Semiconductor memory device and method of manufacturing the same
A semiconductor memory device includes a separation member defining active regions of a substrate. Gate lines intersect the active regions and are each buried in a trench formed in the substrate. Each of the gate lines includes a lower electrode structure and an upper electrode structure on the lower electrode structure. The upper electrode structure includes a source layer substantially covering a sidewall of the trench and including a work-function adjustment element. A conductive layer is on the source layer. A work-function adjustment layer is disposed between the source layer and the conductive layer. The work-function adjustment layer includes a material different from that of the source layer and is doped with the work-function adjustment element.
1. A method of manufacturing a semiconductor memory device, the method comprising:
forming a separation member defining active regions in a substrate; and
forming gate lines intersecting the active regions and buried in the substrate,
wherein the forming of the gate lines comprises:
forming trenches intersecting the active regions in the substrate;
forming a lower electrode structure substantially filling a lower portion of each of the trenches;
sequentially forming a source layer and a first diffusion layer on a sidewall and a bottom surface of each of the trenches, the source layer including a work-function adjustment element;
forming a conductive layer on the first diffusion layer; and
forming a work-function adjustment layer having a work function lower than that of the first diffusion layer by diffusing the work-function adjustment element from the source layer into at least a portion of the first diffusion layer.
2. The method of claim 1 , wherein a portion of the first diffusion layer remains after the forming of the work-function adjustment layer.
3. The method of claim 1 , wherein the source layer and the conductive layer are spaced apart from each other by the work-function adjustment layer.
4. The method of claim 1 , wherein the diffusion of the work-function adjustment element is performed by an annealing process.
5. The method of claim 1 , further comprising:
forming a gate insulating pattern on the sidewall and the bottom surface of each of the trenches before the forming of the lower electrode structure,
wherein a portion of the gate insulating pattern in direct contact with the source layer laterally protrudes on the lower electrode structure in the forming of the work-function adjustment layer.
6. The method of claim 5 , oxygen atoms of the source layer are diffused into the gate insulating pattern when the forming of the work-function adjustment layer.
7. The method of claim 1 , wherein the source layer is formed between the first diffusion layer and a sidewall of each of the trenches.
8. The method of claim 1 , wherein a gap formed between the lower electrode structure and the source layer when the forming of the work-function adjustment layer, and
wherein the gap is substantially filled with oxygen or nitrogen.
9. The method of claim 1 , wherein a work function of the lower electrode structure is higher than a work function of the work-function adjustment layer.
10. The method of claim 1 , wherein the work-function adjustment layer includes a metal or a metal nitride, and
wherein the work-function adjustment element includes lanthanum (La).
11. The method of claim 1 , further comprising:
forming a second diffusion layer on a sidewall of each of the trenches before the forming of the source layer.
12. The method of claim 11 , wherein the work-function adjustment element is diffused into at least a portion of the second diffusion layer from the source layer when the forming of the work-function adjustment layer.
13. A method of manufacturing a semiconductor memory device, the method comprising:
forming trenches intersecting active regions in a substrate;
forming a lower electrode structure substantially filling a lower portion of each of the trenches;
sequentially forming a first diffusion layer, a source layer and a second diffusion layer on the lower electrode structure in the trench, the source layer including a work-function adjustment element;
forming a conductive layer on the first diffusion layer; and
forming a work-function adjustment layer having a work function lower than that of the first and second diffusions layer by diffusing the work-function adjustment element from the source layer into at least a portion of the first and second diffusion layers.
14. The method of claim 13 , wherein the work-function adjustment layer is formed between the first diffusion layer and the second diffusion layer.
15. The method of claim 13 , wherein a portion of the first diffusion layer and a portion of the second diffusion layer remain after the forming of the work-function adjustment layer.
16. The method of claim 13 , wherein source layer remain at least one of between the first diffusion layer and the work-function adjustment layer or between the second diffusion layer and the work-function adjustment layer after the forming of the work-function adjustment layer.
17. The method of claim 13 , the first diffusion layer, the source layer and the second diffusion layer are formed on a sidewall and a bottom surface of each of the trenches.
18. The method of claim 13 , wherein the diffusion of the work-function adjustment element is performed by an annealing process.
19. The method of claim 13 , further comprising:
forming a gate insulating, pattern on the sidewall and the bottom surface of each of the trenches before the forming of the lower electrode structure.
20. The method of claim 13 , wherein the work-function adjustment layer includes a metal or a metal nitride,
wherein the first and second diffusion layers include a same material as the work-function adjustment layer, and
wherein the work-function adjustment element includes lanthanum (La).