Characterization of HARE Deposited Rib Waveguides

1
Characterization of HARE Deposited Rib Waveguides

• Vicky Au ? Prof. Rod Boswell
• Dr Douglas Bulla ? Dr Christine Charles Dr
  Weitang Li ? Prof. John Love

Applied Photonics Group Space Plasma Plasma
Processing The Australian National University
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The HARE Project

• Aim
• A low-loss waveguide at 1400nm wavelength
• Current concerns
• Geometry of waveguide
• Stress in the HARE deposited film which forms
  the waveguide
• OH content in deposition - absorption peak
  located at 1400nm for SiO2 glasses

3
The HARE System
Si
Wafer
Process Chamber
Ge
Plasma Source
Crucibles
E-Gun
4
The HARE Rib WaveguideLithography

• Wet etch of Ge-doped SiO2 HARE-deposited
  film using p-etch solution,
• mask still intact

2mm
4mm

• The HARE rib after etch, mask removed

5
Modelling the HARE Rib Waveguide
10 9 8 7 6 5 4 3 2 1 0

• Input
• Dimensions of waveguide and rib
• Propagating Wavelength l
• Range where solution of refractive index
  is sought

Vertical mm

• Output
• Propagating modes within input range,
  characterised by the effective refractive
  index polarisation

0 2 4 6 8 10 12 14 16 18 20
Horizontal mm
Air n 1
Ge-doped HARE SiO2 n 1.47
SiO2 n 1.457
Si n 3.858 i 0.018

• Cross-section of waveguide

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Multi-moded HARE Rib Waveguide
10 9 8 7 6 5 4 3 2 1 0
Vertical mm
0 2 4 6 8 10 12 14 16 18 20
Horizontal mm

• Ex contour plot of fundamental mode
  propagating in the rib

• Hx contour plot of a higher order mode
  propagating in the rib

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Variation in Compressive Stress with Plasma
Parameters
(1)
where E energy of ions impacting film
during deposition R flux of atoms contributing
to film growth j total flux of ions
impinging on wafer

• The variation in compressive stress with ion
  energy
• as predicted by eqn. (1), assuming E0 10eV
  and r 1

Ref C.A. Davis, Thin Solid Films 226, 30 (1993)
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Analysis of Stress in HARE Deposited Film

• Wafer A - SiO2 deposition - Thickness
  1.6mm
• - Stress induced peeling of
• the deposited SiO2 film

• Scans of bow in wafer, using Tencor
  Alpha-Step200 surface profilometer

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Directional Stress and Birefringence
bow height
bow height

• Surface profilometer scans indicate
  direction-dependent compressive stress

hy
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Mapping the Stress Variation

• Wafer B - Ge-doped SiO2 deposition -
  Thickness 2.60.1mm

Stress, s ?109 N.m2
Y (mm)

• Map of compressive stress using Tencor
  Alpha-Step200 surface profilometer

• Map of bow in wafer due to compressive
  stress in deposited film, using FilmTek400
  ellipsometer

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Infrared Absorption Spectroscopy
Stretching O Si O vibration modes
Wafer A (SiO2) Wafer B (Ge-doped SiO2)
OH stretching
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Future Directions

• Etching wafer using helicon plasma
• Modelling of compressive stress
• Correlation of stress variations across wafer
  with plasma distribution in HARE
• Techniques to reduce stress in deposited films

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Acknowledgments

• Australian Photonics CRC
• SP3 Peter Alexander
• Laser Physics Centre Prof. Barry Luther-Davies
• Dr Robbie Charters
• Dr Graham Atkins
• EME Dr Mladen Petravic
• Workshop Tom McGuinness

Applied Photonics Group Space Plasma Plasma
Processing The Australian National University