AlN PEALD with TMA and forming gas: study of plasma reaction mechanisms

The effect of deposition temperature and plasma dose on plasma-enhanced atomic layer deposition (PEALD) of AlN thin films with forming gas plasma and trimethylaluminum (TMA) has been studied. The temperature has a strong effect on TMA absorption considering the d-TMA absorptions at low deposition temperatures. The plasma effect on AlN growth was studied in terms of three aspects: (1) plasma effect on TMA absorption, (2) plasma effect on the insertion of plasma species and creation of chemical bonds with absorbed surface species, (3) plasma effect on the removal of organic ligands and weakly-bonded surface species. Plasma over-dosing and under-dosing not only affect the film growth rate but also the AlN film properties. A three-effect mathematical model of the plasma effect was built based on the three plasma effects, which is consistent with the AlN experimental growth results. The FTIR and dielectric studies of the PEALD AlN films support the model. Plasma effect on PEALD AIN growth rate follows a similar trend but shifts to longer plasma dose time when deposition temperature decreases.