JPH04313273A - Micro crystal silicon thin-film semiconductor device and liquid display device using the same - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal surface device which enables a high-speed switching to be made by forming a micro crystal silicon layer (muC-Si) on a plastic substrate. CONSTITUTION:A gate electrode 2 is formed on a plastic film substrate 1, a gate insulation film 3 is formed, and then an undoped muC-Si 4 is formed. Then, n(+)-muC-Si 5 for ohmic contact is formed continuously and is machined to a specific shape. thus enabling a muC-Si layer 6 to be formed. Therefore, a film of a TFT(thin film transistor) can be formed at a low temperature, the obtained muC-Si film has no photocon property, it shows a high conductivity and a high mobility and is suited for a high-speed drive, and further a threshold value can be controlled by activation according to ion-implantation + excimer laser at the time of its manufacture. Also, a liquid crystal display device with the TFT achieves a high-speed switching.

Description

[Detailed description of the invention]

0001

[Technical field] The present invention relates to microcrystalline silicon (
Hereinafter, it will be expressed as μC-Si. ) A semiconductor device equipped with a thin film and a display device having the semiconductor device, a display,
Furthermore, it relates to spatial modulation elements, high-definition vision, and the like.

0002

[Prior art] TFTs (thi
N film transistors are widely used in various office automation equipment such as facsimile machines and liquid crystal display devices. For example, in the IDRC '88
PP56-58, Oct. 1988”, also po
Regarding the integrated ly-Si TFT, please refer to "
SID '89 Digest PP238
~241, May, 1989. This species,
In liquid crystal display devices, active matrices using a-Si TFTs have been formed mainly on inexpensive glass using a film-forming process with a film-forming temperature of around 250°C. ~1cm2/v・
sec), it has been difficult to apply it to peripheral drive circuits for high-quality displays. On the other hand, poly with high mobility
In the case of -Si TFTs (~100 cm 2 /v·sec), the process temperature is as high as 1000° C., so cheap glass or plastics cannot be used, making it difficult to reduce costs. Therefore, when TFTs are used in a display device, the following combinations are used.

[Table 1] Therefore, there is a strong desire for the emergence of a TFT that can be formed on a plastic substrate at low temperatures, has higher mobility than a-Si, and has mobility close to that of poly-Si.

0003

[Objective] The object of the present invention is to provide a low-cost substrate, which can be formed on a flexible plastic substrate at low temperature, and which has a
- A μC-Si thin film semiconductor device (μC-Si TFT) which has higher mobility than Si and has mobility close to or higher than poly-Si, and a liquid crystal display device equipped with the semiconductor device and capable of high-speed switching, in other words. The key is to provide high-quality display devices.

0004

[Structure] The first aspect of the present invention is to provide μC on a plastic substrate.
- It relates to a thin film semiconductor device characterized by comprising Si. A second aspect of the present invention relates to a liquid crystal display device comprising the μC-Si TFT.

[0005] To form the μC-Si thin film, (1
) Increasing the degree of hydrogen dilution in the ECR method (electron cyclotron resonance method), (2) Using the ECR method and excimer laser in combination, (3) When using excimer laser alone, applying surface annealing afterwards. I can give an example. Plastic film substrates include polymer substrates such as polyethylene terephthalate, polymethyl methacrylate, polycarbonate, polyether sulfone, polyarylate, and the like.

[0006] Hereinafter, a description will be given with reference to the accompanying drawings. FIG. 1 is a flow diagram showing an example of the method for manufacturing μC-Si TFT of the present invention, FIG. 2 is a schematic diagram of a TFT driving liquid crystal panel, and FIG.
It is a sectional view of T. An example of the method for manufacturing the μC-Si TFT of the present invention will be explained along the flowchart of FIG. (a) A gate electrode 2 made of Cr or the like is formed on a plastic film substrate 1. In this case, a SiO2 layer may be formed as a base layer if necessary. (b) Form a gate insulating film 3. (c) Undoped μC-Si4 is first formed, and then n(+)-μC-Si5 for ohmic contact is successively formed. (d) Processing into a predetermined shape to form a μC-Si layer 6. (e) Form metal wirings 7 and 8. At this time, the source
The n(+) layer between the drains is also etched at the same time. Finally, a passivation layer 9 is formed to complete the process. In the figure, 10 is a gate driver, 11 is a drain driver, and 12 is a TFT panel (1920 x 480
pixel), 13 is a pixel electrode. The steps (a) to (e) above are all performed at room temperature, which not only makes it possible to form TFTs using plastic films, which could previously only be formed using a-Si films, but also allows the resulting TFTs to have characteristics that are similar to those of TFTs. μ
Since C-Si is used, it has higher mobility than a-Si, and a TFT as fast as poly-Si can be realized. This is possible due to the unique effects of the manufacturing method using the ECR method and/or the excimer laser method. In terms of mobility, a-Si is 0.01 to 1
cm2/v・sec, poly-Si has a value of 100~, and μC-Si has a wide range of 1~100 cm2/v・sec,
Depending on the film forming conditions, it is possible to realize a film that is superior to poly-Si. Since the ECR method uses cycloton resonance, it is possible to form a-Si at low temperatures (below 100°C), but in the step (c) using the ECR method, the amount of hydrogen dilution is increased and the micro-level power is increased. By doing so, it is possible to freely form layers ranging from undoped to doped, and at this time, μC-Si with crystals can be realized. Furthermore, by using an excimer laser (wavelength: 193 to 350 nm), excitation of radicals during ECR is promoted, allowing more efficient film formation. In addition, even with excimer laser alone, Si2H6,S
Since it is possible to decompose i3H8 gas and form a film, similar μC
- Formation of Si becomes possible. Excimer laser is ArF
However, when used in conjunction with ECR, 193 nm (A
rF) to 351 nm (XeF). In the case of excimer laser alone, in a-Si film formation,
It can be formed at a wavelength of 193 (ArF) to 241 nm (KrF). Note that in the case of using excimer laser alone, surface annealing may be performed afterwards. The created μC-Si film has ρD=1/107 (1/Ω・cm), ρP=1/10
4 (1/Ω・cm) (at 550 nm), and in the doped film, ρP≒ρD=1/102 to 1/100 (
1/Ω·cm), indicating high conductivity. The first feature of this film is that it has no photoconductivity, which is convenient.
For example, TFTs used as display devices are exposed to light in a complicated manner, but the threshold voltage, on-current value, and off-sensitivity of TFTs due to light are
Changes in current value can be suppressed. Second, it exhibits high conductivity and high mobility, making it suitable for high-speed driving. Thirdly, the threshold value can be controlled by ion implantation and activation by excimer laser.

[0007]

[Example] Example 1 EC on plastic film (PET: polyethylene terephthalate or PES: polyether sulfone)
By the R method, SiH4/O2=0.3, 1 mtorr, r. t
After forming SiO2 with a thickness of 1000 Å, Cr is deposited with a thickness of 1000 Å using a vacuum evaporation method. After that, CCl4/O2=1,1
Etch Cr into a predetermined shape at 0 torr and 100 W. After that, the resist (
OFPR) is removed with O2 plasma 70SCCM, 300W. After that, SiH4/N2=0.6,0.3mt
orr, deposited to a thickness of 2000 Å at 300 W to form a gate insulating film of SiNx. Similarly, due to the resist pattern, S
After etching the iNx into a predetermined shape, the resist is removed. Next, by ECR method, SiH4 10SCCM, 1mto
rr, r. t to form a-Si of 1 μm, followed by P
An n(+) layer of 100 Å is formed under the same conditions except that H3/SiH4=0.1%. After that, n between the source and drain
After removing the (+) layer by etching with SF6+O2 gas system, a passivation layer is formed to a thickness of 1 μm under the same formation conditions as the gate insulating film. Example 2 SiO2 is formed on PMMA (polymethyl methacrylate) by the ECR method (conditions are the same as in Example 1 described above). Furthermore, 1000 Å of Cr was formed by EB evaporation,
Etch into a predetermined shape. Then SiH4/N2=0
．． 6. Deposit 2000 Å at 300 W at 0.3 mtorr to form SiNx. Next, excimer laser (Ar
F, wavelength 193 nm), H2:100SCCM
Si2H6 1SCCM, pressure 10torr, 1
00mJ/cm2, number of shots, 10-102shot
An a-Si film is formed to a thickness of about 1000 Å. Here, excimer laser light (conditions 100 mJ/cm2, 10 s) was applied to the surface under high vacuum of 1/105 torr without flowing gas.
irradiate (hot) to convert into μc. Furthermore, PH3(1
%, He base) gas is introduced to form an n(+) layer of Si2H6 under the same conditions. The subsequent steps are formed under the same conditions as in Example 1. Example 3 [Limited to the process shown in FIG. 1(c). Other processes are the same as in Example 1] In the ECR device, H2: 10SCCM, SiH4 1SCCM,
ArF (
The generation efficiency of Si radicals was increased by irradiating the substrate with an excimer laser of 300 mJ/cm2 (193 nm) in parallel and close to the substrate. n(+) is H2:10SCCM,S
iH4: 1 SCCM, PH3 (1%, He base): 1
It was formed using SCCM, and the subsequent steps were formed under the same conditions as in Example 1.

[0008]

[Effects] The μC-Si TFT of the present invention can be formed at a low temperature, and the resulting μC-Si film has no photoconductivity, exhibits high conductivity and high mobility, and is suitable for high-speed driving. Furthermore, during fabrication, it is possible to control the threshold value by ion implantation and activation using an excimer laser. In addition, in a liquid crystal display device equipped with the μC-Si TFT, since the μC-Si TFT does not have photoconductivity, the TFT used as a display device is frequently exposed to light, but the threshold voltage of the TFT due to light is , on-current value, and off-current value can be suppressed, and furthermore, it exhibits high conductivity and high mobility, thus enabling high-speed switching.

[Brief explanation of the drawing]

FIG. 1 is a flow diagram showing an example of a method for manufacturing a μC-Si thin film semiconductor device of the present invention.

FIG. 2 is a schematic diagram of a TFT-driven liquid crystal panel equipped with the μC-Si thin film semiconductor device of the present invention.

FIG. 3 is a cross section of the TFT panel section and peripheral drive section TFT of the schematic diagram shown in FIG. 2;

[Explanation of symbols]

1 Plastic film substrate 2 Gate electrode 3 Gate insulating film 4 Undoped μC-Si film 5 n(+)-μC-Si film 6 μC-Si film 7 Metal wiring 8 Metal wiring 9 Passivation film 10 Gate driver 11 Drain driver 12 TFT panel (1920 x 480 pixels) 13
pixel electrode

Claims (2)

[Claims] 1. A thin film semiconductor device comprising a microcrystalline silicon layer on a plastic substrate. 2. A liquid crystal display device comprising the microcrystal silicon thin film semiconductor device according to claim 1.