Growth of plasma-polymerized thin films by PECVD method and ...

I.-S. Bae et al. / Surface & Coatings Technology 193 (2005) 142–146 145RF powers. All AFM images showed quite smooth surfaceswith no cracks. In the case of the methylcyclohexane film,for example, the rms roughness decreases from 7.375 to0.257 nm with increasing RF power to 100 W (see Fig. 3aand b). Moreover, the rms roughness of the ethylcyclohexanefilm is also decreased from 7.925 to 0.444 nm withincreasing RF power. In addition, we could clearly see thecluster on the film surface grown. From Fig. 3a and b, wecan see that the clusters of the films have 1 Am size at 30Wof RF power. But it was not entirely the cluster from thesurface of 100 W. This could be explained by the differentdissociation rates of precursor or sputtering effect. In otherwords, when the RF power increases, the element ofprecursors goes well disjointing from air or surface. Sothe polymer is formed by the size of the disjointed element.When the RF power increases, the element size becomessmall because of the plasma bombardment. We confirmedthat the RF power mainly determines the roughness ofsurface.Fig. 4 shows the variation of contact angles of thepolymerized thin films. Contact angle was measured froma drop of liquid resting on a solid surface. The drop ofliquid forming an angle may be considered as resting inequilibrium by balancing the three forces involved. Theangle within the liquid phase is known as the contact angleor wetting. In generally, a hydrophilic surface will have acontact angle less than ~708, and a hydrophobic surface ischaracterized by a contact angle of 70–908 or larger. FromFig. 4, the values of contact angles for ethylcyclohexanefilms are also increased from 72.98 to 79.38 withincreasing RF power to 100 W, while those for methylcyclohexanefilms are also increased from 83.08 to 89.38,respectively. This indicates that the plasma-polymerizedmethylcyclohexane films will relatively have more highsurface energy than that of ethylcyclohexane thin films,and both films could have hydrophobic surface and lowsurface energy with increasing RF power. However, moredetailed experiments are still needed to confine thisphenomenon.4. ConclusionsWe have deposited organic polymer thin films on Si(100)and glass substrates at room temperature using organicmonomer precursors by plasma-enhanced chemical vapordeposition (PECVD) method. Radiofrequency with 13.56MHz was applied for the ignition of the plasma, and theirRF power were changed in the range from 30 to 100 Wunder gas ratio of Ar:H 2 =1:1. Methylcyclohexane andethylcyclohexane were utilized as organic precursors, andH 2 and Ar were used as a bubbler and carrier gas,respectively. The as-grown organic thin films also showedquite high optical transmittance up to 80%. FT-IR and UV–Visible results show that the as-grown films have someoriented structures. And AFM data show quite smooth anddense surface morphology with increasing RF power. Theoptical refractive index of methylcyclohexane polymer filmsshow more higher value than that of ethylcyclohexane filmswhile the contact angles of methylcyclohexane films haverelatively lower values than that of ethylcyclohexane films,indicating more high surface energy for the methylcyclohexanefilms. The maximum growth rate of this study wasfound to be 98 nm/min.Fig. 4. The contact angle of the (a,b) methylcyclohexane and (c,d) ethylcyclohexane thin films.