Surface modification of polymers by plasma-assisted atomic layer deposition

The inhomogeneous and hydrophobic surface characteristics of many polymers can be incompatible with other substances which are required for their further functionalization. Various plasma methods have been used to overcome this problem and to enable functionalization to take place. Plasma modification can nevertheless lead to a nonuniform and chemically unstable surface which results in only a moderate performance in the final application. Deposition of ultrathin layers by atomic layer deposition (ALD) as a surface modification of the polymers is a useful way to bring the desired functionality to polymer surface. ALD at low temperature suffers from slow reaction rates, consequently giving low deposition rates. Among the different ALD methods, plasma assisted ALD (PA-ALD) is suitable for depositions at low temperatures with faster chemical reactions compared to thermal ALD. In this work tetrakis-dimethyl-amido titanium (TDMAT) and plasma excited 02 precursors were used to deposit TiO2 on Si(100) and polymethylmethacrylate (PMMA) substrates. Changes in the process conditions were studied by means of varying plasma power, oxygen pulse length and the point in time of plasma ignition during the ALD cycle. In the case where a mixture of nitrogen and argon was introduced into the reactor to act as a purge gas between precursor pulses and also to facilitate the generation of a plasma during the plasma cycle, the plasma did not show detrimental effects on film adhesion on PMMA substrate, whereas using only argon as a carrier and plasma gas was found to cause poor film adhesion to the PMMA. ATR-FTIR analysis showed lower levels of carbonaceous compounds for the film grown at lower plasma power. The films grown with lower plasma power also showed higher refractive index which suggests the low plasma power is more beneficial for this particular PA-ALD TiO2 process. (C) 2011 Elsevier B.V. All rights reserved.