Formulation Development for Bosch Etch Residue Removal: Effect of Solvent on Removal Efficiency

The Bosch etch process is a critical process step used to create through silicon vias (TSVs) for 3D integrated circuit manufacturing. During the Bosch etch, a fluoropolymer passivation layer is formed on the sidewall of TSVs to help achieve a vertical profile and to protect the exposed dielectric materials. The fluoropolymer residue on the sidewalls in the TSVs must be removed prior to subsequent process steps. The highly fluorinated character of the fluorocarbon polymer residue makes its complete removal challenging due to characteristics such as limited solubility in solvents and slow or no reactivity with components of common cleaning or strip solutions. In this paper, the results of a study of solvents for developing formulations for removal of Bosch etch residue from TSVs are presented. The selection of components for an etch residue remover must take into consideration several key factors including removal efficiency, environmental-health-safety (EHS) guidelines, and material cost. The results demonstrate that the solvent selection has a dramatic impact on polymer removal efficiency, where poor solvent selection can lead to the formation of polymer balls inside the vias. The reported studies include cleaning results using a combination of polar solvents including protic and aprotic solvents, and amide and non-amide solvents. The cleaning performance is compared with a prediction using Hansen solubility parameters. Complete residue removal using TMAH-free and NMP-free formulations for TSV diameters down to 5 μm is demonstrated. Scanning electron microscopy, (SEM), energy-dispersive X-ray spectroscopy (EDS), and Auger electron spectroscopy (AES) were used to characterize the cleaning performance.