Device Simulation for SingleEvent Effects

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Device Simulation for Single-Event Effects

• Mark E. Law
• Dan Cummings, Nicole Rowsey
• SWAMP Center

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2006 Basketball Champs
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2006 Football Champs
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2007 Basketball Champs
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It all pales in comparison to.
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Objectives

• Provide device simulation environment for
  rad-hard applications
• Address Rad-Hard specific issues
• Physics - strain
• Numerics - automatic operation
• Coupled Device / Defect Simulations

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Outline

• Background - FLOODS Code
• Numeric Issues and Enhancements
• Physical Issues and Enhancements
• Conclusions

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FLOOPS / FLOODS

• Multi-dimensional, Object-oriented codes
• P Process / D Device 90 code shared
• Scripting capability for PDEs - Alagator
• Commercialized - ISE / Synopsis
• Sentaurus - Process is based on FLOOPS
• Licensed at over 300 sites world-wide
• Short Course at Vandy Jan. 11-12

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What is Alagator?

• Scripting language for PDEs
• Models are accessible, easily modified
• Equations are split
• Node pieces (recombination, time derivative)
• Element pieces (current, fields)
• Pieces are vectorized
• 128 pieces in tight BLAS loops for performance
• Operations are broken down in scripting
• Precomputation and Caching automatic
• Overall CPU linear in of pieces

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What is Alagator?

• Example use of operators for diffusion equation
• Ficks Second Law of Diffusion
• ddt(Boron) - 9.0e-16 grad(Boron)
• ?C(x,t) / ?t D ?2C(x,t) / ?x2
• All physics is defined on the command line
• Rapidly evolve models for new devices / materials
  / physics

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Outline

• Background - FLOODS Code
• Numeric Issues and Enhancements
• Physical Issues and Enhancements
• Conclusions

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Object Oriented

• Derived Specific Geometry Elements
• Common properties so code is independent

Element Class
Volume
Face
Edge
Node
Face
2 -Edge
3 -Edge
Tri
Quad
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Anisotropic Grid - Mixed Elements

• For many reasons, quads are better shapes for
  device simulation
• Rectangular region created at the command line
• Refinement creates mixed elements and terminated
  lines
• Assembly runs on generalized elements

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ElementInfo Derived Classes

• NodeInfo Base Class - for nodes
• EdgeFluxInfo - Edge Flux Terms
• ReflectInfo - Boundary conditions, contacts
• InterfaceInfo - Interface layers and Material
  boundaries
• ElementInfo - Base Element Assembly Class
• Derived Classes - Allow more element types
• EleEdgeInfo (1D)
• EleTriInfo, EleQuadInfo (2D)
• EleTetInfo (3D) (will add EleBrickInfo)

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Elastic Assembly - Element Assembly

• Data Comes from ElementInfo Class
• All are vectors - 128 long
• Code Fragment of Assembly
• for(i 0 i lt BDim i)
• for(j 0 j lt BDim j)
• sij 0.0
• for(l 0 l lt Ddim l)
• for(k 0 k lt Ddim k)
• //multiply BT, D, B
• tmp.Mult(ev.BM(k, i),ev.BM(l, j),
  Dkl)
• sij tmp
• sij ev.Size()

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Outline

• Background - FLOODS Code
• Numeric Issues and Enhancements
• Physical Issues and Enhancements
• Conclusions

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Philips Unified Mobility Model

• Unifies the description of majority and minority
  carrier bulk mobilities
• temperature dependence
• electronhole scattering
• screening of ionized impurities by carriers
• clustering of impurities

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Bandgap Narrowing
pn diode band diagram
Unified apparent bandgap narrowing
ND
NA
is a function of doping level
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Normal Field Computation

• Dot, magnitude, cross operators
• Compute gradient of scalar terms, vector
  operations
• dot(DevPsi, x)
• Determines magnitude of the gradient of the first
  argument
• In the direction of the second
• dot(DevPsi, x) - vertical (channel) field
• dot(DevPsi,qfn) / Magnitude(qfn)
• Produce field in the current flow direction
• dot(DevPsi, x) - vertical field for mobility
  reduction
• Leads to strain tensor operations

SiO2
Current
Field
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Mobility Degradation at Interfaces
perpendicular field
Surface Roughness
Acoustic Phonon
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Anisotropic Mobility Enhancement

• PMOS (Lgate65 nm)
• Mobility enhanced by a factor of 2.5 in the
  lateral direction uniformly
• DC Drain curves with the gate at -1.0V for a
  65nm and 250 nm gate length, with and without a
  strain enhanced mobility in the lateral
  direction.

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Anisotropic Mobility Transient

• PMOS (Lgate65 nm)
• Mobility enhanced by a factor of 2.5 in the
  lateral direction uniformly
• To observe strain differences, assumed no
  recombination
• Charge was deposited along a vertical line
  through the drain junction
• Charge cloud was assumed to be Gaussian in the
  lateral direction and uniform vertically

• Issue total charge collected is not the same
  for both cases

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Shockley-Read-Hall Recombination
Diodes with different carrier lifetimes
(increasing forward bias)
Nt trap density can be set as a function of
distance
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Example - Modern USJ Formation

• State of the Art USJ Technology
• Si Preamorphization
• Carbon Implant at End of Range
• Significant increase in junction leakage (but
  still small compared to S-D leakage)
• Large local recombination centers at C

Felch, et al., INSIGHT 2007
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Example - Modern USJ Formation

• Centered SRH increase at C sites
• Order of magnitude increase in junction leakage
  (measured was larger)
• 65nm MOS transistor (larger technology node than
  this is aimed at)
• Single event response w/ and w/o carbon

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Summary

• Generalized Element Assembly, Refinement
• Need to work on bricks, unrefinement
• Added Physical Operators
• Directional terms included
• Add Strain
• Built Standard MOS models for distribution
• Lombardi, Phillips, Bandgap, Recombination