PTFE film deposition technology

Method offers the possibility of adjusting PTFE film structure. Increase of activation power resulted in film amorphisation with change of refractive index. The film contains linear macromolecules. Farther modification was made using 40,68 MHz discharge. At a moderate power cross-links were created, leading to increase in the thermal stability. But the macromolecules remain linear in contrast to the plasma deposits.

Both PTFE films deposited with and without plasma have C 1s main peak at 293,22 eV, which is attributed to -CF₂-groups. Other peaks, related to end groups or cross-links are present but at minor percentages. Oxygen is at less than 1%. The surface of the films is like bulk PTFE. The film deposited with mild plasma contains a smaller portion of end groups. Increasing plasma power or placing the substrate directly on the electrode leads to film, which has increased band intensities attributed to branches and cross-links.

Plasma treatment allows the deposition of smooth PTFE film on organic substrates. Deposition of PTFE on PC surface without plasma treatment led to formation of clusters up to 50 nm diameter,  film average roughness was 3,5 nm, while  film deposited with plasma had  roughness of 1,5 nm.  The film grown on inorganic substrate (Au) is smoother – even without plasma treatment its roughness is about 2 nm. The use of plasma also has an effect on the coverage of DVD steps. Without plasma the covered steps retain a rectangular shape. With plasma discharge the coverage more resembles that of the gas phase coating like plasma polymerized polymer, but to an intermediate extent, depending on plasma power. Under certain conditions film fills the trench like a wetting liquid, while at others it grows in the middle of the trench, being repelled from the walls.

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