Investigation of the electron kinetics in O₂capacitively coupled plasma with the use of a Langmuir probe

Abstract

A Langmuir probe was used to measure various electron plasma parameters in O 2 capacitively coupled plasma. It was shown that the variation in these plasma parameters was due to changes in the electron heating mechanisms as the discharge conditions varied. The so called 'α-γ' mode transition in O 2 plasma (100 mTorr) was identified from the power evolution (30-600 W) of the electron energy probability function (EEPF), electron density (n e ) and effective electron temperature (T eff ). The EEPF evolved from Druyvesteyn to bi-Maxwellian with increasing applied power which resulted in a rapid decrease and an abrupt increase in T eff and n e respectively. Comparisons were made to the same mode transition for similar conditions in Ar plasma. The EEPFs were Druyvesteyn in the α mode and evolved into a Maxwellian like EEPF in the γ mode of an Ar plasma. Two distinct trends of n e versus power was observed, it was shown that the measured rf current and rf voltage had a similar behavior. The pressure evolution of the EEPF, n e , and T eff was also investigated in O 2 plasma operated at both 30 and 200 W. At 30 W the number of high energy electrons decreased and flattening of the low energy portion of the EEPF occurred with increasing gas pressure (10-100 mTorr) which indicates a collisionless to collisional heating transition. However, at 200 W the right combination of rf voltage and pressure was met for the discharge to evolve into the γ mode as the pressure increased. This was evident from significant narrowing of the EEPF as the pressure increased.

Plasma Spectroscopy Diagnostics of V2O5 at a Variable of Operating Power and Pressure With Radio Frequency Magnetron Sputtering.

“…The deviation in plasma temperature causes a nonlinear change in the energy of the ions with increased power. In the figure below shows that the average ion energy reaches maximum RF power at about 75W (11,13,14). with increasing RF power.…”

“…For example, the stirring energy of argon atoms is 11.8 eV while the ionization energy is 14.6 eV. Besides, the stirring energy should be greater than or equal to the energy of the electronic case in order for the excitation to occur (7,11). Figure 3.…”

Uses of radio emission spectroscopy for non-contact and in situ diagnostics of low pressure radio frequency plasma processing

“…In order to understand the variations of fundamental plasma parameters with power we now discuss the variation of key plasma parameters, namely the electron density, electron temperature and electron collision frequency over the power range presented in figure 2 above. Measurements of fundamental plasma parameters for capacitively coupled discharges in O2 for this reactor have previously been reported 12,18 . Kechkar et al 18 reported ne values at 100 mTorr ranging from ~7 × 10 15 m -3 at 50 W to ~6 × 10 16 m -3 at 500 W applied power with corresponding electron plasma frequencies (ωp) 13 ranging from 0.8 to 2.38 GHz.…”

“…Measurements of fundamental plasma parameters for capacitively coupled discharges in O2 for this reactor have previously been reported 12,18 . Kechkar et al 18 reported ne values at 100 mTorr ranging from ~7 × 10 15 m -3 at 50 W to ~6 × 10 16 m -3 at 500 W applied power with corresponding electron plasma frequencies (ωp) 13 ranging from 0.8 to 2.38 GHz. The electron temperature (Te) values (at 100 mTorr) ranged from 2.3 eV at 50 W to 0.8 eV at 500 W. Substituting into equation ( 1) above using an O2 mass of 2.6×10 -26 kg for mion, we find the conduction current ranges from 0.214 A at 50 W to 1.1 A at 500 W. To corroborate we compare our calculation with an inline spatially averaged probe measurement measured using a V-I probe (figure 2c 13,18 ).…”

Remote sensing of a low pressure plasma in the radio near field

“…by extracting the geometric resonance frequency shown in figure 4 and employing an estimate of the total sheath width. A calculation of the high voltage sheath size is carried out by employment of the Child sheath law 22) coupled with a combination of Langmuir probe measurements 13,14) for electron density and temperature and I-V measurements for estimation of the sheath voltage. 27) The 'high voltage' sheath width is estimated here as 0.…”