Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
1999-02-14
2001-05-29
Nguyen, Nam (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S298040, C204S298260, C204S298210, C204S298180, C204S298170, C204S298220, C204S298120, C204S298140, C204S298070
Reexamination Certificate
active
06238526
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of ion-emission technique, particularly to an ion source with a channeling sputterable targets for sputtering the material of the target practically without any loss of sputtered particles. The invention also relates to a method for channeled sputtering.
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. An ion source is also used for overcoating of various objects by sputtering. Sputtering is a phenomenon that occur when energetic ionized particles, emitted, e.g., from an ion source, impinge on the surface of a solid or liquid target, causing the emission of particles and erosion of the surface of the solid. The sputtered target particles can appear as charged or neutral atoms or molecules, atom clusters, or chunks. The controlled deposition of sputtered particles to form thin films and coatings has industrial application in electronics, optics, and corrosion and wear-resistant coatings.
In a simplest form an ion-beam sputtering system consists of a sealed vacuum chamber that contains an ion-beam source, a target of a sputterable material, and an object to be treated. The target is installed at angle to the direction of the ion beam emitted by the ion source so that at the point of collision with the surface of the target the beam knocks-out or sputters particles of the target material which fly away from the surface of the target. A part of the sputtered particles deposited onto the surface of the treated object. Such a system is described by Brian Chapman in: Glow Discharge Processes (Sputtering and Plasma Etching), John Willey & Sons, New York, 1980, p. 272).
A disadvantage of the ion-beam sputtering system of the type described above is that a significant part of the particles is scattered away from the object and contaminates the inner walls of the chamber and the surfaces of the ion-beam source.
Attempts have been made to reduce scattering and loss of the sputtered particles in the ion-beam sputtering systems described in U.S. Pat. No. 6,130,507 issued on Oct. 10, 2000 to Yu. Maishev et al. now U.S. Pat. No. 6,130,507 and entitled “Cold-Cathode Ion Source with Propagation of Ions in the Electron Drift Plane”.
Since the ion source is an essential part of the system, given below is a detail description of a closed-loop ion source
10
of the invention which is shown in a cross-sectional view in FIG.
1
. This source is used for emitting ion beams in a radial outward direction in a plane of drift of electrons. In a transverse cross-section (not shown), ion source
10
, as well as its appropriate parts such as a cathode, anode, and magnet, may have a circular, oval, or elliptical cross section. It is understood that, strictly speaking, oval or ellipse do not have a radial direction and that the word “radial” is applicable to a circle only. However, for the sake of convenience, here and hereinafter, including patent claims, the terms “radially inwardly” and “radially outwardly” will be used in connection with any closed-loop configuration of the ion-emitting slit from which the ion beams are emitted inwardly or outwardly perpendicular to the circumference of the ion-beam housing.
Ion source
10
has a hollow housing
40
made of a magnetoconductive material which is used as a cathode. Housing
40
has a closed flat bottom
44
and a flat top side
46
with a through closed-loop ion-emitting slit
52
formed in the side wall of housing
40
around its entire periphery, approximately in the middle of the height of the source housing.
A working gas supply hole
53
is also formed in the side wall of housing
40
.
Hollow housing or cathode
40
contains a similarly-shaped concentric anode
54
which is fixed inside the housing by means of appropriately shaped bodies
56
and
58
of a nonmagnetic dielectric material, such as ceramic. Anode
54
is spaced from the inner walls of cathode
40
at a radial distance G required to form an ionization space
60
. In the direction of the height of housing
40
, anode
54
is aligned with the position of closed-loop slit
52
.
A magnetic-field generation means, which in this embodiment is shown as a permanent magnet
62
, is located inside anode
54
and is spaced from the inner surface of the anode. As shown in
FIG. 1
, magnet
62
is concentric to anode
54
and housing
40
and also has an oval-shaped configuration. It is understood that upper and lower parts
46
and
44
as well as adjacent parts of housing
40
, which form ion-emitting slit
52
, should be electrically connected. This is achieved by making magnet
62
of a conductive material, e.g., such as SmCo alloy. Alternatively, when an electromagnet is used, these parts may be connected via conductors (not shown).
Anode
54
is electrically connected to a positive pole
64
a
of an electric power supply unit
64
by a conductor line
66
which passes into housing
40
via a conventional electric feedthrough
68
. Cathode
40
is electrically connected to a negative pole
64
b
of power supply unit
64
.
In operation (FIG.
1
), vacuum chamber or object OB (not shown) is evacuated, and a working gas is fed into the interior of housing
40
of ion source
10
via inlet opening
53
. A magnetic field is generated by permanent magnet
62
in ionization gap G between anode
54
and cathode
40
, whereby electrons begin to drift in a closed path within the crossed electrical and magnetic fields. In the case of the device of the invention, the electrons begin to drift in gap G between anode
54
and cathode
40
and in ion-emitting slit
52
in the same plane in which the ions are emitted from the slit.
A plasma
70
is formed between anode
54
and cathode
40
and partially inside ion-emitting slit
52
. When the working gas is passed through ionization and acceleration gap G, ion beam IB, which propagates outwardly in the direction shown by arrows C, is formed in the area of ion-emitting slit
52
and in accelerating gap G between anode
54
and 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 anode
54
and cathode
40
reaches a predetermined level, a gas discharge occurs in anode-cathode gap G. As a result, the electrons, which have been generated as a result of ionization, begin to migrate towards anode
54
. After being accelerated by the electric field, the ions pass through ion-emitting slit
52
and are emitted from the ion source. Inside the ion-emitting slit, the crossed electric and magnetic fields force the electrons to move along closed cycloid trajectories. This phenomenon 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 cathode
40
which form ion-emitting slit
52
. The radius of the cycloid is, in fact, the so-called doubled Larmor radius R
L
which is represented by the following formula:
R
L
=mcV/|e|B,
where m 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.
It is required that the height of the electron drifting space in the ion-emission direction be much greater than the aforementioned Larmor radius. This means that a part of the ionization area penetrates into ion-emitting slit
52
where electrons can be maintained in a drifting state over a long period of time. I
Maishev Yuri
Ritter James
Shkolnik Alexander
Velikov Leonid
Advanced Ion Technology, Inc.
Chacko-Davis Daborah
Nguyen Nam
Zborovsky, Agent Ilya
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