Atomic-Level Surface of Copper Induced by Photocatalytic Chemical Mechanical Polishing with High Material Removal Rate under Visible Light Irradiation

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Atomic-level surface is required by interconnect for copper (Cu) in semiconductor and integrated circuit manufacturing, while the material removal rate (MRR) is usuary sacrificed. To achieve the atomic-level surface of Cu, the MRR is normally lower than 240 nm/min. To overcome this challenge, photocatalytic chemical mechanical polishing (PCMP) was developed for Cu, and the MRR is 379 nm/min. The CMP slurry consisted of silica, lanthana, hydrogen peroxide (H 2 O 2 ), tartaric acid, Nile blue sulfide (NBS), triazole, and sodium bicarbonate. After PCMP, surface roughness Sa is 0.103 nm measured by atomic force microscopy. To the best of our knowledge, MRR is the highest for the atomic-level surface of Cu reported so far. Transmission electron microscopy reveals that the thickness of the damaged layer after PCMP is 1.69 nm. Under visible light irradiation, the corrosion current density of Cu increases from 57.54 to 72.89 μA/cm 2 in H 2 O 2 and NBS solution. X-ray photoelectron spectroscopy indicates that the fraction of Cu 2+ enhances from 75.12 to 100% with adding NBS in H 2 O 2 . The absorption intensity of the fluorescent probe decreases 10.4, 50, and 65% in H 2 O 2, NBS and H 2 O 2 and NBS solution, respectively. Density functional theory (DFT) calculates that the Gibbs free energy of the system reduces 94.46 kcal/mol, revealing that Cu 2+ forms coordination bonds with −COO − and −OH groups of tartaric acid. Fourier transform infrared (FTIR) spectroscopy exhibits that the −OH peak of tartaric acid shifts from 3411.35 to 3126.13 cm −1, attributable to coordination bonding between −OH and Cu 2+ ions. It also shows that −COOH deprotonates and transforms to −COO − with the disappearance of the peak at 1743.55 cm −1 and the appearance of the peak at 1594.08 cm −1, subsequently complexing with Cu 2+ ions via coordination bonding. DFT-calculated results are in good agreement with those of FTIR measurements. Our proposed PCMP paves a route to achieve the atomic-level surface of Cu with a high MRR using visible light irradiation.

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