The present disclosure relates to a microphone. In some embodiments, the microphone may comprise a substrate, a diaphragm, a backplate, and a sidewall stopper. The substrate has an opening disposed through the substrate. The diaphragm is disposed over the substrate and facing the opening of the substrate. The diaphragm has a venting hole overlying the opening of the substrate. A backplate is disposed over and spaced apart from the diaphragm. A sidewall stopper is disposed along a sidewall of the venting hole of the diaphragm and thus is not limited by a distance between the movable part and the stable part. Also, the sidewall stopper does not alternate the shape of movable part, and thus will less likely introduce crack to the movable part. In some embodiments, the sidewall stopper may be formed like a sidewall stopper by a self-alignment process, such that no extra mask is needed.