Effects of BCl3 gas on physical damage and Al residues in oxide hard-mask-based Al etching

This paper presents the effects of BCl₃ additive gas on physical damage and the prevention against damage in oxide hard-mask-based Al etching. The BCl₃ addition in the TiN/Ti break-through step effectively passivated the sidewall against the upper TiN/Ti notching damage; however, the TiN/Ti profile was easily distorted under excessive BCl₃ added. The Al bottom notching depth decreased with decreasing BCl₃/Cl₂ ratio in the Al over-etch step. As the BCl₃/Cl₂ ratio is less than or equal to 0.625, the Al bottom notching was eliminated. Nevertheless, the low BCl₃ addition in the Al over-etch step would result in increasing Al residues because insufficient passivation at low BCl₃ flow cannot effectively protect the semi-iso Al sidewall from attack of Cl atoms, and insufficient ion bombardment at this low BCl₃ cannot remove those residues around the damaged sidewall. An optimized condition achieves both notching-free and residue-free profiles.