Influence of ArF Resist Components and Process Conditions on the PEB Sensitivity

Abstract

Control of the critical dimension (CD) during photo lithographic process is becoming more and more critical as the CD size decreases and wafer size increases. Among other factors, PEB (post-exposure bake) sensitivity [ΔCD(nm) /ΔTemp(°C)] of photoresists plays an important role in achieving uniform CD. ArF resists are the preferred materials for the critical layers in the 90 and 65 nm nodes where in the CDs are less than 100 nm. The influence of resist components such as type of PAG, solvent, and blocking ratio as well as the processing conditions were investigated in the ArF resist formulations. It was observed that almost all the resist components influence the PEB sensitivity. Use of bulky and long chain sulfonic acids such as perfluorooctane sulfonic acid, low blocking ratio and low boiling solvents reduce the PEB sensitivity but at the expense of other resist properties such as resolution and line-edge roughness (LER). As expected the cation type of the photoacid generators (PAGs) did not show any effect on the PEB sensitivity. On the processing side, lowering PEB temperature and increasing soft bake (SB) temperature help improve the PEB sensitivity but the LER becomes worse. Results of these studies along with the performance of some of the optimized ArF formulations are presented.