JPH0645607A - Liquid-crystal display device and its manufacture - Google Patents

Abstract

PURPOSE:To form poly-Si which is excellent in crystallinity without causing thermal damage to a substratum film and to obtain a high-mobility TFT by a method wherein a-Si which contains p-type and n-type impurities is formed and the a-Si is irradiated with a laser. CONSTITUTION:When a-Si is irradiated with a laser and crystallized, the threshold energy value of its crystallization is lowered when the a-Si contains conductive impurities. Consequently, when poly-Si is formed at low energy, the poly-Si can be obtained without causing thermal damage to the substratum film of the a-Si to be crystallized. In addition, when a poly-Si TFT is formed by being irradiated with a laser, there exists a phenomenon that the threshold voltage of the TFT is shifted to the negative side. The phenomenon is eliminated in such a way that p-type poly-Si is used in the case of an n-type TFT and that n-type poly-Si is used in the case of a p-type TFT. In addition, when the doping amount of impurities is controlled, it is possible to control the threshold voltage of the TFT.

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 a manufacturing method thereof, and more particularly to a thin film transistor used as a switching element of a liquid crystal display device and a manufacturing method thereof.

[0002]

2. Description of the Related Art A liquid crystal display (LCD) using a thin film transistor (TFT) as a switching element is applied to an OA VDT, a color television and the like because of its features such as thinness, light weight and low power consumption. The problems of this TFT-LCD are high definition, large screen, and low cost.

For high definition and large screen, the size of TFT currently used is reduced to improve the aperture ratio and
It is necessary to reduce the load per line. To this end, amorphous silicon (aS
The mobility of the a-Si TFT in which i) is applied to the semiconductor layer is small (about 0.5 cm ² / V · s), and there is a limit in reducing the TFT size. Therefore, conventionally, a-Si
The film is crystallized and modified into polycrystalline Si (poly-Si),
It is considered to use a poly-Si film as a semiconductor layer of a TFT. Thereby, the mobility can be set to 10 cm ² / V · s or more. As means for crystallizing the a-Si film, laser irradiation or heating at 600 [deg.] C. or higher (described in JP-A-56-92573) is used.

To reduce the cost, it is considered to incorporate an externally mounted drive LSI on the same substrate as the pixel. Since the drive circuit requires high-speed operation, aS
The iTFT has low mobility, and it is difficult to form a circuit. Therefore, at least the part that constitutes the circuit is po
It must be composed of ly-Si TFTs. In order to realize the built-in circuit, the laser is applied only to the part that constitutes the circuit, and that part is made into poly-Si, and the circuit part is po
It is considered that the ly-Si TFT and the pixel portion are composed of an a-Si TFT. As another means, it is considered that heat treatment is applied to form poly-Si including pixels, and all TFTs constituting the LCD are composed of poly-Si TFTs.

[0005]

As shown in the above-mentioned prior art, when a-Si is crystallized, it is heated at 600 ° C. or higher, or is irradiated with an energy beam such as a laser. However, when heating at 600 ° C. or higher, it is not possible to use low-priced glass having a low melting point, and therefore expensive glass such as quartz glass is used. Therefore, there is a problem that the manufacturing cost is high. Even when the excimer laser is irradiated, plasma CVD is performed as in the conventional case.
When a-Si formed by a sputtering method or a sputtering method is crystallized, a high irradiation energy of about 300 mJ / cm ² is required. Therefore, there is a problem that the a-Si base film is thermally damaged. The above-mentioned conventional technology does not consider the above-mentioned problems.

In addition, the po formed as shown in the above-mentioned prior art.
The ly-Si TFT has a problem that the leak current is large.

An object of the present invention is to provide a TFT having high mobility by forming poly-Si having excellent crystallinity without giving heat damage to the underlying film.

A second object of the present invention is to provide the above-mentioned high mobility T.
Applying FT to TFT-LCD, LC with built-in drive circuit
D, to provide high-definition LCD and large-screen LCD.

[0009]

In order to solve the above problems, in the present invention, the structure of the TFT is as follows. a-Si containing p-type and n-type impurities is formed, and the conductivity type of the a-Si is n-type in the case of p-type TFT,
In the case of n-type TFT, p-type is used. Then, the poly-Si formed by irradiating the a-Si with a laser is TF.
Used for T channel layer.

Further, when the present invention is applied to the driving circuit built-in TFT-LCD, a-Si containing p-type and n-type impurities is formed in the channel layers of the pixel TFT and the circuit TFT, and , The conductivity type of the a-Si is n-type for a p-type TFT, p-type for an n-type TFT, and then the a-Si
Poly-Si formed by irradiating Si with a laser is used. Further, since the pixel section TFT can also operate with the current a-Si TFT, only the circuit section TFT may have the above structure.

As another means for solving the above problems, the TFT channel layer has a double-layer structure of poly-Si and a-Si from the side in contact with the gate insulating film, and
-Si is formed by irradiating a-Si containing p-type and n-type impurities with a laser, and the conductivity type of the poly-Si is p-type T.
In the case of FT, it is of n type, and in the case of n type TFT, it is of p type. B and P are particularly effective as the p-type or n-type impurities described above.

One means of the manufacturing method for solving the above problems will be described below. Poly- used for the TFT channel layer
Si was converted into SiH ₄ and B ₂ H ₆ by the plasma CVD method.
And a mixed gas of PH ₃ or H _{2 in the} mixed gas.
Alternatively, a mixed gas to which an inert gas such as He is added is used as a raw material, a film is formed, and then an energy beam such as a laser is irradiated to form the film. Alternatively, in the case of the inverted staggered structure TFT, after forming a gate insulating film, plasma treatment is performed using PH ₃ as a source gas, and then SiH is formed by plasma CVD method.
₄ and B ₂ H ₆ mixed gas, or H in the mixed gas
₂ or a mixed gas containing an inert gas such as He is used as a raw material to form B-containing a-Si. Then, the a-Si is irradiated with a laser to form poly-Si, and a TFT is formed.
Used for the channel layer of.

An excimer laser, which is ultraviolet light having a large absorption coefficient for a-Si, is suitable as a laser used for crystallization of a-Si.

[0014]

When the laser irradiation is carried out to crystallize a-Si, if the a-Si contains an impurity exhibiting conductivity, the crystallization threshold energy value is lowered. Therefore,
Low energy compared to the case without the above impurities
Since it is poly-Si, it does not cause heat damage to the a-Si base film that crystallizes, and po with a large grain size is used.
ly-Si can be obtained. Therefore, a-
The above effect can be obtained by introducing n-type and p-type impurities into Si. Also, by irradiating laser, poly-S
When the iTFT is formed, there is a phenomenon that the threshold voltage of the TFT shifts to the negative side. Therefore, in the case of an n-type TFT, the above-mentioned poly-Si is set to the p-type, and in the case of a p-type TFT, the above-mentioned poly-Si is set to the n-type, whereby the above-mentioned phenomenon can be solved. Further, the threshold voltage of the TFT can be controlled by controlling the impurity doping amount.

The channel layer of the TFT has a two-layer structure of poly-Si and a-Si from the side in contact with the gate insulating film, and
By configuring the poly-Si in the above manner, the junction between the source / drain electrode and the semiconductor layer where the electric field is concentrated is made of a-Si, so that the leakage current is significantly larger than that when the junction is made of poly-Si. It can be reduced. Furthermore, the channel region in which the on-current flows is poly- with excellent crystallinity.
Since it is made of Si, high mobility can be obtained.

The circuit portion T of the TFT-LCD with a built-in circuit
The above-mentioned T is applied to both the FT and the circuit part and the pixel part TFT
By applying FT, a poly-Si TFT having high mobility can be formed without giving heat damage to the underlying film, and a TFT-LCD with a built-in drive circuit can be manufactured with high yield. Further, when the present invention is applied to the pixel portion TFT, the TFT has a high mobility, so that the TFT size can be reduced, and high definition and a large screen can be realized.

As a manufacturing method, poly-Si used for a semiconductor layer of a TFT is formed into a SiH ₄ film by a plasma CVD method.
And a mixed gas of B ₂ H ₆ and PH ₃ , or a mixed gas obtained by adding an inert gas such as H ₂ or He to the mixed gas as a raw material, and then irradiating with an energy beam such as a laser. It is assumed to have been formed. Where the B ₂
By controlling the gas flow rates of H ₆ and PH ₃ gas, a−
Desired B and P can be doped in Si. By controlling the doping amounts of B and P, T
The threshold voltage of the FT can be controlled. Since a-Si is doped with B or P, poly-Si with a large grain size can be obtained even if a laser is irradiated with low energy.
Is obtained. Alternatively, in the case of the inverted staggered structure TFT, after forming the gate insulating film, plasma treatment is performed using PH ₃ as a source gas, and then SiH ₄ is formed by plasma CVD method.
And a mixed gas of B ₂ H ₆ or H _{2 in the} mixed gas.
Alternatively, a mixed gas containing an inert gas such as He is used as a raw material to form a-Si containing B. After that, laser irradiation is performed to form poly-Si, which is used for the channel layer of the TFT. The threshold energy value required for crystallization of a-Si can also be reduced by the above-mentioned method.

The laser used for crystallization is a-Si
An excimer laser having a large absorption coefficient for is suitable. For example, the oscillation wavelength of the XeCl excimer laser is 308n.
It is the ultraviolet light region of m. Therefore, the number of Si surface is 10n
Since it is absorbed in the m region, laser energy can be efficiently converted into heat energy, which is effective for crystallization.

[0019]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 A case where the present invention is applied to a liquid crystal display device having a built-in drive circuit will be described. FIG. 1 schematically shows an active matrix substrate for a liquid crystal display device having a driving circuit built therein. Pixel portion 102 for displaying an image and T provided in the pixel portion
It is composed of a circuit unit 101 for driving the FT. In the present embodiment, the pixel portion 102 and the circuit portion 101
The TFT used for has the structure shown in FIG. That is, TFT
The channel layer of the poly-Si from the side in contact with the gate insulating film.
And a-Si have a two-layer structure, and the poly-Si is B
And is formed by irradiating a-Si containing P with laser. A-Si containing B and P is easily crystallized, and poly- which has excellent crystallinity even when irradiated with a low energy laser.
Si is obtained. Therefore, thermal damage is not given to the a-Si base film. Further, by setting the conductivity type to p-type, the characteristics of the depletion mode of the TFT can be eliminated.

Next, a manufacturing method for realizing this embodiment will be described below. Sputtering method (DC10
After depositing 120 nm of Cr at 0 V and a temperature of 100 ° C., a gate electrode 2 pattern is formed by a photoetching process. The SiN film 3 is deposited by plasma CVD to 350
nm (substrate temperature 350 ° C., pressure 0.6 Torr, power 60
W, gas flow rate SiH ₄ : NH ₃ : N ₂ = 8: 48: 16
0 sccm) and then a-Si4 containing B and P was added to
The film is continuously formed with a film thickness of 0 nm. The conditions for forming the a-Si film are as follows: substrate temperature 300 ° C., pressure 0.6 Torr, power 40.
W, gas flow rate SiH ₄ : 0.1% B ₂ H ₆ (H ₂ dilution): 0.1
5% PH ₃ (H ₂ dilution) = 20: 15: 15 sccm.
After that, as shown in FIG.
/ Cm ² irradiation to crystallize the a-Si film. After laser irradiation, a-Si6 is formed to 150 nm by plasma CVD method.
(Substrate temperature 300 ° C, pressure 0.6 Torr, power-40W,
Gas flow rate SiH ₄ : H ₂ = 15: 40 sccm) is deposited, and then n-type Si 7 is deposited to 40 nm (substrate temperature 250 ° C., pressure 0.6 Torr, power 60 W, gas flow rate SiH ₄ : PH ₃ :
H ₂ = 20: 20: 40 sccm) is deposited, and the Si film in the portion where the TFT is formed is processed into an island shape. C by sputtering method
After forming r, Al, etc., and forming the source / drain electrodes 8, finally, SiN is deposited as a passivation film 9 by 1 μm by a plasma CVD method. FIG. 3 shows a sectional view of the completed inverted stagger structure TFT. The concentration of B and P in the poly-Si controls the doping amount so that a desired threshold voltage is obtained after the TFT is formed. The doping amount can be easily controlled by changing the flow rates of B ₂ H ₆ and PH ₃ gas during film formation.

FIG. 4 shows the mobilities of a TFT formed by the means of the present invention and a TFT formed by laser annealing an a-Si containing no impurities, which has been manufactured conventionally.
FIG. 4 shows the dependence of the mobility on the excimer laser irradiation energy, but the TFT of the present invention shifts the energy at which the mobility becomes maximum to the low energy side, and further obtains a higher mobility than the prior art. Has been. As a result, the present invention is suitable for reducing heat damage to the base film and increasing the mobility of the TFT.

By manufacturing the active matrix substrate as described above, as shown in FIG. 5, the driving LSI 103, which is conventionally attached externally, can be built in on the same substrate as the pixel 102. Therefore, the size and weight of the module can be reduced without changing the screen size.

Although the structure of the TFT is an inverted stagger here, the same effect can be obtained with a normal stagger and coplanar structure.

Example 2 The present invention is applied to the manufacture of a drive circuit built-in active matrix substrate having a driving circuit section made of poly-Si TFTs and a pixel section made of a-Si TFTs. Up to FIG. 11).

Al is sputtered on the glass substrate 10.
After depositing the film 11 with a thickness of 250 nm and patterning the gate electrode and the scanning line, the surface layer is anodized (FIG. 6). The SiN film 13 of 200 n is formed by the plasma CVD method.
An a-Si film 14 doped with m, B and P is continuously formed in a thickness of 40 nm. The conditions for forming the a-Si film are a substrate temperature of 3
00 ℃, pressure 0.6Torr, power 40W, gas flow rate Si
_{H 4: 0.1% B 2 H} 6 (H 2 _{dilution): 0.5% PH 3 (H} 2
Dilution) = 20: 20: 5 sccm. Mass spectrometry results,
The a-Si film formed under the above conditions has a [B concentration]: [P concentration] = 12: 1. By irradiating the a-Si film formed under the above conditions with a laser, poly-Si having low energy and a large grain size can be obtained. or,
Since crystallization can be performed with low energy, poly-Si can be formed without giving heat damage to the base film. After forming the a-Si film 14 doped with B and P, an excimer laser is locally irradiated with an energy of 170 mJ / cm ² only in the circuit built-in portion (FIG. 7). After that, plasma CVD
A-Si16 of 160 nm and n-type Si17 of 4 by
The Si film is continuously formed to a thickness of 0 nm, and the Si film on the portion where the TFT is formed is processed into an island shape (FIG. 8). Next, after forming the ITO film 18 to be the pixel electrode by the sputtering method, patterning is performed (FIG. 9). After that, as a source / drain electrode and a signal line, Cr19 of 60 nm and Al20 is formed by a sputtering method.
Is formed to a thickness of 400 nm and patterned. The source
Using the drain electrode as a mask, n-type Si on the channel of the TFT is selectively removed (FIG. 10). Finally, a SiN film 21 is formed on the entire surface by a plasma CVD method as a passivation film.
Of 1 μm is deposited to complete the target active matrix substrate (FIG. 11).

When irradiated with an excimer laser, crystallization occurs at low energy in a-Si doped with B and P as compared with a-Si containing no impurities. Therefore, according to the manufacturing method of this embodiment, the SiN of the gate insulating film can be made into poly-Si without causing thermal damage, and a TFT having high mobility and small variation can be formed. Therefore,
A TFT-LCD with a built-in drive circuit can be manufactured with good yield. The mobility of the TFT formed by the manufacturing method of this embodiment is
80 cm ² / V · s is obtained.

Further, the same effect can be obtained even if the pixel section TFT is composed of a poly-Si TFT like the above circuit section TFT. Further, in the above embodiment, the structure of the TFT is an inverted staggered structure, but the same effect can be obtained with other positive staggered and coplanar structures.

[0029]

According to the present invention, a high performance TFT can be formed. Furthermore, by using the TFT as a switching element of an LCD, it is possible to provide a high-definition LCD, a large-screen LCD, and an LCD with a built-in driving circuit.

[Brief description of drawings]

FIG. 1 is a schematic view of an active matrix substrate with a built-in driving circuit.

FIG. 2 is a cross-sectional structure diagram at the time of laser irradiation.

FIG. 3 is a completed sectional view of a TFT.

FIG. 4 is a diagram showing dependence of mobility on laser irradiation energy.

FIG. 5 is a configuration diagram of an active matrix substrate.

FIG. 6 is a cross-sectional view after anodization.

FIG. 7 is a cross-sectional view at the time of laser irradiation.

FIG. 8 is a cross-sectional structure diagram after Si etching.

FIG. 9 is a cross-sectional view after ITO patterning.

FIG. 10 is a cross-sectional view after forming a source / drain.

FIG. 11 is a cross-sectional view after forming a passivation film.

[Explanation of symbols]

1 ... Glass substrate, 2 ... Gate electrode, 3 ... SiN, 4 ...
B: P-doped a-Si, 5 ... B: P-doped poly-Si,
6 ... a-Si, 7 ... n type Si, 8 ... source / drain electrodes, 9 ... passivation film, 10 ... glass substrate, 11
... Al, 12 ... Anodized film formation, 13 ... SiN, 14 ... B:
P-doped a-Si, 15 ... B: P-doped poly-Si, 1
6 ... a-Si, 17 ... n type Si, 18 ... ITO, 19 ...
Cr, 20 ... Al, 21 ... SiN, 101 ... Circuit part, 1
02 ... Pixel portion, 103 ... Driving LSI.

Claims (15)

[Claims] 1. A liquid crystal display device comprising a plurality of thin film transistors each having a gate electrode, a gate insulating film, a channel layer, an n-type impurity layer and a source / drain electrode as a switching element on an insulating substrate, the channel being a channel. A liquid crystal display device, wherein the layer is composed of thin film polycrystalline silicon containing p-type and n-type impurities, and the conductivity type of the thin film polycrystalline silicon is p-type. 2. A liquid crystal display device comprising a plurality of thin film transistors each having a gate electrode, a gate insulating film, a channel layer, a p-type impurity layer and a source / drain electrode as a switching element on an insulating substrate as a switching element. A liquid crystal display device, wherein the layer is composed of thin film polycrystalline silicon containing p-type and n-type impurities, and the conductivity type of the thin film polycrystalline silicon is n-type. 3. A plurality of first thin film transistors having a gate electrode, a gate insulating film, a channel layer, an n-type impurity layer, and source / drain electrodes as constituent elements, a gate electrode, and a gate insulating film on an insulating substrate. , A channel layer, a p-type impurity layer, and a plurality of second thin film transistors having source / drain electrodes as constituent elements in a liquid crystal display device, wherein the channel layer of the first thin film transistor is p-type and n-type. A thin film polycrystalline silicon containing a p-type impurity, and the conductivity type of the channel layer of the first thin film transistor is p-type;
2. The liquid crystal display device, wherein the channel layer of the thin film transistor is formed of thin film polycrystalline silicon containing p-type and n-type impurities, and the conductivity type of the channel layer of the second thin film transistor is n-type. 4. The pixel unit according to claim 1, wherein the liquid crystal display device includes a plurality of thin film transistors for driving a pixel electrode for displaying an image, and a plurality of pixel units for driving the pixel unit. 2. A liquid crystal display device comprising a circuit section including the thin film transistor. 5. A first plurality of thin film transistors for driving a pixel electrode for displaying an image on an insulating substrate, and a second plurality of thin film transistors for forming a circuit for driving the first plurality of thin film transistors. A liquid crystal display device comprising a thin film transistor, the thin film transistor including a gate electrode, a gate insulating film, a channel layer, an impurity silicon layer, and source / drain electrodes, wherein the channel layer of the second thin film transistor is p-type and n-type. And a channel layer of the second thin film transistor has a conductivity type opposite to that of the impurity silicon layer of the second thin film transistor. The channel layer of this thin film transistor is composed of thin film amorphous silicon containing p-type and n-type impurities. The liquid crystal display device according to claim. 6. A liquid crystal display device comprising, as a switching element, a plurality of thin film transistors having a gate electrode, a gate insulating film, a channel layer, an impurity silicon layer, and source / drain electrodes as constituent elements on an insulating substrate.
The channel layer of the thin film transistor has a two-layer structure of polycrystalline silicon and amorphous silicon from the side in contact with the gate insulating film, the polycrystalline silicon contains p-type and n-type impurities, and the conductivity of the polycrystalline silicon is A liquid crystal display device, wherein the type is a conductivity type opposite to the conductivity type of the impurity silicon layer. 7. A first plurality of thin film transistors for driving a pixel electrode for displaying an image on an insulating substrate, and a second plurality of thin film transistors for configuring a circuit for driving the first plurality of thin film transistors. A liquid crystal display device comprising a thin film transistor, the thin film transistor including a gate electrode, a gate insulating film, a channel layer, an impurity silicon layer, and source / drain electrodes, wherein the channel layers of the first and second thin film transistors are gated. A two-layer structure of polycrystalline silicon and amorphous silicon is formed from the side in contact with the insulating film, the polycrystalline silicon contains p-type and n-type impurities, and the conductivity type of the polycrystalline silicon is the first and the second. 2. A liquid crystal display device having a conductivity type opposite to that of the impurity silicon layer of the thin film transistor of 2. 8. A first plurality of thin film transistors for driving a pixel electrode for displaying an image on an insulating substrate, and a second plurality of thin film transistors for forming a circuit for driving the first plurality of thin film transistors. A liquid crystal display device comprising a thin film transistor, the thin film transistor comprising a gate electrode, a gate insulating film, a channel layer, an impurity silicon layer, and source / drain electrodes, wherein the channel layer of the second thin film transistor is a gate insulating film. From the contact side, it has a two-layer structure of polycrystalline silicon and amorphous silicon,
A liquid crystal display, wherein the polycrystalline silicon contains p-type and n-type impurities, and the conductivity type of the polycrystalline silicon is opposite to the conductivity type of the impurity silicon layer of the second thin film transistor. apparatus. 9. Claims 1, 2, 3, 4, 5, 6, 7 or 8
[N-type impurity concentration] / [p-type impurity concentration] ≧ 10 when the polycrystalline silicon is n-type, and [p-type impurity concentration] / [n-type when the polycrystalline silicon is p-type Impurity concentration] ≧ 10. A liquid crystal display device. 10. Claims 1, 2, 3, 4, 5, 6, 7, 8
Or 9, wherein the p-type impurity is boron and the n-type impurity is phosphorus. 11. Claims 1, 2, 3, 4, 5, 6, 7,
8. The method for manufacturing a liquid crystal display device according to 8, 9, or 10, wherein the polycrystalline silicon is formed by irradiating a laser. 12. The method of manufacturing a liquid crystal display device according to claim 11, wherein the p-type and n-type impurities are introduced before laser irradiation. 13. The polycrystalline silicon according to claim 12, wherein SiH ₄ and B ₂ H ₆ are formed by plasma CVD.
And a mixed gas of PH ₃ or H _{2 in the} mixed gas.
Alternatively, a method of manufacturing a liquid crystal display device, which comprises forming amorphous silicon using a mixed gas to which an inert gas such as He is added as a raw material and then irradiating a laser. 14. The method according to claim 12, wherein after the gate insulating film is formed, plasma treatment is performed using PH ₃ as a source gas, and then a mixed gas of SiH ₄ and B ₂ H ₆ or the mixed gas is formed by a plasma CVD method. A method for manufacturing a liquid crystal display device, which comprises forming amorphous silicon using a mixed gas obtained by adding an inert gas such as H ₂ or He in a gas as a raw material and then irradiating a laser. 15. A method of manufacturing a liquid crystal display device according to claim 11, 12, 13 or 14, wherein an excimer laser is used as a means for forming the polycrystalline silicon.