Toshikazu Okubo

High-Aspect-Ratio Copper-Via-Filling for Three-Dimensional Chip Stacking II. Reduced Electrodeposition Process Time

Through-chip electrodes for three-dimensional packaging can offer short interconnection and reduced signal delay. Formation of suitable vias by electrodeposition into cavities presents a filling problem similar to that encountered in the damascene process. Because via dimensions for through-chip filling are larger and have a higher aspect ratio relative to features in damascene, process optimization requires modification of existing superconformal plating baths and plating parameters. In this study, copper filling of high-aspect-ratio through-chip vias was investigated and optimized with respect to plating bath composition and applied current wavetrain. Void-free vias 70 mu m deep and 10 mu m wide were formed in 60 min using additives in combination with pulse-reverse current and dissolved-oxygen enrichment. The effects of reverse current and dissolved oxygen on the performance of superfilling additives is discussed in terms of their effects on formation, destruction, and distribution of a Cu(I) thiolate accelerant. (c) 2005 The Electrochemical Society. All rights reserved.

Analytical Study of the Characteristics of Cu ( I ) Species for the Via-Filling Electroplating Using a RRDE

The rotating ring-disk electrode (RRDE) technique was used for investigating the characteristics of the cuprous ion Cu(I) species, which plays an important role in via-filling copper electroplating and is generated in the reaction of copper with the accelerator bis-(3-sulfopropyl) disulfide (SPS) or chloride. Cu(I) species generated during the electrochemical reactions could be detected as a current (I ring ) on a glassy carbon ring electrode. The curves of I ring vs E disk (disk potential) had a peak at a specific potential independent of the various additive concentrations in the bath. The peak height changed with the additive concentrations and the ring potential. It seemed that the peak indicates the amount of Cu(I) species generated on both the cathode and the anode and transported to the neighborhood of the cathode. When HS-(CH 2 ) 3 -SO 3 H (MPS) was added as an alternative to SPS, the peak appeared at E ring = 0.9 (V vs saturated calomel electrode, SCE) but disappeared at E ring = 0.5 (V vs SCE). It was suggested that the MPS does not form the same complexes as SPS with Cu(I) ions. The kind of Cu(I) complex as the intermediate of copper electroplating should not be single. Furthermore, the filling test applied to small trenches was done with different SPS concentrations in order to compare with the Cu(I) amount obtained from the ring-disk measurement. It was found that a higher amount of Cu(I) is not necessary for a better filling capability. This indicates that there is an optimum Cu(I) amount which accelerates only inside the via holes.