Bottom-up Cu Filling of Annular Through Silicon Vias: Microstructure and Texture
Thomas P. Moffat, Daniel Josell
Microstructural and morphological evolution during bottom-up Cu filling of TSV in a CuSO4-H2SO4-Cl- poloxamine electrolyte is examined. Deposition proceeds in two distinct stages beginning with a passive-to-active state transition on the via sidewalls whose depth and ultimate thickness depends on the polymer flux. Growth is conformal or tapered with columnar grains whose width and texture differ between the outer and inner sidewall of the annulus due to area reduction and expansion respectively. The outer sidewall and bottom surface have a preferred texture; <111> // ND (via normal) and <110> // CD (via circumferential). With time the sidewalls passivate and further deposition is localized to the via bottom. The bottom-up growth to fill the TSV is associated with the formation and selective expansion of the <110> // ND textured grains. At higher suppressor concentrations the initial onset and transient period of sidewall deposition is displaced to greater depth and the subsequent transition to bottom-up filling with large <110> // ND texture grains occurs earlier. The dominant <110> // ND texture during bottom-up filling is congruent with Cl- stabilized texture development. The absence of suppression indicates that the polymeric suppressor does not adsorb on the active upward propagating surface.