Semiconductive metal oxide thin film ferroelectric memory transistor
The present invention discloses a novel transistor structure employing semiconductive metal oxide as the transistor conductive channel. By replacing the silicon conductive channel with a semiconductive metal oxide channel, the transistors can achieve simpler fabrication process and could realize 3D structure to increase circuit density. The disclosed semiconductive metal oxide transistor can have great potential in ferroelectric non volatile memory device with the further advantages of good interfacial properties with the ferroelectric materials, possible lattice matching with the ferroelectric layer, reducing or eliminating the oxygen diffusion problem to improve the reliability of the ferroelectric memory transistor. The semiconductive metal oxide film is preferably a metal oxide exhibiting semiconducting properties at the transistor operating conditions, for example, In 2 O 3 or RuO 2 . The present invention ferroelectric transistor can be a metal-ferroelectric-semiconductive metal oxide FET having a gate stack of a top metal electrode disposed on a ferroelectric layer disposed on a semiconductive metal oxide channel on a substrate. Using additional layer of bottom electrode and gate dielectric, the present invention ferroelectric transistor can also be a metal-ferroelectric-metal (optional)-gate dielectric (optional)-semiconductive metal oxide FET.
1. A method of fabricating a ferroelectric memory transistor comprising:
preparing an isolation substrate;
forming a semiconductive metal oxide channel layer on the isolation substrate;
forming a replacement gate stack on the semiconductive metal oxide layer, the replacement gate stack comprising
a sacrificial layer over the semiconductive metal oxide layer;
forming drain and source regions on opposite sides of the replacement gate stack;
filling the areas surrounding the replacement gate stack while exposing the top portion of the replacement gate stack;
removing the sacrificial layer portion of the replacement gate stack;
forming the remainder of the gate stack, the remainder of the gate stack comprising;
a ferroelectric material layer over the semiconductive metal oxide layer; and
a top electrode conductive layer over the ferroelectric material layer, and
forming drain and source regions on opposite sides of the replacement gate stack before forming any of the other recited components of the gate stack.
2. A method as in claim 1 wherein the replacement gate stack further comprises a bottom electrode conductive layer positioned between the semiconductive metal oxide layer and the sacrificial layer.
3. A method as in claim 1 wherein the replacement gate stack further campuses a gate dielectric layer positioned between the semiconductive metal oxide layer and the sacrificial layer.
4. A method as in claim 1 wherein the sacrificial layer material comprises silicon nitride or silicon dioxide.
5. A method as in claim 1 further comprising the formation of a conductive layer for source/drain contact.
6. A method as in claim 1 wherein the filling of the areas surrounding the replacement gate stack while exposing a top portion of the replacement gate stack comprises
the deposition of a dielectric film; and
the planarization of the deposited dielectric film to expose the top portion of the replacement gate stack.
7. A method as in claim 1 wherein the formation of the remainder of the gate stack comprises
deposition of the ferroelectric material layer;
planarization of the ferroelectric material layer;
deposition of the top electrode conductive layer;
photolithography patterning of the top electrode conductive layer; and
etching of the top electrode conductive layer.
8. A method as in claim 1 wherein the formation of the replacement gate stack comprises the deposition of the replacement gate stack, the photolithography patterning of the replacement gate stack and the etching of the replacement gate stack.
9. A method as in claim 1 wherein the top electrode conductive layer is a layer of a metal, taken from the group of layers consisting of a layer of conductive oxide and a multilayer of metal and conductive oxide.
10. A method as in claim 1 wherein the conductive oxide layer comprises a conductive perovskite oxide, a high temperature superconducting oxide, or an oxide film of any metal selected from a group consisting of Mo, W, Tc, Re, Ru, Os, Rh, Ir, Pd, Pt, In, Zn, Sn, Nd, Nb, Sm, La, and V.
11. A method as in claim 1 wherein the semiconductive metal oxide is selected from a group consisting of indium oxide, ruthenium oxide, tungsten oxide, molybdenum oxide, titanium oxide, inn oxide, tin oxide, zinc oxide, CeO 2 , Ga 2 O 3 , SrTiO 3 , LaFeO 3 , and Cr x Ti y O 3 .
12. A method as in claim 1 wherein the semiconductive metal oxide layer comprises a metal oxide film of any metal selected from a group consisting of Mo, W, Tc, Re, Ru, Os, Rh, Ir, Pd, Pt, In, Zn, Sn, Nd, Nb, Sm, La, and V.
13. A method as in claim 1 wherein the ferroelectric material is selected from a group consisting of PZT, SBT, PGO, BaTiO 3 , LiNbO 3 , STO, BST, BSTO, SBTN, PLT and PLZT.