Giulio Pellegrini

Fabrication and simulation of Novel Fabrication and simulation of Novel Ultra Thin 3D Silicon Detector – Plasma Ultra Thin 3D Silicon Detector – Plasma

Diagnostics for Diagnostics for JET and ITER TOKAMAKSJET and ITER TOKAMAKS

G. Pellegrini, J. Balbuena, E. Cabruja, M. Lozano, M.UllanCentro Nacional de Microelectrónica CNM-IMB (CSIC)

F.Garcia, R. Orava Helsinki Institute of Physics (HIP)

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OutlineOutline

•Applications

•New detector concept

•Simulation results

•Fabrication technology

•Conclusions

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ITER (International Thermonuclear Experimental Reactor)

should produce more power than it consumes. This is

expressed in the value of Q, which represents the amount

of thermal energy that is generated by the fusion

reactions, divided by the amount of external heating. A

value of Q smaller than 1 means that more power is

needed to heat the plasma than is generated by fusion. In

the "burning plasma", most of the plasma heating has to

be come from the fusion reactions themselves.

ApplicationsApplications

Corpuscular Diagnostics Plasma: Neutral Particle Analyzers - NPAs

Neutral Particle Beam

Sensitivity is mainly to photons Max. Count rate 100kHzPile-up of the background signals reduces S/N ratioRadiation Hardness has to be 1016 n/cm2

Other applications: neutron dosimetry and imaging

This new detectors where developed to cope with the increasing of the plasma

burning power which roses the neutron and gamma background in such a way that

detectors cannot cope with the particles’ rate. Therefore detectors get saturated and

are not able to detect ions from the plasma, which carry information about the

plasma parameters.

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New Detector ConceptNew Detector ConceptSilicon detectors with 3D electrodes are intrinsically Radiation Hard.Test shows 3D silicon detectors withstand radiation damage of 1015 1/cm2 from neutrons and protons

Time Collection Charge of the order of tens of nanoseconds.This will drastically improve count rate capability beyond 1 MHz

Granularity of the Readout Electrodes will facilitate clusterization.This is a complementary method for background rejection.

The Technology for thinning the Silicon wafer to the desirable thickness is matureThe Technology for thinning the entrance window to tens of nanometers was already successfully tested

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Schematic structureSchematic structure

p d t

LowResistivity

n-type

Al

n-typeHighResistivity

p+ n+ n+p+ p+

10um300um

5mmSOI

100um3um

n+

read out electronic

Strip configuration is ok, pixels are also possible

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Advantages of 3D Advantages of 3D thin thin

•Keep low depletion voltage without increasing depletion capacitance.•Reduce stopping layer in the entrance window.•Increase breakdown voltage in order to withstand radiation damage.•Reduce contribution from background signal

0 25 50 75 100 125 150 175 200 225 250 275 30010-2

10-1

100

101

102

103

104

Detector Thickness (um)

C2

D/C

3D

80x80um2

150x150um2

50x50um2

0 25 50 75 100 125 150 175 200 225 250 275 30010-16

10-15

10-14

10-13

Cap

acit

ante

(F

)

Detector Thickness (um)

3D Planar

Similar pixel area: 80x80um2

larger pixels

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Photons’ Backgroun

d

FRONT PLANE

Geant4 SimulationGeant4 Simulation

BACK PLANE

Strips:pitch 80 umwidth 20 um

The Integral Sensitivity will be of the order of 10-6 or even smaller

F. Garcia et al, Novel Ultra Thin 3D Silicon Detector – Plasma Diagnostics for JET and ITER TOKAMAKS, presented at the 10th International Workshop on Radiation Imaging Detectors in Helsinki, Finland, June 29 - July 3, 2008.

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Sentaurus SimulationSentaurus Simulation

0 20 40 60 80 100 120 1401E-15

1E-14

1E-13

1E-12

1E-11

1E-10

1E-9

1E-8

1E-7

Cu

rre

nt(

A/u

m)

Reverse Bias (V)

Full depletion U3D

•Square pitch: 80um

•Silicon substrate: n-type 1012cm-3

•Holes collection at p+ electrode

•Detector thickness 10um

•Oxide charge 1011cm-2

•Charge carriers swept horizontally towards the electrodes

•Low full depletion: 3.5V

•Short collection time: peak at 2.1ns

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Sentaurus SimulationSentaurus Simulation

Charges collected in the central electrode

Charge collected at different bias volts.At 10V the signal peaks at 10ns but at 30V the peak is at 1ns.

0,0 5,0x10-9 1,0x10-8 1,5x10-8 2,0x10-8 2,5x10-8 3,0x10-80,0

1,0x10-8

2,0x10-8

3,0x10-8

4,0x10-8

5,0x10-8

6,0x10-8

7,0x10-8

Hol

es c

urre

nt (

A)

Time(s)

30V

20V

10V

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FabricationFabrication

Finished wafer with back illumination. Back view.This is a test detector with only p-type polysilicon and no metal.The red squares are the thin (10µm) membranes with 5µm holes

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Front viewFront view

Finished wafer with front illumination. Top view.

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300um

Etched backside

Thin membrane

MembraneMembrane

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Polysilicon

Hole filled with polysilicon

10umMembrane

Cross sectionCross section

SiO2

n-type silicon

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Detail of the surfaceOxide of the SOI wafer

First fabrication test run demonstrated the feasibility of the process.A new mask set with 3D-thin detectors and test structures has been designed and the detectors are being fabricated at CNM clean room facilities.

Cross sectionsCross sections

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3d-thin (9)

Pad conf. thin (8)

Pad conf thick (4)Test structures (4)

Mask layoutMask layout

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StripsStrips

•DC coupled•128 channels•80 um pitch•5um holes•10um thick•Area=1cm2

•p-n or n-p configuration (p-stop isolation)•Oxide thickness (variable).

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PadPad

•Only one channel.•All strips of the same type shorted to the same electrode.•10 um thick•Oxide thickness (different values).•Area= 0.5x0.5 cm2

•80um pitch•5um holes

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ConclusionsConclusions

•The concept has been tested and fabrication has been performed.

•Simulation shows full depletion of 3.5V and breakdown voltage of 150V.

•Signal collection time is on the order of 1 ns at 30V biasing.

•Detector capacitance for a single cell of the U3DTHIN two orders of magnitude smaller than planar one with the same thickness.

•First complete fabrication run finished, to be tested.