Surface film formation by chemical vapor deposition of di-p-xylylene : ellipsometrical, atomic force microscopy, and x-ray studies

Thin and transparent poly(p-xylylene) (PPX) layers in the range 2-1550 nm have been prepared by means of chemical vapor deposition (CVD) via vapor-phase pyrolysis of the cyclic di-p-xylylene dimer. Ellipsometrical measurements are employed on those materials to study in detail the dependence of layer formation on sublimation temperature (80-140 °C) and deposition time (5-360 min). The layer growth rate on silicon wafers is found to be 0.3, 1.0, 6.3, and 11.8 mm/min at sublimation temperatures of 80, 100, 120, and 140 °C, respectively. The PPX layers are optically transparent in the investigated range of wavelengths from 190 to 1700 nm. Atomic force microscopy (AFM) studies show a surface roughness of 2-4 nm and larger values, 5-9 nm, at a high sublimation temperature of 140 °C or large deposition times tdc > 120 min. Wide angle X-ray diffraction (WAXD) experiments describe a monoclinic crystalline a-form with reflections (020) and (110) at 2¿Cu = 17.7 and 22.8°, respectively. Small angle X-ray scattering (SAXS) studies reveal a lamellar structure with a long period of 8.3 nm.