JPH07183536A - 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 in 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. A nickel-containing acetate solution 205 which promotes crystallization is applied onto the amorphous silicon film 203. Nickel contained in an acetate solution is 10ppm 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. A this point, the silicon film 203 starts crystallizing as nickel in contact with the silicon film starts diffusing. The crystallization of the silicon film tapes placed nearly along a direction vertical to the substrate 201. After a crystallization process, the silicon film 203 is improved in crystallinity by irradiation with laser rays 216. Only TFTs located in a peripheral circuit region are subjected to the irradiation process.

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.

[0010]

[Embodiment 1] This embodiment relates to a configuration 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 TFT formed in the peripheral circuit region and the pixel region has a structure using a crystalline silicon film in which crystal growth is performed in a direction perpendicular to the substrate by adding a catalytic element that promotes crystallization. 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. Has become.

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. FIG. 1 is a schematic view of an active type liquid crystal display device manufactured in this example, as viewed from above. The peripheral area TFT and the pixel area TFT shown in this embodiment are
They are formed on the same substrate in the state shown in FIG. Figure 1
In the peripheral circuit areas A and B and their redundant circuits A ′,
B'is shown. The redundant circuits A ′ and B ′ are used when there are defects in the peripheral circuit areas A and B.

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

Then, by plasma CVD method, an intrinsic (I type) having a thickness of 500 to 1500Å, for example, 1000Å
The amorphous silicon film 203 is formed. Then, a solution (here, an acetate solution) 205 containing nickel element which is a catalytic element for promoting crystallization is applied. The concentration of nickel in the acetic acid solution is 10 ppm. 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.

Here, nickel, which is a catalytic element that promotes crystallization of the amorphous silicon film, was introduced into the amorphous silicon film by applying a solution containing the catalytic element. However, plasma treatment, vapor deposition method, sputtering method or CVD method was used. Nickel may be introduced by forming a nickel film or a film containing nickel by.

Then, in a nitrogen atmosphere, 500 to 620
The silicon film 203 is crystallized by performing heat annealing at 4 ° C., for example, 550 ° C. for 4 hours. At this time, the nickel that is in contact with the nickel film and the silicon film diffuses, and crystallization occurs. Then, crystallization is performed in a direction substantially perpendicular to the substrate. (Fig. 2 (A), Fig. 3 (A))

After the crystallization step by the 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 irradiation with laser light is 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.

When crystallization was completed, the nickel concentration in the silicon film was about 10 ¹⁸ / cm ³ . And
After patterning the silicon film 203, dry etching is performed to form an island-shaped active layer region 208.

Thereafter, 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 it is used as a mask in the active layer region (which constitutes a source / drain and a channel) by an ion doping method (also called a 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 of 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))

[0028]

According to the present invention, the TFT formed in the pixel region and the peripheral circuit region of the active matrix type liquid crystal display device is crystallized by the introduction of the catalytic element for promoting the crystallization, and is further formed in the peripheral circuit region. By irradiating the crystalline silicon film forming the TFT with the laser light or the intense light, the TFT suitable for the peripheral circuit region can be selectively formed.

[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 ... Acetate solution 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 (4)

[Claims] 1. A crystalline silicon film formed on a substrate having an insulating surface, wherein the crystalline silicon film contains a catalytic element for promoting crystallization, and the crystalline silicon film is formed on the substrate. Crystals are grown in a substantially vertical direction, and the crystalline silicon film is used to form TFTs arranged in a pixel region of an active matrix type liquid crystal display device and TFTs arranged in a peripheral circuit region. 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. 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 formed by using a crystalline silicon film obtained by crystallizing the region to which the catalytic element is added, and the crystalline silicon in the peripheral circuit region is formed. A semiconductor device characterized in that the crystallinity of the film is enhanced by irradiation with laser light or intense 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. A step of contacting, a step of heat-treating the amorphous silicon film to crystallize a region provided with the catalytic element directly or indirectly, and a step of crystallizing a region where crystal growth is performed in the step. A step of irradiating a part with laser light or strong light, and a TFT arranged in a peripheral circuit portion of an active matrix liquid crystal display device using a crystalline silicon film in a region irradiated with laser light in the step And a method for manufacturing a semiconductor device. 4. A crystalline silicon film comprising a plurality of TFTs arranged on a substrate having an insulating surface, wherein the TFT is added with a catalytic element for promoting crystallization and crystal-grown in a direction substantially perpendicular 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, A semiconductor device characterized in that a crystalline silicon film forming a TFT arranged in a peripheral circuit region has its crystallinity enhanced by irradiation with laser light or strong light.