Multianode linear silicon drift detectors for soft Xray diffraction and spectroscopy

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Multi-anode linear silicon drift detectors for
soft X-ray diffraction and spectroscopy
Jan onský, R. Koornneef, J. Huizenga, R.W.
Hollander, C.W.E. van Eijk Radiation Technology
Group, Interfaculty Reactor Institute,
TUDelft (e-mail sonsky_at_iri.tudelft.nl ) P.M.
Sarro, L.K. Nanver Delft Institute of
Microelectronics and Submicron Technology
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Outline

• Motivation
• Charge sharing X-ray spectroscopy
• Wafer quality
• Radiation entrance window
• Position resolution
• Conclusion

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Motivation

• Detector requirements
• large total active area (2.5 x 1.5 cm2)
• 1D-position sensitive detector
• position resolution of 200 mm
• detection of X-rays down to 180 eV
• noise of less than 10 rms el.
• high count rate operation (105 cps)
• near room temperature operation

• Applications
• X-ray diffraction experiments

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Motivation - existing technologies

• Fully depleted pn-CCD
• high-ohmic wafer allows detection of X-rays
  with energies up to 10 keV
• energy resolution of 130 eV (5 rms el.)
• position resolution of 150 mm
• integrator (100 cps)

• Pixel detector
• match the required position and energy resolution
• small active area per pixel
• high number of read-out channels
• flip-chip bump bonding

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Charge sharing X-ray spectroscopy
Multi-anode linear Silicon Drift Detector

• ideal configuration for the diffraction
  experiments
• anode pitch determines the position resolution
• low noise features

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Charge sharing ... (2)

• MLSDD prototype
• anode pitch of 250 mm
• total detector size is 2.5 x 1.3 cm2
• bi-directional with 52 anode pixels on each side
• drift field of 390 V/cm

X-ray spectrum per anode pixel

• Results
• exceptional bad spectroscopic performance despite
  of the low noise
• shift of peak towards lower energies
• low energy tails

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Charge sharing ... (3)

• Traditional MLSDD X-ray spectrum calculation
• charge cloud evolution

• lateral spread of the electron cloud due to
  diffusion

• using the spatial map of charge collection
• monochromatic X-ray source (6 keV)
• energy resolution due to statistic and noise is
  400 eV
• different anode pitch

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Charge sharing ... (4)

• Traditional MLSDD experiment vs. calculation
• absorption efficiency
• given experimental conditions (Ed, T)
• energy resolution

anode pitch 250 mm
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Charge sharing ... (5)
Multi-anode Sawtooth SDD

• Sawtooth shaped p strips induce potential
  gutters
• The depth of the potential gutters depends
• drift field
• period px
• pitch py
• angle a

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Charge sharing ... (6)

• MSSDD prototype design
• large detectors of a total active area of 2.5x1.3
  cm2
• 4 sections with a 0, 30, 45, and 60
• The strip pitch py 200 mm (180 mm p implant,
  20 mm oxide)
• anode pitch varied from 250 mm or 500 mm
• Anodes isolated with p implantation

4-in. wafer
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Charge sharing ... (7)
MSSDD bonding
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Charge sharing ... (8)

• MSSDD X-ray spectroscopy
• large MSSDD (a 60) fabricated on NTD wafers
• anode pitch of 250 mm

• Results
• split events elliminated
• energy resolution of 190 eV at -60C
• energy resolution of 350 eV at RT

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Wafer quality

• Wafer doping non-uniformity
• Deviation of electron trajectories from expected
  straight lines
• Confining potential gutters are disturbed

• Conclusion
• Neutron Transmutation Doped wafers are must!!!

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Radiation entrance window

• MSSDD with strips on both sides
• Fixed oxide charge between p strips
• Signal charge trapping, especially for soft
  X-rays

• MSSDD with semi-continuous implant
• 8 wide strips on the radiation entrance side
• Total area covered with oxide is only a few
  percent (3.6)!
• Staircase potential distribution
• Drift field or drift length are not limited!

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Radiation entrance window ... (2)

• Does the confinement work also for the
  semi-continuous configuration ?
• one-side driven confinement

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Radiation entrance window ... (3)

• How to make a shallow p implant (lt 100 nm)?
• Low energy Boron implantation (lt10 keV)
• BF2 pre-amorphization
• Rapid Thermal processing

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Conclusions

• Detector performance/Status
• detector prototype with an area of 2.5 x 1.3 cm2
• design optimized for detection of low energy
  X-rays
• position resolution of 250 mm (200 mm easily
  possible)
• energy resolution of 190 eV (18 rms el.) per
  anode pixel
• count-rate probably around 50-80k cps

• Could we do better ?
• Better position resolution...
• Better noise...
• Imaging ?

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Conclusions

• MSSDD achievable position resolution ?
• while having the charge confined within one anode
  pixel
• position resolution anode pitch

• Results
• position resolution of 100 - 150 mm
• drift field of 1000 V/cm

• Results off-center drift
• better than 100 mm _at_ smaller drift fields

charge produced by a 10 keV X-ray photon is
confined at any depth of wafer