고전류밀도에서 첨가제에 따른 구리도금의 표면 특성 연구
The Effect of Additives on the High Current Density Copper Electroplating
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초록
전류밀도는 전기도금법에서 생산성과 직접적인 연관이 있고, 생산성의 증가를 위해선 고전류밀도가 필요하다. 회전전극(RDE)의 회전 속도를 증가시키면 고유속을 얻을 수 있다. 유속 조절을 위해 회전전극과 원통형 회전 전극을사용하였고, 전압과 전류의 관계를 알아보기 위해 정전류, 정전압 실험과 linear sweep voltammetry 실시하였다. 회전 전극의 회전 속도가 400 rpm이상 조건에서, 수소가 발생하지 않고 1000 A/m²이상의 최대전류밀도가 가능하였다. 25℃와62℃ 조건에서 구리의 확산계수는 각각 5.5×10^(-6)cm² s^(-1) 와 10.5×10^(-6)cm² s^(-1)로 계산되었다. 수소가 발생하지 않으면서안정적으로 구리를 전착할 수 있는 조건은 -0.05 V (vs Ag/AgCl)이었다. 첨가제인 glue와 thiourea를 넣음으로써 구리의침상성장을 막을 수 있었다. 표면 거칠기는 UV-Vis Spectrophotometer를 이용하여 분석되었다. 600 nm 영역에서 반사도는 측정 되었고 표면 거칠기가 개선될수록 표면 반사도가 증가하였다.
Abstract
The current density in copper electroplating is directly related with the productivity and then to increase the productivity, the increase in current density is required. To obtain the high mass flow rate, rotating disk electrode(RDE)was employed. High rotational speed in RDE can increase the mass flow rate and then high speed electroplating was possible using RDE to control mass flow. Two types of cathode were used. One is RDE and another is rotating cylindrical electrode(RCE). A constant-current, constant-voltage and linear sweep voltammetry were applied to investigate current and voltage relationship. The maximum current density without evolution of hydrogen gas was increased with rotational speed. Over 400 rpm, maximum current density was higher than 1000 A/m². The diffusion coefficients of copper calculated from the slope of the plots are 5.5×10^(-6)cm² s^(-1) at 25℃ and 10.5×10^(-6)cm² s^(-1) at 62℃. The stable voltage without evolution of hydrogen gas was -0.05 V(vs Ag/AgCl). Additives were added to prevent dendritic growth on cathode deposits. The surface roughness was analyzed with UV-Vis Spectrophotometer. The reflectance of the copper surface over 600 nm was measured and was related with the surface roughness. As the surface roughness improved, the reflectance was also increased.
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