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CDF sensors processed on 6” wafers
OUTLINE: Material description Masks layout Sensor performances Process related
problems Conclusions
DPG Frühjahrstagung
Heidelberg, 15. - 19.März 99
•Frank Hartmann
Institut für Experimentelle
Kernphysik
Die CDF Silizium Sensoren in 6“ Technologie
Sensor Dimensions
Type Width(mm)
Length(mm)
Diagonal(mm)
SVXII L2 40.30 74.30 84.53
SVXII L4 60.17 74.30 95.61
ISL 59.26 74.77 95.41
Only 1 of these sensor can fit in a 4” wafer.
6” = cheaper6” detectors are even
longer than their 4” counterparts
Double sidedAC coupledPolySi BiasedSingle metalCommon P-stopsThickness 300mu
Type Pitch P (m) Pitch N (m)
SVXII L2 60 60
SVXII L4 65 65
ISL 112 112
Performances
SVXII L2 SVXII L4 ISL
P-side 6.1 pF 5.8 pF 5.25 pF
N-side 6.8 pF 6.6 pF 6.5 pF
Capacitance
Other parameters:SVXII L2p/n
SVXII L4p/n
ISL p/n
Coupling capacitor 100/130 pF 100/130 pF 150/150 pF
Bias resistance 4-6 M 4-6 M 4-6 M
Interstripresistance
> 2 G > 2 G > 2 G
ProblemsCoupling capacitor variation across the wafer
Uneven metal deposition due to sputtering problems
At the edges of the wafer the coupling capacitor falls below specifications
ProblemsCoupling capacitor breakdown voltage
Creation of pin-holes during operation in test beam
“Weak” coupling capacitor
Different “mix” of wet and dry oxide fixed the problem
Breakdown voltage of ISL sensors is currently under test with respect to bonding force at KA
ProblemsLeaky strips
Isolated strips and regions show high leakage current
Good strip
Leaky strip
Most strips are about 1 nA but a few go as high as A
Log scale
ProblemsLeaky strips
Leaky strips do not affect neighbors
The noise on them follow predictions (proportional to the square root of the current)
Get worse on the p-side if bias is present (MOS effect)
Breakdown at the Junction edges
Verified with Infrared CameraPresent even on the n-side when
defects are present at the p-stops edges
Most likely related to handling and cleaning conditions
Dust
Leaky strips (2)
Dust particles during processing
-> Inaccessible short between implant and p-stop (N-side)
-> fully biased strip Large effect on p-side stripsDistortion in local field--> clean room
improvements
Effect of isolation-diff shorts on the current profile Sensor ISL 1690-09 chip1
12914055-20
-224
0,1
1
10
100
1000
10000
100000
256
231
206
181
156
131
1068156316
-20
-45
-70
-95
-120
-145
-170
-195
-220
-245
strip# (n-side)cu
rre
nt
(nA
)
P-side leakage profile
N-side leakage profile
Pin-holes
SVXII and ISL sensors are double side and the bias will be split. PH is a connection of the implant to input of the PA (virtual GND)The PA will then have to deal with a DC coupled stripCurrent is not driven by the Si but by the bias circuit.Neighbors channels
will be noisy.
Pin-holes
On the N-side the electric field is weak. The effect is enhanced and up to 5 channels on each side will show higher noise.
Low interstrip resistance
•First appearance at 2nd step of quality control at KA
100nA10nA
1G
100k
3M
200k
Leakage current
Interstrip resistance
Bias resistor
Rbias
RintSolve: add. cleaning (charge up?)
Will it remain good after cleaning?