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.

Influence of Glycerol on Copper Electrodeposition from Pyrophosphate Bath: Nucleation Mechanism and Performance Characterization

“…Li et al 5 demonstrated that the addition of HEDP could significantly elevate the current efficiency of pyrophosphate bath, and the improved performance was very close to that of cyanide bath. Jin et al 6 optimized the pyrophosphate bath by adding organic additives of polyethylene glycol 4000, poly(ethylene glycol)-poly(propylene glycol)-poly(ethylene glycol) triblock copolymer and polyethylene glycol p-(1,1,3,3-tetramethylbutyl)-phenyl ether. Starosvetsky et al 7 improved the nucleation density and adhesion of copper coating via the addition of 2,5-dimercapto-1,3,4-thiadiazole into pyrophosphate bath.…”