Capacitor and forming method thereof, and dram and forming method thereof

A method for forming a capacitor, comprising:

• providing a substrate with an electric contact portion;
• forming a supporting layer and a sacrificial layer which are alternately laminated on a surface of the substrate, wherein the topmost layer is a supporting layer;
• forming a capacitor hole penetrating through the supporting layer and the sacrificial layer and exposing the electric contact portion;
• forming a bottom electrode layer covering an inner surface of the capacitor hole, in which the bottom electrode layer connects to the electric contact portion;
• forming a protective layer covering a surface of the bottom electrode layer;
• removing the sacrificial layer, during which the bottom electrode layer being protected by the protective layer;
• removing the protective layer;
• and
• sequentially forming a capacitor dielectric layer and a top electrode layer on an inner surface and an outer surface of the bottom electrode layer and a surface of the supporting layer.