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0891-EE07-28.1

Fabrication of planar SiON optical waveguide and its characterization Yu-Jeong Cho and Yeong-Cheol Kim Dept. Materials Engineering, Korea University of Technology and Education, Chonan, 330-708, South Korea ABSTRACT Silicon oxynitride (SiON) was deposited as a core layer on a silica (SiO2) under-cladding layer by using plasma enhanced chemical vapor deposition (PECVD). The refractive index of the SiON core layer was varied between 1.45 and 1.78 by changing the gas flow ratio of SiH4, N2O and NH3. Etching experiments were performed using a dry etching equipment to fabricate the SiON core. An optical planar waveguide with a core and under-cladding thicknesses of 6 μm and 8 μm, respectively, and a refractive index contrast (∆n) of 7 % has been fabricated. INTRODUCTION Silica based single-mode planar waveguides have been applied to various kinds of waveguided optical passive devices. Recently, optical splitters for cable television (CATV), personal hand phone systems (PHS), and demultiplexers for wavelength-division multiplexing (WDM) transmission systems have become subjects of practical concerns [1-4]. Nowadays, the deposition of the core layer is of great interest for many applications in integrated optics because the planar waveguide devices are based on doped silica (SiO2) thick layers [5–7]. Among materials considered for waveguides, SiO2 is the most promising because of its low cost, low optical loss, and high coupling efficiency with optical fibers. CVD processes, such as low pressure chemical vapor deposition (LPCVD) and atmospheric pressure chemical vapor deposition (APCVD), have disadvantages of a high deposition temperature and a very low growth rate [8, 9]. The deposition of the silicon oxynitride (SiON) thick layer using plasma enhanced chemical vapor deposition (PECVD) has several advantages, such as low deposition temperature and high deposition rate [10]. It is deposited as a transparent amorphous film whose refractive index can be varied from 1.45 (SiO2) to 2.1 (Si3N4), therefore permitting a controlled matching of the waveguide dimensions and mode profile with the fiber, which is necessary for efficient component pig-tailing [11, 12]. Fresnel reflections at the fiber–waveguide interface are as low as 0.01dB/interface because the materials of the fiber and the waveguide are essentially the same [13, 14]. In this paper, we fabricated SiO2 and SiON layers for a SiON waveguide by PECVD. EXPERIMENTAL SiO2 and SiON layers were deposited by using PECVD. A (100) p-type silicon (Si) wafer was used as a substrate. SiO2 films were deposited from an appropriate gaseous mixture (1:9) of pure silane (SiH4) and nitrous oxide (N2O). SiON films were deposited from appropriate gaseous mixtures of pure SiH4 and N2O and ammonia (NH3). Table 1 shows the process conditions used for the deposition of the SiON films. The substrate was heated to the temperature of 300 ℃. The working pressure and RF power were 150 mtorr and 70 W, respectively, and the total gas flow rate was kept at 100 sccm in all experiments.