Defect analysis in low temperature atomic layer deposited Al2O3 and physical vapor deposited SiO barrier films and combination of both to achieve high quality moisture barriers
Authors: Maindron Tony , Jullien Tony , André Agathe 
Published: May 2016

Al2O3 [20 nm, atomic layer deposition (ALD)] and SiO films' [25 nm, physical vacuum deposition (PVD)] single barriers as well as hybrid barriers of the Al2O3/SiO or SiO/Al2O3 have been deposited onto single 100 nm thick tris-(8-hydroxyquinoline) aluminum (AlQ3) organic films made onto silicon wafers. The defects in the different barrier layers could be easily observed as nonfluorescent AlQ3 black spots, under ultraviolet light on the different systems stored into accelerated aging conditions (85 °C/85% RH, ∼2000 h). It has been observed that all devices containing an Al2O3 layer present a lag time τ from which defect densities of the different systems start to increase significantly. This is coherent with the supposed pinhole-free nature of fresh, ALD-deposited, Al2O3 films. For t &gt; τ, the number of defect grows linearly with storage time. For devices with the single Al2O3 barrier layer, τ has been estimated to be 64 h. For t &gt; τ, the defect occurrence rate has been calculated to be 0.268/cm2/h. Then, a total failure of fluorescence of the AlQ3 film appears between 520 and 670 h, indicating that the Al2O3 barrier has been totally degraded by the hot moisture. Interestingly, the device with the hybrid barrier SiO/Al2O3 shows the same characteristics as the device with the single Al2O3 barrier (τ = 59 h; 0.246/cm2/h for t &gt; τ), indicating that Al2O3 ALD is the factor that limits the performance of the barrier system when it is directly exposed to moisture condensation. At the end of the storage period (1410 h), the defect density for the system with the hybrid SiO/Al2O3 barrier is 120/cm2. The best sequence has been obtained when Al2O3 is passivated by the SiO layer (Al2O3/SiO). In that case, a large lag time of 795 h and a very low defect growth rate of 0.032/cm2/h (t &gt; τ) have been measured. At the end of the storage test (2003 h), the defect density remains very low, i.e., only 50/cm2. On the other hand, the device with the single PVD-deposited SiO barrier layer shows no significant lag time (τ ∼ 0), and the number of defects grows linearly from initial time with a high occurrence rate of 0.517/cm2/h. This is coherent with the pinhole-full nature of fresh, PVD-deposited, SiO films. At intermediate times, a second regime shows a lower defect occurrence rate of 0.062/cm2/h. At a longer time span (t &gt; 1200 h), the SiO barrier begins to degrade, and a localized crystallization onto the oxide surface, giving rise to new defects (occurrence rate 0.461/cm2/h), could be observed. At the end of the test (2003 h), single SiO films show a very high defect density of 600/cm2. Interestingly, the SiO surface in the Al2O3/SiO device does not appeared crystallized at a high time span, suggesting that the crystallization observed on the SiO surface in the AlQ3/SiO device rather originates into the AlQ3 layer, due to high humidity ingress on the organic layer through SiO pinholes. This has been confirmed by atomic force microscopy surface imaging of the AlQ3/SiO surface showing a central hole in the crystallization zone with a 60 nm depth, deeper than SiO thickness (25 nm). Using the organic AlQ3 sensor, the different observations made in this work give a quantitative comparison of defects' occurrence and growth in ALD-deposited versus PVD-deposited oxide films, as well as in their combination PVD/ALD and ALD/PVD.