fabrication and characterization of thin d e-detector for spectroscopic application
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Fabrication and Characterization of thin D E-Detector for Spectroscopic Application. Göran Thungström 1 , Lars Westerberg 2 , Reimar Spohr 3 , C. Sture Petersson 1 ,4 - PowerPoint PPT PresentationTRANSCRIPT
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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
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Outline
– Introduction
–Detector fabrication
–Processing Remarks
–Characterisation
–Conclusion
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Introduction
Single track irradiations
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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
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Li7Be
9BeBC
N
O
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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+
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• Processing– Re-growth of SiO2
– Opening of detector window 2x2 mm2
Si n -type <100>
SiO 2
n+
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• Processing– Etching in 25 w% TMAH at
80 C for 14 h.
SiO 2
n+
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• 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+
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• 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
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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.
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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
– 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
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-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
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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
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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