Fabricating silicon germanium waveguides by low pressure chemical vapor deposition

Abstract

Low loss optical waveguide structures combining the high bandwidth of light transmission and the economics of silicon substrates have been made possible by Low Pressure Chemical Vapor Deposition (LPCVD). This work explores the fabrication, modeling, and testing of LPCVD Si Ge waveguides. Thesis research was conducted during a six-month internship at Applied Materials, a semiconductor equipment manufacturing company. The present work can be divided into two parts: developmental work on the Applied Materials' Epi Centura® LPCVD reactor and use of this reactor to fabricate optical waveguides. Development was performed on the reactor to improve its performance for the deposition of epitaxial SiGe films in several essential aspects. The wafer heating and flow uniformity was given greater flexibility by employing a 3-zone heating lamp module, AccuSETT® flow controllers, and flow baffles. 1 [sigma]58% was achieved for thickness uniformity. The incorporation of an in-line purifier in the GeH.t supply line was found to reduce the oxygen concentration below the SIMS detection limit. Process conditions were identified for seleclive silicon epitaxial growth on silicon surfaces and not on oxide surfaces. Atomic force microscopy was used to characterize the surface roughness of polycrystalline SiGe films deposited-on nitride and oxide layers. The effect of C incorporation on the suppression of B diffusion was confirmed using this reactor. The addition of C to the SiGe lattice was shown to nullify the strain associated with epitaxial deposition on Si. Using the optimized reactor, optical waveguides were fabricated to determine the optimum processing conditions to produce low transmission loss structures. XRD scans on these samples confirm that low Ge concentration and relaxed structures were fabricated. Attenuation measurements in straight waveguide sections confirm that low loss transmission is achievable. The basic equations of optical transmission in planar waveguides are presented and solved for square cross-section strip SiGe waveguide design. The Marcatili method was used to model the electric field mode profiles in the waveguide core and cladding. Curved structures were designed to explore the crosstalking and coupling effects between adjacent waveguides.