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HANDBOOK OF THIN-FILM
DEPOSITION PROCESSES AND
TECHNIQUES
Edited by
Krishna Seshan
Intel Corporation
Santa Clara, California
Foreword
Gordon E. Moore
Increasingly any references to the current technology for the manufacture
of integrated circuits as “semiconductor technology” is a misnomer.
By now the processing relating to the silicon itself contributes
relatively few steps to the total while the various processes associated with
the deposition and patterning of the increasing number of metal and
insulating films have grown in importance. Where the first metal-oxidetransistor
circuits of the 1960’s took five masking steps to complete, and
even early silicon-gate circuits with single metal layer interconnections
took only seven, modern circuits with as many as six layers of metal take
well in excess of twenty. Not only are there more layers, but the composition
of those layers is often complex. Metal conduction layers might require
barrier films to prevent inter-diffusion or to enhance adhesion. Insulators
not only isolate circuit elements electrically, but are used to prevent ions
from harming the electrical properties of the transistors. In fact, if the
technology for integrated circuit manufacture as practiced today were
named for the majority of the processing steps, the technology could
probably be more accurately described as thin-film technology.
Consistent with this change, the processing for the deposition and
patterning of films has received major research and engineering emphasis
and has evolved rapidly over the last few decades. Where in the ’60’s,
thermal oxidation or vapor deposition was sufficient for the insulators and
evaporation or sputtering of aluminum took care of the needs for conductors,
a large variety of sophisticated deposition techniques have grown with
the industry. Today one can control both the electrical and mechanical
properties while achieving uniform and reproducible films from a few
atomic layers thick to several micrometers. The chemistry and physics of
the films are becoming increasingly better understood, but as they are, the
demands of the device designer become more stringent. For example,
where the dielectric constant of silicon oxide-based insulators was accepted
as a design parameter to live with for thirty years or so, capacitance
associated with interconnections now can be a real limitation on circuit
performance. Designers want an insulator with all the good properties they
have come to love with SiO2, but with a dielectric constant as close to that
of a vacuum as possible. Similarly, with conductors no one will be happy
until we have room temperature super-conducting films in multi-layered
structures.
The simple furnaces and evaporators of yesteryear have become
multi-chamber creations of stainless steel that allow a series of processes
to be done without exposing the work to air. The lithography machines for
creating the desired precise and fine-scaled patterns now cost several
million dollars each as the industry pushes the limits of optical systems in
the continuing pursuit of performance and small size. The cumulative
investment in developing and improving processes must exceed a hundred
billion dollars by now. Such a huge investment of money and technical
talent has created a vast amount of knowledge, much of which is summarized
in this volume.
The film technology developed primarily for the silicon integrated
circuit industry is finding its way into several other areas of application. It
has become a general technology for designing and constructing complex
structures, layer-by-layer. Micro-electromechanical devices (MEMs) use
the same deposition and patterning techniques. Micro-fluidic gadgets with
micro-sized pipes, valves and all the plumbing necessary to make tiny
chemical factories or analytical laboratories are increasingly important, and
again use the film technologies that grew up around semiconductor integrated
circuits. Even the gene chips the biotech industry uses to speed up
their analysis come from the same bag of tricks.
This book takes a snapshot of the state of the art in various
technologies relating to thin films. It brings together in one convenient
location a collection of the research results that have been gathered by
many groups over the last few decades. It will be something that the
concerned engineer will return to time after time in the course of his or her
work. This is the forefront of science and process engineering with
important bearing on many modern industries.
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