Semiconductor memory device having a circuit formed on a single crystal semiconductor layer with varied germanium concentration

1. A semiconductor memory device comprising:

a semiconductor substrate;

a memory cell array portion formed on the semiconductor substrate, and including memory cells for storing data;

a single-crystal semiconductor layer formed on an insulating layer on the memory cell array portion, and connected to the semiconductor substrate by being formed in a hole extending through the insulating layer and the memory cell array portion; and

a circuit portion formed on the single-crystal semiconductor layer,

wherein a germanium (Ge) concentration in a lower portion of the single-crystal semiconductor layer is higher than that in an upper portion thereof on the memory cell array portion.

2. The device of claim 1 , wherein the memory cell array portion includes the memory cells three-dimensionally stacked in a direction perpendicular to the semiconductor substrate.

3. The device of claim 1 , wherein

the memory cell array portion comprises memory cell strings arranged in a matrix, and

each memory cell string comprises:

a silicon pillar including a pair of columnar portions extending in a direction perpendicular to the semiconductor substrate and juxtaposed in a column direction, and a connecting portion formed to connect lower ends of the pair of columnar portions;

control gates extending in a row direction to perpendicularly intersect the columnar portions, and stacked in the direction perpendicular to the semiconductor substrate; and

memory cell transistors formed at intersections of each columnar portion and the control gates, and having current paths connected in series in the direction perpendicular to the semiconductor substrate.

4. The device of claim 1 , wherein the single-crystal semiconductor layer comprises a single-crystal SiGe layer formed on the insulating layer on the memory cell array portion and connected to the semiconductor substrate by being formed in the hole, and a single-crystal Si layer formed on the single-crystal SiGe layer.

5. The device of claim 4 , wherein a Ge concentration in the SiGe layer is not less than 50 atm%.

6. The device of claim 4 , wherein the SiGe layer contains a dopant impurity.

7. The device of claim 4 , wherein the semiconductor substrate is an Si substrate.

8. The device of claim 1 , wherein an interconnection in the memory cell array portion and an interconnection in the circuit portion are connected via a contact plug formed immediately above the interconnection in the memory cell array portion.

9. The device of claim 8 , wherein a sidewall insulating film is formed on a side surface of the contact plug.

10. The device of claim 8 , further comprising STI formed in the single-crystal semiconductor layer, and extending from a first surface of the single-crystal semiconductor layer to a second surface thereof opposing the first surface,

wherein the contact plug is formed in the STI.

11. The device of claim 8 , wherein the interconnection in the circuit portion is made of one of Al and Cu.

12. The device of claim 1 , wherein an Si concentration in an upper portion of the single-crystal semiconductor layer is higher than that in a lower portion thereof.

13. The device of claim 1 , wherein a C concentration in an upper portion of the single-crystal semiconductor layer is higher than that in a lower portion thereof.

14. The device of claim 1 , wherein a diameter of the hole is not more than half a depth thereof.

15. The device of claim 1 , wherein the single-crystal semiconductor layer is a gradation layer in which the Ge concentration gradually decreases from the lower portion toward the upper portion.