JPH05107560A - Liquid crystal display device and production thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] To realize a liquid crystal display device having a display area and a peripheral circuit area on the same substrate. A gate insulating film 33 in contact with a channel region of a TFT forming a peripheral circuit is an insulating film containing oxygen, and a gate insulating film 3 in contact with a channel region of a TFT forming a pixel portion.
2 is an insulating film containing no oxygen. [Effect] By containing oxygen, even if the channel region of the TFT constituting the peripheral circuit is made of polycrystalline silicon formed by laser irradiation, an increase in off current can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a structure of a thin film transistor used in the liquid crystal display device and a method of manufacturing the thin film transistor.

[0002]

2. Description of the Related Art As a thin film transistor (TFT) used in a liquid crystal display device, an amorphous silicon (a-Si) TFT having an inverted stagger structure has been conventionally used. a
The carrier mobility of the -Si film is about 0.5 cm ² / Vs or less, and the driving capability is sufficient for use in a pixel portion of a liquid crystal display device, and the off current is small. It is difficult to form a driving device formed on the same substrate as the display device. As an attempt to improve the carrier mobility of TFT, there is a method of forming a polycrystalline silicon (p-Si) film by laser annealing a part of the a-Si film (Japanese Journal of Applied Physics 29. , No.10, L1775 (1990): Japanese Journal of
Applied Physics, 29, No. 10, L1775 (1990)). As a gate insulating film of these TFTs, silicon dioxide (S
iO ₂ ), silicon nitride (SiN), silicon oxynitride (SiON), etc. are used.

However, TF using a p-Si film is generally used.
At T, since the off current is high, a-Si
A TFT using a film is more suitable. In a TFT using an a-Si film, SiN is usually used as a gate insulating film. This is because SiN and a-Si can be used, for example, to form the same plasma CVD apparatus, so that the interface is cleaned and the threshold voltage is low, and the diagonal size is already 10 inches or more. Liquid crystal display devices are being produced. Therefore, as a TFT structure for a liquid crystal display device having a built-in drive circuit, a TFT using a p-Si film for the drive circuit portion, an a-Si film for the pixel portion, and SiN for the gate insulating film are desirable. ..

However, according to the experimental results of the inventor himself,
In a TFT formed by irradiating a laser, when SiN is used as a gate insulating film, a-Si which is not irradiated by the laser is used.
The characteristics of TFT are good, but p-
The Si TFT has a problem that it is a depletion type and has a high off current. On the other hand, SiO is used as a gate insulating film.
_{When 2} is used, the characteristics of the laser-irradiated p-Si TFT are good, but the laser-irradiated a-Si T
It has been found that the FT characteristic has a problem that the threshold voltage is high. In the prior art, the gate insulating film of the TFT of the drive circuit section and the gate insulating film of the TFT of the pixel section are formed of the same material, and a liquid crystal display device having a good characteristic and having a built-in drive circuit cannot be configured. There is a problem that the number of ICs connected is reduced by incorporating the drive circuit, and an inexpensive liquid crystal display device cannot be supplied.

[0005]

As described above, in the prior art, the gate insulating film of the TFT of the driving circuit section and the gate insulating film of the TFT of the pixel section are formed of the same material, and have good characteristics.
There is a problem that a liquid crystal display device having a built-in drive circuit cannot be configured. Therefore, by incorporating a drive circuit, the number of connected ICs can be reduced and an inexpensive liquid crystal display device cannot be supplied.

An object of the present invention is to provide a p-Si TFT having a high carrier mobility and an a-S having a low off current and a low threshold voltage.
It is to provide a TFT structure and a manufacturing method thereof that enable a liquid crystal display device having a peripheral circuit and a pixel portion while maintaining the characteristics of the iTFT.

[0007]

In order to achieve the above object, in the present invention, the structure of the TFT is as follows. That is, in the TFT that constitutes the drive circuit, the gate electrode,
The structure is composed of SiN, SiO ₂ , and p-Si in this order, and the structure is composed of a gate electrode, SiN, and a-Si in the pixel section. In the above TFT, when Al or Ta is used as the gate electrode, the gate electrode and SiN are used.
An oxide film formed by anodizing the gate electrode may be formed between the two.

In order to achieve the above object, the present invention provides T
The manufacturing method of FT was as follows. For example, in the case of a TFT having an inverted staggered structure, after forming a gate electrode and SiN which is a gate insulating film, a gate insulating film containing oxygen such as SiO ₂ is selectively formed only in the TFT forming a peripheral driving circuit. To form. As an example of the formation method, monosilane (S
The substrate is irradiated with the laser in an atmosphere of iH ₄ ) and oxygen, or the substrate is irradiated with the laser in oxygen. Then, a polycrystalline silicon layer is formed, and then a source and drain regions are formed. The polycrystalline silicon layer is formed by first depositing an amorphous silicon layer and then irradiating it with an energy beam such as a laser.

[0009]

According to the method of manufacturing a TFT of the present invention, in the case of a TFT having an inverted stagger structure, for the TFT forming the peripheral driving circuit, SiO ₂ or SiO ₂ is selectively formed after forming SiN as a gate insulating film. Forming SiON, then a-Si
After forming the layer, laser irradiation is performed to form a p-Si layer. For the TFT in the pixel portion, a-Si layer is formed after forming SiN as a gate insulating film. When a TFT for a peripheral circuit is formed by using this manufacturing method, when a part of the a-Si film is converted into a p-Si film by laser annealing or the like, it is thermally affected and SiN An insulating film containing oxygen that prevents nitrogen in the film from diffusing into the silicon layer can be easily formed at the interface with the p-Si film.

The TFT for the peripheral drive circuit of the present invention manufactured as described above is a gate insulating film made of SiN and p-.
Since the SiO ₂ film or SiON film containing oxygen is formed between the Si films, it is possible to prevent the diffusion of nitrogen due to the thermal effect of laser irradiation when forming the p-Si film. It is effective to prevent the depletion type from becoming a depletion type and to reduce the off current. Further, since the p-Si film is also formed, the carrier mobility is high and the operation of the drive circuit is enabled. Since the TFT in the pixel portion is not subjected to laser irradiation, the low off-current and low threshold voltage characteristics which are the features of the TFT using the a-Si film are not impaired.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. FIG. 1 is a cross-sectional view of a semiconductor element for explaining the structure of the present invention, showing a cross-sectional view of a TFT that constitutes a pixel portion and a TFT that constitutes a peripheral driving circuit. TFTs having this structure are the same insulating substrate. Formed on. In this embodiment, a visual display terminal (VDT) having a diagonal of 10 inches on the display is realized.
In this case, the number of pixels in the display unit is 480 × 640 × (3)
Therefore, the TFT used in the display unit has a normal inverted stagger structure T
The TFT used in the circuit portion is a FT, and the channel region has two layers of polycrystalline silicon and amorphous silicon,
The gate insulating film in contact with the polycrystalline silicon is an insulating film containing at least oxygen.

In FIG. 1, 1 is an insulating substrate and 2 is a gate.
Electrode 4 is a polycrystalline silicon layer, 5 is an amorphous silicon layer, 6 is a source, 7 is a drain electrode, 8 is a Cr electrode, and 9 is an Al electrode. Reference numeral 31 denotes an alumina film (Al ₂ as a gate insulating film formed by anodic oxidation of Al when the gate electrode is formed of aluminum (Al).
O ₃ ), 32 is a silicon nitride (SiN) film as a gate insulating film, and 33 is at least silicon (Si)
And a SiO ₂ film or a SiON film as a gate insulating film containing oxygen (O).

According to the present invention, the gate electrode 2 and the gate insulating films 31 and 32 up to the SiN film are first formed on the insulating substrate 1.
Next, a gate insulating film 33 containing at least oxygen is selectively formed for the TFTs forming the peripheral circuit. next,
Amorphous silicon (a-Si layer) is formed, and then a polycrystalline silicon layer (p-Si layer) 4 formed by irradiating a region on the substrate forming the peripheral circuit with a laser is formed. Next, the a-Si layer 5 is formed, then the source 6 including the n + layer and the drain region 7 are formed, and then the Cr electrode 8 is formed.
And an Al electrode 9 are formed.

With such a structure, the TFT for the peripheral drive circuit has the gate insulating film 32 made of SiN and p.
A gate insulating film 33 made of a SiO ₂ film containing oxygen or a SiON film is formed between the -Si films 4. Therefore, p
Since nitrogen diffusion due to the thermal effect of laser irradiation when forming the -Si film 4 can be prevented, it is possible to prevent the characteristics of the TFT from becoming a depletion type and to reduce the off current. is there. Further, since the p-Si film 4 is also formed, the carrier mobility is high and the operation of the drive circuit is enabled. Since the TFT in the pixel section does not perform laser irradiation,
The low off-current, which is a feature of the TFT using the a-Si film 5,
It does not impair the low threshold voltage characteristics.

Next, a manufacturing method will be described. First, a gate electrode 2 is formed on a glass substrate 1 having a diagonal of 12 inches by a sputtering method.
2000 Å of Al film is deposited. After patterning the gate electrode 2, a voltage is applied to the gate electrode 2 in a liquid containing tartaric acid and ethylene glycol to form an Al film of 1000 Å
The portion is anodized to form an Al ₂ O ₃ film 31 having a thickness of 2000Å. After that, the SiN film 32 is removed by plasma CVD.
000Å Accumulate. Next, in an atmosphere containing SiH ₄ and O ₂ or an atmosphere containing SiH ₄ , O ₂ and N ₂ , an excimer laser of 200 mJ /
cm ^{2 is} irradiated to selectively form SiO ₂ or SiON film 33 of 100 Å. Next, a-
The Si film 5 is deposited at 400 Å.

Here, an excimer laser is irradiated with 200 mJ / cm ² in a He atmosphere in a portion where peripheral circuits are formed on the substrate to convert the a-Si film into the p-Si layer 4. Then, the a-Si layer 5 is 2,000 liters by the plasma CVD method.
accumulate. In the peripheral circuit part, the channel region has a two-layer structure of the p-Si layer 4 (400 Å) and the a-Si layer 5 (2000 Å), and in the pixel part, a single-layer structure of the a-Si layer 5 (2400 Å) is obtained. Next, a-Si is formed by the plasma CVD method.
(N + layer) 6 and 7 are deposited at 300 Å. After the Si layer is cut into islands by a photo and etching process, ITO that is a transparent electrode is deposited by a sputtering method and patterned by a photo and etching process. Then, the Cr electrode 8 and the Al electrode 9 are deposited by the sputtering method. The source 6 and the drain region 7 are separated by a photo-etching process, and then the passivation film 10 is formed.
Is completed.

As for the TFT characteristics, as shown by the solid line in FIG. 2, in the peripheral circuit section, a good enhanced type operation in which the current sharply rises from around the gate voltage of 0V is performed. In the present invention, the TFT characteristics are carrier mobility: 1
0 cm ² / Vs, threshold voltage: 2 V, off current: 2 pA,
In the pixel area, carrier mobility: 0.5 cm ² / V
s, threshold voltage: 1.5 V, off current: 1 pA. On the other hand, the broken line in the figure is the same as that of the TFT of the pixel portion, that is, the gate insulating film is an Al ₂ O ₃ film 31, a SiN film 3
P-Si formed by laser using a conventional structure composed of only 2 and not formed with the SiO ₂ film 33.
The characteristics of the TFT having the layer 4 are shown. Carrier mobility: 10
Although cm ² / Vs has the same characteristics as the TFT of the present invention, it has a threshold voltage of −2 V and an off current of 1 nA, which is a depletion type and cannot provide good display. On the other hand, on another 12 inch glass substrate, a polarizing plate, a color filter,
When a transparent electrode is formed and liquid crystal is sealed between the substrate and the previous substrate, a 10-inch size VDT liquid crystal display device is completed.

FIG. 3 shows the overall structure of a liquid crystal display device using the thin film semiconductor device. The device is composed of a TFT liquid crystal panel 50, a scanning circuit 51, and a sampling control circuit 53 which serves as a time function intermediate conversion means. A scanning signal is sent from the scanning circuit 51 to each liquid crystal display element of the liquid crystal panel 50 via the scanning lines 71 to 73, and a signal is sent from the sampling circuit 52 via the signal lines 74 to 76. With the above structure, the TFT of the present invention is a TFT liquid crystal panel 50.
The switch corresponds to the switch 60a, and the liquid crystal element corresponds to 60b. Further, the switch 61 in the sampling circuit 52
˜63 and the switch element (not shown) of 51 in the scanning circuit can also be formed by the TFT of the present invention.

Next, the operation of FIG. 3 will be briefly described. The FST signal and the CKV signal are input as timing signals to the scanning circuit 51. Scan signals Vg1-Vgn are output by these signals. On the other hand, the sampling control circuit 53 is supplied with a digital data signal data which determines the display state of the liquid crystal, and is generated by converting this signal into a sampling signal .phi.1-.phi.m which becomes a time function signal. The amplitude of the sampling signals φ1 to φm is determined by the logic level of the switches forming the sampling control circuit 53, and is 0 to 5 V for a MOS switch, for example. The amplitude of the sampling signals φ1 to φm is substantially equal to the amplitude (for example, 0 to 5 V) of the digital data signal which is the input signal of the sampling control circuit 53. Sampling circuit 52
The luminance reference signal VB is applied to the liquid crystal at the timing of the sampling signals φ1-φm.

Next, a second embodiment of the present invention is shown in FIG. In this embodiment, the gate insulating film is formed after forming the channel region. First, after forming the Cr electrode 8 on the insulating substrate 1, the source region 6 and the drain region 7 are formed by the plasma CVD method.
Then, after the a-Si film 5 is formed to 1000 Å, the peripheral circuit region is laser-annealed to form p-Si.
Convert to layer 4. Then, in an oxygen atmosphere, the peripheral circuit region is laser-annealed to selectively form a SiO ₂ film 33 as a gate insulating film on the surface of the p-Si layer 4 by 100Å. A SiN film 32 as a gate insulating film is deposited at 3500 Å by plasma CVD method. Next, the gate electrode 2 is deposited by the sputtering method. In the structure of the present invention, since the gate insulating film is formed on the channel region, p-
When a TFT having a high carrier mobility is formed by using a Si film, a-
No matter whether the Si film 4 is formed thick or thin, there is no difference in mobility and the margin of manufacture is high.

[0021]

According to the present invention, the TFTs forming the peripheral circuit region formed on the same insulating substrate have the effect of reducing the off current while maintaining a large carrier mobility.
Moreover, there is an effect that the TFT in the pixel region can maintain the ability to enable stable display. Finally, there is an effect that the peripheral drive circuit can be built in the liquid crystal display substrate.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a current-voltage characteristic diagram of a semiconductor device according to an embodiment of the present invention.

FIG. 3 is an overall configuration diagram of a TFT liquid crystal panel.

FIG. 4 is a cross-sectional view of a liquid crystal display device according to another embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Gate electrode 31 Gate insulating film (anodic oxide film) 32 Gate insulating film containing no oxygen 33 Gate insulating film containing oxygen 4 Polycrystalline silicon layer (p-Si) 5 Amorphous silicon layer (a-Si) 6 Source region (n + layer) 7 Drain (n + layer) 8 Cr electrode 9 Al electrode 10 Passivation film 50 Liquid crystal panel 51 Scanning circuit 52 Sampling circuit 53 Sampling control circuit 60a Pixel part TFT 60b Liquid crystal cells 61-63 Peripheral circuit TFT

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 29/784

Claims (7)

[Claims] 1. A pixel region composed of a plurality of pixels in which liquid crystal is sealed between transparent insulating substrates, and a peripheral circuit region forming a drive circuit for driving the pixels are provided on an insulating substrate as constituent elements of a semiconductor element. In a liquid crystal display device having a thin film semiconductor device structure including a gate electrode, a gate insulating film, a channel region, a source region and a drain region, the gate contacting the semiconductor layer in the peripheral circuit region. A liquid crystal display device, wherein the gate insulating film and the gate insulating film of the semiconductor element in the pixel region are made of different materials. 2. The gate insulating film in contact with the channel region of the semiconductor element in the peripheral circuit region is made of an insulating film containing oxygen, and the gate insulating film of the semiconductor device in the pixel region contains oxygen. A liquid crystal display device characterized by comprising a non-insulating film. 3. The semiconductor device according to claim 1, wherein the channel region in contact with the gate insulating film of the semiconductor element in the peripheral circuit region is formed of polycrystalline silicon, and the channel region of the semiconductor element in the pixel region is formed of amorphous silicon. Liquid crystal display device. 4. A liquid crystal display device according to claim 1, wherein the semiconductor element has a structure in which a gate electrode, a gate insulating film and a channel region are formed in this order on an insulating substrate. .. 5. A liquid crystal display device according to claim 1, wherein the semiconductor element has a structure in which a channel region, a gate insulating film, and a gate electrode are formed in this order on an insulating substrate. .. 6. A step of forming a gate electrode on an insulating substrate and an oxygen-free gate insulating film thereon, and a semiconductor layer of the oxygen-free gate insulating film in a peripheral circuit region. A liquid crystal comprising: a step of changing a contact side into a gate insulating film partially containing oxygen; and a step of forming a channel region, a source region and a drain region on the gate insulating film. Manufacturing method of display device. 7. The method for manufacturing a liquid crystal display device according to claim 6, wherein the gate insulating film containing oxygen is formed by energy beam irradiation in a gas containing at least oxygen.