Investigation from the Lithography of the Possible of Forming Less Than 8 μm Pitch Required for Advanced Packaging

In recent years, there has been a strong demand for the miniaturization of Cu wiring on package substrates using SAP technology. To meet this requirement, it has been shown that increasing the NA of lithography equipment also for back-end processes, as with front-end process, is an effective approach. However, in the back-end process, there are many situations where exposure to a relatively large area is required from the standpoint of productivity and yield, and dealing with substrate warpage and material thickness uniformity becomes an important issue. Therefore, it is essential to carefully evaluate the balance between resolution and Depth of Focus (DOF) in relation to the required wiring width. In this study, we investigated the formation of wiring with pitches of 8 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> or less, which could serve as future miniaturization targets, using two types of lenses with different resolutions. As a result, both lenses successfully formed wiring with pitches of 6 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> and 8 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mu \mathrm{m}$</tex> ‘ Furthermore, it was revealed that the process margin of the low-NA lens was consistently wider than that of the high-NA lens. These findings highlight the importance of selecting an appropriate resolution in accordance with the generational transition of wiring technology. From the perspective of lithography, this study provides valuable guidance for future process design.