Impact of Thermal Treatment on PECVD Al2O3 Passivation Layers

We present a detailed study about the influence of post-deposition temperature treatment on PECVD Al2O3 passivation layers. Fourier transform infrared spectroscopy (FTIR) and quasi-steady-state photoconductance (QSSPC) were applied for characterization. We observed several indications of structural changes of the Al2O3 layer with annealing duration, temperature and layer thickness. A shift and an increase of the Si-O vibrational mode (1100- 980 cm-1) in the FTIR measured with changing temperature and layer thickness is presented. Structural changes of the Al2O3 layer with annealing duration, temperature, and layer thickness, caused by changes in the oxygen concentration within the SiOx layer are observed for the different FTIR spectra. We also detected a water band at 1650-1630 cm-1 and other OH components around 3200 cm-1-400cm-1 depending on annealing temperature and time. For a temperature of 820 °C, a dramatic change of the Al2O3 peak (650-700 cm-1) is observed. This is probably due to the crystallization of the film.