Ion mass and scaling effects in PIII simulation

Abstract

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 m i and pulse rise time t r 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 t r / m i . 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 x ini, 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 t r / m i ratios are presented, encompassing the range of m i=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.