Abstract
The effect on the energy distributions of metal and gas ions in a bipolar high-power impulse magnetron sputtering (HiPIMS) discharge as the negative and positive pulse lengths are altered are reported. The results presented demonstrate that the selection of the pulse lengths in a HiPIMS discharge is important in optimizing the amount of accelerated ions. A short enough negative pulse is needed so that ions do not escape to the substrate before being accelerated by the positive pulse that follows the main negative HiPIMS pulse. The length of the positive pulse should also be long enough to accelerate the majority of the ions, but a too long positive pulse depletes the process chamber of electrons so much that it makes it difficult to initiate the next HiPIMS pulse. When pulse lengths of negative and positive pulses are properly selected, the fraction of ions, both metal and gas, accelerated by the positive pulse voltage is close to 100%.
Highlights
Bipolar high-power impulse magnetron sputtering (HiPIMS) refers to the application of positive voltage pulses following the conventional negative HiPIMS pulses and has recently attracted significant attention due to its capability of accelerating plasma ions toward the surface of the growing film [1,2,3,4,5], potentially overcoming the deposition rate problem in HiPIMS [6] and as a possible solution for ion bombardment during sputter deposition of insulating materials [7]
The results presented demonstrate that the selection of the pulse lengths in a HiPIMS discharge is important in optimizing the amount of accelerated ions
The effects of negative and positive pulse lengths on the high-energy fraction of Ti+ and Ar+ ions in a bipolar HiPIMS discharge has been systematically investigated by comparing integrated ion flux intensities between high- and lowenergy ranges from measured Ion energy distributions functions (IEDFs)
Summary
Bipolar high-power impulse magnetron sputtering (HiPIMS) refers to the application of positive voltage pulses following the conventional negative HiPIMS pulses and has recently attracted significant attention due to its capability of accelerating plasma ions toward the surface of the growing film [1,2,3,4,5], potentially overcoming the deposition rate problem in HiPIMS [6] and as a possible solution for ion bombardment during sputter deposition of insulating materials [7]. The mechanism behind the observed ion acceleration during the positive pulse in bipolar HiPIMS is the generation of an electric field by increasing the plasma potential (Vp) in, at least part of, the plasma region in-between the cathode and substrate as suggested by Wu et al [6] and measured by Velicu et al [1]. For ions to be accelerated they need to reach the area of the potential fall while the accelerating positive pulse is applied It follows that the factors influencing the fraction of accelerated ions include the time of ion creation (i.e. length and shape of the ion-generating HiPIMS pulse), the length and timing of the positive pulse, all in relation to the location of the accelerating field in the plasma volume. We can draw a conclusion on where in the plasma volume the majority of ions are accelerated in our particular case
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