Ion mass and scaling effects in PIII simulation

Simulation of plasma immersion ion implantation (PIII) is a necessary and valid tool to optimise the treatment homogeneity by adjusting parameters like voltage, plasma density, pulse rise time or pulse length. It can be shown that the ion mass mi and pulse rise time tr are not two independent parameters. Instead, for sufficiently long pulses, when the plasma sheath reaches the stationary state, the dose distributions obtained are characterised by the quotient tr/mi. Therefore, for lower ion masses, shorter rise times must be used to obtain the same relative range distribution. The spatial homogeneity is not affected as the natural scaling length, the initial matrix sheath thickness xini, depends only on the voltage and ion density and is independent of the ion mass. In this report two-dimensional particle-in-cell (PIC) simulations for PIII treatment of trench structures with different tr/miratios are presented, encompassing the range of mi=4–131 (corresponding to He+–Xe+), at a pulse rise time of 0.5 μs and a pulse voltage of −45 kV. The implantation profiles are shifted more to the surface for lower masses, as their relative rise time is longer.