EUV Resist Requirements: Absorbance and Acid Yield

摘要

The challenge in obtaining good resist performance in terms of resolution, line width roughness and sensitivity at EUV wavelength forces to make more efficient use of photons that reach the wafer plane than has been the case for traditional optical lithography. Theory demonstrates that the current absorbance levels of EUV resists are quite far from optimal and absorbance should be increased. The most attractive pathway to achieve this is by increasing the fluorine content of EUV resists. The viability of this approach has been demonstrated using non-chemically amplified PMMA as model resist and comparing its photospeed with a fluorinated analogue. It has been demonstrated that the photospeed increases due to improved resist absorbance by ～1.5X, which is close to 1.7X that is predicted by the difference in absorbance. Further modeling studies support the experimental results and indicate an optimum for total film absorbance of ～0.20-0.25. Compared to current platforms this would correspond to an increase in photospeed by ～1.7X which is accompanied with an improvement in LWR of ～ 1.14X. Combining this approach with the trends in EUV resists to increase PAG loading and include sensitizer in order to improve photospeed will likely provide a path for EUV resists that will meet the specifications that are required for the 32nm and 22nm node.