Abstract
The effects of mask characteristics on high-aspect-ratio contact hole (HARC) etching profiles were investigated. The evaluation of etching profiles produced with different taper angle masks confirmed that the bowing amount and mask selectivity worsened with decreasing mask taper angle. The relationship between mask taper angle and distribution of scattered ion flux on the sidewall of a tapered mask was calculated. The scattered ion flux was heavily concentrated in the upper part of the sidewall in the case of a tapered mask, and this was considered to be the main cause of the bowing formation. Direct observation of an etched sidewall by atomic force microscopy (AFM) revealed that the roughness of the necking was strongly related to the roughness of the bottom part of the etched sidewall. To evaluate the dependence of twisting on nonuniform necking, the incident ion flux in a circular hole was calculated. As a result, in the case of nonaxisymmetric necking, an imbalance of ion flux in the bottom of the hole appeared and broke the etching symmetry in the bottom part of the hole, causing twisting. In addition, the probability of twisting was found to increase with increasing necking growth rate irrespective of mask electrification. Therefore, mask deformation and nonuniform necking in the upper part of the sidewall during HARC etching are considered the main factors causing bottom degradation. Accordingly, a vertical and nondeformed mask is very important for a smaller critical dimension (CD) and HARC etching.