JPH09307115A - Thin film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure the stability of the process of forming a thin film transistor and to prevent a source resistance and a drain resistance from being increased to make it possible to maintain the high driving capability of the transistor by a method wherein conductive films are electrically connected with source and drain electrodes and a semiconductor film. SOLUTION: Conductive films 2 formed insularly by patterning are respectively provided under the lower layers of source and drain electrode regions 10 and 11 and the films 2 are electrically connected with the source and drain electrodes 10 and 11 and a semiconductor film 5. Therefore, in the case where the film 5 is formed into a thin film, an increase in a contact resistance between the electrodes 10 and 11 and in source and drain resistances is never caused even when the film 5 is etched through at the time of the formation of contact holes 9, a full ohmic contact can be obtained and a thin film transistor, which is good in off-characteristics, can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor, and more particularly to a thin film transistor used in an active matrix type liquid crystal display device, an image sensor and the like.

[0002]

2. Description of the Related Art As a semiconductor device in which a thin film transistor is formed on an insulating substrate such as glass, an active matrix type liquid crystal display device and image using the thin film transistor as a switching element for each pixel and a peripheral drive circuit for the switching element Sensors and the like are known.

Thin film silicon semiconductors are generally used for thin film transistors used in these devices. The thin film silicon semiconductor is roughly classified into two types, that is, an amorphous silicon semiconductor and a crystalline silicon semiconductor.

Amorphous silicon semiconductors have a low production temperature and can be produced relatively easily by a vapor phase method, and therefore have high mass productivity and are most commonly used.
However, since it is difficult to reduce the transistor size due to the structure, it is difficult to increase the aperture ratio of the pixel, and physical properties such as carrier mobility are inferior to those of a crystalline silicon semiconductor.

Therefore, in order to obtain more excellent high speed characteristics and high aperture ratio, there is a strong demand for practical use of a thin film transistor made of a crystalline silicon semiconductor.

On the other hand, as the crystalline silicon semiconductor, single crystal silicon (c-Si), polycrystalline silicon (p-Si), microcrystalline silicon (μc-Si), amorphous silicon containing a crystalline component, and Semi-amorphous silicon having an intermediate state between crystalline and amorphous is known.

As a method for obtaining these thin film silicon semiconductors having crystallinity, (1) a film having crystallinity is directly formed (2) a semiconductor film is formed and heat energy is applied to the film. Crystallization (3) A method is known in which a semiconductor film is formed and crystallized by the energy of laser light.

As a future technique, for example, a thin film transistor having a high-speed characteristic that constitutes a peripheral driving circuit of an active matrix type liquid crystal display device and a thin film transistor used for a pixel switching element are simultaneously formed on the same substrate. Is desired.

However, in the conventional thin film transistor, a leak current is generated at the grain boundary of the crystal, and it is difficult to obtain good off characteristics. It is known that thinning a semiconductor film is effective as one of methods for obtaining good off characteristics.

On the other hand, when a thin film transistor using a crystalline silicon film is used in an active matrix type liquid crystal display device, it is resistant to the semiconductor film by a backlight for brightening the display or a halogen lamp for use as a projection. Since light enters and characteristic changes such as an increase in off-current and a change in threshold voltage that reduce reliability are caused, a thin film transistor having a light-shielding film formed in a lower layer of a channel region may be used.

[0011]

The thin film transistor in which the semiconductor film is made thin has the following problems.

FIG. 6 is a sectional view showing a conventional thin film transistor in which a semiconductor film is thinned. In FIG. 6, 61
Is an insulating substrate, 63 is a light-shielding film, 64 is an insulating film, 65 is a semiconductor film, 66 is a gate insulating film, 67 is a gate electrode, and 68.
Is an interlayer insulating film, 69 is a contact hole, 70 is a source electrode, and 71 is a drain electrode.

As shown in FIG. 6, when the semiconductor film 65 is etched to form a contact hole 69 for electrically connecting the semiconductor film 65 to the source electrode 70 and the drain electrode 71, the semiconductor film 65 is thinned. As a result, the semiconductor film 65 is also etched, and a sufficient ohmic contact cannot be obtained, resulting in an increase in contact resistance.

Further, by thinning the semiconductor film,
There is a problem that the driving frequency of the peripheral driving circuit, which requires high-speed operation due to high source resistance and drain resistance, is limited by the contact resistance, the source resistance and the drain resistance.

The present invention has been made in view of the conventional problems as described above. Even when the semiconductor film is thinned to improve the off characteristics, the process stability is ensured and the source is reduced. It is an object of the present invention to provide a thin film transistor capable of preventing an increase in resistance and drain resistance and maintaining high driving capability.

[0016]

In order to achieve the above object, a thin film transistor according to claim 1 of the present invention comprises:
A conductive film patterned in an island shape is provided under the source electrode region and the drain electrode region, and the conductive film is electrically connected to the source electrode and the drain electrode and the semiconductor film. Is characterized by.

A thin film transistor according to a second aspect is the thin film transistor according to the first aspect, wherein the conductive film is
It is characterized by being formed of an anodizable metal or an alloy containing an anodizable metal.

A thin film transistor according to claim 3 is the thin film transistor according to claim 1 or 2, wherein
A light-shielding film is provided below the channel region, and the conductive film is made of the same material as the light-shielding film.

According to a fourth aspect of the present invention, in the thin film transistor according to the third aspect, the channel region and the light shielding film are electrically separated by an anodic oxide film of the light shielding film.

According to the thin film transistor of the present invention, a conductive film patterned in an island shape is provided under the source electrode region and the drain electrode region, and the conductive film includes the source electrode, the drain electrode, and the semiconductor film. In addition, when the semiconductor film is thinned by being electrically connected to and, even when the semiconductor film is etched at the time of forming the contact hole, the contact resistance, the source resistance, and the drain resistance are increased. In addition, a sufficient ohmic contact can be obtained, and a thin film transistor with excellent off characteristics can be obtained.

Furthermore, since the conductive film is formed of an anodizable metal or an alloy containing an anodizable metal, an insulative anodized film can be formed by anodization. The steps of forming a pattern by etching the conductive film, forming an insulating film, and forming an opening in the insulating film can be omitted, and
Since no step is formed between the conductive film and the anodized film, the semiconductor film formed thereon can be flattened, and cracking of the semiconductor film at the step portion can be prevented. it can.

Further, since the light-shielding film is provided below the channel region and the conductive film is made of the same material as the light-shielding film, the conductive film can be formed simultaneously with the formation of the light-shielding film. The conductive film can be formed without adding.

Further, since the channel region and the light-shielding film are electrically separated by the anodic oxide film of the light-shielding film, a step is formed between the conductive film and the anodic oxide film on the light-shielding film. Does not occur, the semiconductor film formed thereon can be flattened, and cracking of the semiconductor film at the step portion can be prevented.

[0024]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described with reference to FIGS.

(Embodiment 1) Referring to FIG. 1 and FIG.
A first embodiment of the present invention will be described. FIG. 1 is a sectional view of a thin film transistor according to a first embodiment of the present invention, and FIG. 2 is a process drawing showing a manufacturing process of a thin film transistor according to the first embodiment of the present invention.

In FIG. 1, 1 is an insulating substrate, 2 is a conductive film, 3 is a light-shielding film, 4 is an insulating film, 5 is a semiconductor film, 6 is a gate insulating film, 7 is a gate electrode, 8 is an interlayer insulating film, Reference numeral 9 is a contact hole, 10 is a source electrode, and 11 is a drain electrode.

First, as shown in FIG. 2A, after cleaning the surface of the insulating substrate 1 made of glass having an outer size of about 300 mm × 300 mm, tantalum (for forming the conductive film 2 and the light shielding film 3 is formed). Refractory metals such as Ta), molybdenum (Mo) and tungsten (W) or phosphorus (P)
Is doped with polysilicon to a thickness of 100 by a sputtering method or a chemical vapor deposition method (CVD method).
It is deposited on the insulating substrate 1 to a thickness of about nm to 1 μm. The film thickness of the refractory metal such as Ta, Mo and W or the polysilicon doped with P has a light-shielding property that does not cause the characteristic variation such that the reliability is deteriorated when the thin film transistor is irradiated with light. Is required and is determined by the type of film and the intensity of light when it is actually used. Also,
It is also necessary to consider the effect of heat from the light source.

Next, a pattern is formed on the conductive film 2 and the light-shielding film 3 by etching. At this time, patterning is performed so that the conductive film 2 is located under the source electrode 10 region and the drain electrode 11 region, and the light-shielding film 3 is located under the channel region.

Further, an insulating film 4 made of a silicon oxide film is deposited on the conductive film 2 and the light shielding film 3 by a sputtering method or a CVD method so as to have a thickness of about 300 nm to 1 μm. At this time, the film thickness of the insulating film 4 is determined by the film quality of the insulating film 4 and the step coverage. That is, it is necessary to have a film thickness capable of sufficiently covering the step due to the conductive film 2 and the light shielding film 3 and sufficiently ensuring the insulating property with the semiconductor film 5 formed in the upper layer.

Then, the portions of the insulating film 4 located below the source electrode 10 region and the drain electrode 11 region are opened by etching, and the amorphous silicon film to be the semiconductor film 5 is formed to 30 nm by sputtering or CVD.
Deposit to a thickness of about.

Next, as shown in FIG. 2B, the amorphous silicon film is changed to a polycrystalline silicon film by the solid phase growth method or the laser annealing method to form the gate insulating film 6 and the gate electrode 7. .

Impurity ions are introduced into the portions of the semiconductor film 5 located under the source electrode 10 region and the drain electrode 11 region by the ion doping method and activated by the laser annealing method or the thermal diffusion method. The insulating film 8 is deposited.

Next, as shown in FIG. 2C, a contact hole 9 is formed in a portion located under the source electrode 10 region and the drain electrode 11 region by etching to form the source electrode 10 and the drain electrode 11. To obtain a thin film transistor.

In order to obtain a thin film transistor having good off characteristics, the film thickness of the semiconductor film 5 must be 30 nm or less. In the conventional thin film transistor, when the film thickness of the semiconductor film is 30 nm or less, there is a possibility that the semiconductor film is etched due to etching when forming the contact hole, and sufficient ohmic contact cannot be obtained. In the thin film transistor of the present invention, the source electrode 10 and the drain electrode 11, the semiconductor film 5 and the conductive film 2 are electrically conductive even if the semiconductor film 5 is etched by the etching for forming the contact hole 9. Connected to each other,
Sufficient ohmic contact is obtained.

In this embodiment, the case where the conductive film 2 and the light shielding film 3 are made of the same material has been described.
The same effect is obtained also in the thin film transistor in which the light shielding film 3 is not formed, and the same effect is obtained even when the conductive film 2 and the light shielding film 3 are made of different materials.

(Embodiment 2) Referring to FIGS. 3 to 5,
A second embodiment of the present invention will be described. 3 is a cross-sectional view of a thin film transistor according to the second embodiment of the present invention, FIG. 4 is a process diagram showing a manufacturing process of the thin film transistor according to the second embodiment of the present invention, and FIG. 5 is for performing anodic oxidation. 3 is a plan view showing the resist pattern of FIG.

In FIG. 3, 1 is an insulating substrate, 2 is a conductive film, 3 is a light-shielding film, 5 is a semiconductor film, 6 is a gate insulating film, and 7 is a gate insulating film.
Is a gate electrode, 8 is an interlayer insulating film, 9 is a contact hole, 10 is a source electrode, 11 is a drain electrode, and 14 is an anodized film.

First, as shown in FIG. 4A, after cleaning the surface of the insulating substrate 1 made of glass having an outer size of about 300 mm × 300 mm, Ta for forming the conductive film 2 and the light shielding film 3, A refractory metal 12 such as Mo and W capable of anodic oxidation is deposited on the insulating substrate 1 to a thickness of about 100 nm to 1 μm by a sputtering method or a CVD method. The film thickness of the refractory metal 12 capable of anodic oxidation is required to have a light-shielding property that does not cause a characteristic change such that reliability is deteriorated when the thin film transistor is irradiated with light. It is determined by the intensity of light when actually used. It is also necessary to consider the effect of heat from the light source.

Next, a resist pattern 13 is formed by photolithography. At this time, as shown in FIG. 5, the resist pattern 13 connects the portions of the lower layer of the channel region where the light-shielding film 3 is to be formed to each other.

Then, as shown in FIG. 4B, the first anodic oxidation is performed in this state, and the resist pattern 1 is formed.
The anodic oxide film 14 is formed by oxidizing the refractory metal 12 capable of anodic oxidation in the portion where 3 is not formed.

Further, as shown in FIG. 4C, after removing the resist pattern 13, the light-shielding film 3 is subjected to a second anodic oxidation, and only a part of the upper side of the light-shielding film 3 is anodized.
Set to 4. At this time, since the portions forming the light-shielding film 3 located under the channel region were connected to each other by the resist pattern 13, the light-shielding film 3 was electrically connected to each other by the refractory metal 12 capable of anodic oxidation. Therefore, only the light-shielding film 3 can be selectively anodized. Further, the thickness of the anodic oxide film 14 formed by the second anodic oxidation can ensure a thickness having a light-shielding property that does not cause a characteristic change such that reliability is deteriorated when the thin film transistor is irradiated with light. And
The film thickness is required to ensure sufficient insulation with the semiconductor film 5 formed in the upper layer.

Next, as shown in FIG. 4D, an amorphous silicon film to be the semiconductor film 5 is deposited to a thickness of about 30 nm by the sputtering method or the CVD method, and the solid phase growth method or the laser annealing method is used. To change the amorphous silicon film into a polycrystalline silicon film.

Then, the gate insulating film 6 and the gate electrode 7 are formed.
To form Further, impurity ions are introduced into portions of the semiconductor film 5 located under the source electrode 10 region and the drain electrode 11 region by the ion doping method and activated by the laser annealing method or the thermal diffusion method, and then the interlayer insulating film 8 is formed. Deposit.

Then, the source electrode 1 is etched.
A contact hole 9 is formed in a portion located under the 0 region and the drain electrode 11 region, and a source electrode 10 and a drain electrode 11 are formed to obtain a thin film transistor.

In the thin film transistor of the present invention, the semiconductor film 5 is formed by etching when forming the contact hole 9.
Even if is etched, the source electrode 10 and the drain electrode 11, the semiconductor film 5 and the conductive film 2 are electrically connected, and a sufficient ohmic contact can be obtained.

Furthermore, since no step is formed between the conductive film 2 and the anodic oxide film 14, the semiconductor film 5 formed in the upper layer can be made flat and cracks in the semiconductor film 5 at the step portion can be prevented. Can be prevented.

Although the case where the conductive film 2 and the light shielding film 3 are made of the same material has been described in the present embodiment,
The same effect is obtained also in the thin film transistor in which the light shielding film 3 is not formed, and the same effect is obtained even when the conductive film 2 and the light shielding film 3 are made of different materials.

[0048]

As described above, according to the method of manufacturing a thin film transistor of the present invention, the conductive film patterned like islands is provided under the source electrode region and the drain electrode region. Is electrically connected to the source electrode and the drain electrode and the semiconductor film, so that the contact resistance, the source resistance and the drain resistance are not increased even when the semiconductor film is thinned. A sufficient ohmic contact can be obtained, and a thin film transistor with excellent off characteristics can be obtained.

Furthermore, since the conductive film is formed of an anodizable metal or an alloy containing an anodizable metal, an insulating anodized film can be formed by anodization. The steps of forming a pattern by etching the conductive film, forming an insulating film, and forming an opening in the insulating film can be omitted, and
The semiconductor film can be made flat and cracks in the semiconductor film can be prevented.

Further, since the light-shielding film is provided below the channel region and the conductive film is made of the same material as the light-shielding film, the conductive film can be formed simultaneously with the formation of the light-shielding film. The conductive film can be formed without adding.

Further, since the channel region and the light-shielding film are electrically separated by the anodic oxide film of the light-shielding film, the semiconductor film can be made flat and cracks in the semiconductor film can occur. Can be prevented.

As described above, if it becomes possible to form a thin film transistor having high performance and excellent off characteristics, particularly in a liquid crystal display device, a thin film transistor for pixel switching which is required for a high definition and large area active matrix substrate. It is possible to realize a driver monolithic active matrix substrate in which an active matrix portion and a peripheral driving circuit portion are formed on the same substrate while satisfying both the reduction of the off characteristics of the device and the high performance of the thin film transistor for the peripheral driving circuit at the same time. Thin film integrated circuits such as the above can be formed on the same substrate, and the module can be made compact, high performance, low cost, and system-on-panel.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a thin film transistor according to a first embodiment of the present invention.

2A to 2C are process diagrams showing a manufacturing process of the thin film transistor according to the first embodiment of the present invention.

FIG. 3 is a sectional view of a thin film transistor according to a second embodiment of the present invention.

4A to 4D are process diagrams showing a manufacturing process of a thin film transistor according to a second embodiment of the present invention.

FIG. 5 is a plan view showing a resist pattern for performing anodization.

FIG. 6 is a cross-sectional view showing a thin film transistor in which a conventional semiconductor film is thinned.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Conductive film 3 Light-shielding film 4 Insulating film 5 Semiconductor film 6 Gate insulating film 7 Gate electrode 8 Interlayer insulating film 9 Contact hole 10 Source electrode 11 Drain electrode 12 Refractory metal 13 resist pattern 14 Anodizable Oxide film 61 Insulating substrate 63 Light-shielding film 64 Insulating film 65 Semiconductor film 66 Gate insulating film 67 Gate electrode 68 Interlayer insulating film 69 Contact hole 70 Source electrode 71 Drain electrode

Claims (4)

[Claims] 1. A conductive film patterned in an island shape is provided under the source electrode region and the drain electrode region, and the conductive film electrically connects to the source electrode and the drain electrode and the semiconductor film. A thin film transistor which is connected. 2. The thin film transistor according to claim 1, wherein the conductive film is formed of an anodizable metal or an alloy containing an anodizable metal. 3. The thin film transistor according to claim 1, wherein a light shielding film is provided below the channel region, and the conductive film is made of the same material as the light shielding film. 4. The thin film transistor according to claim 3, wherein the channel region and the light shielding film are electrically separated by an anodic oxide film of the light shielding film.