An Investigation On Key Processes Of Lift-off Technology For MEMS Application

Lift off technology is an important part of MEMS device manufacturing technology.Its basic processes are photolithography,metal thin film deposition and removing the photoresist in the solvent which does not corrode the metal thin film.The metal which is on the photoresist will be stripped as the photoresist is removed,and then the required metal is shaped.This paper studies several major defects in lift off process,and analyzes the reasons of them,and then adjusts and optimizes the various processes of lift off process through the study of the process experiment.We did an analysis of the causes of red mark defect on silicon surface,and then adjusted and optimized the cleaning step of stripping process,completely solved the defect by adding an IPA cleaning step.The reason for the retention defect was found in the stripping process of standardization.This defect was solved through the process optimization.The reason for the re-deposition defect was also analyzed and expounded.This defect was eliminated by adding a water gun flushing steps after the sonication stripping step.We studied the causes of the retention defect on wafer edge,and fundamentally solved this defect through optimized coating step of photo process.We analyzed the reason of the ears defect basic on the principle of negative photoresist.It was got that a good photoresist down "8" shape appearance through the adjustment and optimization of the exposing and developing step of photo process.And then,we enhanced the thermal stability of the photoresist by improved the temperature and increased the time of baking step,so that it can withstand high temperatures without deformation;Finally,with the adjustment and optimization of the sputtering process,the ears defects was solved.Ultimately,we have achieved a perfect product appearance and greatly improved the yield of the product through by the adjustment and optimization of all above steps.