A method for forming a capacitor array includes depositing a first nitride layer, a first oxide layer, and a second nitride layer in sequence over first and second contacts on a substrate; etching the first nitride layer, the first oxide layer, and the second nitride layer to form first and second openings exposing the first and second contacts; conformally depositing a bottom electrode layer over the first and second nitride layers and the first oxide layer and on the first and second contacts; etching the second nitride layer and the first oxide layer to form a third opening having a bottom position higher than a top surface of the first nitride layer; removing the first oxide layer through the third opening; forming a capacitor dielectric layer over the bottom electrode layer; forming a top electrode layer over the capacitor dielectric layer.