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Sandia National Laboratories
Materials & Processing for Si Compatibility
Charles T. Sullivan
[email protected], 505/844-9254
Center for Compound Semiconductor Science and Technology
Microsystem Science, Technology and Components Center
Shawn Lin and Jim Fleming
Introductory overviewPhotonic Bandgap Materials
Optical Interconnects for High Performance Computing WorkshopOak Ridge 11/8-9/99
Sandia National Laboratories
Possible Options for On-Chip Waveguide Interconnects
• Hard dielectric waveguides
– low-loss optical fiber compatibility
» low index contrast N ~ 0.005
» = 0.1 dB/cm to < 0.01 dB/cm
» e.g., LPCVD-based buried BPSG/TEOS
– higher-index for higher-density routing
» high index contrast N > 0.1
» < 0.1 dB/cm ?
» e.g., LPCVD-based SiON/TEOS
• Polymeric waveguides
– low-temperature post-processing
» low index contrast N ~ 0.05-0.005
» ~ 0.1 dB/cm to 0.5 dB/cm, depending on » e.g., fluorinated acrylates or polyimides
Sandia National Laboratories
Possible Applications of PBG Materials
1) Passive devices - Infrared Mirrors - Thermal Emissivity Modification - Prisms - Optical Communications - Cavities - Spectroscopy - Military and Optical Communications - Waveguides - 90° bends possible in three dimensions 2) Active devices - Ultra-Fast Switches - Si Infrared LED’s - Si Infrared Lasers 3) Integrated devices - Photonic circuits
Potential Applications
Wavelength (µm)T
rans
mit
tanc
e (%
)
0 10 12 14 16 18 20
1000
100
10
1
The Photonic Bandgap is present at any angle of incidence
(a) = 0° (b) = 30° (c) = 40° (d) = 50° (e) = 60°
a b c d e
<011>
<100>
Wavelength (m)T
rans
mis
sion
Bandstop is LargelyIndependent of Angle
Sandia National Laboratories
Simulated Electric Field Patterns for90-degree Waveguide Bend
2D Square Lattice 3D Square Lattice
Sandia National Laboratories
90-degree Waveguide Bend at Millimeter-Wave Frequencies
<01>
<10>
Tra
nsm
issi
on E
ffic
ienc
y
Frequency (GHz)75 9080 1059585 110100
theory
experiment
1.2
1.0
0.8
0.6
0.4
0.2
0
Sandia National Laboratories
0 2 4 6 8 10 12 14 16
0.2
0.4
0.6
0.8
1.0
1.2
0
Wavelength of Mid-gap, (microns)
Min
imum
Fea
ture
Siz
e (m
icro
ns)
Highly Complex
More straight- forward, but limited by stress
Opt
ical
C
omm
un
icat
ion
s
Mil
itar
y A
ppli
cati
ons
The minimum feature size for a lattice with bandgap
of 1.5 micron is 0.18 microns!
The Microfabrication Challenge
Sandia National Laboratories
3D Silicon Photonic Crystal at Mid-IR Frequencies
Side View
Top View
poly-Si
Si substrate
Technology Challenges
- precise stacking;- smooth planarization;- large area uniformity.
4-layer crystal
Sandia National Laboratories
Mold Process Flow
4) Deposit thin SiN, CMP stopping layer.
5) Pattern the second level.
6) Fill gaps between patterned poly with oxide.
7) Chemical mechanically polish, stopping on SiN.
Mold Process Flow
1) Deposit oxide with thickness equal to that of the layer.2) Pattern and etch mold.
3) Fill mold with polysilicon. Poly thickness equal to that of the layer thickness. (Only works for designs where W ~T)
Sandia National Laboratories
The Simple Cubic StructureFabricated Using the Mold Process
0
20
40
60
80
100
120
4 6 8 10 12 14 16
Tra
nsm
itta
nce
(%
)
Wavelength ( m)
Simple Cubic
10L
Sandia National Laboratories
Fillet Flow Process
Fillet Process Flow
2) Pattern oxide with lines and spaces, 6500Å lines, 6500Å space. Etch oxide in HF, remove ~900Å isotropically.
1) Deposit SiN (first layer only), poly with layer thickness (2200Å) and SiN hard mask (500Å). Deposit 5000Å oxide sacrifical layer.
3) Deposit 1800Å polysilicon fillet layer
4) Form fillet using anisotropic RIE.
5 Remove sacrifical oxide in HF.
6) Etch SiN in hot phosphoric acid.
7) Use fillet as a mask for poly etch.
8) Fill spaces between lines with oxide.
9) CMP, stopping on the SiN.
Sandia National Laboratories
1.5µm Bandgap Fillet Structure
1.3 1.5 1.7
Wavelength (m)
1.4 1.6 1.8T
rans
mis
sion
Ef f
i ci e
ncy
100
20
bandgap
Measured Results
3L
4L
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Novel Structures Under Investigation
Sandia National Laboratories
Singlemode 3D Defect Cavity
1
2
3 4
56
7
6.4m(0.6)
9.2m (0.8 )
Defect Volume: 0.23
cavitymode
Modal Volume: 0.83
Higher-QResults