JP3146702B2 - Method for manufacturing thin film transistor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor, and more particularly to a method of forming a thin film insulated gate transistor, a so-called MIS transistor, on thin film silicon.

[0002]

2. Description of the Related Art In SRAMs, liquid crystal display devices, and the like, a configuration is often adopted in which a transistor, that is, a MIS transistor is a so-called thin film transistor formed on a silicon thin film formed on a substrate.

In this case, there is a solid phase growth method (SPC) as a method for making the silicon thin film into large grains.

The SPC is flat, can form crystal grains having a particle size of about 1 μm, and has an electron mobility of 100 μm.
cm ² · V ^-1 · s ^-1, but in this case, in a thin film having a thickness of 100 µm or less, relatively many defects exist in the crystal grains, and the carrier mobility is further increased. It is difficult to increase it, and there is also a problem in reliability and the like.

[0005]

SUMMARY OF THE INVENTION The present invention aims to solve the problems of characteristics and reliability due to the crystallinity of a silicon thin film forming such a thin film transistor. Also,
The present invention aims to improve the breakdown voltage of a thin film transistor.

[0006]

SUMMARY OF THE INVENTION The present invention relates to FIGS.
As shown in FIG.
Step of forming silicon thin film 12 (FIGS. 1A and 1
B) and the silicon oxide film 1
3 (FIG. 1C) and the silicon oxide film 1
3, an ultraviolet pulse laser beam 23 in an atmosphere containing nitrogen.
And forming a gate insulating film 15 by forming a nitride film 14 on at least the surface of the silicon oxide film 13 (FIG. 2A).

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, a silicon oxide film 13 is formed on a silicon thin film 12 formed on a substrate 11, and this is irradiated with an ultraviolet pulse laser beam in an atmosphere containing nitrogen to form a nitride film 14 on the silicon oxide film 13. Is formed at least on the surface, so that a dense gate insulating layer 15 without pinholes and the like is formed, and the laser annealing improves the crystallinity of the silicon thin film 12,
That is, the effect of reducing the trap density is simultaneously achieved.

Therefore, by forming the gate insulating layer 15 which is dense and has excellent electrical characteristics, high breakdown voltage, high reliability,
Since the silicon thin film 12 having excellent hot carrier resistance and excellent crystallinity can be formed, a highly reliable transistor can be formed.

Further, in this case, the use of a pulsed laser beam makes it possible to avoid an increase in the temperature of the substrate 11 due to the irradiation of the laser beam. In particular, a large-area panel can be formed at a low cost in accordance with a liquid crystal display device or the like.

An example of the present invention will be described in detail with reference to the drawings.

In this example, for example, a thin film transistor for driving a liquid crystal display device is formed. In this case, FIG.
A, as shown in FIG.
A substrate 11 made of a substrate, such as (Hoya Glass Co., Ltd. product) or AN glass (Asahi Glass Co., Ltd.), is prepared, and impurities such as Pb, Al, and Na from the substrate 11 are placed thereon.
An isolation layer 16 made of SiN or the like for blocking the like is formed by, for example, plasma CVD.

Then, a polycrystalline silicon thin film 1 is
2 is formed to a thickness of, for example, about 400.degree.

As shown in FIG. 1B, the silicon thin film 12 is patterned by, for example, photolithography, and an island is finally formed at a portion where a thin film transistor is to be formed.

As shown in FIG. 1C, this silicon thin film 1
The silicon oxide film 13 covers the island 2 entirely.
Is formed to a thickness of, for example, about 400 ° by CVD or the like.

Then, the surface of the silicon oxide thin film 12 is subjected to nitriding treatment by irradiation with an ultraviolet pulse laser beam, that is, an excimer laser beam. This treatment is performed, for example, by using an excimer laser such as XeCl (308 nm) in an atmosphere containing nitriding, such as N ₂ O, or NH ₃ , for example, at 0 ° C.
By irradiating several to several hundred pulses of ³ J / cm ³ of pulse laser light, a gate insulating layer 15 having a silicon nitride SiON layer 14 formed on the surface of the silicon oxide film 13 is formed as shown in FIG. 2A. .

As shown in FIG. 2B, a polycrystalline silicon film 16 having a low resistivity as a whole is formed by CVD or the like.

Thereafter, the polycrystalline silicon film is pattern-etched by, for example, photolithography to form a gate electrode 17, and ion implantation of n-type or p-type impurities is performed using this as a mask to form a source region or a drain region 18. Is formed to form a thin film transistor.

Thereafter, although not shown, the formation of an interlayer insulating layer, the formation of Al wiring, and the like are performed as usual, and various target devices are constructed.

According to the method of the present invention, the silicon oxide film 13 is formed on the silicon thin film 12 formed on the base 11.
Is formed and is irradiated with an ultraviolet pulse laser beam in an atmosphere containing nitrogen to form a gate insulating layer 15 having a nitride film 14 formed on at least the surface thereof, so that a dense gate insulating layer 15 without pinholes or the like is formed. As well as being formed, the laser annealing simultaneously improves the crystallinity of the silicon thin film 12, ie, reduces the trap density.

Further, in this case, since the temperature rise of the substrate 11 due to the irradiation of the laser beam can be avoided by using the pulsed laser beam, a glass substrate having a relatively low melting point can be used as the substrate 11. .

[0021]

As described above, according to the present invention, the base 11
The silicon oxide film 1 is formed on the silicon thin film 12 formed thereon.
3 is formed and irradiated with an ultraviolet pulse laser beam in an atmosphere containing nitrogen to form a gate insulating layer 15 having a nitride film 14 formed on at least the surface thereof. While trying to form
By this laser annealing, the crystallinity of the silicon thin film 12 is improved, that is, the trap density is reduced, so that the high withstand voltage, high reliability, and hot carrier resistance are excellent.
In addition, since the silicon thin film 12 having excellent crystallinity can be formed, a highly reliable transistor can be formed.

Further, since a glass substrate having a relatively low melting point can be used as the substrate 11, a large area pulse can be formed at a low cost particularly when applied to a liquid crystal display device or the like.

[Brief description of the drawings]

FIG. 1 is a process diagram (part 1) of an example of the method of the present invention.

FIG. 2 is a process diagram (part 2) of an example of the method of the present invention.

[Explanation of symbols]

11 substrate, 12 silicon thin film 12, 13 silicon oxide film, 14 nitride film, 15 gate insulating layer

Claims (1)

(57) [Claims] A step of forming a silicon thin film on a substrate, a step of forming a silicon oxide film on the silicon thin film by a chemical vapor deposition method, and forming the silicon oxide film in an atmosphere containing nitrogen. Irradiating an ultraviolet pulse laser beam to form a nitride film on the surface of the silicon oxide film to form a gate insulating layer.