EMISSION ACTINOMETRIC INVESTIGATIONS OF ATOMIC-HYDROGEN AND CH RADICALS IN PLASMA-ENHANCED CHEMICAL-VAPOR-DEPOSITION PROCESSES OF HEXAMETHYLDISILOXANE

Spectral investigations were carried out in a plasma-enhanced chemical vapour deposition (PECVD) process using hexamethyldisiloxane (HMDSO) thin film deposition. The experiments were performed in a closed react or with r.f. plasma generation in the pressure range of 20-40 Pa and p ower range of 10-20 W. It is shown that the emission lines of atomic h ydrogen (486 nm) and CH radicals (431 nm) are the most informative lin es from the point of view of the process dynamic control, because hydr ogen is the final product of the discharge and CII is an indicator for the last intermediate products (CxHy) of the process obtained. Other species (Si and O) are built in the deposited coating. The excitation energy of the hydrogen lines (approximate to 12 eV) permit the use of the argon emission line at 750 nm as an actinometer (approximate to 11 eV). A problem for using actinometry is the large difference of the e xciting level of the CH band (approximate to 3 eV). That is why in the following article is shown as only a first approximation for characte rising this PECVD process. By adding argon (up to 10%) the process dyn amic was controlled in the hydrogen and CH radicals concentration meas urement mode. The measurement was realised by using spectral signals m easured at 5-8 (peak and its background) different wavelengths in the quasi parallel mode of an acoustooptical spectrometer. The measured cu rves of the relative H and CH concentrations demonstrate the CH accumu lation due to plasma chemical conversion of HMDSO during the first two stages of the process duration. The final stage of the process is cha racterised by the dissociation of CH radicals, which results in a sync hronous increase of the hydrogen signal and decrease of the CH radical s signal causing the existence of free carbon, which appears as carbon enriched coverage on reactor walls. (C) 1998 Elsevier Science S.A.