Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Electron or ion source
Reissue Patent
2002-10-10
2003-12-23
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Electron or ion source
C250S42300F
Reissue Patent
active
RE038358
ABSTRACT:
This invention relates to a cold cathode ion beam deposition apparatus with segregated gas flow, and corresponding method. More particularly, this invention relates to a cold cathode ion beam deposition apparatus wherein different gases are caused to flow through different flow channels toward an area of energetic electrons in order to provide a more efficient ion beam deposition apparatus and corresponding method.
BACKGROUND OF THE INVENTION
An ion source is a device that causes gas molecules to be ionized and then focuses, 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 technical and technological purposes, including but not limited to, cleaning, activation, polishing, etching, and/or deposition of thin film coatings. Exemplary ion sources are disclosed, for example, in U.S. Pat. Nos. 6,037,717; 6,002,208; and 5,656,819, the disclosures of which are all hereby incorporated herein by reference.
FIGS. 1 and 2
illustrate a conventional ion source. In particular,
FIG. 1
is a side cross-sectional view of an ion beam source with a circular ion beam emitting slit, 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 ion beam emitting slit as opposed to a circular ion beam emitting slit.
Referring to
FIGS. 1-3
, the ion source includes hollow housing
3
made of a magnetoconductive material such as mild 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
15
is defined. Ion emitting slit
15
includes an inner periphery
17
as well as an outer periphery
19
.
Working gas supply aperture or hole
21
is formed in bottom wall
9
. Flat top wall
11
functions as an accelerating electrode. A magnetic system in the form of a cylindrical permanent magnet
23
with poles N and S of opposite polarity is placed inside housing
3
between bottom wall
9
and top wall
11
. The N-pole faces flat top wall
11
, while the S-pole faces bottom wall
9
of the ion source. The purpose of the magnetic system, including magnet
23
with a closed magnetic circuit formed by the magnet
23
, cathode
5
, side wall(s)
7
, and bottom wall
9
, is to induce a substantially transverse magnetic field (MF) in an area proximate ion emitting slit
15
.
A circular or oval shaped anode
25
, electrically connected to positive pole
27
of electric power source
29
, is arranged in the interior of housing
3
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 ring
31
(e.g., of ceramic). Anode
25
defines a central opening
33
therein in which magnet
23
is located. Negative pole
35
of electric power source
29
is connected to housing
3
(and thus to cathode
5
) generally at
37
, so that the cathode and housing are grounded (GR).
Located above housing
3
(and thus above cathode
5
) of the ion source of
FIGS. 1-3
is vacuum chamber
41
. Chamber
41
includes evacuation port
43
that is connected to a source of vacuum (not shown). An object or substrate
45
to be treated (e.g., coated, etched, cleaned, etc.) is supported within vacuum chamber
41
above ion emitting slit
15
(e.g., by gluing it, fastening it, or otherwise supporting it on an insulator block
47
). Thus, substrate
45
can remain electrically and magnetically isolated from the housing of vacuum chamber
41
, yet electrically connected via line
49
to negative pole
35
of power source
29
. Since the interior of housing
3
can communicate with the interior of vacuum chamber
41
, all lines that electrically connect power source
29
with anode
25
and substrate
45
may pass into the interior of housing
3
and/or chamber
41
via conventional electrically feed through devices
51
.
The conventional ion beam source of
FIGS. 1-3
is intended for the formation of a unilaterally directed tubular ion beam
53
, flowing in the direction of arrow
55
toward a surface of substrate
45
. Ion beam
53
emitted from the area of slit
15
is in the form of a circle in the
FIG. 2
embodiment and in the form of an oval (i.e., race track) in the
FIG. 3
embodiment.
The ion beam source of
FIGS. 1-3
operates as follows. Vacuum chamber
41
is evacuated, and a working gas
57
is fed into the interior of housing
3
via aperture
21
. Power supply
29
is activated and an electric field is generated between anode
25
and cathode
5
, which accelerates electrons
59
to high energy. Electron collisions with the working gas in or proximate gap or 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 a region including slit
15
. An electric field is produced in slit
15
, oriented in the direction of arrow
55
(substantially perpendicular to the transverse magnetic field) which causes ions to propagate toward substrate
45
. Electrons in the ion acceleration space in slit
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
15
. These circulating electrons contribute to ionization of the working gas, so that the zone of ionizing collisions extends beyond the electrical gap
63
between the anode and cathode and includes the region proximate slit
15
.
For purposes of example, consider the situation where a silane gas
57
is utilized by the ion source of
FIGS. 1-3
. The silane gas, including the silane inclusive molecules therein, passes through the gap at
63
between anode
25
and cathode
5
. Unfortunately, certain of the elements in silane gas are insulative in nature (e.g., silicon carbide may be an insulator in certain applications). Insulating deposits (e.g., silicon carbide) can quickly build up on the respective surfaces of anode
25
and/or cathode
5
proximate gap
63
. This can interfere with gas flow through the gap or slit, or alternatively it can adversely affect the electric field potential between the anode and cathode proximate slit
15
. In either case, operability and/or efficiency of the ion beam source is adversely affected. In sum, the flow of gas which produces a substantial amount of insulative material buildup in electrical gap
63
on the anode and cathode may be undesirable in certain applications.
Moreover, electrical performance of the ion source is sensitive to parameters of gases within gap
63
(i.e., the electrical gap between the anode
25
and cathode
5
). For example, electrical performance of the source is sensitive to characteristics such as the density of the gas within gap
63
, the residence time of the gas within gap
63
, and/or the molecular weight of the gas within gap
63
. Changes in gas chemistry at gap
63
(intentional or unintentional) can alter the characteristics of ion beam
53
(e.g., with regard to energy and/or current density). This problem is particularly troublesome at high total flow conditions where the beam
53
can undergo a significant discontinuous transition between two operational modes (e.g., high energy/low current and low energy/high current).
U.S. Pat. Nos. 5,508,368; 5,888,593: and 5,973,447 relate to ion sources, each of these patents being hereby incorporated herein by reference. Unfortunately, the sources of the '368, '593 and '447 patents primarily relate to thermionic emissive (hot) electron cathodes. This is undesirable, as cold-cathode sources such as that of the instant invention typically operate at higher voltages and/or lower gas flows. These advantages of cold-cathode sources translate into the ability to deposit much harder materials more efficiently (e.g., ta-C versus conventional DLC), a
Guardian Industries Corp.
Nixon & Vanderhye P.C.
Tran Thuy Vinh
Wong Don
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