few centimeters
from that electrode, which can be in contact or otherwise with the
second electrode. In the case where a thin layer of zinc oxide, for
example, is to be deposited, the first electrode can consist either
of zinc oxide or of metallic zinc with a pure gaseous oxygen
atmosphere or an atmosphere consisting of oxygen mixed with a
neutral gas such as argon.
This second method can certainly be used for the above-mentioned
substances, but it is unsuitable for semi-conductor materials, for
the thin layers thus obtained consist of very small micro-crystals
so that certain electrical properties such as the mobility and
service life of the charge carriers are subjected to detrimental
influence. Moreover, this second method is characterized by a
relatively considerable dissipation of energy and a relatively low
depositing speed which can, moreover, vary within wide limits.
The object of the invention is therefore a method for depositing
thin layers which does not have the above-metnioned
disadvantages.
It also provides a device for producing thin layers, either on
insulating supports or on electrically conductive or
semi-conductive supports.
Lastly, it provides a device enabling thin layers of material
having electrical, semi-conductive, piezo-electrical, magnetic
and/or optical properties, as well as thin layers of material
having a high melting point such as refractory materials to be
produced.
SUMMARY OF THE INVENTION
The method enabling thin layers to be deposited in a vacuum on the
surface of a substrate arranged adjacent to the opening of a cavity
in which a gas is injected at a pre-determined pressure is
characterized in that a plasma is formed inside the cavity
previously lined on the inside with the substance to be
deposited.
The method also enables layers to be deposited on the surface of a
substrate when the cavity consists directly of the substance to be
deposited.
The device implementing the method according to the invention is
characterized in that it comprises, on the one hand, a
high-frequency excitation means generating an electromagnetic
field, and, on the other hand, inside a vacuum container, at least
a substrate support, a substrate, a cavity lined on the inside with
the substance to be deposited and having an opening adjacent to the
substrate and a means for injecting a gas at a pre-determined
pressure into said cavity, promoting the forming of a plasma within
said cavity where there is the electromagnetic field.
The device implementing the method according to the invention is
also characterized in that the support for the substrate comprises
an electrical heating means enabling the substrate to be brought to
a pre-determined temperature.
In a particular embodiment, the device according to the invention
is characterized in that it comprises, moreover, an electrode in
the cavity, this electrode being connected to an appropriate
electrical potential so as to produce a spark suitable for causing
the starting up of the plasma.
The cavity has, to great advantage, a cylindrical shape, the
cylindrical wall being provided, on its inside, with longitudinal
ribs. Moreover, the insulating container may, to great advantage,
be cooled.
The invention will be described herebelow with reference to the
accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view of an embodiment of the
device according to the invention.
FIG. 2 is a transversal sectional view of an embodiment of the
cavity having a great advantage, used in the device according to
the invention.
FIG. 3 is a longitudinal sectional view of another embodiment of
the device according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to FIG. 1, a cylindrical cavity 2, whose wall consists
of, or is lined on the inside with the substance to be deposited,
is arranged inside the tube 1, made of quartz or ceramic material,
for example. One of the transversal faces of the cavity is provided
with an opening 3. The high-frequency excitation device consists,
here, of an induction winding 4 surrounding the tube 1 at the level
of the cavity 2. This winding is connected to a high frequency
voltage supply 5. A substrate support 6 is placed so as to have a
substrate 7 adjacent to the opening 3 in the cavity 2. The
electrical heating device 8 enables the substrate 7 to be brought
to a required temperature. In the embodiment shown by way of an
example, the substrate support 6 is arranged so as to be able to
pivot about an axis 9 in order to bring several substrates
successively before the opening 3.
As shown in FIG. 2, the cylindrical wall of the cavity comprises,
on the inside, longitudinal ribs 10 so as to reduce the
transmission of heat through the wall.
The operation of this device is as follows:
A gas is injected into the cavity 2 through the duct 11 so as to
produce an atmosphere at a pre-determined pressure therein. When a
high frequency current through the induction winding 4, the
electromagnetic field it induces inside the cavity forms a plasma
thereon. The discharge which takes place in the plasma causes a
great increase in the temperature of the inside wall of the cavity,
this producing a distilling of the inner wall and the establishing
of a vapor pressure of the substance to be deposited. This
distilled substance escapes through the opening 3 and is deposited
on the substrate 7. In the arrangement according to the invention,
the plasma is confined inside the cavity.
It has been noted that the thin layers thus obtained consist of
crystals which are appreciably larger and better formed than those
obtained by reactive projection. It has also been noted that the
crystalline direction of the thin layers is perfect.
In this device according to the invention, the walls of the cavity
constitute a thermal screen. In certain embodiments, the latter
have been reinforced by arranging a second cavity round the first.
This screen effect enables the energy dissipated in the plasma to
be increased so as to bring the inside surface of the cavity to a
very high temperature in the order of several thousands of degrees
without danger for the insulating tube 1.
In the particular embodiment shown in FIG. 1, the device comprises,
moreover, an electrode 12 in the opening 3 formed in the cavity 2.
This electrode 12 is connected to an appropriate electrical
potential supply V so as to produce a spark suitable for promoting
the starting up of the plasma.
In a varied version of an embodiment, the tube 1 is surrounded by a
cooling funnel. It is thus possible to obtain high evaporating
speeds and relatively high vapor pressures inside the cavity, this
promoting molecular combination.
In a particular example of an embodiment, a cylindrical cavity
consisting of zinc oxide, 50 mm in diameter and 60 mm in height,
has been placed in a quartz tube. An induction winding consisting
of three turns made of copper tubing 6 mm in diameter, connected to
a high-frequency power generator, has been arranged about the tube,
on the level of the cavity.
After having produced a vacuum in the order of 10.sup..sup.-5 mm Hg
in the tube 1, and after having heated the substrate to a
temperature of 200.degree.C, oxygen has been injected in the cavity
in order to produce a pressure in the order of 5.10.sup..sup.-2 mm
Hg therein. The pressure in the container in which the substrate is
placed is appreciably lower subsequent to the loss of head at the
outlet of the cavity.
After having started up the high-frequency generator so that it
supplies a power of 4 kw at 3 mc/s, the rated power is reached
after barely a few minutes, and the zinc oxide is then deposited on
the substrate in the form of a thin layer which has reached a
thickness of 0.5 micron in one minute.
According to another form of the invention, the induction means
implemented to generate the plasma inside the cavity is placed in
the vacuum about the cavity. Various precautions are taken in that
case to avoid the pollution of the substrate. This embodiment,
shown in FIG. 3, comprises a cylindrical cavity 20 placed in a
vacuum container shown in the figure only by its base 30. This
cavity 20 is lined inside with the material 21 to be sprayed, it
comprises, at its upper part, a central opening 22, and at its
lower part, a gas inlet 23. The lateral face 24 of that cylindrical
cavity 20 is surrounded by the turns 25 of an induction circuit 26,
fed by a HF supply, not shown, arranged outside the container. This
induction circuit 26 consists of a hollow conductor internally
cooled by a water circuit 27, 27'. The induction circuit is held in
position by an insulating base 28 fixed to the base 30 of the
container. The conductor forming the induction circuit is itself
lined with a layer of protective insulating material 29, made of
teflon, in a series of experiments, and of glass in another series
of measurements. A protective screen 31 made of insulating material
completes the protection of the substrate with respect to any
pollution caused by the metal forming the induction circuit. A seal
ring 32 made of refractory material which is a bad heat conductor
arranged round the opening 22 of the cavity 20 provides a poor heat
contact between the cavity 20 and the insulating screen 31 while
providing satisfactory sealing.
The embodiments described obviously have no limiting character,
and, needless to say, varied versions may easily be conceived by
the man in the art. The excitation of the plasma in the cavity has,
for example, also been obtained by means of a wave guide device.
The cavity has also been divided into fragments in certain cases,
so as to enable a penetration of the electromagnetic field in the
case of very conductive or refractory substances.
The applicant has also produced a device in which the cavity is
drilled with several openings so that several substrates are
covered simultaneously.
Moreover, the cavity has been divided into several compartments
without an appreciable reduction in the depositing speed having
been noticed.
It must be understood that the devices according to the invention
may be used to great advantage, for producing thin layers of
various substances: piezo-electric, semi-conductive, optical,
magnetic, insulating substances, materials having great dielectric
constancy, refractory materials or compounds thereof having a high
metling point.
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