We investigated microstructures, i.e., textures and grain sizes, which affect reliability and resistivity of through-silicon via (TSV). We used electron backscattering diffraction to clarify the textures and grain sizes in the copper TSV depth direction in specimens made from an 8-in. wafer with copper plating times of 60, 90, and 240 min. Textures for the three types of TSV specimens were random throughout the depth direction. Average grain size differed among top, middle and bottom regions, and decreased in the order, middle > bottom > top for 60 and 90 min plating specimens. Grain size dependence on the shortening of plating time was small. Three-dimensional LSI chip stacking has been studied for high density packaging and high speed performance, because the high aspect ratio of through-silicon via (TSV) allows short interconnects and reduces signal delays. 1,2 Copper (Cu) has been selected for plating the TSV because of its good compatibility with multilayer interconnects in LSIs.Cu electroplating at a high aspect ratio TSV takes much time, and hence it occupies almost 40% of the total TSV cost. 2 In order to lower the process cost, shortening of electroplating time has been investigated. Several groups 1,3-5 reported that they realized a short time plating for the TSV with dimensions of 10 lm diameter and 70 lm depth in 37-60 min under the optimum periodical pulse current application and with oxygen bubbling.However, microstructures, like grain sizes, textures, and grain size distributions both in Cu films and interconnects, have been reported to exert a marked influence on the resistivity and reliability for electro-migration. 6-8 The resistivity decreases with the increase of average grain size 8 and preferred orientation. The electro-migration resistance also increases with the increase of average grain size and preferred orientation, and the decrease of grain size distribution. 6-8 Therefore, it is natural to think that grain sizes, textures and grain size distributions in addition to voids or seams may cause serious problems in reliability 6,7 for electro-migration and resistivity 8 of future TSVs with much higher aspect ratios. Therefore, it is very important to investigate how microstructures change by shortening the plating time from the viewpoints of reliability and resistivity.In this study, we investigated grain sizes and textures at the top, middle, and bottom regions of high aspect ratio TSVs of 10 lm diameter and 70 lm depth as a function of Cu plating time from 60 to 240 min to clarify how these microstructures change by shortening the electroplating time.
ExperimentalThe detailed bath composition is shown in Table I. The basic bath consisted of CuSO 4 Á5H 2 O and H 2 SO 4 . The additives were Cland EPITHAS EWF-S. EPITHASEWF-S was supplied from C. Uyemura & Co., Ltd.Plating times to fill the high aspect ratio TSVs of 10 lm diameter and 70 lm depth in specimens made with an 8-in. wafer were changed by varying flow rate of electrolyte, peak current density, and duty. Uniform filling was realized...