A monolithic three dimensional NAND string includes a semiconductor channel having at least one end extending substantially perpendicular to a major surface of a substrate, a plurality of control gates extending substantially parallel to the major surface of the substrate, including a first control gate located in a first device level and a second control gate located in a second device level, a charge storage material located in the first device level and in the second device level, a blocking dielectric located between the charge storage material and the plurality of control gates, and a tunneling dielectric located between the charge storage material and the semiconductor channel. The tunneling dielectric has a straight sidewall, portions of the blocking dielectric have a clam shape, and each of the plurality of control gates is located at least partially in an opening in the clam-shaped portion of the blocking dielectric.