Thin film transistor substrate

• US 9,246,010 B2
• Filed: 05/24/2011
• Issued: 01/26/2016
• Est. Priority Date: 07/14/2010
• Status: Active Grant

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Misaki, Katsunori
• Primary Examiner(s): Jackson, Jr., Jerome
• Application Number:
  US13/698,750
• Publication Number:
  US 20130063675A1
• Time in Patent Office: 1,708 Days
• US Class Current: 1/1
• CPC Class Codes: G02F 1/13458 Terminal pads
• CPC Class Codes: G02F 1/136227 Through-hole connection of the pixel electrode to the active element through an insulation layer
• CPC Class Codes: G02F 1/1368 in which the switching element is a three-electrode device G02F1/136277 takes precedence
• CPC Class Codes: H01L 27/1225 with semiconductor materials not belonging to the group IV of the periodic table, e.g. InGaZnO
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate

Abstract

In an oxide semiconductor layer, a degree of oxidation S1 of a portion located on the side of the gate insulating film, and a degree of oxidation S2 of surface layer portions located in connection regions with source and drain electrodes have a relation of S2<S1 within a range in which the oxide semiconductor layer has predetermined electric resistance, and a degree of oxidation S3 of a surface layer portion of the channel region is made higher than the degrees of oxidation S1, S2 of the other regions within the range in which the oxide semiconductor layer has the predetermined electric resistance, by annealing the oxide semiconductor layer in an oxygen-containing atmosphere after formation of the source electrode and the drain electrode.

Claims

1. A thin film transistor substrate, comprising:

a base substrate; and

a plurality of thin film transistors provided on the base substrate;

a protective insulating film provided so as to cover the thin film transistors; and

a plurality of pixel electrodes provided on the protective insulating film so as to correspond to the thin film transistors, respectively, wherein

each of the thin film transistors includes a gate electrode, a gate insulating film provided so as to cover the gate electrode, a semiconductor layer made of an oxide semiconductor and provided on the gate insulating film so as to overlap the gate electrode, and a source electrode and a drain electrode which are provided on the gate insulating film so as to be separated from each other on the semiconductor layer and so that a portion of the source electrode and a portion of the drain electrode are connected to the semiconductor layer,

a channel region is provided in a portion of the semiconductor layer which is located between the source electrode and the drain electrode,

a ratio of oxygen to all metal elements of a first portion of the semiconductor layer located at a lower surface of the semiconductor layer which is arranged directly on the gate insulating film is S1,

a ratio of oxygen to all metal elements of second portions of the semiconductor layer located at an upper surface of the semiconductor layer at connection regions with the source and drain electrodes is S2, where S2<

S1,

a ratio of oxygen to all metal elements of a third portion located at the upper surface portion of the semiconductor layer between the second portions is S3, where S1<

S3 and S2<

S3,

the first portion is located between the second portions and the gate insulating film in a vertical direction at positions overlapping with the source and drain electrodes when seen from a top plan view, and

the first portion is located between the third portion and the gate insulating film in the vertical direction at a position overlapping with the channel region in the top plan view.

2. The thin film transistor substrate of claim 1, wherein

the semiconductor layer has a stacked structure formed by stacking a plurality of layers.

3. The thin film transistor substrate of claim 2, wherein

the semiconductor layer has a two-layer structure defined by sequentially stacking a first semiconductor layer and a second semiconductor layer, and

in the semiconductor layer, a portion located adjacent to the gate insulating film corresponds to the first semiconductor layer, the second portions are in contact with the source and drain electrodes and correspond to portions of the second semiconductor layer which are in contact with the source and drain electrodes, and the third portion of the channel region corresponds to a channel region portion of the second semiconductor layer.

4. The thin film transistor substrate of claim 2, wherein

the semiconductor layer has a three-layer structure defined by sequentially stacking a first semiconductor layer, a second semiconductor layer, and a third semiconductor layer, and

in the semiconductor layer, a portion located adjacent to the gate insulating film corresponds to the first semiconductor layer, the second portions are located in contact with the source and drain electrodes and correspond to portions of the second semiconductor layer and the third semiconductor layer which are located in contact with the source and drain electrodes, and the third portion of the channel region corresponds to channel region portions of the second semiconductor layer and the third semiconductor layer.

5. The thin film transistor substrate of claim 1, wherein

the semiconductor layer is defined by a single layer, and in all portions of the semiconductor layer except for the third portion of the channel region, the ratio of oxygen to all metal elements decreases from the gate insulating film to the source electrode and the drain electrode.

6. The thin film transistor substrate of claim 1, wherein

at least a surface layer portion of the gate insulating film is comprised of silicon oxide.

7. The thin film transistor substrate of claim 1, wherein

the protective insulating film is comprised of silicon oxide.

8. The thin film transistor substrate of claim 1, wherein

the semiconductor layer is comprised of an indium gallium zinc oxide-based oxide semiconductor.

9. A liquid crystal display device, comprising:

the thin film transistor substrate of claim 1;

a counter substrate placed so as to face the thin film transistor substrate; and

a liquid crystal layer provided between the thin film transistor substrate and the counter substrate.

10. A method for manufacturing the thin film transistor substrate of claim 1, comprising:

a first patterning step of forming the gate electrode by forming a conductive film on the base substrate and patterning the conductive film by using a first photomask;

a gate insulating film formation step of forming the gate insulating film so as to cover the gate electrode;

a second patterning step of forming the semiconductor layer of the thin film transistor by forming on the gate insulating film a semiconductor film comprised of an oxide semiconductor so as to have the relation of S2<

S1, and patterning the semiconductor film by using a second photomask;

a third patterning step of forming the source electrode and the drain electrode by forming a conductive film so as to cover the semiconductor layer and patterning the conductive film by dry etching using a third photomask;

a fourth patterning step of forming a contact hole in a region corresponding to the drain electrode by forming a protective insulating film by a vapor deposition method so as to cover the source electrode and the drain electrode and patterning the protective insulating film by using a fourth photomask; and

a fifth patterning step of forming the pixel electrode so as to connect to the drain electrode, by forming on the protective insulating film a conductive film so as to connect to the drain electrode via the contact hole, and patterning the conductive film by using a fifth photomask, wherein

in the semiconductor layer, S3 is made higher than S1 and S2 by annealing the substrate having both the source electrode and the drain electrode formed thereon in an oxygen-containing atmosphere after the third patterning step.