Page 103 - DLIS402_INFORMATION_ANALYSIS_AND_REPACKAGING

Information Analysis and Repackaging

Notes 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 modelling 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 modelling tools—finds its roots in bipolar 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 re emerge as a controlling factor in future IC technology as well.
Process control issues—both for the intrinsic devices and all the associated parasitic—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 modelling 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
modelling (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[8]; 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
modelling 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).

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