Because particulate contamination is the largest yield detractor in semiconductor fabrication, a support technology is evolving for inspecting product (patterned) wafers to identify sources of contamination. We will describe a variety of optical phenomena that are used to detect the presence of particles and some of their performance limitations. The Lloyd's mirror configuration can be used in a coincidence geometry to suppress the pattern signals; we will show performance data from a prototype of such a system. Most of the techniques we will describe rely on the particles protruding above the surrounding pattern. There are two dominant limitations to this approach. One limitation are the classes of pattern features that will be incorrectly identified as particles. The other is that semiconductor devices are becoming increasingly sensitive to particles smaller than the vertical pattern height.
J. Samuel Batchelder,
"Review Of Contamination Detection On Patterned Surfaces", Proc. SPIE 0774, Lasers in Microlithography, (1 September 1987); doi: 10.1117/12.940381; https://doi.org/10.1117/12.940381