Paper PS2-WeA5
Fabrication of Organic Polymers with Tuned Properties and Their Correlation to Plasma-diagnostic Parameters

Wednesday, October 17, 2007, 3:00 pm, Room 607

Poly-parylene is one of the rare organic polymers which have passed the FDA criteria as long-term compatible for the human body. Films of the derivates C and N have been deposited applying cvd and pecvd (microwave). By a combined application of plasma diagnostics and surface analysis, is is possible to tailor the properties of the polymer poly-parylene over a wide range. In the border region, the plasma density rapidly falls with growing distance from the wall due to the strong shielding at microwave frequencies. In contrast to the usual expectation, the plasma density decreases with growing pressure for both ambients, argon and parylene. The electron temperature exhibits the expected hyperbolic behavior vs. pressure. Nevertheless, the higher deposition rate is the most significant proof of the higher density of polymer-building species as compared to cvd. As first consequence, in a pulsed plasma the ratio of the time constants of diffusion can be modeled applying the simplest approach proposed by Brown. For same power input, the plasma density in parylene is lower by more than one order of magnitude compared with argon, which is due to numerous other tracks of molecule excitation and electron loss. At the upper energy end, parylene-C definitely behaves as an electropositive gas, main loss of electrons caused by diffusion, whereas at low or medium energies, pressure-independent electron attachment is supposed to become the dominating loss mechanism leading to significantly lower plasma densities as compared to argon. Infrared spectroscopy shows the conservation of the ring structure during the plasma treatment. The contact angle exhibits a relatively flat response with respect to discharge pressure for cvd, stronger dependence for pecvd. The surfaces of the cvd-films are classically hydrophobic and lipophilic. This behavior is less pronounced in the pecvd-films. Films copolymerized with CF₄ are both hydrophobic and lipophobic in character and show very high roll-off angles (super-hydrophobicity). Subsequent plasma treatment with Ar/O₂ significantly reduces the contact angle against water (down to 30^o). The dielectric constant has found to be very low with only a slight increase to low frequencies with nearly the same value at optical frequencies. Compared with previous works, the range for influencing these surface properties has been farther opened.