JPH09162410A - Thin film transistor and its manufacturing method and liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin film transistor of high performance and high reliability and its manufacturing method and a liquid crystal display device by obtaining p-Si of good film quality. SOLUTION: A high temperature conductive thin film layer 2 is patterned an a translucent glass substrate 1. And on it, a base material insulating film layer 3 is accumulated. A p-Si semiconductor layer 4 farmed by laser crystallization is patterned. At this time, the high temperature conductive thin film layer 2 is so positioned as to overlap the area of the semiconductor layer 4. The accumulation of a gate insulating film 5, patterning of a gate electrode 6, accumulation of an inter-layer insulation film layer 7, and formation of a source electrode 9 and a drain electrode 10 are performed.

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 having high performance and high reliability, a manufacturing method thereof, and an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, development of an active matrix type liquid crystal display has been progressing toward cost reduction and high definition by incorporating a driver for driving pixels on the same substrate. Therefore, as a semiconductor material, amorphous silicon (Amorphous silicon: hereinafter referred to as “a
-Si "is abbreviated as" Si ") and has a higher carrier mobility.
-Si "is abbreviated). Above all, a p-Si thin film transistor (Thin Film Trans
sistor: hereinafter abbreviated as "TFT") has already been put to practical use in viewfinders of video cameras.

However, the above p-Si TFT has one
Since it is necessary to use an expensive quartz substrate that can withstand a high temperature process of 000 ° C. or more, it is very difficult to achieve a large screen in terms of cost and yield.

Therefore, the maximum process temperature is set to a-SiTF.
Development of a low-temperature process p-SiTFT that enables use of a large-area and inexpensive glass substrate by reducing the temperature to 450 ° C. or lower, which is similar to that of T, is underway.

As a conventional technique, after forming crystallized p-Si on a glass substrate by a laser annealing method or the like, a low pressure CVD method (LPCVD method) and a normal pressure CVD method (A
Attempts have been made to lower the temperature of the process by depositing a gate insulating film by the PCVD method) or the plasma CVD method (P-CVD method).

[0006]

However, although the p-Si TFT manufactured by the above method can obtain higher carrier mobility than the p-Si TFT manufactured by the high temperature process of 1000 ° C. or higher, the threshold voltage and the leak are high. It has been proved that it is inferior in terms of current, etc., and that its characteristics deteriorate significantly rapidly against AC stress (AC drive stress).

This is a p-type produced by laser crystallization or the like.
It is considered that the film quality of Si is much inferior to that of p-Si produced by a high temperature process of 1000 ° C. or higher, and that of a laser-crystallized p-Si film is similar to that of p-Si produced by a high temperature process. It is necessary to improve the quality of the film.

Since this problem is greatly related to the reliability of the TFT, it becomes a particularly important problem when considering the built-in driver which requires high reliability.

The present invention has been made in view of the above points, and an object thereof is p-Si having a good film quality.
In order to obtain a thin film transistor having high performance and high reliability, a method of manufacturing the thin film transistor, and a liquid crystal display device.

[0010]

In order to achieve the above object, the present invention is characterized in that a high thermal conductive thin film layer is interposed between a transparent glass substrate and a base insulating film layer.

Specifically, the first to third solving means of the present invention relate to a thin film transistor, and the following solving means has been taken.

That is, the first solution is a thin film transistor having a base insulating film layer deposited on a translucent glass substrate and a semiconductor layer deposited on the base insulating film layer, and has high thermal conductivity. The thin film layer is interposed between the translucent glass substrate and the base insulating film layer so as to overlap at least the region of the semiconductor layer.

A second solution is characterized in that, in the first solution, a polycrystalline silicon thin film by laser crystallization is adopted as the semiconductor layer.

A third solution is characterized in that, in the first solution, a diamond thin film, an indium tin oxide thin film or a non-translucent metal thin film is adopted as the high thermal conductive thin film layer.

The fourth to sixth solving means of the present invention relates to a method of manufacturing a thin film transistor, and the following solving means are taken.

That is, the fourth means for solving the problem is to first deposit a high thermal conductive thin film layer in a predetermined region on a transparent glass substrate. Then, a base insulating film layer is further deposited on the translucent glass substrate. Then, a semiconductor layer is deposited on the underlying insulating film layer so as to overlap the region of the high thermal conductive thin film layer.

A fifth solution is characterized in that, in the fourth solution, a polycrystalline silicon thin film by laser crystallization is adopted as a semiconductor layer.

A sixth solution is characterized in that, in the fourth solution, a diamond thin film, an indium tin oxide thin film or a non-translucent metal thin film is adopted as the high thermal conductive thin film layer.

A seventh solution of the present invention relates to a liquid crystal display device, characterized in that a display electrode is connected to the thin film transistor according to claim 1, 2 and 3, and both are arranged in a matrix. .

With the above structure, in the first to seventh means for solving the problems of the present invention, the high thermal conductive thin film layer interposed between the translucent glass substrate and the base insulating film layer provides high performance and high reliability. A thin film transistor and a liquid crystal display device having the same can be obtained.

This is because when the p-Si of the semiconductor layer is formed by the laser annealing method or the like, the high thermal conductivity thin film layer serves as a heat source to retain heat of the laser-heated Si layer and, as a result, the laser. Since the cooling rate of the Si layer after irradiation is lower than that when the high thermal conductive thin film layer is not formed, p-Si having large crystal grains is formed, and p-Si is formed.
It is considered that this is because the film quality of Si is improved.

Further, in the case of a liquid crystal display device, if a non-translucent metal thin film is used for the high thermal conductive thin film layer, the non-translucent metal thin film also functions as a light-shielding film in addition to the above-mentioned action. The deterioration of the OFF characteristics caused by irradiating the channel portion of the thin film transistor with the light for prevention can be prevented, and the display quality of the liquid crystal display device can be improved.

Further, since the high reliability is ensured in the low temperature process, it is possible to use a large-area glass substrate which is advantageous in terms of the cost and yield of the substrate and is inexpensive, and to increase the screen size of the liquid crystal display device. It is also possible to plan.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a sectional structure of a thin film transistor according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a transparent glass substrate 1, on which a high thermal conductive thin film layer 2 made of a diamond thin film having a film thickness of 200 nm is patterned into a predetermined shape. There is.

A base insulating film layer 3 made of, for example, a SiO ₂ film having a film thickness of 200 nm is further deposited on the transparent glass substrate 1, and the high thermal conductive thin film layer 2 is formed on the transparent glass substrate 1 and the base. It is interposed between the insulating film layer 3.

A film thickness of, for example, 8 is formed on the base insulating film layer 3.
A semiconductor layer 4 made of polycrystalline silicon (p-Si) having a thickness of 5 nm is patterned into a predetermined shape, the semiconductor layer 4 is formed by laser crystallization, and a source region 4b and a drain region are provided on both sides of the channel region 4a with a channel region 4a interposed therebetween. 4c is formed. The semiconductor layer 4 is deposited on the base insulating film layer 3 so as to overlap the region of the high thermal conductivity thin film layer 2. That is, the high thermal conductive thin film layer 2 is interposed between the translucent glass substrate 1 and the base insulating film layer 3 so as to overlap the region of the semiconductor layer 4.

On the semiconductor layer 4, for example, a film thickness of 85 n
A gate insulating film 5 made of a SiO ₂ film of m is deposited, and a gate electrode 6 made of, for example, a Ta film having a film thickness of 200 nm is patterned in a predetermined shape on the gate insulating film 5.

A film thickness of, for example, 20 is formed on the gate electrode 6.
An interlayer insulating film layer 7 made of a 0 nm SiO ₂ film is deposited, and the interlayer insulating film layer 7 covers the gate electrode 6.

Contact holes 8 are formed in the gate insulating film 5 and the interlayer insulating film layer 7 so as to reach the source region 4b and the drain region 4c of the semiconductor layer 4, respectively.

On the interlayer insulating film layer 7, for example, a film thickness 7
A 00 nm Al film is patterned into a predetermined shape, and the contact hole 8 is filled with the Al film to form a source electrode 9 and a drain electrode 10 for making contact with the source region 4b and the drain region 4c. This constitutes a thin film transistor.

Next, the manufacturing procedure of the above-described thin film transistor will be described with reference to FIG.

First, as shown in FIG. 2A, a diamond thin film is formed on a transparent glass substrate 1 by a high frequency plasma CV.
After being deposited by the D method so as to have a film thickness of 200 nm, it is patterned into a predetermined shape, and the high thermal conductive thin film layer 2 is deposited in a predetermined region on the translucent glass substrate 1.

Next, as shown in FIG. 2B, a base insulating film layer 3 made of a SiO ₂ film is further formed on the translucent glass substrate 1 by atmospheric pressure CVD at 450 ° C. to a film thickness of 200 nm.
And the high thermal conductive thin film layer 2 is interposed between the translucent glass substrate 1 and the underlying insulating film layer 3,
Plasma CVD of a-Si: H is performed on the underlying insulating film layer 3.
Is deposited at 270 ° C. to a film thickness of 85 nm and patterned into a predetermined shape. The patterned a-Si: H is subjected to dehydrogenation treatment at 450 ° C. for 90 minutes and then crystallized using a XeCl excimer laser having a wavelength of 308 nm to obtain a semiconductor layer 4 made of p-Si. . At this time, the semiconductor layer 4 is deposited so as to overlap the region of the high thermal conductivity thin film layer 2.

After that, as shown in FIG. 2C, a gate insulating film 5 made of a SiO ₂ film is deposited on the semiconductor layer 4 by an atmospheric pressure CVD method at 450 ° C. to a film thickness of 85 nm. , Ta film is sputtered to a film thickness of 200 nm and patterned into a predetermined shape to form the gate electrode 6
To form

Thereafter, as shown in FIG. 2D, impurity ions such as phosphorus and boron are implanted into the semiconductor layer 4 by ion doping using the gate electrode 6 as a mask, and the semiconductor layer 4 is exposed to the channel region 4a. A source region 4b and a drain region 4c are formed on both sides of the sandwiched region.

Thereafter, as shown in FIG. 2E, an interlayer insulating film layer 7 made of a SiO ₂ film is deposited on the gate insulating film 5 by atmospheric pressure CVD at 450 ° C. to a film thickness of 200 nm. Then, after covering the gate electrode 6 with the interlayer insulating film layer 7, the semiconductor layer 4 is subjected to hydrogen (H ⁺ ) plasma treatment at 300 ° C. for 2 hours.

Finally, as shown in FIG. 2F, contact holes 8 are formed in the gate insulating film 5 and the interlayer insulating film layer 7.
Is formed, and the Al film is sputtered to have a film thickness of 700 nm, and then patterned into a predetermined shape to form the source electrode 9 and the drain electrode 10 to complete the thin film transistor.

As described above, in this embodiment, the high thermal conductive thin film layer 2 made of the diamond thin film and the semiconductor layer 4 made of p-Si are provided between the transparent glass substrate 1 and the base insulating film layer 3.
The film quality of the semiconductor layer 4 can be improved and the thin film transistor having high performance and high reliability can be obtained.

According to the inventor's confirmation, the gate electrode 6 of the thin film transistor having the above-mentioned structure has a voltage of ± 16 V (frequency 1 MHz, duty 50%), and the source electrode 9 and the drain electrode 10 have an AC stress of 0 V (AC drive). When stress is applied, the TFT life is improved by about two digits as compared with the thin film transistor in which the high thermal conductive thin film layer 2 is not provided (see FIG. 4).

This means that when the high thermal conductive thin film layer 2 interposed between the translucent glass substrate 1 and the underlying insulating film layer 3 forms p-Si of the semiconductor layer by the laser annealing method or the like. And plays a role of retaining heat of the laser-heated Si layer.
It is presumed that this is due to the formation of Si.

Although a diamond thin film is used as the high thermal conductive thin film layer 2 in the above-mentioned embodiment, an indium tin oxide thin film (ITO thin film) may be used instead of the diamond thin film, or a thin film made of Ta, Cr or the like may be used. Even if a translucent metal thin film is used, the same effect can be obtained.

Further, in the above embodiment, the high heat conductive thin film layer 2 is patterned in a region in which the interposition of the high heat conductive thin film layer 2 is slightly larger than the semiconductor layer 4 as in the embodiment. For example, the high thermal conductive thin film layer 2 may be formed on the entire surface of the transparent glass substrate 1 without patterning, or may be patterned in the same shape. Alternatively, the high thermal conductive thin film layer 2 may be patterned only in a region (a channel region 4a of the semiconductor layer 4 and a boundary region between the channel region 4a, the source region 4b and the drain region 4c) capable of ensuring the thin film transistor operation.

Further, in the above embodiment, the base insulating film layer 3
Although the film thickness was set to 200 nm, according to the confirmation experiment by the present inventor, the same operational effect as in the above-described embodiment can be obtained even when the film thickness is 400 nm.
It has been confirmed that the film thickness of up to 200 nm, that is, the smaller the film thickness, is more effective.

FIG. 3 shows an example of an active matrix array for a liquid crystal display. Each pixel is manufactured by connecting the display electrode 13 to the n-channel TFT 11 as shown in FIG.
3 are arranged in a matrix. In addition to this, the scanning line driving circuit 14 and the data line driving circuit 15 are shown in FIG.
Like the inverter circuit shown in (1), it is manufactured on the same substrate by the C-MOS structure in which the n-channel TFT 11 and the p-channel TFT 12 are combined.

Since the n-channel TFT 11 and the p-channel TFT 12 all have the structure shown in FIG. 1 and are manufactured through the steps shown in FIG. 2, the scanning line drive circuit 14
The data line driving circuit 15 can ensure high reliability.

When a non-translucent metal thin film such as Ta or Cr is used as the high thermal conductive thin film layer 2 in the TFT,
Since this non-translucent metal thin film also plays the role of a light-shielding film, it is possible to prevent the deterioration of the OFF characteristic that occurs when the light for display is applied to the channel portion of the TFT, and to display the liquid crystal display device. The quality can be improved.

Further, since the high reliability of the liquid crystal display device can be secured in the low temperature process, it is advantageous from the viewpoint of the cost and yield of the substrate, and it is possible to use the glass substrate having a large area at a low cost, which is a large liquid crystal display. It can also be screened.

[0049]

As described above, according to the present invention,
Due to the heat retention effect of the high thermal conductivity thin film layer, the p-
Since the quality of the Si film can be improved, it is possible to provide a thin film transistor having high performance and high reliability and a liquid crystal display device using the thin film transistor. Furthermore, in the liquid crystal display device of the present invention, O generated by irradiating the channel region of the thin film transistor with light for display due to the light shielding effect of the non-translucent metal thin film.
Since it is possible to prevent the deterioration of the FF characteristics, it is possible to improve the display quality of the liquid crystal display device. Further, by using the method of manufacturing a thin film transistor of the present invention,
Since high reliability can be ensured in a low-temperature process, a large-area glass substrate can be used at a low cost to fabricate a liquid crystal display device using an active matrix array in which thin film transistors are integrated, and the screen of a liquid crystal display can be increased. You can also

[Brief description of the drawings]

FIG. 1 is a sectional structural view of a thin film transistor.

FIG. 2 is a manufacturing process diagram of a thin film transistor.

FIG. 3 is a plan configuration diagram of a liquid crystal display device.

FIG. 4 is a diagram showing changes in characteristics of thin film transistors due to AC stress application, with and without a high thermal conductivity thin film layer.

[Explanation of symbols]

 1 translucent glass substrate 2 high thermal conductivity thin film layer 3 underlying insulating film layer 4 semiconductor layer 11 n-channel TFT 13 display electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kyoji Uraoka 1006 Kadoma, Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yutaka Miyata, 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (7)

[Claims] 1. A thin film transistor comprising: a base insulating film layer deposited on a transparent glass substrate; and a semiconductor layer deposited on the base insulating film layer. A thin film transistor having a high thermal conductivity thin film layer interposed between the insulating film layer and the insulating film layer so as to overlap at least a region of the semiconductor layer. 2. The thin film transistor according to claim 1, wherein the semiconductor layer comprises a polycrystalline silicon thin film formed by laser crystallization. 3. The thin film transistor according to claim 1, wherein the high thermal conductive thin film layer comprises a diamond thin film, an indium tin oxide thin film, or a non-translucent metal thin film. 4. A step of depositing a high thermal conductive thin film layer in a predetermined region on a transparent glass substrate; a step of further depositing a base insulating film layer on the transparent glass substrate; And a step of depositing a semiconductor layer on the layer so as to overlap the region of the high thermal conductivity thin film layer. 5. The method of manufacturing a thin film transistor according to claim 4, wherein the semiconductor layer comprises a polycrystalline silicon thin film formed by laser crystallization. 6. The method of manufacturing a thin film transistor according to claim 4, wherein the high thermal conductivity thin film layer is formed of a diamond thin film, an indium tin oxide thin film, or a non-translucent metal thin film. 7. A liquid crystal display device characterized in that a display electrode is connected to the thin film transistor according to claim 1, 2 or 3, and both are arranged in a matrix.