Three-dimensional memory device having pocket structure in memory string and method for forming the same
Embodiments of 3D memory devices having a pocket structure in memory strings and methods for forming the same are disclosed. In an example, a 3D memory device includes a substrate, a selective epitaxial layer on the substrate, a memory stack including interleaved conductive layers and dielectric layers on the selective epitaxial layer, and a memory string including a channel structure extending vertically in the memory stack and a pocket structure extending vertically in the selective epitaxial layer. The memory string includes a semiconductor channel extending vertically in the channel structure, and extending vertically and laterally in the pocket structure and in contact with the selective epitaxial layer.
1. A three-dimensional (3D) memory device, comprising:
a substrate;
a selective epitaxial layer on the substrate;
a memory stack comprising interleaved conductive layers and dielectric layers on the selective epitaxial layer; and
a memory string comprising a channel structure extending vertically in the memory stack and a pocket structure extending vertically in the selective epitaxial layer;
wherein the memory string comprises a semiconductor channel extending vertically in the channel structure, and extending vertically and laterally in the pocket structure and in contact with the selective epitaxial layer, and
wherein the semiconductor channel extends vertically above and beneath the pocket structure, and the semiconductor channel extends laterally in the pocket structure for about 20 nm.
2. The 3D memory device of claim 1 , wherein a lateral dimension of the channel structure is not greater than a lateral dimension of the pocket structure.
3. The 3D memory device of claim 2 , wherein the lateral dimension of the channel structure is the same as the lateral dimension of the pocket structure.
4. The 3D memory device of claim 1 , wherein the memory string comprises a memory film laterally between the memory stack and the semiconductor channel in the channel structure, the memory film extending vertically in the channel structure and extending laterally in the pocket structure.
5. The 3D memory device of claim 4 , wherein the memory film comprises a blocking layer, a storage layer, and a tunneling layer.
6. The 3D memory device of claim 1 , wherein the memory string comprises a cap layer surrounded by the semiconductor channel, a lateral dimension of the cap layer in the pocket structure being greater than a lateral dimension of the cap layer in the channel structure.
7. The 3D memory device of claim 1 , wherein the selective epitaxial layer comprises single crystalline silicon, and the semiconductor channel comprises polysilicon.
8. The 3D memory device of claim 1 , wherein the semiconductor channel is flat at a lower end of the memory string.
9. The 3D memory device of claim 1 , further comprising a source contact structure extending vertically through the memory stack and in contact with the selective epitaxial layer.
10. The 3D memory device of claim 1 , wherein the semiconductor channel is flat at a lower end of the memory string.
11. A three-dimensional (3D) memory device, comprising:
a substrate;
a selective epitaxial layer on the substrate;
a memory stack comprising interleaved conductive layers and dielectric layers on the selective epitaxial layer; and
a memory string comprising a channel structure extending vertically in the memory stack and a pocket structure extending vertically in the selective epitaxial layer,
wherein a lateral dimension of the channel structure is not greater than a lateral dimension of the pocket structure;
a semiconductor channel extends vertically above and beneath the pocket structure; and
the semiconductor channel extends laterally in the pocket structure for about 20 nm.
12. The 3D memory device of claim 11 , wherein the memory string extends vertically and laterally in the pocket structure and in contact with the selective epitaxial layer.
13. The 3D memory device of claim 11 , wherein the semiconductor channel extends vertically in the channel structure, and extending vertically and laterally in the pocket structure and in contact with the selective epitaxial layer.
14. The 3D memory device of claim 11 , wherein the semiconductor channel is flat at a lower end of the memory string.
15. The 3D memory device of claim 11 , wherein the lateral dimension of the channel structure is the same as the lateral dimension of the pocket structure.
16. The 3D memory device of claim 11 , wherein the memory string comprises a memory film laterally between the memory stack and the semiconductor channel in the channel structure, the memory film extending vertically in the channel structure and extending laterally in the pocket structure.
17. The 3D memory device of claim 16 , wherein the memory film comprises a blocking layer, a storage layer, and a tunneling layer.
18. The 3D memory device of claim 11 , wherein the memory string comprises a cap layer surrounded by the semiconductor channel, a lateral dimension of the cap layer in the pocket structure being greater than a lateral dimension of the cap layer in the channel structure.