습식 전해 증착을 통한 관통-실리콘-비아(TSV) 배선공정 연구

Abstract

In the semiconductor industry, significant improvement in the shrinkage of Cu interconnection was achieved to increase the performance of semiconductor devices and follow the Moore`s road map. However, it will be discarded due to physical and economical limitations, and will select the various creative methods to achieve the continuous development in semiconductor devices. 3D chip staking was one of most candidates for integrating the semiconductor device, and the through-Si-via (TSV) interconnection was most advanced technology in 3D interconnection. In this dissertation, Cu TSV interconnection process was systematically investigated to attain both the fast TSV filling rate and control of Cu microstructure in the TSV together. Firstly, TSV filling with pulse wave form currents was focused. Pulse current with low frequency was unacceptable in the TSV filling process, because a highly acidic electrolyte attacked the seed layer and Cu deposit obtained with low current efficiency during comparably longer off time period. An increased frequency critically enhanced the filling rate of Cu, which was mainly related to the improvement of the current efficiency and lower dissolution rate. Various methods for improving the pulse current were investigated. Off time was substituted to reverse time to accelerate the relaxation of ion depletion, but the desorption of suppressor was occurred. In order to induce the re-adsorption of suppressor, additional off time period was applied. In order to eliminate the substitution between the accelerator and suppressor, TSV filling with using the suppressor as only additive in the electrolyte was investigated. The influence of suppressor concentration on Cu deposition was investigated by cyclic-voltammetry (CV) to measure saturation, desorption, and re-adsorption. The CV results and TSV filling behavior were matched to understand the role of the suppressor in TSV filling. Bottom-up Cu filling behavior in the TSV could be simply controlled by changing the suppressor concentration and current density. TSV filling progress was linear over time in specific conditions, though the potential-time response during the TSV filling process changed dynamically with bottom-up filling sequence. TSV filling performance was significantly improved by accepting the single additive bath with the pulse wave form current, because the controlled ion depletion enhanced suppression at the top surface. In pulse conditions, high density nanoscale twin structure was observed, which were caused by induced stress during the on time because of high peak current density. Application of pulse deposition reduced thermal extrusion of Cu that was related to the advanced mechanical property of the nanotwin Cu. Influence of pre-annealing on the microstructure and thermal extrusion of TSV was also investigated.