Acetic acid and phosphoric acid adding to improve tantalum chemical mechanical polishing in hydrogen peroxide-based slurry

摘要

Tantalum (Ta) is difficult to polish mechanically because of the formation of the hard oxide, Ta_2O_5, on its surface. In the IC metallization process, increasing the chemical removal rate of the barrier metal, tantalum (Ta), during chemical mechanical polishing (CMP) is essential to achieve global planarity and enhance the efficiency of the process. This study explores how the addition of acetic acid (CH_3COOH) and phosphoric acid (H_3PO_4) accelerates Ta CMP in hydrogen peroxide (H_2O_2) slurries. Experimental results indicated that CH_3COOH and H_3PO_4 were adsorbed on Ta, modifying its surface; in particular, the time taken for the Ta surface to be passivated into dense Ta_2O_5 was effectively increased, enabling Ta to be easily etched and removed. An impedance study further confirmed that the addition of CH_3COOH or H_3PO_4 changed the reaction mechanism between Ta and H_2O_2 slurries and displayed the lack of dense oxide film to be formed. Therefore, the chemical removal rate of Ta was substantially enhanced. After Ta CMP in H_2O_2-based slurries with CH_3COOH or H_3PO_4, the surface roughness from 32.52 nm could be decreased to 16.21 or and 13.81 nm, respectively.