Simulation predicts that NTD resist profiles should often have retrograde sidewall angles due to the attenuation of light as it propagates down through the resist. Resist shrinkage induced from both the de-protection during PEB and from exposure to electrons during SEM can cause CD and sidewall changes. The interplay between the shrinkage and the retrograde sidewalls is discussed.
Deprotection-induced shrinkage is measured by AFM while SEM induced shrinkage is estimated from repeated SEM measurements. SEM images for various features are analyzed and compared to simulation.