Stress development in plasma-deposited silicon dioxide thin-films due to hydrogen evolution

The kinetics of stress change in plasma-enhanced chemical vapor deposited (PECVD) silicon dioxide dielectric films, during annealing, is studied. When silicon dioxide is deposited in excess nitrous oxide, a fraction of the oxide is in the form SiO_3/2OH, instead of SiO₂, which on annealing condenses to SiO₂ and H₂O. The condensed water subsequently diffuses out of the film inducing a stress change (increase in tension or decrease in compression) in the film. A theoretical model relating the hydrogen (or water) concentration to the stress change is developed. Secondary ion mass spectrometry analysis revealed a relatively flat hydrogen concentration profile along the thickness of the film, indicating that the stress change is not diffusion limited. The model thus accounts for first order kinetics for bond breaking accompanied by fast diffusion with a fraction of the atoms or molecules undergoing a trap and release process. From the theoretical fit for the experimental data, activation energy of 1.1 eV for bond breaking is obtained. The model allows predicting the time dependent stress evolution in the PECVD film subjected to a prescribed temperature history.