Influence of thickness and dielectric properties on implantation efficacy in plasma immersion ion implantation of insulators

Abstract

Passivation layer on polyimide deposited by combined plasma immersion ion implantation and deposition and cathodic vacuum arc techniqueEffects of mesh-assisted carbon plasma immersion ion implantation on the surface properties of insulating silicon carbide ceramics Plasma immersion ion implantation of insulators is an interesting topic both theoretically and industrially. The net energy of the incident ions is dictated by the surface potential and for conductors is equal to the voltage applied to the backside or sample stage. However, the poor electrical conductivity of insulating materials can lead not only to charging during ion bombardment but also reduced surface potential due to the capacitance effect. In the work described in this paper, we theoretically and experimentally investigate the influence of the thickness and dielectric properties of insulating materials on the implantation efficacy. The use of mesh-assisted PIII by covering the insulating materials with an electrically conducting cage to enhance the implantation efficacy is also compared experimentally. Our theoretical results suggest that a low plasma density induces less surface charges and higher surface potential. Our experimental data show good agreement with the theoretical results and mesh-assisted PIII does yield net improvement.

Direction for the Future - Successive Acceleration of Positive and Negative Ions Applied to Space Propulsion

“…In plasma immersed ion implantation (PIII) sudden negative bias pulses are applied to a surface such that positive ions are implanted in the material [19]. Several authors have seen that implanting into a dielectric substrate results in a significant voltage build-up in the wafer, reducing the effective implant energy [20,21]. In our case, a film composed of fluorine and sulfur can deposit on the acceleration grids.…”

“…This film is also detectable by measuring a decrease in the current on the grids. In the presence of a dielectric layer on the plasma grid, a certain voltage will be dropped in the dielectric such that the effective acceleration voltage is [21] V where δ is the thickness of the dielectric film and Q is the surface charge. For a quick estimate using δ ∼ 1 µm, Q ∼ 1 × 10 16 and ε r = 3.7 as for pure sulfur, the voltage drop in the dielectric is about 50 V, which is of the order of the measured energy loss for negative ions.…”

Ion energy measurements during plasma immersion ion implantation of an insulator

“…If the pulse length is long enough and/or the plasma density high enough, the insulator will charge up to the floating potential where the flux of electrons and ions to the surface is equal [8]. To minimize surface charging and improve the depth of treatment, a metal mesh can be placed around the insulator and pulse biased together with the object [9][10][11][12].…”

“…To date, there have been limited experimental studies of the effects of surface charging on the IED during PIII of insulators. Experimental studies have investigated the effects of the use of metal grids and the thickness and dielectric constant of the insulator on the implantation depth of ions [9,10]. The effects of an insulator on IEDs at dc and radio frequency (RF) biased substrates have been studied using computer simulation [23,24] and have shown that near a metal/insulator interface the ion flux and energy distribution are significantly affected by sheath distortion.…”