Oto Brzobohaty
Institute of Scientific Instruments ASCR
Publications
Determination of electron density and temperature in a capacitively coupled RF discharge in neon by OES complemented with a CR model
A method of determination of electron temperature and electron density in plasmas based on optical emission spectroscopy complemented with collisional-radiative modelling (OES/CRM) was studied in this work. A radiofrequency (13.56 MHz) capacitively coupled discharge in neon at 10 Pa was investigated by intensity calibrated optical emission spectroscopy. The absolute intensities of neon transitions between 3p and 3s states were fitted with a collisional-radiative (CR) model in order to determine the electron temperature and electron density. Measuring techniques such as imaging with an ICCD camera were adopted for supplementary diagnostics. The obtained results were compared with the results of compensated Langmuir probe measurement and one-dimensional particle-in-cell/Monte Carlo (PIC/MC) simulation. The results of OES/CRM and PIC/MC method were in close agreement in the case of electron temperature in the vicinity of a driven electrode. The determined value of electron temperature was about 8 eV. In bulk plasma, the measured spectra were not satisfactorily fitted. In the case of electron density only relative agreement was obtained between OES/CRM and Langmuir probe measurement; the absolute values differed by a factor of 5. The axial dependence of electron density calculated by PIC/MC was distinct from them, reaching the maximum values between the results of the other two methods. The investigation of power dependence of plasma parameters close to the driven electrode showed a decrease in electron temperature and an increase in electron density together with increasing incoming RF power. The calculated spectra fitted very well the measured spectra in this discharge region. Download
Influence of substrate material on plasma in deposition/sputtering reactor: experiment and computer simulation
The aim of this work was to investigate the influence of the substrate material on the plasma enhanced chemical vapour deposition and the plasma sputtering of thin films in low pressure (3-20 Pa) parallel-plate radio frequency (rf) discharges. It was observed that the deposition or sputtering rates differed above different materials, e. g. above a substrate and substrate electrode. Moreover, the substrates placed on the bottom rf electrode seemed to be mirrored in the thickness of a thin film deposited or sputtered on the upper grounded electrode. The influence of the substrate material on the plasma parameters was studied via particle in cell/Monte Carlo computer simulation. According to our finding the mirroring of the substrate was caused by different secondary electron emission yields of the substrate material and material of the substrate electrode. This difference in the secondary electron yield affected plasma density above the substrate leading to higher or lower deposition or sputtering rates on the grounded electrode. Therefore, the role of secondary electrons in the discharge was studied. Spatial distributions of impact positions on the grounded electrode for electrons and ions emitted from the rf electrode and created in the ionization avalanche of the secondary electrons were calculated in order to simulate the mirroring of the substrates. Download