Sustainable solvent metal lift-off for compound semiconductor fabrication with improved manufacturability

Abstract

Due to concerns regarding substrate damage, wet photoresist removal has been adopted over dry etch techniques for certain metal lift-off processes on substrates and metals that are susceptible to plasma damage. Wet photoresist removal generally requires the use of polar aprotic solvents and historically n-methyl pyrrolidone (NMP) has been broadly adopted. A successful lift-off process requires consideration of both the solvent used to remove the photoresist as well as the correct photoresist retrograde profile. As features become smaller and more critical, the overall photoresist profile becomes more challenging. The use of bottom anti-reflective coatings (BARC) has become necessary to better control the reflected light and minimize potential defectivity during patterning. However, addition of the BARC layer complicates the resist removal process by requiring a secondary cleaning step since wet photoresist strip chemistries, such as NMP, generally do not remove it. There have been several developmental efforts in the metal lift-off industry to formulate a solvent, which could remove both photoresist and BARC, concurrently. In the first half of this paper, various wet photoresist removers are compared to determine the most effective wet resist strip for removal of both photoresist and BARC in one step. The second half of the paper summarizes two different metal liftoff processes and compares the performance of the best chemistry from initial experimentation, Technistrip® MLO-07, to NMP.