Lift-off resist processing has been used for a variety of applications as a way of patterning metal layers using additive deposition methods. Many different processes have been used for this purpose, each involving either single or multiple layers of resist which are processed to form a reentrant profile. In this study, we examine two specific applications where lift-off processing is especially challenging. In the first case, a high resolution i-line lift-off process was needed for an application having severe surface topography caused by thick surrounding ohmic structures. Conventional bi-layer resist processing provided poor critical dimension control due to adjacent reflective surfaces and swing effects caused by resist thickness non-uniformity. A solution was found by incorporating a developable anti-reflective coating into the resist stack to reduce reflectance and resulting swing effects. The result was a lift-off process with high resolution used to image gate trenches over severe topology with critical dimension control maintained. The second application involved creating a T-gate profile using conventional optical lithography methods and modern positive DUV resists. Problems related to interlayer mixing and dissolution were overcome by introducing a photostabilization process to harden the stem layer and maintain its fidelity during the coating of subsequent resist layers. The result was an all optical, positive DUV tri-layer resist stack performed using two separate optical exposures, which produced a 200 nm T-shaped gate structure.

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