The influence of ultrasonic agitation on copper electroplating of blind-vias for SOI three-dimensional integration

Three-dimensional (3D) integration, which employs through-silicon-vias (TSVs) to electrically interconnect multiple-stacked chips, is a promising technology for significant reduction in interconnect delay and for hetero-integration of different technologies. To fabricate void-free TSVs, this paper presents a copper electroplating technique with the assistance of ultrasonic agitation to fill blind-vias, and discusses the influence of ultrasonic agitation on copper electroplating. Blind-vias with an aspect ratio of 3:1 are used for copper electroplating with both direct current (DC) and pulse-reverse current modes, combined with either ultrasonic agitation or mechanical agitation. Experimental results show that blind-vias with small aspect ratio can be completely filled using pulse-reverse current, regardless of the agitation methods. For DC, ultrasonic agitation is superior to mechanical agitation for copper electroplating in filling void-free vias. These results indicate that agitation, though is a secondary control factor to pulse-reverse current, can enhance mass transfer in blind-vias during copper electroplating and can improve the filling capability of copper electroplating.