JP2503615B2 - Thin film transistor and manufacturing method thereof - Google Patents

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to a thin film transistor used as a switching element in a liquid crystal display device of a liquid crystal television, for example, and a method for manufacturing the same.

In recent years, as a liquid crystal display device used for a liquid crystal television or the like, high contrast and high time division driving are required, and therefore, use of an active matrix type has been proposed. This active matrix type liquid crystal display device is
A substrate in which a plurality of transparent electrodes to be pixels and switching elements connected to the transparent electrodes are arranged in a matrix, an opposite substrate provided with the other transparent electrode facing the plurality of transparent electrodes arranged in the substrate, and And a liquid crystal sealed between the substrates. Then, it has been proposed to use a thin film transistor as the switching element.

[Conventional technology]

Some of the conventional thin film transistors as described above include a light shielding structure for preventing light from entering the channel region of the semiconductor layer from the outside. The cross-sectional structure is shown in FIG.

In the figure, a gate insulating layer 3 is formed so as to cover a gate electrode 2 provided on an insulating substrate 1, and an a-Si (amorphous silicon) semiconductor layer 4 is further formed thereon. Then, on the channel region of the semiconductor layer 4, a blocking layer 5 that is an insulating layer for protecting the channel region is formed. From the blocking layer 5 to the semiconductor layer 4, n ⁺ for ohmic contact is formed. The -a-Si layer 6 and the source and drain electrodes 7 and 8 are formed. A thin film transistor is formed by the above configuration.

Then, in order to prevent light from entering the channel region of the semiconductor layer 4 from the outside, an insulating layer 9 is formed on the semiconductor layer and the source and drain electrodes 7 and 8, and the channel region on the insulating layer 9 is formed. A metal layer 10 for light shielding is formed at a position facing each other.

[Problems of conventional technology]

In the conventional thin film transistor having the light shielding structure as described above, after forming the thin film transistor, a step of further forming the insulating layer 9 and the metal layer 10 for obtaining the light shielding structure must be added. Is greatly increased.

In addition, since the insulating layer 9 needs to be formed to have a thickness equal to or larger than the thickness of the source and drain electrodes 7 and 8, there is a problem that the thickness of the entire element increases accordingly.

[Object of the Invention]

The present invention has been made in view of the above conventional problems, and an object thereof is to obtain a light-shielding structure without the additional steps as described above, and to keep the entire element thin. It is to provide a thin film transistor and a method of manufacturing the same.

[Main points of the invention]

In order to achieve the above-mentioned object, the present invention provides a blocking layer itself with a light-shielding function by providing a multilayer structure in which an opaque metal layer is sandwiched by insulating layers, and at the same time, at least the metal layer It is characterized in that a portion in contact with the source and drain electrodes is oxidized to have an insulating property.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a manufacturing process diagram showing an embodiment of a method of manufacturing a thin film transistor according to the present invention.

First, as shown in FIG. 1 (a), a metal material such as Cr (chromium), which will be a gate electrode, is deposited on the upper surface of an insulating substrate 1 such as glass or quartz by sputtering, vacuum deposition, or the like. Is patterned by using the photolithography method to form the gate electrode 2. Then, SiT (silicon nitride) is formed on the entire surface including the gate electrode 2.
A gate insulating film 3 such as is deposited by a plasma CVD method or the like.

Next, similarly, the a-Si semiconductor layer 4 and the first insulating layer 11 such as SiN (silicon nitride) are sequentially deposited by the plasma CVD method or the like, and then Ta (tantalum) or Al is deposited thereon.
An opaque metal layer 12 such as (aluminum) is deposited by sputtering, vacuum evaporation, or the like, and a second insulating layer 13 such as SiN is further deposited thereon by the plasma CVD method or the like. Then, the first insulating layer 11, the metal layer 12, and the second insulating layer 13 are collectively patterned by using a photolithography method, so that the metal layer 12 is formed on the channel region of the a-Si semiconductor layer 4. A blocking layer 14 having a structure in which the first insulating layer 11 and the second insulating layer 13 are sandwiched is formed. Further, the a-Si layer 4 under the blocking layer 14 is patterned to form a device area.

The patterning for forming the blocking layer 14 can be performed by batch etching the multilayer films (11, 12, 13) by using, for example, wet etching using buffer hydrofluoric acid as an etching solution. .
Alternatively, only the second insulating layer 13 may be dry-etched, and the metal layer 12 and the first insulating layer 11 thereunder may be collectively wet-etched.

Next, the peripheral portion of the metal layer 12 is anodized to form an oxide layer 15. That is, FIG. 2 (b)
As shown in Fig. 1, in solution 16 such as oxalic acid,
The entire element shown in is immersed, and in this state, the electrode (17) on the anode (+) side is connected to the exposed portion of the metal layer 12, and the solution 16
The electrode (18) on the cathode (-) side is placed inside and an electric field is applied between these electrodes. Then, the portion of the metal layer 12 connected to the anode side in contact with the solution 16 is gradually oxidized from the surface toward the inside, and the oxidized portion is the oxidized layer 15
Remains as. It should be noted that this anodic oxidation should be performed to such an extent that the oxide layer 15 has an insulating property to prevent a current from flowing through the metal layer 12 between the source and drain electrodes formed in the subsequent step.

Then, as shown in FIG. 1C, the a-Si semiconductor layer 4 including the blocking layer 14 on which the oxide layer 15 is formed.
N ⁺ -a-Si layer 6 for ohmic contact on the entire upper surface
Is deposited by a plasma CVD method or the like, and subsequently, a metal material such as Cr to be the source and drain electrodes is deposited thereon by sputtering, vacuum evaporation or the like. Then, the metal material and the n ⁺ -a-Si layer 6 are formed by photolithography.
Blocking layer by patterning
A source electrode 7 and a drain electrode 8 are formed from above 14 to above the a-Si layer 4. At this time, the blocking layer 14 prevents damage to the a-Si layer 4 at the time of depositing the metal material, and prevents etching performed at the subsequent patterning from reaching the a-Si semiconductor layer 4. Work.

The thin film transistor obtained through the above steps has a multilayer structure in which the blocking layer 14 is composed of the first insulating layer 11, the opaque metal layer 12, and the second insulating layer 13,
In addition to the function as a conventional blocking layer for preventing damage to the a-Si semiconductor layer 4 in the manufacturing process, a-Si
The metal layer 12 has a light-shielding function of preventing light from entering the channel region of the semiconductor layer 4 from the outside. Moreover, since at least the portion of the metal layer 12 that contacts the source and drain electrodes 7 and 8 is the oxide layer 15, the source electrode 7
The drain electrode 8 and the drain electrode 8 are not short-circuited via the metal layer 12.

Therefore, in this example, as described above, the blocking layer
Since 14 itself can have a light-shielding function, it is not necessary to add the conventional light-shielding structure composed of the insulating layer 9 and the metal layer 10 as shown in FIG. 2, and the manufacturing process for that can be reduced. it can. Furthermore, since there is no thick insulating layer 9 as in the prior art, the thickness of the entire element can be kept thin.

Although the a-Si semiconductor layer is used as the semiconductor layer in the above-mentioned embodiments, it is needless to say that another semiconductor material may be used as long as the characteristics of the semiconductor thin film are good.

Further, the insulating layer forming the blocking layer is not limited to the SiN film as described above. Similarly, the metal layer forming the blocking layer may be any opaque metal that can be anodized, and is not limited to Ta and Al described above.

〔The invention's effect〕

As described above, according to the present invention, by providing the blocking layer itself with the light-shielding function, it is possible to completely reduce the additional manufacturing steps for newly providing the light-shielding structure as in the related art. Moreover, the thick insulating layer required for the conventional light-shielding structure can be eliminated, so that the entire element can be kept thin.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram showing an embodiment of a method of manufacturing a thin film transistor of the present invention, and FIG. 2 is a sectional view of a conventional thin film transistor having a light shielding structure. 1 ... Insulating substrate, 2 ... Gate electrode, 3 ... Gate insulating layer, 4 ... a-Si semiconductor layer, 6 ... N ⁺ -a-Si layer, 7 ... Source electrode, 8 ... Drain Electrode, 11 ... First insulating layer, 12 ... Metal layer, 13 ... Second insulating layer, 14 ... Blocking layer, 15 ... Oxide layer.

Claims (2)

(57) [Claims] 1. A thin film transistor in which a gate electrode, a gate insulating film, a semiconductor layer, a blocking layer, and a source and drain electrode are sequentially laminated on an insulating substrate, wherein the blocking layer is an opaque metal layer and insulating layers are upper and lower surfaces. A thin film transistor having a sandwiched multi-layer structure, wherein at least a portion of the metal layer that is in contact with the source and drain electrodes is an insulating layer formed by anodic oxidation. 2. A step of forming a gate electrode on an insulating substrate, covering the gate electrode with a gate insulating layer, and then forming a semiconductor layer on the gate insulating layer; and forming a semiconductor layer on the channel region of the semiconductor layer. As a blocking layer, a step of forming a multilayer blocking layer in which upper and lower surfaces of an opaque metal layer are sandwiched by insulating layers, and at least a portion of the peripheral portion of the metal layer that is in contact with the source and drain electrodes is anodized. And a step of forming source and drain electrodes from the blocking layer having the multilayer structure to the semiconductor layer.