Large Area Silicon Sensors: Study and Mitigation...(0.4x0.4 mm2) W014 (P1) No W014 (P4) No W014 (P7) No INFINEON Batch VC820647 Device Edge Wafer (Device ID) RH Sensitivity Main Standard-edge

Humidity Sensitivity of

Large Area Silicon Sensors:

Study and Mitigation

Xavi Fernández-Tejero a, P.P. Allport b, K. Dette c, V. Fadeyev d, C. Fleta a,

D. Gillberg e, L. Gonella b, K. Hara f, C. Helling d, B. Hommels g, J. Keller e,

C. Kleing, T. Koffas e, V. Latonova h,i, M. Mikestikova h, R.S. Orr c, S. Pyatt b,

U. Soldevila j, E. Staats e, J. Thomas b, M. Ullán a, Y. Unno k and S. Wada f

a Centro Nacional de Microelectrónica (CNM, CSIC), Spainb University of Birmingham, United Kingdom

c University of Toronto, Canadad Santa Cruz Institute for Particle Physics (SCIPP), University of California, USA

e Carleton University, Canadaf University of Tsukuba, Japan

g University of Cambridge, United Kingdomh Academy of Sciences of the Czech Republic, Czech Republic

i Charles University, Czech Republicj Instituto de Física Corpuscular (IFIC, CSIC), Spain

k KEK, Japan

December 17th 2019

12th International “Hiroshima” Symposium on the Development and Application

of Semiconductor Tracking Detectors (HSTD12)

Introduction

Observations

o Breakdown Voltage Dependence

o Leakage Current Stability Dependence

o Hotspot Imaging at Breakdown Voltage

o Cleaning and Baking Influence

Incidence Rate

o Statistical Study

o Irradiation Influence

Mechanisms

o Sensor Edge Configuration

o Passivation Thickness

Mitigation Investigation

Summary of Findings and Conclusions

-02-

Outline

J. Fernández-Tejero – HSTD12 – December 2019

Introduction

-03-

• Measurements on Hamamatsu large area prototypes for the Step-2 of the ATLAS ITk Strip

Sensor Market Survey (ATLAS12) show first indications of breakdown voltage

dependence with relative humidity variations, also seen in sensors assembled in

modules (see Poster ID 233 – link).

• Sensitivity of large area prototype batches for the Market Survey Step-3 (ATLAS17) were

extensively tested by many ATLAS institutes.

• This presentation summarizes the findings by the ATLAS ITk strip sensor community, for

prototype batches ATLAS12 and ATLAS17, from Hamamatsu and Infineon, to investigate

the mechanisms and evaluate the impact and implications of the humidity sensitivity

for the ATLAS strip sensor production in particular and for large area silicon sensors in

general.


Intro | Observations | Incidence | Mechanisms | Mitigation | Conclusion

Large area sensors from Hamamatsu

6-inch wafer from Infineon

https://indi.to/ND2ry

Observations – Breakdown Voltage Dependence (Large Area Sensors)

-04-

Breakdown voltage (VBD) of ATLAS12EC and ATLAS17LS large area (Main)

sensors sensitive to changes in relative humidity (RH):

VPX22728-W028

ATLAS12EC – Main Sensor

RH↑ ⇒ VBD↓


VPX26244-W040

ATLAS17LS – Main Sensor

0

1

2

3

0 500 1000Le

ak

ag

e C

urr

en

t [µ

A]

Bias [V]

TEST 3 + Measurement 5%

0

1

2

3

0 500 1000Le

ak

ag

e C

urr

en

t [µ

A]

Bias [V]

Storage 20% + Measurement 5%

0

1

2

3

0 500 1000Le

ak

ag

e C

urr

en

t [µ

A]

Bias [V]

TEST 1 + Measurement 60%

0

1

2

3

0 500 1000Le

ak

ag

e C

urr

en

t [µ

A]

Bias [V]

4h Storage 60% + Measurement 60%

After 2h of storage at ~5% RH

TEST 1 TEST 2 TEST 3 TEST 4

ATLAS17LS Main Sensor (VPX26244-W019)

…however, sensor storage at low RH mitigates early breakdown on ATLAS12 and ATLAS17 large

area sensors, recovering the breakdown voltage prior to the high humidity tests:

VBD≈420V VBD≈375V VBD≈310V VBD≈420V

Sensor with initial early

breakdown (see “Cleaning and

Baking Influence” section)


-05-

Breakdown voltage of ATLAS17LS Miniature sensors (Mini, MiniSS and MiniLS)

seems less sensitive but also showing clear influence.

…additionally, some mini sensors show small RH dependence of baseline current, in contrast to large

area sensors

Increasing RH

50% → 65%

Increasing RH

50% → 65%


RH↑ ⇒ VBD↓

VPX26244 Mini 7VPX26244 Mini 6

50%

5%

50%

5%

50%

5%

Mini Sensor (1x1 cm2) MiniSS Sensor (3x1 cm2) MiniLS Sensor (5x1 cm2)

Mini Sensor (1x1 cm2) Mini Sensor (1x1 cm2)


Observations – Breakdown Voltage Dependence (Miniature Sensors)

Observations – Leakage Current Stability Dependence

-06-

• Large area sensors showing dependence on current stability only at bias near the breakdown

voltage at high RH

• Quick response of leakage current to RH


• Long periods biasing sensors in high RH can lead on an irreversible high leakage current

and low VBD

Vbias=-250V Vbias=-300V



Uncontrolled RH

Low RH

ATLAS12 (VPX12318 W644)

0.12

0.17

0.22

0.27

0.32

0.37

0.42

0.47

0 2 4 6 8

Leakage C

urr

ent

[µA

]

Time [h]

ATLAS12 (VPX22728 W003)

Low RH

Uncontrolled RH

-600V

-500V

V≈320VRH=~60%

Observations – Hotspot Imaging at Breakdown Voltage

-07-

ATLAS12 and ATLAS17 large area

sensor hotspots, at breakdown voltage,

mainly located at the Bias/Guard/Edge

Rings (edge structure)




ATLAS12A – Main Sensor


Lock-in Infrared Thermography (LIT)[1]

characterization at high RH

[1] M. Vellvehi, et al., Lock-in Infrared Thermography: a tool to locate and analyse failures in power devices, 2017 CDE. doi: 10.1109/CDE.2017.7905234

ISOPROPANOL CLEANING:

• ATLAS17LS MAIN sensor (VPX26244-W019) showing low breakdown voltage

• We decided to clean the sensor with isopropanol and repeat the RH sensitivity test

Results:

Clear increase on initial breakdown voltage (from ~420V to ~925V)

Still similar humidity sensitivity

Observations – Cleaning and Baking Influence

-08-

RH 5%

RH 60%

ISOPROPANOL

RH 60%

RH 5%


(1) 5 min. submerged in isopropanol

applying ultrasounds

(2) 5 min. submerged in deionized

water

(3) 10 min. at 100ºC with low RH

(~5%)

• After the isopropanol cleaning, new

hotspots found on different areas, but

always located at the Edge structure

RH=~60% V≈255V


Initial early breakdown seems solved after the isopropanol cleaning, but the sensor is still

sensitive to RH

SENSOR BAKING:

Results:

Increased breakdown voltage (from ~925V to >1000V)

Still similar humidity sensitivity

PLASMA CLEANING:

Results:

High breakdown voltage

Still similar humidity sensitivity -09-

RH 5%

RH 60%

BAKING


150ºC 24h with low RH (~5%)

Observations – Cleaning and Baking Influence

PLASMA

Plasma parameters:

• 200 ml/min O2 flow

• 500 W

• 5 min.

RH 5%

RH 60%



Incidence Rate – Statistical Study (Market Survey Step-3 Batches)

-10-

HAMAMATSU Batch VPX26244

Device Edge Wafer (Device ID) RH Sensitivity

Main

Slim-edge

W002 High

W019 High

W035 High

W037 High

W038 Low

W040 High

MiniLS

(5x1 cm2)

W003 (1) High

W004 (1) High

W005 (1) No

MiniSS

(3x1 cm2)

W004 (2) High

W006 (2) High

Mini

(1x1 cm2)

W002 (2) No

W002 (3) Low

W002 (4) No

W004 (7) High

W005 (?) High

W006 (?) High

W017 (8) No

W049 (8) No

Diode

(0.8x0.8 cm2)

W015 (P1) High

W038 (P1) No

W038 (P2) High

W038 (P3) No

Diode

(0.4x0.4 mm2)

W014 (P1) No

W014 (P4) No

W014 (P7) No

INFINEON Batch VC820647Device Edge Wafer (Device ID) RH Sensitivity

MainStandard-edge

W001 No

W004 Low

Slim-edge

W004 High

MiniSS

(3x1 cm2)W006 (1) High

Mini

(1x1 cm2)

W004 (8) High

W006 (1) High

Diode

(0.8x0.8 cm2)Standard-edge

W001 (E) No

W001 (W) No

W005 (W) No

W006 (W) No

W007 (W) No

Diode

(0.2x0.2 mm2)

Slim-edge W007 (TestEdge) No

(Slim-edge) – 60 µm W007 (TestEdge) High

Humidity Sensitivity tests performed in batches from

ATLAS ITk Strip Sensor Market Survey Step-3:

Hamamatsu Batch VPX26244: 26 devices

Infineon Batch VC820647: 13 devices

CRITERIA: Devices tested at high humidity showing a

decrease in breakdown voltage…

lower than 200 V → No sensitivity

between 200 and 300 V → Low sensitivity

higher than 300 V → High sensitivity

• Both batches are highly sensitive to RH variations

• Devices with higher dimensions and/or with slim-

edge seem to be more sensitive


HAMAMATSU Batch VPX29549 (Special Passivation)


Main Slim-edgeW071 No

W072 Low

MiniSS

(3x1 cm2) Standard-edgeW068 (2) No

Mini

(1x1 cm2)

W068 (8) No

Slim-edge

W068 (4) No

W068 (6) No

W071 (3) No

W071 (4) Low

W071 (7) No

W071 (8) High

Diode

(0.4x0.4 mm2)

W064 (?) No

W068 (?) No

W068 (?) No

W068 (?) No

W071 (P2) No

W071 (P7) No

W071 (P11) No

HAMAMATSU Batch VPX30816


Main

Slim-edge

W208 Low

MiniSS

(3x1 cm2)

W172 (2) No

W179 (2) No

W182 (2) No

Mini

(1x1 cm2)

W172 (6) No

W172 (7) No

W177 (6) No

W177 (7) Low

W179 (6) No

W179 (7) No

W182 (6) No

W182 (7) No

W185 (6) No

W185 (7) No

• After the Market Survey, Hamamatsu fabricated a “Special Passivation” batch (VPX29549) to

investigate the humidity sensitivity of the Market Survey sensors, and a final prototype batch

(VPX30816)

• “Special Passivation” batch shows clear improvement, but the

passivation layer is only for investigation purposes, not for

sensor production.

• Last batch VPX30816 shows the best response to humidity,

only with 2 out of 14 devices sensitive.

Humidity Sensitivity tests also performed in:

HPK “Special Passiv” Batch VPX29549: 17 devices

HPK Final Batch VPX30816: 13 devices


Incidence Rate – Statistical Study (Batches After Market Survey)

-11-

Incidence Rate – Irradiation Influence• Sensors showing sensitivity to RH variations were irradiated and tested to evaluate the evolution

of the dependence

• ATLAS12 and ATLAS17 sensors drastically reduce their humidity sensitivity after (0.5-1)e15 neq/cm2

proton irradiation (measuring at -20ºC)

• Post-irradiated sensors not sensitive to changes in relative humidity

0 200 400 600 800 1000

voltage[-V]

9-10

8-10

7-10

6-10

5-10

4-10

3-10

leak[-

A]

30%

50%

70%

irrad

ATLAS12EC - MAINATLAS17LS - Mini

PROTON 5e14 neq/cm2

NEUTRON 5e14 neq/cm2

-12-J. Fernández-Tejero – HSTD12 – December 2019

PROTON 1e14 neq/cm2

ATLAS17LS - Mini ATLAS17LS - Mini

PROTON 5e14 neq/cm2

ATLAS17LS - Mini

PROTON 2e15 neq/cm2


Mechanisms – Sensor Edge Configuration



• The sensor edge configuration in the new large area sensors is one of the new features of the

future HL-LHC strip sensors.

• Devices with “Slim-edge” seems to be more sensitive to humidity changes than devices with

“Standard-edge” (Statistical Study in slides 10 and 11).

• Additionally, the metal separation between guard ring and edge ring can be critical if the

passivation thickness is not thick and conformal enough to cover the metal steps:

Guard ring Edge ring

D(HPK) = 125 µm

D(IFX) = 105 µm

h

passivation

HPK: 180 µm

IFX: 180 µm

Si e

dg

e

h

Guard ring

Edge ring

• Metal separation (D) between guard ring and edge ring: 125 µm (HPK) and 105 µm (IFX)

• Dielectric strength:

o Air dielectric strength: SAir=3 V/µm

o SiO2 dielectric strength: SSiO2=103 V/µm (Passivation)

Vmax = D·Sair + 2·h·SSiO2 ⇒ h(Vmax=1kV) ≥ 0.3-0.4 µm

• If the passivation thickness (h) is close to 0.3-0.4 µm, we can be close to the dielectric

breakdown between the guard ring metal and edge metal

• High sensitivity of Infineon batch compatible with their lower metal separation (D)

• Dielectric strength (S) can be reduced in high humidity, facilitating the breakdown

• Passivation thickness and conformity may vary between batches

RH↑ ⇒ S↓ [2]

[2] C.M. Osburn, et al., Dielectric Breakdown in SiO2 Films, J. Electrochem. Soc., Vol. 119, No. 5, 1972

Mechanisms – Passivation Thickness



• The passivation thickness was measured in miniature sensors from the 4 prototype batches

using different techniques in different ATLAS institutes.

Guard ring Edge ring

D(HPK) = 125 µm

D(IFX) = 105 µm

h1

passivation

HPK: 180 µm

IFX: 180 µm

Si e

dge

h1

Sensor from HPK batch VPX26244 showing less conformal metal step coverage (h1<h2) in

guard and edge rings.

Sensor from HPK batch VPX30816 showing conformal passivation (h1=h2) and no humidity

sensitivity.

Sensor from HPK “special passivation” batch VPX29549 showing less conformal metal step

coverage, but no sensitivity probably due to the different passivation material.

Sensor from IFX batch with thicker conformal passivation, but showing moderate humidity

sensitivity probably due to the lower separation between metals.

h2h2

• The high sensitivity of batch VPX26244 could be partially associated to a

thinner and/or less conformal passivation.




• Sensitive miniature sensor selected from the highly sensitive Hamamatsu batch

(VPX26244), and glued + wire-bonded to a PCB board:

50%

5%

• Manual sensor passivation using a Silicone Conformal Coating Aerosol (RS ref: 494-714):




MANUAL PASSIVATION WITH COATING AEROSOL:

• Extensive humidity sensitivity test after manual passivation, showing clear improvement

even at humidity conditions near the dew point:

50%

5%

COATING

• No variation of baseline current

• No influence of long exposition (1 week) to ambient

humidity (55%)

• Highly stable leakage current even for long periods

(5h) biasing the sensor at high humidity (55%):

Vbias = 600 V

RH 55%

• Encouraging results – Total coverage, not proving anything yet

• Further experiments: Humidity sensitivity test coating only the sensor edge area to

try and demonstrate passivation mechanism AND radiation tolerance of coating

• Still, in a first approach, possible mitigation method demonstrated

Summary of Findings and Conclusions

-17-

Observations:

• Humidity sensitivity of breakdown voltage observed for ATLAS12 and ATLAS17 MAIN sensors.

• After measurements at high humidity, fast recovery of breakdown voltage placing the sensor in low

humidity.

• Humidity sensitivity less common on miniature sensors but showing clear influence.

• Long periods biasing a sensor in high humidity can lead on an irreversible high leakage current and low

breakdown voltage.

• Hotspots at breakdown voltage mainly located at the edge structure of the sensor.

• Cleaning and Baking clearly improve breakdown voltage at low humidity, but still sensitive to humidity.

Incidence Rate:

• HPK batch VPX26244 and IFX batch highly affected by humidity changes.

• Humidity sensitivity less common on devices from subsequent HPK batches.

• Less sensitivity observed as sensors get irradiated.

Mechanisms:

• Influence of Guard/Edge ring metals separation and passivation thickness and conformity of step

coverage.

• Dielectric strength also can be reduced at high humidity, facilitating the breakdown.

Mitigation Investigation:

• Manual passivation with Silicone Conformal Coating Aerosol totally mitigates the humidity sensitivity,

even in highly sensitive batches and humidity conditions near the dew point.

• Further experiments to be performed coating only the edge region and testing radiation tolerance.


Intro | Observations | Incidence | Possible Causes | Mitigation | Conclusion

• Procedures established to keep low humidity conditions for reception and storage.

• Sensors should be handle in clean conditions.

• Sensors will work at dry environment therefore no expected problems of humidity during experiment.

Actions Taken for Sensor Production

Backup Slides


-19-

BACKUP: Breakdown Voltage Dependence – ATLAS07

No humidity sensitivity observed for ATLAS07 prototype sensors (only for high RH ~70%):


BACKUP: Breakdown Voltage Dependence

-20-

• The variation range of VBD, for

different RH, is reduced when the

temperature decreases

Low temperature seems to reduce

the humidity sensitivity dependence

of breakdown voltage20ºC

-11ºC

ATLAS17LS - Mini

ATLAS17LS - Mini

0ºC

ATLAS17LS - Mini


-21-

• Hamamatsu initially doesn’t observe these

dependence, then started repeat tests on time of the

humidity sensitivity of ATLAS17LS MAIN sensors

• Long period of storage at 25ºC and ambient humidity

(50%), and tested at ambient humidity (50%)

• Different levels of breakdown voltage degradation

observed

• The observed time dependence explains why we are

seeing the humidity sensitivity at RH levels

comparable to the conditions of HPK QC tests


BACKUP: Breakdown Voltage Dependence

POST-ISOPROPANOL

-22-

BACKUP: Microscope Inspection of Hotspots after Cleaning/Baking

• Prior to cleaning/baking, several stains found on hotspot areas

After the cleaning/baking, the sensor looks pretty clean

Initial early breakdown voltage solved

But humidity sensitivity seems not related with sensor cleanness

POST-ISOPROPANOL POST-BAKE

POST-BAKE

POST-BAKE

POST-PLASMA

POST-PLASMA

POST-PLASMA

INITIAL INSPECTION

POST-ISOPROPANOL


-23-

BACKUP: Repairing Treatments – Bake-out

stable unstable

humidity,

time

bake-out

pote

ntial

During the Hamamatsu-ATLAS meeting in September 2017, a model for sensor stability was

presented, based on findings on an ATLAS12EC sensor:

• The sensor can reside in a “stable” state, and an “unstable” state

• A potential barrier exists between the stable and unstable states, favoring the latter

• Boltzmann statistics / Arrhenius equation applies to transition

• High humidity encourages the transition into the unstable state over time

• Bake-out (16h at 160ºC and dry environment) is supposed to bring the sensor back in the

stable state

• Procedure can be repeated and leads to longer lifetime in stable state


-24-

BACKUP: Repairing Treatments – Bake-out

Bake-out should be done in dry conditions to avoid possible sensor degradation:

Uncontrolled RH

Low RH


BACKUP: Sensors with Special Passivation

0

1

2

3

0 200 400 600 800 1000

Le

akag

e C

urr

en

t [µ

A]

Bias [V]

VPX29549-W071 (special passivation)

RH 5% (Storage RH 20%)


RH 45% (3h Storage RH 50%)




0

1

2

3

0 200 400 600 800 1000

Le

akag

e C

urr

en

t [µ

A]

Bias [V]

VPX29549-W072 (special passivation)






• ATLAS17LS batch with special passivation for

humidity sensitivity studies, NOT considered to be

included on production

• Preliminary results for three MAIN sensors:

- W064: Decrease of VBD for RH > 65%

- W071: Decrease of VBD for RH > 65%

- W072: No decrease of VBD

• Relative humidity of 65% at 20ºC can lead on

water condensation on sensor surface (dew point

14ºC)

Two independent groups confirmed that no

humidity sensitivity is observed for safe dew point

conditions

• First MAIN sensors found without sensitivity

• Passivation seems to play a key role on humidity

sensitivity

-25-Plots overlap


Documents

Large Area Silicon Sensors: Study and Mitigation...(0.4x0.4 mm2) W014 (P1) No W014 (P4) No W014 (P7) No INFINEON Batch VC820647 Device Edge Wafer (Device ID) RH Sensitivity Main Standard-edge