An investigation of phosphate based ECMP electrolyte performance on feature scale planarization

Abstract

Conventional copper chemical mechanical planarization (CMP) techniques are being pushed to their limits by increasing industrial standards caused by device miniaturization and the use of new materials. There is a need to investigate alternative methods of polishing to maintain and/or improve planarization standards while operating at low downforce. In this study, electrochemical mechanical planarization (ECMP) is considered as an alternative and/or an extension to current CMP processes. ECMP is unique due to the combination of an applied voltage to oxidize Cu and an abrasion from a polishing pad, which potentially allows the system to achieve high levels of planarization through the use of an appropriately tailored electrolyte. An electrolyte containing 1.0 M potassium phosphate salt concentration with a pH value of 2 and a benzotriazole (BTA) concentration of 0.001 M was tested for its planarization capability on patterned Cu structures using a custom built ECMP tool. Feature sizes of the Cu structures were varied from 1 to 6 μm. Similar planarization results were achieved using three pad types. All experiments were performed at 0.5 V versus Ag/AgCl reference. The average step height reduction (SHR) was ~840 nm while the decrease in the average metal thickness removed (λ_avg) was on the order of ~430 nm. Because features were approximately 50% of the substrate area, the total average metal thickness removed was approximately half of the SHR for all three pad types.