AVS 49th International Symposium
    Photonic Materials Topical Conference Thursday Sessions
       Session PH-ThA

Paper PH-ThA8
Influence of Ge Content and Process Parameters on the Optical Quality of Low Temperature PECVD Deposited Silica Waveguides

Thursday, November 7, 2002, 4:20 pm, Room C-111B

Session: Optical Lightguides
Presenter: M. Dainese, Royal Institute of Technology, Sweden
Authors: M. Dainese, Royal Institute of Technology, Sweden
L. Wosinski, Royal Institute of Technology, Sweden
H. Fernando, Royal Institute of Technology, Sweden
X. Cao, Royal Institute of Technology, Sweden
Correspondent: Click to Email
Silica-on-Silicon technology for Planar Lightwave Circuits, based on Plasma-CVD, is a candidate for monolithic optoelectronic integration due to its potential compatibility with VLSI technology. But the standard fabrication process, that includes a final high temperature (@>=@1000°) consolidation step, is not compatible with this purpose. We propose a modified, full low temperature, PECVD-based process that has been optimized to obtain an as-deposited material with high optical quality. Using a capacitively coupled reactor, with 380kHz RF power supply and platen temperatures between 250° and 300°, we have investigated the properties of the as-deposited material, with emphasis on germanium doped silica glass, which forms the light guiding layer. The set of characterisation techniques includes: prism coupler, wet etch rate, FTIR, XPS, ERDA. The results show that, for pure silica, stoichiometry is controlled by the N@sub 2@O/SiH@sub 4@ flow ratio, whereas RF power affects the material structure and homogeneity, together with by-products release during surface processes. For a given SiH@sub 4@ flow and flow ratio, there is an optimum value for the deposition pressure which maximise the deposition rate (here 1750Å/min). In case of germanium doping (up to 6.5at%), the high reactivity and low surface mobility of germane radicals make the deposition more sensitive to platen temperature and produce films with higher porosity and co-ordination disorder, compared to pure silica. We demonstrate that increasing the flow ratio is not enough anymore to obtain correct stoichiometry and RF power becomes a critical variable with respect to this. The final result is a material with low optical losses (0.3dB/cm at 1.55µm), with no absorption due to higher order harmonics of either Si-H or N-H bond vibrations. Examples of photonic devices will be presented.