Characteristics of sputtered TaX absorbers for x-ray mask

The materials of x-ray absorbers for x-ray mask have been changed from gold (Au) and tungsten-based alloys to tantalum (Ta) and Ta-based compounds in x-ray lithography (XRL). Different candidates of x-ray absorber, especially Ta-based (TaX) compounds, were sputtered and evaluated in this study. By incorporating silicon or germanium into tantalum, amorphous TaSi-based and TaGe-based compounds were formed and qualified as the absorber materials. Because the reproducibility of as-deposited stress by tuning the sputtering parameters is not so well for these compounds right after sputtering, we utilized the step annealing by RTA to control the stress such that within ± 20 MPa is obtainable. Furthermore, with N 2 plasma treatment in PECVD chamber the slope of stress with respect to annealing temperature is smaller and posses good stability after longtime exposure to the air. Finally, the etching properties of TaX compounds were compared with and without trilayer structure of oxide/absorber/oxide. And, 0.35 μ m patterns are etched successfully with vertical sidewall by Cl 2 etchant.