Metal corrosion and passivation swelling defect study of ultra low pattern density thick metal etch process

In thick metal process with ultra low pattern density, the defined metal line easily suffered metal corrosion defect and passivation swelling defect (can not detect Cl element) issue. Poor metal sidewall profile or the profile with much polymer remaining was the suspected root cause of metal corrosion defect. The defect showed the reliability concern, so an improved method was necessary to reduce the defect. For improving the corrosion defect, dry etch recipe and strip procedure optimization showed be the solution to reduce the defect. Dry etch recipe was the major focus because the evidence showed poor sidewall profile would trap more polymer by-product. Thus, dry etch recipe developing specially focused on metal sidewall profile improvement and polymer by-product reduction. The optimized etch recipe passed corrosion test, even at high RF hours of dry etchers. Optical microscope inspection also couldn't detect any swelling defect. All testing items including WAT (wafer acceptance test) and yield got comparable or even better result to the condition before improvement. The paper mainly described how to improve metal corrosion and passivation swelling defect. It also provided some hints to understand the two kinds of defects further.