Page 17 - Sami Franssila Introduction to Microfabrication

xvi Preface

Older textbooks present microfabrication as a tool- covered but from the very beginning, the discussion
box of MEMS or as the technology for CMOS centres on wafers and structures on wafers: therefore,
manufacturing. Both approaches lead to unsatisfac- silicon wafering process, and resulting wafer properties
tory views on microfabrication. Ten years ago, chemi- are emphasized. Epitaxy, CVD, PVD, spin coating and
cal–mechanical polishing was not detailed in textbooks, electroplating are discussed, with resulting materials
and five years ago discussion on CMP was included properties and microstructures on the centre stage, rather
in multilevel metallization chapter. Today, CMP is a than equipment themselves. Lithography and etching
generic technology that has applications in CMOS front- then follow. This order of presentation enables more
end device isolation and surface micromechanics, and is realistic examples to be discussed early on.
used to fabricate photonic crystals and superconducting The basic steps in silicon technology, such as oxida-
devices. It therefore deserves a chapter of its own, inde- tion, diffusion and ion implantation are discussed next,
pendent of actual or potential applications. Similarly, followed by CMP and bonding. Moulding and stamp-
wafer cleaning used to be presented as a preparatory step ing techniques have also been included. In contrast to
for oxidation, but it is also essential for epitaxy, wafer older books, and to books with CMOS device empha-
bonding and CMP. Device-view, be it CMOS or some sis, this book is strong in back-end steps, thin films,
other, limits processes and materials to a few known
etching, planarization and novel materials. This reflects
practices, and excludes many important aspects that are
the growing importance of multilevel metallization in
fruitful in other applications.
ICs as well as the generic nature of etch and deposi-
The aim of the book is for the student to feel
tion processes, and their wide applicability in almost
comfortable both in a megafab and in a student lab. This
all microfabrication fields. Packaging is not dealt with,
means that both research-oriented and manufacturing-
again in line with wafer-level view of microfabrication.
driven aspects of microfabrication must be covered. In
order to keep the amount of material manageable, many This also excludes stereomicrolithography and many
things have had to be left out: high density plasmas are miniaturized traditional techniques like microelectrodis-
mentioned, but the emphasis is on plasma processing in charge machining.
general; KOH and TMAH etching are both described, Microfabrication is an engineering discipline, and
but commonalities rather than differences are shown; volume manufacturing of microdevices must be dis-
imprint lithography and hot embossing are discussed but cussed. Discussions on process equipment have often
polymer rheology is neglected; alternatives to optical been bogged by the sheer number of different designs:
lithography are mentioned, but discussed only briefly. should the students be shown both 13.56 MHz diode
Emphasis is on common and conceptual principles, and etcher, triode, microwave, ECR, ICP and helicon plas-
not on the latest technologies, which hopefully extends mas, and should APCVD, LPCVD, SA-CVD, UHV-
the usable life of the book. CVD and PECVD reactors all be presented? In this
book, the process equipment discussion is again tied
to structures that result on wafers, rather than in the
STRUCTURE OF THE BOOK equipment per se: base vacuum interaction with thin-
film purity is discussed; the role of RTP temperature
The structure of this book differs from the traditional
uniformity on wafer stresses is considered; and surface
structure in many ways. Instead of discussing individual
reaction versus transport controlled growth in different
process steps at length first and putting full processes
CVD reactors is analysed. Cleanroom technology, wafer
together in the last chapter, applications are presented
throughout the book. The chapters on equipment are fab operations, yield and cost are also covered. Moore’s
separated from the chapters on processes in order to law and other trends expose students to some current
keep the basic concepts and current practical implemen- and future issues in microfabrication processes, materi-
tations apart. als and applications.
The introduction covers materials, processes, devices In many cases, treatment has been divided into
and industries. Measurements are presented next, and two chapters: for example, Chapter 5 treats thin film
more examples of measurement needs in microfabrica- basics, and Chapter 7 deals with more advanced topics.
tion are presented in almost every chapter. A general Lithography and etching have been divided similarly.
discussion of simulation follows, and more specific sim- This enables short or long course versions to be designed
ulation cases are presented in the chapters that follow. around the book. The figures from the book are available
Materials of microfabrication are presented next: to teachers via the Internet. Please register at Wiley
silicon and thin films. Silicon crystal growth is shortly for access www.wileyeurope.com/go/microfabrication.