The first edition of this book concentrated on relating scatter from optically smooth surfaces to the microroughness on those surfaces. After spending six years in the semiconductor industry, Dr. Stover has updated and expanded the third edition. Newly included are scatter models for pits and particles as well as the use of wafer scanners to locate and size isolated surface features. New sections cover the multimillion-dollar wafer scanner business, establishing that microroughness is the noise, not the signal, in these systems. Scatter measurements, now routinely used to determine whether small-surface features are pits or particles and inspiring new technology that provides information on particle material, are also discussed. These new capabilities are now supported by a series of international standards, and a new chapter reviews those documents.

New information on scatter from optically rough surfaces has also been added. Once the critical limit is exceeded, scatter cannot be used to determine surface-roughness statistics, but considerable information can still be obtained - especially when measurements are made on mass-produced products. Changes in measurement are covered, and the reader will find examples of scatter measurements made using a camera for a fraction of the cost and in a fraction of the time previously possible. The idea of relating scatter to surface appearance is also discussed, and appearance has its own short chapter. After all, beauty is in the eye of the beholder, and what we see is scattered light.

When the last edition was published, I really didn't expect another one would be written. Instrumentation was being sold that could measure down to the practical noise floor associated with Rayleigh scatter from air molecules. The math for scatter from optically smooth surfaces was understood and experimentally confirmed. Round-robin tests had been performed, finally confirming that we all spelled BRDF the same way. What else could possibly be needed? Then, I entered the semiconductor industry for several years, where signals are scatter from small isolated defects, and roughness scatter is a noise source, and realized that the book really only covered half of the scatter issues for that industry. Other industries became concerned about scatter from much-rougher surfaces (solar energy and appearance, to name two), and this opened another set of scatter-related problems. My SPIE course, which was the inspiration for the book, kept changing to keep up with industry concerns, and eventually I realized that there was material for another edition. Then, a friend told me that the book was old enough that some of his colleagues assumed I was dead, and that pushed me into action. As a result, the book you are holding has three new chapters, several new sections, and a rewrite of the older material. I expect in another decade or two that there will be enough material for yet another edition, but without serious advances in medical science as well, I doubt if I will be writing it.

Several hundred million dollars worth of scatterometers have been sold in the semiconductor industry since publication of the last edition. They are called "particle scanners" but are just scatterometers automated for beam scanning and wafer handling. As you read this, several thousands of these instruments are hard at work, and they remain so 24-7. International standards are used to support the specification of these instruments, and I was lucky enough to become involved in writing them in both ASTM and SEMI. Chapter 12 reviews scatter-related standards.

Just as we learned to model scatter from residual roughness on optics, some really smart people leaned how to model scatter from discrete surface defects. Scatter signals can now be used to determine whether that flash of light in a scanner is from a pit or a particle. Unfortunately, a lot of these models are proprietary (but not all), and there is a chapter on capabilities and availability of discrete scatter models.

Beauty is in the eye of the beholder, and, as you are well aware, what we see is scattered light. As a result, industries concerned with appearance have also learned about BRDF and its measurement. Examples are new car interiors, beer cans, and movie scenes of everything from dinosaurs to spacecraft. These kinds of problems often require full hemispherical measurement (not just incident plane scans), and array camera instrumentation has been developed. There is a new chapter on appearance (Chapter 10) and new sections involving instrumentation and scatter from optically rough surfaces.

So once again, dear scatterbrains, I am hoping you find the new edition worth my time and your (company's?) money.

John C. Stover

Tucson, Arizona

June 2012