Flash devices and methods of manufacturing the same

A method of manufacturing a flash device, comprising:

• forming a well region in a semiconductor substrate, so that a portion of the semiconductor substrate above the well region constitutes a semiconductor layer;
• forming a plurality of mask layers on the semiconductor layer;
• forming an opening in a top most one of the mask layers;
• forming a further mask layer as a spacer on inner walls of the opening;
• extending the opening into the well region through the plurality of mask layers and the semiconductor layer with the further mask layer as a hard mask;
• forming back gate dielectric layers on inner walls of the opening;
• forming a back gate conductor in the opening;
• forming an insulating cap including the further mask layer in the opening to cover the back gate dielectric layers and the back gate conductor;
• patterning the semiconductor layer into semiconductor fins with the insulating cap as a hard mask;
• forming a front gate stack to intersect the semiconductor fins, wherein the front gate stack includes a floating gate dielectric layer, a floating gate conductor, a control gate dielectric layer, and a control gate conductor disposed in sequence from bottom up, and the floating gate dielectric layer separates the floating gate conductor from the semiconductor fins;
• and
• forming source and drain regions connected to a channel region provided by each of the semiconductor fins,
• wherein the back gate conductor and the semiconductor fins on opposite sides of the back gate conductor are made from the semiconductor layer, and the back gate dielectric layers separating the back gate conductor from the respective semiconductor fins constitute a sandwich arrangement, wherein the insulating cap separates the back gate conductor from the control gate conductor, and wherein the well region serves as a part of a conductive path to the back gate conductor.