The present disclosure provides a capacitor structure, including a substrate having a conductive region; a trench in the conductive region and having a bottom portion and an inner sidewall portion; a spacer over the inner sidewall portion of the trench; a first conductive layer over the bottom portion and the spacer in the trench; a first dielectric layer over the first conductive layer and in the trench; a second conductive layer over the first dielectric layer and in the trench; and a second dielectric layer over the second conductive layer and in the trench, wherein the spacer comprises an angle in a range of from about 85 to about 89 degrees with respect to the bottom portion of the trench and comprises a flared opening opposite to the bottom portion of the trench. The present disclosure also provides a method for manufacturing the capacitor structure.