Characterizing Transport Limitations during Copper Electrodeposition of High Aspect Ratio Through-Silicon Vias

Diffusion-controlled mass transport of cupric ions during copper electrodeposition of high aspect ratio through-silicon via (TSV) structures is analyzed using a steady-state diffusion-reaction model. The model yields a single dimensionless parameter, i.e., the Thiele modulus (mu), which is used to characterize the cupric ion mass transport limitations prevailing in the system. The Thiele modulus allows comparative analysis of numerous TSV metallization studies reported in the literature, even though these studies utilize operating parameters vastly different from one another. It is shown that literature studies reporting mass transport induced void formation during TSV filling correspond to a Thiele modulus mu > 1 indicative of severe cupric ion depletion within the TSV. Conversely, studies reporting void-free TSV filling correspond to a Thiele modulus mu < 1 indicative of minimal cupric ion depletion. The Thiele modulus is used to develop general guidelines for selecting operating parameters, such as the current density, during metallization of various TSV sizes. (c) 2012 The Electrochemical Society. All rights reserved.