JPH06181178A - Fabrication of thin film transistor - Google Patents

Abstract

PURPOSE:To enhance reliability by irradiating a thin amorphous silicon film formed on a substrate with ultraviolet pulse laser beam to form a thin crystallized silicon film and then oxidizing the surface of the thin crystallized silicon film to form a gate insulation layer. CONSTITUTION:A thin silicon film is formed on the main surface of a substrate 1 by low temperature CVD(chemical vapor deposition) and Si ions are implanted therein to form a thin amorphous silicon film. The thin amorphous silicon film 2 is then irradiated with an ultraviolet pulse laser beam 3 to form a thin crystallized silicon film 4 which is subjected to thermal oxidation in a heating furnace thus forming a gate insulation layer 5 of SiO2. Furthermore, a polysilicon semiconductor layer 6 formed by CVD or the like is patterned by selective etching thus forming a gate electrode 7. Thereafter, impurity ions are implanted using the gate electrode 7 as a mask to form a drain region 8 thus constituting a thin film transistor.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In SRAMs, liquid crystal display devices, etc., a transistor, that is, a MIS transistor, is often used as 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 (LPC) as a method of forming large crystal grains in the silicon thin film.

This LPC is flat and can form crystal grains with a grain size of about 1 μm, and its electron mobility is 100.
cm ² · V ⁻¹ · s ^−1, but in this case, in a thin film with a thickness of 100 μm or less, there are relatively many defects in the crystal grains, and the carrier mobility is higher than this. It is difficult to raise it, and there is also a problem in reliability.

[0005]

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

The present invention also improves the breakdown voltage of the thin film transistor.

The first aspect of the present invention, as shown in FIG. 1 and FIG. 2 showing an example of manufacturing process thereof, an amorphous silicon thin film 2 is formed on a substrate 1 in a low temperature chemical vapor phase. A step of forming by a growth method (FIG. 1A), and irradiating the amorphous silicon thin film 2 with an ultraviolet pulsed laser light, generally an excimer laser light 3, and specifically heating it to near the melting point of the amorphous silicon. And crystallize to form the crystallized silicon thin film 4 (FIG. 1B) and the step of oxidizing the surface of the crystallized silicon thin film 4 to form the gate insulating layer 5.

The second aspect of the present invention is to form a silicon thin film 12 on a substrate 11 (FIGS. 3A and 3B) as shown in FIGS. A step of forming the silicon oxide film 13 on the silicon thin film 12 (FIG. 3C), and irradiating the silicon oxide film 13 with an ultraviolet pulse laser beam 23 in an atmosphere containing nitrogen to at least the surface of the silicon oxide film 13. And the step of forming the nitride film 14 to form the gate insulating layer 15 (FIG. 4A).

[0008]

In the first aspect of the present invention described above, the amorphous silicon thin film 2 is heated to near the melting temperature and crystallized by annealing by irradiation with the ultraviolet pulsed laser light, that is, the excimer laser light 3 to form the crystallized silicon thin film 4. Since it is formed, the crystallized silicon thin film 4 thus formed is composed of large-diameter single crystal grains having excellent crystallinity with few crystal defects in the crystal grains.

Since the crystallized silicon thin film 4 having excellent crystallinity is formed as described above, when a thin film transistor is formed on this, a highly reliable transistor can be formed.

Since the crystallized silicon thin film 4 is crystallized by heat annealing near the melting temperature of the amorphous silicon thin film 2 by irradiation with the ultraviolet pulsed laser light as described above, the gate of the transistor is gated. Although the insulating layer 5 is formed by thermally oxidizing the surface of the crystallized silicon thin film 4 as described above, no inconvenience such as impairing the crystallinity of the crystallized silicon thin film 4 occurs.

Since the gate insulating layer 5 is thus formed by the oxide film formed by oxidizing the surface of the crystallized silicon thin film 4 itself forming the transistor, the interface between the silicon thin film and the gate insulating layer 5 is formed. Is formed as an electrically excellent interface, so that the transistor formed thereby is not restricted by the characteristics of this interface.

Further, by using the gate insulating layer 5 formed by oxidizing the surface of the silicon thin film 4 as described above, the breakdown voltage between each gate and the drain and between the gate and the source is about 1.
The transistor can be set to 0 MV / cm, has higher reliability, has a large on-current, and can have a transistor with excellent weak inversion characteristics.

In the second aspect of the present invention, the silicon oxide film 13 is formed on the silicon thin film 12 formed on the substrate 11, and the silicon oxide film 13 is irradiated with ultraviolet pulsed laser light in an atmosphere containing nitrogen to form a nitride film. Since 14 forms at least the gate insulating layer 15 formed on the surface, 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 trap density. The effect of the reduction processing is also simultaneously performed.

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, 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, the substrate 11 should be an inexpensive glass substrate having a relatively low melting point. In particular, a large-area panel can be constructed at a low cost by adapting to a liquid crystal display device or the like.

[0016]

The present invention will be described in detail with reference to the drawings.

First, an example of the first aspect of the present invention will be described with reference to FIGS. As shown in FIG. 1A, a base 1 such as a quartz substrate or a Si substrate on which an insulating layer such as SiO ₂ is formed is prepared, and low temperature CVD (chemical vapor deposition) at a temperature of about 500 ° C. is formed on one main surface thereof. ) Method, eg reduced pressure CV
A silicon thin film having a thickness of, for example, 80 nm is formed by D, and Si ⁺ is ion-implanted into this to form an amorphous silicon thin film 2.

As shown in FIG. 1B, the amorphous silicon thin film 2 is entirely irradiated with ultraviolet pulsed laser light, that is, excimer laser light 3. Incidentally, the conventional use of general excimer laser light is used in a low temperature process, but in the present invention, for example, KrF (308 nm) is used.
One pulse is irradiated at 210 mJ · cm ^-2 .

At this time, the amorphous silicon thin film 2 is once heated to a temperature close to its melting point, large single crystal grains grow in the subsequent cooling process, and the crystalline silicon thin film 4 is formed.

The crystalline silicon thin film thus formed
The film 4 is, for example, dry O₂ By heating furnace at 1000 ℃
Thermal oxidation or O₂ S by annealing inside lamp
iO ₂To form the gate insulating layer 5.

Further, in some cases, as shown in FIG. 1D.
And then an atmosphere containing nitrogen such as N ₂ O or NH
₃Excimer laser such as XeCl (308
nm), for example, 0.3 J / cm³Pulsed laser light
Irradiation of several to several hundreds of pulses₂Gate insulating layer 5
A silicon nitride SiON layer 51 is formed on the surface of the
It is possible to improve the breakdown voltage and reliability of the gate insulating layer.
it can.

Next, as shown in FIG. 2A, this gate insulating layer, for example, the gate insulating layer 5 having silicon nitride 51 is formed.
Is subjected to etching by, for example, photolithography to form a desired pattern.

Then, as shown in FIG. 2B, a low-resistivity polycrystalline silicon semiconductor layer 6, for example, which covers the gate insulating layer 5 and constitutes a gate electrode, is formed by CVD or the like.

As shown in FIG. 2C, the gate electrode 7 is formed by forming the polycrystalline silicon semiconductor layer 6 into a desired pattern by selective etching such as photolithography.

Next, using this gate electrode 7 as a mask, n
Type or p type impurities are ion-implanted to form a source region or a drain region 8 to form a thin film transistor.

After that, although not shown, as usual, formation of an interlayer insulating layer, formation of Al wiring, and the like are performed to form various desired devices.

According to the method of the present invention, the amorphous silicon thin film 2 is heated to near the melting temperature and crystallized by annealing by irradiation with ultraviolet pulsed laser light, that is, excimer laser light 3 to form a crystallized silicon thin film 4. Because
The crystallized silicon thin film 4 thus formed is composed of large-diameter single crystal grains having excellent crystallinity with few crystal defects in the crystal grains.

Since the crystallized silicon thin film 4 is crystallized by heating annealing near the melting temperature of the amorphous silicon thin film 2 by irradiation with the ultraviolet pulsed laser light, as described above, the gate of the transistor is formed. Although the insulating layer 5 is formed by thermally oxidizing the surface of the crystallized silicon thin film 4 as described above, no inconvenience such as impairing the crystallinity of the crystallized silicon thin film 4 occurs.

Since the gate insulating layer 5 is thus formed by the oxide film formed by oxidizing the surface of the crystallized silicon thin film 4 itself that forms the transistor, the silicon thin film 4 and the gate insulating layer 5 are separated from each other. Since the interface is formed as an electrically excellent interface, it is possible to prevent the transistor formed thereby from being restricted by the characteristics of the interface.

Next, an example of the second invention will be described with reference to FIGS. 3 and 4.

In this example, a thin film transistor for driving a liquid crystal display device is constructed, and in this case, as shown in FIG.
As shown in A, for example, a low melting glass such as NA40
A base 11 made of a substrate such as (commercial name manufactured by Hoya Glass Co., Ltd.) or AN glass (commercial name manufactured by Asahi Glass Co., Ltd.) is prepared.
The isolation layer 16 made of SiN or the like for blocking the above is formed by plasma CVD, for example.

On top of this, a polycrystalline silicon thin film 1 is formed.
2 is formed, for example, by low pressure CVD to a thickness of about 400 Å.

As shown in FIG. 3B, the silicon thin film 12 is patterned by, for example, photolithography to finally form an island in a portion where a thin film transistor is to be formed.

As shown in FIG. 3C, this silicon thin film 1
The silicon oxide film 13 is entirely covered to cover the island 2
Is formed to a thickness of, for example, about 400 Å by CVD or the like.

Then, the surface of the silicon oxide thin film 12 is subjected to nitriding treatment by irradiation with ultraviolet pulsed laser light, that is, excimer laser light. This treatment is performed, for example, by using an excimer laser such as XeCl (308 nm), for example, 0 in an atmosphere containing nitrogen such as N ₂ O or NH _3.
By irradiating several to several hundreds of pulses of ³ J / cm ³ pulsed 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. 4A. .

As shown in FIG. 4B, a low resistivity polycrystalline silicon film 16 is formed on the entire surface by CVD or the like.

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

After that, although not shown, as usual, the formation of the interlayer insulating layer and the formation of the Al wiring and the like are carried out to construct various desired devices.

According to the second method of 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. Since the nitride film 14 forms the gate insulating layer 15 formed at least on the surface, the dense gate insulating layer 15 without pinholes is formed, and the laser annealing improves the crystallinity of the silicon thin film 12, that is, At the same time, the effect of reducing the trap density is achieved.

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, the substrate 11 can be a glass substrate having a relatively low melting point. .

[0041]

As described above, according to the first aspect of the present invention, the crystallized silicon thin film 4 is formed by the large-diameter single crystal grains having excellent crystallinity with few crystal defects in the crystal grains. Since the transistor is formed on the crystallized silicon thin film 4 having excellent crystallinity as described above, a highly reliable transistor can be formed.

Since the gate insulating layer 5 is formed by an oxide film formed by oxidizing the surface of the crystallized silicon thin film 4 itself forming the transistor, the interface between the silicon thin film and the gate insulating layer 5 is electrically conductive. Since it can be formed as an excellent interface and the withstand voltage can be improved, a transistor with high reliability, high gate-drain, gate-source withstand voltage, large on-current, and excellent weak inversion characteristics can be obtained. Can be configured.

In the second aspect of the present invention, the silicon oxide film 13 is formed on the silicon thin film 12 formed on the substrate 11, and the silicon oxide film 13 is irradiated with ultraviolet pulsed laser light in an atmosphere containing nitrogen to form a nitride film. 14 forms at least a gate insulating layer 15 formed on the surface to form a dense gate insulating layer 15 without pinholes and the like, and this laser annealing improves the crystallinity of the silicon thin film 12, that is, the trap density. Since the silicon thin film 12 having excellent withstand voltage, high reliability and hot carrier resistance and excellent crystallinity can be formed, it is possible to form a highly reliable transistor. it can.

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

[Brief description of drawings]

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

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

FIG. 3 is a process diagram (1) of another example of the method of the present invention.

FIG. 4 is a process diagram (2) of another example of the method of the present invention.

[Explanation of symbols]

 1 Base 2 Amorphous Silicon Thin Film 3 Ultraviolet Pulse Laser Light 4 Crystallized Silicon Thin Film 5 Gate Insulating Layer 11 Base 12 Silicon Thin Film 12 13 Silicon Oxide Film 14 Nitride Film 15 Gate Insulating Layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 29/784

Claims (2)

[Claims] 1. A step of forming an amorphous silicon thin film on a substrate by a low temperature chemical vapor deposition method, and crystallization by irradiating the amorphous silicon thin film with ultraviolet pulsed laser light to obtain a crystallized silicon thin film. And a step of forming the gate insulating layer by oxidizing the surface of the crystallized silicon thin film. 2. A step of forming a silicon thin film on a substrate, a step of forming a silicon oxide film on the silicon thin film, and irradiating the silicon oxide film with ultraviolet pulsed laser light in an atmosphere containing nitrogen. And a step of forming a gate insulating layer by forming a nitride film on at least the surface of the silicon oxide film.