Abstract
This paper shows the calculation of ion energy distributions (IEDs) in low frequency r.f. plasmas (380 kHz) at the powered electrode for a range of pressures and applied voltages, and also incorporating the effects of charge exchange collisions in the sheath.
Voltage and current waveforms were obtained from the powdered electrode and used to calculate the sheath thickness throughout the negative part of the r.f. cycle (i.e. when ions are attracted to the electrode), using the Child-Langmuir equation. The r.f. cycle is split up into a number of segments, and it is assumed that the sheath responds rapidly to the changes in the electrical parameters.
A modified version of the Davis-Vanderslice equation was used to determine the IED for each segment. This requires an estimation of the cross-section for charge exchange, so that a value of L/λ can be determined and used in the expression.
An IED can thus be determined for each of the segments of the r.f. cycle and can be summed together to produce an overall IED, with each segment being weighted to account for the intensity of ion bombardment during the segment (related to the instantaneous current) and the different time spans of some of the segments.
The results generally indicate an overall IED comparable with a d.c. diode discharge with an L/λ of about 4, compared with a typical d.c. diode discharge which has an L/λ of about 10. The calculation of the IED at 10 mTorr argon pressure does not, however, behave in this way and cannot be directly compared with a d.c. diode discharge.
Voltage and current waveforms were obtained from the powdered electrode and used to calculate the sheath thickness throughout the negative part of the r.f. cycle (i.e. when ions are attracted to the electrode), using the Child-Langmuir equation. The r.f. cycle is split up into a number of segments, and it is assumed that the sheath responds rapidly to the changes in the electrical parameters.
A modified version of the Davis-Vanderslice equation was used to determine the IED for each segment. This requires an estimation of the cross-section for charge exchange, so that a value of L/λ can be determined and used in the expression.
An IED can thus be determined for each of the segments of the r.f. cycle and can be summed together to produce an overall IED, with each segment being weighted to account for the intensity of ion bombardment during the segment (related to the instantaneous current) and the different time spans of some of the segments.
The results generally indicate an overall IED comparable with a d.c. diode discharge with an L/λ of about 4, compared with a typical d.c. diode discharge which has an L/λ of about 10. The calculation of the IED at 10 mTorr argon pressure does not, however, behave in this way and cannot be directly compared with a d.c. diode discharge.
| Original language | English |
|---|---|
| Pages (from-to) | 86-90 |
| Number of pages | 5 |
| Journal | Surface & Coatings Technology |
| Volume | 59 |
| Issue number | 1-3 |
| DOIs | |
| Publication status | Published - 1 Oct 1993 |