JPH0730119A - Manufacture of thin film transistor for liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce surface leak current value by forming a gate electrode layer on an insulating substrate, and over it, a semiconductor layer with an insulating layer in between, and over it, a source/drain electrode layer containing, at least, a molybdenum, and after that, removing a molybdenum oxide. CONSTITUTION:On a glass substrate 1, a gate electrode layer 2 consisting of a molybdenum/tantalum alloy is formed, and after that, a gate insulating layer 3 of SiOx is formed. Then semiconductor layers, amolphous silicon a-Si4 and low resistance amolphous silicon layer 5n<+>a-Si, a continuously formed for patterning. After forming a display pixel electrode of ITO, an Mo layer, an Al layer, and an Mo layer are sequentially laminated together for film formation, and then patterned, so that source/drain electrodes 7 and 8 are formed. Then, a coating of haxamethyldisilane is applied to the substrate, and after heating the surface of the source/drain electrodes is analyzed with XPS, the fact that a trace amount of molybdenum oxide remaines is found.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film transistor, and more particularly to a method for manufacturing a thin film transistor used in a liquid crystal display device having improved current-voltage characteristics.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been widely used as display devices for OA equipment such as Japanese word processors and personal computers because of their great advantages such as thinness, light weight, and low power consumption. There is a strong demand for improvement in image display quality. In particular, an active matrix type liquid crystal display device in which a three-terminal element such as a thin film transistor (hereinafter abbreviated as TFT) is connected to each display pixel as a switch has a higher contrast than other liquid crystal display devices. Attention has been paid to the fact that the ratio is high, the response speed is remarkably excellent, and the conventional semiconductor manufacturing technology can be applied to manufacturing, and research on improving the characteristics of the TFT used is also actively conducted.

Regarding a conventional method for manufacturing a TFT for a liquid crystal display device, an inverted staggered type TFT whose sectional structure is shown in FIG.
Will be described as an example. A gate electrode layer 2 is formed on an insulating substrate 1 made of glass or the like, and a gate insulating layer 3 is formed thereon.
Is formed on the entire surface. Further, as a semiconductor layer, amorphous silicon (a-Si) 4 and low resistance amorphous silicon
The (n ⁺ a-Si) layer 5 is sequentially laminated and patterned. After that, a display electrode (not shown) is formed using ITO (indium tin oxide layer) by a sputtering method and patterned. Then, for example, the source electrode layer 6 and the drain electrode layer 7 having a three-layer structure of molybdenum (Mo) / aluminum (Al) / molybdenum (Mo) are formed. The source / drain electrode layer has such a three-layer structure and molybdenum (Mo) is formed as the first layer to prevent aluminum (Al) from diffusing into the semiconductor layer. Molybdenum (Mo) is formed in order to prevent hillock generation due to the second layer of aluminum (Al). Finally, if necessary, a protective layer is formed and patterned. In this way, a TFT array substrate having a liquid crystal display device TFT is obtained.

An alignment layer is formed on the TFT array substrate thus manufactured, and a rear glass substrate having a light-shielding layer, a counter electrode, and an alignment layer formed in this order on the surface is made to face the alignment layer, and a gap is formed in the gap. A liquid crystal composition is sealed to form a liquid crystal cell, and an external circuit is connected to such a liquid crystal cell and housed in a case to form a liquid crystal display device.

[0005]

However, the source / drain electrode layer having a three-layer structure of molybdenum (Mo) / aluminum (Al) / molybdenum (Mo) is oxidized or naturally formed by an ashing process after the electrode layer is formed. The molybdenum (Mo) layer is oxidized by oxidation or the like, and molybdenum oxide (M
oO _x ) is easier to generate. This molybdenum oxide (MoO
_x ) is soluble in water and alkaline liquid and has high conductivity, the molybdenum oxide (MoO _x ) 8 eluted in the washing process with pure water in the subsequent process is the back channel of the TFT when dried. The redeposition on the side surface facilitates the flow of surface leak current in the TFT. As a result, even when the gate pulse applied to turn on / off the TFT is turned off, if the source or drain electrode has a potential difference, a current flows and the on / off control cannot be performed. So-called current-
It causes deterioration of voltage characteristics. As a result, there is a problem that image defects such as image unevenness of the liquid crystal display device occur.

The present invention has been made in response to such a problem, and by removing molybdenum oxide on the surface of a TFT, the surface leak current value which causes the deterioration of the current-voltage characteristic is reduced to prevent image unevenness. An object of the present invention is to provide a method of manufacturing a TFT for a liquid crystal display device capable of producing the TFT.

[0007]

A method of manufacturing a TFT for a liquid crystal display device according to the present invention comprises a step of forming a gate electrode layer on an insulating substrate and a semiconductor layer on the gate electrode layer with a predetermined insulating layer interposed therebetween. And a step of forming a source / drain electrode layer containing at least molybdenum (Mo) on the semiconductor layer, and a step of removing molybdenum oxide generated from molybdenum (Mo). And

In the source / drain electrode layer according to the present invention, containing at least molybdenum (Mo) means that the material for forming the source or drain electrode layer is a single layer of molybdenum (Mo), or other metal such as It shows that it may have a laminated structure with aluminum (Al). Further, even an alloy of molybdenum (Mo) and another metal is included in the present invention when molybdenum oxide is generated from the surface of the alloy layer. The method for removing molybdenum oxide according to the present invention includes methods by physical, mechanical and chemical means. In the present invention, the molybdenum oxide is removed as a volatile or easily decomposable molybdenum compound. However, a very small amount of molybdenum oxide can be removed efficiently, which is particularly preferable. This method will be described below.

Molybdenum oxide (MoO _x ) has various oxidation states, but the most stable oxide is MoO ₃ . this
MoO ₃ reacts with, for example, ammonia (NH ₃ ) to produce (NH
₄ ) Removed as ₂ Mo ₃ O ₁₀ . Therefore, for example, when hexamethyldisilazane (HMDS) is applied to a substrate and heated, it causes a trimethylsilylation reaction with hydroxyl groups (OH) on the substrate surface to generate ammonia (NH ₃ ), so that molybdenum oxide (MoO _x ) is generated. Can be removed. Thus, the treatment is preferably performed with a reagent that reacts with molybdenum oxide to form a volatile or easily decomposable molybdenum compound, or a reagent that generates a reagent that forms these compounds. A schematic diagram in the case of using the above-mentioned hexamethyldisilazane (HMDS) is shown in FIG.

A known method can be used for the step of forming a gate electrode layer on the insulating substrate according to the present invention and the step of forming a semiconductor layer on the gate electrode layer with a predetermined insulating layer interposed therebetween. Absent. For example, the material used is
Molybdenum-tantalum alloy (MoTa) etc. as the gate electrode layer, SiO _x layer or SiN _x layer etc. as the gate insulating layer,
As the semiconductor layer, single crystal silicon, polycrystalline silicon, amorphous silicon, or the like can be used, and as the semiconductor layer and the source electrode or the like, a low resistance amorphous silicon layer or the like can be used. Furthermore, a method for forming a gate insulating layer or a semiconductor layer is used for a liquid crystal display device T
Known methods such as the plasma CVD method, the sputtering method and the photolithography method used for FT can be used.

The method for manufacturing a TFT for a liquid crystal display device of the present invention is also applied to a method for manufacturing a TFT having a structure in which a semiconductor layer 5 is further laminated on a semiconductor layer 4 with an insulating layer interposed therebetween in addition to the structure shown in FIG. it can.

[0012]

[Function] When the molybdenum oxide (MoO _x ) generated from the source / drain electrode layer containing molybdenum (Mo) is removed, even if a cleaning process with pure water is performed in a subsequent process, T
There is no redeposit on the back channel side surface of FT.
As a result, the surface leak current of the liquid crystal display device TFT can be prevented.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A TFT for a liquid crystal display device of the present invention will be described in detail below by taking an inverted staggered type TFT as an example. Example 1 A gate electrode layer made of molybdenum-tantalum alloy (MoTa) having a film thickness of 3500 angstroms was formed on a glass substrate by a sputtering method, and then a gate insulating layer made of SiO _x was formed by a plasma CVD method. Furthermore, a semiconductor layer composed of an amorphous silicon (a-Si) layer and a low resistance amorphous silicon (n ⁺ a-Si) layer was continuously formed by the plasma CVD method and patterned. After forming a display pixel electrode using ITO (indium tin oxide layer), sputter a molybdenum (Mo) layer, an aluminum (Al) layer and a molybdenum (Mo) layer in this order to a thickness of 1000 angstroms, 4000 angstroms and 1000 angstroms, respectively. Then, the source / drain electrodes were formed by patterning after forming a laminated film by the method. afterwards,
Apply hexamethyldisilazane (HMDS) to the substrate surface 1
Heated at 00 ° C for 3 minutes . The surface of the source / drain electrodes at this time was analyzed using XPS. The measurement results are shown in Table 1. Finally, plasma CVD a protective layer consisting of SiN _x layer
To obtain a TFT for a liquid crystal display device.

The current-voltage characteristics of the obtained liquid crystal display device TFT were measured. The measurement result is shown in FIG.

Comparative Example 1 After forming a source / drain electrode composed of a molybdenum (Mo) layer, an aluminum (Al) layer and a molybdenum (Mo) layer, a treatment with hexamethyldisilazane (HMDS) was not performed.
TF for liquid crystal display device using the same material and method as in Example 1
I got T. The surface of the source / drain electrode after forming the source / drain electrode was analyzed using XPS. The measurement results are shown in Table 1. In addition, the obtained liquid crystal display device TFT
Was measured for current-voltage characteristics. The measurement result is shown in FIG.

[0016]

[Table 1] As is clear from Table 1, the TFT obtained in Example 1 has
Compared to Comparative Example 1, the residual amount of molybdenum oxide (MoO _x ) is extremely small. Further, FIG. 3 shows that the TFT obtained in Example 1 has a smaller current value when the gate pulse is off than in Comparative Example 1.

[0017]

According to the method of manufacturing a TFT for a liquid crystal display device of the present invention, molybdenum oxide generated from molybdenum (Mo) is formed after the step of forming a source / drain electrode layer containing at least molybdenum (Mo) on a semiconductor layer. Since there is a step of removing the substance, it is possible to prevent the conductive substance from adhering to the back channel side. As a result, the liquid crystal display device using the TFT obtained by the manufacturing method of the present invention does not cause image unevenness and is excellent in image display quality. In addition, since defects due to TFTs are reduced, the manufacturing yield of liquid crystal display devices is also improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a liquid crystal display device TFT.

FIG. 2 is a schematic diagram in the case of removing molybdenum oxide using HMDS.

FIG. 3 is a diagram showing current-voltage characteristics of a liquid crystal display device TFT.

[Explanation of symbols]

1 ... Substrate, 2 ... Gate electrode layer, 3 ... Gate insulating layer, 4 ... Amorphous silicon (a-Si) layer, 5
……… Low resistance amorphous silicon (n ⁺ a-Si) layer, 6…
Source electrode layer, 7 Drain electrode layer, 8
Molybdenum oxide (MoO _x ).

Claims (1)

[Claims] 1. A step of forming a gate electrode layer on an insulating substrate, a step of forming a semiconductor layer on the gate electrode layer via a predetermined insulating layer, and at least molybdenum (Mo) on the semiconductor layer. A method of manufacturing a thin film transistor for a liquid crystal display device, which comprises a step of forming a source / drain electrode layer containing the element and a step of removing a molybdenum oxide generated from the molybdenum (Mo).