Molecular layer deposition of polyethylene terephthalate thin films

Thin films of polyethylene terephthalate (PET) have been grown using sequential surface chemical reactions on silicon substrates. The surface has been sequentially exposed to terephthaloyl chloride (TC) and ethylene glycol (EG) in an ASM F-120 atomic layer deposition reactor. Precursor pulses were alternated with 30 s of N-2 purge. The process has been studied as a function of temperature, precursor pulsing time, and number of cycles. The films were deposited in the temperature range 145-175 degrees C and the precursors were held at 130 degrees C (TC) and 70 degrees C (EG). Before deposition the silicon surface was functionalized using 3-aminopropyltriethoxysilane to ensure nucleation of the film. The film growth exhibits self-limiting behavior and linear growth rate dependence that confirms its molecular layer deposition nature. The deposited films have been identified as PET by means of attenuated total reflectance FTIR which reveals the presence of characteristic carbonyl and aromatic groups. Film thickness was measured by spectroscopic ellipsometry. The maximum deposition rate of 3.3 angstrom/cycle was obtained. Surface morphology was investigated using AFM showing average roughness (Ra) of 3.5 nm. (C) 2012 American Vacuum Society. [DOI: 10.1116/1.3662846]