Update on TCAD Simulation

Mathieu Benoit

Introduction• The Synopsis Sentaurus Simulation tool

– Licenses at CERN– Integration in LXBatch vs Engineering Machine

• Principles of TCAD simulation – Process simulation

• implantation• Lithography• Diffusion/Activation

– Device simulation• DC Simulation • Transient simulation

• Simulation results on medipix-like n-in-p thin pixel sensors

The Synopsis Sentaurus Simulation tool

• 2 Licenses available at CERN through europractice– One license for RD50– One license available to all (microelectronics group)– 20 licenses (2000 €) to be delivered to CLIC-LCD in mid-February

• 2 possibility to perform simulation : – Sentaurus workbench tools allow for automatic handling of LSF protocol -

> lxbatch• Limited number of CPU, RAM per simulation

– Running on a local engineering machine• Many CPU available for parallel computing• Large amount of RAM

Parameter exploration

3D simulation

The Synopsis Sentaurus Simulation tool

• Example : 2D Process Pixel simulation – 47120 nodes , 7 min of simulation– 64.7% of time spent in solver

Pardisio (277.6 s)• Example : 2D DC Device simulation

– 157s of simulation to obtain solution a one bias point

• Example : 2D Transient simulation (mip)– 3h09m of simulation -> 1h06m of

real time running on 3 CPU (lxplus)– 1.375 Gb of RAM used

Process Simulation• 1st Backside implantation

– Oxide deposition (40nm)– Boron implantation (10^15/cm2, 60 keV)– Contact etching (oxide)

• 2nd P-Spray Implantation (n-readout)– Deposition of a screening oxide (200nm)– Deposition of a nitride layer (200nm)– Boron implantation (10^12/cm2, 120 keV )

• 3rd Read-out implantation– Etching of the nitride layer in implant location – Etch of oxide in implanted down (40 nm of screening oxide left)– Implantation of phosphorus (10^15/cm2, 60 keV)

• 4th Diffusion/activation of the implants– Heating of the wafer in the oven in a nitrogen atmosphere (3 min @1050 C (RTA) or

≈10 min at 960C (classic) )

• 5th Contact etching and metal deposition – Opening of pillar in 40nm oxide for contact between metal and implants– Deposition of ≈ 800nm of Aluminum– Passivation (not simulated)– Opening in passivation (not simulated)

Process Simulation

N+ Implant• Provide Ohmic contact

with Aluminum• Form the main junction of

the diode

Al Electrode• Provide Ohmic contact

with implant• Formation of field plates

around implant

P-Spray insulation • Cut the electron channel

between electrodes• Increase radiation hardess

(ionizing damage)

Process Simulation

N+ Implant• Provide Ohmic contact

with Aluminum• Form the main junction of

the diode

Al Electrode• Provide Ohmic contact

with implant• Formation of field plates

around implant

P-Spray insulation • Cut the electron channel

between electrodes• Increase radiation hardess

(ionizing damage)

Process SimulationDoping width

Pixel pitch

Thickness• P-Spray Dose/Energy• N implant dose/Energy• P+ implant dose/Energy• Diffusion time/temperature

The 2D Pixel model is parametrized

5th "Trento" Workshop on Advanced Silicon Radiation Detectors, Manchester, UK

9

TCAD Device simulation principles

)()(

)()(

npcqV

nDEnRGqdt

dnq nnnn

It can be proven the analytical

solution is part of an Hilbert space. By choosing a set of basis

function covering this Hilbert space, we can truncate this set

and obtain an aproximate solution if the solution is locally

polynomial over each mesh element ’s domain

10

PhysicsPhysics ModelsMobility Concentration-dependent mobility (fit to

experimental data), Parallelfield dependent mobility (fit to

experimental saturation velocities)

Generation recombination and trapping

Modified concentration dependent Shockley-Read-Hall

Generation/recombination (for treatment of defects)

Impact ionization Selberherr’s Impact ionization model

Tunneling Band-to-band tunnelling, Trap-Assisted tunneling

Oxide physics Fowler-Nordheim tunnelling, interface charge accumulation

11

Generation/Recombination

• Modified Shockley-Read-Hall G/R– A sum of SRH contribution by each trap– Γ is the degeneracy of the trap, ni the intrinsic

concentration of carriers

)()(

)()(

2

,

kTEfEi

ipi

kTEiEf

ini

ii

ipn

ennenp

npnR

RR

12

Generation/Recombination• Transient behaviour of traps

σn,p is trap capture cross-section

vn,p is thermal velocity

ni is intrinsic concentration

FtA,TD the probability of ionization

NtA,TD space charge density

))1(

())1((

))1(

())1((

kTEE

itAtApp

kTEE

itAtAnnttA

kTEE

itDtDnn

kTEE

itDtDppttD

tiit

itti

enF

pFvenFFnvdt

dN

enF

nFvenFFpvdt

dN

pptrapp

nntrapn

11

Electron capture

Electronemmision

Holecapture

Holeemmision

holecapture

holeemmision

electroncapture

electronemmision

Device Simulation

• While computing power is limited, focus was put on 2D simulation of pixel geometries– Valid for « decoupled » region of a pixel

• Rise time of the pulse • Charge sharing

– Not valid for corners region, fondamentally 3D quantities• Leakage current• 3-4 pixel charge sharing

2D simulation assume a z dimension of 1um to conserve dimension in the drift-diffusion equation

Device Simulation

• DC Simulation :– Three thicknesses studied : 50,100,150 um– Three doped region width studied : 35,40,45 um– 4 bias voltages : -2.5V, -5V ,-7.5V, -10V

• Transient simulation :– M.I.P trajectory normal to surface– impact a 0, 1 ,2 ,3, 5 um from middle point

between pixels

Device Simulation: Potential distribution

-2.5V -5V

-7.5V -10V

P-spray insulation

-2.5V -5V

-7.5V -10V

Charge collection

• See Animation

Pulse Shape and Rise time

50 um thick sensors, 55um pitch , 45um electrodes

Pulse Shape and Rise time

50,100,150 um thick sensors, 55um pitch , 45um electrodes

Pulse Shape and Rise time

50,100,150 um thick sensors, 55um pitch , 45um electrodes

Pulse Shape and Rise time

50 um thick sensors, 55um pitch , 45um electrodes

Charge Sharing

50um thick sensors, 55um pitch , 45um electrodesΔX is the distance front middle point between pixels

Charge Sharing

50um thick sensors, 55um pitch , 40um electrodesΔX is the distance front middle point between pixels

Conclusion

• TCAD Simulation software deployed at CERN– 20 license on the way to perform massive parameter scan

and analysis– Possibility right now to perform complex 2D Simulation– Preliminary results show rise time not an issue for timing,

timing in pixel cluster might be an issue• To-Do

– Extend simulation to 3D – Input Eta functions in digitizer to compare with actual results – More studies possible (biasing through vias ?, Heat, stress

effects ?)