34-36 ICP v2 10/9/09 13:32 Page 36
industry dry etching
rhombus4
theoretical response of device in
terms of reflection (R), transmission
(T) and loss (L) was calculated using
two-dimensional (2-D) simulations.
Cross-section approach was
employed with CAvity Modelling
Framework (CAMFR) simulation tool.
Numerical results for 363 nm-wide
air-slot for a fundamental TE0 optical
mode at the constant wavelength of l
= 1.55 µm are presented in Fig. 3.
The single air-slot efficiency is highly
dependent on total structure depth,
as presented in Fig. 3c. For non-
optimum etch depth conditions (1.96
mm-deep air-slot) both low reflectivity
R of ~17% and high feature loss L
(~78%) are observed.
The reason for such a behaviour is
that a vast amount of power carried
by TE0 optical mode, propagating
from the left to the right where the
mirror is located, is coupled into the Fig. 3. Air-slot reflectors fabricated with Cl2/Ar/N2 ICP dry etching and the
substrate. The substrate coupling computed device behavior: a), b) SEM micrographs of deeply etched, highly
loss effect is indicated by a vertical features; c) 2-D simulation results (reflection and loss) in the function
logarithmic plot of electric field of total etch depth, where two distinct cases are presented on the right (log
distribution within the structure. In plot of electric field distribution for TE0 optical mode within the structure).
contrary, high reflectivity and low loss
case may be observed for a deeper
2.95-mm-deep mirror, which provides with minimal damage has been avoided due to the usage of HSQ as
reflectivity of R ~ 67% and negligible demonstrated for a wide range of both electron-beam lithography resist
structure loss (~7%). Therefore, InP-based materials. Highly and dry etching hard-mask.
fabrication process for the anisotropic process produces The high-aspect ratio ICP dry etching
experimental purposes involves deep transfer of both micron- and technique will be used for the
anisotropic etching of 363-nm-wide nanometer-scale features in a single fabrication of intra-cavity reflectors
features with use of optimized etch step. Intermediate etching and DBR grating structures used
Cl2/Ar/N2 inductively coupled plasma stages (i.e. PMMA pattern transfer to in InP-based mode-locked (M-L)
etching. An optimized dry etching underlying SiO2/Si3N4 layer) could be lasers.
References
[1] L. Hou, P. Stolarz, R. Dylewicz, J. Javaloyes, B. Qiu, Dry Etching”, UK Semiconductors Conference 2009,
M. Sorel, J. H. Marsh, A. C. Bryce, “160 GHz Passively Sheffield, UK.
Mode-Locked AlGaInAs 1.55 Ìm Strained Quantum Well [4] R. Dylewicz, A. C. Bryce, M. Sorel, R. M. De La Rue,
Compound Cavity Laser”, to be published soon. R. Wasilewski, P. Mazur, “Fabrication of submicron-sized
[2] R. Dylewicz, R. Green, M. Sorel, A. C. Bryce and features in InP/InGaAsP/AlGaInAs by optimized inductively
R. M. De La Rue, “Characterization of Deeply Etched Uniform coupled plasma etching with Cl2/Ar/N2 chemistry”, to be
Sidewall Gratings in InP/InGaAsP Ridge Waveguides”, published soon.
European Conference on Lasers and Electro-Optics - [5] R. Dylewicz, A. C. Bryce, M. Sorel and R. M. De La Rue,
CLEO Europe 2009, Munich, Germany. “High Aspect Ratio Inductively Coupled Plasma (ICP) Etching
[3] R. Dylewicz, R. Green, M. Sorel, A. C. Bryce and of InP/InGaAsP/AlGaInAs Using Cl2/Ar/N2 Gas Mixture”,
R. M. De La Rue, “Sidewall Gratings Fabricated in InP-based European Conference on Lasers and Electro-Optics - CLEO
Ridge Waveguides by Optimized Inductively Coupled Plasma Europe 2009, Munich, Germany.
Acknowledgements
The authors would like to thank the technical staff of the James Watt Nanofabrication Centre at the University of Glasgow as well as the
Institute of Photonics, University of Strathclyde, UK. The work was supported by the Engineering and Physical Sciences Research Council
(EPSRC) of the United Kingdom (project EP/E065112/1 – High Power, High Frequency Mode-locked Semiconductor Lasers).
36 www.compoundsemiconductor.net September 2009
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