Abstract: A method for fabricating a capacitor includes firstly providing a substrate. A doped first dielectric layer and an undoped second dielectric layer are then formed on the substrate sequentially. Next, many trenches are formed in the first and the second dielectric layers. Afterwards, an ion implantation process is performed in the largest space between the adjacent trenches to form an ion-implanted region in a portion of the second dielectric layer in upper parts of the trenches. A wet etching process is then performed to remove a portion of the second dielectric layer in the ion-implanted region and a portion of the first dielectric layer at bottoms of the trenches. Thereafter, a first conductive layer and a capacitor dielectric layer are formed sequentially on surfaces of the trenches. Finally, a second conductive layer is formed in the trenches.