Vertical semiconductor device and method for fabricating the vertical semiconductor device

1. A method for fabricating a vertical semiconductor device, comprising:

forming a first multi-layer stack in which a source sacrificial layer is positioned over a lower source layer, the lower source layer over a lower structure;

forming a second multi-layer stack in which dielectric layers and sacrificial layers are alternately stacked over the first multi-layer stack;

forming a vertical structure that penetrates the second multi-layer stack and the first multi-layer stack, and includes a channel layer insulated from the lower source layer;

forming a vertical contact recess that penetrates the second multi-layer stack and the first multi-layer stack and exposes the source sacrificial layer;

forming a horizontal contact recess extending from the vertical contact recess by removing the source sacrificial layer;

exposing a side of the channel layer of the vertical structure by extending the horizontal contact recess;

forming a source channel contact that fills the horizontal contact recess, and includes a first conductive layer in contact with the channel layer and a second conductive layer doped with a dopant which is different from a dopant of the first conductive layer, and

forming a barrier oxide formed on the first and second conductive layers,

wherein the source channel contact includes a concave portion and a convex portion, the concave portion and the convex portion are directly contacted with the barrier oxide,

wherein the convex portion of the source channel contact has a peak, and the peak is provided by the second conductive layer, and

wherein the concave portion and the convex portion of the source channel contact are fully covered by the barrier oxide.

2. The method of claim 1 , wherein the forming of the source channel contact includes:

forming the first conductive layer in contact with the channel layer in the horizontal contact recess;

forming a second conductive layer over the first conductive layer to fill the horizontal contact recess without voids; and

forming the source channel contact in the horizontal contact recess by etching the second conductive layer and the first conductive layer.

3. The method of claim 2 , wherein in the forming of the source channel contact:

the etching of the second conductive layer and the first conductive layer includes wet etching.

4. The method of claim 2 , wherein in the forming of the source channel contact:

the second conductive layer has a slower etch rate than the first conductive layer during the wet etching.

5. The method of claim 2 , wherein in the forming of the source channel contact:

an etched surface of the source channel contact after the wet etching has the peak by the second conductive layer.

6. The method of claim 1 , wherein the second conductive layer includes a material having a different wet etch rate than the first conductive layer.

7. The method of claim 1 , wherein the first conductive layer includes polysilicon containing a first dopant, and the second conductive layer includes polysilicon containing a second dopant, where the first dopant and the second dopant are different materials.

8. The method of claim 1 , wherein the second conductive layer includes carbon-conductive polysilicon.

9. The method of claim 8 , wherein the first conductive layer includes phosphorus-conductive polysilicon.

10. The method of claim 1 , wherein the second conductive layer has a thickness that is thinner than a thickness of the first conductive layer.

11. The method of claim 1 , wherein the barrier oxide is formed by oxidizing an exposed surface of the first and second conductive layer.

12. The method of claim 1 , further comprising, after the forming of the barrier oxide:

forming a sealing spacer over the barrier oxide;

forming gate recesses by removing sacrificial layers of the second multi-layer stack; and

filling the gate recesses with gate electrodes.

13. The method of claim 1 , wherein the forming of first multi-layer stack includes:

forming the lower source layer over the lower structure;

forming the source sacrificial layer over the lower source layer; and

forming un upper source layer over the source sacrificial layer.