JP3512766B2 - Thin film transistor and liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The invention disclosed in this specification includes:
The present invention relates to a structure of a thin film semiconductor device such as a thin film transistor and a manufacturing method thereof.

[0002]

2. Description of the Related Art It is known to use a thin film transistor in a liquid crystal display to obtain a display device having a high display function and replacing a cathode ray tube. This is called an active matrix type liquid crystal display device. In this active matrix type liquid crystal display device, a thin film transistor is arranged on each of the pixel electrodes arranged in a matrix to perform high-performance display. In order to enhance the display function, it is necessary that the characteristics of the thin film transistor are as high as possible.

The thin film transistor used in such an active matrix type liquid crystal display device has a problem that it must be formed on a glass substrate. That is, since the glass substrate is used as the substrate, there is a problem that the manufacturing process thereof is limited. Not only a thin film transistor, but also a semiconductor device is required to diffuse impurities into silicon, activate impurities in silicon, and improve the crystallinity of silicon. For example, it is necessary to heat to 800 to 1000 ° C. or higher). However, the temperature that can be applied to the glass substrate is generally about 600 ° C., and various new techniques are required to manufacture a high-performance semiconductor device at a temperature below this temperature. For example, there is a technique of irradiating an amorphous silicon film with a laser beam so as to have crystallinity, or a technique of using a laser beam for diffusion and activation of impurities. Irradiation with laser light is a very useful technique as long as it allows low productivity, because thermal damage to the glass substrate is extremely small.

FIG. 2 is a schematic sectional view of a conventionally known thin film transistor (generally called a TFT). FIG. 2 shows a thin film transistor formed on the glass substrate 201. 202 is a base silicon oxide film,
It functions to prevent impurities from entering the active layer from the glass substrate. The active layer includes a source region 203, a channel forming region 204, and a drain region 205. A silicon oxide film or a silicon nitride film is formed as the gate insulating film 200 so as to cover the active layer. Gate electrode 206
Is made of metal or semiconductor. Also, the entire element is
Interlayer insulating film 2 made of a suitable insulator such as a silicon oxide film
It is covered with 07. Further, a source electrode 208 is drawn out from the source region 203, and a drain electrode 209 is drawn out from the drain region 205.

Source region 203, drain region 205,
The active layer formed of the channel formation region 204 is made of crystalline silicon. As the crystalline silicon film, for example, an amorphous silicon film crystallized by laser light irradiation as described above is used. However, there is currently no technique for forming single crystal silicon on a glass substrate, and although the formed film is said to have crystallinity, it has a film quality with many defects and levels. It is the current situation. In order to reduce defects and levels in the silicon film, hydrogen atoms are used,
A method of neutralizing dangling bonds (unpaired bonds) of silicon which causes defects and levels is adopted. This is the same even when the active layer is made of amorphous silicon instead of crystalline silicon.

As described above, it is necessary to contain hydrogen in the silicon semiconductor film formed on the glass substrate. However, when hydrogen is to be contained in the active layer made of a silicon semiconductor, there is a problem that hydrogen diffuses from the active layer into the gate insulating film. On the other hand, in the structure shown in FIG. 2, the presence of mobile ions in the gate insulating film is extremely undesirable. That is, when mobile ions are present in the gate insulating film, fluctuations in threshold value and C
There is a problem that hysteresis occurs in the --V characteristic. Therefore, including hydrogen in the active layer is a useful method on the one hand, but on the other hand, there is a disadvantage in that hydrogen diffuses into the gate insulating film.

[0007]

DISCLOSURE OF THE INVENTION The invention disclosed in the present specification is such that, in the structure of a semiconductor device, hydrogen is contained in an active layer composed of a silicon semiconductor, and the hydrogen is contained in other regions and other parts. An object is to provide a configuration that does not have an adverse effect.

[0008]

A main structure disclosed in the present specification has an active layer formed of a silicon film and a gate insulating film formed on the active layer, and the gate insulating film is formed. The film is a silicon oxide film, and a thin film represented by SiO _x N _y is formed between the active layer and the gate insulating film.

In the above structure, the silicon film may be an amorphous silicon film or a crystalline silicon film. Examples of the crystalline silicon film include a polycrystalline silicon film, a microcrystalline silicon film, an amorphous silicon film partially containing a crystal structure, and a silicon film in which a crystal structure and an amorphous structure are mixed.

The active layer is a semiconductor layer forming a thin film transistor, and is generally composed of a source / drain region having one conductivity type and a channel forming region. The active layer also includes an offset gate region and a lightly doped region, if necessary. When a crystalline silicon film is used as the active layer, the concentration of hydrogen contained in the active layer is preferably 0.001 to 5 atom%.

In the above structure, the base film of the active layer
Then, a silicon nitride film or a silicon oxide film may be adopted.
Further, as a base film, SiO_xN_yUsing a thin film
It is even more effective. This is the base film of the active layer
Formed as SiO_xN _yThin film and active layer
Formed on the upper and side surfaces of the_xN_yThin indicated by
The membrane substantially covers the active layer (actually
Source / drain contact regions are present and fully active
Included in the active layer (by not covering the layer)
A structure that substantially confines the stored hydrogen.
You can

Further, when a crystalline silicon film containing a metal element that promotes crystallization of silicon is used as the silicon film forming the active layer, it is useful to adopt the above structure.
That is, in order to make a crystalline silicon film formed of a metal element that promotes crystallization into a semiconductor having higher electric characteristics, by adopting the above structure when hydrogenated, the effect of hydrogenation can be further improved. Can be increased. Of course, this effect is extremely useful when hydrogen ions are positively included in the active layer by ion implantation of hydrogen or the like.

As the metal element that promotes the crystallization,
The effect is remarkable when Ni (nickel) is used. If the amount of the metal element that promotes crystallization is too large, the semiconductor characteristics of the silicon semiconductor are deteriorated (becomes close to the characteristics of the metal), and if it is too small, the effect of promoting crystallization becomes small. Therefore, the optimum concentration is preferably 1 × 10 ¹⁵ to 1 × 10 ¹⁹ cm ⁻³ .

As the metal element that promotes the crystallization,
Other than Ni, Fe, Co, Ru, Rh, Pd, Os, I
r, Pt, Cu, Ag and Au can be used. What is important as an element that promotes crystallization of this amorphous silicon is that they are interstitial atoms.

The metal elements listed above diffuse into the silicon film in the heat treatment step. Then, at the same time as the above-mentioned intrusion type element diffuses, crystallization of silicon proceeds. That is, the penetration type metal promotes the crystallization of the amorphous silicon film by the catalytic action even before it diffuses.

Further, since the above-mentioned invasion type element is rapidly diffused into the silicon film, its introduction amount (addition amount).
Is important. That is, when the introduction amount is small, the effect of promoting crystallization is small, and good crystallinity cannot be obtained. If the amount of introduction is too large, the semiconductor characteristics of silicon will be impaired.

Therefore, the optimum range of the amount of the metal element introduced into the amorphous silicon film is important. For example, when Ni is used as the metal element that promotes crystallization, the Ni element is introduced into the amorphous silicon film so that the concentration in the crystallized silicon film is 1 × 10 ¹⁵ cm ⁻³ or more. The effect of promoting crystallization can be obtained by controlling
The Ni concentration in the crystallized silicon film is 1 × 1.
It has been proved that if the amount of Ni element introduced is controlled so as to be 0 ¹⁹ cm ⁻³ or less, semiconductor characteristics are not impaired. The concentration here is defined by the minimum value obtained by SIMS (secondary ion analysis method). In addition, regarding metallic elements other than Ni listed above,
The effect can be obtained in the same concentration range as.

In addition to the metal elements listed above, Al and Sn
Also in the case of using, the crystallization of the amorphous silicon film can be promoted. However, Al and Sn form an alloy with silicon and do not diffuse and penetrate into the silicon film. In this case, in crystallization, the portion where an alloy with silicon is formed becomes a crystal nucleus, and the crystal growth proceeds from that portion. When Al or Sn is used as described above, crystal growth is performed only from a portion into which Al or Sn is introduced (that is, an alloy layer of these elements and silicon). There is a problem that its crystallinity is generally poor as compared with the case of using. For example, there is a problem that it is difficult to obtain a crystalline silicon film that is uniformly crystallized. Further, there is a problem that the existence of the alloy layer hinders the production of the device, and further that the existence of the alloy layer lowers the reliability of the device.

The thin film represented by SiO _x N _y is x and y.
Are 0 <x <2 and 0 <y <4/3, and their relative permittivity is 4
6 and its band gap is 5.3 to 7.0 eV. The thin film represented by SiO _x N _y is dichlorosilane
(SiH ₂ Cl ₂ ) or ammonia (NH ₄ ) and nitric oxide (N ₂ O)
A film can be formed by using and.

The main structure of another invention is a step of forming an active layer made of a silicon semiconductor on a substrate having an insulating surface,
The method is characterized by including a step of forming a thin film of SiO _x N _y to cover the active layer and a step of forming a gate insulating film made of a thin film of SiO _x N _y .

In the above structure, examples of the substrate having an insulating surface include a glass substrate, a semiconductor substrate having an insulating film formed thereon, and a conductor substrate having an insulating film formed thereon.

In the above structure, the step of forming a silicon semiconductor is a method of forming an amorphous silicon film by a plasma CVD method or a low pressure thermal CVD method, or an amorphous silicon formed by a plasma CVD method or a low pressure thermal CVD method. The film is crystallized by irradiating it with a laser beam or by applying heat treatment, or an amorphous silicon film formed by a plasma CVD method or a low pressure thermal CVD method is crystallized with Ni or the like. A method of crystallization by the action of a promoting element can be mentioned.

According to another aspect of the invention, a step of forming an active layer made of a silicon semiconductor on a substrate having an insulating surface, a step of containing hydrogen in the active layer, and a step of covering the active layer with S.
forming a thin film of iO _x N _y ;
And a step of forming a gate insulating film made of a silicon oxide film on the thin film represented by O _x N _y .

In the above structure, examples of the method of containing hydrogen in the active layer include hydrogen ion implantation, heat treatment in a hydrogen atmosphere, and exposure to hydrogen plasma.

Also in this structure, it is useful to use, as the silicon film, a silicon film having crystallinity by using a catalytic element that promotes crystallization.

[0026]

In a structure in which a silicon semiconductor containing hydrogen or containing hydrogen is used as an active layer and a gate insulating film is provided on the active layer, SiO _x N _y is formed between the active layer and the gate insulating film. By forming the thin film shown, hydrogen in the active layer can be prevented from diffusing into the gate insulating film. Then, a thin film transistor having excellent electrical characteristics and stability can be obtained. Further, by forming a thin film represented by SiO _x N _y using chlorsilane or dichlorsilane, chlorine in the film is 1 × 10 ¹⁵ to
It can be contained at a concentration of 1 × 10 ²⁰ cm ⁻³ , and this chlorine acts to immobilize mobile ions, and the function and stability as a gate insulating film can be enhanced.

Further, SiO _x N _y is also used as a base film for the active layer.
By using the thin film represented by, it is possible to realize a configuration in which the active layer is substantially covered with the thin film represented by SiO _x N _y . Then, the hydrogen contained in the active layer can be confined in the active layer, and the effect can be enhanced. At the same time, it is possible to prevent hydrogen in the active layer from diffusing out of the active layer.

The thin film represented by SiO _x N _y has not only a barrier effect against hydrogen ions, but also O (oxygen) in the film acts so as to eliminate hysteresis in the CV characteristic, and SiN bond is formed. Na and heavy metals (F
e, Ni, Co) ions to prevent drift.

In particular, when the active layer is crystallized using a metal element such as Ni, since this metal element is contained in the active layer, at least the upper surface of the active layer (the surface in contact with the gate insulating film). Is very useful to cover with a thin film of SiO _x N _y . That is, N that functions as mobile ions
It is possible to prevent a metal element such as i from diffusing into the gate insulating film.

[0030]

[Embodiment] [Embodiment 1] FIG. 1 shows an outline of a manufacturing process of this embodiment. The thin film transistor described in this embodiment can be used for a switching element arranged in a pixel of an active liquid crystal display device, a driver circuit forming a peripheral circuit of the liquid crystal display device, and other thin film integrated circuits.

In this embodiment, a glass substrate is used as the substrate 101. First, a silicon nitride film 101 is formed as a base film on a glass substrate to a thickness of 1000 Å by a plasma CVD method. Here, the silicon nitride film 101 is formed by a plasma CVD method using SiH ₄ and NH ₄ . In addition to the plasma CVD method, a low pressure thermal CVD method can be used.

Next, an amorphous silicon film is formed to a thickness of 1000 Å by the plasma CVD method or the low pressure thermal CVD method. Then, the amorphous silicon film is crystallized by heating, irradiation with laser light, or a combination thereof to obtain a crystalline silicon film.
Here, a method is adopted in which nickel, which is a metal element that promotes crystallization, is included in a solution, and this solution is applied to the surface of the amorphous silicon film to introduce the nickel element into the amorphous silicon film. To do.

Specifically, a nickel acetate salt solution is dropped onto the surface of the amorphous silicon film, and the nickel is held in contact with the amorphous silicon film by spin coating. Introduced. The introduction of these metal elements may be performed by a sputtering method or a plasma CVD method. In such a state that nickel, which is a metal element that promotes crystallization, is in contact with the amorphous silicon film, heat treatment is performed to crystallize the amorphous silicon film. This heat treatment may be performed at a temperature of 450 ° C. to 550 ° C. for 4 hours to 8 hours. Here, in a nitrogen atmosphere, 55
Heat treatment is performed at 0 ° C. for 4 hours.

After obtaining the crystalline silicon film, patterning is performed.
The active layer of the thin film transistor is formed. Thus thin
The active layer 103 of the film transistor is formed. This activity
The oxygen concentration in the layer is 2 × 10¹⁹~ 5 x 10¹⁹cm
^-3Is desirable. Next, by the plasma CVD method
, 10-100Å thick SiN_xO_yThin indicated by
The film 104 is formed. Here, dichlorosilane (SiH
₂Cl₂) Is used as a source gas for the plasma CVD method using SiN_xO
_yThe thin film shown by is formed. This thin film 104 is hydrogen
Since it functions as a barrier layer against ions,
And are needed. Here, dichlor is used as the source gas
Silane was used, but SiH_FourAnd NH_FourAnd N ₂0 and raw material
You may use it as gas. (Fig. 1 (A))

Next, a silicon oxide film 105 is formed to a thickness of 1000 Å by plasma CVD method or sputtering method. This silicon oxide film functions as a normal gate insulating film. Then, the gate electrode 106 is formed of a metal or a semiconductor having one conductivity type. Here, the gate electrode 106 is formed using an N-type crystalline silicon semiconductor heavily doped with phosphorus.

Next, phosphorus ions are implanted using the gate electrode 106 as a mask. Thus, phosphorus ions are implanted into the regions 107 and 109, and the source region 107 and the drain region 109 are formed in a self-aligned manner. At the same time, the channel formation region 108 is formed. After that, laser light irradiation is performed to activate the source 107 and the drain region 109 and to anneal damage during ion implantation. (Fig. 1 (B))

Next, a silicon oxide film 110 is formed as an interlayer insulating film, and a source electrode 111 and a drain electrode 112 are formed through a hole forming process to complete the thin film transistor shown in FIG.

The thin film transistor shown in FIG. 1 has a source region 107, a drain region 109 and a channel forming region 10.
Since the active layer composed of 8 is covered with the SiN _x O _y film, hydrogen in the active layer does not diffuse to the outside.
In particular, since the SiN _x O _y film 104 exists between the silicon oxide film 105 forming the gate insulating film and the active layer, hydrogen does not diffuse into the gate insulating film and the characteristics can be improved. It is possible to provide a configuration that does not deteriorate.

[Embodiment 2] FIG. 3 shows an outline of the manufacturing process of this embodiment. In the thin film transistor described in this example, hydrogen is injected into the crystalline silicon semiconductor layer forming the active layer by an ion implantation method or a plasma doping method to positively contain hydrogen in the active layer, and It is characterized by neutralizing anti-bonding hands. Further, it is characterized in that the surface of the active layer is covered with a thin film of SiN _x O _y in order to confine hydrogen injected into the active layer.

The thin film transistor described in this embodiment can be used for a switching element arranged in a pixel of an active liquid crystal display device, a driver circuit forming a peripheral circuit of the liquid crystal display device, and other thin film integrated circuits.

FIG. 3 shows an outline of the manufacturing process of this embodiment.
In this embodiment, a glass substrate is used as the substrate 101. First, a thin film 100 represented by SiO _x N _y is formed on a glass substrate as a base film by plasma CV to a thickness of 1000 Å
It is formed by the D method. Here, a film is formed by a plasma CVD method using dichlorosilane.

Next, an amorphous silicon film is formed to a thickness of 1000 Å by the plasma CVD method or the low pressure thermal CVD method. Then, the amorphous silicon film is crystallized by heating, irradiation with laser light, or a combination thereof to obtain a crystalline silicon film.
Here, nickel, which is a catalytic element that promotes crystallization, is introduced by a nickel acetate salt solution. Specifically, nickel is introduced into the amorphous silicon film by applying a nickel acetate salt solution to the surface of the amorphous silicon film by spin coating. Then, the amorphous silicon film is crystallized by performing heat treatment at 550 ° C. for 4 hours. After obtaining the crystalline silicon film, patterning is performed to form an active layer of the thin film transistor. Thus, the active layer 103 of the thin film transistor is formed. (Fig. 3 (A))

Active layer 1 made of crystalline silicon
In the state where 03 is exposed, hydrogen ion is implanted. Here, ion implantation is performed with an acceleration voltage of 40 KeV and a dose amount of 2 × 10 ¹⁶ cm ⁻³ .

Thus, hydrogen is contained in the active layer to neutralize dangling bonds in the active layer and reduce the level in the active layer. Note that it is effective to perform heat treatment at a temperature of 300 to 500 ° C. in order to activate the injected hydrogen and enhance its effect.

Next, by plasma CVD, 10 to 100
A thin film of SiN _x O _y having a thickness of Å is formed. Here, a film is formed by a plasma CVD method using dichlorosilane as a source gas. (Fig. 3 (B))

Then, a silicon oxide film 105 is formed to a thickness of 1000 Å by plasma CVD method or sputtering method. This silicon oxide film functions as a normal gate insulating film. And the material which has aluminum as the main component is 5
A film having a thickness of 000Å is formed, and the gate electrode 113 is formed using the film containing aluminum as a main component. Further, an oxide layer 114 is formed around the gate electrode 113 containing aluminum as a main component in the anodic oxidation process. This step is performed by performing anodic oxidation in the electrolytic solution using the gate electrode 113 as an anode. here,
The oxide layer 114 is formed to a thickness of about 2000Å. The oxide layer 114 serves as a mask in a later impurity ion implantation process, and the offset gate region can be formed by the thickness thereof.

Next, phosphorus ions are implanted using the gate electrode 113 and the oxide layer around it as a mask. And
Phosphorus ions are implanted into the regions 107 and 109 to form the source region 107 and the drain region 109 in a self-aligned manner. At the same time, the channel formation region 108 is formed. Further, in the impurity ion implantation step, the offset gate region 115 is also formed at the same time. After that, the source 107 is irradiated with laser light.
Then, activation of the drain region 109 and annealing for damage during ion implantation are performed. (Fig. 3 (C))

Next, a silicon oxide film 110 is formed as an interlayer insulating film, a source electrode 111 and a drain electrode 112 are formed through a hole forming process, and the thin film transistor shown in FIG. 3D is completed.

In the thin film transistor shown in FIG. 3D, the active layer composed of the source region 107, the drain region 109, and the channel forming region 108 is covered with a thin film of SiO _x N _y on its lower surface, upper surface, and side surface. As a result, the hydrogen is trapped in the active layer and does not diffuse to the outside.

[Embodiment 3] In this embodiment, in the manufacturing process of Embodiment 2 shown in FIG. 3, instead of performing the hydrogen ion implantation performed in the step (A), a heat treatment is performed in a hydrogen atmosphere. By doing so, hydrogen is contained in the active layer 103.

The heat treatment for containing hydrogen in the active layer 103 is performed by applying a temperature of 300 to 500 ° C. in 100% hydrogen or a mixed atmosphere of hydrogen and an inert atmosphere.

[Embodiment 4] In this embodiment, in the manufacturing process of Embodiment 2 shown in FIG. 3, instead of performing the hydrogen ion implantation in the step (A), the active layer 1 is applied to the hydrogen plasma.
It is characterized in that the active layer 103 is made to contain hydrogen by exposing 03.

This hydrogen plasma treatment is carried out by placing a sample in the state shown in FIG. 3A in a reduced pressure atmosphere of hydrogen and applying high frequency energy to the atmosphere. In this hydrogen plasma treatment, it is effective to heat the sample to about 300 to 500 ° C.

[Embodiment 5] In this embodiment, by forming a thin film of SiO _x N _y on the gate insulating film,
The present invention relates to a structure in which a gate insulating film is sandwiched between thin films represented by SiO _x N _y . FIG. 4 shows the manufacturing process of this embodiment. First SiO _x N _y as a base film on the surface of the glass substrate 401
A thin film 402 shown by is formed. Here, a plasma CVD method using dichlorosilane (SiH ₂ Cl ₂ ) as a source gas is used to form the thin film 402 represented by SiO _x N _y as 100
Form a film with a thickness of 0Å.

Next, an amorphous silicon film is formed to a thickness of 1000Å by the plasma CVD method or the low pressure thermal CVD method. Then, a nickel acetate solution is applied onto the amorphous silicon film by spin coating to introduce nickel element into the amorphous silicon film. Then, the amorphous silicon film is crystallized by performing heat treatment at 550 ° C. for 4 hours. Further, by patterning this amorphous silicon film, an active layer 403 composed of a crystalline silicon film is formed. Of course, the active layer may be formed by using amorphous silicon, a crystalline silicon film crystallized by ordinary heating, or a crystalline silicon film crystallized by laser light irradiation.

After forming the active layer 403, the active layer 403
Is carried out. This step is performed by implanting hydrogen ions into the active layer 403. This step is performed by an ion implantation method or a plasma doping method. The implantation conditions are, for example, an acceleration voltage of hydrogen ions of 40 KeV and a dose amount of 2 × 10 ¹⁶ cm ⁻³ . Thus, hydrogen ions are implanted into the active layer 403, and the dangling bonds of silicon are neutralized by this hydrogen. Thus
It is possible to reduce defects and levels in the active layer 403.

The hydrogenation step of the active layer 403 may be heat treatment in a hydrogen atmosphere. In this case, heat treatment may be performed at a temperature of 300 to 500 ° C. in a hydrogen atmosphere at normal pressure or under pressure, or an atmosphere containing hydrogen.

After the hydrogenation process of the active layer 403 is completed, a thin film 404 represented by SiO _x N _y is formed to cover the active layer 403. The thin film indicated by 404 is also formed by the plasma CVD method using dichlorosilane (SiH ₂ Cl ₂ ) as a source gas.

Thus, the state shown in FIG. 4A is obtained. In this state, the active layer 403 may be covered with a thin film of SiO _x N _y on its upper surface, lower surface and side surfaces, that is, the active layer may be wrapped with a thin film of SiO _x N _y. it can. In this state, the active layer 403 is hydrogenated and contains a large amount of hydrogen. And Si
The thin film represented by O _x N _y plays a role of a barrier for confining hydrogen in the active layer.

After obtaining the state shown in FIG. 4 (A), a film containing silicon of one conductivity type as a main component is formed to a thickness of 5000Å by the low pressure thermal CVD method. Here, an N-type crystalline silicon film is formed. Then, patterning is performed to form the gate electrode 406. Then, using the gate electrode 406 as a mask, impurity ions are implanted by an ion doping method or a plasma doping method. As the impurity ions, phosphorus is used to form an N-channel type thin film transistor, and boron is used to form a P-channel type thin film transistor. here,
In order to form an N-channel type thin film transistor, phosphorus is ion-implanted by an ion implantation method.

In the ion implantation step, the source region 408 and the drain region 410 are formed in a self-aligned manner. At the same time, the channel formation region 409 is also formed in a self-aligned manner. After that, laser light irradiation is performed to anneal (recrystallize) the active layer amorphized by the bombardment of ions and to activate the implanted impurity ions. As the laser light, for example, an XeCl excimer laser is used. In this step, the source region 408 and the drain region 4
Recrystallization with 10 and activation of impurities implanted in this region are performed.

After the laser beam irradiation process for annealing and activating the source / drain regions is completed, a thin film 407 represented by SiO _x N _y is formed. The thin film 407 represented by SiO _x N _y is plasma C using dichlorosilane.
It is performed by the VD method.

Thus, the state shown in FIG. 4B is obtained. After that, a silicon oxide film is formed as an interlayer insulating film 411 by using a plasma CVD method. At this time, hydrogen can be prevented from entering the gate insulating film 405 by the action of the thin film 407 represented by SiO _x N _y .

Then, through the hole forming process, the source electrode 41
2 and the drain electrode 413 are formed. The source / drain electrodes may be formed using an appropriate metal such as aluminum. Thus, the thin film transistor is completed as shown in FIG.

[Embodiment 6] This embodiment is an example in which the invention disclosed in this specification is applied to the structure shown in FIG.
The thin film transistor illustrated in FIG. 5A has a glass substrate 50.
It is formed on 1. FIG. 5A shows SiO _x N forming the base film formed on the glass substrate 501.
a thin film 502 indicated by _y , a semiconductor layer 503 forming a channel formation region, a source region 504 and a drain region 505 which are semiconductor layers having one conductivity type, a thin film 506 indicated by SiO _x N _y , and a silicon oxide film. It also has a gate insulating film 507 and a gate electrode 508.

The semiconductor layer 503 is crystallized by the action of the catalytic element that promotes crystallization. A semiconductor layer 503 forming a channel forming region, a semiconductor layer 504 forming a source region, and a semiconductor layer 505 forming a drain region.
Has a thin film 502 formed of SiO _x N _y on the lower surface and a thin film 506 formed of SiO _x N _y on the upper and side surfaces, so that hydrogen or a metal element that promotes crystallization is contained in these semiconductor layers. Can be locked up. Then, hydrogen or a metal element existing in the active layer can be prevented from entering the gate insulating film 507.

[Embodiment 7] This embodiment is an example in which the invention disclosed in this specification is applied to the structure shown in FIG.
The thin film transistor illustrated in FIG. 5B has a glass substrate 50.
9 is formed. FIG. 5B shows SiO _x N forming the base film formed on the glass substrate 509.
A thin film 510 indicated by _y , a gate electrode 511, a gate insulating film 512 made of silicon oxide, a thin film 513 indicated by SiO _x N _y , a semiconductor layer 514 in which a channel formation region is formed, and a semiconductor layer 515 which becomes a source region. And a semiconductor layer 516 which serves as a drain region.

The semiconductor layer 514 is made of amorphous silicon. In the structure shown in FIG. 5B, since the periphery of the gate insulating film 512 is covered with the thin film 513 represented by SiO _x N _y , hydrogen is prevented from entering the gate insulating film 512 from the semiconductor layer 514. can do. In particular, when amorphous silicon is used for the semiconductor layer 514, a large amount of hydrogen is contained in the semiconductor layer 514, so that the thin film 513 represented by SiO _x N _y acts.
It is important to prevent hydrogen from entering the gate insulating film 512.

[0069]

EFFECTS OF THE INVENTION By utilizing the invention disclosed in the present specification, it is possible to satisfy both the requirements of containing hydrogen in the active layer and not containing hydrogen in the gate insulating film as much as possible. Thus, a thin film transistor having excellent electrical stability can be obtained.

[Brief description of drawings]

FIG. 1 shows a manufacturing process of an example.

FIG. 2 shows a configuration of a conventional thin film transistor.

FIG. 3 shows a manufacturing process of an example.

FIG. 4 shows a manufacturing process of an example.

FIG. 5 shows a manufacturing process of an example.

[Explanation of symbols]

101 ... Glass substrate 102 Silicon nitride film 103 Active layer 104 SiO _x N Thin film 105 indicated by _y ... Silicon oxide film (gate insulating film) 106 ... Gate electrode 107 ... Source region 108 ... ........ Channel forming region 109 ..... Drain region 110 ......... Interlayer insulating film 111 ......... Source electrode 112 .. ........ Drain electrode 113 ... Gate electrode 114 ... Oxide layer 115 ... Offset gate region 100 ... · · · · · · · SiO _x N thin film 201 ......... glass substrate 202 ......... acid represented by _y Silicon film 203 ... Source region 204 ... Channel formation region 205 ... Drain region 206 ... Gate Electrode 207 ... Interlayer insulating film 208 ... Source electrode 209 ... Drain electrode 401 ... Glass substrate 402 films represented by ......... SiO _x N thin film 403 ......... active layer 404 ......... SiO _x represented by _y N _y 405 ·・ ・ ・ ・ ・ ・ ・ ・ Silicon oxide film (gate insulating film) 406 ・ ・ ・ ・ ・ ・ Gate electrode 407 ・ ・ ・ ・ ・ ・ ・ Thin film 408 represented by SiO _x N _y .... Source region 409 ..... Channel formation region 410 ..... Drain region 41 ......... interlayer insulating film 412 ......... source electrode 413 ......... drain electrode

Continuation of front page (56) Reference JP-A-2-140915 (JP, A) JP-A-3-29316 (JP, A) JP-A-6-97073 (JP, A) JP-A-3-95939 (JP , A) JP 3-185736 (JP, A) JP 62-147759 (JP, A) JP 6-112490 (JP, A) JP 6-13610 (JP, A) JP 7-161996 (JP, A) JP 5-55581 (JP, A) Yunosuke Kawazu et al. , Low-Temperature Crystallizatio n of Hydrogenated Amorphas Silicon Induced by Nickel Silicone Formula, J APANESE JOURNAL OF SAPPY 1985. 29, NO. 12, PP. 2698-2704 (58) Fields surveyed (Int.Cl. ⁷ , DB name) G02F 1/1368 H01L 21/20 H01L 21/318 H01L 21/336 H01L 29/786

Claims (4)

(57) [Claims] 1. A SiOxNy (0 <x formed on a substrate.
<A first thin film represented by 2, 0 <y <4/3), is formed in contact with the first thin film, using a nickel
An active layer made of a crystallized crystalline silicon film , and a first thin film which is in contact with an upper surface and a side surface of the active layer.
SiOxNy (0 <x <2, 0 formed in contact with the surface of
<Y <4/3) and a second thin film represented by the second silicon oxide film in formed in contact with the upper surface of the thin-film
When the a gate electrode formed in contact with the upper surface of the silicon oxide film, an upper surface and a side surface of the gate electrode, and the silicon oxide film
SiOxNy (0 <x <2, 0 formed in contact with the upper surface of the
<Y <4/3), and the active layer is composed of the first thin film and the second thin film.
And the lower surface of the silicon oxide film is covered with the second thin film.
Is covered so that it does not come into contact with the conductive layer, and the upper surface is covered with the third thin film.
A thin film transistor characterized by being more covered . 2. A SiO x N y film formed on a substrate and containing chlorine.
First thin film represented by (0 <x <2, 0 <y <4/3)
And is formed in contact with the first thin film, using nickel
An active layer made of a crystallized crystalline silicon film , and a first thin film which is in contact with an upper surface and a side surface of the active layer.
SiO x N y (0 <x
<2, 0 <y <4/3) and a silicon oxide film formed in contact with the upper surface of the second thin film
And a gate electrode formed in contact with the upper surface of the silicon oxide film.
And the top and side surfaces of the gate electrode and the silicon oxide film
SiO x N y (0 <x
<2, 0 <y <4/3) with a third thin film
However, the active layer is composed of the first thin film and the second thin film.
And the lower surface of the silicon oxide film is covered with the second thin film.
Is covered so that it does not come into contact with the conductive layer, and the upper surface is covered with the third thin film.
A thin film transistor characterized by being more covered. 3. The first thin film according to claim 2, wherein
The second thin film and the third thin film have a size of 1 × 10 ¹⁵ to 1 ×.
A thin film containing chlorine at a concentration of 10 ²⁰ cm ^-3
Transistor. 4. A liquid crystal display device using the thin film transistor according to any one of claims 1 to 3 .