Super flash and method for manufacturing same

A method for manufacturing a super flash, comprising the following steps:

• step 1, forming a first gate trench in a region for forming a floating gate and a control gate, wherein the first gate trench is located at the top of a region for forming a source region, a bottom surface of the first gate trench is lower than a top surface of a semiconductor substrate, and a top surface of the first gate trench is higher than the top surface of the semiconductor substrate;
• step 2, forming the source region in a surface region of the semiconductor substrate at the bottom of the first gate trench;
• step 3, forming the floating gate, comprising the following sub-steps:
• step 31, forming a first oxide layer on side and bottom surfaces of the first gate trench;
• step 32, forming a second nitrogen oxide layer on the surface of the first oxide layer;
• step 33, forming a TiN layer of the floating gate on the surface of the second nitrogen oxide layer;
• step 34, sequentially forming a third nitrogen oxide layer and a fourth oxide layer on the surface of the TiN layer;
• and
• step 35, fully etching the fourth oxide layer, the third nitrogen oxide layer, the TiN layer, the second nitrogen oxide layer, and the first oxide layer, so that the fourth oxide layer, the third nitrogen oxide layer, the TiN layer, the second nitrogen oxide layer, and the first oxide layer are retained only on a side surface of the first gate trench and form a spacer structure, wherein the fourth oxide layer, the third nitrogen oxide layer, the TiN layer, the second nitrogen oxide layer, and the first oxide layer on the bottom surface of the first gate trench outside the spacer structure and outside the first gate trench are removed;
• the retained TiN layer forms the floating gate;
• the second nitrogen oxide layer forms a barrier layer for the diffusion of oxygen in the first oxide layer to the floating gate, the third nitrogen oxide layer forms a barrier layer for the diffusion of oxygen in the fourth oxide layer to the floating gate, reducing the amount of oxygen entering the floating gate and ensuring that the TiN layer of the floating gate from the bottom to the top of the floating gate is kept in a continuous structure;
• and the oxygen entering the floating gate makes the TiN layer of the floating gate present a nanocrystalline structure, thus increasing the ability of the floating gate to capture stored charges;
• and
• step 4, filling the first gate trench to form the control gate, wherein the top of the floating gate is higher than the top surface of the control gate.