Thicker hard molds are typically required to etch deeper
capacitor vias in
DRAM structures. Instead of increasing hard mold thickness, hard molds can be formed with increased etch selectivity relative to the underlying
semiconductor structure. For example,
boron-based hard molds comprising a relatively high percentage of
boron (e.g., greater than 90%) can be formed. The etch selectivity of the hard mold can be improved by performing an
ion implantation process using different types of ions.
Ion implantation can occur before or after the hard mold is opened using the pattern of the
DRAM capacitor vias. Some designs also tilt the
semiconductor substrate relative to the
ion implantation process and rotate the substrate to provide greater
ion penetration throughout the entire depth of the opening in the hard mold.