| 摘要 |
PURPOSE:To enhance a TDDB characteristic at an EEPROM by a method wherein, when a tunnel insulating film is formed between a floating gate and a tunnel region, the tunnel insulating film is formed to be thicker than a target film thickness and, after that, it is etched back to the target film thickness. CONSTITUTION:A tunnel opening part 8a is made in a gate insulating film 8 by a dry or wet etching operation; after that, so-called cleaning treatments such as an acid treatment used to remove a resist residue, a hydrofluoric acid treatment used to remove a residual oxide film and an aqua regia treatment used to prevent a heavy metal, a noble metal and the like from being diffused to silicon at a heat treatment are executed. In succession, tunnel insulating films (4+13) which are thicker than a target film thickness are formed in the tunnel opening part which has been made. Then, the films are etched back to the tuunel insulating film 4 having a target film thickness; the excessively formed tunnel insulating film 13 is removed; after that, a floating gate 2 is produced. Thereby, the upper-layer part of the tunnel insulating films whose quality is not good can be removed; it is possible to sharply eliminate a factor which quickens a fatigue (TDDB) caused by a so-called field stress.
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