The effect of extreme power densities applied to a planar magnetron

• In plasma assisted thin film growth control over the energy and direction of the incoming species is desired. If the growth species are ionized this can be achieved by the use of a substrate bias. ions may be accelerated by an applied potential, whereas neutral particles may not. Thin films grown by ionized physical vapor deposition (I­PVD) have lately shown promising results regarding film structure and adhesion. high power pulsed magnetron sputtering (HPPMS) is a newly developed technique, which relies on the creation of a dense plasma in front of the sputtering target to produce a large fraction of ions of the sputtered material.High power pulses of length ~100 µs are applied to a conventional planar magnetron. The highly energetic nature of the discharge, which involves power densities of several kW per cm2 creates a very dense plasma in front of the target. Previous measurements on the plasma properties indicate peak plasma densities in the order of 1019-1020 electrons per m3 and average electron energies of a few eV in a close vicinity to the target. This allows a large fraction of the sputtered material to be ionized.This work is focused onto two areas: 1. the ionization fraction of the sputtered material and the ionization process itself and 2. how the highly energetic discharge and the plasma dynamics affects the magnetic environment of the magnetron. Knowledge and control of the process is of interest in thin film growth when relating film properties to process parameters.Optical emission spectroscopy (OES) measurements of the plasma indicate that the degree of ionization of sputtered Ti is very high, over 90 % in the peak of the pulse. Even at relatively low applied target power (~200 Wcm-2 peak power) the recorded spectrum is totally dominated by radiation from ions. The distribution of electronically excited states roughly follows a Boltzmann distribution, with a characteristic temperature of 0.6 eV in the case of Ta. This indicates that the distribution of excited states differs significantly from the distribution of ionized states within Ta. We expect a high degree of ionization of the sputtered material, this requires a significant amount of electrons with energies over the ionization potential, which is between 6 and 7 eV for many metals. Sputtered material is ionized close to the target to be transported into a cooler plasma region. The recorded HPPMS spectra were compared to a spectrum taken from a d.c. magnetron discharge, showing a completely different appearance. The dependence on the choice of target material is also discussed, and is assumed to strongly affect the fraction of ions.Magnetic measurements performed with a coil type probe show significant deformation in the magnetic field of the magnetrons during the pulse. Spatially resolved measurements show evidence of a dense azimuthally Ex B drifting current. Circulating currents mainly flow within 2 away cm from the target surface in an early part of the pulse, to later diffuse axially into the chamber and decrease in intensity. We record peak current densities of the ExB drift to be in the order of 105 A/m2. Comparisons between Langmuir probe measurements and the magnetic field deformation also indicates that the expanding highly energetic plasma creates diamagnetic and paramagnetic changes of the magnetic field.

Ämnesord

NATURVETENSKAP  -- Fysik (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences (hsv//eng)

Publikations- och innehållstyp

vet (ämneskategori)

lic (ämneskategori)