Fabrication of waveguides using low-temperature plasma processing techniques

Abstract

The proliferation of the use of light as the transfer medium in communications has brought about some unique technical challenges. Among these is the development of devices that route optical signals at points where optoelectronic conversions are necessary. In this article we discuss the fabrication of silicon oxide waveguides on silicon substrates, describing low-temperature plasma deposition processes and the relationship between crucial optical parameters of the films and the significant processing parameters. The waveguides are buried-ridge, single-mode waveguide structures fabricated using two deposition techniques: plasma-enhanced chemical vapor deposition and low-pressure chemical vapor deposition. We will present the plasma deposition conditions established to control the two refractive index differences (Δn) of 0.065 and 0.020 between the guiding and cladding layers for two different waveguide designs. Uniformity of the Δn as a function of plasma conditions and dopant species will be presented for the guiding layer. The analytical techniques used to evaluate the properties of the guiding layers doped with fluorine and nitrogen consisted of Auger spectroscopy, infrared spectroscopy, ellipsometry, and prism coupling techniques. In addition, we will present the plasma etching conditions required to fabricate of the waveguiding ridge structures. The etch rates and uniformities obtained in two different reactors using either SF6 or CF4 chemistries will be discussed.