Process monitoring and surface characterization with in-line XPS metrology

Patterning of contact layers with minimal half pitch below 90nm has proven to be a very difficult task. in general, difficulties in contact patterning are driven by the low depth-of-focus (DoF) toward isolated contacts and/or the higher mask error enhancement factor (MEEF) for denser contact arrays. As for the illumination source shape, the traditional choice is between conventional illumination and off-axis illumination (OAI). Recent results obtained at IMEC on immersion scanners at 1.2 and 1.35 numerical aperture (NA), however, show that combined illumination sources, called Soft Annular and Soft QUASAR, are advantageous for through-pitch contact printing, in terms of MEEF and process latitude, without the use of assist features.