CERN RD39 Collaboration: Cryogenic Tracking Detectors

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CERN RD39 Collaboration Cryogenic Tracking
Detectors
Fabrication of edgeless detectors for RD39
http//rd39.web.cern.ch/RD39/welcome.html
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CERN RD39 Collaboration Cryogenic Tracking
Detectors
Process technologies
Old techniques - Traditional sawing - Laser
dicing - Chemical edge treatment
Problems with high leakage current
Another approach -Deep plasma etching
(G.Pellegrini et al, RD39) -Dicing with
picosencond laser -Operational
conditions(Current Injection,cryogenic)
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CERN RD39 Collaboration Cryogenic Tracking
Detectors
Plasma etching I

• Standard (Cryo) DRIE etch process
• Etch-rate approx. 4 µm/min
• Vertical sidewalls / very little undercut
• Mask Oxide / photoresist

• ICP cutting process
• Etch-rate 7.6 µm/min
• Positive sidewall / small undercut
• Mask Aluminum (photoresist / oxide)

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CERN RD39 Collaboration Cryogenic Tracking
Detectors
Plasma etching II
Etch parameters Temperature -110ºC ICP-Power 1-2
kW CCP-Power 1-3 W SF6 flow max. 100 sccm O2 flow
12-20 sccm Pressure 10-20 mTorr
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CERN RD39 Collaboration Cryogenic Tracking
Detectors
Picosecond laser
The heat effect zone in the target material is
minimal because the material is directly
deposited in electrons and protons and there is
no melting process. By focusing the laser into a
20 µm beam for a short period of time, the
deposition energy level becomes high enough for
cold ablation process. The deposited material
shoots away at very high speed upwards from the
target. The result of this process is clean cut
without any debris.
http//www.singulase.fi/
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CERN RD39 Collaboration Cryogenic Tracking
Detectors
Picosecond laser
Technological problem Method is currently
applicaple only for thin Si substrates ...but
detectors are thin...
Courtesy of http//www.singulase.fi/
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CERN RD39 Collaboration Cryogenic Tracking
Detectors
Summary and future plans

• ICP etching process is operational in Helsinki
• First CMS ministrip detectors have been etched
• Irradiation is planned for April (neutrons at
  Louvain)
• Singulase Ltd has been contacted for laser
  cutting demonstration
• Testing of full size edgeless modules by cosmic
  rays (FinnCrack
• setup in Helsinki) planned for Q4/2006.