Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Electron or ion source
Reexamination Certificate
2003-04-22
2004-11-02
Wells, Nikita (Department: 2881)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Electron or ion source
C250S42300F, C250S431000
Reexamination Certificate
active
06812648
ABSTRACT:
This invention relates to a method of cleaning an ion source, and/or to a corresponding apparatus/system. In certain example embodiments, both the anode and cathode of the ion source are negatively biased during at least part of a cleaning mode in order to clean the ion source.
BACKGROUND OF THE INVENTION
An ion source is a device that causes gas molecules to be ionized and then accelerates and emits the ionized gas molecules and/or atoms in a beam toward a substrate. Such an ion beam may be used for various purposes, including but not limited to cleaning a substrate, activation, polishing, etching, and/or deposition of thin film coatings/layer(s). Example ion sources are disclosed, for example, in U.S. Pat. Nos. 6,359,388; 6,037,717; 6,002,208; and 5,656,819, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1-2
illustrate a conventional ion source. In particular,
FIG. 1
is a side cross-sectional view of an ion beam source with an ion beam emitting slit defined in the cathode, and
FIG. 2
is a corresponding sectional plan view along section line II—II of FIG.
1
.
FIG. 3
is a sectional plan view similar to
FIG. 2
, for purposes of illustrating that the
FIG. 1
ion beam source may have an oval and/or racetrack-shaped ion beam emitting slit as opposed to a circular ion beam emitting slit. Any other suitable shape may also be used.
Referring to
FIGS. 1-3
, the ion source includes a hollow housing made of a magnetoconductive material such as steel, which is used as a cathode
5
. Cathode
5
includes cylindrical or oval side wall
7
, a closed or partially closed bottom wall
9
, and an approximately flat top wall
11
in which a circular or oval ion emitting slit and/or aperture
15
is defined. The bottom
9
and side wall(s)
7
of the cathode are optional. Ion emitting slit/aperture
15
includes an inner periphery as well as an outer periphery.
Deposit and/or maintenance gas supply aperture or hole(s)
21
is/are formed in bottom wall
9
. Flat top wall
11
functions as an accelerating electrode. A magnetic system including a cylindrical permanent magnet
23
with poles N and S of opposite polarity is placed inside the housing between bottom wall
9
and top wall
11
. The N-pole faces flat top wall
11
, while the S-pole faces bottom wall
9
. The purpose of the magnetic system with a closed magnetic circuit formed by the magnet
23
and cathode
5
is to induce a substantially transverse magnetic field (MF) in an area proximate ion emitting slit
15
. The ion source may be entirely or partially within wall
50
. In certain instances, wall
50
may entirely surround the source and substrate
45
, while in other instances the wall
50
may only partially surround the ion source and/or substrate.
A circular or oval shaped conductive anode
25
, electrically connected to the positive pole of electric power source
29
, is arranged so as to at least partially surround magnet
23
and be approximately concentric therewith. Anode
25
may be fixed inside the housing by way of insulative ring
31
(e.g., of ceramic). Anode
25
defines a central opening therein in which magnet
23
is located. The negative pole of electric power source
29
is connected to cathode
5
, so that the cathode is negative with respect to the anode.
Generally speaking, the anode
25
is generally biased positive by several thousand volts. Meanwhile, the cathode (the term “cathode” as used herein includes the inner and/or outer portions thereof) is generally held at, or close to, ground potential. This is the case during all aspects of source operation, including during a mode in which the source is being cleaned.
The conventional ion beam source of
FIGS. 1-3
is intended for the formation of a unilaterally directed tubular ion beam, flowing in the direction toward substrate
45
. Substrate
45
may or may not be biased in different instances. The ion beam emitted from the area of slit/aperture
15
is in the form of a circle in the
FIG. 2
embodiment and in the form of an oval (e.g., race-track) in the
FIG. 3
embodiment.
The conventional ion beam source of
FIGS. 1-3
operates as follows in a depositing mode when it is desired to ion beam deposit a layer(s) on substrate
45
. A vacuum chamber in which the substrate
45
and slit/aperture
15
are located is evacuated, and a depositing gas (e.g., a hydrocarbon gas such as acetylene, or the like) is fed into the interior of the source via aperture(s)
21
or in any other suitable manner. A maintenance gas (e.g., argon) may also be fed into the source in certain instances, along with the depositing gas. Power supply
29
is activated and an electric field is generated between anode
25
and cathode
5
, which accelerates electrons to high energy. Anode
25
is positively biased by several thousand volts, and cathode
5
is at ground potential or proximate thereto as shown in FIG.
1
. Electron collisions with the gas in or proximate aperture/slit
15
leads to ionization and a plasma is generated. “Plasma” herein means a cloud of gas including ions of a material to be accelerated toward substrate
45
. The plasma expands and fills (or at least partially fills) a region including slit/aperture
15
. An electric field is produced in slit
15
, oriented in the direction substantially perpendicular to the transverse magnetic field, which causes the ions to propagate toward substrate
45
. Electrons in the ion acceleration space in and/or proximate slit/aperture
15
are propelled by the known E x B drift in a closed loop path within the region of crossed electric and magnetic field lines proximate slit/aperture
15
. These circulating electrons contribute to ionization of the gas (the term “gas” as used herein means at least one gas), so that the zone of ionizing collisions extends beyond the electrical gap between the anode and cathode and includes the region proximate slit/aperture
15
on one and/or both sides of the cathode
5
.
For purposes of example, consider the situation where a silane and/or acetylene (C
2
H
2
) depositing gas is/are utilized by the ion source of
FIGS. 1-3
in a depositing mode. The silane and/or acetylene depositing gas passes through the gap between anode
25
and cathode
5
. Unfortunately, certain of the elements in acetylene and/or silane gas is/are insulative in nature (e.g., carbide may be an insulator in certain applications). Insulating deposits (e.g., carbide deposits, carbon deposits, and/or oxide deposits which may be insulating or semi-insulating in nature) resulting from the depositing gas can quickly build up on the respective surfaces of anode
25
and/or cathode
5
proximate the gap therebetween, and/or at other electrode locations. This can interfere with gas flow through the gap and/or aperture
15
, and/or it can reduce net current thereby adversely affecting the electric field potential between the anode and cathode proximate slit/aperture
15
. Such deposits resistively limit the amount of current that can flow through the source; this adversely interferes with the operability and/or efficiency of the ion source especially over significant lengths of time. This unfortunately can also result in micro-particles from the deposits making their way into a film being deposited on the substrate. In either case, operability and/or efficiency of the ion beam source is adversely affected.
These undesirable build-ups eventually have to be cleaned off the anode and/or cathode. Conventionally, cleaning has been conducted by running the source as shown in
FIG. 1
while introducing oxygen gas into the source. Unfortunately, this type of ion source cleaning technique does not do an adequate job of cleaning the anode, and anode/cathode surfaces distant from the aperture
15
tend not to be cleaned very well.
In view of the above, it will be apparent to those skilled in the art that there exists a need for a more efficient technique for cleaning an ion source.
BRIEF SUMMARY OF THE INVENTION
In certain example embodiments of this invention, both the anode and cathode of the ion sourc
Frati Maximo
Luten Henry A.
Shaw Denis
Veerasamy Vijayen S.
Guardian Industries Corp.
Nixon & Vanderhye P.C.
Smith, II Johnnie L.
Wells Nikita
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