Semiconductor device

• US 8,759,820 B2
• Filed: 08/09/2011
• Issued: 06/24/2014
• Est. Priority Date: 08/20/2010
• Status: Active Grant

• Current Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Original Assignee: Semiconductor Energy Laboratory Co., Ltd.
• Inventors: Godo, Hiromichi, Murayama, Keisuke
• Primary Examiner(s): TRAN, MINH LOAN
• Application Number:
  US13/205,910
• Publication Number:
  US 20120043541A1
• Time in Patent Office: 1,050 Days
• Field of Search: 257/40, 257/59, 257/72, 257/E29.117, 257/E29.299
• US Class Current: 257/40
• CPC Class Codes: H01L 29/42384 for thin film field effect transistors, e.g. characterised by the thickness or the shape of the insulator or the dimensions, the shape or the lay-out of the conductor
• CPC Class Codes: H01L 29/78633 with a light shield
• CPC Class Codes: H01L 29/78648 arranged on opposing sides of the channel
• 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

An object is to provide a transistor in which light deterioration is suppressed as much as possible and electrical characteristics are stable, and a semiconductor device including the transistor. The attention focuses on the fact that light is reflected by a film used for forming a transistor and multiple interaction occurs. When the optical thickness of the film which causes the reflection is roughly an odd multiple of λ₀/4 or roughly an even multiple of λ₀/4, reflectance in a wavelength region of light which is absorbed by an oxide semiconductor is increased without a loss of a function of the film with respect to the transistor, whereby the amount of light absorbed by the oxide semiconductor is reduced and an effect of reducing light deterioration is increased.

Claims

1. A semiconductor device comprising:

an oxide semiconductor layer;

a first layer;

a second layer over and in contact with the first layer; and

a third layer over and in contact with the second layer,

wherein the oxide semiconductor layer, the first layer, the second layer and the third layer overlap each other,

wherein each of the first layer, the second layer and the third layer has a property of transmitting light in a wavelength λ

₀,

wherein optical thickness of the second layer is roughly an odd multiple of λ

₀/4, and

wherein a refractive index of the second layer is the highest or the lowest of the first layer, the second layer and the third layer.

2. The semiconductor device according to claim 1, wherein the oxide semiconductor layer is formed over a substrate.

3. The semiconductor device according to claim 1, wherein the second layer is an insulating layer.

4. The semiconductor device according to claim 1, wherein the second layer is a conductive layer.

5. The semiconductor device according to claim 1, wherein the wavelength λ

₀ is a peak wavelength of a spectrum calculated by multiplying a spectral intensity of external light by a light absorption coefficient of the oxide semiconductor layer.

6. The semiconductor device according to claim 1, wherein the wavelength λ

₀ lies within a range of from 300 nm to 450 nm.

7. A semiconductor device comprising:

an oxide semiconductor layer;

a first layer;

a second layer over and in contact with the first layer; and

a third layer over and in contact with the second layer,

wherein the oxide semiconductor layer, the first layer, the second layer and the third layer overlap each other,

wherein each of the first layer, the second layer and the third layer has a property of transmitting light in a wavelength λ

₀,

wherein optical thickness of the second layer is roughly an even multiple of λ

₀/4,

wherein a refractive index of the second layer is higher than that of the first layer, and

wherein the refractive index of the second layer is lower than that of the third layer.

8. The semiconductor device according to claim 7, wherein the oxide semiconductor layer is formed over a substrate.

9. The semiconductor device according to claim 7, wherein the second layer is an insulating layer.

10. The semiconductor device according to claim 7, wherein the second layer is a conductive layer.

11. The semiconductor device according to claim 7, wherein the wavelength λ

₀ is a peak wavelength of a spectrum calculated by multiplying a spectral intensity of external light by a light absorption coefficient of the oxide semiconductor layer.

12. The semiconductor device according to claim 7, wherein the wavelength λ

₀ lies within a range of from 300 nm to 450 nm.

13. A semiconductor device comprising:

an oxide semiconductor layer;

a first layer;

a second layer over and in contact with the first layer;

a third layer over and in contact with the second layer;

a fourth layer over and in contact with the third layer,

wherein the oxide semiconductor layer, the first layer, the second layer, the third layer and the fourth layer overlap each other,

wherein each of the first layer, the second layer, the third layer and the fourth layer has a property of transmitting light in a wavelength λ

₀,

wherein optical thickness of the second layer is roughly an odd multiple of λ

₀/4,

wherein a refractive index of the second layer is the highest of the first layer, the second layer and the third layer,

wherein optical thickness of the third layer is roughly an even multiple of λ

₀/4,

wherein a refractive index of the third layer is lower than that of the second layer, and

wherein the refractive index of the third layer is higher than that of the fourth layer.

14. The semiconductor device according to claim 13, wherein the oxide semiconductor layer is formed over a substrate.

15. The semiconductor device according to claim 13, wherein the second layer is an insulating layer.

16. The semiconductor device according to claim 13, wherein the second layer is a conductive layer.

17. The semiconductor device according to claim 13, wherein the wavelength λ

₀ is a peak wavelength of a spectrum calculated by multiplying a spectral intensity of external light by a light absorption coefficient of the oxide semiconductor layer.

18. The semiconductor device according to claim 13, wherein the wavelength λ

₀ lies within a range of from 300 nm to 450 nm.

19. A semiconductor device comprising:

an oxide semiconductor layer;

a first layer;

a second layer over and in contact with the first layer;

a third layer over and in contact with the second layer;

a fourth layer over and in contact with the third layer,

wherein the oxide semiconductor layer, the first layer, the second layer, the third layer and the fourth layer overlap each other,

wherein each of the first layer, the second layer, the third layer and the fourth layer has a property of transmitting light in a wavelength λ

₀,

wherein optical thickness of the second layer is roughly an odd multiple of λ

₀/4,

wherein a refractive index of the second layer is the lowest of the first layer, the second layer and the third layer,

wherein optical thickness of the third layer is roughly an even multiple of λ

₀/4,

wherein a refractive index of the third layer is higher than that of the second layer, and

wherein the refractive index of the third layer is lower than that of the fourth layer.

20. The semiconductor device according to claim 19, wherein the oxide semiconductor layer is formed over a substrate.

21. The semiconductor device according to claim 19, wherein the second layer is an insulating layer.

22. The semiconductor device according to claim 19, wherein the second layer is a conductive layer.

23. The semiconductor device according to claim 19, wherein the wavelength λ

₀ is a peak wavelength of a spectrum calculated by multiplying a spectral intensity of external light by a light absorption coefficient of the oxide semiconductor layer.

24. The semiconductor device according to claim 19, wherein the wavelength λ

₀ lies within a range of from 300 nm to 450 nm.