Optical modeling and resist metrology for deep-UV photolithography

摘要

This thesis first presents a novel and highly accurate methodology for investigatingthe kinetics of photoacid diffusion and catalyzed-deprotection of positive-tonechemically amplified resists during post exposure bake (PEB) by in-situ monitoring thechange of resist and capacitance (RC) of resist film during PEB. Deprotection convertsthe protecting group to volatile group, which changes the dielectric constant of resist. Sothe deprotection rate can be extracted from the change of capacitance. The photoaciddiffusivity is extracted from the resistance change because diffusivity determines the rateof change of the acid distribution. Furthermore, by comparing the R and C curves, thedependence of acid diffusivity on reaction state can be extracted. The kinetics ofnon-Fickean acid transportation, deprotection, free volume generation andabsorption/escaping, and resist shrinkage is analyzed and a comprehensive model isproposed that includes these chemical/physical mechanisms.Then in this thesis a novel lithographic technique, liquid immersion contactlithography (LICL) is proposed and the simulations are performed to illustrate its main features and advantages. Significant depth-of-field (DOF) enhancement can be achievedfor large pitch gratings with deep-UV light (????=248nm) illumination with both TM andTE polarizations by liquid immersion. Better than 100nm DOF can be achieved by whenprinting 70nm apertures. The simulation results show that it is very promising to applythis technique in scanning near field optical microscopy.Finally, a rigorous, full vector imaging model of non-ideal mask is developed andthe simulation of the imaging of such a mask with 2D roughness is performed. Line edgeroughness (LER) has been a major issue limiting the performance of sub-100nmphotolithography. A lot of factors contribute to LER, including mask roughness, lensimperfection, resist chemistry, process variation, etc. To evaluate the effect of maskroughness on LER, a rigorous full vector model has been developed by the author. Wecalculate the electromagnetic (EM) field immediately after a rough mask by usingTEMPEST and simulate the projected wafer image with SPLAT. The EM field and waferimage deviate from those from an ideal mask. LER is finally calculated based on theprojected image.