Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Reexamination Certificate
2001-09-21
2002-09-24
McDonald, Rodney G. (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
C204S192130, C204S298030, C204S298060, C204S298190, C204S298260
Reexamination Certificate
active
06454910
ABSTRACT:
FIELD OF INVENTION
This invention relates generally to ion and plasma technology, and more particularly it pertains to ion-assisted deposition from magnetrons wherein the ions from an ion source compact, react with, or otherwise modify the thin film deposited by a magnetron.
BACKGROUND ART
Deposition of thin films by sputtering is widely used. The technology of magnetrons with planar targets is described by Waits in Chapter II-4 of
Thin Film Processes
(John L. Vossen and Werner Kern, eds.), Academic Press, New York (1978) beginning on page 131. Sputtering targets with other than planar shapes have also been used in magnetrons, as described in U.S. Pat. No. 2,146,025—Penning and in U.S. Pat. No. 3,616,450—Clarke. A related deposition technology is the use of energetic ion beams directed at sputter targets to deposit thin films on substrates as described by Harper in Chapter II-5 of the aforesaid
Thin Film Processes
beginning on page 131. These publications are incorporated herein by reference.
The modification of thin films by the simultaneous bombardment of a depositing film with energetic ions is called ion-assisted deposition. The acceleration of ions to form energetic beams of such ions has been accomplished electrostatically as described in U.S. Pat. No. 3,156,090—Kaufman and in the aforementioned chapter II-4 by Harper in
Thin Film Processes
. The ion generation in these ion sources has been by a direct-current discharge. It is also possible to use electrostatic ion acceleration with a radio-frequency discharge, as described in U.S. Pat. No. 5,274,306—Kaufman, et al.
The acceleration has also been accomplished electromagnetically with a discharge between an electron-emitting cathode and an anode. The accelerating electric field is established by the interaction of the electron current in this discharge with a magnetic field located in part or all of the discharge region. This interaction generally includes the generation of a Hall current normal to both the magnetic field direction and the direction of the electric field that is established. For the Hall current to be utilized efficiently, it must traverse a closed path.
A Hall-current ion source can have a circular discharge region with only an outside boundary, where the ions are accelerated continuously over the circular cross section of this region. This type of Hall-current ion source is called an end-Hall ion source and has a generally axial magnetic field shape as shown in U.S. Pat. No. 4,862,032—Kaufman et al., and as described by Kaufman, et al., in
Journal of Vacuum Science and Technology A
, Vol. 5, No. 4, beginning on page 2081. These publications are incorporated herein by reference.
A Hall-current ion source can also have an annular acceleration region with both inner and outer boundaries, where the ions are accelerated only over an annular cross section. This type of Hall-current ion source is called a closed-drift ion source and usually has a generally radial magnetic field shape as shown in U.S. Pat. No. 5,359,258—Arkhipov, et al., and U.S. Pat. No. 5,763,989—Kaufman, and as described by Zhurin, et al., in
Plasma Sources Science & Technology
, Vol. 8, beginning on page R1.
As described in the prior-art discussion of the aforesaid U.S. Pat. No. 5,763,989, closed-drift ion sources can be divided into magnetic layer and anode layer types, with the presence of a dielectric wall and a longer discharge region being the primary distinguishing features of the magnetic layer type. The operation of the anode-layer type can be further divided into quasineutral and vacuum regimes. As further described by Zhurin, et al., in the aforesaid article in
Plasma Sources Science & Technology
, operation in the vacuum regime is characterized by a high discharge voltage and a low discharge current. All of the above described Hall-current ion source types and their operating regimes use an electron-emitting cathode such as a hot filament or a hollow cathode, except for the anode-layer type operating in the vacuum regime. For the electron current to sustain the discharge, the latter depends on electron emission from cathode-potential surfaces that results from ion bombardment of those surfaces, from field-enhanced emission, and from neutralization arcs. An example of an anode-layer type of ion source operating in the vacuum regime is described in U.S. Pat. No. 6,147,354—Maishev, et al. The above ion source publications are also incorporated herein by reference.
The cross sections of the acceleration regions in the preceding discussion are described above as being circular or annular, but it should be noted the cross sections can have other shapes such as an elongated or “race-track” shape. Such alternative shapes are described in the references cited. It should also be noted that the magnetic field shape can depend on the desired beam shape. For example, an ion beam directed radially outward would have a magnetic field generally at right angles to the magnetic field used to generate an axially directed ion beam.
Ion-assisted deposition has been carried out using ion-beam sources for both sputtering from a target and the ion-assist bombardment of the depositing film. In such deposition, a gridded ion source is almost always used for generating the ion beam directed at the sputter target, as described in U.S. Pat. No. 4,419,203—Harper, et al., and U.S. Pat. No. 4,490,229—Mirtich, et al.
Ion-assisted deposition has also been carried out using a magnetron to sputter from a sputtering target and an ion source for the generation of ion-assist ions, as described in U.S. Pat. No. 5,525,199—Scobey and U.S. Pat. No. 6,153,067—Maishev, et al.
Ion-assisted deposition can enhance properties of deposited thin films by increasing their density, increasing their hardness, modifying their stress, promoting crystalline alignment, selecting a preferred molecular bond, increasing their adhesion to the substrates upon which they are deposited, and promoting the formation of a particular compound (such as an oxide or nitride) by bombarding with ions of one of the elements (such as oxygen or nitrogen ions). These property enhancements are described by Harper, et al. in Chapter 4 of
Ion Bombardment Modification of Surfaces: Fundamentals and Applications
(Auciello, et al, eds.), Elsevier Science Publishers B. V., Amsterdam (1984), beginning on page 127; by Kay, et al. in Chapter 10 of Handbook of Ion Beam Processing Technology (Cuomo, et al., eds.) Noyes Publications, Park Ridge, N.J. (1989) beginning on page 170; and by Roy, et al. in Chapter 11 of the aforesaid
Handbook of Ion Beam Processing Technology
, beginning on page 194. The above ion-assisted deposition publications are also incorporated herein by reference.
An acceptable energy range for ion-assist ions in low-damage deposition can be determined from the above publications. Essentially all deposition processes appear to show some degree of damage at ion-assist energies above 300 eV. Quite a few processes show damage at energies greater than 100 eV, while some show damage at energies greater than 50 eV. For low-damage, ion-assisted applications, then, the ion energies should definitely be less than 300 eV and preferably less than 100 eV. In general, gridded ion sources as described by Harper in the aforesaid Chapter II-5 of
Thin Film Processes
have limited ion-beam current capacity at low energies and are therefore not well suited to ion-assist deposition at the low end of the <300 eV energy range. In comparison, Hall-current ion sources usually have substantial ion-current capacity at 100 eV, or even less.
A general trend in thin-film deposition has been the increasing suppression or elimination of damage-producing mechanisms, with the objective of producing deposited films that are nearly or completely free from damage. The control of impurities has been important in reducing damage in the form of departures from uniform and controlled composition.
Impurities have been decreased by reducing or eliminating the sputtering of non-target hardware. A general reduction of contamina
Kahn James R.
Kaufman Harold R.
Thompson Kirk A.
Zhurin Viacheslav V.
Edmundson Dean P.
Kaufman & Robinson, Inc.
McDonald Rodney G.
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