Investigation of the Mechanism and Critical Parameters for the Lift-Off Lithography Process with Negative Photoresist

The lift-off process offers a reliable approach for achieving designed patterns in semiconductor manufacturing. This study investigates the application of a negative photoresist-based lift-off process for pattern transfer of a 380 nm-thick Cr/Au layer. The underlying mechanism and critical parameters of the lithography process, such as soft bake temperature, exposure energy, exposure gap, and post-exposure bake (PEB) temperature, were investigated in detail. Undercut morphology, undercut width, post-development defects, and photoresist morphology after metal evaporation were characterized. Experimental results show that these parameters critically affect the exposure process by controlling the concentration and distribution of photo-acid generators in the photoresist, thereby defining the final undercut morphology. Furthermore, the study outlines a methodology for varying process parameters to define the process window and identify optimal conditions. It was confirmed that the morphology and width of the developed undercut are crucial to a successful lift-off, and an undercut width of at least 3.00 µm is required to ensure satisfactory outcomes.