Methods for fabricating dual bit flash memory devices
View Patent ↗Methods for fabricating dual bit memory devices are provided. In an exemplary embodiment of the invention, a method for fabricating a dual bit memory device comprises forming a charge trapping layer overlying a substrate and etching an isolation opening through the charge trapping layer. An oxide layer is formed overlying the charge trapping layer and within the isolation opening. A control gate is fabricated overlying the isolation opening and portions of the charge trapping layer adjacent to the isolation opening. The oxide layer and the charge trapping layer are etched using the control gate as an etch mask and impurity dopants are implanted into the substrate using the control gate as an implantation mask.
1. A method for fabricating a dual bit memory device, the method comprising:
forming a charge trapping layer overlying a substrate;
etching an isolation opening through the charge trapping layer;
forming an oxide layer overlying the charge trapping layer and within the isolation opening, wherein the oxide layer within the isolation opening forms an isolation region;
fabricating a control gate overlying the isolation opening and portions of the charge trapping layer adjacent to the isolation opening;
etching the oxide layer and the charge trapping layer using the control gate as an etch mask, wherein the portions of the charge trapping layer comprise a first and second storage element of a dual bit memory device, wherein the isolation region separates the first and second storage elements; and
implanting impurity dopants into the substrate using the control gate as an implantation mask to form an impurity doped bitline region within the substrate.
2. The method of claim 1 , further comprising the step of conformally depositing an insulating layer overlying the control gate and the impurity doped bitline region.
3. The method of claim 2 , further comprising the step of removing a portion of the insulating layer to expose the control gate.
4. The method of claim 3 , further comprising the step of forming a polycrystalline silicon layer overlying the exposed control gate.
5. The method of claim 1 , wherein the step of etching an isolation opening through the charge trapping layer comprises the following steps:
depositing a sacrificial layer overlying the charge trapping layer;
removing a portion of the sacrificial layer to form sacrificial members overlying the charge trapping layer; and
etching the isolation opening through the charge trapping layer using the sacrificial members as a mask.
6. The method of claim 5 , further comprising the step of forming sidewall spacers about sidewalls of the sacrificial members and wherein the step of etching the isolation opening through the charge trapping layer using the sacrificial members as a mask comprises the step of etching the isolation opening through the charge trapping layer using the sacrificial members and sidewall spacers as a mask.
7. The method of claim 6 , wherein the step of forming sidewall spacers comprises forming sidewall spacers of silicon nitride.
8. The method of claim 5 , further comprising the step of removing the sacrificial members after the step of fabricating the control gate.
9. The method of claim 5 , further comprising the step of depositing an intermediate layer overlying the charge trapping layer before the step of depositing a sacrificial layer overlying the charge trapping layer.
10. The method of claim 9 , wherein the step of removing a portion of the sacrificial layer to form sacrificial members overlying the charge trapping layer comprises the step of removing a portion of the intermediate layer that does not underlie the sacrificial members.
11. The method of claim 9 , wherein the step of depositing an intermediate layer comprises the step of depositing an intermediate layer of a material that is different from the sacrificial layer.
12. The method of claim 11 , further comprising the step of forming a silicon oxide layer overlying the charge trapping layer before the step of depositing an intermediate layer.
13. The method of claim 12 , wherein the step of depositing an intermediate layer comprises depositing an intermediate layer having a composition different from the composition of the silicon oxide layer.
14. The method of claim 13 , wherein the step of depositing an intermediate layer comprises depositing a polycrystalline silicon layer.
15. The method of claim 14 , wherein the step of depositing a sacrificial layer comprises depositing a silicon oxide layer.
16. The method of claim 5 , wherein the step of fabricating a control gate comprises:
depositing a conductive material overlying the oxide layer and between the sacrificial members; and
etching the conductive material such that the oxide layer is exposed.
17. The method of claim 16 , wherein the step of depositing a conductive material comprises depositing polycrystalline silicon.
18. The method of claim 1 , wherein the step of forming a charge trapping layer comprises the step of forming a charge trapping layer of a silicon-rich silicon nitride.