Smooth, Flat, and Ultra-High-Uniformity Thickness Distributions Bumps Using the Durendal Process

Tuesday, September 17
3:30pm to 3:55pm


In this paper, we present the theory, computer modeling and experimental results of our new cluster tool arranged electroplate-electroetch (Durendal) process sequences.  This new process and hardware greatly improves bump thickness uniformity over plating-only processes.  Electroplated thickness non-uniformities are largely driven by spatially-variable electrodynamics and mass transfer resistances.  Specially chosen plating additives are adsorbed at the surface and alter the deposition kinetics, reducing the impact of the solution-phase non-uniformity effects, generally leading to improved feature shape and thickness distributions.  But plating additives ability to suppress and correct for the underlying physical driving forces leading to the non-uniformites are limited, and means of obtaining for ever-more uniform distributions are needed. There are problems associated with performing a dep-etch process within a single plating cell/solution, and will discuss how our two-module sequential process overcomes them.  After plating bumps in a first module to a thickness greater than the final target, the wafer is transferred to a second (Durendal) module, where the excess film metal is electrolytically removed.  Using our primary etch mode operating conditions (power, temperature, flow, electrolyte composition, etc.) lead to removal driven by the underlying electrodynamic influences (e.g. spatial distributions of individual die on the wafer, non-uniform feature distribution within each die, and edge of feature exposure/growth effects). Using the secondary etch mode corrects non-uniformity’s associated with variability in mass transfer accessibility (individual feature height, shape, depths and feature to feature width variations), as well as can reduce surface roughness. The combination of these processes improves the wafer-level variance’s, die level distribution, and feature flatness to such an extent, that in some cases the uniformity exceeds the resolution/capability of current thickness distribution metrology.

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