Technology CAD
Encyclopedia
Technology CAD is a branch of electronic design automation
that models semiconductor fabrication
and semiconductor device operation. The modeling of the fabrication is termed Process TCAD, while the modeling of the device operation is termed Device TCAD. Included are the modelling of process steps
(such as diffusion
and ion implantation
), and modelling of the behavior of the electrical devices
based on fundamental physics, such as the doping profiles of the devices. TCAD may also include the creation of compact models (such as the well known SPICE
transistor
models), which try to capture the electrical behavior of such devices but do not generally derive them from the underlying physics. (However, the SPICE simulator itself is usually considered as part of ECAD
rather than TCAD.)
From the diagram on the right:
process. Their accuracy and robustness over process technology, its variability and the operating conditions of the IC--environmental, parasitic interactions and testing, including adverse conditions such as electro-static discharge--are critical in determining performance, yield and reliability. Development of these technology and design rule files involves an iterative process that crosses boundaries of technology and device development, product design and quality assurance. Modeling and simulation play a critical role in support of many aspects of this evolution process.
The goals of TCAD start from the physical description of integrated circuit devices, considering both the physical configuration and related device properties, and build the links between the broad range of physics and electrical behavior models that support circuit design. Physics-based modeling of devices, in distributed and lumped forms, is an essential part of the IC process development. It seeks to quantify the underlying understanding of the technology and abstract that knowledge to the device design level, including extraction of the key parameters that support circuit design and statistical metrology. Although the emphasis here is on Metal Oxide Semiconductor (MOS) transistors--the workhorse of the IC industry--it is useful to briefly overview the development history of the modeling tools and methodology that has set the stage for the present state-of-the-art.
technology, starting in the late 1960s, and the challenges of junction isolated, double-and triple-diffused transistors. These devices and technology were the basis of the first integrated circuits; nonetheless, many of the scaling issues and underlying physical effects are integral to IC design, even after four decades of IC development. With these early generations of IC, process variability and parametric yield were an issue—a theme that will reemerge as a controlling factor in future IC technology as well.
Process control issues--both for the intrinsic devices and all the associated parasitics--presented formidable challenges and mandated the development of a range of advanced physical models for process and device simulation. Starting in the late 1960s and into the 1970s, the modeling approaches exploited were dominantly one- and two-dimensional simulators. While TCAD in these early generations showed exciting promise in addressing the physics-oriented challenges of bipolar technology, the superior scalability and power consumption of MOS technology revolutionized the IC industry. By the mid-1980s, CMOS became the dominant driver for integrated electronics. Nonetheless, these early TCAD developments set the stage for their growth and broad deployment as an essential toolset that has leveraged technology development through the VLSI and ULSI eras which are now the mainstream.
IC development for more than a quarter-century has been dominated by the MOS technology. In the 1970s and 1980s NMOS was favored owing to speed and area advantages, coupled with technology limitations and concerns related to isolation, parasitic effects and process complexity. During that era of NMOS-dominated LSI and the emergence of VLSI, the fundamental scaling laws of MOS technology were codified and broadly applied. It was also during this period that TCAD reached maturity in terms of realizing robust process modeling (primarily one-dimensional) which then became an integral technology design tool, used universally across the industry. At the same time device simulation, dominantly two-dimensional owing to the nature of MOS devices, became the work-horse of technologists in the design and scaling of devices. The transition from NMOS to CMOS
technology resulted in the necessity of tightly coupled and fully 2D simulators for process and device simulations. This third generation of TCAD tools became critical to address the full complexity of twin-well CMOS technology (see Figure 3a), including issues of design rules and parasitic effects such as latchup
. An abbreviated but prospective view of this period, through the mid-1980s, is given in; and from the point of view of how TCAD tools were used in the design process.
The dominance of interconnects for giga-scale integration (transistor counts in O(billion)) and clocking frequencies in O (10 gigahertz)) have mandated the development of tools and methodologies that embrace patterning by electro-magnetic simulations—both for optical patterns and electronic and optical interconnect performance modeling—as well as circuit-level modeling. This broad range of issues at the device and interconnect levels, including links to underlying patterning and processing technologies, is summarized in Figure 1 and provides a conceptual framework for the discussion that now follows.
Figure 1 depicts a hierarchy of process, device and circuit levels of simulation tools. On each side of the boxes indicating modeling level are icons that schematically depict representative applications for TCAD. The left side gives emphasis to Design For Manufacturing
(DFM) issues such as: shallow-trench isolation (STI), extra features required for phase-shift mask
ing (PSM) and challenges for multi-level interconnects that include processing issues of chemical-mechanical planarization
(CMP), and the need to consider electro-magnetic effects using electromagnetic field solver
s. The right side icons show the more traditional hierarchy of expected TCAD results and applications: complete process simulations of the intrinsic devices, predictions of drive current scaling and extraction of technology files for the complete set of devices and parasitics.
Figure 2 again looks at TCAD capabilities but this time more in the context of design flow information and how this relates to the physical layers and modeling of the electronic design automation (EDA) world. Here the simulation levels of process and device modeling are considered as integral capabilities (within TCAD) that together provide the "mapping" from mask-level information to the functional capabilities needed at the EDA level such as compact models ("technology files") and even higher-level behavioral models. Also shown is the extraction and electrical rule checking (ERC); this indicates that many of the details that to date have been embedded in analytical formulations, may in fact also be linked to the deeper TCAD level in order to support the growing complexity of technology scaling.
, Silvaco
and Crosslight
. The open source GSS, Archimedes and Aeneas has some of the capabilities of the commercial products. TCAD Central maintains an information resource for available TCAD software.
Electronic design automation
Electronic design automation is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits...
that models semiconductor fabrication
Semiconductor fabrication
Semiconductor device fabrication is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photolithographic and chemical processing steps during which electronic circuits are gradually created on a wafer...
and semiconductor device operation. The modeling of the fabrication is termed Process TCAD, while the modeling of the device operation is termed Device TCAD. Included are the modelling of process steps
Semiconductor process simulation
Semiconductor process simulation is the modeling of the fabrication of semiconductor devices such as transistors. It is a branch of electronic design automation, and part of a sub-field known as technology CAD, or TCAD....
(such as diffusion
Dopant
A dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...
and ion implantation
Ion implantation
Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into another solid. This process is used to change the physical, chemical, or electrical properties of the solid...
), and modelling of the behavior of the electrical devices
Semiconductor device modeling
Semiconductor device modeling creates models for the behavior of the electrical devices based on fundamental physics, such as the doping profiles of the devices. It may also include the creation of compact models , which try to capture the electrical behavior of such devices but do not generally...
based on fundamental physics, such as the doping profiles of the devices. TCAD may also include the creation of compact models (such as the well known SPICE
SPICE
SPICE is a general-purpose, open source analog electronic circuit simulator.It is a powerful program that is used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior.- Introduction :Unlike board-level designs composed of discrete...
transistor
Transistor
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current...
models), which try to capture the electrical behavior of such devices but do not generally derive them from the underlying physics. (However, the SPICE simulator itself is usually considered as part of ECAD
Electronic design automation
Electronic design automation is a category of software tools for designing electronic systems such as printed circuit boards and integrated circuits...
rather than TCAD.)
- See SPICESPICESPICE is a general-purpose, open source analog electronic circuit simulator.It is a powerful program that is used in integrated circuit and board-level design to check the integrity of circuit designs and to predict circuit behavior.- Introduction :Unlike board-level designs composed of discrete...
for an example of a circuit simulator - See semiconductor device modelingSemiconductor device modelingSemiconductor device modeling creates models for the behavior of the electrical devices based on fundamental physics, such as the doping profiles of the devices. It may also include the creation of compact models , which try to capture the electrical behavior of such devices but do not generally...
for a description of modeling devices from dopantDopantA dopant, also called a doping agent, is a trace impurity element that is inserted into a substance in order to alter the electrical properties or the optical properties of the substance. In the case of crystalline substances, the atoms of the dopant very commonly take the place of elements that...
profiles. - See semiconductor process simulationSemiconductor process simulationSemiconductor process simulation is the modeling of the fabrication of semiconductor devices such as transistors. It is a branch of electronic design automation, and part of a sub-field known as technology CAD, or TCAD....
for the generation of these profiles - See BACPACBACPACBACPAC, or the Berkeley Advanced Chip Performance Calculator, is a software program to explore the effect of changes in IC technology. The use enters a set of fairly fundamental properites of the technology and the program estimates the system level performance of an IC built with these assumptions...
for an analysis tool that tries to take all of these into account to estimate system performance
Introduction
Technology files and design rules are essential building blocks of the integrated circuit designIntegrated circuit design
Integrated circuit design, or IC design, is a subset of electrical engineering and computer engineering, encompassing the particular logic and circuit design techniques required to design integrated circuits, or ICs...
process. Their accuracy and robustness over process technology, its variability and the operating conditions of the IC--environmental, parasitic interactions and testing, including adverse conditions such as electro-static discharge--are critical in determining performance, yield and reliability. Development of these technology and design rule files involves an iterative process that crosses boundaries of technology and device development, product design and quality assurance. Modeling and simulation play a critical role in support of many aspects of this evolution process.
The goals of TCAD start from the physical description of integrated circuit devices, considering both the physical configuration and related device properties, and build the links between the broad range of physics and electrical behavior models that support circuit design. Physics-based modeling of devices, in distributed and lumped forms, is an essential part of the IC process development. It seeks to quantify the underlying understanding of the technology and abstract that knowledge to the device design level, including extraction of the key parameters that support circuit design and statistical metrology. Although the emphasis here is on Metal Oxide Semiconductor (MOS) transistors--the workhorse of the IC industry--it is useful to briefly overview the development history of the modeling tools and methodology that has set the stage for the present state-of-the-art.
History
The evolution of technology computer-aided design (TCAD)--the synergistic combination of process, device and circuit simulation and modeling tools—finds its roots in bipolarBipolar junction transistor
|- align = "center"| || PNP|- align = "center"| || NPNA bipolar transistor is a three-terminal electronic device constructed of doped semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are so named because their operation involves both electrons...
technology, starting in the late 1960s, and the challenges of junction isolated, double-and triple-diffused transistors. These devices and technology were the basis of the first integrated circuits; nonetheless, many of the scaling issues and underlying physical effects are integral to IC design, even after four decades of IC development. With these early generations of IC, process variability and parametric yield were an issue—a theme that will reemerge as a controlling factor in future IC technology as well.
Process control issues--both for the intrinsic devices and all the associated parasitics--presented formidable challenges and mandated the development of a range of advanced physical models for process and device simulation. Starting in the late 1960s and into the 1970s, the modeling approaches exploited were dominantly one- and two-dimensional simulators. While TCAD in these early generations showed exciting promise in addressing the physics-oriented challenges of bipolar technology, the superior scalability and power consumption of MOS technology revolutionized the IC industry. By the mid-1980s, CMOS became the dominant driver for integrated electronics. Nonetheless, these early TCAD developments set the stage for their growth and broad deployment as an essential toolset that has leveraged technology development through the VLSI and ULSI eras which are now the mainstream.
IC development for more than a quarter-century has been dominated by the MOS technology. In the 1970s and 1980s NMOS was favored owing to speed and area advantages, coupled with technology limitations and concerns related to isolation, parasitic effects and process complexity. During that era of NMOS-dominated LSI and the emergence of VLSI, the fundamental scaling laws of MOS technology were codified and broadly applied. It was also during this period that TCAD reached maturity in terms of realizing robust process modeling (primarily one-dimensional) which then became an integral technology design tool, used universally across the industry. At the same time device simulation, dominantly two-dimensional owing to the nature of MOS devices, became the work-horse of technologists in the design and scaling of devices. The transition from NMOS to CMOS
CMOS
Complementary metal–oxide–semiconductor is a technology for constructing integrated circuits. CMOS technology is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits...
technology resulted in the necessity of tightly coupled and fully 2D simulators for process and device simulations. This third generation of TCAD tools became critical to address the full complexity of twin-well CMOS technology (see Figure 3a), including issues of design rules and parasitic effects such as latchup
Latchup
Latchup is a term used in the realm of integrated circuits to describe a particular type of short circuit which can occur in an improperly designed circuit...
. An abbreviated but prospective view of this period, through the mid-1980s, is given in; and from the point of view of how TCAD tools were used in the design process.
Modern TCAD
Today the requirements for and use of TCAD cross-cut a very broad landscape of design automation issues, including many fundamental physical limits. At the core are still a host of process and device modeling challenges that support intrinsic device scaling and parasitic extraction. These applications include technology and design rule development, extraction of compact models and more generally design for manufacturability (DFM)..The dominance of interconnects for giga-scale integration (transistor counts in O(billion)) and clocking frequencies in O (10 gigahertz)) have mandated the development of tools and methodologies that embrace patterning by electro-magnetic simulations—both for optical patterns and electronic and optical interconnect performance modeling—as well as circuit-level modeling. This broad range of issues at the device and interconnect levels, including links to underlying patterning and processing technologies, is summarized in Figure 1 and provides a conceptual framework for the discussion that now follows.
Design for manufacturability (IC)
Achieving high-yielding designs in the state of the art, VLSI technology has become an extremely challenging task due to the miniaturization as well as the complexity of leading-edge products...
(DFM) issues such as: shallow-trench isolation (STI), extra features required for phase-shift mask
Phase-shift mask
Phase-shift masks are photomasks that take advantage of the interference generated by phase differences to improve image resolution in photolithography...
ing (PSM) and challenges for multi-level interconnects that include processing issues of chemical-mechanical planarization
Chemical-mechanical planarization
Chemical Mechanical Polishing/Planarization is a process of smoothing surfaces with the combination of chemical and mechanical forces. It can be thought of as a hybrid of chemical etching and free abrasive polishing.-Description:...
(CMP), and the need to consider electro-magnetic effects using electromagnetic field solver
Electromagnetic field solver
Electromagnetic field solvers are specialized programs that solve Maxwell's equations directly. They form a part of the field of electronic design automation, or EDA, and are commonly used in the design of integrated circuits and printed circuit boards...
s. The right side icons show the more traditional hierarchy of expected TCAD results and applications: complete process simulations of the intrinsic devices, predictions of drive current scaling and extraction of technology files for the complete set of devices and parasitics.
Figure 2 again looks at TCAD capabilities but this time more in the context of design flow information and how this relates to the physical layers and modeling of the electronic design automation (EDA) world. Here the simulation levels of process and device modeling are considered as integral capabilities (within TCAD) that together provide the "mapping" from mask-level information to the functional capabilities needed at the EDA level such as compact models ("technology files") and even higher-level behavioral models. Also shown is the extraction and electrical rule checking (ERC); this indicates that many of the details that to date have been embedded in analytical formulations, may in fact also be linked to the deeper TCAD level in order to support the growing complexity of technology scaling.
TCAD Providers
Current major suppliers of TCAD tools include SynopsysSynopsys
Synopsys, Inc. is one of the largest companies in the Electronic Design Automation industry. Synopsys' first and best-known product is Design Compiler, a logic-synthesis tool. Synopsys offers a wide range of other products used in the design of an application-specific integrated circuit...
, Silvaco
Silvaco
Silvaco, inc. is a privately owned provider of electronic design automation software and TCAD process and device simulation software. Silvaco was founded in 1984 by Dr. Ivan Pesic...
and Crosslight
Crosslight Software
Crosslight Software Inc. is an international company headquartered in greater Vancouver, BC, Canada. It provides Technology Computer Aided Design tools for semiconductor device and process simulations. Crosslight Software Inc. was a spin-off from National Research Council of Canada in 1993...
. The open source GSS, Archimedes and Aeneas has some of the capabilities of the commercial products. TCAD Central maintains an information resource for available TCAD software.