Nonvolatile memory device and method for fabricating the same
View Patent ↗A nonvolatile memory device and a method for fabricating the same decreases power consumption and prevents contamination of an insulating layer. The nonvolatile memory devices includes a semiconductor substrate; a tunneling oxide layer formed on a predetermined portion of the semiconductor substrate; a floating gate formed on the tunneling oxide layer, the floating gate having a trench structure; a control gate formed inside the trench structure of the floating gate; and a gate insulating layer disposed between the floating gate and the control gate.
1. A method for fabricating a nonvolatile memory device, comprising:
forming a tunneling oxide layer on a predetermined portion of a semiconductor substrate;
forming a first polysilicon layer for formation of a floating gate on the tunneling oxide layer;
forming a trench in the first polysilicon layer, the french having a predetermined depth;
forming a gate insulating layer in the trench formed in the first polysilicon layer;
forming, on the gate insulating layer, a second polysilicon layer for formation of a control gate;
performing chemical mechanical polishing with respect to the second polysilicon layer and the gate insulating layer; and
etching a portion of the first polysilicon layer using a photoresist pattern, wherein a remaining portion of the first polysilicon layer forms the floating gate.
2. The method of claim 1 , wherein the first polysilicon layer has a thickness of 4500˜5500 Å.
3. The method of claim 1 , wherein forming the first polysilicon layer comprises low-pressure chemical vapor deposition.
4. The method of claim 1 , wherein the trench formed in the first polysilicon layer comprises an etching process using chlorine gas (Cl 2 ).
5. The method of claim 1 , wherein the trench formed in the first polysilicon layer has a depth of 2500˜3500 Å.
6. The method of claim 1 , wherein the second polysilicon layer has a thickness of 3500˜4500 Å.
7. The method of claim 1 , wherein said etching is isotropic etching.
8. The method of claim 1 , further comprising:
forming, after forming the control gate, insulating sidewalls on lateral sides of the floating gate;
forming source/drain regions in the semiconductor substrate on either side of the floating gate; and
forming a silicide layer on upper surfaces of the floating gate and the control gate and on the semiconductor substrate in correspondence with the source/drain regions.
9. The method of claim 3 , wherein forming the first polysilicon layer comprises covering the tunneling oxide layer with the first polysilicon layer.
10. The method of claim 1 , wherein forming the gate insulating layer comprises:
forming a lower oxide layer having a thickness of about 50˜70 Å by low pressure chemical vapor deposition, wherein the lower oxide layer covers all surfaces within the trench and an upper surface area of the first polysilicon layer adjacent to the trench;
forming a nitride layer having a thickness of about 60˜80 Å over the lower oxide layer by low pressure chemical vapor deposition; and
forming an upper oxide layer over the nitride layer.
11. The method of claim 10 , wherein forming the second polysilicon layer fills a remaining space in the trench.
12. The method of claim 11 , wherein chemical mechanical polishing the second polysilicon layer and the gate insulating layer exposes an upper surface area of the first polysilicon layer adjacent to the trench.
13. The method of claim 12 , wherein the photoresist pattern is formed over an entire top surface of the control gate, entire top surfaces of the gate insulating layer, and a portion of the upper surface area of the first polysilicon layer adjacent to the trench.
14. The method of claim 12 , wherein the second polysilicon layer and the gate insulating layer are completely within the trench after chemical mechanical polishing.
15. The method of claim 8 , wherein forming the source/drain regions comprises implanting impurity ions into the semiconductor substrate using the floating gate, the gate insulating layer, the control gate, and the insulating sidewalls as a mask.
16. The method of claim 8 , further comprising forming an insulating layer covering the semiconductor substrate and all structures Thereon after forming the suicide layer.
17. The method of claim 16 , further comprising forming contact holes in the insulating layer to expose the silicide layer over the source/drain regions and the control gate.
18. The method of claim 17 , further comprising forming conductive plugs in the contact holes.
19. The method of claim 1 , wherein forming the tunneling oxide layer comprises thermal oxidation of the semiconductor substrate at a temperature of about 700˜800°C.
20. The method of claim 1 , wherein the tunneling oxide layer has a thickness of about 90˜100 Å.