A collaboaration between Gencoa and the University of Liverpool has resulted in a Monte Carlo code that can predict the plasma districbution and hence target erosion for any magnetron geometry and magnetic array type. The code uses data supplied by the 3D finite element modelling of the magnetic field to predict the electron movement and ionisation impacts over the target surface in 3D. The software allows direct simulation of the target erosion, eliminating the requirement for a plasma test in the design process. This powerfull tool allows the optimisation of existing magnetic designs and the creation of new magnetic designs with minimal testing and risks.

  

Magnetic Modelling The use of 2D & 3D magnetic modelling is the first stage in the simulation process. It resolves the magnetic problem and provides accurate magnetic data such as field strength and electron trajectories at any position over the target surface.

Electron Density Distribution Initial positions are generated with a probability distribution based on the shape of the magnetic loop. At the beginning electrons are generated with Maxwellian distribution with temperature 5 eV, while ions have room temperature. During the process the particles interact with each other as described further, and also they interact with the borders – at the target there are secondary electrons produced by ion bombardment, at the plane of the symmetry the particles are mirrored to the other half of the geometry, and on the other borders particles disappear. During the time they undergo movement under the influence of the electromagnetic field and their positions are being recorded as shown. Collisions are generated using the null-collision technique according. Instead of evaluating an immediate probability of a collision each step of the trajectory calculation, the time of free flight is calculated from the maximum cross section as follows:

Ionisation impact and erosion distribution

The example below illustrates a scanning FFE type plasma in terms of ionisation distribution and target erosion depth. At any point in time the erosion can be estimated and then the results are averaged over time to provide the final end target erosion and to optimise the magnetics.

 

45% Percent Guarantee This modelling has been put to good use. As an example, Gencoa are so confident of the performance of the HY magnetics that we will refund the HY cost if at least 45% of the target is not achieved (by weight). This based upon a 100, 125 , 150 & 200mm wide bonded target type under normal operating conditions. The actual target use should be 50-60% - anything less than 45% and you will 'get the cost of the HY magnetic supplement refunded'.