1. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering UniMAP – PSDC INSEP Training Program 2007 by Syarifah Norfaezah Sabki School of Microelectronic Engineering

2. 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

3. 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

4. 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

5. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering DEVICE STRUCTURE GENERATING DEVICE STRUCTURE IN MEDICI/DAVINCI

6. 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 statements  PROFILE statements

7. 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 TSUPREM4 Used to transfer surface features and doping profiles from TSUPREM4 onto existing MEDICI mesh

8. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering STRUCTURE INFORMATION REGION Used to define regional properties where no material data already exists ELECTRODE Adds location of electrodes to structure RENAME Rename electrodes or regions PROFILE Allows addition of doping information either by creating simple profiles or inputting from a process simulator REGRID Allows regridding of mesh based on some internal quantities

9. 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

10. 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= [QT.FILES= ] [PROFILE] [ { ASCII.IN | (TSUPREM4 [ ELECT.BOT [Y.TOLER= ] [POLY.ELE] [X.MIN= ] [X.MAX= ] [Y.MIN= ] [Y.MAX= [FLIP.Y] [SCALE.Y= ] ) | (TIF [ELECT.BOT [Y.TOLER= ] [POLY.ELE] ] ) } DEVICE STRUCTURE: MESH

11. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering DEVICE STRUCTURE: MESH PARAMETERTYPEDEFINITIONDEFAULT RECTANGUlogical Specifies that the simulation mesh uses rectangular coordinates True CYLINDRIlogical 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.FLIlogical 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

12. 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= | ({ WIDTH= | X.MAX= } [X.MIN= ] )} [ {NODE= | N.SPACES= } ] [SPACING= | H2= } ] [H3= ] [RATIO= ] [MIN.SPAC= ] [ SUMMARY ]

13. 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= | ({DEPTH= | Y.MAX= } [Y.MIN= ] ) } [ {NODE= | N.SPACES= } ] [ {SPACING= | [MIN.SPAC= ] [SUMMARY]

14. 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= 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 }

15. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering DEVICE STRUCTURE: REGION Semiconductor material Parameters [X.MOLE= ] [X.END= | X.SLOPE= } {X.LINEAR | Y.LINEAR} ] ) Insulator Materials | OXIDE | NITRIDE | SAPPHIRE | OXYNITRI | HFO2 | INSULATO }

16. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering DEVICE STRUCTURE: REGION Location{ ( [ {X.MIN= | IX.MIN= } ] [ {X.MAX= | IX.MAX= } ] [ {Y.MIN= | IY.MIN= } [{Y.MAX= | IY.MAX= }] [ { (ROTATE R.INNER= R.OUTER= X.CENTER= Y.CENTER= ) |POLYGON X.POLY= Y.POLY= ) } ] ) | (X= Y= ) |CONVERT } [VOID]

17. 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= [VOID] { ( [ {TOP | BOTTOM | LEFT | RIGHT | INTERFAC | PERIMETE} ] [ { X.MIN= } ] [X.MAX= | IX.MAX= } ] [ { Y.MIN= | IY.MIN= }] [ {Y.MAX= | IY.MAX= } ] [ { ( ROTATE X.CENTER= Y.CENTER= R.INNER= R.OUTER= ) | (POLYGON X.POLY= Y.POLY= ) } ] ) | [X= Y= ] | [REGION= ] } [MAJORITY] Lattice Temperature AAM Parameters [THERMAL]

18. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering DEVICE STRUCTURE: PROFILE The PROFILE statement defines profiles for impurities and other quantities to be used in the device structure PROFILE [REGION= ] [X.MIN= ] [ {WIDTH= | X.MAX= } ] [Y.MIN= ] [ {DEPTH= | Y.MAX= } ] Output Doping File [OUT.FILE= ] Uniform Profiles { (UNIFORM {N-TYPE | P-TYPE | IMPURITY= | OTHER= } N.PEAK= ) Analytic Profiles | ( {N-TYPE | P-TYPE IMPURITY= | OTHER= } {N.PEAK= | DOSE= } { (Y.CHAR= [Y.ERFC] ) | Y.JUNCTI= } {X.CHAR= | XY.RATIO= } [X.ERFC]

19. 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

20. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering EXAMPLE: RESULTS Basic SiGe Mesh Corresponding doping profile

21. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering DEVICE STRUCTURE IMPORTING DEVICE STRUCTURE FROM MEDICI/TSUPREM4

22. 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

23. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering From TSUPREM4 MESH in.file=s4filename tsuprem4 elec.bot poly.elec y.max=3 RENAME electr oldname=1 newname=source RENAMEelectr oldname=2 newname=drain SAVEmesh out.file=mdfile From previous MEDICI execution MESH in.file=mdfile EXAMPLE: IMPORTING STRUCTURE FILE

24. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering Default structure depth in TSUPREM4 is 200  m. 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

25. 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

26. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering REGRID

27. 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

28. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering CHOICE OF MODELS : RECOMBINATION & GENERATION MODELDESCRIPTION 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

29. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering CHOICE OF MODELS : MOBILITY MODELLOW FIELD TRANSVERS E 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

30. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering CHOICE OF MODELS : MOBILITY MODELLOW FIELD TRANSVE RSE 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

31. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering CHOICE OF MODELS : ENERGY GAP & CARRIER DENSITY MODEL0DESCRIPTION FERMIDIR Fermi Dirac statistics instead of Boltzman. Recommended to be used in conjunction with: INCOMPLEIncomplete ionization of impurities BGN Bandgap 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

32. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering CHOICE OF MODELS : ENERGY BALANCE MODELDESCRIPTION ET.MODEL Uses the energy transport model where the spatial derivative of the mobility is included in the diffusion term of the current equation COMP.ET Invokes an energy balance eq. suitable for compound material such as GaAs TMPMOB A carrier temperature based mobility – alternative to FLDMOB EF.TMP Solves effective electric fields exactly in Si instead of approx for use in TMPMOB TMPTAUW Invokes an electron temperature model for the electron energy relaxation

33. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering CHOICE OF MODELS : ENERGY BALANCE MODELDESCRIPTION II.TEMP Uses the energy transport model where the spatial derivative of the mobility is included in the diffusion term of the current equation EFI.TMP Invokes an energy balance eq. suitable for compound material such as GaAs

34. 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 <0.2  m 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

35. 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

36. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering SOLUTION TECHNIQUE STATEMENTS STATEMENTSDESCRIPTION SYMBOLIC Selects with equations to solve as well as the method of the solution either coupled (Newton) or de-coupled (Gummel) METHOD Control the iteration process – number of iterations use of numerical damping, selection of linear solver LOG To open the file which will contain terminal values calculated during the solution process SOLVE Starts the solution process either DC, AC or transient

37. UniMAP – PSDC INSEP Training Program 2007 School of Microelectronic Engineering SOLUTION TECHNIQUE: SYMBOLIC Solve only Poisson’s equation symbolic 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 method symbolic carr=1 electron newton Solve Poisson’s equation and both hole and electron Drift-Diffusion (DD) equations symbolic carr=2 newton

38. 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)

39. 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

40. 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

41. 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 t

42. 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 13.4567e+4 22.7543e+02 31.6734e+00 41.0000e+00 51.0000e+00 … 1.0000e+00 20 1.0000e+00