Disturbance of a Langmuir Probe at the Steady-State Sheath Boundary in a Drifting Plasma

Abstract

The disturbance resulting from the presence of a positively biased Langmuir probe at an equilibrium steady-state ion sheath boundary in the drifting plasma is simulated by the twodimensional particle-in-cell (PIC) method in rectangular coordinates. The positive potential of the probe was found to shield electrons on the side of the probe away from the sample surface from the negative potential of the sample surface and thereby cause an increase in the electron current drawn by the probe. The drifting ions on the same side of the probe are slowed by it and thereby raising the ion density in front of the probe. The electron currents of the probe are calculated at different probe positions from the sample surface. It is found that the sheath boundary as defined by the probe current is wider than the unperturbed boundary. The widening of the sheath boundary agrees well with experimental sheath boundary measurements.

Demagnification and Magnification Effects in One-Step Noncontact Pattern Transfer by Direct-Current Plasma Immersion Ion Implantation

“…Plasma generation is not considered in the simulation, and electrons possess the Boltzmann distribution at a temperature of 2.5 eV. The PIC ions are refilled in the first layer cells (from the top) for every 38 time steps assuming that ions drift from the presheath [12], [13]. The space potential of each node is calculated by iterating the finite difference equations of Poisson's formula [14], [15], and the location of the PIC particles is updated by Newton's equation of motion.…”

One-step, non-contact pattern transfer by direct-current plasma immersion ion implantation

“…The Bohm velocity of 2447 m s −1 is given to the PIC ions drifting towards the metal masks. Plasma generation is not considered in the simulation but the PIC ions will be refilled at the first layer cells of the top region assuming that ions drift from the pre-sheath [18,19]. The time step used is 7.17 When the masks are biased to −500 V, the ions are confined to a length of 80 µm with a bell-shape distribution (figure 4(h)).…”

A hybrid Boltzmann electrons and PIC ions model for simulating transient state of partially ionized plasma

“…By using the Boltzmann relation to describe electron density, the cell length and time step can be chosen to resolve the ion motion, but not necessarily small enough to resolve the electron motion. The Boltzmann relation has been used extensively in simulating plasma immersion ion implantation process with great success [4][5][6][7][8][9][10]. The advantage is that it will save a lot of simulation time.…”