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Polysilicon Waveguides for Silicon Photonics

Published online by Cambridge University Press:  15 February 2011

Anuradha M. Agarwal ,
Marcie R. Black ,
James S. Foresi ,
Ling Liao ,
Yaping Liu  and
L. C. Kimerling
Anuradha M. Agarwal
Affiliation:
Materials Science and Engineering Department, MIT, Cambridge, MA 02139.
Marcie R. Black
Affiliation:
Materials Science and Engineering Department, MIT, Cambridge, MA 02139.
James S. Foresi
Affiliation:
Materials Science and Engineering Department, MIT, Cambridge, MA 02139.
Ling Liao
Affiliation:
Materials Science and Engineering Department, MIT, Cambridge, MA 02139.
Yaping Liu
Affiliation:
Materials Science and Engineering Department, MIT, Cambridge, MA 02139.
L. C. Kimerling
Affiliation:
Materials Science and Engineering Department, MIT, Cambridge, MA 02139.
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Abstract

Photonic integrated circuits in silicon require waveguiding through a material compatible with silicon VLSI technology. Polysilicon (polySi), with a high index of refraction compared to SiO2 and air, is an ideal candidate for use in silicon optical interconnect technology. Inspite of its advantages, the biggest hurdle to this technology is that losses of 350dB/cm have been measured in as-deposited polySi waveguide structures, as against ldB/cm losses measured in waveguides fabricated in crystalline silicon. We report methods for reducing scattering and absorption, which are the main sources of losses in this system. To reduce surface scattering losses we fabricate waveguides in smooth recrystallized amorphous silicon and Chemo-Mechanically Polished (CMP) polySi, both of which reduce losses by about 40dB/cm to 15dB/cm. Atomic Force Microscopy (AFM) and spectrophotometry studies are used to monitor surface roughness which has been reduced from an RMS roughness value of 19–20nm down to about 4–6nm. Bulk absorption/scattering losses can depend on size, structure, and quality of grains and grain boundaries which we investigate by means of Transmission Electron Microscopy (TEM). Although the lowest temperature deposition has twice as large a grain size as the highest temperature deposition, the losses appear to not be greatly dependent on grain size in the 0.1pm to 0.4pm range. Additionally, absorption/scattering at dangling bonds is investigated before and after a low temperature Electron-Cyclotron Resonance (ECR) hydrogenation step. After hydrogenation, we obtain the lowest reported polySi loss values at λ = 1.54μm of about 15dB/cm.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 403: Symposium I – Polycrystalline Thin Films: Structure, Texture, Properties and Applications II , 1995 , 327
Copyright
Copyright © Materials Research Society 1996

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