THIN-FILM TRANSISTOR, METHOD OF PRODUCING THE SAME, AND DEVICES PROVIDED WITH THE SAME

• US 20110140100A1
• Filed: 12/09/2010
• Published: 06/16/2011
• Est. Priority Date: 12/10/2009
• Status: Active Grant

• Current Assignee: Samsung Display Company Limited (Samsung Group)
• Original Assignee: Fujifilm Corporation (Fujifilm Holdings Corporation)
• Inventors: Tanaka, Atsushi, Ono, Masashi, Suzuki, Masayuki, TAKATA, Masahiro
• Granted Patent: US 8,692,252 B2
• Time in Patent Office: Days
• US Class Current: 257/43
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate
• CPC Class Codes: H01L 29/78696 characterised by the structure of the channel, e.g. multichannel, transverse or longitudinal shape, length or width, doping structure, or the overlap or alignment between the channel and the gate, the source or the drain, or the contacting structure of the channel H01L29/78612 takes precedence; transistors having a drain offset region or a lightly doped drain [LDD] H01L29/78621

Abstract

A thin-film transistor including an oxide semiconductor layer is disclosed. The oxide semiconductor layer includes a first area, a second area and a third area forming a well-type potential in the film-thickness direction. The first area forms a well of the well-type potential and has a first electron affinity. The second area is disposed nearer to the gate electrode than the first area and has a second electron affinity smaller than the first electron affinity. The third area is disposed farther from the gate electrode than the first area and has a third electron affinity smaller than the first electron affinity. At least an oxygen concentration at the third area is lower than an oxygen concentration at the first area.

Claims

1. A thin-film transistor comprising an oxide semiconductor layer, a source electrode, a drain electrode, a gate insulating film and a gate electrode formed on a substrate,

wherein the oxide semiconductor layer comprises a first area, a second area and a third area forming a well-type potential in a film-thickness direction, the first area forming a well of the well-type potential and having a first electron affinity, the second area being disposed nearer to the gate electrode than the first area and having a second electron affinity smaller than the first electron affinity, and the third area being disposed farther from the gate electrode than the first area and having a third electron affinity smaller than the first electron affinity, and

wherein at least an oxygen concentration at the third area is lower than an oxygen concentration at the first area.

2. The thin-film transistor as claimed in claim 1, wherein an oxygen concentration at the second area is lower than the oxygen concentration at the first area.

3. The thin-film transistor as claimed in claim 1, wherein the first area and the second area have different cationic composition ratios, and the first area and the third area have different cationic composition ratios.

4. The thin-film transistor as claimed in claim 1, wherein the second area and the third area have bandgaps larger than a bandgap at the first area.

5. The thin-film transistor as claimed in claim 1, wherein the oxide semiconductor layer is amorphous.

6. The thin-film transistor as claimed in claim 1, wherein each area of the oxide semiconductor layer comprises at least one element selected from the group consisting of Al, Sc, Ti, Mn, Fe, Ga, Y, In, Sn, Ho, Er, Tm, Yb and Lu, and at least one element selected from the group consisting of Mg, Ca, Ni, Zn, Sr and Ba.

7. The thin-film transistor as claimed in claim 1, wherein each area of the oxide semiconductor layer comprises at least one of In and Ga.

8. The thin-film transistor as claimed in claim 1, wherein each area of the oxide semiconductor layer comprises a(In₂O₃)·

b(Ga₂O₃)·

c(ZnO), where a≧

0, b≧

0, c≧

0, a+b≠

0, b+c≠

0 and c+a≠

0.

9. The thin-film transistor as claimed in claim 8, wherein a value of b/(a+b) at the first area of the oxide semiconductor layer is smaller than values of b/(a+b) at the second area and the third area.

10. The thin-film transistor as claimed in claim 9, wherein the value of b/(a+b) at the first area of the oxide semiconductor layer is not more than 0.95.

11. The thin-film transistor as claimed in claim 10, wherein the values of b/(a+b) at the second area and the third area are not less than 0.5.

12. The thin-film transistor as claimed in claim 11, wherein the value of b/(a+b) at the first area of the oxide semiconductor layer is 0.25, and the values of b/(a+b) at the second area and the third area are 0.75.

13. The thin-film transistor as claimed in claim 1, wherein the substrate is flexible.

14. The thin-film transistor as claimed in claim 13, wherein the substrate comprises

anyone of the group of resin materials consisting of saturated polyester resin, polyethylene terephthalate resin, polyethylene naphthalate resin, cross-linked diester fumarate resin, polycarbonate resin, polyether sulfone resin, polysulfone resin, polyallylate resin, cyclic polyolefin resin, cellulose resin, polyimide resin, polyamideimide resin, maleimide-olefin resin, polyamide resin, acrylic resin, fluorine resin, epoxy resin, silicone resin film, polybenzoxazole resin, episulfide compound, liquid crystal polymer, cyanate resin and aromatic ether resin,

any one of the group of plastic materials consisting of a composite plastic material containing silicon oxide particles, a composite plastic material containing nanoparticles, such as metal nanoparticles, inorganic oxide nanoparticles or inorganic nitride nanoparticles, a composite plastic material containing a metal or inorganic nanofiber or a metal or inorganic microfiber, a composite plastic material containing carbon fiber and/or carbon nanotube, a composite plastic material containing glass flake, glass fiber and/or glass beads, composite plastic material containing a clay mineral or particles having a mica-derived crystal structure, and a multilayer plastic material including at least one bonded interface formed between thin glass and any one of the group of resin materials,

a substrate comprising a composite material with barrier performance including at least one bonded interface formed between alternately laminated layers of an inorganic material and any one of the group of resin materials, or

any one of the group of substrates consisting of a stainless steel substrate, a multilayer metal substrate including a stainless steel layer and a layer of a different metal, an aluminum substrate, and an aluminum substrate with an oxide film formed by an oxidation treatment applied to a surface thereof.

22. A display device comprising the thin-film transistor as claimed in claim 1.

23. An image sensor comprising the thin-film transistor as claimed in claim 1.

24. An X-ray sensor comprising the thin-film transistor as claimed in claim 1.

25. An X-ray digital imaging device comprising the X-ray sensor as claimed in claim 24.

26. The X-ray digital imaging device as claimed in claim 25 capable of photographing a moving image.

15. A method of producing a thin-film transistor including an oxide semiconductor layer, a source electrode, a drain electrode, a gate insulating film and a gate electrode formed on a substrate, the method comprising:

a film formation step of forming the oxide semiconductor layer through sputtering, wherein the oxide semiconductor layer comprises a first area, a second area and a third area forming a well-type potential in a film-thickness direction, the first area forming a well of the well-type potential and having a first electron affinity, the second area being disposed nearer to the gate electrode than the first area and having a second electron affinity smaller than the first electron affinity, and the third area being disposed farther from the gate electrode than the first area and having a third electron affinity smaller than the first electron affinity,

wherein the film formation step comprises forming the first area under a first value of oxygen partial pressure/argon partial pressure in a film formation chamber, forming the second area under a second value of oxygen partial pressure/argon partial pressure in the film formation chamber, and forming the third area under a third value of oxygen partial pressure/argon partial pressure in the film formation chamber lower than the first value of oxygen partial pressure/argon partial pressure.

16. The method as claimed in claim 15, wherein the second value of oxygen partial pressure/argon partial pressure is lower than the first value of oxygen partial pressure/argon partial pressure.

19. The method as claimed in claim 15, wherein the substrate is not exposed to atmosphere during the film formation step.

17. A method of producing a thin-film transistor including an oxide semiconductor layer, a source electrode, a drain electrode, a gate insulating film and a gate electrode formed on a substrate, the method comprising:

a film formation step of forming the oxide semiconductor layer through sputtering, wherein the oxide semiconductor layer comprises a first area, a second area and a third area forming a well-type potential in a film-thickness direction, the first area forming a well of the well-type potential and having a first electron affinity, the second area being disposed nearer to the gate electrode than the first area and having a second electron affinity smaller than the first electron affinity, and the third area being disposed farther from the gate electrode than the first area and having a third electron affinity smaller than the first electron affinity,

wherein the film formation process comprises applying oxygen-containing radicals to a surface on which the first area is formed during and/or after formation of the first area.

20. The method as claimed in claim 17, wherein the substrate is not exposed to atmosphere during the film formation step.

18. A method of producing a thin-film transistor including an oxide semiconductor layer, a source electrode, a drain electrode, a gate insulating film and a gate electrode formed on a substrate, the method comprising:

a film formation step of forming the oxide semiconductor layer through sputtering, wherein the oxide semiconductor layer comprises a first area, a second area and a third area forming a well-type potential in a film-thickness direction, the first area forming a well of the well-type potential and having a first electron affinity, the second area being disposed nearer to the gate electrode than the first area and having a second electron affinity smaller than the first electron affinity, and the third area being disposed farther from the gate electrode than the first area and having a third electron affinity smaller than the first electron affinity,

wherein the film formation process comprises applying ultraviolet light in an ozone atmosphere to a surface on which the first area is formed during and/or after formation of the first area.

21. The method as claimed in claim 18, wherein the substrate is not exposed to atmosphere during the film formation step.