Optimization of resist strip recipe for aluminum metal etch processes

This paper discusses experimental results used to develop an optimized resist strip process for an Advanced Strip and Passivation (ASP+) chamber on Applied Materials Decoupled Plasma Source (DPS) 5200 metal etch platform. The scope of the experiment is to develop a resist strip process on a new ASIC BiCMOS product. To meet tight capacity schedule, the resist removal process must be relatively short. This experiment does not look for the shortest strip time, but considered various gas flow, passivation, and strip sequences to keep the resist strip time well below the total metal etch time. A design of experiment (DOE) was run to measure the response of key recipe parameters. The parameters evaluated were strip time, passivation time, passivation and strip sequence, CF₄ flow, and temperature. The response was the amount of residual resist remaining after the strip process is completed. The result showed that temperature was the major factor in effective resist removal followed by CF₄ flow and passivation/strip sequence. A second DOE was run to verify the results and lower margin. Based on the results of the DOE, a robust strip recipe was designed and implemented in manufacturing for all metal etch processes. The new process is shorter than the metal etch process, and does not affect the throughput of the system. Also, no residual resist is found since the new recipe and post-strip inspection procedure was implemented.