Line edge roughness (LER) is one of the most important issues in sub-100 nm lithography. We have designed and implemented an experiment to study the coupled effect from acid depletion and percolation property of development process of Chemically Amplified Resist (CAR) on Line Edge Roughness (LER). The resist selected is UV-5 (a positive tone CAR from Shipley), known to be fairly sensitive to acid loss. After development, the resist is analyzed using high-resolution SEM (LEO 1550 VP), and an in-house made software is used for LER measurements. Our results indicate that the effect on LER and Critical Dimension (CD) variation depends on image modulation, and that aggressive lithography (low modulation image) will be more sensitive to the environment. In addition, it is shown that percolation development with stochastic energy deposition model can explain all the observed phenomena. (c) 2005 American Vacuum Society.