Post Exposure Bake Sensitivity Research Articles

Global critical dimension uniformity improvement for mask fabrication with negative-tone chemically amplified resists by zone-controlled postexposure bake

The multizone hotplate approach of the APB5500 bake system achieves temperature uniformity significantly superior to conventional bake tools, resulting in unmatched global critical dimension (CD) uniformity from the postexposure bake (PEB) process. Progress toward 65-nm next-generation lithography, however, requires the application of negative-tone chemically amplified resists (nCARs) like NEB22. This nCAR is characterized to show a strong sensitivity to postexposure delay (PED) in vacuum during electron-beam writing of 0.5 nm/h, and also a strong PEB sensitivity of 7.8 nm/°C, both resulting in systematic CD errors. These CD errors are compensated with the APB5500 bake system during PEB by automatically applying an appropriate nonuniform temperature profile. This temperature profile is calculated by an algorithm considering the resist and mask heat transfer properties. A CD uniformity improvement from 8.9 to 6.7 nm total range (25%) on a state of the art production mask is achieved.

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

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.