Chemistry: electrical and wave energy – Apparatus – Coating – forming or etching by sputtering
Reexamination Certificate
1999-01-30
2001-04-10
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Apparatus
Coating, forming or etching by sputtering
C204S298160, C204S298190
Reexamination Certificate
active
06214183
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of ion-emission technique, particularly to an apparatus which combines in itself an ion-beam and magnetron-plasma source intended for cleaning, activation, polishing, etching, or thin-film coating of surfaces. The invention also relates to a method for sputtering conductive and nonconductive materials with the use of the aforementioned apparatus.
BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART
An ion source is a device that ionizes gas molecules and then, accelerates, focuses, and emits them as an ion beam. This beam is then used for various technical and technological purposes such as cleaning, activation, polishing, thin-film coating, or etching.
An example of an ion source is the so-called Kaufman ion source, also known as a Kaufman ion engine or an electron-bombardment ion source described in U.S. Pat. No. 4,684,848 issued to H. R. Kaufman in 1987.
This ion source consists of a discharge chamber, in which a plasma is formed, and an ion-optical system which generates and accelerates an ion beam to an appropriate level of energy. A working medium is supplied to the discharge chamber which contains a hot cathode that functions as a source of electrons and is used for firing and maintaining a gas discharge. The plasma, which is formed in the discharge chamber, acts as an emitter of ions and creates, in the vicinity of the ion-optical system, an ion-emitting surface. As a result, the ion-optical system extracts ions from the aforementioned ion-emitting surface, accelerates them to a required energy level, and forms an ion beam of a required configuration. Typically, aforementioned ion sources utilize two-grid or three-grid ion-optical systems.
A disadvantage of such a device is that it requires the use of ion accelerating grids and an ion beam of low intensity. Another disadvantage is that this apparatus is not suitable for operation with reactive gases.
Attempts have been made to provide ion sources with ion beams of higher intensity by holding the electrons in a closed space between a cathode and an anode where the electrons could be held. For example, U.S. Pat. No. 4,122,347 issued in 1978 to Kovalsky et al. describes an ion source with a closed-loop trajectory of electrons for ion-beam etching and deposition of thin films, wherein the ions are taken from the boundaries of a plasma formed in a gas-discharge chamber with a hot cathode. The ion beam is intensified by a flow of electrons which are held in crossed electrical and magnetic fields within the accelerating space and which compensate for the positive spatial charge of the ion beam.
A disadvantage of devices of such type is that they do not allow formation of ion beams of chemically-active substances because of the use of a hot cathode and because of strong localization of the plasma-formation zone. Other disadvantages of the aforementioned devices are short service life and high non-uniformity of ion beams.
U.S. Pat. No. 4,710,283 issued in 1997 to Singh et al. describes a coldcathode type ion source with crossed electric and magnetic fields for ionization of a working substance wherein entrapment of electrons and generation of the ion beam are performed with the use of a grid-like electrode. This source is advantageous in that it forms belt-like and tubular ion beams emitted in one or two opposite directions.
However, the ion source with a grid-like electrode of the type disclosed in U.S. Pat. No. 4,710,283 has a number of disadvantages consisting in that the grid-like electrode makes it difficult to produce an extended ion beam and in that the ion beam is additionally contaminated as a result of sputtering of the material from the surface of the grid-like electrode. Furthermore, with the lapse of time the grid-like electrode is deformed whereby the service life of the ion source as a whole is shortened.
Other publications (e.g., Kaufman H. R. et al. (End Hall Ion Source, J. Vac. Sci. Technol., Vol. 5, Jul/Aug., 1987, pp. 2081-2084; Wykoff C.A. et al., 50-cm Linear Gridless Source, Eighth International Vacuum Web Coating Conference, Nov. 6-8, 1994)) disclose an ion source that forms conical or belt-like ion beams in crossed electrical and magnetic fields. The device consists of a cathode, a hollow anode with a conical opening, a system for the supply of a working gas, a magnetic system, a source of electric supply, and a source of electrons with a hot cathode. A disadvantage of this device is that it requires the use of a source of electrons with a hot or hollow cathode and that it has electrons of low energy level in the zone of ionization of the working substance. These features create limitations for using chemically-active working substances. Furthermore, a ratio of the a cathodeanode distance to the Larmor radius is significantly greater than 1, and this decreases the energy of electrons in the charge gap, and hence, hinders ionization of the working substance. Configuration of the electrodes used in the ion beam of such sources leads to a significant divergence of the ion beam and degradation of the cathode material because of sputtering. As a result, the ion beam cannot be delivered to a distant object and is to a greater degree subject to contamination with the material of the electrode. In other words, the device described in the aforementioned literature is extremely limited in its capacity to create an extended uniform belt-like ion beam. Another disadvantage for target sputtering is a low energy of ions which does not allow effective sputtering of nonconductive, e.g., dielectric materials.
Russian Patent No. 2,030,807 issued in 1995 to M. Parfenyonok, et al. describes an ion source that comprises a magnetoconductive housing used as a cathode having an ion-emitting slit, an anode arranged in the housing symmetrically with respect to the emitting slit, a magnetomotance source, a working gas supply system, and a source of electric power supply.
FIGS. 1 and 2
schematically illustrate the aforementioned known ion source with a circular ion-beam emitting slit. More specifically,
FIG. 1
is a sectional side view of an ion-beam source with a circular ion-beam emitting slit, and
FIG. 2
is a sectional plan view along line II—II of FIG.
1
.
The ion source of
FIGS. 1 and 2
has a hollow cylindrical housing
40
made of a magnetoconductive material such as Armco steel (a type of a mild steel), which is used as a cathode. Cathode
40
has a cylindrical side wall
42
, a closed flat bottom
44
and a flat top side
46
with a circular ion emitting slit
52
.
A working gas supply hole
53
is formed in flat bottom
44
. Flat top side
46
functions as an accelerating electrode. Placed inside the interior of hollow cylindrical housing
40
between bottom
44
and top side
46
is a magnetic system in the form of a cylindrical permanent magnet
66
with poles N and S of opposite polarity. An N-pole faces flat top side
46
and S-pole faces bottom side
44
of the ion source. The purpose of a magnetic system
66
with a closed magnetic circuit formed by parts
66
,
40
,
42
, and
44
is to induce a magnetic field in ion emitting slit
52
. It is understood that this magnetic system is shown only as an example and that it can be formed in a manner described, e.g., in aforementioned U.S. Pat. No. 4,122,347. A circular annular-shaped anode
54
which is connected to a positive pole
56
a
of an electric power source
56
is arranged in the interior of housing
40
around magnet
66
and concentric thereto. Anode
54
is fixed inside housing
40
by means of a ring
48
made of a non-magnetic dielectric material such as ceramic. Anode
54
has a central opening
55
in which aforementioned permanent magnet
66
is installed with a gap between the outer surface of the magnet and the inner wall of opening
55
. A negative pole
56
b
of electric power source is connected to housing
40
which is grounded at GR.
Located above housing
40
of the ion source of
FIGS. 1 and 2
is a sealed vacuum chamber
57
which has an evacuation port
59
conn
Maishev Yuri
Ritter James
Shkolnik Alexander
Velikov Leonid
Advanced Ion Technology, Inc.
Cantelmo Gregg
Nguyen Nam
Zborosky IIya
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