CERN, 14-16 November 2005 Claudio Piemonte RD50 workshop Claudio Piemonte a, Maurizio Boscardin a, Alberto Pozza a, Sabina Ronchin a, Nicola Zorzi a, Gian-Franco

Claudio Piemonte RD50 workshop CERN, 14-16 November 2005

Claudio Piemontea, Maurizio Boscardina, Alberto Pozzaa, SabinaRonchina, Nicola Zorzia, Gian-Franco Dalla Bettab, Luciano Bosisioc

\

a ITC-irst, Microsystems Division, via Sommarive 18, 38050 Povo di Trento, Italy b University of Trento, DIT, Trento, Italy

c Physics Department, University of Trieste and INFN, Trieste, Italy

First electrical characterization First electrical characterization

of 3D detectors with electrodes of 3D detectors with electrodes

of the same doping typeof the same doping type


Single-Type Column 3D detector concept Fabrication of 3D-STC detectors Layout and preliminary electrical results Conclusions

OutlineOutline


STC-3D detectors - concept (1)STC-3D detectors - concept (1)

Sketch of the detector:

grid-like bulk contact

ionizing particle

cross-sectionbetween twoelectrodes

n+ n+

electrons are swept away by the transversalfield

holes drift in the central region and diffuse towards p+contact

n+-columns

p-type substrate

Adv. over standard 3D: etching and column doping performed only once

Functioning:

[C. Piemonte et al, Nucl. Instr. Meth. A 541 (2005)]


3DSTC detectors - concept (2)3DSTC detectors - concept (2)

Further simplification: holes not etched all through the wafer

p-type substraten+ electrodes

Uniform p+ layer

Bulk contact is provided by a backsideuniform p+ implant single side process.

No need of support wafer.


Potential distribution(vertical cross-section)

Potential distribution(horizontal cross-section)

null field regions0V

-10V

-5V

50m

300

m

-15VDrawbacks: • once full depletion is reached it is not possible to increase the electric field between the columns• large low field region

3DSTC detectors - 3D simulations3DSTC detectors - 3D simulations

Both can be improved using higher substrate doping concentration


Fabrication process (1)Fabrication process (1)

n+ diffusion

contact

metal

oxide

hole

MAIN STEPS:

1. Hole etching with Deep RIE machine (step performed at CNM, Barcelona, Spain)

2. n+ diffusion (column doping)

3. passivation of holes with oxide4. contact opening5. metallization

10 m

Hole depth: 120μm

CHOICES FOR THIS PRODUCTION:

• No hole filling (with polysilicon)• Holes are not etched all through the wafer• Bulk contact provided by a uniform p+ implant


Si High Resistivity, p-type, <100>

• Surface isolation:• p-stop

• p-spray

• FZ (500 m) resistivity > 5.0 k cm

• Cz (300m) resistivity > 1.8 k cm

• Substrates used for this production:

• Sintering• Standard @ 420˚C for FZ

• 380˚C for Cz to minimize thermal donor activation

Fabrication process (2)Fabrication process (2)


Mask layoutMask layout

Small version of strip detectors

Planar and 3D test structures

“Low density layout”to increase mechanicalrobustness of the wafer

“Large” strip-like detectors


Planar test structures measurementsPlanar test structures measurements

Standard planar test structures

Electrical parameters compatible with standard planar processes

High variation due to different substrates

Ileak measured below full depletion due to Vbreak

Parameter Unitp-spray p-stop

Na [1E12 cm-3]Vdep [V]Ileak [nA/cm2]Vbreak [V] 60 - 140 155 - 175Tox [nm] 570 - 585 860 - 875Qox [1E10cm-2] 9.5 - 11 6 - 9.6So [cm/s] 1.3 - 1.7 7 - 7.5

typical range

1 - 3.5200 - 500

1 - 2050 - 60


3D diode – layout:3D diode – layout:

Different 3D-diode layouts:

• Different isolation geometry (p-stop)

• Different column connections

• Different inter-colum distances (ranging from 80μm to 100μm)

Bulk

Guard ring

p-stop

10x10 holes matrix

Single hole p-stop

p-stop around the entire region


3D diode – IV measurements:3D diode – IV measurements:

Vback

Guard ring (n+) p-spray

Depletion region

High field region

diode

─ guard ring

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

0 20 40 60 80 100Vbias [V]

I lea

k [

A]

p-stop case

diode

─ guard ring

1st punch through

2nd punch through

1.0E-12

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

0 10 20 30 40 50 60Vbias [V]

I lea

k [A

]

diode

─ guard ring

p-spray case

Breakdown

Vback

Guard ring (n+)p-stops

e- layer

- -

Depletion region

Ileak = 0.68 ± 0.2 pA/column @ 20V

Ileak = 0.59 ± 0.12 pA/column @ 20V


3D diode – CV measurements3D diode – CV measurements (preliminary)(preliminary)

Capacitance measurement versus back on a 300m thick wafer with ~150m deep columns, 100m picth

Back

1/C2

0

2

4

6

8

10

12

0 10 20 30 40 50 60

Vbias [V]

Cd

iod

e [p

F]

0.00

0.50

1.00

1.50

2.00

2.50

0 10 20 30 40 50 60

Vbias [V]

C-2

[p

F-2

]

1 2

Phase 1

Phase 2

region between col.is not fully depleted large capacitance

full dep. between columns~ 7V

region between col.is fully depleted depletion proceedsonly towards the back(almost like a planar diode)

full depletion ~40Vdepletion width of ~150m

Cd

1/C

d2 [

pF

-2]

Cd

[pF

]

f=10kHz


Strip detectors - layout detectors - layout

metal

p-stop

hole

Contact opening n+

Inner guard ring (bias line)


• Two different p-stop layouts:

Strip detectors – layout:Strip detectors – layout:

Different strip-detector layouts:

• Number of columns ranging from 12000 to 15000 • Inter-columns pitch 80-100 m• Holes Ø 6 or 10 m

Single p-stop for each hole

Common p-stop for each strip

Punch-through structures

• AC coupling: • DC coupling:

DC pads


Current distribution @ 40V of 70 different devices

Good process yield

Strip detectors – IV measurements:Strip 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

Average leakage current per

column < 1pA

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

Leakage current < 1pA/column in most of the detectors


ConclusioConclusionn• The first production has proved:

The feasibility of 3D-stc detectors Low leakage currents (< 1pA/column) Breakdown @ 50V for p-spray and >100V for p-stop structures Good process yield (typical detector current < 1pA/column)

• Samples have been given to: Glasgow (UK): CCE measurements with on 3D diodes

SCIPP (USA): CCE measurements on large strips


3D-stc TCAD 3D-stc TCAD simulationssimulationsSimulation of the electric field along a cut-line from the electrode to the center of the cell

Na=1e12 1/cm3

Na=5e12 1/cm3

Na=1e13 1/cm3 DRAWBACK:3D-stc: once full depletion is reached it is not possible to increase the electric field between the columns

Maximum electric field depends on substrate doping

Documents

CERN, 14-16 November 2005 Claudio Piemonte RD50 workshop Claudio Piemonte a, Maurizio Boscardin a, Alberto Pozza a, Sabina Ronchin a, Nicola Zorzi a, Gian-Franco