Tomas Nyberg

Deposition of Ti2AlC and Ti3AlC2 epitaxial films by magnetron sputtering

Thin films of the Mn+1AXn-phases Ti2AlC and Ti3AlC2 have been deposited by dc magnetron sputtering. In agreement with the Ti–Si–C system, the MAX-phase nucleation is strongly temperature dependent. At 900°C epitaxial films of Ti2AlC and Ti3AlC2 were grown, but at 700°C only a cubic (Ti,Al)C phase was formed. In addition, a perovskite carbide, Ti3AlC was grown at 800°C. A bulk resistivity of 0.51μΩm, 0.44μΩm, and 1.4μΩm was measured for the Ti3AlC2, Ti2AlC, and Ti3AlC films deposited at 900°C, respectively. By nanoindentation the hardness and Young’s module was determined for an epitaxial Ti3AlC2 film to 20GPa and 260GPa, respectively.

Frequency response in pulsed DC reactive sputtering processes

Abstract By simple arguments as well as results from a recently developed computer simulation model we have found out that for high frequency pulsed DC reactive sputtering the target poisoning does not reflect the periodicity of the pulsed DC power supply. The degree of target poisoning does not change markedly during a single duty cycle. The degree of poisoning essentially exhibits the same continuous time independent behavior as observed for the conventional continuous reactive sputtering process. Furthermore, it is shown that the distribution width of the transit times for sputtered atoms by far exceeds the period time for pulsed DC frequencies higher than 5–10 kHz. This causes a large overlap between sputter eroded material between consecutive pulses during processing resulting in an essentially continuous arrival rate of sputtered atoms to the substrate surface. This implies also that the deposition rate will be constant and will not follow the pulsed sputter erosion variation from the target. These findings show that, with respect to film stoichiometry and homogeneity, the high frequency pulsed DC reactive sputtering process behaves identically as the continuous reactive sputtering process. No chemical reaction effects or gas gettering variations will follow the periodicity of the pulsed DC power supply at high frequencies.

Process stabilization and increase of the deposition rate in reactive sputtering of metal oxides and oxynitrides

Reactive sputtering processes normally exhibit undesirable hysteresis effects which are more pronounced for oxide than nitride deposition. We present a method to reduce and ultimately eliminate these effects for reactive sputtering of metal oxides and oxynitrides. This is achieved by the addition of nitrogen to the oxygen process, which in addition leads to a higher deposition rate. These observations can be qualitatively explained and theoretically predicted using an extension of the Bergs model to two different reactive gases. Although the nitrogen addition leads to pronounced changes of the processing characteristics, incorporation of nitrogen into the growing film is very small.

Eliminating the hysteresis effect for reactive sputtering processes

Reactive sputter processes frequently exhibit stability problems. The cause of this is that these processes normally exhibit hysteresis effects in the processing curves. Eliminating the hysteresis ...

High rate reactive magnetron sputter deposition of titanium oxide

A systematic experimental study of reactive sputtering from substoichiometric targets of TiOx with x ranging from 0 to 1.75 is reported. Experimental results are compared with results from modeling. The developed model describes the observed behavior and explains the origins of the unexpectedly high deposition rate. The behavior is shown to originate from the presence of titanium suboxides at the target surface caused by preferential sputtering of the oxide. The model can be used for optimization of the target composition with respect to the deposition rate and film composition in a stable hysteresis-free reactive sputtering process.

Dynamic simulations of pulsed reactive sputtering processes

In the reactive sputtering process numerous parameters interact in a complex and nonlinear way. Thus, if any parameter is changed during operation, it is not an easy matter to predict the response of the other involved parameters. The static behavior of the reactive sputtering process has previously been carefully investigated. However, studies of the time dependent behavior of this process are rare. It is important to study the dynamic behavior to gain a more complete understanding of the process. Furthermore, the increased use of pulsed power sources has set focus on the process dynamics. A model describing the time-dependent behavior of the pulsed reactive sputtering process is proposed in this work. The model suggests that the time to reach process equilibrium may vary substantially depending on the process history. This memory effect has been experimentally verified. Finally, the simulations clearly point out that for high repetition frequencies (>1 kHz) of the pulsed direct current (dc) reactive sputtering process there will be no time-dependent variations of the chemical compositions either at the target surface or at the growing film at the substrates. At these high frequencies the chemistry of the process will act identical as to the continuous dc reactive sputtering process having the average pulsed dc power supplied to the target.In the reactive sputtering process numerous parameters interact in a complex and nonlinear way. Thus, if any parameter is changed during operation, it is not an easy matter to predict the response of the other involved parameters. The static behavior of the reactive sputtering process has previously been carefully investigated. However, studies of the time dependent behavior of this process are rare. It is important to study the dynamic behavior to gain a more complete understanding of the process. Furthermore, the increased use of pulsed power sources has set focus on the process dynamics. A model describing the time-dependent behavior of the pulsed reactive sputtering process is proposed in this work. The model suggests that the time to reach process equilibrium may vary substantially depending on the process history. This memory effect has been experimentally verified. Finally, the simulations clearly point out that for high repetition frequencies (>1 kHz) of the pulsed direct current (dc) reactive spu...

Modelling of low energy ion sputtering from oxide surfaces

The main aim of this work is to present a way to estimate the values of surface binding energy for oxides. This is done by fitting results from the binary collisions approximation code Tridyn with data from the reactive sputtering processing curves, as well as the elemental composition obtained from x-ray photoelectron spectroscopy (XPS). Oxide targets of Al, Ti, V, Nb and Ta are studied. The obtained surface binding energies are then used to predict the partial sputtering yields. Anomalously high sputtering yield is observed for the TiO 2 target. This is attributed to the high sputtering yield of Ti lower oxides. Such an effect is not observed for the other studied metals. XPS measurement of the oxide targets confirms the formation of suboxides during ion bombardment as well as an oxygen deficient surface in the steady state. These effects are confirmed from the processing curves from the oxide targets showing an elevated sputtering rate in pure argon.

Target compound layer formation during reactive sputtering

It is well known that a compound layer may form at the target surface during reactive sputtering. However, the significance of this layer for the response to a change in target conditions has so far not been carefully investigated. The standard model for the reactive sputtering process [S. Berg et al., J. Vac. Sci. Technol. A 5, 202 (1987)] does not allow for calculations of the compound thickness at the target surface. For simplicity it has been assumed that a single monolayer is responsible for the poisoning of the target. However, experiments clearly indicate that the compound layer thickness may be significantly thicker than one monolayer. For several reasons it is important to be able to quantify the thickness of this layer. The formation of the compound layer introduces memory effects into the system when the processing conditions are changed. The sputter erosion time for the compound layer depends on its thickness. We will present an extension of the basic reactive sputtering model that allows for ...

Studies of reactive sputtering of multi-phase chromium nitride

We have presented a model for reactive sputter deposition of two-phase materials. This model has been applied to reactive sputtering of chromium nitride where it is assumed that either Cr2N or CrN is formed. In order to test the validity of the model, a number of deposition experiments has been performed where the film composition for different reactive gas supplies has been estimated by means of in situ soft x-ray emission spectroscopy. The results have been compared with predicted film compositions according to the model and the experimental findings agree qualitatively with the simulations.

Diamond deposition in a microwave electrode discharge at reduced pressures

Abstract Diamond deposition on heated Si-substrates was studied under microwave discharge generated by an electrode-antenna either in a “point-to-plane” arrangement or in a “parallel-plane” arrangement at gas pressures of 1–15 Torr in a mixture of hydrogen with methane and oxygen. Diamond growth of 1 μm h −1 was obtained on surfaces up to 2 cm in diameter at microwave power of 150–200 W. No metal impurities from the electrode were detected in the diamond films. Typical gas mixture was 4% methane and 0.5% oxygen in hydrogen at a total pressure of 15 Torr. The role of additional r.f. potential during the film deposition was studied in the case of “point-to-plane” electrode arrangement. Correlation of the power absorbed in the plasma and the optical emission of H atoms have been observed.