UniMAP – PSDC INSEP Training Program 2007 by Syarifah Norfaezah Sabki School of Microelectronic Engineering
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering UniMAP – PSDC INSEP Training Program 2007
by Syarifah Norfaezah Sabki
School of Microelectronic Engineering
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• 2D cross-section of wafer– X-coordinate: parallel to the wafer surface– Y-coordinate: depth into the wafer
• Grid structure:– The continous physical process are modeled
numerically by using finite difference (for diffusion) and finite element (for oxide flow) solution techniques.
– Each region is divided into a mesh of non-overlapping triangular elements
– Solution values are calculated at the mesh nodes (at the corners of the triangular elements), value between the nodes are interpolated
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• MEDICI solves Poisson’s equation & the current continuity of electrons and holes in two dimensions
• These equations can be extended to include the heat equation and the energy balance equations
• The following modes of analysis can be considered: DC simulation, AC simulation & transient simulation
• A wide range of mobility & recombination/generation models available
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• Advanced Application Modules are available– Lattice temperature AAM – solves the heat equation– Optical device AAM – enhanced radiation effects, ray
tracing– Heterojunction device AAM – conduction across a
material boundary with discontinuous energy– Programmable device AAM – allows a charge
boundary condition on a floating electrode– Circuit analysis AAM – allows devices to be treated as
circuit elements in a SPICE type circuit– Anisotropic device AAM – allows anisotropic material
parameters useful in the treatment of SiC type applications
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE
GENERATING DEVICE STRUCTURE IN MEDICI/DAVINCI
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE DEFINITION
SEQUENCE OF STATEMENTS: MESH statement X.MESH statements Y.MESH statements Z.MESH statements (Davinci only) ELIMINATE statements (optional) TSUPREM4 statements (optional) REGION statements ELECTRODE statementsPROFILE statements
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
STRUCTURE INFORMATION
MESH
Initiates a mesh and must appear first when defining a structure. Can be used to import an existing mesh and invoke the Automatic Conforming Boundary (ABC) mesher
X.MESH
Y.MESH
ELIMINATE
Used to specify exact locations of mesh lines. X.MESH & Y.MESH produce a rectangular grid which can be reduced in density by using ELIMINATE to remove excess nodes away from area of interest
TSUPREM4Used to transfer surface features and doping profiles from TSUPREM4 onto existing MEDICI mesh
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
STRUCTURE INFORMATION
REGIONUsed to define regional properties
where no material data already exists
ELECTRODE Adds location of electrodes to structure
RENAME Rename electrodes or regions
PROFILEAllows addition of doping information either by creating simple profiles or inputting from a process simulator
REGRIDAllows regridding of mesh based on
some internal quantities
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: MESH
• The MESH statement initiates the mesh generation or reads a previously generated mesh
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
[extracted from user guide]
MESH
Initial Mesh Generation{ ( [ { RECTANGULAR | CYLINDRI } ] [DIAG.FLI])
Mesh File Input| (IN.FILE=<c> [QT.FILES=<c>] [PROFILE][ { ASCII.IN | (TSUPREM4 [ ELECT.BOT [Y.TOLER=<n>] [POLY.ELE][X.MIN=<n>] [X.MAX=<n>] [Y.MIN=<n>] [Y.MAX=<n> [FLIP.Y] [SCALE.Y=<n>])| (TIF [ELECT.BOT [Y.TOLER=<n>] [POLY.ELE] ] )}
DEVICE STRUCTURE: MESH
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: MESH
PARAMETER TYPE DEFINITION DEFAULT
RECTANGU logical
Specifies that the simulation mesh uses rectangular coordinates True
CYLINDRI logical
Specifies that the simulation mesh uses cylindrical coordinates. If this parameter is specified, the horizontal axis represents the radial direction and the vertical axis represents the z-direction
False
DIAG.FLI logical
Specifies that the direction of diagonals is changed about the horizontal center of the grid. If this parameter is false, all diagonals are in the same direction
False
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• The X.MESH specifies the placement of nodes in the x direction• Description:
If an initial mesh is being generated, X.MESH and Y.MESH statements should immediately follow the MESH statement
DEVICE STRUCTURE: X.MESH
X.MESH
{LOCATION=<n> | ({ WIDTH=<n> | X.MAX=<n> }
[X.MIN=<n>] )}
[ {NODE=<n> | N.SPACES=<n>} ]
[SPACING=<n> | H2=<n>} ] [H3=<n>] [RATIO=<n>]
[MIN.SPAC=<n>] [ SUMMARY ]
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: Y.MESH
The following Y.MESH statement specifies the placement of nodes in the y direction
Y.MESH
{LOCATION=<n> | ({DEPTH=<n> | Y.MAX=<n>} [Y.MIN=<n>] ) }
[ {NODE=<n> | N.SPACES=<n>} ]
[ {SPACING=<n> | [MIN.SPAC=<n>]
[SUMMARY]
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: REGION
The region statement defines the location of materials in a rectangular mesh
REGION
NAME=<c>
Semiconductor Materials
{ ( { SILICON | GAAS | POLYSILI | GERMANIU | SIC | SEMICOND | SIGE | ALGAAS | A-SILICO | DIAMOND | HGCDTE | INAS | INGAAS | INP | S.OXIDE | ZNSE | ZNTE | ALINAS | GAASP | INGAP | INASP }
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: REGION
Semiconductor material Parameters
[X.MOLE=<n>] [X.END=<n> | X.SLOPE=<n>} {X.LINEAR | Y.LINEAR} ]
)
Insulator Materials
| OXIDE | NITRIDE | SAPPHIRE | OXYNITRI | HFO2 | INSULATO
}
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: REGION
Location{ ( [ {X.MIN=<n> | IX.MIN=<n>} ] [ {X.MAX=<n> | IX.MAX=<n>} ] [ {Y.MIN=<n> | IY.MIN=<n>} [{Y.MAX=<n> | IY.MAX=<n> }] [ { (ROTATE R.INNER=<n> R.OUTER=<n> X.CENTER=<n> Y.CENTER=<n>)
|POLYGON X.POLY=<a> Y.POLY=<a>) } ] ) | (X=<n> Y=<n>)
|CONVERT
}
[VOID]
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: ELECTRODE
The ELECTRODE statement specifies the placement of electrodes in a device structure
ELECTRODE
NAME=<c> [VOID]
{ ( [ {TOP | BOTTOM | LEFT | RIGHT | INTERFAC | PERIMETE} ] [ { X.MIN=<n>} ] [X.MAX=<n> | IX.MAX=<n>} ] [ { Y.MIN=<n> | IY.MIN=<n>}] [ {Y.MAX=<n> | IY.MAX=<n>} ] [ { ( ROTATE X.CENTER=<n> Y.CENTER=<n> R.INNER=<n> R.OUTER=<n>) | (POLYGON X.POLY=<a> Y.POLY=<a>) } ] )
| [X=<n> Y=<n>]
| [REGION=<c>] }
[MAJORITY]
Lattice Temperature AAM Parameters
[THERMAL]
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE: PROFILEThe PROFILE statement defines profiles for impurities and other quantities to be used in the device structure
PROFILE
[REGION=<c>]
[X.MIN=<n>] [ {WIDTH=<n> | X.MAX=<n>} ]
[Y.MIN=<n>] [ {DEPTH=<n> | Y.MAX=<n>} ]
Output Doping File
[OUT.FILE=<c>]
Uniform Profiles
{ (UNIFORM {N-TYPE | P-TYPE | IMPURITY=<c> | OTHER=<c>}
N.PEAK=<n>)
Analytic Profiles
| ( {N-TYPE | P-TYPE IMPURITY=<c> | OTHER=<c>} {N.PEAK=<n> |
DOSE=<n>} { (Y.CHAR=<n> [Y.ERFC] ) | Y.JUNCTI=<n>} {X.CHAR=<n> |
XY.RATIO=<n>} [X.ERFC]
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
EXAMPLE: CREATING 1D SiGe HBT
$ Structure Generation of 1D SiGe Bipolar
Mesh
X.mesh width=0.5 spaces=1
Y.mesh width=0.1 H2=0.005 Ratio=1.2
Y.mesh width=0.1 H2=0.005
Y.mesh width=0.6 H2=0.005 H2=0.050
Region silicon
Region SiGe Y.min=0.100 y.max=0.125 x.mole=0 x.end=0.2 Y.linear
Region SiGe Y.min=0.125 y.max=0.200 x.mole=0.2
Region SiGe Y.min=0.200 y.max=0.230 x.mole=0.2 x.end=0.0
Electr Name=Emitter Top
Electr Name=base Y.min=0.125 Y.max=0.125 Majority
Electr Name=collector bottom
Profile N-type N.peak=2e16 Uniform
Profile N-type N.peak=5e19 Y.min=0.80 y.char=0.125
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
EXAMPLE: RESULTS
Basic SiGe Mesh
Corresponding doping profile
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
DEVICE STRUCTURE
IMPORTING DEVICE STRUCTURE FROM MEDICI/TSUPREM4
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
MESH STATEMENTS
• IN.FILE – name of input file which contains structure.• Tsuprem4 – logical parameter signaling that IN.FILE was created
by TSUPREM4• TIF – logical parameter signaling that IN.FILE is in universal (TIF)
format • ELECT.BOT – logical flag signaling that the structure bottom
(substrate) electrode is supposed to be appended to the structure• POLY.ELEC – logical parameter signaling that all polysilicon
regions in the imported structure are to be converted to electrode
NOTE: Once Poly Region is converted to Electrode, its doping information is lost and intrinsic work function of 4.6eV is assign to it
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• From TSUPREM4 MESH in.file=s4filename tsuprem4 elec.bot poly.elec
y.max=3RENAME electr oldname=1 newname=sourceRENAME electr oldname=2 newname=drainSAVE mesh out.file=mdfile
• From previous MEDICI execution
MESH in.file=mdfile
EXAMPLE: IMPORTING STRUCTURE FILE
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• Default structure depth in TSUPREM4 is 200m. Use Y.MAX or alternatively TRUNCATE the device within TSUPREM4 first
• X.SPLIT, WIDTH and N.SPACES allow the structure to be expanded at point x.split by an amount width and subdivided into n.spaces. A typical use of this would be to model various channel lengths without repeating the process simulation
MESH ADJUSTMENT
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• REGRID statement• Regrid doping log ratio=2 in.file=test.dop
smooth=1
Which test for the log of the doping being greater than 2 between mesh points. It uses a doping file stored from the original PROFILE statement so that information on doping is not lost through successive refinements. A number of different techniques from smooth=-1 to 2 can be selected (-1 is usually the best)
• Regrid potential ratio=1.1• Regrid min.carr ratio=2 log smooth=-1
MESH ADJUSTMENT
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
REGRID
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• Increasing mesh density results in increasing accuracy of potential and carrier concentrations
• Care must be taken in aligning the mesh to the current flow
• High density mesh needs computing space and time
MESH ISSUES
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
CHOICE OF MODELS : RECOMBINATION & GENERATION
MODEL DESCRIPTION
SRH Shockley – Read – Hall recombination
CONSRH SRH + concentration dependent lifetime
Note: lattice temp dependence can also be modeled by specifying non-zero values of EXN.TAU and EXP.TAU on the MATERIAL statement (Lattice temp AAM only)
AUGER Auger recombination
R.TUNNEL SRH including tunneling in presence of strong electric fields
IMPACT.I Classic Chynoweth expression
II.TEMP Invokes a temperature based version of the impact ionization model for use with the energy balance model
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
CHOICE OF MODELS : MOBILITY
MODEL LOW FIELD
TRANSVERSE FIELD
PARALLEL FIELD
COMMENTS
CCSMOB Carrier-carrier scattering
CONMOB Concentration dependence from tables 300K
ANALYTIC Analytic alternative to CONMOB with temp. dependence
PHUMOB Carrier-carrier scattering, different donor and acceptor scattering, screening, useful for bipolars
LSMMOB Treats surface scattering and bulk effects
GMCMOB Modified LSMMOB to include impurity scattering
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
CHOICE OF MODELS : MOBILITY
MODEL LOW FIELD
TRANSVERSE FIELD
PARALLEL FIELD
COMMENTS
SRFMOB Basic and enhanced model for surface scattering. Requires vertical grid spacing > inversion layer
SRFMOB2
UNIMOB Needs rectangular grid in inversion layer – models surface scattering
PRPMOB General model for degradation of mobility with transverse electric field – applies all over –not just at surface
TFLDMOB Univ. Texas mobility model
FLDMOB Carrier heating and velocity saturation effects
HPMOB Accounts for both parallel and perpendicular field dependence
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
CHOICE OF MODELS : ENERGY GAP & CARRIER DENSITY
MODEL0 DESCRIPTION
FERMIDIRFermi Dirac statistics instead of Boltzman. Recommended to be used in conjunction with:
INCOMPLE Incomplete ionization of impurities
BGNBandgap narrowing modelling – especially important for bipolars
QM.PHILI
Accounts for quantum mechanical effects in MOSFET inversion layers using Van Dort’s bandgap widening model. Implemented as a shift in the energy gap just as in BGN modeling
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
CHOICE OF MODELS : ENERGY BALANCE
MODEL DESCRIPTION
ET.MODELUses the energy transport model where the spatial derivative of the mobility is included in the diffusion term of the current equation
COMP.ETInvokes an energy balance eq. suitable for compound material such as GaAs
TMPMOBA carrier temperature based mobility – alternative to FLDMOB
EF.TMPSolves effective electric fields exactly in Si instead of approx for use in TMPMOB
TMPTAUWInvokes an electron temperature model for the electron energy relaxation
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
CHOICE OF MODELS : ENERGY BALANCE
MODEL DESCRIPTION
II.TEMPUses the energy transport model where the spatial derivative of the mobility is included in the diffusion term of the current equation
EFI.TMPInvokes an energy balance eq. suitable for compound material such as GaAs
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
MODEL DECISION: MOS
• Use mobility model specifically calibrated on MOSFETS as surface scattering effects are a dominant feature such as CONMOB LSMMOB FLDMOB
• For <0.2m technologies, one of the newer models i.e UNIMOB, GMCMOM or TFLDMOB should be considered i.e TFLDMOB (for NMOS)
• When modeling breakdown CONSRH, IMPACT.I are important
• AUGER and BGN which has a small effect on the source/drain resistance can be included but both of these will not significantly impact the results
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
• Carrier-carrier scattering is a more important mechanism for bipolars and PHUMOB would be a good choice. Bandgap narrowing and the recombination mechanisms are also important so a full set would be:
CONMOB PHUMOB AUGER CONSRH BGN IMPACT.I
• Change the lifetimes and bandgap coefficients on the material statement:
material silicon
v0bgn=n0.bgn=con.bgn=taun=taup=
• For a general device, then an all purpose choice would be:
CONMOB FLDMOB PRPMOB CONSRH AUGER BGN IMPACT
MODEL DECISION: BIPOLAR
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
SOLUTION TECHNIQUESTATEMENTS
STATEMENTS DESCRIPTION
SYMBOLICSelects with equations to solve as well as the method of the solution either coupled (Newton) or de-coupled (Gummel)
METHODControl the iteration process – number of iterations use of numerical damping, selection of linear solver
LOGTo open the file which will contain terminal values calculated during the solution process
SOLVE Starts the solution process either DC, AC or transient
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
SOLUTION TECHNIQUE: SYMBOLIC
• Solve only Poisson’s equationsymbolic carr=0
• Solve Poisson’s equation and electron-current continuity equation using Gummel’s method
symbolic carr=1 electron gummel• Solve Poisson’s equation and electron-current
continuity equation using coupled methodsymbolic carr=1 electron newton
• Solve Poisson’s equation and both hole and electron Drift-Diffusion (DD) equations
symbolic carr=2 newton
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
SOLUTION TECHNIQUE: METHOD & LOG
• Method – contains more than fifty parameters, only a few are normally used
• Itlimit, which controls the number of iterations which are tried before the bias is cut back by the program
method itlimit=100• Log
log outfile=drain.ivl (filename)
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
SOLUTION TECHNIQUE: SOLVE
• There are two fundamental rules when using the solve statement:– At the beginning of the simulation, all electrode potentials are set to
0V– Terminal values stay unchanged until they are addressed by the
next solve statement. In other words, terminal values are not implicity reset to their initial values in subsequent solve statements
• When the program solves for a new bias condition, it must rely on an initial guess. There are three types (initial, previous, project) which are automatically selected by the program
• Rules for succesful solution strategy:– Specify all models (with the possible exception of impact.i before
the first solve statement– Build-up solution gradually
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
SOLUTION TECHNIQUE: SOLVE
• DC ANALYSIS• Apply 1V gate electrode
solve v(gate)=1• Ramp voltage of gate electrode at 1V interval for 5 times
solve elec=gate vstep=1 nstep=5• Ramp current of base while applying 5V at collector
solve elec=base istep=1e-6 nstep=10
v(collector)=5
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
SOLUTION TECHNIQUE: SOLVE
• TRANSIENT ANALYSIS
solve v(base)=1 tstep=1e-13 tstop=1e9
• To define a pulse we need two solve statements:Solve v(base)=1 tstep=1e-13 tstop=1e-9
Solve v(base)=0 tstep=1e-13 tstop=5e-9
V
tstop tstop t
UniMAP – PSDC INSEP Training Program 2007
School of Microelectronic Engineering
SOLUTION TECHNIQUE:CONVERGENCE ISSUE
• The primary causes of non-convergence are:– Poor initial guess – bias step too large (for some structures even
0.1V can be too large)– Lack of necessary physical models– Poor simulation grid– Depletion layer touching the electrode
V-error
px.tol
itlimit #of iterations
Iter V-error
1 3.4567e+4
2 2.7543e+02
3 1.6734e+00
4 1.0000e+00
5 1.0000e+00
… 1.0000e+00
20 1.0000e+00