Improvement of CD variation control for attenuated phase-shift mask

Abstract

As the required accuracy of the mask arises, Cr shading film thickness has been thinner gradually. CD linearity with the thinner Cr film thickness has better performance. However, it is difficult to apply thinner Cr film thickness simply under the condition of OD > 3, which is needed for wafer printing. So, we tried to develop new shading film. We adopted MoSi film, because MoSi film has almost no micro loading effect compared with Cr film. MoSi shading film with att.PSM satisfied OD > 3 at 193nm wavelength with good resist profile. But the issue was dry-etching selectivity, because shading layer material was the same of att. PSM layer material. Therefore super thin Cr etching stopper was inserted between MoSi shading layer and MoSi att.PSM layer. The mask CD performance of new blank was evaluated for CD linearity, CD through pitch, and global loading effect. This blank and mask process reduce loading effect, therefore the mask CD performance is improved remarkably. In conclusion, the mask manufacturing process margin was able to be expanded by this new blank and method, and it is expected that we can achieve the required specifications for att.PSM in 45nm node and beyond.