Multiple-beam ion-beam assembly

Details Multiple-beam ion-beam assembly Multiple-beam ion-beam assembly

1999-10-18

2001-05-22

Shingleton, Michael B. (Department: 2817)

Electric lamp and discharge devices: systems

Discharge device load with fluent material supply to the...

Electron or ion source

C315S111210, C118S7230MP, C118S7230CB, C118S7230ER, C250S492210, C250S492300

Reexamination Certificate

active

06236163

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. More specifically, the invention relates to an ion-beam assembly consisting of two or more coaxially arranged ion-beam sources of the aforementioned type.
BACKGROUND OF THE INVENTION
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 on-beam source with a circular ion-beam emitting slit, and
FIG. 2
is cross-sectional plan view along line II—II of FIG.
1
.
The ion source
22
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. The 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 the flat bottom
44
. The flat top side
46
functions as an accelerating electrode. Placed inside the interior of the hollow cylindrical housing
40
between the bottom
44
and the 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 the bottom side
44
of the ion source. The purpose of a magnetic system with a closed magnetic circuit formed by parts the
66
,
46
,
42
, and
44
is to induce a magnetic field in ion emitting slit
52
. 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. The anode
54
is fixed inside housing
40
by means of a ring
48
made of a non-magnetic dielectric material such as ceramic. The 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 the housing
40
, which is grounded at GR.
Located above the 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 the chamber
57
above the ion emitting slit
52
. The object OB is electrically connected via a line
56
c
to the negative pole
56
b
of the power source
56
. Since the interior of the housing
40
communicates with the interior of the vacuum chamber
57
, all lines that electrically connect the power source
56
with the anode
54
and the object OB should pass into the interior of the housing
40
and the 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
,
57
a
,
57
b
, and
57
c.
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.
The vacuum chamber
57
is evacuated, and a working gas is fed into the interior of the housing
40
of the ion source via a gas-supply tube
53
a
. An electric field is generated in the ion generation gap
58
and the ion-emitting slit
52
due to an electrical potential applied from the electric power supply
56
between the anode
54
and the upper cathode plate
46
. As a result, a glow discharge occurs in the gap
58
after the potential reaches a predetermined value. A magnetic field is generated by the magnet
66
across the ion-emitting slit
52
whereby free electrons of the glow discharge begin to drift in a closed path within the crossed electrical and magnetic fields. When the working gas is passed through the ionization gap, the 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 the ion-emitting slit
52
and in the accelerating gap between the anode
54
and the cathode
40
.
The above description of the electron drift 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 the anode
54
and cathode
40
reaches a predetermined level, a gas discharge occurs in the anode-cathode gap. As a result, the electrons, which, under of effect of concurrent electrical and magnetic fields, move along complex trajectories, are accumulated and held in the area of the ion-emitting slit
52
and in the anode-cathode gap
58
. In fact, the aforementioned electrons drift along the closed-loop slit
52
and exist there over a long period of time. After being accelerated by the electric field, the ions generated in the anode-cathode gap due to collision of neutral molecules with electrons, pass through the ion-emitting slit
52
and are emitted from the ion source.
Strictly speaking, the aforementioned complex trajectories are closed cycloid trajectories. The phenomenon of drift of electrons in the crossed electric and magnetic fields is known as “magnetization” of electrons. The magnetized electrons remain drifting in a closed space between two parts of the cathode, i.e., between those facing parts of the cathode
40
which form the ion-emitting slit
52
. The radius of the cycloids is, in fact, the 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.
A distinguishing feature of the ion source of the type shown
FIGS. 1 through 3
is that efficient operation of the source is possible only when the source has the ion-emitting slit and the anode-cathode gap of predetermined geometrical dimensions. More specifically, the width of the ion-emitting slit
52
and the height of the gap
58
should be on the same order as the aforementioned Larmor radius.
When a working medium, such as argon which has neutral molecules, is injected into the slit, the molecules are ionized by the electrons present in this slit and are accelerated by the electric field. As a result, the thus formed ions are emitted from the slit towards the object. Since the spatial charge of electrons has high density, an ion beam of high density is formed. This beam can be converged or diverged by known technique for specific applications.
Thus, th

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