1. Field
Exemplary embodiments of the present invention relate to a nonvolatile memory device and a method for fabricating the same, and more particularly, to a nonvolatile memory device having a three-dimensional (3D) structure including a plurality of memory cells that are vertically stacked from a substrate and a method for fabricating the same.
2. Description of the Related Art
A nonvolatile memory device is a memory device that maintains data stored therein even though power supply is cut off. Various nonvolatile memory devices, for example, a flash memory and so on are examples of a nonvolatile memory device.
The improvement in integration degree of a nonvolatile memory device having a two-dimensional (2D) structure that includes memory cells that are formed in a single layer over a semiconductor device has approached a limit. Accordingly, a nonvolatile memory device having a 3D structure has been proposed. The nonvolatile memory device having a 3D structure includes a plurality of memory cells that are formed along a channel layer extending vertically from a semiconductor substrate. More specifically, the nonvolatile memory device having a 3D structure may be divided into a structure having a line-shaped channel layer and a structure having a U-shaped channel layer.
In the structure having a line-shaped channel layer, the fabrication process thereof is relatively simple. However, since a source line is formed by ion implanting impurities into a silicon substrate, a doping profile is changed by a subsequent heat treatment or the like, thereby increasing source resistance. In addition, a method that forms a source line of a conductive material such as a metal to reduce resistance has been proposed. In this method, however, the doping profile of a source area under the channel layer may be difficult to control. Accordingly, since a gate induced drain leakage (GIDL) current is not sufficiently secured, an erase operation may not be performed normally.
Alternatively, the structure having a U-shaped channel layer may solve the above-described problem. However, the fabrication process thereof is complex. Furthermore, as the channel length is increased, a cell current is reduced.