We demonstrate a superpolishing electrolyte, which consists of acid additives in conventional Cu polishing electrolytes (H 3 PO 4 ), for efficiently planarizing Cu damascene features. The significant additive concentration gradient in features, resulting in a selective Cu dissolution rate within features, is explored as a major mechanism that yields such electrolytes with high planarization efficiency. Moreover, another additive, polyethylene glycol as a suppressor, is also employed to reduce oxygen bubbling on polished films. Consequently, a smooth surface with a complete step height elimination is obtained in a 70 m trench after electropolishing.Chemical mechanical polishing ͑CMP͒ of Cu and barrier metals is widely recognized as the most promising technology for planarizing Cu damascene interconnects. 1-4 However, conventional Cu-CMP slurries contain mechanically hard abrasives that scratch and damage polished Cu surfaces. Recently, Cu electropolishing has been explored as a replacement of Cu-CMP due to its higher polishing rate, lower waste stream, no scratching, and no mechanical stress on substrates. TSMC company announced CMP-free and CMP-less approaches by integrating Cu electropolishing. 5 Sony company announced a 25 m wide line formed by soft polishing technology. 6 They used a complexing agent to block Cu surface and introduced a soft pad to remove Cu complex outside of pattern, thereby producing selective electrochemical dissolution.Cu electroplating generally produces a step on/between damascene features after deposition. Moreover, planarization efficiency ͑PE͒ of Cu electropolishing is a strong function of the feature size ͑also for Cu CMP͒. 7,8 Those issues necessitate additional modifications to conventional polishing techniques. Because Cu dissolution rate depends on the pH value of polishing electrolytes and increases with solution conductivity, an addition of acid additives into polishing electrolytes can enhance Cu removal rate. Based on this mechanism and additive distributions controlled in diffusion limit, a presence of concentration gradient of additives in damascene features forms a selective electrochemical dissolution, thus enhancing step height reduction and improving PE of Cu electropolishing. In this article, we demonstrate a superpolishing electrolyte with high PE by adding acid additives into the polishing electrolyte (H 3 PO 4 ). Additionally, oxygen formation during Cu electropolishing often causes severe etched pits on polished surfaces. With polyethylene glycol ͑PEG͒ as a suppressor in the electrolyte, the overpotential of oxygen formation is significantly elevated, thus leading to less damage on polished surfaces. A polishing electrolyte with those additives can planarize damascene interconnects even with feature sizes in several tens of micrometers.
ExperimentalThe patterned wafer used in PE measurements was composed of a 30 nm thick ionized metal plasma ͑IMP͒-TaN layer as the diffusion barrier, a 200 nm thick IMP-Cu film as the seed layer, and a 1.7 m electroplated Cu as the ...
