2016 Materials science lecture series: advanced materials - 21 October 2016
Oct 21, 2016 - 11.00 uur
Agoralaan Gebouw D
Lokaal Room C104
de heer Rajesh RAMANETI
MRS/E-MRS joint student chapter, Hasselt University with IMO-IMOMEC: 2016 materials science lecture series: advanced materials.
Speaker: Prof. dr. Diederik Depla - Draft research group, dept.of solid State Sciences, Ghent University.
Topic: Modelling and experiments to understand magnetron sputter deposition.
Chaired by: Prof. Dr. Ken Haenen, IMO-IMOMEC, Hasselt University
Friday 21 October 2016, 11:00 -12:00
Room C104, building D, Hasselt University, Campus Diepenbeek.
Magnetron sputtering is a mature technique for the deposition of thin films, both at laboratory and industrial level.
Conceptually, the technique is quite simple and the process can be summarized in a few lines. It is a Physical Vapour Deposition technique in vacuum, based on a magnetically enhanced glow discharge which allows to deposit thin films. Between a cathode or target, and anode a glow discharge is ignited. The ions in the plasma are accelerated towards the target, and sputter the target material. In this way, a vapour is formed which condenses on the substrate as a thin film or coating.
The technique permits to deposit metals, complex alloys, and by the addition of a reactive gas compounds such as nitrides, oxides and sulphides Behind this apparent simplicity however a complex interplay between different physical and chemical processes is hidden. A guided tour, from target to substrate, reveals the many processes that affect the desired high quality coating for a given application.
Starting at the target, sputtering is of course the first process which comes into sight. Well-developed models to calculate the sputter yield, i.e. the number of atoms sputtered per incoming ion, exist in literature, but to calculate the deposition rate from these models, process specific parameters, such as the discharge voltage, and the gas pressure need to be known. As even the target roughness can affect the deposition rate, a combination by modelling and dedicated experiments are needed to predict the deposition rate.
Another “target” process is the ion-induced electron emission which provides the necessary electrons to sustain the discharge. The electronic properties of the target top layer define not only the discharge voltage, but also the negative ion yield. The presence of these latter species can define the film texture of oxides deposited in reactive mode. Hence, the description of the target condition as a function of the reactive gas flow is one of the key research topics in Ghent. Modelling guides the experimental research, but is also used to predict the process behaviour.
This research line is now further explored for HIPIMS, or high power impulse magnetron sputtering. The initial film growth is defined by the ratio between the diffusion rate of the adatoms on the growing film, and the deposition flux. It is therefore not surprising that the microstructure, and film texture are intimately related to the available energy per arriving atom (EPA). Plasma diagnostics, and modelling of the energy flux towards the growing film, in combination with the determination of the deposition rate permits to quantify in this way structure zone models.
The latter “models” give an overview of characterized thin film properties as function of the deposition conditions. By conversion of the deposition parameters into growth parameters such as EPA, it is possible to overcome the difficulty to relate experimental results in different deposition set-ups. With the above support by plasma diagnostics, modelling and thin film characterisation, several material systems are investigated. The current research mainly focuses on the compositional influence on the film growth. Examples of studied oxides are yttrium stabilized zirconia, doped MgO, and doped CeO2.
The behaviour of both fibre and biaxially textured thin films as a function of the chemical composition is explored. The same strategy is applied to high-entropy alloys which are equimolar mixtures of 5 or 6 different metals. Not only fundamental driven research is performed in this context. A new research line on embedded sensors in composites, and the industrial collaboration illustrate the application driven research which closes the tour from target to substrate