The effective control of Cu through-silicon via extrusion for three-dimensional integrated circuits by a metallic cap layer

The Effect of Pitch Distance on the Statistics and Morphology of Through-Silicon Via Extrusion

“…All the vias measured and used in the statistical analysis were located away from the free edge of the sample. The extrusion morphology was analyzed using the Gwyddion modular program [25] and the average extrusion and maximum extrusion of each via were obtained using a method described elsewhere [8]. Since maximum extrusion is the most pertinent to device reliability, analysis and discussion in the rest of the paper would be focused on the maximum extrusion.…”

“…Not only would the statistical variation of via extrusion be detrimental to the reliability of a 3D IC, the change of extrusion due to pitch distance would also be undesirable in a 3D IC that contained vias with different pitch distances. Previously, we have demonstrated that a cap layer was effective in reducing the magnitude and variation of Cu extrusion [8], [17]. The effect of a cap layer on the extrusion behaviors of vias with different pitch distances was investigated herein.…”

“…The stress demonstrated in FEA drove plastic deformation near the top of the via to manifest as via extrusion. Under the test conditions, several deformation mechanisms were known to be operative in the TSVs, including dislocation glide and climb, creep and grain boundary sliding accommodated by grain boundary diffusion, and interfacial sliding [8], [11], [18], [29]. Depending on the microstructure of the via and the stress it was subjected to, one or more mechanisms could dominate to result in the observed morphology and height variations.…”

“…The effect of a cap layer on the extrusion behaviors of vias with different pitch distances was investigated herein. A set of small-pitch and large-pitch samples identical to those described in section II were coated with 50nm of tantalum (Ta) using a procedure reported elsewhere [8] and then annealed. The schematic cross-sectional illustration of the TSVs coated with a Ta cap was illustrated in Fig.…”

“…Among the ensuing thermo-mechanical reliability concerns, via extrusion is a particularly important one [7]. Via extrusion, also known as "Cu protrusion" and "Cu pumping", manifests as the irreversible upward protrusion of Cu and formation of bumps on the top surface of the vias [8], [9]. This deformation can be large enough to damage the adjacent structures, in particular the back-end-of-line (BEOL) interconnect layers, and subsequently degrade and even fail the 3D IC device [9]- [11].…”