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 with a three-dimensional structure in which a plurality of memory cells 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 which maintains data stored therein even when power supply is interrupted. Currently, various nonvolatile memory devices, for example, a flash memory and the like are widely used.
Recently, as improving the degree of integration of a nonvolatile memory device with a two-dimensional structure in which memory cells are formed in a single layer on a semiconductor substrate reaches a fabrication limit, a nonvolatile memory device with a three-dimensional structure in which a plurality of memory cells are formed along a channel layer vertically projecting from a semiconductor substrate has been suggested in the art. In detail, nonvolatile memory devices with a three-dimensional structure are generally divided into a structure which has a straight channel layer and a structure which has a U-shaped channel layer.
In the case of the conventional structure having the straight channel layer, while manufacturing processes are relatively simple and easy, since a source line is formed by implanting impurities into a silicon substrate, there are concerns in that a doping profile is likely to be changed by a subsequent annealing process and the like and source resistance is likely to increase. Although a method for forming a source line using a conductive substance such as a metal to reduce resistance has been proposed in the art, it may be difficult to control the doping profile of the source region under the channel layer.
In the case of the conventional structure having the U-shaped channel layer, while the above-described concerns may be solved, since the gate electrode of a pass transistor is formed long, channel resistance may increase. According to this fact, concerns are likely to occur in that the threshold voltage of the pass transistor increases and memory cell driving current is reduced.