Download - Development of 3D silicon detectors at ITC-irst Claudio Piemonte ITC-irst Trento [email protected]
Development of 3D silicon detectors at ITC-irst
Claudio PiemonteITC-irst [email protected]
C. Piemonte IFAE 20 - 04 - 2006 Pavia
OutlineOutline
• 3D detectors: concept & status
• ITC-irst activity on 3D:
• Single-Type Column 3D detector concept
• Simulation, Design, Process and First Characterization
• Future Activity
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Standard planar detectors (1)Standard planar detectors (1)
n--substrate
n+ - bulk contact
p+
E fieldNormal operation:bulk is over-depleted =>electric field separates the pairsand forces the carriers to drift
For uniform charge depositioncarriers are collected one by one
Planar devices:junctions are located closeto surface of the silicon bulk
~1m
~300m
~1m
-
+-
+V1<V2
12
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Standard planar detectors (2)Standard planar detectors (2)
Collection time = time needed to collect the last carrier (hole)
It depends on: 1. bias voltage
2. substrate thickness
0.E+00
1.E-08
2.E-08
3.E-08
4.E-08
5.E-08
6.E-08
7.E-08
0 100 200 300 400 500
Voltage (V)
Co
llect
ion
tim
e (
s)
electrons
holes
Rough estimation of the collection time vs bias voltage for electrons and holes in a 300m thick subst.
We can reduce the collection time thinning the substratebut we have smaller signal!!
C. Piemonte IFAE 20 - 04 - 2006 Pavia
3D detectors - concept3D detectors - concept
Proposed by Parker et al. NIMA395 (1997)
n-columns p-columns
wafer surface
ionizing particle
n-type substrate
All the carriers are collectedat the same time!
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Designing structure with small electrode pitch (i.e. 50m):
• very low full depletion voltage• short collection distance
more radiation hard than planar detectors!!
The distance between the electrodes dependsonly on the detector layout.
The collection time is independent from the substrate thickness!
3D detectors - advantages3D detectors - advantages
3D detectors can find applicationin high energy physics experimentswhere radiation damage is a concern
C. Piemonte IFAE 20 - 04 - 2006 Pavia
1) Electrodes are dead regions
2) Non standard fabrication process
- long R&D needed - concerns on the yield
3D detectors - disadvantages3D detectors - disadvantages
The problem can be partiallysolved tilting the detector
no signal from this particle track
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Groups involved in 3DGroups involved in 3D
• SLAC (Sherwood Parker)
• double columns filled with doped polysilicon, holes all the way through the wafer thickness (150m)
• University of Glasgow
• double columns: one Schottky & one diffused, deep hole
• VTT (Finland)
• Semi 3D: single column boron doped on n-type Si; limited depth (150-200micron)
• ITC-irst
•Single-Type-Column : single column phosphorus doped on p-type Si; limited depth (150-200micron).
workshop on 3D held in february 2006 in Trento : http://tredi.itc.it/
C. Piemonte IFAE 20 - 04 - 2006 Pavia
3D detectors @ ITC-irst3D detectors @ ITC-irst
Development of 3D sensors at ITC-irst started almost 2 years ago in collaboration with INFN.
1.Simulations of 3D-STC detectors;
2.Technology used in the first two fab. runs;
3.Electrical characterization of first prototypes;
4.Future Activity on 3D.
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Single-Type-Column 3D detectors - conceptSingle-Type-Column 3D detectors - concept
n+ n+n+ n+n+ n+
ionizing particle
electrons are swept away by the transversal field
holes drift in the central region and diffuse towards p+ contact
p-type substraten+ electrodes
Uniform p+ layer
NIM A 541 (2005) 441–448 “Development of 3D detectors ..” C. Piemonte et al
Main features of proposed 3D-STC:• column etching and doping performed only once• holes not etched all through the wafer• bulk contact is provided by a backside uniform p+ implant
Simplification of the fabrication process
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Depletion mechanismDepletion mechanism1) 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.
DRAWBACK of 3D-stc: once full depletion is reached it is not possible to increase the electric field between the columns
C. Piemonte IFAE 20 - 04 - 2006 Pavia
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.
Signal & Charge collectionSignal & Charge collection
1 2
34
(25,25)(20,20)(10,10)
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
1E-12 1E-11 1E-10 1E-09 1E-08 1E-07 1E-06 1E-05 1E-04Time (s)
Col
lect
ed c
harg
e (a
.u.)
250um_25-25
250um_20-20
250um_10-10
Same Vbias, different impact point
charge collectedis ¼ for interactionin the middle point
First phaseTransversal movement (fast)
Second phaseHole vertical movement(slow)
e h
250
m50
m
50m
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Mask layoutMask layout
Small version of strip detectors
Planar and 3D test structures
1. “Low density layout” to increase mechanical robustness of the wafer
2. Strip detector = “easy” to electrical test
“Large” strip-like detectors
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Strip detectors - layoutStrip detectors - layout
metal
p-stop
hole
Contact opening
n+
Inner guard ring (bias line)
Different strip-detector layouts:• Number of columns from 12000 to 15000 • Inter-columns pitch 80-100 m• Holes Ø 6 or 10 m
C. Piemonte IFAE 20 - 04 - 2006 Pavia
n+ diffusion
contact
metal
oxide
hole
Deep RIE performed at CNM, Barcelona (it
will be available at IRST within this year) Wide superficial n+ diffusion around the hole
to assure good contact Passivation of holes with oxide
3D process3D process
hole
Hol
e de
pth
~ 1
20μ
m
hole metal strip
Si: High Resistivity, p-type, <100> Surface isolation: p-stop or p-spray Holes are “empty”
C. Piemonte IFAE 20 - 04 - 2006 Pavia
Current distribution @ 40V of 70 different devices
Good process yield
Strip detectors – IV measurementsStrip detectors – IV measurements
1.0E-10
1.0E-09
1.0E-08
1.0E-07
1.0E-06
1.0E-05
0 50 100 150 200Vbias [V]
I lea
k [A
]
p-spray
p-stop
Bias line
Guard ring
Number of columns per detector: 12000 - 15000
0
5
10
15
20
25
30
0 5 10 15 20 25 30 35 40 45 50 >50
I bias line [nA]
Det
ecto
rs c
ou
nt
Average leakage Leakage current < 1pA/column
C. Piemonte IFAE 20 - 04 - 2006 Pavia
3D diode – CCE measurements3D diode – CCE measurements
• CCE @ 0V ≈ tc/tw
• 100% CCE @ low voltages
• Vdep(CCE)<Vdep(CV)
tc
tw
a b• Substrate thickness = 500m• Column depth = 150m
Carlo Tosi, Mara Bruzzi, Antonio De SioINFN and University of Florence
C. Piemonte IFAE 20 - 04 - 2006 Pavia
On going activityOn going activity
End second run (may 2006)
University of Glasgow (UK): CCE measurements with on 3D diodes and short strips
SCIPP (USA): CCE measurements on large strips
INFN Firenze (Italy): CCE meas with on 3D diodes;
University of Freiburg (D); measurements on short strips
Ljubljana: TCT and neutron irradiation
C. Piemonte IFAE 20 - 04 - 2006 Pavia
New process (within the year)New process (within the year)
Actual Process• p-type Si• hole depth ~ 200m• no hole filling• single column• single side
New Process• n-type Si• DRIE ~ 250m• no hole filling• double columns• double side
C. Piemonte IFAE 20 - 04 - 2006 Pavia
New LayoutNew Layout
Actual Layout(basically microstrip)
New Layout(mainly Pixel)
p-diff n-diff
bump region
metal
C. Piemonte IFAE 20 - 04 - 2006 Pavia
ConclusionConclusion
• 3D detectors are extremely interesting devices for high luminosity
colliders (inner tracking layers).
• R&D is ongoing at ITC-irst:
- fabricated first prototypes of 3D-stc detectors with excellent
results
- within the year double column detectors will be ready.