Semiconductor memory device and manufacturing method thereof

1. A semiconductor memory device comprising:

a first source layer;

a second source layer on the first source layer;

a stack structure over the second source layer; and

a conductive common source line penetrating the stack structure,

wherein the second source layer includes a protective layer in contact with the conductive common source line and a conductive layer surrounding the protective layer,

wherein the conductive common source line has a portion in contact with the conductive layer of the second source layer between a bottom of the conductive common source line and the protective layer, and

wherein the portion protrudes under the protective layer.

2. The semiconductor memory device of claim 1 , wherein an upper surface, a lower surface, and a first sidewall of the protective layer are in contact with the conductive layer.

3. The semiconductor memory device of claim 2 , wherein a second sidewall of the protective layer is in contact with the conductive common source line.

4. The semiconductor memory device of claim 1 , wherein the protective layer includes a material having an etch selectivity with respect to oxide, nitride, and poly-silicon.

5. The semiconductor memory device of claim 1 , wherein the stack structure includes insulating patterns and gate patterns alternately stacked with each other.

6. The semiconductor memory device of claim 1 , wherein the conductive layer includes:

an upper portion covering an upper surface of the protective layer;

a lower portion covering a lower surface of the protective layer; and

a sidewall portion covering a first sidewall of the protective layer, and

wherein the upper portion of the conductive layer includes a buffer pattern in contact with the conductive common source line.

7. The semiconductor memory device of claim 6 , wherein the buffer pattern includes silicon oxide.

8. A semiconductor memory device comprising:

a stack structure including insulating patterns and gate patterns alternately stacked with each other;

a first source layer including a conductive layer and a first protective layer in the conductive layer;

a channel structure penetrating the stack structure, the channel structure being connected to the first source layer; and

a conductive common source line penetrating the stack structure, the conductive common source line being in contact with the first protective layer,

wherein the conductive common source line has a portion in contact with the conductive layer of the first source layer between a bottom of the conductive common source line and the first protective layer, and

wherein the portion protrudes under the protective layer.

9. The semiconductor memory device of claim 8 , wherein the conductive layer includes a first cavity,

wherein the first protective layer is formed in the first cavity.

10. The semiconductor memory device of claim 9 , wherein the first protective layer includes a second cavity,

wherein the first source layer further includes a second protective layer in the second cavity.

11. A semiconductor memory device comprising:

a first source layer;

a second source layer on the first source layer;

a stack structure including insulating patterns and gate patterns over the second source layer;

a channel structure penetrating the insulating patterns, the gate patterns, and the second source layer,

wherein the second source layer includes a conductive layer in contact with the channel structure, a protective layer surrounded by the conductive layer, and a buffer pattern in a portion of the conductive layer, and

wherein the buffer pattern includes oxide of the conductive layer and is cut by the protective layer and the stack structure.

12. The semiconductor memory device of claim 11 , further comprising a common source line in contact with the conductive layer and the protective layer.

13. The semiconductor memory device of claim 11 , wherein the protective layer incudes a material having an etch selectivity with respect to the conductive layer.

14. The semiconductor memory device of claim 13 , wherein the protective layer includes at least one of SiCO, SiC, and SiCN.

15. The semiconductor memory device of claim 13 , wherein the conductive layer includes poly-silicon.