Multi-anode linear silicon drift detectors for soft X-ray diffraction and spectroscopy

Jan Šonský, R. Koornneef, J. Huizenga,

R.W. Hollander, C.W.E. van EijkRadiation Technology Group,

Interfaculty Reactor Institute, TUDelft(e-mail: sonsky@iri.tudelft.nl )

P.M. Sarro, L.K. NanverDelft Institute of Microelectronics and Submicron Technology

Outline

• Motivation

• Charge sharing: X-ray spectroscopy

• Wafer quality

• Radiation entrance window

• Position resolution

• Conclusion

Motivation

Detector requirements large total active area (2.5 x 1.5 cm2) 1D-position sensitive detector

position resolution of ~ 200 m

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

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 m 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

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

Charge sharing ... (2)

MLSDD prototype anode pitch of 250 m 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

Results exceptional bad spectroscopic

performance despite of the low noise shift of peak towards lower energies low energy tails

0 10 20 30 40 50 601

10

100

1000 241Am

coun

tsenergy (keV)

X-ray spectrum per anode pixel

Traditional MLSDD: X-ray spectrum calculation charge cloud evolution

lateral spread of the electron cloud due to diffusion

0.0

180

190

200

210

220

0.0

0.2

0.4

0.6

0.8

0.30.6

0.91.2

Pote

ntia

l (-V

)

y (m m ) x (mm)

0 1 2 3 4 5 6 70

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

e n e r g y ( k e V )

inte

nsity

(a.u

.)

p = 1000 mx p = 500 mp = 250 m

x

x

p = 500 mT = 210 Kx

Charge sharing ... (3)

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

Charge sharing ... (4)

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

energy resolution

0 10 20 30 40 50 600.1

1

10

100241Am

coun

ts

energy (keV)

anode pitch = 250 m

3 10 20 30 40 50 60 70

0

0

10

50

20

100

30

150

40

200

50

250

3 10 20 30 40 50 60 70energ y (keV)

3 10 20 30 40 50 60 70energ y (keV)

inte

nsity

(a.

u.)

inte

nsity

(a.

u.)

3 10 20 30 40 50 60 70

p = 500 mx

p = 1000 mx

Charge sharing ... (5)

Multi-anode Sawtooth SDD

x

z

0.0

180

190

200

210

220

0.0

0.2

0.4

0.6

0.8

0.30.6

0.91.2

Pote

ntia

l (-V

)

y (m m ) x (mm)

x-axisy-axis

-Pot

entia

l

py

px

Sawtooth shaped p+ strips induce potential gutters

The depth of the potential gutters depends: drift field period px

pitch py

angle

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 m (180 m p+ implant, 20 m oxide)

anode pitch varied from 250 m or 500 m Anodes isolated with p+ implantation

x

y

n+

p+

guard

z

2.5 cm

1.3

cm

4-in. wafer

Charge sharing ... (7)

MSSDD: bonding

Charge sharing ... (8)

MSSDD: X-ray spectroscopy large MSSDD ( = 60°) fabricated on NTD wafers anode pitch of 250 m

F W H M = 191 eV

1 2 3 4 5 6 7

2000

1500

1000

500

0

energ y (keV)

inte

nsity

(a.

u.)

1 2 3 4 5 6 7

800

600

400

200

0

energ y (keV)in

tens

ity (

a.u.

)

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

Wafer quality

Wafer doping non-uniformity Deviation of electron trajectories from expected

straight lines Confining potential gutters are disturbed

x (m

m)

x (m

m)

9 . 2

9 . 2

0

0

2

2

4

4

6

6

8

8

1 0

1 0

1 2

1 2

y ( m m )

y ( m m )

Q = 3.0 10 el.· 5

9.6

9.6

10.0

10.0

10.4

10.4

10.8

10.8

Q = 2.5 10 el.· 31 2 1 0 8 6 4 2 01 1 . 2

1 1 . 6

1 2 . 0

1 2 . 4

1 2 . 8

1 3 . 2

1 3 . 6

y , d r i f t c o o r d i n a t e ( m m )

x, la

tera

l coo

rdin

ate

(mm

)

Conclusion: Neutron Transmutation Doped wafers are must!!!

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!

Radiation entrance window ... (2)

Does the confinement work also for the semi-continuous configuration ?

one-side driven confinement

0 4 0 8 0 1 2 0 1 6 0 2 0 0 2 4 0 2 8 00 . 0 1

0 . 1

1

1 0

500 m

250 m

2-sides driven

1-side driven

confinem ent m in im um

Max

imal

gut

ter

dept

h (V

)

w afer depth ( m )0 1 2 3 4 5 6 7

e n e r g y ( k e V )

inte

nsity

(a.

u.)

1

10

100

1000

S trip s

S em i-c o ntinuo usim p lant

Radiation entrance window ... (3)

How to make a shallow p+ implant (< 100 nm)?

Low energy Boron implantation (<10 keV) BF2 pre-amorphization

Rapid Thermal processing

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 m (~200 m 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 ?

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

0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 01 0 0

10 1

10 2

10 3

10 4

10 5

10 6

10 7

10 8

ano d e p itc h ( m )

500 m

290 m

drif

t fie

ld (

V/cm

)

= 30° = 45° = 60°

Results position resolution of 100 - 150 m drift field of ~ 1000 V/cm

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

Conclusions

Results: off-center drift better than 100 m @ smaller drift

fields