3D detectors overview

1
3D detectors overview

• Celeste Fleta
• 4 May 2007

2
3D detectors

• Proposed by S. Parker et al. (1997).
• 3-d array of p and n electrodes that penetrate
  into the detector bulk
• Lateral depletion
• Max. drift and depletion distance set by
  electrode spacing
• Reduced collection time and depletion voltage
• Thicker detectors possible
• Low charge sharing
• BUT non-standard (planar) technology

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RD Programs

• RD50 Study of 3D structures for detectors
  capable of withstanding sLHC fluences.
• ATLAS 3D Study of 3D ATLAS pixel sensors for the
  sLHC and, possibly, for the ATLAS B-layer
  replacement.
• FP420 will have 3D ATLAS pixel sensors.
• Glasgow/Diamond project on 3D detectors for
  synchrotron applications

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3D status

• Single type column
• ITC-irst. p-type Si. Pad and strip detectors.
• VTT/HEP. n-type Si. Strip and pixel (Medipix2)
  detectors.
• Double-sided
• CNM. n and p-type silicon. Pad, strip, pixels
  (Medipix2, ATLAS, Pilatus)
• ITC-irst. p-type Si. Pixel (ATLAS, ALICE,
  Medipix1) detectors.
• Standard 3D
• Stanford. n-type Si. Strips, ATLAS pixel.
• Glasgow/Diamond. n-type silicon Pad, strip and
  pixel detectors.

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Single-type column 3D ITC-irst

• Simplified fabrication process
• Column etching and doping performed only once
• Holes do not go through the wafer
• Columns not filled, just doped with P and
  passivated with SiO2
• Back contact provided by a blanket B implantation
  at the back side single-sided process

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Collection mechanism
P
P

• Electrons swept away by transversal field and
  drift to nearest column (40 mm)
• Holes drift in central region and diffuse/drift
  to p contact (300-500 mm)

Complete charge collection slow!
N--
Plus, when full depletion between columns is
reached, the lateral electric field cannot be
increased further, so STC detectors are not
expected to be radiation hard
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Electrical test

• 3D diode
• 10x10 holes, 80 mm pitch
• 90Sr source with with scintillator trigger
• Shaping time 1.5 ms

CCE measurements show depletion stages seen at
simulation
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Double-sided 3D at CNM

• Electrodes etched from opposite sides of the
  wafer
• Double side processing
• No sacrificial wafer is required
• Short charge collection times because both
  carrier types mainly drift horizontally
• High drift velocity as the electric field can be
  increased even after full depletion.

• Fabrication sequence
• Back side holes (etch poly layer P doping
  TEOS passivation)
• Front side holes (etch poly layer B doping
  TEOS passivation)
• The electrodes are only partially filled with poly

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Potential and field distribution

• Overlap region (50 to 250µm)
• Field pattern like in a regular 3D device
• Charge carriers swept horizontally towards the
  electrodes
• Near surface
• Reduced field strength
• Increased drift distance
• Longer collection times

• Still, the double-sided 3D is almost as good as
  the Standard 3D.
• At 20 V
• Signal pulse peak in 0.2 ns
• 97 charge collected in 5 ns
• (25 ns for a planar device at 100V)

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Fabrication at CNM

• Hole aspect ratio 241
• Diameter 10mm

Note that the poly and TEOS layers reach the
bottom of the hole and the B profile is smooth at
the corners

• First run almost finished.
• Wafer will include
• Medipix2
• ATLAS pixel
• Pilatus
• Short and long strips
• Pad diodes

(P)
N- Silicon
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3D detectors for synchrotron applications

• Project Glasgow/Diamond Light Source to develop
  3D detectors for X-ray diffraction experiments at
  the DLS synchrotron

• Fabrication by IceMOS Technology Ltd.
• Silicon MEMS company based in Belfast
• Standard 3D detectors on N-type Si
• 3-stages production plan
• Hole etching optimization
• Doping optimization
• Device production (2-3 runs)
• Prototype 3D detectors will be integrated and
  tested with existing r/o electronics
• Medipix2, Pilatus, Hermes and Beetle chips

The DLS Synchrotron at Oxfordshire
In progress!
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Process flow at IceMOS

• N-electrodes
• P-electrodes
• Contacts and passivation

1
2

• N-type Silicon, 500 mm
• Oxidation
• Hole patterning and DRIE etching (300 mm)
• Poly filling and doping with P

3
4
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Process flow at IceMOS

• N-electrodes
• P-electrodes
• Contacts and passivation

1
2
3
4
10 mm diameter, 150 mm depth, 55 mm pitch
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Process flow at IceMOS

• N-electrodes
• P-electrodes
• Contacts and passivation

5
6
5. Poly planarization frontback 6. Oxidize to
protect columns 7. Repeat 3-4 for P-type
electrodes
7
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Process flow at IceMOS

• N-electrodes
• P-electrodes
• Contacts and passivation

8
9
8. Grind-polish to expose holes in frontback
side 9. Oxidize to protect surfaces 10. Open
contacts, metal, passivation
10
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Process flow at IceMOS

• N-electrodes
• P-electrodes
• Contacts and passivation

8
9
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Wafer design Medipix2

• Photon counting chip designed for medical imaging
• Pitch 55mm
• 256x256 pixels

Readout in p columns
n columns shorted together (bias)
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Wafer design Pilatus2

• Photon counting chip designed for synchrotron
  applications
• Pitch 172mm, 60x97 pixels
• Three different designs 1, 4 or 9 cells per pixel

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Wafer design Strip detectors

• Beetle strip detectors
• R/O chip used in the LHCb vertex front end
• 3D detector 128 strips, pitch 80mm, 100
  columns/strip, DC coupled
• Hermes strip detectors
• Chip designed at BNL for spectroscopy
  applications
• 3D detector 32 strips, pitch 125mm, 10
  columns/strip, DC coupled.
• Two layouts square, hexagonal

125um
144um
125um
125um
Hermes 3D (Hex)
Hermes 3D