High thickness material lift-off using multi-layer photoresist

Lift-off process is an alternative to deposition, lithography, and etching of materials. Lift-off is a simple and economical process because it does not require subsequent wet or dry etching. Lifting-off nanometer thick films is a well-developed and repeatable process. However, lifting-off a few micrometer thick films may be challenging. Previously, different techniques were proposed to lift-off micrometer thick films. Herein, a novel method for lifting-off high thickness materials is proposed using a multi-layer AZ 5214E photoresist. The novel method was successful in lifting-off 4 mu m thick copper while the copper could even be deposited up to 6 mu m with tri-layer AZ 5214E. With four layers of AZ 5214E, the photoresist thickness can be even thicker than 9 mu m. As detailed in the study, the photoresist layer thickness can be adjusted by varying the number of layers. This enables the selection of the appropriate number of layers to achieve the desired material thickness. To show the merits of the proposed method, the method is compared to the bi-layer method with AZ 4562 photoresist which is used for lifting-off high thickness materials. In addition to lifting-off thick materials, the proposed method is faster compared to lifting-off using bi-layer AZ 4562. Despite the ability to lift-off thick films, both methods could suffer from lift-off flags if the deposition process is not anisotropic. Solutions to remove the lift-off flags, and reduce the undercut width are demonstrated.