1. OVERVIEW ON PROCESS & DEVICE SIMULATION
by Syarifah Norfaezah

2. Electronic applications rely on Integrated Circuits (ICs)
Integrated circuits are often classified by the number of transistors and other electronic components they contain :
SSI (Small scale integration) : up to 100 electronic components per chip
MSI (Medium scale integration) : From 100 to 3000 electronic components per chip
LSI (Large scale integration) : From 3000 to 100,000 electronic components per chip
VLSI (Very large scale integration) : From 100,000 to 1,000,000 electronic components per chip
ULSI (Ultra large scale integration) : More than 1,000,000 electronic components per chip
ICs are made up of basic semiconductor interconnected by metal layers and packaged in various types of packaging
Among of basic devices are NMOS, PMOS, BJT, resistor, capacitor, inductor etc.

3. Semiconductor Technology
SOI/Si
Silicon Substrate
Semiconductor Technology
CMOS
Bipolar
BiCMOS
Devices
NMOS
PMOS
BJT
HBT
BJT/HBT
CMOS

4. Semiconductor Technology
GaAs/AlGaAs
GaAs substrate
Semiconductor Technology
Bipolar
FET
HEMT
…..
Devices
BJT
HBT
JFET
MESFET
…..

5. TECHNOLOGY COMPUTER AIDED DESIGN (TCAD)
The synergistic combination of process, device and circuit simulation and modeling tools
The goals start from the physical description of IC devices considering both the physical configuration and related device properties and build the links between the broad range of physics & electrical behavior models that support device and circuit design.

6. TECHNOLOGY COMPUTER AIDED DESIGN (TCAD)
Is a branch of electronic design automation that models semiconductor fabrication
Modeling under TCAD:
Modeling of process steps (eg. diffusion, ion implantation)
Modeling of the behavior of the electrical devices (based on fundamental physics, eg. doping profiles)
May also include the creation of compact models (eg. SPICE transistor models)

7. TECHNOLOGY COMPUTER AIDED DESIGN (TCAD)
Hierarchy of technology CAD tools building from the process level to circuits. Left side icons show typical manufacturing issues (DFM: Design for Manufacturability); right side icons reflect MOS scaling results based on TCAD

8. Basically, it can be used to:
TCAD TOOLS
Basically, it can be used to:
Simulate fabrication processes
Simulate device structures
Simulate device electrical (optical) characteristics
Extract and optimize device parameters
Simulate semiconductor manufacturing processes
Efficient for device-level simulation, although it has circuit simulation feature

9. TCAD TOOLS – PROCESS SIMULATION
History of commercial process simulators:
Development of Stanford University Process Modeling (SUPREM) program
Improved models SUPREM II and SUPREM III
Technology Modeling Associates (TMA), 1979, was the first company to commercialized SUPREM III
Later SILVACO commercialized SUPREM and named the product ATHENA
TMA commercialized SUPREM IV (2D) version and called it TSUPREM4
Integrated System Engineering (ISE) came out with 1D process simulator TESIM and 2D process simulator DIOS
About the same time, TMA develop new 3D process & device simulator
After TMA was acquired by Avanti, Taurus product was released in 1998

10. TCAD TOOLS – PROCESS SIMULATION
Semiconductor process simulation is the modeling of the fabrication of semiconductor devices.
The goal of process simulation:
An accurate prediction of the active dopant distribution
The stress distribution
The device geometry
Process simulation is typically used as an input for device simulation (modeling of device electrical characteristics)

11. TCAD TOOLS – PROCESS SIMULATION
A result from semiconductor process – final geometry and the concentration of dopants.

12. TCAD TOOLS – PROCESS SIMULATION
The fabrication of IC devices requires series of processing steps called a process flow
Process simulation involves modeling of all essential steps in the process flow.
The input for process simulation is the process flow and a layout.
TCAD has traditionally focused mainly on the transistor fabrication part of the process flow ending with the formation of contacts – also known as front end of line manufacturing. Back end (eg. Interconnect, dielectric, etc.) is not considered

13. TCAD TOOLS – PROCESS SIMULATION
Typically, the devices are constructed on a starting semiconductor material - substrate or wafer
The device structure is then formed by applying sequence of process steps
The common process steps include:
Oxidation
Lithography
Etching
Diffusion and dopant activation
Ion implantation
Metallization

14. TCAD TOOLS – PROCESS SIMULATION
Process simulators use a combination of Finite Element Analysis (FE) and/or finite volume methods (FV)
Process simulation uses FE/FV mesh to compute and store the dopant and stress profiles
The accuracy of the profile strongly depends on maintaining a proper density of mesh points at any time during simulation
The density of points should be just enough to resolve all dopant and defect profiles but not more because the computation expense of solving the diffusion equations increases with the number of mesh points
The number of mesh increase dramatically if adaptive meshing is performed

15. TCAD TOOLS – PROCESS SIMULATION
MESH can cause computation expense
The right mesh is very crucial
More mesh is needed at critical areas such as at interfaces or doping area
Mesh of a p-n junction device

16. PROCESS SIMULATION - example
2D profile of PMOS structure generated in TSUPREM4

17. PROCESS SIMULATION - example
Concentration of implanted dopant (boron) at different doses and annealed at different temperatures

18. TCAD TOOLS – PROCESS SIMULATION
There has always been a desire to have more accurate simulations.
Simplified physical models have been most commonly used in order to minimize computation time.
But shrinking device dimensions put increasing demands on the accuracy of dopant and stress profiles so new process models are added for each generation of devices to match new accuracy demands
The trend of adding more physical models and considering more detailed physical effects will continue and may accelerate

19. DEVICE CHARACTERISTIC
Once the fabrication process has been completed, the characteristics of the device can be determined.
For example, dc current-voltage (I-V) characteristics of various terminals at various conditions, capacitance, ac analysis.
The device electrical characteristics can be obtained using device simulation - also known as modeling of device electrical characteristics

20. DEVICE SIMULATION?
Device simulation is a simulation tool that predicts electrical, thermal and optical characteristics of semiconductor devices
With the most advanced physical models commercially available, device simulation allows device designs to be optimized for best performance without fabrication, eliminating the need for costly experiments

21. TCAD TOOLS – DEVICE SIMULATION
BENEFIT/PURPOSES:
Analyze electrical, thermal and optical characteristics of devices without having to manufacture the actual device
Determine static & transient terminal currents & voltages under all operating conditions of interest
Understand internal device operation through potential, electric field, carrier, current density, recombination and generation rate distribution
Optimize device designs without fabrication and find ideal structural parameters
Investigate breakdown and failure mechanisms, such as leakage paths and hot carrier effects
Use the Physical Model and Equation Interface (PMEI) to perform simulations that incorporate user-defined physical models & equations

22. TCAD TOOLS – DEVICE SIMULATION
SIMULATION FEATURES
Simulation of arbitrarily shaped 1D, 2D & 3D
Consistently solves Poisson’s equation, the electron & hole current continuity equations, the electron & hole energy balance equations, the lattice heat equation.
Steady state, transient and AC small signal analysis with automatic I-V curve tracing and time-step algorithms
Ray tracing to simulate transmission, reflection and refraction across interfaces, as well as absorbtion and emission
Advanced adaptive mesh generation, which provides optimal grids with excellent solution and structure resolution using a minimum number of mesh points
Arbitrary doping from analytic functions, tables and process simulation
Supports multiple materials such as Si, Ge, GaAs, SiGe, AlGaAs, InP, GaInAs, GaInGaPAs and SiC
Optional physical model and equation interface which allows user to define and solve new physical models and partial differential equations

23. DEVICE SIMULATION - example
Contours of the quantized electron concentration in a 2D sub-micron MOSFET computed using the Shrodinger solver. Horizontal scale is 0.6nm vertical scale is 65Ǻ

24. DEVICE SIMULATION - example
Gate characteristics of a sub-micron MOSFET showing increase in threshold voltage due to quantum effects

25. DEVICE SIMULATION - example
Detail from a 20 field ring device comparing conventional mesh with quadtree (capable to minimizes the number of mesh points need for efficient simulation of large power device structures without sacrificing the accuracy required in critical device regions)

26. DEVICE SIMULATION - example
Peak temperature, the capacitor voltage, the total current, and the voltage at the IC input during the event

27. TCAD TOOLS
ACTIVITIES
OUTCOMES
TOOLS
Process Simulation
Device Structure
TSUPREM4
TAURUS WORK
BENCH
(GUI)
Device Simulation
Electrical characteristic
MEDICI(2D)
DAVINCI(3D)
Device Modeling
Device model parameters
AURORA
Circuit Simulation
Functional circuit/system
HSPICE

28. TAURUS-WORKBENCH (TWB)
Process and device simulators are integrated with TWB
TWB helps to:
Optimize IC fabrication processes
Shorten product development cycle and time to market
Perform design for manufacturability and maximize yield
Evaluate design tradeoffs
TWB is:
Natural, easy-to-use graphical user interface
Extensive design of experiments (DOE) capabilities
Comprehensive data management
Interactive post-simulation graphical and statistical data analysis

29. TAURUS-WORKBENCH (TWB)
MAJOR FEATURES
Hierarchical system with an intuitive graphical user interface
Encapsulation of simulations in Modules/Commands
Complete data management for storage of simulations and results
Parallel network execution of simulated splits
Built-in icon editor to create Module/simulator Driver/Tool icons
Open architecture, capable of tightly integrating a variety of tools
Built-in design experiments
Flexible post-processing with user-defined macros and tools

30. TAURUS-WORKBENCH (TWB) - example
TWB workspace

31. TAURUS-WORKBENCH (TWB) - example
Structure of Taurus WorkBench Experiment

32. TAURUS-WORKBENCH (TWB) - example
Taurus Layout

33. Process simulation consists of process recipe (left-side) and wafer flow (right-side)

34. SUMMARY
Traditional wafer processing is costly and takes months to get the results – process & device simulation is a solution
TCAD tools are capable of simulating these manufacturing processes through TaurusWorkBench which create, manage and destroy experiments and data, and also drives and integrate simulators (TSUPREM4, MEDICI, etc.) and tools (graphics).

35. THANK YOU
“The longest journey begins with a single step”