JPH08297299A - Thin-film transistor and liquid crystal display device using the same - Google Patents

Abstract

PURPOSE: To provide a thin-film transistor(TFT) which has excellent reliability at a high yield by embodying the TFT which is free from the occurrence of an insulation defect and shorting defect therein. CONSTITUTION: The structure of a gate electrode 6 of the TFT is constituted by completely coating a first metallic layer 4 having a two-layered structure consisting of pure Al for a lower layer 2 and an Al alloy mixed with Ta of a high melting metal as an impurity for an upper layer 3 with a second metallic layer 5 having the m.p. higher than the m.p. of the Al. The deformation, such as hillock, arising in the Al at the time of a heat treatment is suppressed and the occurrence of the insulation defect and shorting defect in the TFT is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor and a liquid crystal display device using the transistor as a switching element.

[0002]

2. Description of the Related Art In recent years, thin film transistors (hereinafter referred to as TFTs)
The liquid crystal display device to which the () is applied is becoming larger and higher in definition. The liquid crystal display device is provided with a TFT as a switching element at each intersection of a plurality of gate lines and a plurality of source lines provided so as to be orthogonal to these gate lines.
By turning ON / OFF, the signal supplied from the source line is supplied to the pixel electrode to control the display of the pixel.

However, since the wiring length of the wiring such as the gate line and the source line becomes longer with the increase in size of the liquid crystal display device in recent years, the increase of the wiring resistance becomes a problem. TFTs corresponding to the number of pixels are connected to the gate line,
Also, various parasitic capacitances are connected. Therefore, since the gate signal supplied to the gate line causes a signal delay problem due to the time constant defined by the wiring resistance and various parasitic capacitances, normal switching operation can be completed within a predetermined time. Difficult cases also occur. To solve this problem, 1. Increase the gate line width.

[0004] 2. Select a material with low specific electrical resistance.
There is a method. However, the above-described method of widening the gate line width is not usually used because it reduces the aperture ratio of the pixel portion. In the above method 2, aluminum (Al) has been conventionally considered as a material having a low specific resistance for the gate electrode, but this Al causes hillocks on the surface when heated to several hundreds of degrees Celsius. There's a problem. Therefore, hillocks are generated on the surface of the gate electrode when the insulating film or the like is formed after the gate electrode is formed, and the hillocks cause a short circuit between the gate electrode and the source electrode. As a solution to this problem, a small amount of refractory metal (S
It has been clarified that the inclusion of (i, Ta, etc.) suppresses the generation of hillocks during heating.

[0005]

FIG. 2 shows a TFT having a gate electrode formed of an AlSi alloy having a low specific electric resistance.
FIG. A first metal layer 22 made of an aluminum alloy in which Al is mixed with a refractory metal Si and a first metal layer 22 on the surface of an insulating substrate 21 such as a glass substrate.
The second metal layer 23 made of chromium (Cr) formed so as to completely cover the gate electrode 24 constitutes the gate electrode 24, the insulating layer 25 is provided so as to cover the gate electrode 24, and the semiconductor layer 26, The structure is such that the source electrode 27 and the drain electrode 28 are sequentially provided thereon.

In this structure, the first metal layer, AlS
When the i alloy has a thickness of 200 nm or more in order to increase the size and the definition, hillocks are generated at the end portion 29 of the gate electrode due to the heat treatment in the manufacturing process, and the i-alloy is completely covered with the second metal layer 23. Therefore, the withstand voltage of that portion deteriorates, and a short circuit defect occurs between the gate electrode 24 and the source electrode 27. In addition, the phosphoric acid-based etching solution used in the conventional wet etching of Al was improved.
-274004), the cross-sectional shape of the gate electrode 24 is about 60
Even if processed into a taper shape of °, it was not possible to completely eliminate the occurrence of short circuit defects. Further, wet phosphoric acid-based etching cannot remove Si, which is an impurity, and dry etching or the like is required, which causes a problem in productivity.

Next, the AlTa alloy has the advantage that Ta itself is removed by etching because Ta is a solid solution in Al, and Ta residue is not generated.
When the gate electrode 24 is formed of Ta alloy, the specific electric resistance is about 5 times that of pure Al, so that the film thickness must be increased, and as a result, the covering characteristics of the insulating layer 25 are deteriorated and the gate electrode 24 and There is a problem that a short circuit defect is generated between the source electrode 27 and the source electrode 27.

[0008]

In order to solve the above problems, a thin film transistor of the present invention and a liquid crystal display device using the same are provided with a gate electrode on an insulating substrate, and the insulating substrate and the gate electrode are insulated from each other. The film is a thin film transistor in which a semiconductor layer is further provided thereon, and a source electrode and a drain electrode are provided on the semiconductor layer so as to face each other immediately above the gate electrode, and the gate electrode is a lower layer made of pure aluminum, A first metal layer having an upper two-layer structure made of an aluminum alloy in which tantalum is mixed as an impurity, and a second metal layer made of a metal having a melting point higher than that of aluminum and provided above the first metal layer. And the second metal layer has a configuration in which the first metal layer is completely covered.

[0009]

According to the present invention, with the above-mentioned structure, the pure Al in the lower layer of the first metal layer lowers the resistance of the gate electrode, the AlTa alloy in the upper layer suppresses hillocks, and Since it is completely covered with the second metal layer made of a high melting point material, the AlTa alloy and the second metal layer completely prevent deformation such as hillock due to heat treatment during the manufacturing process. By forming the cross-sectional angle B of the end of the upper layer and the cross-sectional angle A of the end of the lower layer of the first metal layer under the conditions of the present invention, a sharp edge is formed at the end of the first metal layer. This is to prevent hillocks generated at this end.

[0010]

Embodiments of the present invention will be described in detail below with reference to the drawings and the manufacturing method and construction thereof.

FIG. 1 is a sectional structure of a TFT according to an embodiment of the present invention. A film thickness of 100 to 100 is continuously formed on the surface of the insulating substrate 1 such as a glass substrate by a sputtering method or a vapor deposition method.
Lower layer 2 made of pure Al of 500 nm and film thickness 50-250
A first metal layer 4 is formed by depositing a top layer 3 of nm AlAl alloy. Then, a desired resist pattern is formed by using a usual photolithography method, and phosphoric acid (H ₃ P) having a concentration of 85% is used as an etching solution.
O ₄ ), concentration 61% nitric acid (HNO ₃ ), acetic acid (CH ₃ C
16: 4: 4: OOH) and water (H ₂ O), respectively.
Volumetric mixing at a ratio of 1 and pure Al and Al at 20-50 ° C
The Ta alloy is simultaneously patterned to form the first metal layer 4 in a desired shape. At this time, the sectional angle A formed by the end 2a of the lower layer 2 of the first metal layer 4 and the insulating substrate 1 is 60 degrees or less, and the sectional angle B formed by the end 3a of the upper layer 3 and the insulating substrate 1. Is formed at an angle smaller than the sectional angle A. Further, at this time, since the impurity Ta of the AlTa alloy of the upper layer 3 can be removed at the same time, no Ta residue is generated. The range of the mixing ratio of the etching solution is H ₃ PO ₄ : HNO ₃ : C.
It suffices if H ₃ COOH: H ₂ O = 16: 4 to 7: 4: 1.

Next, a film thickness of 100 to 20 is formed by sputtering or vapor deposition so as to completely cover the first metal layer 4.
A second metal layer 5 made of 0 nm Cr is formed, and a gate electrode 6 is obtained together with the first metal layer 4. Second metal layer 5
May be composed of any one of W, Ti, and Ta in addition to Cr, or may be an alloy of these.

Next, a gate insulating layer 7 made of a silicon nitride (SiNx) film as an insulating film is formed on the surfaces of the insulating substrate 1 and the gate electrode 6 so as to cover the gate electrode 6 and have a film thickness of 200 to 300 nm. To do. This gate insulating layer 7
Is formed by, for example, a plasma CVD method. further,
Amorphous silicon (a-S) is formed on the gate insulating layer 7.
The semiconductor layer 8 made of i) is formed to have a predetermined film thickness, and aluminum (Al) and titanium (Ti) are formed on the surface of the semiconductor layer 8 by a sputtering method or a vapor deposition method in a region other than the channel formation region immediately above the gate electrode 6. ) And the like, the source electrode 9 and the drain electrode 10 are formed so as to face each other.

As described above, pure Al is used as the lower layer and the upper layer made of an AlTa alloy that suppresses hillocks is provided on the lower layer, thereby suppressing the generation of hillocks without increasing the specific resistance value. is there.

Further, by completely covering the first metal layer 4 with the second metal layer 5 having a melting point higher than that of Al, deformation of Al such as hillock due to heat treatment in the TFT manufacturing process is prevented. Occurrence is suppressed.

Due to the synergistic suppression effect, the interlayer insulation failure due to the deterioration of the breakdown voltage of the gate insulating layer 7 due to the generation of hillocks and the like can be prevented. The occurrence of short circuit defects is extremely reduced, and the yield of TFTs can be significantly improved.

Further, by making the sectional angle A 60 degrees or less and the sectional angle B smaller than the sectional angle A, it is possible to eliminate a sharp edge at the end of the first metal layer 4.

For example, the edges 11 and 12 are both 1
It is an obtuse angle close to 80 °, and this angle is useful for suppressing an increase in the interface energy of the edges 11 and 12. Therefore, it is possible to suppress the preferential occurrence of hillocks at the edges 11 and 12.

Moreover, the edges 11 and 12 are 180 °
If the obtuse angle is close to, it is easy to cover with the second metal layer 5, and the disadvantage that only the edges 11 and 12 are not covered is eliminated.

Further, according to the present embodiment, the pure Al of the lower layer 2 of the first metal layer 4 of the gate electrode 6 and the AlTa alloy of the upper layer 3 can be etched at the same time, and the impurity removing step found in the AlSi alloy or the like is required. Therefore, the manufacturing cost can be reduced.

Although the gate insulating layer 7 has a single layer structure in this embodiment, it may be a multilayer insulating layer having different film qualities.

By using the thin film transistor of this embodiment as a switching element of a liquid crystal display device, a liquid crystal display device with few display defects can be obtained. The liquid crystal display device has a structure in which a liquid crystal material is sandwiched between two insulating substrates facing each other, and the above-mentioned embodiment is provided on one main surface of the insulating substrates facing each other, that is, a surface in contact with the liquid crystal material. The thin film transistor may be provided.

[0023]

As described above, according to the present invention, the deformation of Al hillock or the like due to the heat treatment during the manufacturing process of the TFT is suppressed, so that the breakdown voltage of the insulating layer is deteriorated due to the deformation. Interlayer insulation failure associated therewith is prevented. For example, the occurrence of short-circuit defects between the gate electrode and the source and drain electrodes is extremely reduced, and a TFT with high yield and excellent reliability can be manufactured.

When such a TFT is used as a switching element of a liquid crystal display device, the wiring resistance of the gate line can be greatly reduced, the problem of delay of the gate signal can be solved, and the yield is high and the reliability is excellent. It is possible to realize a liquid crystal display device.

[Brief description of drawings]

FIG. 1 is a sectional view of a thin film transistor according to an embodiment of the present invention.

FIG. 2 is a sectional view of a conventional thin film transistor.

[Explanation of symbols]

 1 Insulating Substrate 2 Lower Layer 2a End of Lower Layer 3 Upper Layer 3a End of Upper Layer 4 First Metal Layer 5 Second Metal Layer 6 Gate Electrode 7 Gate Insulating Layer 8 Semiconductor Layer 9 Source Electrode 10 Drain Electrode A Cross Section Angle B Section angle

Claims (4)

[Claims] 1. A gate electrode is provided on an insulating substrate,
An insulating film is provided on the insulating substrate and the gate electrode,
Further, a semiconductor layer is provided above the semiconductor layer, the source electrode and the drain electrode are provided on the semiconductor layer so as to face each other except a channel forming region immediately above the gate electrode, and the gate electrode is a lower layer made of pure aluminum and is made of tantalum. A first metal layer having an upper two-layer structure made of an aluminum alloy in which is mixed as an impurity, and a second metal layer provided above the first metal layer made of a metal having a melting point higher than that of aluminum. A thin film transistor having the second metal layer completely covering the first metal layer. 2. A sectional angle A formed by an end portion of a lower layer of the first metal layer forming the gate electrode and the main surface of the insulating substrate is 60.
The thin film transistor according to claim 1, wherein a cross-sectional angle B formed by an end portion of the upper layer of the first metal layer and the main surface of the insulating substrate is smaller than the cross-sectional angle A by a degree or less. 3. The thin film transistor according to claim 1, wherein the second metal layer is any one metal of Cr, W, Ti, and Ta, or an alloy thereof. 4. A liquid crystal display device comprising a liquid crystal material sandwiched between two insulating substrates facing each other, wherein one of the insulating substrates has a surface in contact with the liquid crystal material. , 2 or 3, wherein the thin film transistor is provided as a switching element.