Invited Paper PS1-TuA1
Looking Down the Rabbit Hole: Impact of Porosity in Plasma-deposited Inorganic Layers on Their Moisture Permeation Barrier Performance

Tuesday, October 30, 2012, 2:00 pm, Room 24

Although very promising results in terms of moisture and oxygen permeation barrier properties have been achieved by organic/ inorganic multi-layers, the impact of the organic interlayer on the global barrier performance is still under discussion. It is generally considered that the organic interlayer acts as smoothening layer for the macro-defects present at the surface or in the barrier layer. It is also hypothesized that the organic interlayer infiltrates into the nano-pores present in the barrier layer, therefore affecting the barrier itself at microstructure level.

In the present work the moisture permeation barrier performance of multi-layers deposited by means of initiated- and plasma enhanced- CVD methods [1] is addressed, with the aim of unraveling the role of the organic interlayer. Calcium test measurements allowed discriminating between the water permeation through the macro-defects/pinholes and the permeation through the matrix porosity. It has been found that the improvement in terms of barrier properties, due to the filling/infiltration of the SiO₂ layer nano-pores by an organosilicon interlayer [2], universally correlates with the residual open micro- (i.e. < 2 nm) porosity in the inorganic (SiO₂ or Al₂O₃) layer, independently of the deposition method (PECVD or plasma-assisted ALD). The residual nano-porosity has been evaluated by means of ellipsometric porosimetry which allows carrying out adsorption/desorption isothermal of a probe molecule in the open porosity. In detail, only for WVTR values of the SiO₂-like layer larger than 10^-3 g m^-2 day^-1, a barrier improvement factor is observed upon deposition of the organic interlayer, although limited to values between 5 and 10. This outcome, in combination with the evaluation of the macro-defect density upon organosilicon layer deposition on the SiO₂ layer, provides the evidence that smoothening plays a major role in the improvement of the barrier performance.

Next to the growth and characterization studies of the organosilicon/SiO₂ multi-layer, the control on the residual open nano-porosity of high growth rate roll-to-roll atmospheric pressure plasma deposited SiO₂ layers is addressed. Upon 2 nm thick Al₂O₃ layer deposition, the water vapor transmission rate of the SiO₂ layer decreases of a factor 10³, due to the filling of the residual SiO₂ nano-porosity.

[1] G. Aresta, J. Palmans, M.C.M. van de Sanden, M. Creatore, (2012), accepted for publication in J.Vac. Sci. Technol.