Voltage pulse-modulated electrochemical removal of copper surface layers using citric acid as a complexing agent

Voltage induced removal of surface layers from wiring lines is an essential component of the electrochemical mechanical planarization (ECMP) technique used for low-pressure processing of copper interconnects. Our present work examines citric acid as a complexing agent for controlling such electro-dissolution of Cu (disc samples) in the absence of mechanical polishing by using voltage pulse modulation. It is shown that the electrochemical rate of Cu removal in low-pH H2O2 based citric acid solutions can be maintained at a substantial level without using mechanical abrasion and by applying relatively low activation voltages. These specific features of the citric acid electrolyte may help to avoid strong diffusion limited effects and voltage induced decomposition of ions in ECMP of Cu. Possible contributions of faradaic and nonfaradaic reactions to Cu removal in this system are discussed.