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

040729 Department of Information Technology and

MediaSensor Technology

2

Outline

– Introduction

–Detector fabrication

–Processing Remarks

–Characterisation

–Conclusion

040729 Department of Information Technology and

MediaSensor Technology

3

Introduction

Single track irradiations

040729 Department of Information Technology and

MediaSensor Technology

4

040729 Department of Information Technology and

MediaSensor Technology

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

040729 Department of Information Technology and

MediaSensor Technology

6

Li7Be

9BeBC

N

O

040729 Department of Information Technology and

MediaSensor Technology

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+

040729 Department of Information Technology and

MediaSensor Technology

8

• Processing– Re-growth of SiO2

– Opening of detector window 2x2 mm2

Si n -type <100>

SiO 2

n+

040729 Department of Information Technology and

MediaSensor Technology

9

• Processing– Etching in 25 w% TMAH at

80 C for 14 h.

SiO 2

n+

040729 Department of Information Technology and

MediaSensor Technology

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+

040729 Department of Information Technology and

MediaSensor Technology

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

040729 Department of Information Technology and

MediaSensor Technology

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.

040729 Department of Information Technology and

MediaSensor Technology

13

Processing remarks

Si

Si

040729 Department of Information Technology and

MediaSensor Technology

14

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)

040729 Department of Information Technology and

MediaSensor Technology

15

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

040729 Department of Information Technology and

MediaSensor Technology

16

• 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

040729 Department of Information Technology and

MediaSensor Technology

17

• 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

040729 Department of Information Technology and

MediaSensor Technology

18

• 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

040729 Department of Information Technology and

MediaSensor Technology

19

-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

– 2) ch: 317 result in an E=3304 keV

– 3) ch: 404 result in an E=4174 keV

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

3

4

040729 Department of Information Technology and

MediaSensor Technology

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

040729 Department of Information Technology and

MediaSensor Technology

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

3) E=1263 result in X=8.8 um

4) E=625 result in X=4.5 um

040729 Department of Information Technology and

MediaSensor Technology

22

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

040729 Department of Information Technology and

MediaSensor Technology

23

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)

040729 Department of Information Technology and

MediaSensor Technology

24

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%

040729 Department of Information Technology and

MediaSensor Technology

25

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