Method for manufacturing a non-volatile memory device
View Patent ↗An increase of charge storing capacity, prevention of an over-erase, and a reduction of ΔVth may be achieved when a 2-bit/cell non-volatile memory device includes a gate of a predetermined width above a semiconductor substrate, an insulating layer between the gate and the semiconductor substrate and at lateral sides of the gate, having a greater width than the gate, a pair of storage layers at the lateral sides of the gate, a pair of blocking layers at the lateral sides of the gate and covering the pair of storage layers, a source and a drain formed in the semiconductor substrate at first opposed locations external to the gate, and a trap impurity implanted into the insulating layer at second locations external to the gate.
1. A method for manufacturing a non-volatile memory device, comprising:
forming a bottom insulating layer on a semiconductor substrate;
forming a gate of a predetermined width on the bottom insulating layer;
forming a sidewall insulating layer on the gate;
forming trap sites comprising a trap impurity in the bottom insulating layer at first locations external to the gate;
forming a pair of storage layers at lateral sides of the gate;
forming a source and a drain in the semiconductor substrate at second locations external to the pair of storage layers by ion implantation; and
forming a pair of blocking layers at opposite sides of the gate and covering the pair of storage layers.
2. The method of claim 1 , wherein forming the trap sites comprises forming the trap sites near an interface of the semiconductor substrate with the bottom insulating layer.
3. The method of claim 2 , wherein the trap impurity has a maximum concentration closer to the interface of the semiconductor substrate with the bottom insulating layer than to an upper surface of the bottom insulating layer.
4. The method of claim 1 , wherein the trap impurity comprises nitrogen, germanium, and/or oxygen.
5. The method of claim 1 , wherein forming the trap sites comprises thermal diffusion or a plasma method.
6. The method of claim 1 , wherein forming the trap sites comprises implanting nitrogen at a temperature of 700-900° C. from NO gas and/or N 2 gas.
7. The method of claim 6 , wherein forming the trap sites comprises implanting nitrogen from N 2 gas in or under an Ar or He plasma atmosphere.
8. The method of claim 1 , wherein the insulating layers and the blocking layers each independently comprise an oxide layer, and the storage layers comprise a nitride.
9. The method of claim 1 , wherein forming the pair of storage layers comprises:
forming a storage layer material above the semiconductor substrate; and
anisotropically etching the storage layer material so as to form the pair of storage layers on the lateral sides of the gate.
10. The method of claim 9 , wherein anisotropically etching the storage layer material comprises etching the storage layer material until a height of the storage layer becomes less than that of the gate.
11. The method of claim 1 , wherein forming the pair of blocking layers comprises:
forming a blocking layer material above the semiconductor substrate; and
anisotropically etching the blocking layer material so as to form the pair of blocking layers on both lateral sides of the gate.
12. The method of claim 11 , wherein anisotropically etching the blocking layer comprises etching the blocking layer until the gate is exposed.
13. The method of claim 1 , wherein each of the storage layers is capable of independently storing a bit of data.
14. The method of claim 1 , wherein forming the trap sites comprises implanting nitrogen at a temperature of 700-900° C. from NO gas.
15. The method of claim 1 , wherein the trap sites are chemically more unstable than the bottom insulating layer.
16. The method of claim 1 , wherein the trap impurity atoms break the crystal structure of the bottom insulating layer.
17. The method of claim 1 , wherein the trap impurity atoms do not form a stable compound by reaction with the insulating layer.
18. The method of claim 1 , wherein the trap impurity is nitrogen.
19. The method of claim 18 , wherein the trap impurity has a concentration of about 10 22 atoms/cm 3 .
20. The method of claim 1 , wherein the trap sites are formed by a thermal diffusion method.