Seed step-coverage enhancement process for a high-aspect-ratio through-silicon via using a pyrophosphate solution

Abstract

A seed step-coverage enhancement process (SSEP) was investigated in order to improve the poor stepcoverage of the Cu seed layer when it is deposited by physical vapor deposition with a high-aspect-ratio through-silicon via (TSV) to inhibit void generation during a subsequent electroplating TSV gap-fill process. The SSEP was performed by means of electroplating after the deposition of the Cu seed layer in TSV using an alkaline pyrophosphate solution, which is effective when used to prevent the dissolution of the Cu seed layer. The molar ratio of pyrophosphate ions to Cu ions in the plating solution and the current density were optimized for the SSEP by considering the surface uniformity of the electroplated Cu film through electroplating on the defective seed layer. In order to improve the wettability of the pyrophosphate solution in the TSV pattern, polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether was added to the solution. Finally, we significantly strengthened the seed step-coverage at the bottom-corner of the TSV, the weakest point in terms of seed step-coverage, and achieved a void-free filling of the TSV in the subsequent TSV gap-fill process.