TECHNICAL
PUBLICATIONS
Progress on Gallium Nitride Semiconductor Growth by Plasma Sputtering
Abstract–– Plasma sputtering based growth of Gallium Nitride (GaN) is explored as a scalable and cost-effective method for obtaining thin crystalline III-V nitride films. Structural and optical characterization of the first series of growths on sapphire substrates indicates the growth of GaN, albeit with poor structural and optical properties.
(click here for PDF)
Biased Target Ion
Beam Deposition of GMR Multiayers
Abstract–– Multilayers like those used in giant
magnetoresistive spin-valves can be improved if better
layer thickness uniformity, lower contamination levels,
reduced interfacial roughness and less interlayer mixing
can be achieved. Atomistic simulations have revealed that
optimization of the energy of the depositing atoms and the
application of very low energy inert gas ion assistance
reduce both interfacial roughness and interlayer mixing.
Modulation of the energy of these fluxes as each layer
growth progresses has been predicted to give even better
quality interfaces. Unfortunately, these concepts cannot
be implemented in conventional physical vapor deposition
(PVD) or ion beam deposition (IBD) processes used to
deposit these materials. A new biased target ion beam
deposition (BTIBD) system that enables these conditions
to be achieved has recently been developed. Unlike
conventional IBD, it uses a low energy ion source. The
higher ion energy required for the sputtering is obtained
by applying a negative bias voltage to the metal targets.
This system enables low energy ion assistance at the
growth surface. By modulating the bias voltage during
each layer growth, it is also possible to change the
average energy of the depositing atoms and therefore
enable control of the atomic assembly at interfaces. We
have used BTIBD to grow model Ta (40 Å)/Ni80Fe20 (40
Å)/Co (15 Å)/Cu (tCu)/Co (45 Å)/FeMn (100 Å)/Cu (20
Å) spin-valves that show improved GMR ratios and
coupling fields over traditional IBD grown multilayers.
(click here for PDF)
Biased Target Ion Beam Deposition
of Spin-valves
Abstract–– A further reduction of defect concentration in
spin-valve multilayers is difficult in today’s growth
processes. Multilayers with better layer thickness
uniformity, lower contamination and reduced interfacial
roughness and interlayer mixing can have significantly
improved properties. Atomistic simulations revealed that
a modulation of the energy of depositing atoms during
deposition of each material layer or the application of
very low energy inert gas ion assistance could reduce both
interfacial roughness and interlayer mixing. These
concepts, unfortunately, cannot be implemented in the
conventional physical vapor deposition (PVD) or ion
beam deposition (IBD) processes currently used to
deposit these materials. A new biased target ion beam
deposition (BTIBD) system that enables these conditions
to be achieved has recently been developed. Unlike the
conventional IBD, it uses low energy ion source. The high
ion energy required for the sputtering is obtained by
applying a negative bias voltage to the metal target. This
system enables the low energy ion assistance at the
growth surface. By modulating the bias voltage during
each layer growth, it is also possible to change the
average energy of the depositing atoms and therefore
enables control of the atomic assembly at interfaces. We
have used this approach to grow Ta (40 Å)/Ni80Fe20 (40
Å)/Co (15 Å)/Cu (tCu)/Co (45 Å)/FeMn (100 Å)/Cu (20
Å) spin-valves and show improved GMR ratio and
coupling field over traditional IBD grown multilayers.
(click here for PDF)
Low Energy Ion Beam
Etching
James R. Kahn
and Harold R. Kaufman
Abstract–– Etch-rate
profiles have been obtained for copper, tantalum,
stainless steel and quartz using a commercial
end-Hall ion source. These profiles can be used to
predict uniformity and etch rates in practical
etching configurations. Compared to a gridded ion source, the lower ion energy of an end-Hall ion
source is offset in etching rate by its large ion-current capacity,
while the lower ion energy can be a significant advantage in damage-sensitive
etching applications. (click here for PDF)
Broad-Beam Industrial Ion Sources
Staff of Kaufman & Robinson, Inc.
Introduction–– A broad ion beam is typically several centimeters or more in
diameter. The beam diameter is also much larger than the
Debye length, which is the typical distance an electric field
can penetrate into a plasma. If a broad beam is to be kept
near ground potential, it must be neutralized (see Tech. Note
KRI-02). For neutralization, there must be approximately
equal numbers of electrons and positively charged ions in
each volume of the ion beam. For a dielectric target, the
electrons and ions must arrive in equal numbers. The target
can be either a sputter target or a substrate. The ion energy
in a broad ion beam is 2000 eV or less. (A singly charged ion
“falling” through a potential difference of 2000 V acquires
an energy of 2000 eV.) To minimize damage, the energy
is usually 1000 eV or less. High energy implanting-type
applications are not consider-ed here. Concern about damage
to processed surfaces has led to decreased ion energies.
There are two general categories of broad-beam ion sources:
gridded and gridless.
(click here for PDF)
Ion-Beam Neutralization
Staff of Kaufman & Robinson, Inc.
Introduction–– As described in Technical Note KRI-01, an ion beam from
a broad-beam industrial source must be neutralized. This is
done by emitting electrons from a neutralizer. A hot-filament,
plasma-bridge, or hollow-cathode type of neutralizer may be
used. The ion source in Fig. 1 could be either gridded or
gridless. For a gridless source, the neutralizer is a called a
cathode-neutralizer. The target can be a sputter target or a
substrate being etched.
(click here for PDF)
Gas Cleanliness
Staff of Kaufman & Robinson, Inc.
Introduction–– Gas cleanliness is important to some vacuum-process
equipment and processes. For example, contamination can
decrease the lifetime of hollow cathodes and plasma-bridge
neutralizers by a factor of ten or more. The techniques
required to assure gas cleanliness are reviewed herein.
(click here for PDF)
Ion-Assist Doses
Staff of Kaufman & Robinson, Inc.
Introduction–– Ion assisted deposition has evolved from a collection of
individual “recipes,” to the use of ion energy per deposited atom
as a measure of this dose,[1,2] to the variation of this dose with
material melting temperature.[3] The energy range of interest
for most applications has narrowed, focusing at present on the
low-energy range from about 25 eV to about 100 eV.[3] Dense,
low-defect films are believed to be generated in this range by
lattice vibrations. Ion collision effects tend to be confined to
the surface below ~25 eV, while damage is introduced into the
film by the excessive penetration of ions above ~100 eV.
(click here for PDF)
In-Situ Cleaning for Thin-Film Deposition
Staff of Kaufman & Robinson, Inc.
Introduction–– Thin films are deposited on substrates in a variety of vacuum
deposition processes. The properties of such a deposited
film depends on the cleanliness of the substrate surface on
which the film is deposited. Contamination on this surface
can result in reduced adhesion of the film to the substrate,
more rapid degradation of the film after deposition, greater
contact resistance for electrically conducting films, and poor
optical qualities for optical films.
(click here for PDF)
Modular Linear Ion Sources
H.R.
Kaufman, J.R. Kahn, and R.E. Nethery
Abstract–– The modular linear
ion source described herein uses cylindrical
end-Hall modules in a linear array. The modules
are operated in parallel so that there is a single
gas flow to the ion source, a single discharge
power supply, and a single hollow-cathode electron
source, similar to a non-modular design. The
spacing between the modules can be varied to
obtain a wide range of operating characteristics
while keeping a high degree of ion-dose uniformity along the length.
The ion beam is fully neutralized to provide stable operation that is not dependent on
workpiece material.(click here for PDF) |
