Treatment of gate dielectric for making high performance metal oxide and metal oxynitride thin film transistors
Embodiments of the present invention generally include TFTs and methods for their manufacture. The gate dielectric layer in the TFT may affect the threshold voltage of the TFT. By treating the gate dielectric layer prior to depositing the active channel material, the threshold voltage may be improved. One method of treating the gate dielectric involves exposing the gate dielectric layer to N 2 O gas. Another method of treating the gate dielectric involves exposing the gate dielectric layer to N 2 O plasma. Silicon oxide, while not practical as a gate dielectric for silicon based TFTs, may also improve the threshold voltage when used in metal oxide TFTs. By treating the gate dielectric and/or using silicon oxide, the threshold voltage of TFTs may be improved.
1. A thin film transistor fabrication method, comprising:
depositing a gate dielectric layer over a gate electrode and a substrate;
exposing the gate dielectric layer to an oxygen containing plasma;
sputter depositing an oxynitride a semiconductor layer over the gate dielectric layer, the semiconductor layer comprising oxygen, nitrogen, and one or more elements selected from the group consisting of zinc, gallium, indium, cadmium, tin, and combinations thereof;
depositing a conductive layer over the semiconductor layer; and
etching the conductive layer to define source and drain electrodes and an active channel, the active channel exposing a portion of the semiconductor layer.
2. The method of claim 1 , wherein the gate dielectric layer comprises silicon nitride, silicon oxide, or a bi-layer of silicon nitride and silicon oxide.
3. The method of claim 1 , further comprising exposing the gate dielectric layer to a hydrogen plasma after exposing the gate dielectric to the oxygen containing plasma.
4. The method of claim 1 , wherein the exposing is performed in-situ with the gate dielectric layer deposition.
5. The method of claim 1 , wherein the oxygen containing plasma comprises N 2 O.
6. A thin film transistor fabrication method, comprising:
depositing a silicon nitride layer over a gate electrode and a substrate;
depositing a silicon oxide layer over the silicon nitride layer;
sputter depositing an oxynitride semiconductor layer over the silicon oxide layer, the semiconductor layer comprising oxygen, nitrogen, and one or more elements selected from the group consisting of zinc, gallium, indium, cadmium, tin, and combinations thereof;
depositing a conductive layer over the semiconductor layer; and
etching the conductive layer to define source and drain electrodes and an active channel, the active channel exposing a portion of the semiconductor layer.
7. The method of claim 6 , further comprising exposing the silicon oxide layer to N 2 O plasma.
8. The method of claim 7 , further comprising exposing the silicon oxide layer to hydrogen plasma after exposing the silicon oxide layer to N 2 O plasma.
9. The method of claim 7 , wherein the exposing occurs in situ with the silicon oxide layer deposition.
10. The method of claim 7 , further comprising exposing the silicon oxide layer to oxygen plasma after the exposing to N 2 O plasma.
11. A thin film transistor fabrication method, comprising:
depositing a silicon oxide layer over a gate electrode and a substrate;
sputter depositing an oxynitride a semiconductor layer over the silicon oxide layer, the semiconductor layer comprising oxygen, nitrogen, and one or more elements selected from the group consisting of zinc, gallium, indium, cadmium, tin, and combinations thereof;
depositing a conductive layer over the semiconductor layer; and
etching the conductive layer to define source and drain electrodes and an active channel, the active channel exposing a portion of the semiconductor layer.
12. The method of claim 11 , further comprising exposing the silicon oxide layer to N 2 O plasma.
13. The method of claim 12 , further comprising exposing the silicon oxide layer to hydrogen plasma after exposing the silicon oxide layer to N 2 O plasma.
14. The method of claim 12 , wherein the exposing occurs in situ with the silicon oxide layer deposition.
15. The method of claim 12 , further comprising exposing the silicon oxide layer to oxygen plasma after the exposing to N 2 O plasma.
16. A thin film transistor, comprising:
a silicon oxide layer disposed over a gate electrode and a substrate;
an oxynitride semiconductor layer disposed over the silicon oxide layer, the semiconductor layer comprising oxygen, nitrogen, and one or more elements selected from the group consisting of zinc, gallium, indium, cadmium, tin, and combinations thereof; and
a source electrode and a drain electrode disposed over the semiconductor layer, the source and drain electrodes spaced from each other to expose a portion of the semiconductor layer.
17. The transistor of claim 16 , further comprising a silicon nitride layer disposed on the gate electrode and substrate, and below the silicon oxide layer.