Radiant energy – Ion generation – Arc type
Reexamination Certificate
1999-03-06
2001-06-12
Berman, Jack (Department: 2878)
Radiant energy
Ion generation
Arc type
C250S42300F, C315S111810, C315S111910
Reexamination Certificate
active
06246059
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of ion-emission technique, particularly to cold-cathode type ion-beam sources having closed-loop ion-emitting slits with electrons drifting in crossed electric and magnetic fields.
BACKGROUND OF THE INVENTION AND DESCRIPTION OF THE PRIOR ART
An ion source is a device that ionizes gas molecules and then focuses, accelerates, and emits them as a narrow beam. This beam is then used for various technical and technological purposes such as cleaning, activation, polishing, thin-film coating, or etching.
For better understanding the principle of the present invention, it would be expedient to describe in detail a known ion-beam source of the type to which the invention pertains. Such an ion source is described, e.g., in Russian Patent No. 2,030,807 issued in 1995 to M. Parfenyonok, et al. The patent 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 ion-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
,
46
,
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 U.S. Pat. No. 4,710,283 issued to Singh, et al. in 1987. 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
connected to a source of vacuum (not shown). An object OB to be treated is supported within chamber
57
above ion emitting slit
52
by an insulator block
61
rigidly attached to the housing of vacuum chamber
57
by a bolt
63
but so that object OB remains electrically isolated from the housing of vacuum chamber
57
. However, object OB is electrically connected via a line
56
c
to negative pole
56
b
of power source
56
. Since the interior of housing
40
communicates with the interior of vacuum chamber
57
, all lines that electrically connect power source
56
with anode
54
and object OB should pass into the interior of housing
40
and vacuum chamber
57
via conventional commercially-produced electrical feedthrough devices which allow electrical connections with parts and mechanisms of sealed chambers without violation of their sealing conditions. In
FIG. 1
, these feedthrough devices are shown schematically and designated by reference numerals
40
a
and
57
a
. Reference numeral
57
b
designates a seal for sealing connection of vacuum chamber
57
to housing
40
.
The known ion source of the type shown in
FIGS. 1 and 2
is intended for the formation of a unilaterally directed tubular ion beam. The source of
FIGS. 1 and 2
forms a tubular ion beam IB emitted in the direction of arrow A and operates as follows.
Vacuum chamber
57
is evacuated, and a working gas is fed into the interior of housing
40
of the ion source. A magnetic field is generated by magnet
66
in the accelerating gap between anode
54
and cathode
40
, whereby electrons begin to drift in a closed path within the crossed electrical and magnetic fields. A plasma
58
is formed between anode
54
and top cathode plate
46
. When the working gas is passed through an ion-acceleration and ionization gap
52
a
(hereinafter referred to as “ionization gap”), tubular ion beam IB, which is propagated in the axial direction of the ion source shown by an arrow A, is formed in the area of an ion-emitting slit
52
and in ionization gap
52
a
between anode
54
and top cathode plate
46
.
The above description of the operation of the ion source is simplified to ease understanding of the principle of the invention. In reality, the phenomenon of generation of ions in the ion source with a closed-loop drift of electrons in crossed electric and magnetic fields is of a more complicated nature and consists in the following.
When, at starting the ion source, a voltage between anode
54
and cathode
40
reaches a predetermined level, a gas discharge occurs in gap
52
a
. As a result, the electrons, which have been generated as a result of ionization, begin to migrate towards anode
54
under the effect of the electric field, colliding with the molecules of working gas and moving along specific trajectories described below. The space in which the electrons drift is confined between an inner part
46
a
and an outer part
46
b
of top cathode plate
46
, which form ion-emitting slit
52
, and the surface of anode
54
facing top cathode plate
46
.
The principle of operation of the ion-beam source to which the present invention pertains can be better understood after consideration of a direct current vacuum magnetron a part of which is shown schematically on FIG.
1
A. If one assume that in ion source of
FIG. 1
ion-emitting slit
52
is absent and that the magnetic field B between cathode
46
′ and anode
54
′ passes parallel to the planes of the anode and cathode (i.e., perpendicular to the plane of the drawing), then such a system can be considered as the aforementioned direct current vacuum magnetron (hereinafter referred to as “DC magnetron”).
In a DC magnetron, the electrons, which are emitted from cathode
46
′, move toward anode
54
′. However, their trajectory is curved under the effect of magnetic field B. When the strength of magnetic field B exceeds a predetermined critical value B
cr
, the electrons do not reach the surface of anode
54
′ and return back to cathode
46
′. More specifically, the electrons begin to move along cycloidal trajectories shown in FIG.
1
A. As a result, the electrons are accumulated in the space between cathode
46
′ and anode
54
′, and their concentration can reach a significant value. It is known that height H of such a cycloid is equal to so-called doubled Larmor radius R
L
which is represented by the following formula:
R
L
=m
e
V/|e|B,
where m
e
is a mass of the electron, B is the strength of the magnetic field inside the slit, V is a velocity of the electrons in the direction perpendicular to the direction of the magnetic field, and |e| is the charge of the electron (see D. L. Smith. “Thin-Film Deposition”. Principles and Practice. McGraw-H
Maishev Yuri
Ritter James
Shkolnik Alexander
Velikov Leonid
Advanced Ion Technology, Inc.
Berman Jack
LandOfFree
Ion-beam source with virtual anode does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Ion-beam source with virtual anode, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Ion-beam source with virtual anode will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2463759