Stijn Mahieu

Reactive sputter deposition

Simulation of the Sputtering Process.- Electron Emission from Surfaces Induced by Slow Ions and Atoms.- Modeling of the Magnetron Discharge.- Modelling of Reactive Sputtering Processes.- Depositing Aluminium Oxide: A Case Study of Reactive Magnetron Sputtering.- Transport of Sputtered Particles Through the Gas Phase.- Energy Deposition at the Substrate in a Magnetron Sputtering System.- Process Diagnostics.- Optical Plasma Diagnostics During Reactive Magnetron Sputtering.- Reactive Magnetron Sputtering of Indium Tin Oxide Thin Films: The Cross-Corner and Cross-Magnetron Effect.- Reactively Sputter-Deposited Solid Electrolytes and Their Applications.- Reactive SputteredWide-Bandgap p-Type Semiconducting Spinel AB2O4 and Delafossite ABO2 Thin Films for Transparent Electronics.- Oxide-Based Electrochromic Materials and Devices Prepared by Magnetron Sputtering.- Atomic Assembly of Magnetoresistive Multilayers.

Compositional effects on the growth of Mg(M)O films

The influence of the composition on the crystallographic properties of deposited Mg(M)O (with M=Al, Cr, Ti, Y, and Zr) films is studied. For a flexible control of the composition, dual reactive magnetron sputtering was used as deposition technique. Two different approaches to predict the composition are discussed. The first is an experimental way based on the simple relationship between the deposition rate and the target-substrate distance. The second is a route using a Monte Carlo based particle trajectory code. Both methods require a minimal experimental input and enable the user to quickly predict the composition of complex thin films. Good control and flexibility allow us to study the compositional effects on the growth of Mg(M)O films. Pure MgO thin films were grown with a (111) preferential out-of-plane orientation. When adding M to MgO, two trends were noticed. The first trend is a change in the MgO lattice parameters compared to pure MgO. The second tendency is a decrease in the crystallinity of the MgO phase. The experimentally determined crystallographic properties are shown to be in correspondence with the predicted properties from molecular dynamics simulations.

Sputter deposition processes

Publisher Summary Sputter deposition is a widely used technique to deposit thin films on substrates. The technique is based on ion bombardment of a source material, the target. Ion bombardment results in a vapor due to a purely physical process, i.e., the sputtering of the target material. This technique is part of the class of physical vapor deposition techniques, which includes thermal evaporation and pulsed laser deposition. The most common approach for growing thin films by sputter deposition is the use of a magnetron source in which positive ions present in the plasma of a magnetically enhanced glow discharge bombard the target. This technique forms the focus of this chapter. The target can be powered in different ways, ranging from direct current (DC) for conductive targets to radio frequency (RF) for nonconductive targets, to a variety of different ways of applying current and/or voltage pulses to the target. Since sputtering is a purely physical process, adding chemistry to, for example, deposit a compound layer must be done ad hoc through the addition of a reactive gas to the plasma, i.e. reactive sputtering. The undesirable reaction of the reactive gas with the target material results in a nonlinear behavior of the deposition parameters as a function of the reactive gas flow. To model this behavior, the fluxes of the various species toward the target must be determined. Equally important are the fluxes of species incident at the substrate because they not only influence the reactive sputter deposition process, but also control the growth of the desired film.

Angular-resolved energy flux measurements of a dc- and HIPIMS-powered rotating cylindrical magnetron in reactive and non-reactive atmosphere

A rotating cylindrical magnetron equipped with a titanium target was sputtered in dc and in HIPIMS mode, both in metallic and in the oxide regime. For all sputter modes, the same process conditions and the same average sputtering power of 300u2009W were used. An angular-resolved study was performed, 90° around the rotating cylindrical magnetron, which obtained the total energy flux arriving at the substrate. Furthermore, the energy flux per adparticle was calculated by measuring the deposition rate for all sputter modes and regimes. There is only a small difference in total arriving energy flux between the dc mode and the HIPIMS mode. A maximum arriving energy flux of ca 0.26u2009mWu2009cm−2 was measured, when normalized to the sputtering power. Concerning the deposition rate, up to a 75% decrease was found from dc to HIPIMS mode. Furthermore, the emission and the transport of the particles have a similar angular profile for all sputter modes. Among the HIPIMS modes, a decrease in deposition rate was measured with increasing pulse length. Therefore, the energy which arrives per adparticle is the highest for the HIPIMS modes. A difference in the angular shape of the energy per arriving adparticle is noticed between the dc and the HIPIMS modes. The dc mode has a maximum arriving energy per adparticle at around 50°, while this is at 60° for the HIPIMS mode.

Influence of particle and energy flux on stress and texture development in magnetron sputtered TiN films

The real-time stress evolution during reactive dc magnetron sputter deposition of TiN films in Ar+N2 plasma discharge was measured in situ using a multiple-beam optical stress sensor, while the film texture was determined ex situ using x-ray diffraction. The influence of atomic N/Ti flux and energy flux, previously quantified by combining plasma characterization and Monte Carlo simulations (2009 J. Phys. D: Appl. Phys. 42 053002), was investigated by varying either the N2 partial pressure at fixed total pressure, the total working pressure or the bias voltage applied to the substrate. The contribution of thermal stress was carefully taken into account from thermal probe measurements to evaluate the intrinsic (growth) stress from the measured film force data. A clear correlation between stress, film texture and energy flux is evidenced: while underdense (1?1?1)-textured TiN films with ?V?-shaped columnar growth (zone T) are under tensile stress (up to +0.6?GPa), dense TiN films with zone II microstructure develop a (0?0?2) texture and large compressive stress (up to 3?GPa) when the energy flux is higher than ?150?eV per incoming particle. However, it is shown that a positive or negative bias voltage, though increasing the energy flux, did not promote a (0?0?2) texture. It is concluded that compressive stress development and (0?0?2) preferential growth are both kinetically driven processes in magnetron sputtered TiN layers, but exhibit distinct dependence with the substrate fluxes.

Rotating cylindrical magnetron sputtering: Simulation of the reactive process

A rotating cylindrical magnetron consists of a cylindrical tube, functioning as the cathode, which rotates around a stationary magnet assembly. In stationary mode, the cylindrical magnetron behaves similar to a planar magnetron with respect to the influence of reactive gas addition to the plasma. However, the transition from metallic mode to poisoned mode and vice versa depends on the rotation speed. An existing model has been modified to simulate the influence of target rotation on the well known hysteresis behavior during reactive magnetron sputtering. The model shows that the existing poisoning mechanisms, i.e., chemisorption, direct reactive ion implantation and knock on implantation, are insufficient to describe the poisoning behavior of the rotating target. A better description of the process is only possible by including the deposition of sputtered material on the target.

The origin of Bohm diffusion, investigated by a comparison of different modelling methods

Bohm diffusion causes the electrons to diffuse perpendicularly to the magnetic field lines. However, its origin is not yet completely understood: low and high frequency electric field fluctuations are both named to cause Bohm diffusion. The importance of including this process in a Monte Carlo (MC) model is demonstrated by comparing calculated ionization rates with particle-in-cell/Monte Carlo collisions (PIC/MCC) simulations. A good agreement is found with a Bohm diffusion parameter of 0.05, which corresponds well to experiments. Since the PIC/MCC method accounts for fast electric field fluctuations, we conclude that Bohm diffusion is caused by fast electric field phenomena.

Experimental determination and simulation of the angular distribution of the metal flux during magnetron sputter deposition

To understand the film growth during magnetron sputter deposition a detailed knowledge of the flux of sputtered species from the target towards the substrate is vital. One important parameter is the angular distribution of the impinging neutral target atoms on the substrate, since it is responsible for, for example, self-shadowing effects. The determination of the angular distribution of the metal flux at an arbitrary point in the deposition chamber is achieved by a pinhole camera, where the information of the angular distribution is converted into a thickness profile. This paper describes the construction of such a pinhole camera which is capable of differential pumping, the determination of the angular distribution for a wide variety of target materials, and which can easily be inserted into a deposition chamber. The angular distributions of different materials (Cu, W, Al, Ti, Mg) at different parameters (pressure, lateral position and vertical position) are experimentally determined and compared with simulations obtained from a newly developed Monte Carlo code. It was also investigated whether parameters derived from the angular distribution are related to the degree of thermalization of the impinging particles.

High power impulse magnetron sputtering using a rotating cylindrical magnetron

Both the industrially favorable deposition technique, high power impulse magnetron sputtering (HIPIMS), and the industrially popular rotating cylindrical magnetron have been successfully combined. A stable operation without arcing, leaks, or other complications for the rotatable magnetron was attained, with current densities around 11u2002Au2009cm−2. For Ti and Al, a much higher degree in ionization in the plasma region was observed for the HIPIMS mode compared to the direct current mode.Both the industrially favorable deposition technique, high power impulse magnetron sputtering (HIPIMS), and the industrially popular rotating cylindrical magnetron have been successfully combined. A stable operation without arcing, leaks, or other complications for the rotatable magnetron was attained, with current densities around 11u2002Au2009cm−2. For Ti and Al, a much higher degree in ionization in the plasma region was observed for the HIPIMS mode compared to the direct current mode.

Rotatable magnetron sputtering: downscaling for better understanding

Abstract In coating applications, magnetron sputtering is frequently the technology of choice. In industrial continuous in-line sputtering processes, such as web coating and glass coating, rotatable magnetrons have, to a large extent, supplanted the more classic rectangular sputter magnetrons and constitute the heart of many coating systems with target lengths up to 4u2005m. However, for many people in the coating business, rotatable magnetrons are quite unknown. When comparing the two types, it looks as if rotatable magnetrons offer significant advantages over planars, as long as the required cylindrical targets are available. Rotabable magnetrons are still a relatively new technology, and have not been fully investigated on a lab scale due to the lack of availability of small systems. Experiments with an in house developed downscaled rotatable magnetron have allowed some of their typical characteristics to be identified. Especially in reactive sputtering, rotatable magnetrons exhibit unusual properties. In this article, it is shown that this peculiar behaviour can be understood as the result of redeposition of previously sputtered material back on the target outside the current discharge plasma zone. This redeposition is, to a large extend, also responsible for the poisoning characteristics as a function of rotation speed of the cathode cylinder. It is also shown that in reactive sputtering, rotatable magnetrons generate two beams of high energy and negatively charged particles which seriously influence the morphology of the growing layer. In between both beams, there is a zone of silence where only sputtered low energy material is deposited and in which fragile materials, such as perovskites can be grown.