1. of Single-Type-Column 3D silicon detectors
Device simulation
of Single-Type-Column 3D silicon detectors
Claudio Piemonte
ITC-irst Trento (Italy)

2. Outline Introduction Single-Type Column 3D detector concept
Simulation of the static characteristics
Simulation of the signal response
Conclusion

3. Introduction
Development of 3D sensors is being carried out at ITC-irst in
collaboration with INFN.
Work done so far is described in 3+1 talks:
Simulations of 3D-STC detectors Claudio Piemonte
(ITC-irst)
Technology used in the first two fab. runs Sabina Ronchin
Electrical characterization of first prototypes - Nicola Zorzi +
Electrical characterization at Glasgow D. Pennicard
(Glasgow University)

4. “Standard” 3D detectors - concept
Proposed by Parker et al. NIMA395 (1997)
n-columns
p-columns
ionizing particle
wafer surface
Short distance between electrodes:
low full depletion voltage
short collection distance
more radiation tolerant
than planar detectors!!
n-type substrate

5. Single-Type-Column 3D detectors - concept
[ Presented in June 2004 at the Hiroshima conference ]
Sketch of the detector:
Functioning:
n-columns
ionizing particle
cross-section
between two
electrodes n+
electrons are
swept away by
the transversal
field
holes drift in the
central region and
diffuse towards p+
contact
p-type substrate
grid-like bulk contact

6. 3DSTC detectors - concept (2)
Main feature: hole etching and doping are performed only once
Further simplification: holes not etched all through the wafer
p-type substrate
n+ electrodes
Uniform p+ layer
No need of support wafer.
Bulk contact is provided by a backside
uniform p+ implant
single side process.

7. Structure used for static simulations
3D simulations are necessary DEVICE3D tool by Silvaco n+
cell
50mm
p-type substrate
Wafer thickness:300mm
Holes: 5mm-radius
250mm-deep
Important to exploit the structure
symmetries to minimize the region
to be simulated

8. Simulated potential distribution (1)
Potential distribution (vertical cross-section)
50mm
300mm
Potential distribution
(horizontal cross-section)
in scale
not in scale 0V
-10V
-5V
-15V
null field lines

9. Simulated potential distribution (2)
Potential and Electric field along a cut-line
from the electrode to the center of the cell
Na=1e13 1/cm3
Na=1e12 1/cm3
Na=5e12 1/cm3
Na=5e12 1/cm3
Na=1e12 1/cm3
Na=1e13 1/cm3
To increase the electric field strength one can act on the
substrate doping concentration

10. Capacitance in 3D-STC 3D diode Cback=CbackTot/100 Cint=CintTot/40
matrix of
10x10 holes
Cback=CbackTot/100
Cint=CintTot/40
guard ring
Structure for simulation of Cback
Structure for simulation of Cint
half pitch
oxide not
included in
the structure
Cback=4 x simulated
value
Cint=2 x simulated
value

11. Capacitance simulations (1)
Capacitance simulation on a 300μm thick wafer with 150mm deep columns, 80mm picth, Na=5e12cm-3
Phase 1
high Cback
~ zero Cint
undepleted Si
Phase 1
Phase 2
Phase 2
max Cint
slowly dec.
Cback
undepleted Si

12. Capacitance simulations (2)
col-to-back capacitance
meas.
Comparison between measurements
(on 3D diodes) and simulations
simul.
300μm thick wafer
190mm deep columns
2e12cm-3 subst. conc.
100mm col. pitch
80mm col. pitch
1/C2 characteristic
80mm col. pitch
From 1/C2 curves:
full depl. between columns clearly
visible (higher for 100mm pitch)
diode-like behavior in phase 2
100mm col. pitch

13. Capacitance simulations (3)
1) Vbias=0V
2) Vbias=2V
3) Vbias=5V
4) Vbias=20V
Do not consider the hot spot in the pictures,
it is the charge released by a particle.
The 1/C2 curve of the col-to-back
capacitance can be used to extract
both the intercolumn as well as
the col-to-back full depletion. 2 3 4

14. Signal in 3D-STC detectors (1)
e h
First phase
Transversal movement
Ramo theorem:
250mm
electric
field
weighting
field
50mm
50mm 1 2 3 4
generation
10mm from
column 1 2 3 4
generation
in the middle
between two
columns
induced by e
induced by h
induced by e
induced by h

15. Signal in 3D-STC detectors (2)
Second phase
Hole vertical movement
hole velocity orthogonal to weighting field
no signal induced
weighting field no longer orthogonal
signal induced
180um from top
140um from top
a hole moving towards the back
induces a current pulse shifted
in time according to the generation
depth

16. Simulation of a localized charge deposition
Only the transversal movement
is visible x 1 3 z 1 2 3 4
80mm
electrons
(10,10)
250mm y
50mm
holes
50mm
transv. movem.
vert. movem.
induced by e
induced by h
total current
The current plot in log-log scale
shows very clearly the fast
transversal component and the
slow hole vertical one.

17. Simulation of a uniform charge deposition (1)2 3 4
Uniform Vertical deposition (10,10)
Bias voltage = 50V (> full depl.)
All the electrons collected by electrode 1
electron collection
peak
vertical hole
movement
transversal hole
induced by e
induced by h
total current
log-log plot
linear scale plot

18. Simulation of a uniform charge deposition (2)1 2 3 4
Uniform Vertical deposition (25,25)
Bias voltage = 50V (> full depl.)
Electrons equally shared
between four columns
same signals on the
four columns
log-log current plot
linear-scale current plot

19. Full charge collection time
Same Vbias, different impact point 1 2 3 4
(25,25)
(20,20)
(10,10)
tail independent
from impact position
In the worst case of a track centered
the central region, 50% of the
charge is collected at t ~ 300ns
Outside this region, 50% of the
charge is collected within 1ns.
charge collected
is ¼ for interaction
in the middle point

20. Conclusion
3D-STC detector:
Advantage: “simple” fabrication process.
Disadvantage: Very long full charge collection times.
=>
extremely interesting device to tune the technology for
the production of standard 3D detectors
can be used in those applications not requiring
charge information in short time

21. Additional slides

22. CCE versus bias voltage
Vbias=2V