Study of the Impact of Pitch Distance on the Statistical Variation of TSV Protrusion and the Underlying Mechanisms

In this work, we investigated the effect of pitch distance on the statistical variation of Cu protrusion in TSVs and its underlying mechanisms. The magnitude and statistical spread of Cu protrusion in 120 vias from two TSV arrangements with pitch distances of 10 μm and 40 μm were studied. A notable increase in the magnitude of protrusion was observed in vias with 10 μm pitch distance, yet, the protrusion height variation in TSVs with different pitch distances were similar. Finite element analysis was performed to show the effect of pitch distance on stress in and around the Cu vias. Topography and microstructure characterizations were carried out to study the effect of pitch distance on the magnitude, statistical spread, morphology, and mechanisms of protrusions. The results showed that smaller pitch distance made for larger stresses and larger protrusions but the variation of protrusion was weakly dependent of the pitch distance. The microstructural studies revealed a correlation between the protrusion topography and the grain structure. Moreover, even though the statistical spread of small pitch vias remained largely identical to that of the large pitch vias, a ring shape morphology was observed more often in vias with smaller pitch distance. Mechanisms that could be responsible for the statistical variation of protrusion and the different protrusion morphologies were discussed.