Effect of Metal Overhang on Electric Field for Pixel Sensors

Kavita Lalwani, Geetika Jain, Ranjeet Dalal, Kirti Ranjan & Ashutosh Bhardwaj Department of Physics & Astrophysics, University of Delhi, INDIA

SIMULATION GROUP MEETING13 January, 2015Delhi, India

SIMULATION GROUP MEETING13 January, 2015Delhi, India

Simulation Group Meeting, 23/1/2015

1

Simulated Structure for pixel sensor (three Pixel)

D=

200

um

2

xyz=1002001 um3

3 Pixel StructureBulk Type = BoronBulk Density = 21012cm-3

Bulk profile=constant Aluminium=0.55umGate SiO2=0.25um Field SiO2 = 0.7um Areafactor = NIL2 Contact Vias

Parameters Used Frontside Implant Type = PhosphorusFrontside Implant Density = 11019cm-3

Frontside Implant Profile = Gaussian,y=1.5um, x=1.05um

Backside Implant Type = BoronBackside Implant Density = 11019cm-3

Backside Implant Profile = Gaussian,y=1.5um, x=1.05um

Pstop density = 11016cm-3

Pstop implant profie= Gaussian, y=1.0um, x= 0.7um

Configuration-Pstop, implant wide

Metal overhang = 0, 4umT=253K

For Non Irradiated Pixels-Qf=1e11cm-2 + 2Nit traps [1]

For Irradiated Pixels- Radiation Damage Model=2bulktraps + Qf +2Nit traps [2]Qf= 2e12cm-2

Fluence = 0 (Non irradiated case), 1e15, 2e15, 5e15, 1e16cm-2

References-[1] Dissertation , “X ray Radiation damage studies and Design of a silicon pixel sensors for science at the XFEL, by Jiaguo Zhang, 2013.[2] “Simulation of Irradiated Si Detectors”, Ranjeet Dalal et al, Proceeding of Vertex 2014

2]

2D Electric Field Profiles for Non Irradiated Pixel SensorsConfiguration-Pstop, implant wide

MO=0um MO=4um

Maximum electric field is at the curvature ofn+ strips

3

Applied reverse bias = 1000V

Maximum electric field is under the MO

It is expected that effect of MO would be significant for non irradiated pixel sensors

N+ implant

No Metal overhang

P Bulk

N+ implant

Metal overhang

P Bulk

N+ implant

Cutline of 1umCutline of 0.1 um

Non irradiated pixel sensors

MO has significant effect on maximum electric field for non-irradiated pixel sensors.

There is decrease in maximum electric field for MO of 4um compared to structure without MO.

Applied reverse bias = 1000V

MO effect on Electric Field

Gap bw pstop

Implant edge Implant edge

Gap bw pstop

implant pstop edge implant pstop edge

4

2D Electric Field Profile for Irradiated Pixel Sensors Configuration-Pstop, implant wide

MO = 4umMO = 0um

Maximum electric field is at the curvature of n+ strips It is expected that effect of MO would not be very significant for irradiated pixel sensors 5

Applied reverse bias =1000V

fluence = 2e15cm-2

Qf=2e12cm-2

No Metal overhang

n+ implant

P bulk

fluence = 2e15cm-2

n+ implant

P bulk

Metal overhang

fluence = 2e15cm-2

Qf=2e12cm-2

Irradiated Pixel sensors

Electric Field for cut line of 1 um (Configuration: Pstop, Wide implant)T= 253K, D=200um, X=100um, Nb=2e12cm-3

Configuration-Pstop, implant wide

6Applied reverse bias= 1000V

MO effect on Electric Field

MO does not have significant effect on maximum electric field at fluences of 1e15, 2e15 cm-2 for irradiated pixel sensors.

There is small decrease in maximum electric field at fluence of 5e15 cm-2 for MO of 4um compared to structure without MO

Similar results are observed for configuration pstop, normal implant

small variation inmax Efield at f=5e15cm-2

Cutline of 1um

Qf=2e12cm-2

f=1e15cm-2

f=2e15cm-2

f=5e15cm-2

MO has small effect on maximum electric field at fluence of 1e16cm-2

7

Applied reverse bias =1000V

Irradiated Pixel sensors

small change inmax Efield at f=1e16cm-2

implant pstop edge

Gap bw pstopImplant edge

Cutline of 1um2D Electric Field Profile , MO=4um (fluence =1e16cm-2 )

Qf=2e12cm-2

fluence = 1e16cm-2

Metal overhang

P bulk

Qf=2e12cm-2

n+ implant

8

Fluences (cm-2) MO=0um MO=4um MO=0um MO=4um

f=0 (Non irradiated case)

1.72105 1.33105 1.81105 9.82104

f=1e15 1.14105 1.14105 1.09105 1.09105

f=2e15 1.97105 1.94105 1.35105 1.43105

f=5e15 2.67105 2.55105 1.46105 1.64105

f=1e16 3.09105 2.93105 1.78105 1.76105

Cutline=1um

Configuration- Pstop, implant wide

Cutline=0.1um

Comparison of Maximum Electric Field (Non Irradiated vs Irradiated Pixel Sensors)

Applied reverse bias = 1000V

Electric field unit V/cm

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Summary

Electric field simulations are performed to study the effect of metal overhang for both non irradiated as well irradiated pixel sensors.

-For Non irradiated pixel senors MO has a significant effect on maximum electric field

- For irradiated pixel senors MO does not have significant effect on maximum electric field at fluences of 1e15, 2e15 cm-2

There is small decrease in maximum electric field at fluence of 5e15 cm-2 and 1e16cm-2

for MO of 4um compared to structure without MO Similar results are observed for configuration pstop, normal implant

Future Plan

Study the effect of various design parameters like pstop depth, pstop concentration, effective doping concentration etc on electric field profiles for non irradiated and irradiated pixel sensorsStudy the design optimization for the pixel structures- 1) X (width)=50um & depth =200um 2)X (width) = 25um & depth = 200um

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Thank you

Back-up Slides

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12

Electric Field in Bulk

Irradiated pixel sensors at f=1e15cm-2

Non IrrNon Irradiated pixel sensors at QF=1e11cm-2 + interface trap

Conf-Pstop, Implant Wide (cutline of 1.0um)

MO Effect on Electric Field at different fluences for Irradiated Strip sensors

13

Fluence = 1e15cm-2

Fluence = 2e15cm-2

Fluence = 5e15cm-2

Fluence = 1e16cm-2

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MO Effect on Electric Field at different fluences for Irradiated Strip sensors

Conf-Pstop, Implant Wide (cutline of 0.1um)

f=1e15cm-22f=2e15cm-22

f=5e15cm-22 f=1e16cm-22

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Leakage Current Plot for irradiated sensors

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Net Doping, f= 1e16, MO=4um

Non Irradiated Pixel Sensors

QF=1e11cm-2Incorporated following two interface traps

Interface trap levels

Density(cm-3) (e) and (h)

0.60eV (e-level) 0.6e11 1e-15, 1e-15

0.39eV (h-level) 0.4e11 1e-15, 1e-15

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Irradiated Pixel Sensors

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Fixed interface charge density (QF) =2e12cm-2

Incorporated following two interface traps

Interface trap levels

Density(cm-3) (e) and (h)

0.60eV (e-level) 12e11 1e-15, 1e-15

0.39eV (h-level)

8e11 1e-15, 1e-15

trap levels Density(cm-3) at f=1e15,2e15,5e15cm-2

(e) and (h)

0.51eV (e-level) 4e15, 8e15,2e16 2e-14, 2.6e-14

0.48eV (h-level)

3e15,6e15,1.5e16 2e-14, 2e-14

Bulk Damage Model