JP2002343974A - Thin film transistor and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a thin-film transistor which enables high-efficient activation of impurities without increasing an area of a polycrystalline silicon film or increasing the lamp power of RTA. SOLUTION: The method of manufacturing a thin-film transistor comprises a step of forming an amorphous silicon film on a glass substrate, processing the amorphous silicon film into a polycrystalline silicon film and then forming the polycrystalline silicon film into an insular polycrystalline silicon film, forming a gate electrode, implanting impurities into the insular polycrystalline silicon film, and annealing using strong light. The amorphous silicon films are formed on both faces of the glass substrate, and only the amorphous silicon film formed on one face is processed into the polycrystalline silicon film, and the amorphous silicon film formed on the other face increases the substrate temperature at the time of annealing.

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 (TFT) provided on an insulating film formed on a glass substrate, particularly for an active matrix type liquid crystal display (liquid crystal display) used for a thin film integrated circuit. The present invention relates to a method for manufacturing a thin film transistor used for a thin film integrated circuit.

[0002]

2. Description of the Related Art In recent years, a semiconductor device having a thin film transistor on an insulating substrate such as glass, for example, an active matrix type liquid crystal display device using the thin film transistor for driving pixels has been developed. In general, a thin film silicon semiconductor is used for a thin film transistor used in these devices.

[0003] Some thin-film silicon semiconductors are composed of polycrystalline silicon having crystallinity. A thin film transistor using such polycrystalline silicon uses amorphous silicon. Compared with the thin film transistor, the electron mobility is two orders of magnitude or more, and there are various advantages such as miniaturization of a display element and integration of a driving circuit on the same substrate.

In recent years, in the field of liquid crystal display devices, there has been active development of technology for manufacturing a thin film transistor array with a built-in drive circuit using a polycrystalline silicon thin film transistor on a glass substrate which is inexpensive and easy to increase in area. In fact, some have already begun to put into practical use.

In order to form a polycrystalline thin film transistor at a low temperature, it is important to develop a technique for activating the impurities implanted into the polycrystalline silicon thin film at a low temperature simultaneously with a technique for forming the polycrystalline silicon thin film at a low temperature. As a technique for forming a high-quality polycrystalline silicon thin film at a low temperature on a large-area substrate, a low-temperature crystallization method using an excimer laser is usually used.

On the other hand, thermal anneal processing using a heating furnace is often used for activating impurities, but in the case of thermal anneal processing, there is a problem that the activation rate is greatly reduced when the processing temperature is lowered. there were.

[0007] In order to solve these contradictory problems, as a method of performing annealing at a high temperature for a short period of time and improving the activation rate of impurities, a rapid therapy is used.
Rmal Anneal (RTA) and excimer laser activation have been proposed. Regarding RTA activation, for example, Electronic Display Forum '96 Lectures 1-12-
1-28.

Here, a method of manufacturing a thin film transistor used in an active matrix type liquid crystal display device used in a conventional liquid crystal display device will be described with reference to the drawings. First, as shown in FIG. 2A, a silicon oxide film serving as a buffer layer 12 is formed on a glass substrate 11 by using a plasma CVD method.

After that, without taking out the glass substrate 11 on which the silicon oxide thin film is formed into the atmosphere, the plasma CV
Using method D, amorphous silicon (a-Si) is deposited to a thickness of 50 nm.

Next, in order to reduce hydrogen in the a-Si film, heat treatment is performed at 400 ° C. to 450 ° C. for about 60 minutes in a reduced-pressure nitrogen atmosphere, and then excimer laser annealing is performed. The film is polycrystallized and polycrystalline silicon (po
ly-Si) film 13 is formed. Note that a 308 nm wavelength XeCl excimer laser is used for the excimer laser annealing.

Then, after the a-Si film is crystallized to form a polycrystalline silicon film, the polycrystalline silicon film is processed into a desired shape to form a silicon oxide film to be the gate insulating film 14.

Thereafter, as shown in FIG. 2B, a gate electrode 15 is formed, and the LDD (Li
Impurities are implanted to form a ghtly doped drain (region). Here, phosphorus ions were implanted.
After injecting impurities for forming the LDD region, a photoresist 2 is formed so as to cover the LDD region of the thin film transistor.
2, a mask for impurity implantation is formed, and phosphorus ions are implanted as impurities into the source region and the drain region.
By doing so, the polycrystalline silicon film 13 becomes an intrinsic polycrystalline silicon region (channel region) 13 containing no impurity.
a, a low-concentration impurity implantation region (LDD region) 13b,
It is divided into a high-concentration impurity implantation region (SD region) 13c.

After the impurity is implanted, as shown in FIG. 2C, activation of the implanted impurity is performed by RTA. The RTA device used for activation uses a Xe arc lamp as a light source.

After performing an impurity activation process by RTA, a silicon oxide film serving as an interlayer insulating film 16 is formed as shown in FIG. Then, after forming the interlayer insulating film 16, the interlayer insulating film 1 on the source region and the drain region is formed.
6, a contact hole is opened, and wirings 17 and 18 are formed.

Finally, a protective insulating film 19 made of silicon nitride is formed, and an annealing process is performed in a hydrogen atmosphere, so that dangling bonds in the polycrystalline silicon thin film are bonded to hydrogen ions, thereby achieving crystallization. It is possible to eliminate silicon in a non-crystallized state or in a microcrystalline state, so that a thin film transistor in which characteristics are not deteriorated can be completed.

[0016]

However, in the activation by RTA shown in the conventional example, the effect is determined by the temperature rise due to the heat absorption in the polycrystalline silicon. Therefore, the heat capacity is increased according to the area of the polycrystalline silicon film. To increase the effect of the activation, the area of the polycrystalline silicon film must be increased or the lamp power of the RTA must be increased.

However, increasing the area of the polycrystalline silicon film or increasing the lamp power of the RTA has a problem that the risk of warpage or cracking of the glass substrate is increased.

The present invention has been made in order to solve the above problems.
Increase the area of the polycrystalline silicon film or RTA
Another object of the present invention is to provide a method of manufacturing a thin film transistor having a high efficiency of impurity activation without increasing the lamp power of the thin film transistor.

[0019]

In order to achieve the above object, a method of manufacturing a thin film transistor according to the present invention comprises the steps of: forming an amorphous silicon film on a glass substrate; Processing into a film, forming an island-shaped polycrystalline silicon film, forming a gate electrode, implanting impurities into the island-shaped polycrystalline silicon film, and performing an annealing process using strong light And a method for manufacturing a thin film transistor, comprising: a step of forming an amorphous silicon film on both surfaces of a glass substrate; forming only an amorphous silicon film formed on one surface into a polycrystalline silicon film; The amorphous silicon film formed on the other surface is characterized in that the substrate temperature is increased during the annealing process.

With this configuration, when activating the island-shaped polycrystalline silicon film to be the active layer of the thin film transistor, the lamp light is absorbed by the a-Si film present on the back surface of the glass substrate, and the heat reduces the substrate temperature. By increasing the temperature, the p-Si film acts synergistically to increase the efficiency of the thermal annealing process. Thereby, various characteristics of the thin film transistor can be improved.

In the method of manufacturing a thin film transistor according to the present invention, it is preferable that the amorphous silicon film is formed by an LPCVD method. LPCV for forming a-Si film
By using the D method, an a-Si film can be simultaneously formed on both surfaces, and the number of manufacturing steps can be reduced.

In the method of manufacturing a thin film transistor according to the present invention, it is preferable that the annealing process is performed on both surfaces of the glass substrate. This is to effectively utilize the temperature rise on the back surface of the substrate.

In the method for manufacturing a thin film transistor according to the present invention, it is preferable that the output of the lamp light source in the annealing process is different between the front and back of the glass substrate. This is because the front surface is used for activating impurities and the back surface is used for raising the substrate temperature.

Further, in the method of manufacturing a thin film transistor according to the present invention, it is preferable that the amorphous silicon film formed on the surface on which the thin film transistor is not formed be removed after the completion of the annealing.

Next, in order to achieve the above object, a thin film transistor according to the present invention is characterized by being manufactured by the above-described method of manufacturing a thin film transistor.
With this configuration, when activating the island-shaped polycrystalline silicon film to be the active layer of the thin film transistor, the lamp light is absorbed by the a-Si film present on the back surface of the glass substrate, and the heat increases the substrate temperature. In this case, the p-Si film acts synergistically to improve the efficiency of the thermal annealing treatment, and thus it is possible to obtain a thin film transistor having improved characteristics.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing a thin film transistor according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a process sectional view of a method for manufacturing a thin film transistor according to an embodiment of the present invention.

First, as shown in FIG. 1A, a silicon oxide film serving as the buffer layer 12 is formed. After that, LPC
An amorphous silicon (a-Si) film 21 is formed on both surfaces of a glass substrate by a VD method.

Next, the polycrystalline silicon film 13 is formed only on the surface on which the thin film transistor is to be formed by polycrystallizing the a-Si film by excimer laser annealing. As the excimer laser, a XeCl excimer laser having a wavelength of 308 nm is used.

Then, after the a-Si film is crystallized to form a polycrystalline silicon film 13, the polycrystalline silicon film 13 is processed into a desired shape to form a silicon oxide film serving as a gate insulating film 14. Thereafter, a gate electrode 15 is formed, and phosphorus ions are implanted as impurities to form an LDD region in the thin film transistor.

Next, after impurity implantation for forming the LDD region, as shown in FIG.
A mask for impurity implantation is formed with the photoresist 22 so as to cover the DD region, and phosphorus ions are implanted as impurities into the source region and the drain region. Thus, the polycrystalline silicon film 13 has an intrinsic polycrystalline silicon region (channel region) 13a containing no impurity, a low-concentration impurity implantation region (LDD region) 13b, and a high-concentration impurity implantation region (SD region). 13c.

After the formation of the silicon oxide film 16 serving as the second insulating film, the impurity implanted by RTA is activated. In the present embodiment, a Xe lamp is employed as a light source of the RTA device used for activation, and the substrate is irradiated with lamp light with different lamp outputs from two directions.

In the present embodiment, the a-Si film on the back surface of the glass substrate absorbs the lamp light, thereby increasing the temperature of the substrate. That is, the p-Si of the RTA lamp light
The heat from the a-Si film, in addition to the absorption into the substrate, makes it possible to efficiently supply heat for activating the implanted impurities.

After the activation treatment, the front surface (TFT forming surface) is protected by masking with a resist, and the a-Si film on the back surface is removed with hydrofluoric nitric acid. After removing the resist, an interlayer insulating film is formed again as shown in FIG.
A contact hole is opened, and wirings 17 and 18 are formed. Finally, a protective insulating film 19 made of silicon nitride is formed, the a-Si film on the back surface of the substrate is removed, and an annealing process is performed in a hydrogen atmosphere, so that dangling bonds in the polycrystalline silicon thin film are converted to hydrogen ions. By bonding, silicon which is not crystallized or in a microcrystalline state can be eliminated and a thin film transistor whose characteristics are not deteriorated can be completed.

As described above, according to the present embodiment, in activating the island-like polycrystalline silicon film to be the active layer of the thin film transistor, the a-
The lamp light is absorbed by the Si film, and the heat acts synergistically on the p-Si film by increasing the substrate temperature,
The efficiency of the thermal annealing process can be increased. Thereby, various characteristics of the thin film transistor can be improved.

[0035]

As described above, according to the method of manufacturing a thin film transistor according to the present invention, the activation of the island-like polycrystalline silicon film to be the active layer of the thin film transistor is achieved.
The lamp light is absorbed by the a-Si film present on the back surface of the glass substrate, and the heat increases the substrate temperature.
Acting synergistically on the Si film, it is possible to increase the efficiency of the thermal annealing process. Thereby, various characteristics of the thin film transistor can be improved. That is,
By forming the a-Si film on the back surface of the glass substrate, it is possible to improve the characteristics and reliability of the thin film transistor.

[Brief description of the drawings]

FIG. 1 is a process cross-sectional view of a method for manufacturing a thin film transistor according to an embodiment of the present invention.

FIG. 2 is a process sectional view of a conventional method for manufacturing a thin film transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Glass substrate 12 Buffer layer (silicon oxide) 13 Non-single-crystal silicon 13a Intrinsic polycrystalline silicon region (channel region) 13b Low concentration impurity implantation region (LDD region) 13c High concentration impurity implantation region (SD region) 14 Gate insulating film ( Silicon oxide) 15 gate electrode (MoW alloy) 16 interlayer insulating film (silicon oxide) 17, 18 SD wiring (Al / Ti) 19 protective insulating film (silicon nitride) 21 amorphous silicon film 22 photoresist

 ──────────────────────────────────────────────────続 き Continuing on the front page F term (reference)

Claims (6)

[Claims] A step of forming an amorphous silicon film on a glass substrate; a step of processing the amorphous silicon film into a polycrystalline silicon film; a step of forming an island-shaped polycrystalline silicon film; Forming an impurity, implanting impurities into the island-like polycrystalline silicon film, and performing an annealing process using strong light, wherein the amorphous silicon film is The amorphous silicon film formed on both surfaces of the glass substrate, only the amorphous silicon film formed on one surface is processed into the polycrystalline silicon film, and the amorphous silicon film formed on the other surface is A method of manufacturing a thin film transistor, wherein a substrate temperature is increased during an annealing process. 2. The method according to claim 1, wherein the amorphous silicon film is formed by an LPCVD method. 3. The method of manufacturing a thin film transistor according to claim 1, wherein the annealing is performed on both surfaces of the glass substrate. 4. The method for manufacturing a thin film transistor according to claim 1, wherein outputs of the lamp light source in the annealing process are different between the front and back of the glass substrate. 5. The method of manufacturing a thin film transistor according to claim 1, wherein the amorphous silicon film formed on a surface on which the thin film transistor is not formed is removed after the completion of the annealing. 6. A thin-film transistor manufactured by the method for manufacturing a thin-film transistor according to claim 1.