This review discusses the development of X-ray photoelectron spectroscopy, XPS, used as a characterization
and metrology method for ultra-thin films in the semiconductor wafer processing industry. After
a brief explanation of how the relative roles of XPS and Auger electron spectroscopy, AES, have changed
over the last 15 years or so in the semiconductor industry, we go into some detail as to what is implied by
metrology, as opposed to characterization, for thin films in the industry, and then describe how XPS, and
particularly angle resolved XPS, ARXPS, have been implemented as a metrology “tool” for thickness, chemical
composition, and non-destructive depth profiling, of transistor gate oxide material, a key requirement
in front-end processing. We take a historical approach, dealing first with the early use for SiO2 films on
Si(1 0 0), then moving to silicon oxynitride, SiOxNy in detail, and finally and briefly HfO2-based material,
which is used today in the most advanced devices (32nm node).
