Semiconductor device and method for making the same
A semiconductor device includes: a substrate having a base and an array of semiconductor pillars extending from the base, the substrate being formed with a plurality of trenches, each of which extends into the base and has two opposing trench side walls; a first insulative liner layer formed on each of the trench side walls of each of the trenches and divided into upper and lower segments by a gap that leaves a bit-forming surface of each of the trench side walls uncovered by the first insulative liner layer; and a plurality of buried bit lines, each of which extends into the base from the bit-forming surface of a respective one of the trench side walls of each of the trenches.
1. A method for making a semiconductor device, comprising:
(a) forming a plurality of trenches in a substrate;
(b) forming a first insulative liner layer on two opposing trench side walls of each of the trenches;
(c) partially covering the first insulative liner layer with a bit-controlling material such that only an upper segment of the first insulative liner layer on each of the trench side walls is uncovered by the bit-controlling material;
(d) forming a second insulative liner layer on the upper segment of the first insulative liner layer on each of the trench side walls, the second insulative liner layer being made from a material different from those of the first insulative liner layer and the bit-controlling material;
(e) removing atop portion of the bit-controlling material and an intermediate segment of the first insulative liner layer that is covered by the top portion of the bit-controlling material so as to uncover a bit-forming surface of each of the trench side walls; and
(f) diffusing a dopant into the substrate through the bit-forming surface to form a buried bit line that extends inwardly from the bit-forming surface into each of the trench side walls.
2. The method of claim 1 , wherein step (e) is conducted by first removing the top portion of the bit-controlling material so as to expose the intermediate segment of the first insulative liner layer on each of the trench side walls, followed by removing the intermediate segment of the first insulative liner layer on each of the trench side walls so as to uncover the bit-forming surface of each of the trench side walls.
3. The method of claim 1 , wherein step (c) is conducted by filling each of the trenches with the bit-controlling material that covers entirely the first insulative liner layer on each of the trench side walls, followed by removing an upper portion of the bit-controlling material so as to expose the upper segment of the first insulative liner layer on each of the trench side walls.
4. The method of claim 1 , wherein step (d) is conducted by depositing the second insulative liner layer on a top end of the bit-controlling material and on the upper segment of the first insulative liner layer on each of the trench side walls, followed by removing a bottom portion of the second insulative liner layer to expose the top end of the bit-controlling material.
5. The method of claim 1 , wherein the bit-controlling material is selected from SiN, SiO 2 , poly-Si and photoresist.
6. The method of claim 1 , wherein the first insulative liner layer is made from a material selected from SiN, SiO 2 , SiON, and combinations thereof.
7. The method of claim 1 , wherein the second insulative liner layer is made from a material selected from SiN, SiON, and SiO 2 .
8. The method of claim 1 , wherein step (f) is conducted using plasma doping techniques.
9. The method of claim 1 , wherein step (f) is conducted by forming a dopant-doped poly-Si layer on the bit-forming surface through deposition techniques, followed by annealing.
10. The method of claim 1 , wherein step (f) is conducted using phosphine annealing techniques.
11. The method of claim 1 , wherein the substrate is a silicon wafer.
12. The method of claim 11 , further comprising depositing a refractory metal on the bit-forming surface so as to form a conductive silicide layer on the bit-forming surface of each of the trench side walls after step (f).
13. The method of claim 12 , wherein the refractory metal is selected from titanium, tungsten, nickel and cobalt.
14. The method of claim 1 , further comprising filling an insulative isolation material in each of the trenches after step (f) to cover the bit-forming surface of each of the trench side walls.