An Introduc+on to Silvaco-Atlas

Transcription

1 An Introduc+on to Silvaco-Atlas Objectives: To learn how to simulate semiconductor device structures in cross-section (2D) or in 3D. To become familiar with building a structure and simulation code through Deckbuild in order to perform DC and AC simulations. To visualize actual energy band-edge, potential, field, and carrier profile gradients, etc, and output currentvoltage characteristics for devices discussed in ECE135B. To solve Problem Set 4! Refs.: 1. Atlas User Manual 2. nanohub online resources

2 Deckbuild Is the interface we work with to set up our structure and simulation Athena Atlas Simulates our input processing conditions to produce the structure whose performance we want to simulate (to be taught in ECE136L). Tonyplot Simulates the Athena-created or input specified structure (code or by Devedit) for output characterisgcs based on specified material parameters. Displays output characteristics and allows us to visualize them in a variety of formats (contour plots, I- V, C-V, etc). In ECE135B, we will mainly modify Atlas command line input in order to characterize MOSFET performance, and display extracted results in log files or plot them using Tonyplot.

3 How to run Atlas You can run the software from any of the linux labs or you can SSH to any of the machines and run the program remotely. Once you re logged in, you can open a terminal and type in: module load silvaco Then, you d want to start the deckbuild where you can type in your code and run Atlas. Type: Deckbuild & Your working folder will be ee135bzz. Make sure that the saved file name includes your family name so that others wouldn t modify it by mistake.

4 Deckbuild Window Allows you to open input files with.in extension (Ex: superdevice.in )

5 Deckbuild Window This window will open Allows you to open already built-in examples, learn from them, and improve your skills to u:lize the best of the simulator. Double-click

6 Deckbuild Window You will see a list of available examples This window will open Double-click Double-click to load example in deckbuild window

7 Deckbuild Window Created by Athena Simulated through Atlas

8 Input File in Deckbuild (for illustration purpose only) Schrodinger-Poisson solution at zero bias go atlas mesh x.mesh loc=0.0 spac=0.04 x.mesh loc=5.0 spac=0.04 Optional user comments; anything after is read as a comment To run Atlas Mesh specification y.mesh loc=0.0 spac=0.01 y.mesh loc=0.07 spac=0.005 y.mesh loc=0.28 spac=0.005 y.mesh loc=0.35 spac=0.01 region num=1 material=si3n4 y.min=0.0 y.max=0.14 region num=2 material=inas y.min=0.14 y.max=0.21 Regional specifica>on region num=3 material=si3n4 y.min=0.21 y.max=0.35 elec num=1 material=titanium name=source x.min=0.0 x.max=0.5 y.min=0.139 y.max=0.14 elec num=2 material=aluminum name=gate x.min=2.0 x.max=3.0 y.min=0.0 y.max=0.13 elec num=3 material=titanium name=drain x.min=4.5 x.max=5.0 y.min=0.139 y.max=0.14 elec num=2 material=aluminum name=gate x.min=2.0 x.max=3.0 y.min=0.22 y.max=0.35 elec num=1 material=titanium name=source x.min=0.0 x.max=0.5 y.min=0.210 y.max=0.211 elec num=3 material=aluminum name=drain x.min=4.5 x.max=5.0 y.min=0.210 y.max=0.211 doping uniform y.min=0.14 y.max=0.21 n.type conc=5.e16 Doping specification 1. Structure Specification: - Mesh - Region - Electrode - Doping Electrode specification

9 Input File in Deckbuild cont. (for illustration purpose only) material material=inas affinity=4.9 contact name=drain current contact name=drain resistance=350 contact name=source current contact name=source resistance=350 interf qf=1e12 2. Material physical parameters, contacts and interfaces. model schrodinger.n eigens=20 fixed.fermi ^calc.fermi qy.min=0.05 qy.max=0.35 qx.min=2.0 qx.max=3.0 fermi new.eig num.direct=1 qminconc=1.0e13 srh incomplete method itlim=20 nblockit=30 trap maxtrap=6 vsatmod.inc=0.01 carriers=0 output con.band val.band eigens=5 3. Models to be used for simulations and numerical methods to be solved with. solve init solve vgate=0 save outf=trr.str tonyplot trr.str quit 4. Solu=on specifica=on (what to solve for?). 5. Displaying Solutions.

10 Order of Atlas Commands

11 Defining a Structure 1. If a structure is created in Athena or Devedit, use: MESH INFILE=<filename> 2. If a structure is created in the same Deckbuild file, the command: go atlas will automa6cally load the most recently saved structure. In this case, MESH statement in Atlas should not be used. ELECTRODE statement should be defined in Athena in this case. 3. Using the Deckbuild command line: MESH SPACE.MULT=<VALUE> where <Value> is between 0 and 1 for refining the mesh for more accurate details in the simulation, and greater than 1 for coarser mesh for fast simulations. Using this feature, you wouldn t need to re-write the whole mesh in case you needed to change the mesh spacing. X.MESH LOCATION=<VALUE> SPACING=<VALUE> Y.MESH LOCATION=<VALUE> SPACING=<VALUE> where x & y can be positive or negative but has to increase as you proceed in defining the mesh and <VALUE> is in microns.

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13 Specifying Regions and Materials Syntax: REGION number=<integer> <material_type> <position parameters> Example 1: region num=1 material=si3n4 y.min=0.0 y.max=0.14 This defines the material in region 1 to be silicon nitride extending over all values of x (along the length of the device) and from 0 to 0.14μm along its depth. Example 2: region num=1 material=si3n4 x.min=0.0 x.max=0.05 y.min=0.0 y.max=0.14 This does the same as above but restricts the extent of silicon nitride in the x- direction between 0 and 50nm. Note: All points included in the MESH statement needs to have a region defined for them.

14 Specifying Electrodes and Doping Electrode syntax: ELECTRODE NAME=<electrode name> <position_parameters> Example: elec Doping syntax: num=1 name=source x.min=0.0 x.max=0.5 y.min=0.139 y.max=0.14 DOPING <distribumon_type> <dopant_type> <posimon_type> Example: Doping uniform conc=5.e16 n.type region=1 OR: Doping uniform conc=5.e16 n.type region=1 x.min=0 x.max=0.1 \ y.min=0 y.max=0.14 OR (see next page for profile): Doping uniform con=1e16 n.type region=1 Doping Gaussian con=1e20 characteristic=0.5 p.type x.left=0.0 \ x.right=2.0 peak=0.5

15 0.5μm 70% of characteristic

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17 Regrid at Junctions When there are abrupt changes in doping, composition, near contacts, etc, one needs to regrid in order to achieve conversion without defining a fine grid all over the structure: Example: regrid logarithm doping ratio=2 smooth.key=4 This creates a regrid when that resolves changes in doping profiles to 2 orders of magnitude. smooth.key is a built in rou<ne to specify number of triangles at the regrid loca<on with 4 being a default value. before regrid after regrid

18 Specifying Contact Characteristics Examples: contact name=gate workfunction=4.8 When a workfunction is specified, contact is treated as a Schottky contact. barrier enables dipole or image force barrier lowering: contact name=anode workfunction=4.9 barrier alpha=1e-7 sets the image force lowering coefficient to 1nm. contact name=source con.resistance=0.05 sets the contact specific resistivity to 0.05 Ωcm 2. contact name=drain resistance=50 capacitance=20e-12 inductance=1e-6 sets series lumped elements with R=50Ω, C=20pF, L=1μH. Since this is a 2D simulation, the channel width is 1 μm, meaning R=50Ω-μm & I in A/μm.

19 Specifying Material & Interface Properties Material statement allow modifying the basic physical parameters of a material used in the input file. Examples: material material=silicon EG300=1.12 mun=1100 sets the bandgap and low field mobility in all regions of the device. material region=2 taun0=2e-7 taup0=1e-5 sets the electron and hole SRH recombination lifetimes in region 2 Interface statement defines interface charge density and surface recombinagon velociges at semiconductor/insulator interfaces. Examples: interface qf=3e10 s.n=1e4 s.p=1e4 sets all interfaces between semiconductors and dielectrics to have a fixed charge density of 3x10 10 cm -2 and the electron and hole surface recombinabon velocibes. interface qf=3e10 x.min=1.0 x.max=2.0 y.min=0.0 y.max=0.5 sets the interface charge density to the rectangle defined above.

20 Specifying Interface Traps Syntax: Inttrap <type> E.level=<real> density=<real> <capture parameters> Examples: inttrap inttrap e.level=0.49 acceptor density=2e10 degen=12 sign=2.48e-15 sigp=2.84e-14 e.level=0.32 donor density=1e10 degen=1 sign=1e-16 sigp=1e-17 degeneracy factor capture cross-section for electrons capture cross-section for holes

21 Specifying Physical Models Physical models used for simula1ons are classified into: mobility, recombina1on, carrier sta1s1cs, impact ioniza1on, and tunneling. Example: models conmob fldmob srh fermidirac activates concentration dependent mobility mobility models, field dependent mobility models, SRH minority carrier recombination model, and Fermi-Dirac statistics model. Some basic models are grouped for simulating certain devices. For example: models MOS print activates CVT, SRH, and fermidirac models. The print lists to the run time output the models and their parameters to be used in the simulation. One can always check these to make sure if his/her models are activated properly. CVT activates the transverse field mobility model.

22 The Drift Diffusion Transport Model Utilizes Poisson s equation to solve for potential/field distribution and the continuity equations for carrier statistics. Ψ is the electrostatic potential φ n & φ p are electron and hole quasi-fermi energies Temperature variations (energy of carriers) not taken into account à Energy Balance Model.

23 Numerical Solution Techniques Specified in the method statement: - Gummel: solves the equations sequentially (decoupled) until a convergence is achieved. - Newton: solves the equations simultaneously (coupled) but takes longer time to converge. - Block: combined Gummel and Newton (some equations coupled and some decoupled). method gummel block newton starts solu)on with a few Gummel itera)ons to generate a be4er guess and then switch to Newton to complete the solu)on. recommended; sets the limit for minimum resolvable carrier method gummel newton climit=1e-4 concentration sets the solver to start with Gummel itera)ons and then switch to Newton if convergence is not achieved. (most recommended) method carrier=2 solves for both electrons and holes (default) method carrier=1 hole solves for holes only

24 DC Solutions The voltage on each electrode is specified using the SOLVE statement: Example: solve init solve vgate=2.0 solve vdrain=1.0 solves for initial guess at thermal equilibrium (zero bias) solves for single bias points Bias sweep: solve vgate=0 vstep=0.05 vfinal=2.0 name=gate Sweeps the gate bias from 0 to 2 V in 0.05 V increments. Family of curves (example Ids-Vds at different Vgs): solve vgate=1 outf=temp1 solve vgate=2 outf=temp2 load infile=temp1 log outf=drain_sweep_vgate1 solve name=drain vdrain=0 vstep=0.05 vfinal=2.0 load infile=temp2

25 AC Solutions Specified on top of DC biases to solve for conductance and capacitance between different nodes: Example: solve vgate=0 vstep=0.05 vfinal=1 name=gate AC freq=1e6 Or: solve vgate=0.5 AC freq=1e9 fstep=1e9 nfsteps=9 ramps the frequency from 1GHz to 10 GHz in 1 GHz step. Displaying Results in Tonyplot One can plot the output log file using tonyplot Example: tonyplot drain_sweep_vgate1.log For a family of curves (example Ids-Vds at different Vgs): tonyplot overlay drain_sweep_vgate1.log drain_sweep_vgate2.log