Vertical Profile Control in Ultrahigh-Aspect-Ratio Contact Hole Etching with 0.05-µm-Diameter Range

Vertical processing of 0.05-µm-class SiO2 holes with an aspect ratio around 20 was realized using a dipole-ring-type magnetron reactive-ion-etching system in a mixture of C4F8/O2/Ar gas. Secondary ion mass spectrometric study of the F and C concentration profiles of the polymer deposited inside the holes in the depth direction revealed that a very small amount of polymer deposition occurred in this system. This indicates that energetic species reached the hole bottoms with excellent verticality, even in an extremely fine feature. In contrast, the CHF3/CO process (tapered shape) resulted in an extremely thick polymer and carbonized region on the sidewalls, suggesting the presence of energetic species sticking to the sidewalls. The effects of energetic species impinging onto the sidewalls and the protection resulting from polymer deposition have been discussed in terms of the etched shape and F/C depth profile. Vertical incidence of the energetic species into the holes is concluded to be a significant factor in realizing a vertical profile.