Fabrication and Characterization of thin D E-Detector for Spectroscopic Application

040729 Department of Information Technology and

MediaSensor Technology

1

Fabrication and Characterization of thin E-

Detector for Spectroscopic Application

Göran Thungström1, Lars Westerberg2, Reimar Spohr3, C. Sture Petersson1,4

1ITM, Mid-Sweden University, Sundsvall, Sweden, 2The Svedberg Laboratory, Uppsala, Sweden, 3GSI, Darmstadt, Germany, 4Royal Institute of Technology,

Department of Electronics, Electrum, Kista, Sweden



2

Outline

– Introduction

–Detector fabrication

–Processing Remarks

–Characterisation

–Conclusion



3

Introduction

Single track irradiations



4



5

CHICSi

”CELSIUS Heavy-Ion Collision Silicon Detector System”

CHICSi—a compact ultra-high vacuum compatible detectorsystem for nuclear reaction experiments at storage rings. I. General structure, mechanics and UHV compatibility, L. Westerberg et.al., Nuclear Instruments and Methods in Physics Research A 500 (2003) 84–95



6

Li7Be

9BeBC

N

O



7

Detector fabrication

• Silicon Wafer– FZ

– <100>

– 1000 to 5000 cm

– 380 m, diameter 100 mm

– N-type

– Double side polished

• Processing– Growth of 0.5 m SiO2

– Doping at 900 C for 30 min using solid phosphorus-oxide source in N2 ambient

Si n-type <100>

SiO 2

n+



8

• Processing– Re-growth of SiO2

– Opening of detector window 2x2 mm2

Si n -type <100>

SiO 2

n+



9

• Processing– Etching in 25 w% TMAH at

80 C for 14 h.

SiO 2

n+



10

• Processing– Doping of detector window by

using a solid boron-oxide source at 950 C for 30 min in N2 followed by annealing 30 min in O2

– Oxide in the detector window is removed by 5% hydro-fluoric-acid

SiO 2

n+

p+



11

• Processing– Electron beam evaporation of

Aluminium.

– 0.1 m

– Detector window metallization is patterned

– Forming Gas Annealing 400 C in 5% H2 and 95% N2 for 30 min.

SiO 2

n+ p+

Al



12

Processing remarks

• Aligning marks– Wet etching undercut

Solution !

Etch the oxide until 1/3 of the

oxide thickness remain. Cover

the aligning marks with resist.

After baking, continue to etch

the detector windows.



13

Processing remarks

Si

Si



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Characterization

• IV characterization– 8.8m E-detector

-2 10-9

-1,5 10-9

-1 10-9

-5 10-10

0

-15 -10 -5 0

Reverse Bias Voltage (V)



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SiO2

n+ p+

Al

c1

c2

c3

++++++ ++++++

Ctotal=c1+c2+c3+c4

c4

Ad

VCox

ox

)0(4 =310pF (oxide cap.)

Ad

VCox

ox

)3(4 “decrease rapidly”

5 10-11

1 10-10

1,5 10-10

2 10-10

2,5 10-10

3 10-10

3,5 10-10

-15 -10 -5 0

Cap

acita

nce

(F

)

Reverse Bias Voltage (V)

• CV-characterization



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• Experimental setup– E Bias: 7V

– E detector 300 m thickness, 200 mm2, 19000 cm, Bias: 40V, Ileak=8 nA

– Pressure: 2*10-2 torr

– Preamplifiers: Ortec 142 A,B

– Shaping Amp.: Ortec 570, 1 s

– Two parameter MCA

20 mm

12 mm

E

E

Vacuum chamber

2 mm

1.5 mm



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• Irradiation with alfa source– Calibration of the E-detector

• Energy/channel=10 keV

• E=10*ch+134 ( keV)

-200

0

200

400

600

800

1000

1200

0 200 400 600 800 1000 1200

232U calibration spectrum

Cou

nts

Channel

8785

keV

6777

keV

6288

keV

5684

keV

5341

keV



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• Resolution of the E detector– 2*d2 (ch2)

– Rfwhm=(ch)

– Efwhm=66 keV

0

200

400

600

800

1000

1200

1400

1600

400 450 500 550 600

241Am Resolution Measurement

Measure

Channel

y = Gaussfit(10,10,540,10)

ErrorValue

0,408232,7011a

7,13071512,7b

0,015288534,24c

0,0216493,9717d

NA1,7119e+05Chisq

NA0,9925R



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-100

0

100

200

300

400

500

0 100 200 300 400 500 600

E-detector signal for different E-detector thicknesses

Cou

nts

Channel

• Measurement of the E-E detector telescope, E-detector

– 1) ch: 153 result in an E=1664 keV



– 4) ch: 468 result in an E=4814 keV1 2

3

4



20

-50

0

50

100

150

200

250

300

0 100 200 300 400 500 600 700 800

Channel (ch)

• Calibration of E-Detectors– E-detectors with different

thickness, irradiated with 241Am

– 1) ch: 645 and E= 3817keV

– 2) ch: 350 and E= 2176 keV

– 3) ch: 186 and E=1263 keV

– 4) ch: 71 and E=625 keV

– Result in a cal. Eq.

– E=5.57*ch+227 (keV)

4

3

21



21

0

1

2

3

4

5

0 5 10 15 20 25 30

Energyloss SRIM-2003.26

Ene

rgyl

oss

(Me

V)

Silicon Thickness (m)

• Estimation of E-detector thickness

– X=-0.0347+7.558*E-0.441*E2-0.00565*E3

1) E=3817 result in X=22 um

2) E=2176 result in X=14.3 um





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Measured E-E plot of a 241Am source, for different E thicknesses

0

E-detector (MeV)

(ch.)

E-D

etec

tor

(MeV

)

2 4 60

0

1

2

3

4 22 um

14.3 um

8.8 um

4.5 um



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Energy Straggling

– d2+res

2+strag2

– res=66 keV

– strag=”SRIM-2003.26”

– d= ”thickness variation”

• d1= 204 keV (22 um)

• d2=102 keV (14.3 um)

• d3=70 keV (8.8 um)

• d4=117 keV (4.5 um)

• XE1=0.62 um

• XE2=0.31 um

• XE3=0.22 um

• XE4=0.36 um

0

50

100

150

200

250

300

0 5 10 15 20 25 30

Bohr theorySRIM-2003.26

Mea. Res. Delta E

Silicon Thickness (m)



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Channeling

• Channeling

E-d

ete

cto

r (c

h)

E-detector (ch)

0

50

100

150

200

320 330 340 350 360 370 380

E-detector signal,E-detector tilted 6 degree

Cou

nts

Channel

X

(um)

0˚ 6˚

8.8 7% -

14.3 7% 1%

22 11% 3%



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Conclusion

• Ultra thin E-detectors for spectroscopic applications has been fabricated and characterized down to a thickness of 4.5 um.

• The fabrication was in use of a common one side mask aligner.

• The detector display low leakage current and the resulting capacitance is close to the detector window capacitance below a threshold voltage

• The detector telescope should be slightly tilted to reduce the probability for channeling

• However, even better thickness uniformity is needed to improve the resolution in the E-E detector telescope

Documents

Fabrication and Characterization of thin D E-Detector for Spectroscopic Application