semiconductor physics 2007/2008 school of microelectronic engineering by syarifah norfaezah

Semiconductor Physics 2007/2008

School of Microelectronic Engineering

by Syarifah Norfaezah



• 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.



SOI/Si

Semiconductor Technology

CMOS Bipolar BiCMOS

NMOS PMOS BJT/HBT

CMOSDevices HBTBJT

Silicon Substrate



GaAs substrate

Semiconductor Technology

Bipolar FET HEMT …..

BJT JFET MESFET …..

GaAs/AlGaAs

HBTDevices



• 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.

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)




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




• 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

TCAD TOOLS



• History of commercial process simulators:

1. Development of Stanford University Process Modeling (SUPREM) program

2. Improved models SUPREM II and SUPREM III3. Technology Modeling Associates (TMA), 1979, was the first

company to commercialized SUPREM III4. Later SILVACO commercialized SUPREM and named the

product ATHENA5. TMA commercialized SUPREM IV (2D) version and called it

TSUPREM46. Integrated System Engineering (ISE) came out with 1D process

simulator TESIM and 2D process simulator DIOS7. About the same time, TMA develop new 3D process & device

simulator8. After TMA was acquired by Avanti, Taurus product was

released in 1998

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)





A result from semiconductor process – final geometry and the concentration of dopants.



• 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




• 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




• 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




• 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



2D profile of PMOS structure generated in TSUPREM4

PROCESS SIMULATION - example



Concentration of implanted dopant (boron) at different doses and annealed at different temperatures

PROCESS SIMULATION - example



• 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




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



• 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

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

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

TCAD TOOLS – DEVICE SIMULATION



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

DEVICE SIMULATION - example



Gate characteristics of a sub-micron MOSFET showing increase in threshold voltage due to quantum effects




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)




Peak temperature, the capacitor voltage, the total current, and the voltage at the IC input during the event




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

TCAD TOOLS



• 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

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

TAURUS-WORKBENCH (TWB)



TAURUS-WORKBENCH (TWB) - example

TWB workspace




Structure of Taurus WorkBench Experiment




Taurus Layout



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



• 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).

SUMMARY



THANK YOU

“The longest journey begins with a single step”

semiconductor physics 2007/2008 school of microelectronic engineering by syarifah norfaezah

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