JP2001345450A - Manufacturing method of thin-film semiconductor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To overcome the defect that in a thin-film semiconductor element the moisture contained in a gate insulation film so reacts on W of the material of a gate electrode film as to generate thereby the change of the characteristic of a transistor in the negative direction thereof and damage its reliability. SOLUTION: A process for removing by the projection of a microwave the moisture contained in the gate insulation film of a transistor is introduced to prevent thereby the change of its characteristic.

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 semiconductor device used for a semiconductor integrated circuit, a liquid crystal display device and the like.

[0002]

2. Description of the Related Art When a polycrystalline silicon thin film transistor is used in an active matrix type liquid crystal display device, a transistor array and peripheral circuits can be integrated. The integration of the peripheral circuit realizes high-definition image display and enables low-cost manufacturing.

Since the performance of a polycrystalline silicon thin film transistor is closely related to the driving characteristics of peripheral circuits, higher performance is expected.

[0004] Referring to FIG.
The problem of the conventional method for creating this will be described. In the thin film transistor, a base film 8, a polycrystalline silicon semiconductor film 2, a gate insulating film 3, a gate electrode film 4, an interlayer insulating film 5, source and drain electrodes 6, 7 are formed in this order on a surface of a substrate 1 such as quartz or glass. It is laminated. The base film 8 is formed for the purpose of preventing the constituent components of the substrate 1 from diffusing into the polycrystalline silicon semiconductor film 2, but may not be formed depending on the material of the substrate 1 or the method of processing the substrate.

The material of the gate insulating film 3 is often silicon oxide or silicon nitride. Film formation is performed using a CVD apparatus. The gate insulating film can be formed by either thermal CVD or plasma CVD. However, in the process of manufacturing a polycrystalline silicon transistor, plasma CVD is often used because it is desirable to lower the process temperature. The gate electrode film 4 is required to have low resistance in order to prevent signal delay and to withstand a heat treatment at 500 to 600 ° C. performed for activating phosphorus and boron impurities implanted by doping. An alloy of Mo and W is known as a material that achieves both low resistance and heat resistance stability (electrode wiring material and electrode wiring board using the same (Japanese Patent Application Laid-Open No. 8-153722)).

[0006]

When silicon nitride is used as the gate insulating film 3, the initial characteristics of the thin film transistor are often insufficient. This is considered to be due to the large amount of fixed charges in the film in the current technology. On the other hand, when silicon oxide is used as the gate insulating film, there is a problem in reliability if the film is formed under conditions with good initial characteristics, and conversely, if the film is formed under conditions with high reliability, the initial characteristics are insufficient. The relationship is inevitable.

The present inventors have conducted a high-temperature voltage application test (BT
Test), the reliability of the semiconductor thin film element was evaluated. The high-temperature voltage application test is a method in which the source and drain of a thin film transistor are grounded at 85 ° C., and a voltage of 30 V is applied to the gate to measure the time variation of transistor characteristics. Then, in a thin film semiconductor device using an alloy of Mo and W as a material of a gate electrode film, it has been found that the reliability of the thin film transistor is greatly affected by the amount of moisture contained in the gate insulating film. FIG. 4 shows test results of the high-temperature voltage application test. As can be seen from FIG. 4, in the thin-film semiconductor element using the gate insulating film a with a large amount of moisture, a change in the transistor characteristics in the negative direction (shift of the threshold voltage Vth of the thin film transistor) is observed, and the gate insulating film with a small amount of moisture In the film b, there is almost no change. This fluctuation in the negative direction is caused by the reaction of water contained in the gate insulating film with W, which is a material of the gate electrode film.

Although the amount of water in the gate insulating film varies depending on the film forming conditions of the gate insulating film, there is a problem that under the film forming conditions in which the amount of water is reduced, process damage occurs during film formation and the initial characteristics of the transistor are impaired. Is generated.

In order to integrate a transistor array and a peripheral circuit using a polycrystalline silicon thin film transistor,
It is important to achieve both good initial characteristics and stable transistor characteristics.

Accordingly, the present invention provides a method for forming a gate insulating film under film forming conditions that does not impair the initial characteristics of a transistor.
Thereafter, by removing water in the gate insulating film by a method that does not impair the initial characteristics, the reaction between W and water constituting the gate electrode film is prevented, and a highly reliable thin film semiconductor device is realized. With the goal.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and is characterized by having a process for removing moisture in a gate insulating film.

The first aspect of the present invention is characterized in that a step of irradiating the gate insulating film with electromagnetic waves having a frequency of 2.4 GHz to 2.5 GHz is provided.

By having the above steps, the thermal energy of the water molecules in the gate insulating film is increased and the thermal diffusion is promoted, so that the water molecules in the gate insulating film are effectively removed.
A highly reliable thin film semiconductor element can be realized.

In a second aspect of the present invention, a substrate comprises:
After adhering a heating plate that absorbs at least a part of a light beam having a wavelength of 0.2 μm to 5.0 μm, a step of irradiating the heating plate with light having the above wavelength to heat the gate insulating film is provided. I have.

With the above steps, the heating plate and the semiconductor film are heated by the energy of the irradiated light beam, and the gate insulating film is heated by heat conduction. According to this method, in addition to the heating plate generating heat, the semiconductor film adjacent to the gate insulating film generates heat, so that the gate insulating film can be heated effectively in a short time, and Water molecules are effectively removed, and a highly reliable thin film semiconductor element can be realized.

In the second aspect of the present invention, it is desirable that the light source of the irradiated light beam is a halogen lamp.

By using the above-mentioned light source, the wavelength becomes 0.1.
A light beam of 2 μm to 5.0 μm can be efficiently obtained, and the gate insulating film can be effectively heated by a small device.

In the present invention, it is preferable that the gate insulating film is a silicon oxide film formed with a mixed gas of TEOS and O ₂ using a plasma CVD apparatus.

By performing the above-described step of removing water by using the above-mentioned gate insulating film, a dense and high-quality gate insulating film having a small water content can be obtained.

[0020]

Next, a specific example of the present invention will be described.

In the thin film semiconductor device according to the present invention, a gate insulating film made of silicon oxide is formed under conditions that improve the initial characteristics, and then the gate of the thin film semiconductor device is manufactured by a method that does not impair the initial characteristics of the thin film semiconductor device. By removing moisture contained in the insulating film, a highly reliable thin film semiconductor device is realized.

(Embodiment 1) A first embodiment of the present invention will be described with reference to FIGS.

The structure of the thin-film semiconductor device according to this embodiment will be described. The configuration of the thin-film semiconductor device manufactured by the method according to the present embodiment is substantially the same as that of the thin-film semiconductor device shown in FIG. 3 in "Prior Art", and thus the configuration will be described with reference to FIG. In the present embodiment, as the substrate 1,
A 1737 glass substrate from Corning was used. As the polycrystalline silicon semiconductor film 2, amorphous silicon (a
A film obtained by polycrystallizing -Si) using an excimer laser was used. As the gate insulating film 3, an SiO ₂ film having a thickness of about 90 nm by plasma CVD using a mixed gas of TEOS (tetraethyl orthosilicate) and O ₂ was used. As the gate electrode film 4, Mo and W of about 300 nm are used.
An alloy film prepared by sputtering was used. As the interlayer insulating film 5, a film obtained by forming a 400 nm SiO ₂ film by plasma CVD using a mixed gas of TEOS and O ₂ was used. As the source electrode 6 and the drain electrode 7, those obtained by sputtering a two-layer film of Ti and Al to have a thickness of 100 nm and 600 nm, respectively, were used. The base film 8 is made of 400 nm SiO 2 by plasma CVD using a mixed gas of TEOS and O _2.
What produced two films was used.

[0024] Note that the thin film semiconductor device, further a polycrystalline silicon film on the n + doped layer and p + doped layer, although formed like protective film composed of the SiN _x film on the surface, in FIG since unnecessary for the description of the present invention Is not shown.

In the thin-film semiconductor device having such a configuration, the gate insulating film 3 is formed, and after the gate electrode 4 is cleaned before being formed, it is put into a chamber and reduced in pressure. The reduced pressure is effective for promoting the desorption of moisture from the surface of the gate insulating film 3. As shown in FIG.
The gate insulating film 3 is irradiated with a microwave 9 of 2.5 GHz with a power of 400 W or more, preferably 1000 W or more. Heating of water molecules by dielectric loss is possible even by irradiation of electromagnetic waves of 1 MHz to 2.4 GHz.
Since the microwave 9 of 4 to 2.5 GHz substantially corresponds to the resonance frequency of water molecules, the energy of the irradiated microwave 9 is efficiently converted to heat energy. Microwave 9
The heat energy given by the irradiation promotes the diffusion of water molecules in the gate insulating film 3 and contributes to the removal of water. According to the experiments of the present inventors, the result is that the moisture in the gate insulating film 3 is reduced to 50% or less as compared with a sample not subjected to the treatment. Irradiation of the microwave 9 of 2.4 to 2.5 GHz has a high rate of conversion into thermal energy in a place with moisture, so that heating of unnecessary parts can be reduced. As a result, more efficient heating can be realized. Efficient heating is effective in shortening the cycle time of the process.

In order to prevent reabsorption of water after the treatment, storage after the treatment until the gate electrode film 4 is formed is performed in a low-humidity environment such as dry nitrogen gas. It is desirable. Further, if the heat treatment step and the film formation step of the gate electrode film 4 are continuously performed in a vacuum system, it is possible to further reduce water absorption.

Conventionally, the reliability of a thin film semiconductor device has been impaired due to the reaction between water in the gate insulating film and W in the gate electrode film. However, by introducing the process steps of the present invention, the moisture in the gate insulating film can be reduced. Is removed, and a highly reliable thin film semiconductor element can be realized.

(Embodiment 2) A second embodiment of the present invention will be described with reference to FIGS. The configuration of the thin-film semiconductor device manufactured in this embodiment is substantially the same as that of the thin-film semiconductor device described in Embodiment 1 shown in FIG. 3 under the same conditions except for a process for processing the gate insulating film. Produced.

The processing on the gate insulating film was performed as follows.

After forming the gate insulating film 3 and performing cleaning before forming the gate electrode 4, it is placed in a chamber and reduced in pressure.
Although the pressure reduction is not always necessary, it is effective to promote the desorption of moisture from the surface of the gate insulating film 3 as in the first embodiment. In the chamber, as shown in FIG. 2, the substrate 1 is clamped on a heating plate 10 that absorbs light having a wavelength of 0.2 μm to 5.0 μm, such as silicon nitride ceramics and aluminum oxide ceramics. An inert gas may be filled between the heating plate 10 and the substrate 1 for the purpose of improving heat conduction. A halogen lamp 11 is suitable as a light source. When a light beam 12 having a wavelength of 0.2 μm to 5.0 μm is applied to the gate insulating film 3, the light beam 12 is hardly absorbed by the gate insulating film 3 itself, but is absorbed by the heating plate 10 and the polycrystalline silicon semiconductor film 2. Converted to heat. Gate insulating film 2 is indirectly heated by conduction heat from heated heating plate 10 and polycrystalline silicon semiconductor film 2. Although indirect heating is performed, by performing the heating by the above-described method, the heat capacity of the heating unit can be reduced as compared with the case where heating is performed by a heater provided outside, and efficient heating is realized. By heating the gate insulating film 3, the diffusion of the water in the gate insulating film 3 is promoted, and the water is effectively removed.

Conventionally, the reliability of a thin film semiconductor device has been impaired due to the reaction between water in the gate insulating film and W in the gate electrode film. However, by introducing the process steps of the present invention, the moisture in the gate insulating film can be reduced. Is removed, and a highly reliable thin film semiconductor element can be realized.

[0032]

As described above, according to the present invention, the water in the gate insulating film can be effectively removed, and the transistor generated by the reaction between the water in the gate insulating film and W in the gate electrode film. Variations in characteristics in the negative direction are prevented, and a highly reliable thin film semiconductor device can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a heat treatment step according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of a heat treatment step according to a second embodiment of the present invention.

FIG. 3 is a structural diagram of a thin film semiconductor device.

FIG. 4 is a diagram showing test results of a high-temperature voltage application test.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Polycrystalline silicon semiconductor film 3 Gate insulating film 4 Gate electrode film 5 Interlayer insulating film 6 Source electrode film 7 Drain electrode film 8 Base film 9 Microwave 10 Heating plate 11 Halogen lamp 12 Light beam

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01L 21/316 H01L 29/78 617V 617M F term (Reference) 4K029 AA06 AA24 BA02 BA03 BA11 BA17 BA21 BB02 BC03 BD01 CA05 4K030 AA11 AA14 BA29 BA44 BB12 CA04 CA12 DA08 FA01 FA10 HA03 JA18 KA23 5F058 BA07 BB04 BB07 BC02 BF07 BF25 BF29 BH17 BH20 BJ10 5F110 AA30 BB01 CC02 DD02 DD13 EE06 EE44 FF02 FF30 NN23 FF30 FF13 GG02

Claims (6)

[Claims] A step of forming a semiconductor film made of polycrystalline silicon on a substrate, a step of forming a gate insulating film made of silicon oxide on the semiconductor film, and applying a frequency to the gate insulating film, the semiconductor film and the substrate. 2.4 GHz to 2.5
A method for manufacturing a thin film semiconductor device, comprising at least a step of irradiating an electromagnetic wave of GHz. 2. A step of forming a semiconductor film made of polycrystalline silicon on a substrate, a step of forming a gate insulating film made of silicon oxide on the semiconductor film, and a step of forming the gate insulating film and the semiconductor film on which the semiconductor film is formed. 0.2 μm as light wavelength
A heating plate that absorbs at least a part of the thickness of the thin film semiconductor element at least partially within a range of from 5.0 to 5.0 μm, and then irradiating the heating plate with light of the wavelength to heat the gate insulating film. . 3. The method according to claim 2, wherein the light source of the light beam is a halogen lamp. 4. A plasma CVD apparatus wherein said gate insulating film is a plasma CVD apparatus.
TEOS and O using _TwoOxide film formed with mixed gas of
3. The film according to claim 1, wherein the film is a film.
The method for manufacturing the thin film semiconductor device described above. 5. The method of manufacturing a thin-film semiconductor device according to claim 1, further comprising a step of forming a gate electrode made of an alloy containing W on said gate insulating film. 6. The method according to claim 5, wherein the gate electrode is made of an alloy of W and Mo.