Method of forming capacitor for semiconductor device

A method of forming a capacitor for a semiconductor device, comprising:

• forming an insulation layer on a substrate surface, the substrate having a contact plug formed thereon;
• forming a silicon germanium layer on the insulation layer;
• forming an oxide layer on the silicon germanium layer;
• forming a hard mask layer on the oxide layer;
• partially etching the hard mask layer to form a hard mask pattern;
• performing a first anisotropic etching process on the oxide layer using the hard mask pattern as an etching mask, thereby forming a first opening through the oxide layer to selectively expose the silicon germanium layer;
• performing a second anisotropic etching process on the selectively exposed silicon germanium layer, thereby forming a second opening through the silicon germanium layer to selective expose the contact plug;
• performing an isotropic etching process on the second opening to laterally widen the second opening in the silicon germanium layer, such that the second opening is wider than at least some portion of the first opening;
• forming a storage electrode on the contact plug in conformity with sidewalls of the first and second openings;
• and,
• forming a dielectric layer and a plate electrode covering the storage electrode.