Capacitor in semiconductor memory and preparation method thereof

The invention provides a capacitor in a semiconductor memory and a preparation method thereof. The preparation method comprises the following steps: providing a semiconductor substrate; forming a sacrificial layer and a top supporting layer on the semiconductor substrate, wherein the top supporting layer at least comprises two sub-supporting layers which are arranged in sequence, and the hardness of the sub-supporting layers is increased in sequence; patterning the top support layer to form a first opening, and removing part of the sacrificial layer to form a capacitor hole; forming a lower electrode in the capacitor hole, wherein the lower electrode covers the inner wall of the capacitor hole; patterning the top support layer to form a second opening, wherein the second opening exposes the sacrificial layer; removing the sacrificial layer, and exposing the outer side wall of the lower electrode; covering a dielectric layer on the exposed surface of the lower electrode; and covering an upper electrode on the