PIXE: A novel technique for elemental analysis

Book Reviews

495

tive assessment of wafers by optical scattering and scanning techniques to detect surface defects, particles and dopant non-~for~ties. Also, some discussion on the new diagnostic challenges associated with the ever shrinking VLSI geometries was refreshing to see. The second section of the book concerns ion implantation technology and has seen more substantial modification. It begins with the chapter on ion sources which, while of an overview nature, can provide valuable perspective to someone trying to understand how an ion source works. This chapter has been updated slightly with an expanded discussion of the important new area of microwave sources. The chapter on ion optics and focusing has been more extensively updated and gives a nice introduction to the major considerations in the optics of transporting ion beams. The following two chapters are new and give a nice boost to the technology side by dealing with very important problems of ion implantation semiconductor processing technology. First comes a discussion of wafer cooling, Faraday design and wafer charging. These seemingly simple areas are anything but trivial in practice, where one is constantly pushing to higher beam currents, more precise implantation dose measurements, and fighting charging and breakdown problems in increasingly thin dielectrics. The chapter discusses current approaches for dealing with these problems and should be very useful for the practicing engineer or technician. By treating the nitty gritty aspects of these areas in an up-to-date, but not too detailed, way it should provide technical insight to anyone practicing ion implantation who is not already expert in these aspects. The second chapter covers the more specialized area of photoresist problems and particle #nt~ation. This additional dose of real-world problems is particularly specialized to VLSI wafer fabrication. With increasing machine currents the interaction of the ion beam with the photoresist causes such effects as outgasing requiring beam dose corrections, and photoresist damage modifying subsequent resist stripping.

Likewise, particle contamination is becoming increasingly important with more and more particles becoming killer defects as the critical feature size of integrated circuits decrease. The third in this sequence of specialized chapters is entitled diagnostics and process control, and discusses the process flow of wafers and the various tools used to diagnose VLSI processing problems at the ion implantation step. Certainly this area has become increasingly important as state-of-the-art circuits contain millions of elements, and several hundred processing steps are required to realize the final product. Problems which are not found quickly are very costly indeed. This chapter retains its primary emphasis on contour mapping of wafers via their conductivity and related properties, but now has a broader perspective. The book concludes with two chapters on implanter safety. The first one deals with the overview discussions of high voltage, radiation, and toxic substances, the major factors which can lead to accidents involving ion implantation. The last chapter then elaborates on the radiation aspects in more detail, discussing ionizing radiation emission, physical origins and sources. Also discussed are the practical aspects of generating ionizing radiation around implanters, its measurement and its reduction by accelerator tube design and shielding. These latter five chapters on practical aspects of ion implantation technology and on the safety of ion implanters provide particular motivation for the purchase of this book. These are topics which are very important to engineers and technicians in the laboratory, and yet are seldom written down in a simple and coherent fashion. Having this material available to hand to someone newly entering the ion implantation laboratory can be a real time saver, sine it can convey perspective and information usually only available by word of mouth and experience. Thus, this book offers the possibility of enhancing performance and safety in the ion implantation laboratory, and qualifies as an important tutorial book for attachment to each ion implantation facility,

PIXE. A NOVEL TECHNIQUE FOR ELEMENTAL ANALYSIS by S.A.E. Johansson and J.L. Campbell (John Wiley and Sons, Chichester and New York, 1988) pp. xii + 347, Hard cover E42.50, ISBN 0 471 92011 8

in a way which satisfies both the newcomer and the more experienced user. The scope of the book is to review the field. Naturally, a large number of pub~~tions are cited, which makes it relatively easy to enter deeper into any of the subjects. The publications cited are well chosen, and certainly among the most significant in the field. Any reader well acquainted with the PIXE literature will miss some papers in the reference lists, but because of the enormous number of published papers, a selection has to be made. The results quoted are presented in a very readable way, linked with text reflecting the large experience of the authors. Generally, reproductions are of good quality, and there are very few significant

Level: Introductory Reviewer: Niels Hertel, Aarhus

This is the first book on PIXE (Proton-Induced X-ray Emission), and is naturally met with great interest both by members of the PIXE community and by groups planning to enter the field. It is a pleasure to see that the book seems to cover the many aspects of PIXE

496

Book Reviews

errors. When errors occur, they are mostly obvious, as in fig. 8.11, in which (a) and (b) has been switched. The first 10 chapters of the book cover general aspects of PIXE, i.e. an introduction to inner shell excitations, X-ray spectra, beam handling and chamber design, sample preparation, detection limits, data analysis of specimens with varying thickness, non-vacuum PIXE and analytic fitting of PIXE spectra. These chapters give a good tr~tment of the techniques and methods developed during the ahnost 20 years PIXE has been used as an analytical tool. In each chapter the major papers on the subject are cited, and tables and figures from the cited papers are used extensively. The next five chapters treat different areas of application, biolo~/m~i~e, atmospheric science, geoscience, art and archawlogy, forensic science etc. These chapters each include a review of sampling, preparation and analysis techniques as well as several examples of applications. The next chapter of the book is on one of the most promising, new developments: Micro-PIXE, which expands the number of applications enormously, and gives entry to areas of elemental analysis not accessible with other methods, Problems such as focusing, sensitivity,

spatial resolution and applications are treated in the usual, thorough manner. The following chapter attempts to compare PIXE to other methods. This is a very difficult task, and many misleading ‘comparisons’ have been published over the years. A very large number of factors play a role in determining the choice of method. The authors of the present work have succeeded in presenting a very fair discussion of the various methods, but even so, the choice of PIXE must be judged in each individual case. Knowledge of the limitations of the many methods available is a must for anyone doing routine PIXE analysis, in order to be able to determine when, and especiaIly when nor to use PIXE. In an appendix, tables on X-ray energies, ionization cross-sections and attenuation coefficients are presented, compiled from various published and unpublished sources. Generally, the book presents the PIXE technique very well. To the newcomer, the book is an excellent way of getting well acquainted with the field, and for the more experienced user, it will serve as a handbook and guide to unexplored regions of PIXE The book is highly recommended.

MULTIPHOTGN PROCESSES edited by S.J. Smith and P.L. Knight (Cambridge University Press, Cambridge, 1988) pp. x + 365, hard cover US $54.50, ISBN 0 52135393 9

erable current interest, refers to the absorption of more than the minimum number of photons required to ionize the atom, and the progress in the understanding of such phenomena is closely related to the development of laser sources of ever increasing intensity and shorter pulse duration. Part II reports on multiphoton processes in molecules. Such studies include a ~mb~ation of fundamental investigations of molecules as we11 as applications in such areas as chemical dynamics and isotope separation. The next three sections of the book are shorter and represent special symposia covering related but somewhat special areas. These include quantized externally driven chaotic systems (III), formation and decay of multiply excited states (IV) and resonant coherent processes (V). Part VI is an overview of the current status of investigations given by a leading researcher in the field, P. Lambropoulos. The book is definitely aimed at the specialist in multiphoton processes. In that sense, it is not well-suited to students or researchers who want a broad introduction to the field. The ever-expanding number of possible applications has generally been neglected, except for some possibilities in chemical physics discussed in Part II. Particularly notable (missing) examples in this connection could be the techniques of resonant ionization spectroscopy (RIS) of atoms and the experimental studies of doubly excited states by resonant stepwise preparation. RIS offers the possibility of very high sensitivity detection of specific atomic species and thus may be

Level: Specialist Harold Haugen, Aarhus

Reuiewer:

Multiphoton processes is a field which has grown rapidly in recent years and exhibits a direct coupling to the steady advances in laser technology. The field is a broad one and has now reached a high level of maturity, as evidenced by the specificity of experiments and the breadth of applications. The present volume is the fourth in a series representing the contributions of invited speakers to the International Conference on Multiphoton Processes. The first conference was held in Rochester, New York in 1977, while the present proceedings derive from ICOMP IV held in Boulder, Colorado in 1987. As such, the book does not represent an introduction to, or even a general overview of, the field. Instead it is a collection of relatively new results in strong field-atom interactions, as well as a selection of related topics of particular interest. The book is divided into six parts, of which the first two represent the primary sections, and reflect the mainstream topics of the meeting. Part I deals with above threshold ionization (ATI) and other high intensity processes in atoms. ATI, which is a topic of consid-