376 research outputs found
Foundations of physical vapor deposition with plasma assistance
Physical vapor deposition (PVD) refers to the removal of atoms from a solid or a liquid by
physical means, followed by deposition of those atoms on a nearby surface to form a thin film
or coating. Various approaches and techniques are applied to release the atoms including
thermal evaporation, electron beam evaporation, ion-driven sputtering, laser ablation, and
cathodic arc-based emission. Some of the approaches are based on a plasma discharge, while
in other cases the atoms composing the vapor are ionized either due to the release of the
film-forming species or they are ionized intentionally afterward. Here, a brief overview of the
various PVD techniques is given, while the emphasis is on sputtering, which is dominated by
magnetron sputtering, the most widely used technique for deposition of both metallic and
compound thin films. The advantages and drawbacks of the various techniques are discussed
and compared
Azimuthal ion movement in HiPIMS plasmas -- Part I: velocity distribution function
Magnetron sputtering discharges feature complex magnetic field configurations
to confine the electrons close to the cathode surface. This magnetic field
configuration gives rise to a strong electron drift in azimuthal direction,
with typical drift velocities on the order of \SI{100}{\kilo\meter\per\second}.
In high power impulse magnetron sputtering (HiPIMS) plasmas, the ions have also
been observed to follow the movement of electrons with velocities of a few
\si{\kilo\meter\per\second}, despite being unmagnetized. In this work, we
report on measurements of the azimuthal ion velocity using spatially resolved
optical emission spectroscopy, allowing for a more direct measurement compared
to experiments performed using mass spectrometry. The azimuthal ion velocities
increase with target distance, peaking at about
\SI{1.55}{\kilo\meter\per\second} for argon ions and
\SI{1.25}{\kilo\meter\per\second} for titanium ions. Titanium neutrals are also
found to follow the azimuthal ion movement which is explained with resonant
charge exchange collisions. The experiments are then compared to a simple
test-particle simulation of the titanium ion movement, yielding good agreement
to the experiments when only considering the momentum transfer from electrons
to ions via Coulomb collisions as the only source of acceleration in azimuthal
direction. Based on these results, we propose this momentum transfer as the
primary source for ion acceleration in azimuthal direction
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