JPH07183535A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve a crystalline silicon film of a TFT in crystallinity and to obtain TFTs used for a picture element region and other TFTs used for a peripheral circuit region through the same process by a method wherein the crystalline silicon film of a TFT arranged is a peripheral circuit region is irradiated with laser rays or string light rays. CONSTITUTION:A prime film 202 of silicon oxide and an amorphous silicon film 203 are formed on a substrate 201. Then, a silicon oxide film 205 is formed and then selectively etched, whereby a region 204 where amorphous silicon is exposed is formed. A nickel-containing acetate solution which promotes the crystallization of amorphous silicon is applied. Nickel contained in an acetate solution is 100ppm in concentration. Thereafter, the substrate 201 is annealed in a nitrogen atmosphere at a temperature of 550 deg.C for four hours to turn the silicon film 203 crystalline. The silicon film 203 starts crystallizing at a region 204 where nickel comes into contact with a silicon film, and the crystal grows along the direction of an arrow in parallel with the substrate 201. After a crystallization process is finished, the silicon film 203 is improved in crystallinity by irradiation with laser rays 216.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an active matrix type liquid crystal display device.

[0002]

2. Description of the Related Art TFT (thin film transistor) is used for a pixel electrode.
There is known an active matrix type liquid crystal display device in which the pixel electrodes are arranged and the pixel electrodes are switched. Further, an integrated structure has also been proposed in which a peripheral circuit region for driving a TFT arranged in a pixel electrode is also formed on the same substrate.

In such an active matrix type liquid crystal display device in which the pixel region and the peripheral circuit region are integrated, it is necessary to make the characteristics of the TFT different in each region.

The TFT arranged in each pixel is required to have a function of retaining charges in the pixel electrode. Therefore, a large mobility is not required, but a small OFF current is required.

On the other hand, TFTs arranged in the peripheral circuit area
Since it is for driving the TFT arranged in the pixel region, it is necessary to allow a large ON current to flow and to have high mobility. ,

[0006]

SUMMARY OF THE INVENTION In an active matrix type liquid crystal display device, the present invention provides a pixel area TFT and a peripheral circuit area TFT formed on the same substrate.
The object is to obtain the required characteristics in the same step.

[0007]

According to the present invention, in an active matrix type liquid crystal display device, TFTs arranged in a pixel region and a peripheral circuit region are formed of crystalline silicon films in different crystal states. And In order to realize the above structure, the present invention is characterized in that a crystalline silicon film forming a peripheral circuit region is irradiated with laser light or strong light.

As a method of obtaining a crystalline silicon film, a method of crystallizing an amorphous silicon film by heating is known. In the present invention, an element which promotes crystallization of amorphous silicon is not used. 550 by introducing into the crystalline silicon film
The method is characterized by adopting a method of crystallizing by a heating step at 4 ° C. for about 4 hours.

As a catalyst element for promoting crystallization, N
i, Pd, Pt, Cu, Ag, Au, In, Sn, Pd
One or more kinds of elements selected from P, As and Sb can be used. Group VIII, IIIb, IVb,
It is also possible to use one or more kinds of elements selected from the Vb group elements.

Further, in the present invention, the crystalline silicon film forming the TFT arranged in the peripheral circuit region is arranged in the pixel region as a crystalline silicon film crystal-grown in a direction substantially parallel to the carrier flow direction in the TFT. It is effective to use a crystalline silicon film forming the TFT to be a crystalline silicon film which is crystal-grown in a direction substantially perpendicular to the carrier flow direction in the TFT. Here, the direction of carrier flow in the TFT is the direction of the line connecting the source and the drain.

When the moving direction of the carrier and the crystal growth direction are substantially the same, the carrier moves in the direction along the crystal grain boundary, so that the movement is less affected by the crystal grain boundary, A TFT having high mobility can be obtained. Such a TFT is optimal for a TFT arranged in a peripheral circuit region that needs to flow a large ON current.

On the other hand, when the carrier moving direction and the crystal growth direction are substantially perpendicular, the carriers move across the crystal grain boundaries, so that the ON current decreases and the OFF current decreases at the same time. be able to. Therefore, a TFT having a small OFF current can be obtained.

[0013]

【Example】

[Embodiment 1] This embodiment relates to a structure in which a TFT using a crystalline silicon film is arranged in a peripheral circuit region and a pixel region in an active matrix type liquid crystal display device. The TFTs formed in the peripheral circuit region and the pixel region have a structure in which crystals are grown in a direction parallel to the substrate. In addition, the crystalline silicon film formed in the peripheral circuit region is further promoted to be crystallized by irradiation with laser light or strong light, so that a larger ON current can be searched for and a larger mobility can be obtained. ing.

Further, in this embodiment, since the crystal growth direction and the carrier movement direction in the TFT are substantially the same, the movement of carriers is not affected by the crystal grain boundaries, and a TFT having high mobility is obtained. Can be realized.

2 and 3 show the manufacturing process of this embodiment. FIG. 2 is a manufacturing process diagram of a TFT for a peripheral circuit, and FIG. 3 is a manufacturing process diagram of a TFT formed in a pixel region. In each figure, the same reference numerals indicate the same parts. Further, each manufacturing process corresponds to each other. Further, FIG. 1 is a conceptual view of the active type liquid crystal display device manufactured in this embodiment as viewed from above. The peripheral area TFT and the pixel area TFT shown in this embodiment are formed on the same substrate in the state shown in FIG.
In FIG. 1, peripheral circuit areas A and B and A ′ and B ′ are shown.
The redundant circuit indicated by is shown. The redundant circuit indicated by A'and B'is used when the peripheral circuit area and A and B are defective.

First, the substrate 201 is cleaned, and a base film 202 of silicon oxide having a thickness of 2000 Å is formed by plasma CVD using TEOS (tetra-ethoxy-silane) and oxygen as source gases.

Then, an intrinsic (I type) having a thickness of 500 to 1500 Å, for example, 1000 Å is formed by the plasma CVD method.
The amorphous silicon film 203 is formed. Then continuously thickness 5
00-2000Å, for example 1000Å silicon oxide film 20
5 is formed by the plasma CVD method. Then, the silicon oxide film 205 is selectively etched to form an exposed region 204 of amorphous silicon. This region 204 will be a region into which nickel will be introduced later as a catalytic element.

Then, a solution (here, an acetate solution) containing nickel element which is a catalytic element for promoting crystallization is applied. Nickel concentration in acetic acid solution is 100ppm
Is. It is effective to improve the wettability of the acetic acid solution by forming an extremely thin oxide film (several tens of liters or less) before applying the acetic acid solution.

Further, nickel may be introduced by forming a nickel film or a film containing nickel by plasma treatment, vapor deposition method, sputtering method or CVD method.

After this, in a nitrogen atmosphere, 500-620
The silicon film 203 is crystallized by performing heat annealing at 4 ° C., for example, 550 ° C. for 4 hours. Crystallization proceeds from a region 204 where the nickel film and the silicon film are in contact with each other as a starting point, and crystal growth proceeds in a direction parallel to the substrate as shown by an arrow. In the figure, a region 204 shows a portion crystallized by direct introduction of nickel, and a region 203 shows a portion crystallized laterally. The crystal in the lateral direction indicated by 203 is 2
It is about 5 μm. The crystal growth direction is roughly <11.
It has been confirmed that the direction is 1> axial. (Fig. 2
(A), FIG. 3 (A))

After the crystallization step by the above heat treatment, the crystallinity of the silicon film 203 is further enhanced by irradiation with the laser beam 216. This step is performed only on the silicon film forming the TFT in the peripheral circuit region as shown in FIG.
The laser light is a KrF excimer laser (wavelength 248n
m, pulse width 20 nsec), and 250 mJ / cm
It performed 2 Shoto in ^second energy density. Other laser light may be used as the laser light. This laser irradiation was performed by heating the substrate to 400 ° C.
This is to further enhance the annealing effect due to laser light irradiation.

This step may be performed by irradiation with strong light. For example, it can be performed by irradiating infrared light having a wavelength of 1.2 μm. Irradiation with infrared light can achieve the same effect as that obtained by heat treatment at high temperature for several minutes.

Next, the silicon oxide film 205 is removed. At this time, the oxide film formed on the surface of the region 204 is also removed at the same time. Then, after patterning the silicon film 203, dry etching is performed to form an island-shaped active layer region 208.
At this time, the region indicated by 204 is a region in which nickel is directly introduced, and is a region in which nickel is present at a high concentration. It has also been confirmed that nickel also exists at a high concentration at the crystal growth tip 217. It has been found that the nickel concentration in these regions is higher than that in the intermediate region. Therefore, in this embodiment, in the active layer 208, these regions having a high nickel concentration are prevented from overlapping the channel formation region.

Then, 10 containing 100% by volume of water vapor.
The surface of the active layer (silicon film) 208 is oxidized by leaving it in the atmosphere of 500 to 600 ° C., typically 550 ° C. for 1 hour to oxidize the surface of the silicon oxide film 209.
To form. The thickness of the silicon oxide film is 1000Å. After forming the silicon oxide film 209 by thermal oxidation, the substrate is placed in an ammonia atmosphere (1 atm, 100%) at 400 ° C.
To hold. Then, in this state, the substrate is irradiated with infrared light having a peak at a wavelength of 0.6 to 4 μm, for example, 0.8 to 1.4 μm for 30 to 180 seconds, and the silicon oxide film 20 is irradiated.
A nitriding process is performed on 9. At this time, the atmosphere was 0.
1-10% HCl may be mixed.

Subsequently, by the sputtering method,
A film of aluminum (containing 0.01 to 0.2% scandium) having a thickness of 3000 to 8000Å, for example, 6000Å is formed. Then, the aluminum film is patterned to form the gate electrode 210. (Fig. 2 (C), Fig. 3
(C))

Further, the surface of the aluminum electrode is anodized to form an oxide layer 211 on the surface. This anodic oxidation is performed in an ethylene glycol solution containing 1-5% tartaric acid. The resulting oxide layer 211 has a thickness of 2
It is 000Å. Since the oxide 211 has a thickness to form the offset gate region in the subsequent ion doping process, the length of the offset gate region can be determined by the anodic oxidation process. (Fig. 2
(D), FIG. 3 (D))

Next, the gate electrode portion, that is, the gate electrode 210 and the oxide layer 211 around the gate electrode portion 210 is used as a mask in the active layer region (which constitutes the source / drain and the channel) by the ion doping method (also called plasma doping method). An impurity (here, phosphorus) that imparts the N conductivity type is added in a self-aligning manner. Phosphine (PH ₃ ) is used as the doping gas, and the acceleration voltage is set to 60 to 90 kV, for example, 80 kV. Dose amount is 1 × 10 ¹⁵ to 8 × 10
^{It is set to 15} cm ^-2 , for example, 4 × 10 ¹⁵ cm ^-2 . As a result, N-type impurity regions 212 and 213 can be formed. As is clear from the figure, the impurity region and the gate electrode are in an offset state separated by a distance x. Such an offset state is particularly effective in reducing a leak current (also referred to as an off current) when a reverse voltage (negative in the case of an N-channel TFT) is applied to the gate electrode.
In particular, in the TFT for controlling the pixels of the active matrix as in the present embodiment, it is desired that the leak current is low so that the charges accumulated in the pixel electrode do not escape in order to obtain a good image, and therefore an offset is provided. That is valid.

After that, annealing is performed by irradiation with laser light. As the laser light, a KrF excimer laser (wavelength 248 nm, pulse width 20 nsec) is used, but other laser may be used. The laser light irradiation conditions are energy density of 200 to 400 mJ / cm ² ,
For example, 250 mJ / cm ² and ² to 10 per place
Shot, for example, 2 shots were irradiated. The effect may be increased by heating the substrate to about 200 to 450 ° C. during the irradiation of the laser light. (Fig. 2 (E),
(Fig. 3 (E))

Then, a silicon oxide film 21 having a thickness of 6000Å is formed.
4 as an interlayer insulator is formed by the plasma CVD method. Further, a transparent polyimide film 215 is formed by spin coating to flatten the surface.

Then, as shown in FIG. 3F, an ITO electrode 300 connected to one end of the output of the TFT formed in the pixel region is formed. This ITO electrode 300 functions as a pixel electrode.

Next, contact holes are formed in the interlayer insulators 214 and 215, and a TFT electrode / wiring 21 is formed by a metal material, for example, a multilayer film of titanium nitride and aluminum.
7 and 218 are formed. At this time, as shown in FIG. 3F, one electrode 218 of the TFT formed in the pixel region is connected to the ITO electrode 300 which is the pixel electrode.

Finally, in a hydrogen atmosphere at 1 atm, 350 ° C.,
Annealing is performed for 30 minutes to simultaneously form an active matrix pixel circuit and a peripheral drive circuit for driving the pixel circuit. (Figure 2 (F), Figure 3 (F))

[Embodiment 2] This embodiment is an example in which the TFT arranged in the pixel region shown in FIG. 3 is configured such that the carrier flow direction and the crystal growth direction are substantially perpendicular to each other. . With such a structure, in the TFT arranged in the pixel region, the carriers move so as to cross the crystal grain boundaries when the carriers move.
The OFF current value can be reduced. Further, the TFT arranged in the peripheral circuit region has a structure similar to that shown in FIG. 2 so that the carriers can move along the crystal grain boundaries and have high mobility. It can be a TFT.

In order to implement this embodiment, in the step shown in FIG. 3, the region 204 into which nickel, which is a catalytic element, is introduced may be set to the front side or the opposite side of the TFT. By doing so, the crystal growth generated in that region is in a direction perpendicular to the line connecting the source / drain regions 212/213, so that carrier movement can cross the crystal grain boundaries. The other steps are the same as those in the first embodiment.

[0035]

According to the present invention, the TFTs formed in the pixel region and the peripheral circuit region of the active matrix type liquid crystal display device are each formed of a crystalline silicon film crystal-grown in a direction parallel to the substrate, and the periphery of the TFT is formed. T formed in the circuit area
By irradiating the crystalline silicon film forming the FT with laser light or intense light, T suitable for the peripheral circuit region is obtained.
An FT can be constructed.

[Brief description of drawings]

FIG. 1 shows an outline of an active matrix type liquid crystal display device.

FIG. 2 shows a manufacturing process of a TFT.

FIG. 3 shows a manufacturing process of a TFT.

[Explanation of symbols]

 201 ... Glass substrate 202 ... Base film (silicon oxide film) 203 ... Amorphous silicon film 205 ... Silicon oxide film 208 ... Active layer 209 ... Oxidation Silicon film (gate insulating film) 210 ... Gate electrode 211 ... Anodic oxide layer 212 ... Source / drain region 213 ... Drain / source region

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location H01L 21/20 8418-4M 21/268 Z 27/12 R

Claims (5)

[Claims] 1. A TFT using a crystalline silicon film in which crystal growth is performed in a direction parallel to a substrate is arranged in a pixel region and a peripheral circuit region of an active matrix type liquid crystal display device. A semiconductor device characterized in that a crystalline silicon film forming a TFT arranged in a region has its crystallinity enhanced by irradiation with laser light or strong light. 2. A substrate constituting an active matrix type liquid crystal display device, wherein a TFT arranged in a pixel region and a TFT arranged in a peripheral circuit region are formed on a surface of the substrate, The TFT arranged in the region and the TFT arranged in the peripheral circuit region are configured by using a crystalline silicon film crystal-grown in a direction parallel to the substrate, and the crystalline silicon film in the peripheral circuit region is a laser. A semiconductor device whose crystallinity is enhanced by irradiation with light or strong light. 3. A step of forming an amorphous silicon film on a substrate having an insulating surface, and a catalyst element for promoting crystallization of the amorphous silicon film directly or indirectly on the amorphous silicon film. And a step of heat-treating the amorphous silicon film so as to grow crystals in a direction parallel to the substrate from a region provided in direct or indirect contact with the catalytic element to a peripheral portion of the region. A step of performing, a step of irradiating a part of the region where crystal growth is performed with laser light or strong light, and an active matrix using the crystalline silicon film in the region irradiated with laser light in the step Of manufacturing a TFT arranged in a peripheral circuit portion of a mold type liquid crystal display device, and a manufacturing method of a semiconductor device. 4. A crystalline structure comprising a plurality of TFTs arranged on a substrate having an insulating surface, wherein the TFT is selectively added with a catalytic element for promoting crystallization, and is crystallized in a direction parallel to the substrate. A part of the TFT is arranged in a pixel region of an active matrix type liquid crystal display device, and another part of the TFT is arranged in a peripheral circuit region of the active matrix type liquid crystal display device. The semiconductor device characterized in that the crystalline silicon film forming the TFT arranged in the peripheral circuit region has its crystallinity enhanced by irradiation with laser light or strong light. 5. A TFT using a crystalline silicon film in which crystal growth is performed in a direction parallel to a substrate is arranged in a pixel region and a peripheral circuit region of an active matrix type liquid crystal display device. The crystalline silicon film constituting the TFT arranged in the region has its crystallinity enhanced by irradiation with laser light or strong light, and its crystal growth direction is substantially the same as the carrier movement direction. In the semiconductor device, the crystalline silicon film forming the TFT disposed in the pixel region has a crystal growth direction substantially perpendicular to a carrier moving direction.