Laser annealing technique for metal oxide TFT
This disclosure provides methods and apparatuses for annealing an oxide semiconductor in a thin film transistor (TFT). In one aspect, the method includes providing a substrate with a partially fabricated TFT structure formed on the substrate. The partially fabricated TFT structure can include an oxide semiconductor layer and a dielectric oxide layer on the oxide semiconductor layer. The oxide semiconductor layer is annealed by heating the dielectric oxide layer with an infrared laser under ambient conditions to a temperature below the melting temperature of the oxide semiconductor layer. The infrared laser radiation can be substantially absorbed by the dielectric oxide layer and can remove unwanted defects from the oxide semiconductor layer at an interface in contact with the dielectric oxide layer.
1. A method to make a thin film transistor (TFT), the method comprising:
providing a substrate;
forming an oxide semiconductor layer over the substrate;
forming a dielectric oxide layer over the oxide semiconductor layer so that the dielectric oxide layer is contacting the oxide semiconductor layer; and
annealing without crystallizing the oxide semiconductor layer by heating the dielectric oxide layer with an infrared (IR) laser radiation under ambient conditions to a temperature below a melting temperature of the oxide semiconductor layer, the oxide semiconductor layer and the dielectric oxide layer forming part of the TFT, wherein a wavelength of the IR laser radiation corresponds to a thickness and a composition of the dielectric oxide layer so that the dielectric oxide layer substantially absorbs the IR laser radiation during annealing.
2. The method of claim 1 , wherein the wavelength of the IR laser radiation is selected to correspond to the composition and thickness of the dielectric oxide layer to absorb at least 70% of the IR laser radiation.
3. The method of claim 1 , wherein the thickness of the dielectric oxide layer is between about 100 nm and about 1000 nm.
4. The method of claim 1 , wherein an absorption coefficient of the dielectric oxide layer is about equal to or greater than 2.0 μm −1 .
5. The method of claim 1 , wherein the dielectric oxide layer includes at least one of SiO 2 and Al 2 O 3 .
6. The method of claim 1 , wherein the temperature for annealing is between about 200° C. and about 500° C.
7. The method of claim 1 , further comprising:
forming a source metal on a source region of the oxide semiconductor layer; and
forming a drain metal on a drain region of the oxide semiconductor layer, wherein a channel region of the oxide semiconductor layer is defined between the source region and the drain region.
8. The method of claim 7 , further comprising:
etching the source metal and the drain metal to expose the channel region of the oxide semiconductor layer, wherein annealing the oxide semiconductor layer occurs after etching the source metal and the drain metal.
9. The method of claim 8 , wherein the dielectric oxide layer is a passivation layer, the passivation layer being formed after the etching the source metal and the drain metal.
10. The method of claim 8 , wherein the dielectric oxide is an etch stop layer, the etch stop layer being formed before etching the source metal and the drain metal.
11. The method of claim 8 , wherein the dielectric oxide layer includes a gate dielectric, the gate dielectric being formed before etching the source metal and the drain metal.
12. The method of claim 7 , further comprising:
forming a gate metal over the substrate, wherein the temperature for annealing is below a melting temperature of the source metal, the drain metal, and the gate metal.
13. The method of claim 1 , wherein the oxide semiconductor layer includes InGaZnO.
14. The method of claim 1 , wherein the IR laser radiation is emitted from a carbon dioxide (CO 2 ) laser.
15. The method of claim 1 , wherein annealing the oxide semiconductor layer by heating the dielectric oxide layer increases a density of the oxide semiconductor layer without crystallizing the oxide semiconductor layer.
16. The method of claim 1 , wherein annealing the oxide semiconductor layer by heating the dielectric oxide layer reduces a defect density in the oxide semiconductor layer without crystallizing the oxide semiconductor layer.
17. The method of claim 1 , wherein annealing the oxide semiconductor layer is localized at a back channel interface of the oxide semiconductor layer, the back channel interface contacting the dielectric oxide layer.
18. A method to make a thin film transistor (TFT), the method comprising:
providing a substrate;
forming an oxide semiconductor layer over the substrate;
forming a source metal on a source region of the oxide semiconductor layer; and
forming a drain metal on a drain region of the oxide semiconductor layer, wherein a channel region of the oxide semiconductor layer is defined between the source region and the drain region;
etching the source metal and the drain metal to expose the channel region of the oxide semiconductor layer;
forming a dielectric oxide layer over the oxide semiconductor layer so that the dielectric oxide layer is contacting the oxide semiconductor layer; and
annealing without crystallizing the oxide semiconductor layer by heating the dielectric oxide layer with an infrared (IR) laser radiation under ambient conditions to a temperature below a melting temperature of the oxide semiconductor layer, the oxide semiconductor layer and the dielectric oxide layer forming part of the TFT, wherein annealing the oxide semiconductor layer occurs after etching the source metal and the drain metal.
19. The method of claim 18 , wherein the dielectric oxide layer is a passivation layer, the passivation layer being formed after the etching the source metal and the drain metal.
20. The method of claim 18 , wherein the dielectric oxide layer is an etch stop layer, the etch stop layer being formed before etching the source metal and the drain metal.
21. The method of claim 18 , wherein the dielectric oxide layer includes a gate dielectric, the gate dielectric being formed before etching the source metal and the drain metal.