Analysis of Lithographic Alignment and Via Definition Challenges in Multilayer TMR Fabrication Processes

The fabrication of TMR devices involves several microfabrication steps, where lithography and layer alignment play a fundamental role in the proper definition of the structures. In this work, the main challenges of lithographic alignment and via definition were investigated in a multilayer fabrication process for TMR devicesFirstly, X-shaped and Plus-shaped alignment marks were tested using different alignment strategies.

The quality of the alignment was evaluated by overlay measurements, taking into account the total offset and its components in the X and Y directions. The results showed that the lowest total overlay offset was obtained for condition X3, with a value of 0.512 µm, although geometry-dependent variations were observed. The error in the X direction was reduced to 0.526 µm by using the Plus-shaped mark with offset correction, demonstrating the importance of directional overlay analysis.

Then, lithographic parameters such as development time, focus offset and exposure dose were investigated. The quality of the via opening was quantitatively evaluated by classifying the vias as closed, partially open and fully open. The best observed condition was obtained using 20 s of pre-development, 60 s of development, an exposure dose of 50 mJ/cm² and a focus offset of 2V. This condition produced a total overlay offset of 0.949 µm and 68.75% fully open vias.The results demonstrate that via definition in multilayer TMR fabrication depends on the combined optimization of alignment, development, focus and exposure conditions.