High-rate deposition of plasma polymerized thin films using PECVD method and characterization of their optical properties

Plasma polymerized organic thin films were deposited at temperature in the range of room temperature to 693 K by plasma enhanced chemical vapor deposition method using the thiophene (C4H4S) precursor. Radio frequency (RF) with 13.56 MHz was applied and the RF power was changed in the range from 30 to 100 W with a gas ratio of Ar:H-2 = 1:1. The as-grown organic thin films were basically characterized with ellipsometry, UV-Vis spectroscopy, and photoluminescence (PL) measurements. In order to compare the difference of optical properties of the plasma polymerized organic thin films, the effects of the RF power and deposition temperature on their structural properties were mainly studied in this work. UV-Vis spectra showed an energy band gap shift from 3.78 to 4.02 eV with increasing RF power and quite high optical transmittance up to 95%. During CVD, moreover. the plasma diagnostics were in situ carried out by using optical emission spectroscopy that showed a strong dependency of intensity on RF powers. To check a possibility of optical device application, PL measurements were also carried out. From the PL data, we could obtain the maximum PL emission intensity at approximately 550 nm wavelength from a plasma polymerized organic thin film grown at room temperature and RF power of 70 W with gas ratio of Ar:H, = 1: 1. The maximum growth rate is obtained to be 115 nm/min. (C) 2003 Elsevier Science B.V. All rights reserved.