Power Device Modeling with TCAD

Power Device Modeling with TCAD

Introduction

Features Essential for Power Device Simulation Device Structure Formation Device Simulation Case Studies

TCAD Power Device Modeling

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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


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Interoperability


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Device Structure Formation

Overview

Structures Tools Meshing Processing Editing


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Device Structure Formation: Tools

ATHENA: ATLAS: DevEdit:


1D, 2D rectangular initial grid, process simulation 1D, 2D, 3D rectangular grid analytical and measured profiles 2D, 3D arbitrary grid GUI and command-line mode advanced structure edit capabilities advanced mesh capabilities

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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


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DevEdit: mesh automatically created on boundary conditions, such as mesh constraints no obtuse triangles refinement on quantities manual interactive refine/unrefine


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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: Note: 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


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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 ATHENA models: Models Implantation Dual Pearson Monte Carlo Diffusion Fermi two.dim Full.cpl power

Assumption

Application

empirical statistical

angled implant with reflec.

Defects in equilibrium Transient defect diffusion defect and impurity binding constant diffusivity depending on temp

Oxidation compress viscous elastic


OED TED co-diffusion clustering for large structures

thick nitride birds-beak

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Device Structure Formation: Process Simulation in 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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Device Structure Formation: Process Simulation in ATHENA


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Device Structure Formation: Process Simulation in 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 =


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Device Structure Formation: Process Simulation in 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 3D


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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


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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)


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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:

R Vapp L

ATLAS Device


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C


Electrical Contacts Slave: allow one electrode to be biased as a function of another electrode for voltage boundary conditions only

Note: 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 TCAD Power Device Modeling

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Thermal Contacts Topology: identical with electrical contacts boxes regions Properties (THERMCONTACT Statement): external temperature thermal resistance


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Device Simulation: Numerics

Algorithms (DC and Transient Analysis) Gummel Newton Block 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

=

max

K +1 K C C m m max

C

C = n, p m = node identifier K= iteration number C0 = CLIM.DD = CLIMIT * (NC * NV)1/4


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0

,C

K m


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 STEP.INIT MINCUR

is the name of the electrode to be ramped initial voltage step 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 NEXTST.RATIO

END.VAL is a current 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


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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


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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


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Structure Creation

ATLAS/ Device3D performs 3D device simulations on a prismatic mesh 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.


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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


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Structure Creation

3D process simulation. TCAD Power Device Modeling

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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


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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.


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Editing the ATHENA Result in DevEdit3D.


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3D MOSFET prepared for Device Simulation.


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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

Vertical MOSFET in Device3D.


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Novel Structures


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Insulated Gate Bipolar Transistor



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Vertical Double-Diffused MOS Transistor



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Gate Controlled Thyristor



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Power Device Modeling with TCAD

Power Device Modeling with TCAD

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