구리 ECMP에서 전류밀도가 재료제거에 미치는 영향

Abstract

Dept. of Mechanical Engineering, Northeasten University(Received November 30, 2014; Revised March 25, 2015; Accepted April 10, 2015)Abstract − RC delay is a critical issue for achieving high performance of ULSI devices. In order to minimizethe RC delay time, we uses the CMP process to introduce high-conductivity Cu and low-k materials on the dam-ascene. The low-k materials are generally soft and fragile, resulting in structure collapse during the conventionalhigh-pressure CMP process. One troubleshooting method is electrochemical mechanical polishing (ECMP)which has the advantages of high removal rate, and low polishing pressure, resulting in a well-polished surfacebecause of high removal rate, low polishing pressure, and well-polished surface, due to the electrochemical accel-eration of the copper dissolution. This study analyzes an electrochemical state (active, passive, transpassive state)on a potentiodynamic curve using a three-electrode cell consisting of a working electrode (WE), counter elec-trode (CE), and reference electrode (RE) in a potentiostat to verify an electrochemical removal mechanism. Thisstudy also tries to find optimum conditions for ECMP through experimentation. Furthermore, during the low-pressure ECMP process, we investigate the effect of current density on surface roughness and removal ratethrough anodic oxidation, dissolution, and reaction with a chelating agent. In addition, according to the Faraday’slaw, as the current density increases, the amount of oxidized and dissolved copper increases. Finally, we confirmthat the surface roughness improves with polishing time, and the current decreases in this process.Keywords −electrochemical mechanical polishing(전기화학 기계적 연마), potentiodynamic curve(변전위 곡선),passivation layer(부동태 층), current density(전류밀도), material removal rate(재료제거율)