Capacitor and its formation method and a dram cell

A capacitor formation method comprises:

• providing a substrate, an electrical contact portion being formed on the substrate;
• forming alternately stacked supporting layers and sacrificial layers on a surface of the substrate;
• forming at least two capacitor holes penetrating the sacrificial layers and the supporting layers and exposing the electrical contact portion, wherein the at least two capacitor holes are provided on the same electrical contact portion;
• forming a lower electrode layer covering an inner surface of the capacitor holes,
• the lower electrode layer being connected to the electrical contact portion;
• removing the sacrificial layers;
• and
• forming a capacitor dielectric layer and an upper electrode layer successively on inner and outer surfaces of the lower electrode layer and on the surface of the supporting layers;
• wherein forming the at least two capacitor holes comprises:
• forming a mask layer on a surface of the alternately stacked supporting layers and sacrificial layers;
• patterning the mask layer so that at least two openings are formed in the mask layer above the electrical contact portion;
• etching the alternately stacked supporting layers and sacrificial layers to the surface of the electrical contact portion along the openings;
• and
• forming the capacitor holes;
• wherein patterning the mask layer comprises:
• performing a doping process on the mask layer to form first portions and second portions arranged at intervals in the mask layer, the first portions and the second portions having different doping densities and with at least two first portions or two second portions in the mask layer above the electrical contact portion;
• selectively removing first portions or second portions in the mask layer above the electrical contact portion;
• and
• patterning the mask layer.