1. Field of the Invention
The present invention relates to an electrically data-rewritable nonvolatile semiconductor memory device and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, an LSI is formed by integrating elements in a two-dimensional plane on a silicon substrate. The only way to increase a storage capacity of memory is by reducing dimensions of (miniaturizing) an element. However, in recent years, even this miniaturization is becoming difficult in terms of cost and technology. Improvements in photolithographic technology are necessary for miniaturization, but, for example, in current ArF immersion lithography technology, a rule of around 40 nm represents the resolution limit, and further miniaturization requires introduction of EUV steppers. However, the introduction of EUV steppers is problematic due to their high cost. Moreover, even if miniaturization is achieved, it is expected that physical limitations such as those of withstand voltage between elements are encountered, unless the drive voltage and so on are scaled. In other words, there is a high possibility that operation as a device becomes difficult.
Accordingly, in recent years, many semiconductor memory devices are proposed in which memory cells are disposed three-dimensionally in order to increase a degree of integration of memory (refer to Japanese Unexamined Patent Application Publication No. 2007-266143).