to two of the most popular commercial TCAD simulation tools, Silvaco and Sentaurus, to characterize performances of VLSI MOSFETs through TCAD tools, and to familiarize readers with compact modeling for VLSI circuit simulation. This volume provides the reader with comprehensive information and a systematic approach to the design, characterization, fabrication, and computation of VLSI MOS transistors through TCAD tools.

The chapters contain different levels of difficulty. Several example programs are supplied for illustration of the software tools and related physics. The book therefore provides a desirable balance between the basic concepts, equations, physics, and recent technologies of MOS transistors through TCAD simulation. The book is organized into eight chapters that encompass the field of TCAD simulation for VLSI MOSFET.

Chapter 1 provides an overview of the role, need, and advantages of TCAD tools in design, characterization, and fabrication of VLSI MOS transistors. The evolution of modern TCAD and its challenges are also provided. Chapter 2 reviews and analyzes the basic concepts and physics involved with nanoscale MOS transistors. The physical approach to the tools is described by basics of band theory, Poisson’s equation, continuity equation, drift diffusion (DD), and hydrodynamic models. The physics of the scattering mechanisms and different mobility models used in TCAD simulations are discussed. Chapter 3 describes the basics and importance of numerical solution techniques applicable to TCAD. The numerical solution of the DD equations coupled with Poisson’s equation and its application to semiconductor device modeling is described. Chapter 4 provides a detailed overview of the two-dimensional/three-dimensional (2D/3D) device simulator Synopsys Sentaurus TCAD. The various tools involved are introduced in a comprehensive manner. The different software-related aspects of this tool for device simulations are described. Complete design examples explaining step by step the construction, simulation, and performance extraction of MOS transistors are provided. Chapter 5 attempts to present the MOSFET simulation using Silvaco TCAD tools. From basic syntax to choice of a complex model is presented in this chapter with emphasis on the usage of the SILVACO simulation software. An overview of the software developed by Silvaco to meet simulation needs of researching conventional and advanced MOSFET structures is also presented. The discussion is presented with examples to perform simulations of different types of MOSFETs. Chapter 6 discusses in detail the physics of nanoscale MOS transistors through TCAD simulations. The various short channel effects involved with nanoscale MOS transistors are demonstrated through actual TCAD simulation results. Different technology aspects and engineering techniques for future MOSFETs are also introduced. Chapter 7 presents a comprehensive overview of compact modeling of MOS transistors for use in VLSI circuit simulation. The mathematical models for characterizing various ultra-deep sub-micron effects of sub-65 nm MOS transistors are introduced. The effects are demonstrated through actual simulation program with integrated circuit emphasis (SPICE)

simulation results using industry standard compact models. The various circuit performances of MOS transistors are discussed. Chapter 8 addresses process simulation of MOSFET using TSUPREM-4. The chapter is devoted to bringing the key fabrication issues and their implementation in TCAD process simulation tool TSUPREM-4. It also considers how the output of process simulator TSUPREM-4 can be linked to device simulator MEDICI in order to analyze the performance of the fabricated device. An extensive list of references is provided at the end of each chapter for more elaborate discussion of the issues and to motivate readers to engage in further research.

I wish to congratulate all contributors and their peers. Their convictions and efforts were key to the success of this enterprise. The compilation of this book would not have been possible without the dedication and efforts of all the contributing authors. Special thanks go to Gagandeep Singh and Laurie Schlags and staff members of CRC Press for their responsiveness and immense patience demonstrated throughout the publishing process of this book.

C.K. Sarkar

of process, device, and circuit simulation data. In general, TCAD includes lithography modeling to simulate the imaging of the mask by the lithography equipment, photoresist characteristics, and processing; front end process modeling for simulating the physical effects of manufacturing steps used to build transistors up to metallization; device modeling using hierarchy of physically based models for the operational description of active devices; compact modeling for active, passive, and parasitic circuit components; interconnect modeling to analyze the operational response of back-end architectures; reliability modeling for simulating the reliability and related effects on process, device, and circuit levels; equipment modeling for simulating the local influence of the equipment on each point of the wafer, especially in deposition, etching, and chemical-mechanical polishing (CMP) processes; package simulation for electrical, mechanical, and thermal modeling of chip packages; materials modeling to predict the physical and electrical properties of materials; modeling for design robustness, manufacturing, and yield to simulate the impact of process variability and dopant fluctuations on IC performance and determine design specifications for manufacturability and yield of ICs; and numerical techniques including grid generators, surface-advancement techniques, solvers for systems of partial differential equations (PDEs), and optimization routines [1,2].

TCAD offers capabilities to analyze how structural factors such as the geometry and processes conditions influence the electrical behavior of devices and circuits. Simulation data help in quantifying the details of the behavioral models for ICs at the transistor and circuit levels and show physical limitations at the processing and manufacturing levels [3,4]. By reverse modeling, the extended TCAD tools can be used to develop IC fabrication technology from product concept (i.e., from the product specification to IC fabrication technology as shown in Figure 1.1) [1]. The extended TCAD tools can also be used to assess the manufacturability of IC fabrication processes as shown in Figure 1.2 [1,5].

FIGURE 1.1

Extended TCAD use to generate product-specific IC process recipe by reverse modeling; in this approach, the sequential steps 1, 2, and 3 represent use of circuit, device, and process CAD, respectively. (From S.K. Saha, Managing technology CAD for competitive advantage: An efficient approach for integrated circuit fabrication technology development, IEEE Trans. Eng. Manage., vol. 46, no. 2, pp. 221–229, May 1999. With permission.)