guiding_light
19th June 2006 - 03:27 PM
http://www.physorg.com/news3804.html Thin photoresists are required for mechanical stability of fine features. Too high an aspect ratio leads to collapse. However, a thinner film absorbs fewer photons. Hence the image recorded in these layers is more rough, susceptible to line-edge roughness (LER).
guiding_light
23rd January 2007 - 08:07 AM
There is a rule of thumb that 1% of the incident light is absorbed every 10 nanometers of depth into photoresist. In a 10 nm cubic volume that can be very few photons (maybe a few hundred). The resulting dose variation from Poisson statistics alone can be significant (>10%).