Processing and Characterization of Inorganic Films for Optical Waveguide Components
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ABSTRACT Optical communications are becoming technologically important on progressively shorter length scales. As computer chip speeds increase longer metal wire interconnects become problematic and may limit device performance. Wide bandwidth optical interconnects may be used to address this problem. Silicon oxide and silicon nitride were explored as prospective optical and processing materials in the making of optical interconnects. Etching of slopes, which would be an important process for making optical interconnects, was studied. Slopes with angles ranging from 5 to 50 degrees were fabricated using a silicon oxide / silicon nitride stack.
INTRODUCTION With increasing shrinking of devices and interconnects in the manufacture of microprocessor chips, the interconnect speed is the limiting factor in determining the ultimate speed of the microprocessor. An alternative to metal interconnects is the optical interconnect technology comprised of emitters, detectors, modulators and the optical waveguide itself. An optical waveguide might contain various components such as mirrors, vertical and horizontal bends, gratings and splitters. This works outlines a process to make angular slopes that may be employed for making mirrors and vertical bends using current CMOS processes. We also present deposition rates, etch rates and optical properties of plasma deposited Silicon nitride and Silicon oxide. Plasma Enhanced Chemical Vapor Deposited (PECVD) Silicon oxide is a prospective cladding and processing material while Silicon nitride in addition of being a prospective mirror material, is used as a sacrificial material for making of structures. Controlled angle etches for waveguide components For fabricating optical waveguides we would need to make controlled angular structures which would be part of the components. Examples of waveguide components that would require controlled angular faces are mirrors, vertical bends and diffraction gratings. Tapered windows have been wet-etched in thermal oxide for increasing the step coverage of the subsequent metallization in making of devices.
These have been done by having a faster etching layer over the thermal
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direction of the impinging ions in an RIE process [3] another way of making structures. In this work the slopes were wet-etched using the first method. Isotropic dry may be used for materials that do not effectively wet etch. Figure 1: Slope etching with an isotropic etching medium.
81 Mat. Res. Soc. Symp. Proc. Vol. 597 © 2000 Materials Research Society
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Slope etching using an isotropic etchant If a stack of films as shown in figure 1 is etched in an isotropic etching medium, then depending on the ratios of the etch rate of the sacrificial material and the etch rate of the working material, a steady slope will be reached in the working material
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