Semiconductor device and its manufacturing method
A semiconductor device comprises a semiconductor substrate; a trench formed in the semiconductor substrate or in a layer deposited on the semiconductor substrate; a first conductive layer deposited in the trench and having a recess in the top surface thereof; a buried layer which buries the recess of the first conductive layer and which is made of a material having a melting point lower than that of the first conductive layer; and a second conductive layer formed on the buried layer inside the trench and electrically connected to the first conductive layer.
1. A semiconductor device comprising:
a semiconductor substrate including a trench having an inner wall;
a first storage node electrode formed in the trench, having a recess with a V-shaped cross section in a top surface thereof;
a capacitor insulating film located between the first storage node electrode and the inner wall;
a buried layer formed on the recess, wherein the buried layer is electrically conductive;
a second storage node electrode formed on the buried layer in the trench;
a collar insulating film located between the second storage node electrode and the inner wall; and
a buried strap formed above the second storage node electrode in the trench.
2. The semiconductor device according to claim 1 , wherein the first and second storage node electrodes and the buried strap each comprise polysilicon and the buried layer comprises germanium or silicon germanium.
3. The semiconductor device according to claim 1 , further comprising an insulating thin-film portion located between the second storage node electrode and the buried strap.
4. A semiconductor device comprising:
a semiconductor substrate having a semiconductor layer of a first conduction type, including a trench having an inner surface;
a gate electrode formed on the semiconductor layer via a gate insulating film;
a source region and a drain region each of a second conduction type formed on a surface layer of the semiconductor layer; and
a trench capacitor electrically connected to one of the source and drain regions, the trench capacitor including
a capacitor insulating film formed on the inner surface, the capacitor insulating film located in a lower portion of the trench,
a collar insulating film formed above the capacitor insulating film in the inner surface, and
a storage node electrode buried in the trench, and electrically connected to one of the source and drain regions, the storage node electrode including
a first conductive layer formed on the capacitor insulating film in the trench to bury the lower portion, and having a recess at the upper surface with a V-shaped cross section a second conductive layer buried in the recess, a third conductive layer formed on the collar insulating film in the trench, and a fourth conductive layer formed above the third conductive layer in the trench.
5. The semiconductor device according to claim 4 , wherein the first, third, and fourth conductive layers each comprise polysilicon and the second conductive layer comprises germanium or silicon germanium.
6. The semiconductor device according to claim 4 , further comprising an insulating thin-film portion located between the third and fourth conductive layers.
7. The semiconductor device according to claim 1 , wherein the buried layer has a flat top surface substantially parallel to a surface of the semiconductor substrate.
8. The semiconductor device according to claim 1 , wherein the first storage node electrode includes at least one of a seam or a void.
9. A semiconductor device comprising:
a semiconductor substrate including a trench having an inner wall;
a first storage node electrode formed in the trench including a seam formed in the first storage node electrode, an entire length of the seam being parallel to the inner wall, and a V-shaped recess formed in a top surface of the first storage node electrode in contact with the seam;
a capacitor insulating film located between the first storage node electrode and the inner wall;
a buried layer formed on the recess, the buried layer including an electrically conducting material;
a second storage node electrode formed on the buried layer in the trench;
a collar insulating film located between the second storage node electrode and the inner wall; and
a buried strap formed above the second storage node electrode in the trench.
10. The semiconductor device according to claim 9 , wherein the first and second storage node electrodes and the buried strap each comprise polysilicon and the buried layer comprises germanium or silicon germanium.
11. The semiconductor device according to claim 9 , further comprising an insulating thin-film member located between the second storage node electrode and the buried strap.
12. The semiconductor device according to claim 9 , wherein the recess has an approximately V-shaped cross section.
13. The semiconductor device according to claim 9 , wherein the buried layer includes a flat upper surface.
14. The semiconductor device according to claim 12 , further comprising an insulating thin-film member located between the second storage node electrode and the buried strap.