Power Device Modeling with TCAD - Silvaco · PDF fileTCAD Power Device Modeling ... GUI and...

Power Device Modeling with TCAD

TCAD Power Device Modeling

Introduction

Features Essential for Power Device Simulation

Device Structure Formation

Device Simulation

Case Studies

Key Features for Power Device Simulation

Non-Isothermal (Self Heating)

MixedMode (Physical Devices Embedded in Lumped Circuits)

Curve Tracer (for Modeling Instabilities such as Snapback)

Advanced Trap Modeling

Ionization Integrals

Advanced Numerics (methods/climit/dvmax)

Advanced Materials

Interoperability

Device Structure Formation

Overview

Structures

Meshing

Processing

Editing

Device Structure Formation: Tools

ATHENA: 1D, 2D rectangular initial grid, process

simulation

ATLAS: 1D, 2D, 3D rectangular grid analytical and

measured profiles

DevEdit: 2D, 3D arbitrary grid

GUI and command-line mode

advanced structure edit capabilities

advanced mesh capabilities

Device Structure Definition: Meshing

ATLAS, ATHENA:

direct specification of mesh coordinates

mesh relax

adaptive meshing for process (risk of obtuse triangles!)

appropriate for simple meshes:

very quick

unflexible

not interactive

rectangular

DevEdit:

mesh automatically created on boundary conditions, such as mesh

constraints

no obtuse triangles

refinement on quantities

manual interactive refine/unrefine

DevEdit Strategy:

set base mesh height / width bigger than device dimension (historical

feature)

locate "critical" areas, add more regions if necessary

set general max.height/width/angle by material

set tighter max constraints per region

for user defined areas (command line mode)

specify refinement quantities (net doping), tune min. spacing

manually refine/unrefine

refine on solution quantities

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DevEdit Strategy:

doping regions not hit by mesh lines will not be refined correctly

Solution:

change mesh constraints

add regions in this area with appropriate mesh-constraints

Caution:

Pay special attention to surface phenomena (MOS, surface charge), define

a surface layer with finer constraints 3), or refine manually

- 11 -

Quality Criteria

no obtuse triangles in semiconductor region

fine grid where required

coarse grid where nothing is happening

not too many lines meeting in one node

smooth grid

smooth solution

smooth terminal characteristics

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Device Structure Formation: Process Simulation in

ATHENA

- 13 -

ATHENA models:

Models Assumption Application

Implantation

Dual Pearson empirical

Monte Carlo statistical angled implant with reflec.

Diffusion

Fermi Defects in equilibrium

two.dim Transient defect diffusion OED TED

Full.cpl defect and impurity binding co-diffusion clustering

power constant diffusivity for large structures

depending on temp

Oxidation

compress thick nitride birds-beak

viscous elastic

ATHENA

Example: Calibration of diffusion properties 1

select the appropriate statements from the models file:

ATHENA -models | grep aluminum > aluminum.mod

define your calibration target with EXTRACT

use the Optimizer for calibration

Tip: Introduce new dopant by redefining an unused existing one

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ATHENA

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ATHENA

Example: Double sided simultaneous doping 2

define dopant source material(s)

deposit topside material

flip the structure

deposit bottom material

Tip: to expose bottom surface, etch away infinite surface layer:

ETCH BELOW P1.Y = <NEW BOTTOM SURFACE POSITION>

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ATHENA

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Device Structure Definition: Editing (Structure

Modification)

ATHENA:

oxidation, deposition, etch (physical, arbitrary polygon)

stretch, mirror, flip, cut (not interactive)

ATLAS:

scale: width, cylindrical

DevEdit:

deposit

stretch/squeeze, join, cut, move, flip, mirror, etch

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Device Structure Definition: Editing

Example: Parametrized shape 3

run DevEdit in command-line mode within DeckBuild

use DeckBuild's SET feature to define parameter values

set a=230

use DeckBuild's SET feature to calculate dependent variables

(coordinates)

set right=$a+250

use variables for substitution

impurity id=2 imp=Boron color=0x8c5d00 \

x1=0 x2=$right y1=0 y2=0 \

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Device Simulation

Device Simulation: Overview

Device Simulation

Physics

Boundary Conditions

Numerics

Mixed mode

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Device Simulation: Physics

Multiple equation solver: Fully coupled solutions for

Poisson equation

carrier continuity equation

carrier temperature equation

lattice heat flow equation (G.K. Wachutka, IEEE Trans CAD, 9,

pp1141-1149, 1990)

Joule heat

recombination/ generation heating/cooling

Peltier/Thomson

- 24 -

Device Simulation: Lifetime Tailoring

Recombination Models

Shockley-Read-Hall, fixed lifetime (SRH) or concentration

dependent (CONSRH)

single trap level (default: midgap)

low concentration lifetime defined per region, per material

(MATERIAL: TAUN0, TAUP0)

local temperature dependent model (MATERIAL: LT.TAUN, LT.TAUP)

C-Interpreter(x,y)

store recombination rate in solution: OUTPUT U.SRH

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Device Simulation: Lifetime Tailoring

Recombination Models

additional traps can be superimposed

(TRAP or DOPING Statement)

arbitrary spatial distribution

discrete acceptor or donor-like traps

recombination parameters: cross-section or lifetime

full trap dynamics or stationary approach (FAST)

optical (OPTR)

Auger (AUGER)

Interface (INTERFACE statement)

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Models

Mobility

Doping concentration (d)

Temperature (T)

Lateral electric field (l)

Transverse electric field (f)

Carrier Carrier scattering (c)

surface mobility (s)

C-Interpreter (d,T,f,composition)

MOS regions:

CVT (l, f, d, T,s)

Bipolar:

KLAASSEN (T, d, c) FLDMOB(f)

- 27 -

Models

Bandgap Narrowing

Slootboom model (BGN)

C-Interpreter

Impact Ionization (IMPACT statement)

Selberherr model (SELBER)

Grant model ()

Crowell & Sze model (CROWELL)

Light interaction (Luminous)

visible light: absorption, refraction, ray-tracing

C-Interpreter: arbitrary distributed generation (cosmic rays)

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Example: Transient IGBT Latchup

VCE ramped to 300V with drift diffusion

save solution

turn on heat flow equation:

MODELS ANALYTIC SRH AUGER FLDMOB SURFMOB LAT.TEMP

IMPACT SELBER

fully coupled solution

METHOD NEWTON

load VCE-solution

transient gate-ramp to 10V

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Example: Light triggered thyristor 12

cylindrical structure with amplifying gate

ramped anode to 1000V

illumination of the gate area

transient turn on

extraction of turn-on delay time

Note: Light can be used as a general tool to get thyristors latched

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Example: Proton irradiated diode 10

define a homogenous SRH-lifetime representing

electron irradiation

define a region where the proton induced traps are located

perform a reverse recovery simulation

extract (Von, Qrr, Irr)

perform an experiment with SRH-lifetime, proton

irradiation depth and dose as variables

create a RSM for Von, Qrr, Irr

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Example: Turn-off of Inhomogenous GTO 5

four finger structure created to represent a 15 cm2 device

structure devided in single cathode and gate regions

set different lifetimes in cathode regions to simulate an overall +- 10%

lifetime inhomogenity

turn on device (1000 A)

transient turn off (gate drive: with 100A/ s)

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Device Simulation: Boundary Conditions

Electrical Contacts

Topology:

define electrodes in ATHENA / DevEdit / ATLAS

Properties (CONTACT Statement):

workfunction

boundary conditions:

current, voltage, floating

options:

dipole barrier lowering, surface recombination

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Electrical Contacts

Lumpled elements:

- 43 -

ATLAS Device

Electrical Contacts

Slave:

allow one electrode to be biased as a function of another electrode

for voltage boundary conditions only

avoid to cover junctions

boundary conditions can be changed during run

don't change lumped elements

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Example: Mixed pn-Schottky diode 7

split the anode electrode in Schottky and ohmic part

start off with voltage ramping

change to current boundary condition

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Example: I-V curve of a coarse gridded diode15

Thermal Contacts

Topology:

identical with electrical contacts

regions

Properties (THERMCONTACT Statement):

external temperature

thermal resistance

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Device Simulation: Numerics

Algorithms (DC and Transient Analysis)

Gummel

Newton

Block iteration scheme:

Coupled Newton Solution of Poisson and Continuity equations

Decoupled solution of lattice heat flow equations

low power dissipation domain: BLOCK NEWTON

high power dissipation (current surges, breakdown): NEWTON

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Error Measures

relative error for carrier concentrations:

C = n, p

m = node identifier

K= iteration number

C0 = CLIM.DD = CLIMIT * (NC * NV)1/4

Error Measures

Default value for CLIM.DD = 4.5e13 cm-3 (CLIMIT=1000)

OK in forward state

breakdown: 1e8 (300 K)

high injection condition 1e15

monitor terminal current balancing

Newton Parameters

DVMAX sets maximum allowed potential updates per Newton

iteration

default is 1

recommended for power applications: > 100000

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Curvetracer

Trace out complex IV curves (Latch-up, breakdown, snapback)

Dynamic Load Line Approach (Goosens et al., IEEE Trans CAD

1994, 13, pp. 310-317)

Parameters: CONTR.NAME is the name of the electrode to be ramped

STEP.INIT initial voltage step

MINCUR current level above the dynamic load line

algorithm will be used

END.VAL stop tracing if level is reached

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Curvetracer

Parameters:

CURR.CONT END.VAL is a current

NEXTST.RATIO multiplier for STEP.INIT in "linear" domains

Example: IGBT breakdown 11)

refined grid from 4)

curvetracer:

curvetrace curr_cont end.val=1e-2 contr.name=collector step.init=1 nextst.ratio=1.2

solve curvetrace

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Example: Thyristor forward breakover 13

ramping over breakover point with curvetracer

extraction of max. bias

ramping again to max. bias

extraction of herlett-zone width

VWF experiment with n-base doping as variable

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Device Simulation: MixedMode

How it works

numerical devices are embedded in a spice circuit (up to 100

nodes, 300 elements, 10 numerical devices)

all numerical devices are solved in a single matrix together with

the spice models

numerical devices are scaled by a width parameter or defined as cylindrical

standalone solutions can be loaded

- 57 -

Input structure

circuit:

spice net list

initial node setting

numerics and options

arbitrary number of dc statements to sweep sources

single transient statement

models and parameters for the numerical devices

- 58 -

Numerics

Full Newton (OPTIONS: FULLN, default): Fast with good

initial guess

Modified two-level Newton (.OPTIONS: M2LN): bad initial g.

Convergence Criteria

numerical devices (.OPTIONS):

RELPOT: relative potential criteria (large voltages)

circuit (.NUMERIC):

TOLDC, TOLTR: relative accuracy for node voltages

VMAX, VMIN: max/min value for node voltages

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Example: Turn-off of Inhomogenous GTO 5

simulate on-state standalone

extract terminal characteristics:

extract name="V_gate" y.val from curve(vint."anode",vint."gate") where x.val = $Von

calculate initial settings:

.nodeset v(1)=2000 v(2)=$"Von" v(3)=$"V_gate" v(4)=$"V_gate" v(5)=-25 v(6)=-15 v(7)=$"v7"

load the standalone solution

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Specialized Models

In General Device3D has the same set of physical models

as S-Pisces

Most parameters of the MODELS, CONTACT, MATERIAL

and INTERFACE statements are supported.

Examples of Supported Models:

CVT, FLDMOB

CONSRH, AUGER, Traps

IMPACT SELB, HEI

FERMI, BGN

Models for GaAs MESFETs are supported

- 62 -

Structure Creation

ATLAS/ Device3D performs 3D device simulations on a prismatic

In XY the mesh is triangular. In XZ and YZ it is rectangular.

This limits the arbitrary nature of 3D structures that can

be handled

The most complex geometry should be in the XY plane

(e.g.. field oxide bird’s beak)

The mesh in the Z direction consists of a set of planes repeating the XY mesh.

Regions can start and end in the Z-direction.

- 63 -

Structure Creation

Structure and Mesh formation for 3D simulation is very

important. Several Options exist for Device3D

1/ Structure definition using ATLAS syntax

limited to rectangular regions in XY

uses analytic functions for doping

syntax is simple extensions of the 2D syntax

2/ Structure definition using DevEdit3D

can draw materials and regions in DevEdit3D

interactive meshing

3/ ATHENA-DevEdit-Device3D interface

4/ 3D Process Simulation

- 64 -

Structure Creation

- 65 -

3D process simulation.

ATHENA-DevEdit-Device3D Interface

Step-by-step guide to getting 2D process simulation results

into 3D device simulator

1/ Do process simulation in 2D. This will be XY plane in 3D.

2/ Import structure into DevEdit3D

3/ Edit structure using REGION/MODIFY or REGION/ADD

restrict regions in Z direction

add new regions

4/ Add additional doping profiles using IMPURITY/ADD

- 66 -

5/ Setup Meshing Rules and create XY Grid

6/ Use Z_PLANE menu to define Z mesh

7/ Save 3D structure and view in Tonyplot3D

8/ Save Command File for future use

9/ Load 3D structure into Device3D using MESH statement

10/ Automate the interface by editing a single

ATHENA-DevEdit-Device3D input file

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ATHENA Process simulation across a MOS channel width.

- 69 -

Editing the ATHENA Result in DevEdit3D.

- 70 -

3D MOSFET prepared for Device Simulation.

Novel Structures

Some novel structures require the mixing of circular, cylindrical

and rectangular structures. (IEDM 95 p657)

In these devices the XZ plane contains non-rectangular structures

DevEdit3D should be used to define the XZ plane.

Y direction is treated as planes of XZ mesh

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Novel Structures

- 72 -

Vertical MOSFET in Device3D.

Novel Structures

- 73 -

Insulated Gate Bipolar Transistor

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Vertical Double-Diffused MOS Transistor

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Gate Controlled Thyristor

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