Evidence of secondary electron emission during PIII pulses as measured by calorimetric probe

Abstract

Secondary electrons are an ubiquitous nuisance during plasma immersion ion implantation (PIII) necessitating excessive current supplies and shielding for X-rays generated by them. However, additional effects – especially at low pulse voltages – can include interactions with the plasma and transient increases in the plasma density. Here, it is shown that the transient thermal flux associated with secondary electrons emitted from the pulsed substrate can be directly measured using a passive calorimetric probe mounted near the chamber wall away from the pulsed substrate holder. A small increase of a directed energy flux from the substrate towards the probe is consistently observed on top of the isotropic flux from the plasma surrounding the probe, scaling with pulse frequency, pulse voltage, pulse length – as well as depending on gas and substrate material. A strong correlation between voltage and substrate-probe distance is observed, which should allow further investigation of low energy electrons with the plasma itself.