TFT SAS memory cell structures
A device having thin-film transistor (TFT) silicon-aluminum oxide-silicon (SAS) memory cell structures is provided. The device includes a substrate, a dielectric layer on the substrate, and one or more source or drain regions being embedded in the dielectric layer. the dielectric layer being associated with a first surface. Each of the one or more source or drain regions includes an N + polysilicon layer on a diffusion barrier layer which is on a conductive layer. The N + polysilicon layer has a second surface substantially co-planar with the first surface. Additionally, the device includes a P − polysilicon layer overlying the co-planar surface, an aluminum oxide layer overlying the P − polysilicon layer; and at least one control gate overlying the aluminum oxide layer. In a specific embodiment, the control gate is made of highly doped P + polysilicon. A method for making the TFT SAS memory cell structure is provided and can be repeated to integrate the structure three-dimensionally.
1. A method for making a thin-film transistor (TFT) silicon-aluminum oxide-silicon (SAS) memory cell structure, the method comprising:
providing a substrate;
forming a first insulation layer on the substrate;
forming one or more source or drain regions on the first insulation layer, each of the one or more source or drain regions being associated with a first surface and including an N+ polysilicon layer, a barrier layer, and a conductive layer, the N+ polysilicon layer being on the barrier layer, the barrier layer overlying the conductive layer, the first surface comprising N+ polysilicon;
forming a second insulation layer on the first insulation layer, the second insulation layer being associated with a second surface, the second surface being substantially co-planar with the first surface;
forming a P− polysilicon layer overlying the first surface and the second surface, the P− polysilicon layer being capable of forming a channel from the source region to the drain region;
forming an aluminum oxide layer overlying the P− polysilicon layer;
forming a P+ polysilicon layer overlying the aluminum oxide layer; and
forming at least one control gate by patterning the P+ polysilicon layer;
wherein the conductive layer comprises a titanium silicide (TiSi 2 ) that is formed through a thermal CVD using a gas mixture of SiH 4 and TiCl 4 and followed by a thermal annealing at about 600° C. to about 800° C.
2. The method of claim 1 wherein the method of forming one or more source or drain regions on the first insulation layer further comprises:
forming a first conductive layer on the first insulation layer;
forming a barrier layer on the conductive layer;
forming a N+ polysilicon layer on the barrier layer; and
patterning the N+ polysilicon layer, the barrier layer, and the conductive layer to form one or more confined regions including the first surface.
3. The method of claim 2 wherein the first insulation layer comprises silicon dioxide.
4. The method of claim 2 wherein the barrier layer is metal-nitride comprising TiN.
5. The method of claim 1 wherein forming a second insulation layer on the first insulation layer further comprises:
depositing the second insulation layer to cover one or more source or drain regions on the first insulation layer; and
performing CMP and/or etch back process so as to form the second surface, the second surface being substantially co-planar with the first surface.
6. The method of claim 5 wherein the second insulation layer comprises silicon oxide deposited by high-density-plasma-assisted chemical vapor deposition.
7. The method of claim 5 wherein the second insulation layer comprises TEOS deposited silicon oxide.
8. The method of claim 1 wherein the method of forming a P− polysilicon layer overlying the first surface and the second surface further comprises:
depositing polysilicon using low pressure chemical vapor deposition (LPCVD) technique with SiH4 and B2H6 precursors at a temperature ranging from 520 Degrees Celsius to 560 Degrees Celsius; and
performing thermal annealing treatment at a temperature ranging from 520 Degrees Celsius to 560 Degrees Celsius after deposition.
9. The method of claim 1 wherein the method of forming a P− polysilicon layer overlying the first surface and the second surface further comprises:
depositing polysilicon using low pressure chemical vapor deposition (LPCVD) technique with Si2H6 and B2H6 precursors at a temperature ranging from 420 Degrees Celsius to 520 Degrees Celsius; and
performing thermal annealing treatment at a temperature ranging from 420 Degrees Celsius to 520 Degrees Celsius after deposition.
10. The method of claim 1 wherein the method forming an aluminum oxide layer on the P− polysilicon layer includes atomic layer deposition (ALD) technique.
11. The method of claim 1 further comprising forming a tunnel dielectric barrier layer between the P− polysilicon layer and the aluminum oxide layer.
12. The method of claim 11 wherein the aluminum oxide layer is capable of trapping charges injected from the P− polysilicon layer through the dielectric barrier.
13. The method of claim 1 wherein the control gate is positioned over at least one N+ polysilicon source and one N+ polysilicon drain region.
14. The method of claim 1 further comprising repeating the process steps to integrate the memory cell structures three-dimensionally.