Semiconductor structure

A semiconductor structure includes a substrate, a MIM capacitor disposed over the substrate, a first insulating layer disposed over the MIM capacitor, an ONON stack disposed over the first insulating layer, a connecting via disposed in the first insulating layer, and a connecting pad disposed in the ONON stack and in contact with the connecting via. The ONON stack covers sidewalls of the connecting pad and a portion of a top surface of the connecting pad. The ONON stack includes a first silicon oxide layer, a first silicon nitride layer, a second silicon oxide layer and a second silicon nitride layer upwardly disposed over the first insulating layer. A thickness of the second silicon nitride layer is greater than a thickness of the second silicon oxide layer and greater than a thickness of the first silicon nitride layer.