| Popis: |
For 193 nm immersion lithography, it is hard to print clear 4X nm dense images (ex. contact holes) on wafer without any modifications due to lower light intensity. In the past, the most common method is to add the scattering bars, which can enhance the light intensity of contact holes. However, with tinier pattern, the distance between scattering bars and contact holes will get quite close. Hence, the error tolerance for mask making was reduced. On the other hand, this method may also cause the pattern twist which will induce pattern crosslink. To solve this issue, a new design method for lithography mask was proposed, which is named “Phase-shifting Scattering Bar”, and it shows better performance in 1D chain array patterns than those with traditional scattering bars. However, for even tinier patterns, it is quite difficult to put these scattering bars on mask. Hence, another special design named “Interlaced Phase-shifting Mask” was proposed to handle such tiny dense patterns. In this design, main patterns are also the scattering bars for adjacent patterns. Hence, there is no need for additional tiny scattering bars, and the mask making requirement can be also relaxed. Both of these two mask design are useful tools to trim and modify light intensity profile on wafer. The image contrast was largely enhanced which means a better resolution and a larger process window can be gained without the cost of new illumination equipments. |
