Atomic layer deposition of P-type oxide semiconductor thin films
Provided herein are methods of depositing p-type metal oxide thin films by atomic layer deposition (ALD). Also provided are p-type metal oxide thin films and TFTs including p-type metal oxide channels. In some implementations, the p-type metal oxide thin films have a metal and oxygen vacancy defect density of less than 10 19 /cm 3 . The p-type metal oxide thin films may be electrically active throughout the entire thicknesses of the thin films.
1. A method of forming a thin film transistor (TFT) comprising:
providing a substrate;
exposing the substrate to a pulse of a first reactant to form an adsorbed layer of the first reactant over the substrate;
exposing the substrate to a pulse of a second reactant to react with the first reactant; and
exposing the substrate to a pulse of an oxidant to form a metal oxide layer, where the metal oxide layer is a tin-based (Sn-based) p-type semiconductor layer including a ternary compound Sn(II)—X—O that includes Sn—X bonds, wherein X is one of titanium (Ti), tungsten (W), boron (B), or niobium (Nb).
2. The method of claim 1 , wherein the first reactant is an Sn(II)-based organometallic reactant.
3. The method of claim 1 , wherein the substrate temperature is between about 50° C. and 300° C.
4. The method of claim 1 , wherein the oxidant is selected from the group consisting of oxygen (O 2 ), ozone (O 3 ), water (H 2 O), hydrogen peroxide (H 2 O 2 ), carbon dioxide (CO 2 ), carbon monoxide (CO), methanol (CH 3 OH), ethanol (C 2 H 6 OH), isopropyl alcohol (C 3 H 7 OH), and combinations thereof.
5. The method of claim 1 , wherein the oxidant is a hydrogen-containing oxidant.
6. The method of claim 5 , wherein hydrogen from the hydrogen-containing oxidant is incorporated in the metal oxide layer.
7. The method of claim 1 , wherein the oxidant is a weak oxidant.
8. The method of claim 1 , wherein exposing the substrate to a pulse of an oxidant includes applying energy to the pulse of the oxidant to form a plasma.
9. The method of claim 1 , wherein the second reactant is selected from the group consisting of tungsten-containing reactants, titanium-containing reactants, niobium-containing reactants, and boron-containing reactants.
10. The method of claim 1 , further comprising exposing the substrate to a dopant pulse.
11. The method of claim 10 , wherein the dopant is hydrogen.
12. The method of claim 1 , further comprising forming a gate electrode and a gate dielectric, wherein the gate dielectric is between the p-type semiconductor layer and the gate electrode.
13. The method of claim 12 , wherein the gate electrode is formed over the metal oxide layer.
14. The method of claim 12 , wherein the metal oxide layer is formed over the gate electrode.
15. The method of claim 1 , wherein the exposing the substrate to a pulse of the second reactant forms an adsorbed layer of the second reactant on the substrate surface.
16. A method of forming a thin film transistor (TFT) comprising:
providing a substrate;
exposing the substrate to a pulse of a metal reactant to form an adsorbed layer of the metal reactant over the substrate;
exposing the substrate to a pulse of an oxidant to react with the adsorbed layer of the metal reactant to form a metal oxide layer, wherein the metal oxide layer is a tin(II)-based p-type semiconductor layer having substantially no tin(IV); and
incorporating a hydrogen content of at least 10 20 atoms/cm 3 into the metal oxide layer, wherein incorporating a hydrogen content of at least 10 20 atoms/cm 3 into the metal oxide layer includes exposing the substrate to a hydrogen-containing atmosphere during the metal reactant and oxidant pulses.
17. The method of claim 16 , wherein the oxidant is a hydrogen-containing oxidant.
18. The method of claim 16 , wherein incorporating a hydrogen content of at least 10 20 atoms/cm 3 into the metal oxide layer includes exposing the substrate to dopant pulses to incorporate hydrogen into the metal oxide layer.
19. The method of claim 16 , wherein incorporating a hydrogen content of at least 10 20 atoms/cm 3 into the metal oxide layer includes annealing the metal oxide layer in a hydrogen atmosphere.
20. A method of forming a thin film transistor (TFT) comprising:
providing a substrate;
exposing the substrate to a pulse of a metal reactant to form an adsorbed layer of the metal reactant over the substrate;
exposing the substrate to a pulse of an oxidant to react with the adsorbed layer of the metal reactant to form a metal oxide layer, wherein the metal oxide layer is a tin(II)-based p-type semiconductor layer having substantially no tin(IV); and
incorporating a hydrogen content of at least 10 20 atoms/cm 3 into the metal oxide layer, wherein the oxidant is a hydrogen-containing oxidant and incorporating a hydrogen content of at least 10 20 atoms/cm 3 into the metal oxide layer includes applying energy to the pulse of the hydrogen-containing oxidant to form a plasma and incorporating hydrogen from the plasma into the metal oxide layer.