JP2013057950A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device using an oxide semiconductor whose characteristic variation due to a heat treatment is suppressed.SOLUTION: There are provided a thin-film transistor comprising: an insulating layer; a gate electrode on the insulating layer; a semiconductor layer which is disposed on the gate electrode through a gate insulating layer and is formed by an oxide layer; and a source electrode and a drain electrode which are disposed on the semiconductor layer apart from each other across the gate electrode, and a display device comprising: a pixel electrode having an electric resistance lower than that of the semiconductor layer which are connected to any one of the source electrode and the drain electrode and are formed by the oxide layer; an optical element which causes at least either a change in optical characteristics or light emission by an electric signal supplied to the pixel electrode; and a film disposed below the pixel electrode and is formed by the same material as the gate insulating layer, wherein the surface on the side of the semiconductor layer of the gate insulating film on the gate electrode has higher smoothness than the surface on the side of the pixel electrode of a film disposed below the pixel electrode.

Description

  The present invention relates to a display device.

Thin film transistors (TFTs) are widely used in liquid crystal display devices, organic EL display devices, and the like.
An amorphous silicon TFT used in a large liquid crystal display device can be uniformly formed at a low cost and a large area, although its mobility is about 1 cm ² / (V · s). However, in recent years, there has been a demand for larger size and higher definition, and active matrix organic EL display devices that require a large drive current have been developed. New low cost, high uniformity, high reliability, and high mobility. An active material is desired.

In the development situation described above, an oxide semiconductor has recently attracted attention as a material that can be applied to a channel layer of a TFT.
For example, TFTs using a transparent conductive oxide thin film mainly composed of ZnO as a channel layer are being actively developed. The thin film can be formed in a large area at a relatively low temperature, and high mobility can be realized as compared with amorphous silicon. For example, Patent Document 1 discloses a TFT using an In—Ga—Zn—O-based amorphous oxide. Since the thin film can be formed at a low temperature and is transparent in the visible range, it is said that a flexible and transparent TFT can be formed on a plastic or film substrate. Furthermore, field effect mobility about 10 times that of amorphous silicon is obtained.

  On the other hand, for example, it has been reported that the conductivity of an oxide semiconductor varies depending on the oxygen concentration during sputtering film formation (see, for example, Non-Patent Document 1). The electrical characteristics are very sensitive to, for example, the oxygen concentration is changed by heat treatment, and as a result, the characteristics deteriorate. This is a major factor that hinders the practical application of TFTs using oxide semiconductors.

JP 2004-103957 A

Applied Physics Letters, 90, 192101 (2007)

  The present invention provides a display device using an oxide semiconductor in which a variation in characteristics due to heat treatment is suppressed.

  According to an embodiment of the present invention, an insulating layer, a gate electrode provided on the insulating layer, and a semiconductor layer provided on the gate electrode via a gate insulating film and formed from an oxide layer A thin film transistor including a source electrode and a drain electrode provided on the semiconductor layer so as to sandwich the gate electrode, and connected to any one of the source electrode and the drain electrode of the thin film transistor An optical element that is formed of the oxide layer and has at least one of a change in optical characteristics and light emission by an electric signal applied to the pixel electrode, and a pixel electrode having an electric resistance lower than that of the semiconductor layer And a film provided under the pixel electrode and formed of the same material as the gate insulating film, and in front of the gate insulating film on the gate electrode Surface side of the semiconductor layer, smoothness is high display apparatus is provided than the side of the pixel electrode surface of the film provided under the pixel electrode.

  According to the present invention, a display device using an oxide semiconductor in which a variation in characteristics due to heat treatment is suppressed is provided.

1 is a schematic cross-sectional view illustrating the structure of a thin film transistor according to a first embodiment of the invention. FIG. 5 is a schematic cross-sectional view in order of the processes, illustrating a method for manufacturing a thin film transistor according to the first example of the invention. FIG. 3 is a schematic cross-sectional view in order of the steps following FIG. 2. It is a graph which illustrates the characteristic of the thin-film transistor which concerns on 1st Example of this invention. It is a typical sectional view which illustrates the structure of the thin film transistor of the 1st comparative example. It is a graph which illustrates the characteristic of the thin-film transistor of the 1st comparative example. It is a typical sectional view which illustrates the structure of the thin film transistor of the 2nd comparative example. It is a schematic diagram which illustrates the structure and experimental result of the thin-film transistor used for experiment. FIG. 5 is a schematic plan view illustrating the configuration of a thin film transistor of a modification example according to the first embodiment of the invention. It is process order typical sectional drawing which illustrates the manufacturing method of the thin-film transistor which concerns on the 2nd Example of this invention. It is process order typical sectional drawing which illustrates the manufacturing method of the thin-film transistor which concerns on the 3rd Example of this invention. FIG. 12 is a schematic cross-sectional view in order of the steps, following FIG. 11. FIG. 6 is a schematic cross-sectional view illustrating the configuration of a display device according to a second embodiment of the invention. It is process order typical sectional drawing which illustrates the manufacturing method of the display apparatus which concerns on the 4th Example of this invention. FIG. 15 is a schematic cross-sectional view in order of the steps, following FIG. 14. FIG. 11 is a schematic cross-sectional view in order of the processes, illustrating a method for manufacturing a display device according to the fifth example of the invention. FIG. 10 is a circuit diagram illustrating an equivalent circuit of another display device according to the second embodiment of the invention; FIG. 10 is a circuit diagram illustrating an equivalent circuit of another display device according to the second embodiment of the invention; It is a flowchart figure which illustrates the manufacturing method of the thin-film transistor which concerns on the 3rd Embodiment of this invention. FIG. 9 is a flowchart illustrating a method for manufacturing a display device according to a fourth embodiment of the invention. It is a flowchart figure which illustrates another manufacturing method of the display apparatus which concerns on the 4th Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the ratio coefficient of the size between the parts, and the like are not necessarily the same as actual ones. Further, even when the same part is represented, the dimensions and ratio coefficient may be represented differently depending on the drawing.
Further, in the present specification and each drawing, the same reference numerals are given to the same elements as those described above with reference to the previous drawings, and detailed description thereof will be omitted as appropriate.

(First embodiment)
FIG. 1 is a schematic cross-sectional view illustrating the structure of a thin film transistor according to the first embodiment of the invention.
That is, FIG. 4A is a schematic plan view, FIG. 4B is a schematic plan view omitted, and FIG. 4C and FIG. It is AA 'line and BB' line sectional drawing.
As shown in FIG. 1, the thin film transistor 11 according to the first embodiment of the present invention includes a gate electrode 120 provided on the main surface 111 of the insulating layer 110, and a gate insulating film on the gate electrode 120. 130, the semiconductor layer 140 formed of an oxide, the channel protective layer 150 provided on the semiconductor layer 140, and a part of the semiconductor layer 140 and a part of the channel protective layer 150 are covered. A source electrode 161 and a drain electrode 162 that are spaced apart from each other.

In FIG. 6A, the insulating layer 110 and the gate insulating film 130 are omitted. In FIG. 5B, the insulating layer 110, the gate insulating film 130, the source electrode 161, and the drain electrode 162 are omitted. Yes.
As illustrated in FIG. 2B, the semiconductor layer 140 includes a source contact region 141 and a drain contact region 142 that are electrically connected to the source electrode 161 and the drain electrode 162, respectively. The source contact region 141 and the drain contact region 142 are provided apart from each other with the gate electrode 120 interposed therebetween.

  The channel protective layer 150 is provided so as to cover the side surface 140 s and the upper surface 140 u of the semiconductor layer 140 except for the source contact region 141 and the drain contact region 142. However, as will be described later, the channel protective layer 150 may be provided so as to cover at least a part of the side surface 140s of the semiconductor layer 140 and the upper surface 140u.

  That is, the thin film transistor 11 includes an insulating layer 110, a gate electrode 120 provided on the insulating layer 110, a semiconductor layer 140 made of an oxide provided on the gate electrode 120 with a gate insulating film 130 interposed therebetween, On the semiconductor layer 140, the gate electrode 120 is provided between the source electrode 161 and the drain electrode 162, the source electrode 161 and the drain electrode 162, and the semiconductor layer 140 so as to sandwich the gate electrode 120. On the electrode 120, a channel protective layer 150 covering at least part of the side surface 140s of the semiconductor layer 140 exposed from the source electrode 161 and the drain electrode 162 is provided.

  The insulating layer 110 is provided on a substrate, for example. At this time, for example, a translucent glass substrate can be used as the substrate. However, the present invention is not limited to this, and for example, a plastic substrate, a substrate with a color filter, or a non-translucent substrate such as silicon or stainless steel can be used. Further, if the substrate is insulating, the substrate itself may be the insulating layer 110. Hereinafter, the case where the insulating layer 110 is an insulating substrate will be described.

  For the gate electrode 120, for example, a refractory metal such as MoW, Ta, or W can be used, and an Al alloy mainly composed of Al with a hillock countermeasure may be used. A metal laminated film may be used. However, the present invention is not limited to this, and any conductive material can be used for the gate electrode 120.

For the gate insulating film 130, for example, silicon oxide (SiO _x ) can be used. However, the present invention is not limited to this, and any insulating film such as silicon nitride (SiN _x ) or silicon oxynitride can be used, and a laminated film of these films may be used.

For the semiconductor layer 140, for example, an amorphous oxide semiconductor such as an In—Ga—Zn—O-based semiconductor can be used. The semiconductor layer 140 made of this amorphous oxide semiconductor is formed by, for example, reactive sputtering. Note that in the amorphous oxide semiconductor layer, for example, a diffraction pattern or the like is not observed even when observed with a transmission electron microscope or X-ray diffraction. Note that the semiconductor layer 140 can be formed using any oxide semiconductor containing Zn, for example, in addition to the above.
Note that the thickness of the semiconductor layer 140 may be about 10 nm in order to ensure electrical characteristics. Specifically, the thickness of the semiconductor layer 140 may be about 10 nm to 100 nm.

  For the channel protective layer 150, for example, silicon oxide having higher acid resistance than the semiconductor layer 140 is used. However, the present invention is not limited to this, and any insulating material containing oxygen can be used. For example, alumina or silicon oxynitride can also be used. Furthermore, a stacked film of these films may be used.

  For the source electrode 161 and the drain electrode 162, any conductive material can be used, and for example, any conductive laminated film such as Ti / Al / Ti or Mo / Al / Mo can be used. In this specific example, a stacked film of a Mo film 166, an Al film 167, and a Mo film 168 is used for the source electrode 161 and the drain electrode 162.

  In the above, the source contact region 141 and the drain contact region 142 may be interchanged with each other, that is, the source electrode 161 and the drain electrode 162 may be interchanged with each other.

In order to maintain the reliability of the thin film transistor 11, for example, a passivation film made of an insulator such as SiN _x is formed so as to cover the entire structure illustrated in FIG. Yes. Further, an insulating layer such as an organic resin for planarization or an insulating layer such as a colored organic resin such as a color filter is formed on the insulating layer, but is omitted in the drawing.
Thus, in general, when a thin film transistor is applied to a TFT-LCD or an active matrix display device for organic EL, a passivation film is formed. At this time, the thin film transistor is heat-treated at a temperature of 150 ° C. or more, for example. The For example, when forming a passivation film using PE-CVD (Plasma Enhanced Chemical Vapor Deposition), the heating temperature is about 250 ° C.

At this time, the semiconductor layer 140 is heated when the passivation layer is formed. However, in the thin film transistor 11 according to the present embodiment, the source contact region 141 and the drain contact region 142 of the semiconductor layer 140 are the source electrode 161 and the drain contact region 142, respectively. The drain electrode 162 is covered. In the region of the semiconductor layer 140 exposed from these electrodes, the upper surface 140 u and the side surface 140 s of the semiconductor layer 140 are covered with the channel protective layer 150. For this reason, the fluctuation | variation of the oxygen concentration in the semiconductor layer 140 when said heat processing is performed is suppressed, and a characteristic does not change.
Thus, according to the thin film transistor 11 according to the present embodiment, it is possible to provide a thin film transistor using an oxide semiconductor in which fluctuations in oxygen concentration caused by heat treatment are suppressed and characteristic fluctuations are suppressed.

(First embodiment)
The thin film transistor 11a (not shown) according to the first example according to this embodiment has the structure illustrated in FIG. Below, the manufacturing method of the thin-film transistor 11a of 1st Example is demonstrated.

FIG. 2 is a schematic cross-sectional view in order of the processes, illustrating the method for manufacturing the thin film transistor according to the first example of the invention.
FIG. 3 is a schematic cross-sectional view in order of the processes following FIG.
2 and 3, the left side of the drawing is a cross-sectional view corresponding to the cross section along line AA ′ of FIG. 1A, and the right side of FIG. 1A is the line CC ′ of FIG. It is sectional drawing equivalent to a cross section. In these drawings, in addition to the thin film transistor portion, the contact portion is also illustrated.

  As shown in FIG. 2A, first, an Al film 121f and a Mo film 122f are sputtered to a thickness of 100 nm and 30 nm on the main surface 111 of the glass substrate 110g (substrate 110g) as the insulating layer 110, respectively. The gate electrode 120 was formed by forming a film and processing it into a predetermined pattern. Photolithography was used for patterning, and mixed acid composed of phosphoric acid, acetic acid, nitric acid, and water was used for etching. At this time, the contact portion 123 of the gate electrode 120 of the thin film transistor was also formed at the same time. The contact portion 123 is also composed of a laminated film of an Al film 121f and a Mo film 122f.

Next, as shown in FIG. 2B, a SiO ₂ film 130 f was deposited as a gate insulating film 130 with a thickness of 200 nm by PE-CVD using TEOS (Tetra Ethyl Ortho Silicate) as a raw material. At this time, the film forming temperature was 350 ° C.

  Further, an oxide layer 140f (oxide layer) made of an In—Ga—Zn—O oxide to be the semiconductor layer 140 was formed to a thickness of 30 nm on the gate insulating film 130 by a reactive DC sputtering method. . At this time, the ratio of oxygen was 5% with respect to argon. Then, the oxide layer 140f was processed into a predetermined pattern across the gate electrode 120 using 2% oxalic acid to form the semiconductor layer 140.

Further, as shown in FIG. 2C, a SiO ₂ film 150f to be the channel protective layer 150 was deposited with a thickness of 200 nm by a TEOS PE-CVD method. At this time, the film forming gas was a mixed gas of O ₂ and TEOS, and the film forming temperature was 350 ° C. Thereafter, the SiO ₂ film 150f is processed into a predetermined pattern covering the side surface 140s and the upper surface 140u of the semiconductor layer 140 except for the regions that will later become the source contact region 141 and the drain contact region 142, and the channel protective layer 150 is formed. Formed.

At this time, the mask exposure and the back exposure using the gate electrode 120 as a mask were used in combination for the photolithography at the time of processing the SiO ₂ film 150f. The etching at this time was performed by RIE (Reactive Ion Etching) using CF ₄ gas.

Thereafter, annealing was performed at 350 ° C. for 1 hour in an air atmosphere to remove damage to the semiconductor layer 140 due to the PE-CVD process of forming the SiO ₂ film 150f.

Then, as illustrated in FIG. 3A, a contact hole 123 h is formed in the SiO ₂ film 130 f serving as the gate insulating film 130 in the contact portion 123 for taking out the gate electrode 120. That is, the SiO ₂ film 130f of the gate insulating film 130 was etched into a predetermined shape using buffered hydrofluoric acid.

  Thereafter, as shown in FIG. 3B, the Mo film 166, the Al film 167, and the Mo film 168 (not shown) to be the source electrode 161 and the drain electrode 162 are sputtered to a thickness of 10 nm, 300 nm, and 50 nm, respectively. A laminated film 160f formed by the method was formed, and this laminated film 160f was processed into a predetermined pattern using a mixed acid, whereby a source electrode 161 and a drain electrode 162 were formed. Thereby, the shape of the thin film transistor 11a is completed. Further, the laminated film 160f of the Mo film 166, the Al film 167, and the Mo film 168 is embedded in the contact hole 123h and processed into a predetermined shape, so that the contact portion 123 is manufactured.

  Thereafter, in order to take element damage during the process, annealing is performed at 230 ° C. for about 1 hour in a clean oven to complete the thin film transistor 11a according to the present embodiment.

FIG. 4 is a graph illustrating characteristics of the thin film transistor according to the first example of the invention.
That is, this figure illustrates characteristics when heat treatment is performed after the thin film transistor 11a according to the first embodiment is completed and the heat treatment conditions are changed. The solid line A1 illustrates the initial characteristics without heat treatment, the broken line A2 illustrates the characteristics after heat treatment at 160 ° C. in an Ar atmosphere, and the alternate long and short dash line A3 illustrates the characteristics after heat treatment at 230 ° C. in an Ar atmosphere. . In the figure, the horizontal axis represents the gate voltage Vg, and the vertical axis represents the drain current Id.

  As shown in FIG. 4, in the thin film transistor 11a, the initial characteristics without heat treatment (solid line A1), the heat treatment at 160 ° C. (dashed line A2), and the heat treatment at 230 ° C. (one-dot chain line A3) are high. An off-ratio is obtained, and the characteristics are hardly changed by the heat treatment. This is an effect that the semiconductor layer 140 is covered with the channel protective layer 150, the source electrode 161, and the drain electrode 162, thereby suppressing the oxygen concentration contained in the semiconductor layer 140 from being changed by the heat treatment. Thereby, a stable operation can be realized.

(First comparative example)
FIG. 5 is a schematic cross-sectional view illustrating the structure of the thin film transistor of the first comparative example.
That is, FIG. 4A is a schematic plan view, FIG. 4B is a schematic plan view omitted, and FIG. 4C and FIG. It is AA 'line and BB' line sectional drawing.
As shown in FIG. 5, in the thin film transistor 91 of the first comparative example, the channel protective layer 150 covers the upper surface 140u of the semiconductor layer 140, but is provided with the side surface 140s exposed. Other than this, it is the same as the thin film transistor 11 according to the present embodiment, and a description thereof will be omitted. That is, the thin film transistor 91 of the first comparative example is the thin film transistor 11 according to the first embodiment or the thin film transistor 11a of the first example, in which the side surface 140s of the semiconductor layer 140 is exposed from the channel protective layer 150. is there.

Note that the structure of the thin film transistor 91 is a general structure when a silicon-based semiconductor such as amorphous silicon or polysilicon is used as the semiconductor layer 140 instead of an oxide semiconductor.
The thin film transistor 91 is manufactured as follows.

  An Al film 121f and a Mo film 122f to be the gate electrode 120 are formed on the main surface 111 of the insulating layer 110 such as a glass substrate by sputtering with a thickness of 100 nm and 30 nm, respectively, and processed into a predetermined pattern. Photolithography is used for patterning, and a mixed acid of phosphoric acid, acetic acid, nitric acid, and water is used for etching.

Thereafter, a SiO ₂ film 130f is deposited as a gate insulating film 130 with a thickness of 200 nm by TEOS PE-CVD. Further, an oxide layer 140f made of In—Ga—Zn—O oxide is formed as a semiconductor layer 140 over the gate insulating film 130 with a thickness of 30 nm by a reactive DC sputtering method. At this time, the ratio of oxygen is 5% with respect to argon.

Then, a SiO ₂ film 150f having a thickness of 200 nm is deposited as a channel protective layer 150 by a TEOS PE-CVD method. Thereafter, the SiO ₂ film 150f is processed into a predetermined pattern. At this time, photolithography in the processing of the SiO ₂ film 150f used a combination of mask exposure and back exposure using the gate electrode 120 as a mask. Etching at this time was performed by RIE using CF ₄ gas.

  Then, the oxide layer 140f is processed into a predetermined pattern using 2% oxalic acid. Thereafter, in order to recover damage to the semiconductor layer 140 during PE-CVD, annealing is performed at 350 ° C. for 1 hour in an air atmosphere. Thereafter, in order to form a contact hole (not shown) for taking out the gate electrode 120, the exposed gate insulating film 130 is removed by etching using buffered hydrofluoric acid. Further, the Mo film 166, the Al film 167, and the Mo film 168 to be the source electrode 161 and the drain electrode 162 are formed by sputtering with a thickness of 10 nm, 300 nm, and 50 nm, respectively, and the above-described mixed acid is used to form a predetermined pattern. Process. Thereafter, in order to recover the damage of the semiconductor layer 140 during the process, annealing is performed at 230 ° C. for 1 hour in an air atmosphere.

The thin film transistor 91 having such a structure has a problem in practical use because its characteristics greatly fluctuate due to the heat treatment in the subsequent formation of the passivation film.
FIG. 6 is a graph illustrating characteristics of the thin film transistor of the first comparative example.
That is, this figure illustrates the characteristics when heat treatment is performed after the thin film transistor 91 of the first comparative example is completed and the heat treatment conditions are changed. The solid line A1 illustrates the initial characteristics without heat treatment, the broken line A2 illustrates the characteristics after heat treatment at 160 ° C. in an Ar atmosphere, and the alternate long and short dash line A3 illustrates the characteristics after heat treatment at 230 ° C. in an Ar atmosphere. . In the figure, the horizontal axis represents the gate voltage Vg, and the vertical axis represents the drain current Id.

  As shown in FIG. 6, in the thin film transistor 91, a high on / off ratio was obtained in the initial characteristics without heat treatment (solid line A1), but in the heat treatment at 160 ° C. (broken line A2), the Id-Vg characteristic curve. Shifts in the direction of low Vg, and a convex portion A2a appears on the Id-Vg characteristic curve. In addition, in the heat treatment at 230 ° C. (the one-dot chain line A3), the on / off ratio is very low, and is almost on (conductive state).

  This is because in the thin film transistor 91, the side surface 140 s of the semiconductor layer 140 is exposed from the channel protective layer 150, so that the oxygen concentration on the surface of the side surface 140 s of the semiconductor layer 140 changes due to the heat treatment. This is because oxygen contained in the layer 140 is released and the resistance of the semiconductor layer 140 is reduced.

(Second comparative example)
FIG. 7 is a schematic cross-sectional view illustrating the structure of the thin film transistor of the second comparative example.
1A is a schematic plan view, and FIG. 1B and FIG. 1C are sectional views taken along lines AA ′ and BB ′ in FIG. 1A, respectively.
As shown in FIG. 7, the thin film transistor 92 of the second comparative example is not provided with the channel protective layer 150. That is, the thin film transistor 92 has a back channel cut structure. The thin film transistor 92 is manufactured as follows.

  An Al film 121f and a Mo film 122f to be the gate electrode 120 are formed on the main surface 111 of the insulating layer 110 such as a glass substrate by sputtering with a thickness of 100 nm and 30 nm, respectively, and processed into a predetermined pattern. Photolithography is used for patterning, and a mixed acid of phosphoric acid, acetic acid, nitric acid, and water is used for etching.

Thereafter, a SiO ₂ film 130f is deposited as a gate insulating film 130 with a thickness of 200 nm by TEOS PE-CVD. Further, an oxide layer 140f made of In—Ga—Zn—O oxide is formed as a semiconductor layer 140 over the gate insulating film 130 with a thickness of 30 nm by a reactive DC sputtering method. At this time, the ratio of oxygen is 5% with respect to argon. Then, the oxide layer 140f is processed into a predetermined pattern using 2% oxalic acid to form the semiconductor layer 140.

  Thereafter, in order to form a contact hole (not shown) for taking out the gate electrode 120, the exposed gate insulating film 130 is removed by etching using buffered hydrofluoric acid. Further, the Mo film 166, the Al film 167, and the Mo film 168 to be the source electrode 161 and the drain electrode 162 are formed by sputtering at a thickness of 10 nm, 300 nm, and 50 nm, respectively, and a predetermined pattern is formed using the above mixed acid. To process. Thereafter, in order to recover the damage of the semiconductor layer 140 during the process, annealing is performed at 230 ° C. for 1 hour in an air atmosphere.

  In the thin film transistor 92 having such a structure, since the channel protective layer 150 is not provided, the upper surface 140u and the side surface 140s of the semiconductor layer 140 are exposed. For this reason, the characteristics fluctuate greatly due to the subsequent heat treatment for forming a passivation film or the like. For example, the characteristics are deteriorated by heat treatment more remarkably than the characteristics of the thin film transistor 91 illustrated in FIG. This is because oxygen contained in the semiconductor layer 140 is released from the exposed upper surface 140u and side surface 140s of the semiconductor layer 140, and the resistance of the semiconductor layer 140 is reduced.

  In general, when a thin film transistor is applied to a TFT-LCD, an active matrix display device for organic EL, or the like, it is necessary to form a passivation film in order to improve reliability. In the thin film transistors 91 and 92 of the comparative example, the electrical characteristics deteriorate when exposed to an inert atmosphere or vacuum at a temperature of 150 ° C. or higher. This is because the resistance of the semiconductor layer 140 is reduced by the release of oxygen from the surface of the oxide layer 140f formed of the In—Ga—Zn—O oxide in the exposed portion. In general, when forming a passivation film using PE-CVD, it is necessary to perform a heat treatment at about 200 ° C. in consideration of the barrier property of the passivation film. However, in the thin film transistors 91 and 92, Electrical characteristics deteriorate.

  At this time, for example, the deteriorated characteristics can be recovered by performing a heat treatment at 350 ° C. or higher in an oxidizing atmosphere. However, when such a high temperature treatment is performed, for example, a reaction between the In—Ga—Zn—O oxide of the semiconductor layer 140 and the source electrode 161 and the drain electrode 162 occurs, and the characteristics deteriorate. Further, when Al is used for the source electrode 161 and the drain electrode 162, hillocks are generated in these electrodes, and this hillock causes a problem of damaging, for example, the passivation film. There are difficulties.

  In contrast, in the thin film transistor 11 according to this embodiment and the thin film transistor 11a according to the first example, the upper surface 140u and the side surface 140s of the semiconductor layer 140 are covered with the channel protective layer 150, the source electrode 161, and the drain electrode 162. . Accordingly, the oxygen concentration contained in the semiconductor layer 140 is suppressed from being changed by the heat treatment, and a stable operation can be realized even if the heat treatment is performed when forming a passivation film, as illustrated in FIG.

  As described above, in a thin film transistor using an oxide semiconductor, not only the upper surface 140u of the semiconductor layer 140 but also the side surface 140s is covered with the channel protective layer 150, and thus favorable characteristics resistant to heat treatment can be obtained. The structure and the effect of the thin film transistor 11 according to the present embodiment have been found based on the following experimental results.

  The inventor foreseen that the characteristics of the thin film transistor 92 of the second comparative example that does not use the channel protective layer 150 are deteriorated by the heat treatment. That is, in the structure that does not use the channel protective layer 150, the semiconductor layer 140 is easily damaged in various processes during the manufacturing process. For example, even in a thin film transistor using a semiconductor layer such as amorphous silicon or polysilicon, there are characteristics in some cases. Deteriorates. Therefore, it was estimated that when an oxide semiconductor whose characteristics are easily changed is used, the oxide semiconductor is more easily damaged.

  On the other hand, for example, in the structure of the thin film transistor 91 of the first comparative example illustrated in FIG. 5, there is a problem when a silicon-based semiconductor such as amorphous silicon or polysilicon is used as the semiconductor layer 140 instead of an oxide semiconductor. It will not be. That is, amorphous silicon, polysilicon, or the like may have surface hydrogen released by heat treatment, but the portion from which hydrogen has been released has a high resistance, so there is generally no problem. For this reason, even if the side surface of the semiconductor layer 140 is exposed, the characteristics are not significantly changed by the heat treatment.

  For this reason, even when an oxide semiconductor is used as the semiconductor layer 140, it is expected that by providing the channel protective layer 150 on the upper surface 140u of the semiconductor layer 140, the characteristic variation is suppressed to an extent that does not cause a problem in practice. did. However, as already illustrated in FIG. 6, the characteristics of the thin film transistor 91 of the first comparative example actually fluctuated greatly due to the heat treatment.

Therefore, the inventor conducted an experiment on the relationship between the electrical characteristics and the arrangement of the channel protective layer 150 and the semiconductor layer 140.
FIG. 8 is a schematic view illustrating the configuration of the thin film transistor used in the experiment and the experimental result. That is, FIG. 4A is a schematic plan view illustrating the configuration of the thin film transistor used in the experiment, and FIG. 4B is an equivalent circuit diagram illustrating the electrical characteristics of the thin film transistor. ) And (d) are graphs illustrating measurement results of characteristics when the heat treatment conditions are changed. In FIGS. 7C and 7D, the horizontal axis represents the gate voltage Vg, the vertical axis in FIG. 5C represents the drain current Id in a logarithmic scale, and the vertical axis in FIG. Id is represented by an equal interval scale. Moreover, in the same figure (c) and the same figure (d), the continuous line A1 illustrates the initial characteristic without heat processing, and the broken line A2 illustrates the characteristic after the heat processing of 160 degreeC in Ar atmosphere. A dotted line A4 in FIG. 4D is a virtual characteristic obtained by extending the characteristic of the broken line A2 in the region of the low gate voltage Vg to the region of the high gate voltage Vg.

  As shown in FIG. 8A, in the thin film transistor 93 used in the experiment, the semiconductor layer 140 has a larger planar shape than the channel protective layer 150. That is, the upper surface 140 u of the semiconductor layer 140 corresponding to the channel region in which the source electrode 161 and the drain electrode 162 are opposed to each other in the region above the gate electrode 120 is covered with the channel protective layer 150. However, the upper surface 140 u and the side surface 140 s of the semiconductor layer 140 other than the channel region are exposed from the channel protective layer 150.

The thin film transistor 93 having such a structure exhibited the characteristics illustrated in FIGS. 8C and 8D.
That is, as illustrated in FIG. 8C, in the thin film transistor 93, in the initial characteristics without heat treatment (solid line A1), a high on / off ratio is obtained, but heat treatment at 160 ° C. (broken line A2). , The on / off ratio is very low and is almost on (conducting). That is, the on / off ratio is further deteriorated from the characteristics of the thin film transistor 91 illustrated in FIG. 6 at 160 ° C. (broken line A2). This is presumably because the thin film transistor 93 has a larger area where the semiconductor layer 140 is exposed from the channel protective layer 150 than the thin film transistor 91.

  As shown in FIG. 8 (d), when the characteristics of FIG. 8 (c) are seen on an equally spaced scale, the characteristics of the heat treatment at 160 ° C. (broken line A2) are the initial characteristics without heat treatment (solid line A1). It has a similar shape. That is, in both the solid line A1 and the broken line A2, the drain current Id increases rapidly at a gate voltage of about −4V or more. However, in the broken line A2, a large current exemplified by the dotted line A4 flows even when the gate voltage is lower than about −4V, and this current (dotted line A4) and the gate voltage of about −4V or more rapidly increase. It is estimated that the current increases to the characteristic of the broken line A2.

  From this characteristic, it was presumed that the characteristic of the broken line A2 of the thin film transistor 93 after the heat treatment at 160 ° C. was a characteristic of a structure in which elements having different characteristics were connected in parallel.

  That is, as illustrated in FIG. 8A, the characteristics in the channel current path 145 c covered with the channel protective layer 150 in the region where the source electrode 161 and the drain electrode 162 face each other, and the channel protective layer 150 is exposed. It is considered that the characteristics in the peripheral current path 145s such as the side surface 140s of the semiconductor layer 140 are combined.

  That is, as shown in FIG. 8B, in the thin film transistor 93, a channel transistor 93a corresponding to the channel current path 145c and a peripheral transistor 93b corresponding to the peripheral current path 145s are connected in parallel. It can be regarded as a structure of things. The channel part transistor 93a is considered to have the characteristic of the solid line A1 illustrated in FIG. On the other hand, the peripheral transistor 93b is considered to have characteristics similar to the characteristics of the dotted line A4 illustrated in FIG.

  As a result, the broken line A2 is considered to have a characteristic in which the channel transistor 93a and the peripheral transistor 93b are connected in parallel, that is, a characteristic obtained by synthesizing the solid line A1 and the dotted line A4.

  Thus, when the semiconductor layer 140 was exposed from the channel protective layer 150, it turned out that a characteristic deteriorates by heat processing. Specifically, it is considered that oxygen is released from the exposed portion of the semiconductor layer 140, thereby reducing the resistance of the semiconductor layer 140, and thus the characteristics are changed.

  For this reason, in the thin film transistor 92 of the second comparative example, since the channel protective layer 150 is not provided, the surface of the semiconductor layer 140 is exposed in a large area of the upper surface 140u and the side surface 140s of the semiconductor layer 140. The characteristics fluctuate greatly.

  Further, in the thin film transistor 91 of the first comparative example, the semiconductor layer 140 is exposed from the channel protective layer 150 on the side surface 140s, and it is assumed that the characteristics have been changed by the heat treatment in this portion. That is, for example, in the broken line A2 illustrated in FIG. 6, as described above, the protrusion A2a occurs, and this also indicates that the characteristic of the broken line A2 is that the channel transistor 93a and the peripheral transistor 93b are in parallel. This suggests that it is a connected characteristic.

  As described above, in the structure of the thin film transistor 91 of the first comparative example illustrated in FIG. 5, there is no problem when a semiconductor such as amorphous silicon or polysilicon is used as the semiconductor layer 140, but the amount of oxygen It has been found that there is a problem in the case of using an oxide semiconductor whose electrical characteristics are greatly dependent on. That is, in the case where an oxide semiconductor is used, if the side surface 140s of the semiconductor layer 140 is exposed, the amount of oxygen fluctuates, for example, by heat treatment in the portion, and as a result, the characteristics are greatly deteriorated. Thus, covering the side surface 140s with the channel protective layer 150 at the same time as the upper surface 140u of the semiconductor layer 140 is not necessary in a conventional thin film transistor using a semiconductor such as amorphous silicon or polysilicon. This is a structure specifically required in a thin film transistor using a semiconductor layer 140 made of a physical semiconductor.

  Here, in the thin film transistor 11 according to this embodiment and the thin film transistor 11 a of the first example, the channel protective layer 150 is a layer provided between the semiconductor layer 140, the source electrode 161, and the drain electrode 162. That is, the channel protective layer 150 covers at least a part of the upper surface 140 u of the semiconductor layer 140. At least a part of the channel protective layer 150 is covered with the source electrode 161 and the drain electrode 162.

  That is, the channel protective layer 150 is for protecting the semiconductor layer 140 and thus is formed after the semiconductor layer 140. The channel protective layer 150 is formed before the source electrode 161 and the drain electrode 162. As described above with reference to FIGS. 2C to 3B, this recovers damage to the semiconductor layer 140 when the channel protective layer 150 is formed on the semiconductor layer 140 by, for example, PE-CVD. Therefore, for example, it is possible to perform high-temperature annealing such as 1 hour at 350 ° C. in an air atmosphere.

  That is, for example, when the semiconductor layer 140 is formed, and then a film to be the source electrode 161 and the drain electrode 162 is formed, and then the channel protective layer 150 is formed, a high temperature for recovery of damage when the channel protective layer 150 is formed. The processing is also performed on the source electrode 161 and the drain electrode 162. When such a high temperature treatment is performed on the source electrode 161 and the drain electrode 162, characteristic degradation and hillocks caused by the reaction between the semiconductor layer 140 and the source electrode 161 and the drain electrode 162 occur as described above. In practice, this process cannot be adopted.

  For this reason, in the thin film transistor 11 according to the present embodiment and the thin film transistor 11a of the first example, in order to enable a high temperature treatment to recover the damage when forming the channel protective layer 150 on the semiconductor layer 140, The channel protective layer 150 is provided between the semiconductor layer 140 and the source electrode 161 and the drain electrode 162.

  In the thin film transistor 11 according to the present embodiment and the thin film transistor 11a of the first example, the channel protective layer 150 covers the upper surface 140u and the side surface 140s of the semiconductor layer 140 not covered with the source electrode 161 and the drain electrode 162. Although provided, embodiments of the present invention are not limited to this. That is, the channel protective layer 150 may be provided so as to cut off at least a part of the current path serving as the peripheral transistor 93b described with reference to FIG. 8, and various modifications are possible.

FIG. 9 is a schematic plan view illustrating the configuration of a thin film transistor of a modification according to the first embodiment of the invention.
In these drawings, the insulating layer 110 and the gate insulating film 130 are omitted. As shown in FIG. 9A, in the thin film transistor 12 of the modification according to this embodiment, the semiconductor layer 140 has a region exposed outside the source electrode 161 and the drain electrode 162. However, the end portion of the semiconductor layer 140 in the channel direction (gate length direction) of the channel region where the source electrode 161 and the drain electrode 162 face each other is covered with the channel protective layer 150.

  That is, in this case, the side surface 140s of the semiconductor layer 140 between the extension line 161p of the side facing the drain electrode 162 of the source electrode 161 and the extension line 162p of the side facing the source electrode 161 of the drain electrode 162 is formed. The channel protective layer 150 is covered. For this reason, in the vicinity region 146s of the side surface 140s between the extension line 161p and the extension line 162p, the side surface 140s is not affected by the heat treatment and has high resistance.

  For this reason, the peripheral current path 145s is blocked in the vicinity region 146s of the side surface 140s between the extension line 161p and the extension line 162p. Accordingly, a thin film transistor using an oxide semiconductor that suppresses fluctuations in oxygen concentration caused by the heat treatment and suppresses characteristic fluctuations even when heat treatment for forming a passivation film or the like is performed by the thin film transistor 12 is provided.

  In addition, as illustrated in FIG. 9B, in the thin film transistor 13 of another modified example according to this embodiment, the semiconductor layer 140 has a region exposed to the outside of the source electrode 161 and the drain electrode 162. Yes. In the region between the extension line 161p of the side of the source electrode 161 facing the drain electrode 162 and the extension line 162p of the side of the drain electrode 162 facing the source electrode 161, the semiconductor layer 140 recedes inward. Has a recess. Also in this case, the end portion of the semiconductor layer 140 in the channel direction (gate length direction) of the channel region where the source electrode 161 and the drain electrode 162 face each other is covered with the channel protective layer 150.

  That is, also in this case, the side surface 140s of the semiconductor layer 140 between the extension line 161p of the side of the source electrode 161 facing the drain electrode 162 and the extension line 162p of the side of the drain electrode 162 facing the source electrode 161 is formed. The channel protective layer 150 is covered.

  For this reason, in the vicinity region 146s of the side surface 140s between the extension line 161p and the extension line 162p, the side surface 140s is not affected by the heat treatment and has high resistance. For this reason, the peripheral current path 145s is blocked in the vicinity region 146s of the side surface 140s between the extension line 161p and the extension line 162p. Thus, even when heat treatment for forming a passivation film or the like is performed by the thin film transistor 13, a thin film transistor using an oxide semiconductor that suppresses a variation in oxygen concentration caused by the heat treatment and suppresses a characteristic variation is provided.

  As described above, the channel protective layer 150 includes the semiconductor layer 140 between the extension line 161p of the side of the source electrode 161 facing the drain electrode 162 and the extension line 162p of the side of the drain electrode 162 facing the source electrode 161. It may be provided so as to cover the side surface 140s and the upper surface 140u. Accordingly, the peripheral current path 145s is substantially blocked in the vicinity region 146s of the side surface 140s between the extension line 161p and the extension line 162p, and the side surface 140s and the upper surface of the semiconductor layer 140 from the source electrode 161 and the drain electrode 162. Even if there is a portion where 140u is exposed, the peripheral current path 145s is cut off, so that it is not substantially affected by the characteristic variation of the semiconductor layer 140 due to the heat treatment.

  In addition, as illustrated in FIG. 9C, also in the thin film transistor 13 a of another modified example according to this embodiment, the semiconductor layer 140 has a region exposed outside the source electrode 161 and the drain electrode 162. Yes. Then, on the gate electrode 120, in the region between the extension line 161p of the side of the source electrode 161 facing the drain electrode 162 and the extension line 162p of the side of the drain electrode 162 facing the source electrode 161, the semiconductor A part of the side surface 140 s of the layer 140 is covered with the channel protective layer 150. That is, also in this case, a part of the end portion of the semiconductor layer 140 in the channel direction (gate length direction) of the channel region where the source electrode 161 and the drain electrode 162 face each other is covered with the channel protective layer 150.

Accordingly, the peripheral current path 145s is substantially cut off at a part of the side surface 140s between the extension line 161p and the extension line 162p, and the side surface 140s and the upper surface 140u of the semiconductor layer 140 are separated from the source electrode 161 and the drain electrode 162. Even if there is an exposed portion, the peripheral current path 145 s is cut off, so that it is not substantially affected by fluctuations in the characteristics of the semiconductor layer 140 due to heat treatment.
As described above, the channel protective layer 150 may be provided on at least a part of the side surface 140 s of the semiconductor layer 140 so as to block the peripheral current path 145 s in the semiconductor layer 140.

  Note that in the structure illustrated in FIGS. 9A, 9 </ b> B, and 9 </ b> C, the region where the semiconductor layer 140 is exposed from the source electrode 161 and the drain electrode 162 is the source electrode 161, the drain electrode 162, and the channel. Etching may be performed using the protective layer 150 as a mask.

  Further, as shown in FIG. 9D, in the thin film transistor 14 of another modification according to the present embodiment, the channel protective layer 150 is not formed in an island shape, but the entire semiconductor layer 140 is formed. Opening portions 161q and 162q are provided in the channel protective layer 150 at portions where the semiconductor layer 140 is in contact with the source electrode 161 and the drain electrode 162.

  Thus, in the thin film transistor 14, only the channel transistor 93a corresponding to the channel current path 145c in the channel region where the source electrode 161 and the drain electrode 162 face each other is formed, and the peripheral transistor corresponding to the peripheral current path 145s. 93b is not formed. Accordingly, a thin film transistor using an oxide semiconductor that suppresses fluctuations in oxygen concentration caused by the heat treatment and suppresses characteristic fluctuations even when heat treatment for forming a passivation film or the like is performed by the thin film transistor 14 is provided.

  Also in this case, the side surface 140s of the semiconductor layer 140 between the extension line 161p of the side of the source electrode 161 facing the drain electrode 162 and the extension line 162p of the side of the drain electrode 162 facing the source electrode 161 and The upper surface 140u is covered with the channel protective layer 150.

(Second embodiment)
The thin film transistor 15 according to the second embodiment of the present invention has the same structure as the thin film transistor 11a described with reference to FIGS. However, it is manufactured by a manufacturing method different from that of the thin film transistor 11a. That is, the number of processes is reduced by simultaneously performing photolithography for processing the channel protective layer 150 and photolithography for processing a portion from which the gate electrode 120 is extracted. Hereinafter, a method for manufacturing the thin film transistor according to this embodiment will be described.

FIG. 10 is a schematic cross-sectional view in order of the processes, illustrating a method for manufacturing a thin film transistor according to the second example of the invention.
This figure is a cross-sectional view corresponding to the cross section taken along the line AA ′ of FIG. In the figure, in addition to the thin film transistor portion, the contact portion is also illustrated.
First, as shown in FIG. 10A, an Al film 121f and a Mo film 122f were formed on the main surface 111 of the glass substrate 110g, which is the insulating layer 110, by sputtering to a thickness of 100 nm and 30 nm, respectively. Thereafter, the gate electrode 120 was formed by processing into a predetermined pattern. Photolithography was used for patterning, and mixed acid composed of phosphoric acid, acetic acid, nitric acid, and water was used for etching. At this time, the contact portion 123 of the gate electrode 120 of the thin film transistor was also formed at the same time. The contact portion 123 is also composed of a laminated film of an Al film 121f and a Mo film 122f.

Next, as shown in FIG. 10B, a SiO ₂ film 130f as a gate insulating film 130 was deposited with a thickness of 200 nm by PE-CVD using TEOS as a raw material. At this time, the film forming temperature was 350 ° C.

  Further, an oxide layer 140 f made of an In—Ga—Zn—O oxide to be the semiconductor layer 140 was formed to a thickness of 30 nm on the gate insulating film 130 by a reactive DC sputtering method. At this time, the ratio of oxygen was 5% with respect to argon. Then, the oxide layer 140f was processed into a predetermined pattern across the gate electrode 120 using 2% oxalic acid to form the semiconductor layer 140.

Further, as shown in FIG. 10C, a SiO ₂ film 150f to be the channel protective layer 150 was deposited with a thickness of 200 nm by a TEOS PE-CVD method. At this time, the film forming gas was a mixed gas of O ₂ and TEOS, and the film forming temperature was 350 ° C. Thereafter, the SiO ₂ film 150f is processed into a predetermined pattern covering the side surface 140s and the upper surface 140u of the semiconductor layer 140 except for the regions that will later become the source contact region 141 and the drain contact region 142, and the channel protective layer 150 is formed. Formed.

Note that the photolithography at the time of processing the SiO ₂ film 150f was performed by combining mask exposure and back surface exposure using the gate electrode 120 as a mask. The etching at this time was performed by RIE using CF ₄ gas.

At this time, after removing the SiO ₂ film 150f of the channel protective layer 150 deposited on the contact portion 123, the SiO ₂ film 130f of the gate insulating film 130 is removed, and the Al film 121f of the contact portion 123 and The laminated film of the Mo film 122f was exposed.

Thereafter, annealing was performed at 350 ° C. for 1 hour in an air atmosphere to remove damage to the semiconductor layer 140 due to the PE-CVD process of forming the SiO ₂ film 150f.

  Thereafter, as shown in FIG. 10D, the Mo film 166, the Al film 167, and the Mo film 168 to be the source electrode 161 and the drain electrode 162 are formed by sputtering at a thickness of 10 nm, 300 nm, and 50 nm, respectively. Thus, a laminated film 160f was formed, and this laminated film 160f was processed into a predetermined pattern using a mixed acid to form a source electrode 161 and a drain electrode 162. Thereby, the shape of the thin film transistor 11a is completed. Further, the laminated film 160f of the Mo film 166, the Al film 167, and the Mo film 168 is provided on the laminated film of the Al film 121f and the Mo film 122f to be the contact part 123, and the contact part 123 is manufactured.

  Thereafter, in order to remove element damage during the process, annealing is performed at 230 ° C. for about 1 hour in a clean oven, whereby the thin film transistor 15 according to the present embodiment is obtained.

In this manner, the processing of the contact hole 123h illustrated in FIG. 3A is performed by processing the channel protective layer 150 and processing the contact portion 123 for taking out the gate electrode 120 by photolithography in the same process. The process can be omitted, making it easier to manufacture.
Also in the thin film transistor 15 manufactured by such a method, a thin film transistor using an oxide semiconductor in which fluctuations in oxygen concentration caused by heat treatment are suppressed and characteristic fluctuations are suppressed is provided.

(Third embodiment)
The thin film transistor according to the third embodiment of the present invention is an improvement of the thin film transistor 11a according to the first embodiment. The channel length can be shortened and the current drive capability of the transistor can be improved. In addition, characteristic deterioration due to the reaction between the drain electrode 162 and the channel can be reduced.

FIG. 11 is a schematic cross-sectional view in order of the processes, illustrating a method for manufacturing a thin film transistor according to the third example of the invention.
FIG. 12 is a schematic cross-sectional view in order of the processes following FIG.
These drawings are cross-sectional views corresponding to the cross section taken along the line AA ′ of FIG. In these drawings, in addition to the thin film transistor portion, the contact portion is also illustrated.

  First, as shown in FIG. 11A, an Al film 121f and a Mo film 122f are formed on the main surface 111 of the glass substrate 110g, which is the insulating layer 110, by sputtering to a thickness of 100 nm and 30 nm, respectively. The gate electrode 120 was formed by processing into a predetermined pattern. Photolithography was used for patterning, and mixed acid composed of phosphoric acid, acetic acid, nitric acid, and water was used for etching. At this time, the contact portion 123 of the gate electrode 120 of the thin film transistor was also formed at the same time. The contact portion 123 is also composed of a laminated film of an Al film 121f and a Mo film 122f.

Next, as shown in FIG. 11B, a SiO ₂ film 130f as a gate insulating film 130 was deposited with a thickness of 200 nm by PE-CVD using TEOS as a raw material. At this time, the film forming temperature was 350 ° C.

  Further, an oxide layer 140 f made of an In—Ga—Zn—O oxide to be the semiconductor layer 140 was formed to a thickness of 30 nm on the gate insulating film 130 by a reactive DC sputtering method. At this time, the ratio of oxygen was 5% with respect to argon. Then, the oxide layer 140f was processed into a predetermined pattern across the gate electrode 120 using 2% oxalic acid to form the semiconductor layer 140.

Further, as shown in FIG. 11C, a SiO ₂ film 150f to be the channel protective layer 150 was deposited by a TEOS PE-CVD method with a thickness of 200 nm. At this time, the film forming gas was a mixed gas of O ₂ and TEOS, and the film forming temperature was 350 ° C. Thereafter, the SiO ₂ film 150f is processed into a predetermined pattern covering the side surface 140s and the upper surface 140u of the semiconductor layer 140 except for the regions that will later become the source contact region 141 and the drain contact region 142, and the channel protective layer 150 is formed. Formed.

Note that the photolithography at the time of processing the SiO ₂ film 150f was performed by combining mask exposure and back surface exposure using the gate electrode 120 as a mask. The etching at this time was performed by RIE using CF ₄ gas.

Thereafter, annealing was performed at 350 ° C. for 1 hour in an air atmosphere to remove damage to the semiconductor layer 140 due to the PE-CVD process of forming the SiO ₂ film 150f.

Next, as shown in FIG. 12A, a SiN film to be a passivation film 181 was deposited by a PE-CVD method. The film forming temperature was 250 ° C.
Then, contact holes 141h and 142h were formed at positions corresponding to the source contact region 141 and the drain contact region 142, respectively. At this time, a contact hole 123h for taking out the gate electrode 120 was also formed.

After that, as shown in FIG. 12B, the Mo film 166, the Al film 167, and the Mo film 168 to be the source electrode 161 and the drain electrode 162 are formed by sputtering with thicknesses of 10 nm, 300 nm, and 50 nm, respectively. Thus, a laminated film 160f was formed, and this laminated film 160f was processed into a predetermined pattern using a mixed acid to form a source electrode 161 and a drain electrode 162. Thereby, the shape of the thin film transistor 15a is completed. Further, the laminated film 160f of the Mo film 166, the Al film 167, and the Mo film 168 is provided on the laminated film of the Al film 121f and the Mo film 122f to be the contact part 123, and the contact part 123 is manufactured.
In this manner, the thin film transistor 15a according to the present embodiment is formed.

In the above, the oxide layer 140 f made of In—Ga—Zn—O oxide exposed from the channel protective layer 150 and covered with the SiN layer that is the passivation film 181 is formed as the SiN film that becomes the passivation film 181. By heating at 160 ° C. or higher at this time, oxygen is released and the resistance is lowered. Since this portion has a low resistance even after the SiN film is removed by etching, the series resistance between the source electrode 161 and the drain electrode 162 and the channel portion can be kept low. Note that the channel portion is protected by the channel protective layer 150 made of the SiO ₂ film 150f containing oxygen, and in this portion, oxygen is not separated from the oxide layer 140f, and high resistance can be maintained.

(Second Embodiment)
FIG. 13 is a schematic cross-sectional view illustrating the configuration of a display device according to the second embodiment of the invention.
The portion of the thin film transistor illustrated in the figure is illustrated as a cross section corresponding to the cross section along line AA ′ of FIG.

  As shown in FIG. 13, the display device 51 according to the second embodiment of the present invention is connected to the thin film transistor 11a according to the first example of the first embodiment and the drain electrode 162 of the thin film transistor 11a. A pixel electrode 140d and an optical element 300 that generates at least one of a change in optical characteristics and light emission by an electrical signal applied to the pixel electrode 140d are provided.

  In this specific example, the thin film transistor 11a is used. However, any one of various thin film transistors 11, 11a, 12, 13, 13a, 14, 15 and 15a according to the first embodiment is used. it can.

  The pixel electrode 140 d is made of an oxide that becomes the semiconductor layer 140 of the thin film transistor 11, and has an electric resistance lower than that of the semiconductor layer 140. That is, the pixel electrode 140d is formed of the oxide layer 140f that becomes the semiconductor layer 140, and the pixel electrode 140d and the semiconductor layer 140 are the same layer. In the pixel electrode 140d portion, a resistance value lower than that of the semiconductor layer 140 is required. For this reason, as will be described later, a measure is introduced to reduce the resistance of the oxide layer 140f used for the semiconductor layer 140 in the pixel electrode 140d portion.

  In this specific example, an organic EL element is used as the optical element 300. That is, on the pixel electrode 140d, a Cu phthalocyanine layer 191 having a thickness of 25 nm serving as a hole injection layer, and an α-NPD (N—N′-Di (1-naphtyl) −) having a thickness of 35 nm serving as a hole transport layer. N, N'-diphenylbenzidine) layer 192, 50 nm thick Alq3 (tris- (8-hydroxyquinoline) aluminum) layer 193 to be the light emitting layer, 0.6 nm thick LiF layer 194, 150 nm thick Al to be the cathode A layer 195 is provided in order, and an organic EL layer is formed. That is, in this specific example, the optical element 300 emits light by an electrical signal applied to the pixel electrode 140d. As the optical element 300, a liquid crystal that changes optical characteristics such as birefringence, optical rotatory power, scattering, and absorption by an electric signal applied to the pixel electrode 140d may be used.

  Note that the structure illustrated in FIG. 13 is further sealed with glass to provide a highly reliable display panel, but is omitted here.

  In the display device 51 according to this embodiment, since any one of the thin film transistors according to the first embodiment of the present invention is used, heat treatment for forming a passivation film or the like after forming the thin film transistors is performed. In addition, a display device using a thin film transistor using an oxide semiconductor in which variation in characteristics due to heat treatment is suppressed can be provided.

  Furthermore, since the pixel electrode 140d can be formed using the oxide layer 140f used for the semiconductor layer 140, the number of steps for forming the pixel electrode 140d is not increased, and the productivity is high.

That is, the semiconductor layer 140 serving as the channel of the thin film transistor 11 is covered with the channel protective layer 150, and oxygen is not easily released from this portion of the oxide layer 140f. On the other hand, since the oxide layer 140f to be the pixel electrode 140d is exposed from the channel protective layer 150, oxygen is easily released by heat treatment in this portion. By utilizing this fact, the oxide layer 140f that becomes the pixel electrode 140d is selectively made to have a low resistance while the oxide layer 140f made of the same material as the semiconductor layer 140 that becomes the channel of the thin film transistor 11 is used for the pixel electrode 140d. Can do.
As described above, the oxygen concentration contained in the pixel electrode 140 d is lower than the oxygen concentration contained in the semiconductor layer 140, thereby making the electric resistance of the pixel electrode 140 d lower than that of the semiconductor layer 140.

(Fourth embodiment)
Hereinafter, as a fourth example, a method for manufacturing a display device according to the present embodiment will be described. FIG. 14 is a schematic cross-sectional view in order of the processes, illustrating the method for manufacturing the display device according to the fourth example of the invention.
15 is a schematic cross-sectional view in order of the steps, following FIG.
Also in these drawings, the thin film transistor portion is illustrated as a cross section corresponding to the cross section taken along the line AA ′ of FIG.

  As shown in FIG. 14A, first, an Al film 121f and a Mo film 122f are formed by sputtering on the main surface 111 of the glass substrate 110g, which is the insulating layer 110, with thicknesses of 100 nm and 30 nm, respectively. The gate electrode 120 was formed by processing into a predetermined pattern. Photolithography was used for patterning, and mixed acid composed of phosphoric acid, acetic acid, nitric acid, and water was used for etching. At this time, the contact portion 123 of the gate electrode 120 of the thin film transistor was also formed at the same time. The contact portion 123 is also composed of a laminated film of an Al film 121f and a Mo film 122f.

Next, as shown in FIG. 14B, a SiO ₂ film 130f as a gate insulating film 130 was deposited with a thickness of 200 nm by PE-CVD using TEOS as a raw material. At this time, the film forming temperature was 350 ° C.

Further, an In—Ga—Zn—O oxide film with a thickness of 30 nm was formed as a semiconductor layer 140 and an oxide layer 140f to be the pixel electrode 140d on the SiO ₂ film 130f by a reactive DC sputtering method. At this time, the ratio of oxygen was 5% with respect to argon. Then, the oxide layer 140f is processed into a shape in which a predetermined channel pattern crossing the gate electrode 120 and the pixel electrode 140d are connected using 2% oxalic acid, and the shapes of the semiconductor layer 140 and the pixel electrode 140d are manufactured. did.

Further, as shown in FIG. 14C, a SiO ₂ film 150f to be the channel protective layer 150 was deposited with a thickness of 200 nm by a PE-CVD method using TEOS. At this time, the film forming gas was a mixed gas of O ₂ and TEOS, and the film forming temperature was 350 ° C. Thereafter, annealing was performed in an air atmosphere at 350 ° C. for 1 hour to remove damage to the oxide layer 140f due to the PE-CVD process when the SiO ₂ film 150f was formed.

Thereafter, the channel protection layer 150 is formed by processing the SiO ₂ film 150f into a predetermined pattern covering the side surface 140s and the upper surface 140u of the semiconductor layer 140 except for the regions that will later become the source contact region 141 and the drain contact region 142. did. At this time, the SiO ₂ film 150f on the pixel electrode 140d was removed by etching, and the oxide layer 140f to be the pixel electrode 140d was exposed from the channel protective layer 150.
Incidentally, at this time, etching of the SiO ₂ film 150f is carried out by RIE using CF _4, subsequent to the SiO ₂ film 150f, and the resist and the semiconductor layer 140 for shaping the channel protective layer 150 as a mask Then, the SiO ₂ film 130f to be the gate insulating film 130 was etched until the Al film 121f and the Mo film 122f to be the contact part 123 of the gate electrode 120 were exposed.

  Thereafter, as shown in FIG. 15A, the Mo film 166, the Al film 167, and the Mo film 168 to be the source electrode 161 and the drain electrode 162 are formed by sputtering at a thickness of 10 nm, 300 nm, and 50 nm, respectively. After forming the laminated film 160f, the laminated film 160f was processed into a predetermined pattern using a mixed acid to form the source electrode 161 and the drain electrode 162. Thereby, the thin film transistor 11a and the contact portion 123 are completed.

Thereafter, as shown in FIG. 15B, a SiN film to be a passivation film 181 was deposited with a thickness of 100 nm by PE-CVD. In addition, by setting the deposition temperature of the SiN film to about 230 ° C., sufficient barrier characteristics can be obtained in the passivation film 181.
Further, a bank 182 having a predetermined shape excluding the pixel electrode 140d and the contact portion 123 was formed using a photosensitive transparent resin. As the photosensitive transparent resin, photosensitive acrylic or photosensitive polyimide can be used, and the baking temperature is 230 ° C., for example. After the bank 182 was formed, the SiN film as the passivation film 181 was removed by etching using the bank 182 as a mask.

Thereafter, an organic EL light emitting portion was formed between the banks 182. That is, the Cu phthalocyanine layer 191 serving as the hole injection layer is 25 nm thick, the α-NPD layer 192 serving as the hole transport layer is 35 nm thick, the Alq3 layer 193 serving as the light emitting layer is 50 nm thick, and the LiF layer 194 having a thickness of 0.6 nm and an Al layer serving as a cathode layer having a thickness of 150 nm were formed by a vapor deposition apparatus.
In this way, the display device 51 illustrated in FIG. 13 is manufactured.

Here, an SiN film is formed at a deposition temperature of 230 ° C. on a portion of the oxide layer 140f that becomes the pixel electrode 140d, and thereby, in the oxide layer 140f that becomes the pixel electrode 140d, oxygen Separation occurs and resistance decreases. On the other hand, the oxide layer 140f to be the semiconductor layer 140 on the gate electrode 120 is covered with the channel protective layer 150 made of the SiO ₂ film 150f containing oxygen, so that the film forming temperature of the SiN film is 230 ° C. The resistance is not reduced even by heating. Similarly, in the subsequent heat treatment for forming the bank 182, oxygen is further released from the oxide layer 140 f in the pixel electrode 140 d, and the resistance is further reduced. High resistance is maintained in the oxide layer 140f to be the semiconductor layer 140.

  As described above, in the display device 51 and the manufacturing method thereof according to the present embodiment, the same material (oxide layer 140f) as the semiconductor layer 140 that becomes the channel of the thin film transistor 11a is used for the pixel electrode 140d, and the semiconductor layer of the channel portion is used. The oxide layer 140f to be 140 is covered with the channel protective layer 150 containing oxide, and the oxide layer 140f to be the pixel electrode 140d is exposed from the channel protective layer 150 and covered with, for example, a SiN film, thereby selectively. The resistance of the oxide layer 140f to be the pixel electrode 140d is reduced.

  As described above, according to the display device 51 and the manufacturing method thereof according to the present embodiment, the step of forming another film for forming the pixel electrode 140d can be omitted, and the oxide in which the characteristic variation due to the heat treatment is suppressed is suppressed. A display device using a semiconductor and a manufacturing method thereof can be provided.

(Fifth embodiment)
In the display device 52 (not shown) according to the fifth embodiment of the present invention, the resistance of the semiconductor layer 140 and the pixel electrode 140d are different by controlling the film structure of the oxide layer 140f to be the semiconductor layer 140. It is something to make.

  That is, according to the experiment by the inventors, it was found that the electrical resistance in the oxide semiconductor layer depends on the film structure of the oxide semiconductor layer in addition to the oxygen concentration contained in the oxide semiconductor layer. For example, the film structure of the oxide semiconductor layer changes depending on the smoothness of the surface of the base layer when the oxide semiconductor layer is formed.

  For example, when the surface of the gate insulating film 130 serving as a base of the semiconductor layer 140 is a rough surface, the semiconductor layer 140 made of an oxide film formed thereon has a columnar structure (columner structure). At this time, when the cross section of the semiconductor layer 140 is observed with an SEM (Scanning Electron Microscope) or a TEM (Transmission Electron Microscope), the crystal is in an amorphous state, but the size is 10 to 30 nm. About a columnar grain is observed.

  On the other hand, when the surface of the underlying gate insulating film 130 is smooth, the semiconductor layer 140 does not have a columnar structure, but has a uniform film structure, and specific grains are not observed by the above observation method.

  Although it depends on the film formation conditions, for example, it was found that the semiconductor layer 140 has a columnar structure when the surface roughness of the underlying gate insulating film 130 is, for example, 10 to 5 nm. Then, it was found that when the surface roughness of the gate insulating film 130 is as smooth as 1 to 0.1 nm, for example, the semiconductor layer 140 has a uniform film structure. And the particle size at the time of columnar structure is 10-30 nm, for example.

  The electric resistance in the columnar structure having a large particle size is relatively lower than the electric resistance of the uniform film structure. That is, the resistivity of the semiconductor layer 140 varies depending on the underlying morphology (form) of the semiconductor layer 140. Then, when the film structure of the semiconductor layer 140 becomes a columnar structure and the particle size increases, the resistivity becomes relatively low.

For example, the resistance value in a columnar structure is 0.1 to 10 Ωcm, whereas in the case of a uniform film structure, the resistance value can be 1 × 10 ⁸ Ωcm or more.

  By applying this experimental result, in the display device 52 according to this embodiment, the particle size of the semiconductor layer 140 is controlled to control the distribution of electrical resistance.

FIG. 16 is a schematic cross-sectional view in order of the processes, illustrating the method for manufacturing the display device according to the fifth example of the invention.
Also in this figure, the thin film transistor portion is illustrated as a cross section corresponding to the cross section along line AA ′ of FIG.
As shown in FIG. 16A, first, an Al film 121f and a Mo film 122f are formed on the main surface 111 of the glass substrate 110g, which is the insulating layer 110, by sputtering to a thickness of 100 nm and 30 nm, respectively. The gate electrode 120 was formed by processing into a predetermined pattern. Photolithography was used for patterning, and mixed acid composed of phosphoric acid, acetic acid, nitric acid, and water was used for etching. At this time, the contact portion 123 of the gate electrode 120 of the thin film transistor was also formed at the same time. The contact portion 123 is also composed of a laminated film of an Al film 121f and a Mo film 122f.

Next, as shown in FIG. 16B, a SiO ₂ film 130f as a gate insulating film 130 was deposited with a thickness of 200 nm by PE-CVD using silane and TEOS as raw materials. At this time, the film forming temperature is 350 ° C.

Thereafter, a resist 130r having an opening only in a channel portion of the thin film transistor was formed, and the SiO ₂ film 130f corresponding to the channel portion was subjected to RIE treatment with a mixed gas of Ar and CF ₄ .

As a result, as shown in FIG. 16C, the smoothed surface 130g is formed in the portion exposed from the resist 130r. That, RIE process in the region of the SiO ₂ film 130f exposed from the resist 130r is applied, the surface of the SiO ₂ film 130f which RIE processing is not performed (i.e., SiO ₂ film 130f that remains deposited in a PE-CVD) Compared to the morphology, the surface is smoothed, and this region becomes the smoothed surface 130g. By this RIE process, the surface of the SiO ₂ film 130f is sufficiently smoothed by cutting the SiO ₂ film 130f to a depth of about 10 nm or more.
The surface roughness of the smoothed surface 130g of the SiO ₂ film 130f is, for example, about 1 to 0.1 nm, and the surface roughness of the portion of the SiO ₂ film 130f that is not subjected to the smoothing surface treatment is, for example, 10 to 10. 5 nm.

Further, as illustrated in FIG. 16D, an In—Ga—Zn—O film is formed as an oxide layer 140f to be the semiconductor layer 140 and the pixel electrode 140d on the SiO ₂ film 130f having the smoothed surface 130g. An oxide film was formed to a thickness of 30 nm by a reactive DC sputtering method. At this time, the ratio of oxygen was 5% with respect to argon.

  When the film structure of the oxide layer 140f was examined, the oxide layer 140f in the upper region 140n other than the smoothing surface 130g had a columnar structure with a particle size of about 10 nm to 30 nm. On the other hand, the oxide layer 140f in the region 140m on the smoothed surface 130g was not a columnar structure, but a uniform structure with an inconspicuous film structure.

In this way, by controlling the smoothness of the surface of the gate insulating film 130 serving as a base, the film structure of the oxide layer 140f formed thereon is selectively changed, whereby the oxide layer 140f In addition, a high resistance region and a low resistance region can be selectively formed.
For example, the resistance value in the case of a columnar structure when the base is rough is 0.1 to 10 Ωcm, whereas the resistance value is 1 × 10 ⁸ Ωcm in the case of a uniform structure when the base is smooth. it can.

After that, the oxide layer 140f is processed into a shape in which a predetermined channel pattern crossing the gate electrode 120 and the pixel electrode 140d are connected using 2% oxalic acid, and the shapes of the semiconductor layer 140 and the pixel electrode 140d are formed. Was made. Thereby, the high-resistance semiconductor layer 140 is formed by the oxide layer 140f corresponding to the smoothing surface 130g, and the low-resistance pixel electrode 140d is formed by the oxide layer 140f corresponding to other than the smoothing surface 130g. Note that in the case where any one of the source electrode 161 and the drain electrode 162 of the thin film transistor and the pixel electrode 140d are electrically connected by the oxide layer 140f, the gate insulating film 130 (SiO2) serving as a base of the connection portion _{The second} film 130f) is set as a non-smoothed region and a low resistance portion.

  Thereafter, for example, the display device 52 according to the present embodiment can be manufactured through the steps described with reference to FIGS. 14C to 15B, but the description thereof is omitted.

  Thus, in the display device 52 and the manufacturing method thereof according to the present embodiment, the pixel electrode 140d is formed of an oxide used for the semiconductor layer 140 and has a lower electrical resistance than the semiconductor layer. That is, the same material as the semiconductor layer 140 to be a channel, that is, the same oxide layer 140f is used for the pixel electrode 140d. However, the film structure is different.

  That is, the oxide layer 140f in the pixel electrode 140d can have a columnar structure. For example, the particle size of the columnar structure is 10 to 30 nm. On the other hand, the oxide layer 140f serving as a channel can have a uniform film structure, and in this case, no grains are observed. Thereby, the resistance of the pixel electrode 140d can be made relatively lower than that of the semiconductor layer 140 corresponding to the channel.

  At that time, as described above, by selectively controlling the smoothness of the surface of the gate insulating film 130 which is a base, the oxide layer 140f in the portion to be the pixel electrode 140d is selectively formed into a columnar structure, and the channel and The resulting oxide layer 140f can have a uniform film structure.

That is, the display device 52 further includes a film that is provided below the pixel electrode 140 d and is formed of the same material as the gate insulating film 130. In the above description, this film is described as the gate insulating film 130.
The surface of the gate insulating film 130 on the gate electrode 120 on the semiconductor layer 140 side is smoother than the surface on the pixel electrode 140d side of the film (gate insulating film 130) provided under the pixel electrode 140d. High nature.

  For example, the unevenness of the surface of the gate insulating film 130 on the gate electrode 120 on the semiconductor layer 140 side can be 0.1 to 1 nm. As a result, the oxide layer 140f thereon has a uniform film structure and a high resistance.

  For example, the unevenness of the surface on the pixel electrode 140d side of the gate insulating film 130 (the film formed of the same material as the gate insulating film 130) under the pixel electrode 140d can be set to 5 to 10 nm. . As a result, the oxide layer 140f thereon has a columnar structure and a low resistance.

  In the above, the smoothing surface 130g is formed by RIE, but the formation method is arbitrary. Conversely, a surface treatment may be performed in which the portion of the pixel electrode 140d is exposed to roughen the surface.

  That is, in the method for manufacturing the display device according to this embodiment, a surface treatment for selectively changing the smoothness of the surface of the gate insulating film 130 can be further performed before the formation of the oxide layer 140f. The surface treatment can be a surface treatment in which the surface of the gate insulating film 130 in the region where the pixel electrode 140d is formed becomes relatively rougher than other portions. That is, the surface to be subjected to the surface treatment may be a portion corresponding to the semiconductor layer 140 to be a channel, or a portion corresponding to the pixel electrode 140d.

The display devices 51 and 52 according to this embodiment can be a matrix type display device in which thin film transistors and pixel electrodes are arranged in a matrix.
FIG. 17 is a circuit diagram illustrating an equivalent circuit of another display device according to the second embodiment of the invention.
That is, FIGS. 5A and 5B illustrate an equivalent circuit of two types of display devices of an active matrix type using an organic EL.

  As shown in FIG. 17A, the active matrix display device 60 using the organic EL according to the present embodiment is connected to the first transistor Tr1 for pixel selection and the power supply line 320, and the organic EL layer A pixel driving transistor DTr for driving 302 (optical element 300) is provided. The gate of the first transistor Tr1 is connected to the scanning line 210, and the source is connected to the signal line 220. Any of the thin film transistors according to the embodiment of the present invention can be used for the first transistor Tr1 and the pixel driving transistor DTr.

In addition, as illustrated in FIG. 17B, the active matrix display device 61 using another organic EL according to the present embodiment includes the first to fourth transistors Tr <b> 1 to Tr <b> 4 for pixel selection, A driving transistor DTr is provided. The gate of the second transistor Tr2 is connected to the _nth scanning line 210n, and the gates of the first transistor Tr1 and the fourth transistor Tr4 are connected to the (n-1) th scanning line 210n _-1 . . The source of the second transistor Tr2 is connected to the signal line 220. Any of the thin film transistors according to the embodiment of the present invention can be used for the first to fourth transistors Tr1 to Tr4 and the pixel driving transistor DTr.

  Since the active matrix display devices 60 and 61 using these organic ELs use any of the thin film transistors according to the embodiment of the present invention, the active matrix display devices 60 and 61 include thin film transistors using an oxide semiconductor that suppresses characteristic variation due to heat treatment. A high-performance and easy-to-manufacture display device can be obtained.

FIG. 18 is a circuit diagram illustrating an equivalent circuit of another display device according to the second embodiment of the invention.
As shown in FIG. 18, in one element of the active matrix display device 62 according to the second embodiment of the present invention, the liquid crystal layer 301 serving as the optical element 300 includes the pixel electrode 140 d, the counter electrode 310, and the like. And is connected in parallel with the auxiliary capacitance Cs formed by the auxiliary capacitance electrode 240. The auxiliary capacitance electrode 240 is connected to the auxiliary capacitance line 230. The pixel electrode 140d is connected to the signal line 220 via the thin film transistor 21. The gate electrode 120 of the thin film transistor 21 is connected to the scanning line 210. The gate electrode 120 of the thin film transistor 21 is sequentially turned on / off by the scanning line 210, and a desired charge is written into the liquid crystal layer 301. The display device 62 performs display.

  Since the active matrix type display device 62 using liquid crystal uses any of the thin film transistors according to the embodiment of the present invention, it is manufactured with high performance by using a thin film transistor using an oxide semiconductor in which characteristic variation due to heat treatment is suppressed. An easy-to-use display device is obtained.

  As described above, the display devices 60, 61, and 62 according to the present embodiment are connected to any of the plurality of thin film transistors according to the embodiment of the present invention arranged in a matrix and the respective gate electrodes of the thin film transistors. A scanning line, a signal line 220 connected to one of the source electrode and the drain electrode of the thin film transistor, and a pixel connected to the other of the source electrode and the drain electrode of the thin film transistor 140 d of electrodes, and the optical element 300 which light-emits by the electrical signal given to the said pixel electrode are provided.

  At this time, the pixel electrode 140d may be formed of the oxide layer 140f serving as the semiconductor layer 140 of the thin film transistor and have a lower electrical resistance than the semiconductor layer 140.

  However, the present invention is not limited to this, and the configuration of the pixel electrode 140d is arbitrary as long as the thin film transistor to be used is any one of the thin film transistors according to the embodiment of the present invention. However, as already described, the pixel electrode 140d is formed of the oxide layer 140f that is to be the semiconductor layer 140 of the thin film transistor and has a lower electrical resistance than the semiconductor layer 140. This is advantageous because the step of forming the conductive film can be omitted.

(Third embodiment)
The third embodiment of the present invention is a method for manufacturing a thin film transistor.
That is, the substrate 110g, the gate electrode 120 provided on the substrate 110g, the semiconductor layer 140 provided on the gate electrode 120 through the gate insulating film 130 and formed of an oxide, and the semiconductor layer 140 The channel protection layer 150 provided between the source electrode 161 and the drain electrode 162 provided apart from each other with the gate electrode 120 interposed therebetween, the source electrode 161 and the drain electrode 162, and the semiconductor layer 140. , A method for manufacturing a thin film transistor. Hereinafter, the characteristic part of the manufacturing method will be described.

FIG. 19 is a flowchart illustrating the method for manufacturing the thin film transistor according to the third embodiment of the invention.
As shown in FIG. 19, in the thin film transistor manufacturing method according to the present embodiment, first, the gate electrode 120 is formed on the substrate 110g (step S110).
Then, the gate insulating film 130 is formed on the gate electrode 120 (step S120).
Then, the semiconductor layer 140 is formed on the gate insulating film 130 (step S130).

  Then, the channel protective layer 150 is formed to cover at least a part of the side surface 140s of the semiconductor layer 140 on the gate electrode 120 (step S140). That is, for example, the channel protective layer 150 is formed so as to cover at least part of the side surface 140 s of the semiconductor layer 140 except for the region connected to the source electrode 161 and the drain electrode 162 of the semiconductor layer 140. At this time, the upper surface 140u of the semiconductor layer 140 is also covered.

  Then, the semiconductor layer 140 and the channel protective layer 150 are heat-treated at a temperature of 160 ° C. or higher (step S150).

Thereafter, the source electrode 161 and the drain electrode 162 are formed on the semiconductor layer 140 and the channel protective layer 150 (step S160). That is, for example, the source electrode 161 and the drain electrode 162 are formed on regions of the semiconductor layer 140 that are connected to the source electrode 161 and the drain electrode 162, respectively.
That is, in the above manufacturing method, the method described with reference to FIGS. 2 and 3 can be used.

  According to the above manufacturing method, damage to the semiconductor layer 140 that occurs when the channel protective layer 150 is formed can be recovered by the heat treatment in step S150. Note that the source electrode 161 and the drain electrode 162 are not damaged by performing step S160 after the heat treatment (step S150). In the heat treatment (step S150), at least a part of the side surface 140s (and the upper surface 140u) that can serve as a current path in the semiconductor layer 140 is protected by the channel protective layer 150, whereby oxygen is released from the semiconductor layer 140. Therefore, the resistance is not lowered. Thus, a method for manufacturing a thin film transistor using an oxide semiconductor in which characteristic variation due to heat treatment is suppressed can be provided.

  In step S140 described above, the channel protective layer 150 is formed on the extension line 161p of the side facing the region where the drain electrode 162 is formed in the region where the source electrode 161 is formed and the region where the drain electrode 162 is formed. It may be formed so as to cover at least part of the side surface 140s of the semiconductor layer 140 between the extension line 162p of the side facing the region where the source electrode 161 is formed. Thereby, said current path can be cut off efficiently.

(Fourth embodiment)
The fourth embodiment of the present invention is a method for manufacturing a display device. That is, the substrate 110g, the gate electrode 120 provided on the substrate 110g, the semiconductor layer 140 provided on the gate electrode 120 through the gate insulating film 130 and formed of an oxide, and the semiconductor layer 140 The channel protective layer 150 provided between the source electrode 161 and the drain electrode 162, the source electrode 161 and the drain electrode 162, and the semiconductor layer 140 which are provided so as to sandwich the gate electrode 20. , A pixel electrode 140d connected to one of the source electrode 161 and the drain electrode 162 of the thin film transistor, an optical signal applied to the pixel electrode 140d, and at least one of a change in optical characteristics and light emission And an optical element 300 that produces the above. Hereinafter, the characteristic part of the manufacturing method will be described.

FIG. 20 is a flowchart illustrating the method for manufacturing the display device according to the fourth embodiment of the invention.
As shown in FIG. 20, in the display device manufacturing method according to the present embodiment, first, the gate electrode 120 is formed on the substrate 110g (step S310).
Then, the gate insulating film 130 is formed on the gate electrode 120 (step S320).

  Then, an oxide layer 140f to be the semiconductor layer 140 and the pixel electrode 140d is formed on the gate insulating film 130 (Step S330).

  Then, the channel protective layer 150 is formed so as to cover at least a part of the side surface of the oxide layer 140f on the gate electrode 120 and to expose the oxide layer 140f in the region where the pixel electrode 140d is formed (step S340). ). That is, for example, the pixel electrode 140d is formed so as to cover at least part of the side surface 140s (and the upper surface 140u) of the oxide layer 140f except for the region connected to the source electrode 161 and the drain electrode 162 of the semiconductor layer 140. The channel protective layer 150 is formed so as to expose the oxide layer 140f in the region.

  Then, the oxide layer 140f and the channel protective layer 150 are heat-treated at a temperature of 160 ° C. or higher, and the electric resistance of the oxide layer 140f exposed from the channel protective layer 150 is reduced to form the pixel electrode 140d (step S350). .

Thereafter, the source electrode 161 and the drain electrode 162 are formed on the semiconductor layer 140 and the channel protective layer 150 (step S360). That is, the source electrode 161 and the drain electrode 162 are formed on the regions of the semiconductor layer 140 that are connected to the source electrode 161 and the drain electrode 162, respectively.
That is, in the manufacturing method described above, the method described with reference to FIGS. 14 and 15 can be used.

  According to the manufacturing method of the display device according to the present embodiment, the step of forming another film to be the pixel electrode 140d can be omitted, and the display device using the oxide semiconductor that has high productivity and suppresses characteristic variation due to heat treatment. And a manufacturing method thereof.

  In the above step S340, for example, the channel protective layer 150 is formed in the extension line 161p on the side facing the region where the drain electrode 162 is formed in the region where the source electrode 161 is formed and the region where the drain electrode 162 is formed. It may be formed so as to cover at least part of the side surface 140s of the semiconductor layer 140 between the extension line 162p of the side facing the region where the source electrode 161 is formed. Thereby, said current path can be cut off efficiently.

FIG. 21 is a flowchart illustrating another method for manufacturing a display device according to the fourth embodiment of the invention.
As shown in FIG. 21, in another manufacturing method, first, the gate electrode 120 is formed on the substrate 110g (step S410).
Then, the gate insulating film 130 is formed on the gate electrode 120 (step S420).
Then, a surface treatment for selectively changing the smoothness of the surface of the gate insulating film 130 is performed (step S421). That is, for example, the portion of the gate insulating film 130 that becomes the base of the semiconductor layer 140 that becomes a channel is smoothed by RIE processing.
At this time, for example, the gate insulating film 130 serving as a base of the pixel electrode 140d is protected by, for example, a resist so as not to be smoothed. Further, any desired region other than the pixel electrode 140d is not smoothed, and an arbitrary conductive region can be produced and used as, for example, a wiring portion.

  Thereafter, the oxide layer is formed on the gate insulating film 130 (step S430). That is, the oxide layer 140f to be the semiconductor layer 140 and the pixel electrode 140d is formed. Thereby, for example, the oxide layer 140f in the portion to be the pixel electrode 140d has a columnar structure and has a relatively low resistance.

  Thus, a step of forming another film to be the pixel electrode 140d can be omitted, and a display device using a highly productive oxide semiconductor and a method for manufacturing the same can be provided.

  Before the formation of the oxide layer 140f in step S330 described in FIG. 20, the surface treatment in the above step S421 for selectively changing the smoothness of the surface of the gate insulating film 130 serving as the base is further performed. Also good.

  That is, the surface smoothness between the gate insulating film 130 under the semiconductor layer 140 and the gate insulating film 130 under the pixel electrode 140d is improved between step S320 and step S330 illustrated in FIG. Change. For example, the surface treatment described above can be a surface treatment that makes the surface of the gate insulating film 130 in the region where the pixel electrode 140d is formed relatively rougher than other portions.

The embodiments of the present invention have been described above with reference to specific examples. However, the present invention is not limited to these specific examples. For example, regarding the specific configuration of each element constituting the thin film transistor, the manufacturing method thereof, the display device, and the manufacturing method thereof, those skilled in the art can implement the present invention in the same manner by appropriately selecting from a well-known range, and similar effects Is included in the scope of the present invention.
Moreover, what combined any two or more elements of each specific example in the technically possible range is also included in the scope of the present invention as long as the gist of the present invention is included.
In addition, on the basis of the above-described thin film transistor, its manufacturing method, display device, and its manufacturing method as embodiments of the present invention, all thin film transistors that can be appropriately modified by a person skilled in the art, its manufacturing method, display device, and The manufacturing method also belongs to the scope of the present invention as long as it includes the gist of the present invention.
In addition, in the category of the idea of the present invention, those skilled in the art can conceive of various changes and modifications, and it is understood that these changes and modifications also belong to the scope of the present invention. .

11, 11a, 12, 13, 13a, 14, 15, 15a, 21, 91, 92, 93 Thin film transistor 51, 52, 60, 61, 62 Display device 93a Channel portion transistor 93b Peripheral transistor 110 Insulating layer
110g substrate (glass substrate)
111 Main surface 120 Gate electrode 121f Al film 122f Mo film 123 Contact portion 123h Contact hole 130 Gate insulating film 130f SiO ₂ film 130g Smoothing surface 130r Resist 140 Semiconductor layer 140d Pixel electrode 140f Oxide layer (oxide layer)
140 m, 140 n region 140 s side surface 140 u upper surface 141 source contact region 141 h contact hole 142 drain contact region 142 h contact hole 145 c channel part current path 145 s peripheral part current path 146 s neighboring area 150 channel protective layer 150 f SiO ₂ film 160 f laminated film 161 source electrode 161 p extension 161q opening 162 drain electrode 162p extension 162q openings 166, 168 Mo film 167 Al film 181 a passivation film 182 bank 191 Cu phthalocyanine layer 192 alpha-NPD layer 193 Alq3 layer 194 LiF layer 195 Al layer 210, 210 _n, 210 _n-1 scanning line 220 signal line 230 auxiliary capacity line 240 auxiliary capacity electrode 300 optical element 301 liquid crystal layer 30 2 Organic EL layer 310 Counter electrode 320 Power line

Claims (6)

An insulating layer;
A gate electrode provided on the insulating layer;
A semiconductor layer provided on the gate electrode via a gate insulating film and formed of an oxide layer;
On the semiconductor layer, a source electrode and a drain electrode that are provided so as to sandwich the gate electrode, and
A thin film transistor comprising:
A pixel electrode connected to one of the source electrode and the drain electrode of the thin film transistor, formed from the oxide layer, and having a lower electrical resistance than the semiconductor layer;
An optical element that generates at least one of a change in optical characteristics and light emission by an electrical signal applied to the pixel electrode;
A film provided under the pixel electrode and formed of the same material as the gate insulating film;
With
The surface of the gate insulating film on the semiconductor layer side above the gate electrode is higher in smoothness than the surface on the pixel electrode side of the film provided under the pixel electrode.   The display device according to claim 1, wherein the unevenness of the surface of the film provided under the pixel electrode on the pixel electrode side is 5 to 10 nm.   3. The display device according to claim 1, wherein unevenness of a surface of the gate insulating film on the gate electrode on the semiconductor layer side is 0.1 to 1 nm.   The grain size of the oxide layer in the pixel electrode is larger than that of the oxide layer in the semiconductor layer, and the grain of the oxide layer in the pixel electrode has a columnar structure that is a columnar grain. 4. The display device according to any one of 3.   The display device according to claim 1, wherein an oxygen concentration contained in the pixel electrode is lower than an oxygen concentration contained in the semiconductor layer. A plurality of the thin film transistors and the pixel electrodes are arranged in a matrix, respectively.
A scanning line connected to each gate electrode of the thin film transistor;
A signal line connected to the other of the source electrode and the drain electrode of the thin film transistor;
The display device according to claim 1, further comprising:

Images