Johan Haemers

Yttria-stabilized zirconia thin films grown by reactive r.f. magnetron sputtering

Abstract Zirconia thin films were deposited on different substrates by reactive r.f. magnetron sputtering. It was found that zirconia layers grew preferentially in the (200) direction with a columnar microstructure that is independent of the oxygen flow, argon to oxygen flow ratios and sputtering pressure. On the other hand the substrate roughness clearly affects the orientation of zirconia. Distinct changes were observed in the case of heated substrates. The heating of the substrates does not change the form of the zirconia, but strongly influences its orientation. When the substrate temperature increases, the crystallographic orientation gets more and more random, typically for the polycrystalline state. A decrease in the optical transmittance and an increase in the colour intensity of the layers with an increase in the substrate temperature was also found. As is shown, the oxygen non-stoichiometry of the zirconia is responsible for these changes.

Target voltage behaviour during DC sputtering of silicon in an argon/nitrogen mixture

Abstract On addition of nitrogen to an argon plasma, the silicon target voltage changes. By following the target voltage during the addition and removal of the reactive gas, the influence of the plasma condition was separated from the influence of the target condition on the target voltage. In this way, we were able to investigate the target surface modification during reactive sputtering. The target surface modification seems to be induced by reactive ion implantation. The target surface modification is not stable and N 2 desorption from a silicon target after reactive sputtering is noticed.

Hysteresis behavior during reactive magnetron sputtering of Al2O3 using a rotating cylindrical magnetron

Rotating cylindrical magnetrons are used intensively on industrial scale. A rotating cylindrical magnetron on laboratory scale makes it possible to study this deposition technique in detail and under well controlled conditions. Therefore, a small scale rotating cylindrical magnetron was designed and used to study the influence of the rotation speed on the hysteresis behavior during reactive magnetron sputtering of aluminum in Ar∕O2 in dc mode. This study reveals that the hysteresis shifts towards lower oxygen flows when the rotation speed of the target is increased, i.e., target poisoning occurs more readily when the rotation speed is increased. The shift is more pronounced for the lower branch of the hysteresis loop than for the upper branch of the hysteresis. This behavior can be understood qualitatively. The results also show that the oxidation mechanism inside the race track is different from the oxidation mechanism outside the race track. Indeed, outside the race track the oxidation mechanism is only...

Target surface condition during reactive glow discharge sputtering of copper

During reactive glow discharge sputtering of copper in an argon/nitrogen plasma, we noticed an abrupt change of the target voltage and the deposition rate when the nitrogen concentration in the plasma exceeds a critical value. To explain this behaviour, the target surface after reactive glow discharge sputtering was examined by x-ray photoelectron spectroscopy (XPS). An experimental arrangement was constructed that allows direct transfer of the glow discharge cathode to the XPS analysis chamber without air exposure. These XPS measurements revealed that several different chemical states of nitrogen are present in the layer that forms on the target surface. The relative concentration of these different states changes when the critical nitrogen concentration in the plasma is exceeded.

Yttria-stabilized zirconia thin films grown by r.f. magnetron sputtering from an oxide target

Abstract Yttria-stabilized zirconia thin films with cubic crystallographic structure were deposited onto glass substrates by r.f. magnetron sputtering from an oxide target. It was found that zirconia growth is strongly dependent on the sputtering power and pressure. At low power and high pressure, zirconia grows preferentially in the (200) direction with columnar microstructurc. In contrast, high power and low sputtering pressures promote the growth of randomly oriented polycrystallinc zirconia. Increasing the argon flow at constant power and sputtering pressure again favours preferential growth of zirconia layers, however, not in the (200) direction as before, but in the (111) direction.

Simplified model for calculating the pressure dependence of a direct current planar magnetron discharge

A simplified model for the direct current planar magnetron discharge allowing one to simulate the pressure dependence over a wide range is presented. For sufficiently strong magnetic fields, the high energy electrons (HEE), the electrons that are responsible for the ionization, move predominantly in arch shaped regions in between interactions with the discharge gas. This allows one to model the discharge as being built up by arches. The influence of the interactions of the HEE on their motion is modeled by calculating the probabilities for transfer of HEE among the arch shaped regions. In this way the ionization distribution of the electrons emitted at a certain position at the target surface can be calculated. The results of this approach agree well with Monte Carlo results. This modeling of the HEE motion combined with simple schemes for determining the ionization and target erosion forms the core of the simplified model. The model is made self-consistent through iteration. It appears that for a given m...

Low pressure behaviour of the sputter magnetron discharge

Summary form only given. For successful simulation of the complete magnetron sputter deposition process, the modelling of the plasma is crucial. This is because the position and extension of the plasma, more specific its ionisation distribution, determines the erosion profile, i.e. the area on the target (cathode) from where the atoms are removed due to argon ion bombardment. The pressure dependence of the width of the erosion profile was experimentally studied: it is nearly constant above a certain pressure (0.51 Pa), but below this pressure, the width increases strongly with decreasing pressure. The width of the ionisation distribution, and thus also of the plasma, along the direction parallel with the target surface has the same pressure dependence. As the ionisation of the argon gas is primarily due to the secondary electrons (SE), which are released from the target by impinging ions, we developed a model for simulating the orbits of these SE. This is done by solving the Lorentz equation of motion for charged particles. The magnetic field is calculated analytically, and the electric field is assumed to vary linearly over a known distance. Our simulations show that the arch shaped ionisation region of a single SE, emitted at a certain position at the cathode surface, does not change with pressure. Thus, the change in the plasma must be due to a change of emission profile of the SE. For explaining this change we investigated the SE movement: due to its arch shaped orbit, a SE is brought back towards the surface after one cycloidal bounce. If the initial energy of the SE is set to zero, as is common practice, it is reflected by the combined influence of the electric and magnetic field. However, if the initial energy is given a realistic value (typical 4 eV), the SE can interact with the cathode which can lead to recapture of the SE. This recapture is only possible before a SE undergoes any interaction with the discharge gas. As a result, the effect only appears at low pressures and affects the SE emitted near the centre of the erosion profile more than the ones close to the edge because the first have a shorter cycloidal bounce. Consequently, lowering the operating pressure favours the SE emitted near the edge and they will relatively be more present. This effect causes the change in SE emission profile and the resulting increase in plasma and erosion profile width. Hence, for modelling the magnetically confined plasma of a magnetron discharge at low pressures the small initial energy of the SE has to be taken into account, and should not be set to zero as is usually done in such simulations.