JP2003151974A - Photo-oxidation method, method of manufacturing semiconductor device using the same, photo-oxidation apparatus and apparatus for manufacturing semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a photo-oxidation method for effectively forming an insulation film by suppressing generation of interface level and fixed charges or the like under lower temperatures, and also provide a method of manufacturing a semiconductor device using the same and a photo-oxidation apparatus. SOLUTION: A substrate 6, on which the Si film is formed, is set into a vacuum chamber 2, it is then heated with a lamp heater 7 under evacuation conditions. Moreover, the substrate 6 is then exposed to a gas, having the oxidation property containing oxygen and rare gas and is irradiated with ultraviolet radiation 5 emitted by a lamp 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to, for example, a polysilicon T in a MOS type silicon thin film transistor (TFT) for a liquid crystal display manufactured on an insulating substrate.
The present invention relates to a manufacturing apparatus and a manufacturing method of an insulating film formed in contact with a semiconductor layer in an FT manufacturing process.

[0002]

2. Description of the Related Art Conventionally, a thin film transistor (TFT) having a MOS transistor formed on a glass substrate or a silicon wafer has been manufactured. The TFT is used as a switching element for a picture element of a liquid crystal display, a driver, or a switching element of a semiconductor memory. As a product using the above TFT, TF
Many T-type liquid crystal displays and integrated circuits are produced. Many MOS type silicon TFTs are included in these products.
Is used, the performance of each TFT is greatly related to the performance of the product itself. The performance of these TFTs can be improved by improving the density and insulating property of the gate insulating film in the TFT.

In the above-mentioned products, amorphous silicon TFTs have been mainly used as TFTs in the field of manufacturing TFT type liquid crystal displays, but recently, polysilicon TFTs, which are used to collectively form a driver on a glass substrate, have been used. Came to be.

Among the polysilicon TFTs used in liquid crystal displays, those in which a quartz substrate is used as a glass substrate and TFTs are formed thereon are high temperature polysilicon TFTs.
Is manufactured in the IC and LSI lines.

On the other hand, a non-alkali glass is used for the glass substrate and a polysilicon TFT is formed on it.
It is called a low temperature polysilicon TFT, and the process temperature is 60.
Manufactured below 0 ° C. At present, as a gate insulating film of a polysilicon TFT, an SiO ₂ -based insulating film is formed by a plasma CVD method at a temperature of 300 ° C to 500 ° C.

As mentioned above, these polysilicon TFs are
In the manufacturing process of T, the gate insulating film has conventionally been formed by deposition. However, the gate insulating film is formed by deposition after exposing the island-shaped silicon film (polysilicon film) to the atmosphere. Therefore, even if the silicon film is washed immediately before the gate insulating film is formed, impurities are likely to be adsorbed on the surface of the silicon film.
Due to the contamination of the silicon-insulating film interface by the impurities and the electric charge of the gate insulating film, the interface state density and the fixed charge density exist at the interface between the polysilicon film which is the semiconductor film and the gate insulating film. Has become. TFT
If these interface state densities and fixed charge densities are large, the TFT will be inferior in current-voltage characteristics and subthreshold slope.

That is, the presence of a large interface state density and a fixed charge density has been an obstacle to the formation of a TFT having excellent characteristics.

[0008]

As a means for forming a silicon oxide film (SiO ₂ film) as a gate insulating film capable of improving the above-mentioned interface state and fixed charge, there is IC.L.
There is an oxide film formation by the thermal oxidation method as used in SI. This thermal oxidation method forms a SiO ₂ film by oxidizing the Si film at a high temperature of 800 ° C. to 1000 ° C. The SiO ₂ film formed by this method has a composition ratio of silicon (Si) and oxygen (O) close to an ideal value of 1: 2, and it is easy to obtain a normal silicon film-gate insulating film interface. However, since the alkali-free glass used in the low-temperature polysilicon TFT has a strain point of about 650 ° C., it has no resistance to the thermal oxidation method and cannot be used.

Further, Japanese Patent Laid-Open No. 11-97713 discloses an attempt to form a SiO ₂ film at a low temperature of 600 ° C. or lower. This is intended to form a SiO ₂ film by irradiating light having a wavelength of 4 μm to 0.5 μm or ultraviolet light in an oxidizing atmosphere to oxidize the surface of the Si film. However, since the oxidizing atmosphere is mainly oxygen, if an oxide film having a thickness of 5 nm or more is to be obtained, mass productivity (manufacturing efficiency) can be provided because of low throughput. could not.

The present invention has been made in view of the above conventional problems, and an object thereof is, for example, a low temperature silicon TFT.
, A photooxidation method capable of efficiently forming an insulating film in which generation of interface states, fixed charges, etc. is suppressed at low temperature, a method for manufacturing a semiconductor device using the same, a photooxidation device, and a semiconductor An object is to provide a device manufacturing apparatus.

[0011]

The photooxidation method of the present invention comprises:
In order to solve the above-mentioned problems, an object to be oxidized is heated under reduced pressure, further exposed to an oxidizing gas containing oxygen and a rare gas, and irradiated with ultraviolet light.

According to the above arrangement, the rare gas is excited by irradiating it with ultraviolet light under reduced pressure. Then, the excited rare gas transfers excitation energy to oxygen molecules to generate oxygen atom radicals.
Since this oxygen atom radical has high reactivity, the object to be oxidized can be quickly oxidized. That is, the rate of photooxidation can be increased.

The wavelength of the ultraviolet light is 120 ± 10.
It is preferably nm. Further, the oxidizing gas is
It is preferable that the oxygen content is 5% to 15% and the rare gas content is 85% to 95%. The rare gas is preferably krypton. According to the above configuration, the rate of photooxidation can be further increased.

Further, the photooxidation method of the present invention is carried out at 100 ° C.
It is preferable to heat to a temperature of 400 ° C.

The method of manufacturing a semiconductor device according to the present invention uses SiO.
_A method of manufacturing a semiconductor device having an insulating film composed of _{2 is characterized in} that the insulating film is manufactured by photooxidizing a Si film by the photooxidation method.

According to the above structure, since the Si film is photo-oxidized, there is no fear that impurities or the like will remain between the Si film and the formed SiO ₂ film. Therefore, the interface state density and the fixed charge density at the interface between the Si film and the SiO ₂ film can be suppressed. As a result, a semiconductor device having excellent current-voltage characteristics can be manufactured. Further, a dense and uniform insulating film can be formed. Also,
Since the above photo-oxidation method is used, throughput can be increased and mass productivity can be improved.

The photo-oxidizing apparatus of the present invention is a photo-oxidizing apparatus for photo-oxidizing an object to be oxidized, wherein the object to be oxidized is exposed to an oxidizing gas containing a rare gas and oxygen under reduced pressure. A heating device for heating the object to be oxidized and an ultraviolet irradiation device for irradiating the object to be oxidized with ultraviolet light are provided.

With the above arrangement, the rare gas is excited by irradiating it with ultraviolet light under reduced pressure. Then, the excited rare gas transfers excitation energy to oxygen molecules to generate oxygen atom radicals.
Since this oxygen atom radical has high reactivity, the object to be oxidized can be quickly oxidized. That is, it is possible to provide a device having a high photooxidation rate.

The semiconductor device manufacturing apparatus of the present invention is made of SiO.
An apparatus for manufacturing a semiconductor device having an insulating film composed of ₂ is characterized by including the photo-oxidizing device for photo-oxidizing a Si film to form the insulating film.

According to the above structure, since the Si film is photo-oxidized, there is no fear that impurities or the like will remain between the Si film and the formed SiO ₂ film (insulating film). Therefore, the interface state density and the fixed charge density at the interface between the Si film and the SiO ₂ film (insulating film) can be suppressed. As a result, it is possible to provide a device capable of manufacturing a semiconductor device having excellent current-voltage characteristics. Further, with the above apparatus, a dense and uniform insulating film can be formed.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION A photo-oxidizing apparatus according to one embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1, the photo-oxidizing device includes a lamp (ultraviolet light irradiating device) 1, a vacuum chamber (decompression chamber) 2
Is equipped with. A lamp heater (heating device) 17 is provided in the vacuum chamber 2. Further, in the vacuum chamber 2, there is provided an installation table 4 on which an object to be photooxidized such as a substrate 6 having a Si film formed thereon is installed.

The photooxidation method of the Si film (oxidation target) on the substrate 6 on which the Si film is formed in the photooxidation apparatus will be described below.

First, the substrate 6 is placed in the vacuum chamber 2. The substrate 6 is installed on the installation table 4 in the vacuum chamber 2. Then, the inside of the vacuum chamber 2 is depressurized, and the substrate 6 is heated by the heater 3. Then, while the oxidizing gas is flown into the vacuum chamber 2, the ultraviolet light 5 is emitted from the lamp 1 to the substrate 6.
Of Si formed on the substrate 6 by irradiating
Photooxidize the film.

The oxidative gas contains oxygen (O ₂ ) gas and rare gas. The volume ratios of the O ₂ gas and the rare gas are O ₂ gas: 5% to 15% and rare gas: 85% to 95%.
Is preferred. Furthermore, of the above oxidizing gases,
Oxidizing gas of O ₂ gas: 10% and Kr gas: 90% is more preferable, and a high-quality (dense and uniform thickness) SiO ₂ film having the fastest oxidation rate was obtained. When this oxidizing gas was used, a SiO ₂ film having a thickness of 15 nm was formed in 30 minutes.

The above-mentioned lamp 1 may be any one as long as it can emit ultraviolet light having a wavelength capable of exciting a rare gas, and a dielectric barrier discharge excimer lamp commercially available from a lamp manufacturer may be used. In the dielectric barrier discharge excimer lamp, a dielectric made of a quartz glass tube is provided between two metal electrodes. A discharge gas is filled in the quartz glass tube. Then, when a rare gas is filled as a discharge gas and a predetermined voltage is applied between the metal electrodes, ultraviolet light 5 is generated. The filling gas that emits light having a wavelength suitable for the rare gas assisted photooxidation of the present invention is argon (Ar). Argon has a radiation level at 126 nm, as can be seen from the emission spectrum (spectral radiation distribution) of argon shown in FIG.

The large size of the substrate 6 is 10
It is also possible to make it about 00 mm square. Moreover, it is preferable that the substrate 6 is heated to 100 ° C. to 400 ° C. by the heater 3.

It is preferable to irradiate the ultraviolet light 5 from the direction of the surface of the substrate 6 on which the Si film is formed. The light intensity of the ultraviolet light 5 is about 5 mW / cm ² at present, but a higher light intensity is preferable because the oxidation rate can be further accelerated. It is expected that the light intensity of the lamp will be 5 mW / cm ² or more due to further improvement in the manufacturing technology of the dielectric barrier discharge excimer lamp (vacuum ultraviolet light excimer lamp) in the future. Further, the oxidation pressure (pressure in the vacuum chamber 2) is preferably 5 Pa to 300 Pa.

The above-mentioned photo-oxidizing apparatus (photo-oxidizing method) is preferably used for photo-oxidizing a Si film into a SiO ₂ film at a low temperature (for example, 100 ° C. to 400 ° C.). Therefore, the above-mentioned photo-oxidation device (photo-oxidation method) includes a thin film transistor (T
FT), thin film diode (TFD), and thin layer integrated circuit using them, particularly an insulating film in a semiconductor device such as an active liquid crystal display device (eg, thin layer transistor type liquid crystal display, thin layer transistor type organic EL display) Can be preferably used for forming a SiO ₂ film as

A polysilicon TFT manufactured by using the photo-oxidation method of the present invention will be described with reference to FIG.

Hereinafter, as shown in FIG. 2, a coplanar type (top gate type) polysilicon TFT most commonly used in low temperature polysilicon TFTs will be described as an example. The low-temperature polysilicon TFT is first formed on the substrate 10 by the undercoat film 1 by, for example, a plasma CVD method.
1 is formed. Examples of the material of the substrate 10 include glass, and non-alkali glass can be used.

Next, a polysilicon film channel 12 is formed on the undercoat film 11. The method of forming the polysilicon film channel 12 is as follows. First,
For example, the undercoat film 1 is formed by the plasma CVD method.
A silicon film is formed on 1. Then, a polysilicon film is formed by a polycrystallizing step of the silicon film. This polycrystallization step is preferably performed by laser crystallization. This laser crystallization is performed by irradiating a silicon film with a laser, melting and solidifying the film to crystallize it. Then, the polysilicon film channel 12 is formed by patterning the island of the polysilicon film.

The thickness of the polysilicon film channel 12 is 30 nm to 200 nm. The laser used for laser crystallization is preferably an excimer laser, and more preferably a XeCl wavelength of 308 nm. The irradiation energy density of this laser light is 300 mJ / cm ^{2 to} 500 per shot.
It is mJ / cm ² .

Next, the undercoat film 11 and the policy
Form gate insulating film 13 on recon film channel 12
It The gate insulating film 13 is the first-layer gate insulating film 13
a and the second-layer gate insulating film 13b. Traditionally
As a gate insulating film on the polysilicon channel
The first-layer gate insulating film and the second-layer gate insulating film of
It was formed by being deposited. On the other hand
In this embodiment, the silicon film (poly
(Including the silicon film channel 12).
The first layer gate film on the polysilicon film channel 12.
(Silicon oxide (SiO ₂) Forming a film). Above photo-oxidation
Is performed under reduced pressure.

The photooxidation method used for forming the first-layer gate insulating film 13a will be described below. The photo-oxidation method includes a step of placing the substrate 10 on which a polysilicon film (including the polysilicon film channel 12) is formed under reduced pressure, a step of contacting the polysilicon film with an oxidizing gas and an irradiation of ultraviolet rays. is doing. This allows
Si of the polysilicon film is oxidized to SiO ₂ . This oxidation proceeds to the inside of the polysilicon film, and a SiO ₂ film is formed on the polysilicon film. Therefore, no deposits remain on the interface (semiconductor-insulator interface) between the polysilicon film and the SiO ₂ film.

In the above-mentioned photo-oxidation method, the oxidation rate and the case where O ₂ alone is brought into contact with the oxidizing gas and the oxidizing gas consisting of the rare gas and O ₂ are brought into contact with each other,
The interface state density and the fixed charge density existing at the interface between the gate insulating film and the Si film are significantly different.

In this embodiment, the oxidizing gas is O
_A mixed gas of ₂ and a rare gas is used. Energy is given to the atoms of the rare gas by ultraviolet light, and electrons are temporarily excited (for example, 9.9 eV in the case of Kr).
O ₂ molecules are dissociated by passing energy from the excited rare gas atoms to become O atom radicals in the O1D state (“Low Temperature Oxidation”).
of Silicon (100) Substrates Using Atomic Oxygen ",
Tomo Ueno et al. Mat. Res. Soc. Symp. Proc. Vol. 5
92 (2000), pp.239-243). Then, the O atom radicals react with Si of the silicon film to generate SiO ₂ . Since the O atom radical is highly reactive,
The rate of oxidation of Si to SiO ₂ in the silicon film can be further increased. As described above, it is preferable to use a gas in which O ₂ and a rare gas are mixed as the oxidizing gas. The wavelength of the ultraviolet light is 120 nm.
± 10 nm is preferable. As described above, in the photooxidation method of the present invention, photooxidation is performed with the aid of the excitation energy of the rare gas. This photooxidation method will be referred to as a rare gas assisted photooxidation method.

Next, a second layer gate insulating film which is a SiO ₂ type insulating film is formed on the first layer gate insulating film by the plasma CVD method. The formation of this second layer gate insulating film is also
Perform under reduced pressure. The thickness of the gate insulating film 13 (laminated structure gate insulating film) is, for example, a first layer gate insulating film thickness of 3 to 10 nm, and a second layer gate insulating film thickness of 30 to
It is 150 nm.

Next, the gate electrode 14 is formed on the gate insulating film 13 (laminated structure gate insulating film). The gate electrode 14 is formed, for example, by forming a conductor film on the gate insulating film 13 by a sputtering method or the like and patterning the conductor film.

Next, the ohmic layer (n ⁺ type Si portion 16
Alternatively, the p ⁺ type Si portion 17) is formed. This ohmic layer is formed by adding an impurity capable of imparting n ⁺ type or p ⁺ type to a part of the polysilicon film channel 12 by, for example, an ion doping method using the gate electrode 14 as a mask.

Next, an interlayer insulating film 18 is formed, and contact holes with the ohmic layer (n ⁺ type Si portion 16 or p ⁺ type Si portion 17) are opened. Then, the source metal 19 or the drain metal 20 is formed in this contact hole. Then, a passivation film 21 is formed on the interlayer insulating film 18, the source metal 19 and the drain metal 20. After that, a passivation film contact hole is opened, and the transparent electrode film 22 is formed in this passivation contact hole. As a result, a polysilicon TFT is formed.

The detailed conditions in each step after forming the gate electrode 14 are as follows.

The gate electrode 14 may be formed by the DC sputtering method or the like. As the electrode material (target), Al
-A conductor such as a Ti alloy is used. Then, the conductor film is, for example, pressure: 4 Pa, Ar gas: 50 sccm, power:
A film having a thickness of 300 nm is formed under the condition of 0.75 W / cm ² . Then, the gate electrode 14 is formed by etching the conductor film. For the etching of the conductor film, for example, a lithography method may be used. Line width 3 μm
If the lithography is more than a degree, phosphoric acid, glacial acetic acid,
This is performed by heating the mixed solution of nitric acid to about 50 ° C. Also, line width 3
When the lithography is about μm or less, etching is performed by a dry etching method using a chlorine-based gas.

Ohmic layer (n ⁺ type Si portion 16 and p ⁺
The type Si portion 17) may be formed by an ion doping method. To form the n ⁺ type Si portion 16, for example, PH ₃ (phosphine) gas is used as a doping gas. At the time of doping, H ₂ is used as phosphine gas.
About 5 sccm of 0.1% diluted phosphine gas and 50 sccm of H ₂ gas are passed. Then, the pressure is adjusted to about 0.3 Pa, and doping is performed by discharging with an appropriate RF power. At this time, for example, the acceleration voltage is 30 k
At V, the dose amount is about 1 × 10 ¹⁵ cm ^-2 . Also,
To form the p ⁺ type Si portion 17, for example, B ₂ H ₆ (diborane) gas is used. During doping, as this diborane, H ₂ dilution of diborane 5 sccm, H ₂
A gas of about 50 sccm is passed. And the pressure is 0.3P
Doping is performed by adjusting to about a and discharging with an appropriate RF power. At this time, the acceleration voltage is 30 kV and the dose amount is about 1 × 10 ¹⁵ cm ^-2 .

The interlayer insulating film 18 is formed by PECVD method.
You can do more. As the source gas, for example, TEOS
(Tetra Ethyl Ortho Silicate) Gas and O₂Mixing with gas
Use mixed gas. When forming the interlayer insulating film 18, TE
OS gas 20sccm, O ₂About 500 sccm of gas
Flow once. At this time, the temperature is 300 ° C. and the RF power is 0.
5 W / cm²To discharge. Thereby, the interlayer insulating film 1
SiO as 8₂Form a system insulation film of about 300 nm
It

The contact holes may be opened by dry etching using CHF ₃ gas or the like.

Source metal 19 and drain metal 2
The formation of 0 may be performed in the same manner as the gate electrode. However, the source metal 19 and the drain metal 20
Is a multilayer film in which a barrier metal such as Ti is formed to a thickness of about 50 nm in the first layer so as not to contact the Si film (polysilicon channel 3), and a conductor layer such as aluminum is formed thereon.

The passivation film 21 is formed by PEC.
The VD method may be used. As the source gas, for example, S
A mixed gas of iH ₄ , NH ₃ and N ₂ gas is used. And
A SiN film as the passivation film 21 is formed from this mixed gas by PECVD to a thickness of about 300 nm. Moisture resistance can be enhanced by the passivation film 21.

To form the transparent electrode film 22, first, a passivation film is opened, and an ITO film is formed in the opening by, for example, a sputtering method using an ITO target.
Etching is performed. The passivation film opening may be performed by etching with a 1:10 BHF solution, for example.
The etching of the ITO film is performed by ferric chloride solution or
It may be performed using a thin BHF solution of 1: 100.

In the above description, an example in which both the N-channel MOS and the P-channel MOS are manufactured for the low temperature polysilicon TFT has been described, but only one of them may be manufactured.

Next, the first gate insulating film 13a and the second gate insulating film 1 in the above-mentioned low temperature polysilicon TFT.
A film forming apparatus for forming the gate insulating film 13 (see FIG. 2) made of 3b will be described with reference to FIG. Hereinafter, a case where the SiO ₂ film (insulating film) is formed using the substrate 6 on which the Si film is formed will be described.

As shown in FIG. 4, the film forming apparatus includes a photo-oxidizing chamber 30, a transfer chamber 31, and a CVD film forming chamber 32. In addition, each of the above-mentioned chambers (photooxidation chamber 30, transfer chamber 31, CV)
The D film forming chambers 32) are connected to each other by a transfer path, and are independent from each other by opening and closing partitions. Further, each chamber can be depressurized.

The photo-oxidizing chamber 30 has the same structure as the photo-oxidizing device (see FIG. 1) and includes a lamp 1 and a heater 3. In this photo-oxidation chamber 30, the loaded substrate 6
The Si film is oxidized to form a SiO ₂ film (which will become the first layer gate insulating film).

The transfer chamber 31 is connected to the CV from the photooxidation chamber 30.
It is provided to transfer the substrate 6 to the D film forming chamber 32.

The CVD film forming chamber 32 is provided with the S of the substrate 6.
Further SiO ₂ is formed on the iO ₂ film (first-layer gate insulating film).
It is for forming a film (second layer gate insulating film). The CVD film forming chamber 32 is equipped with a plasma generator 33 that generates plasma by RF glow discharge, and is capable of forming a SiO ₂ film by the plasma CVD method.

A series of operations in the film forming apparatus will be described below.

First, the substrate 6 is placed in the photooxidation chamber 30.
At this time, the photo-oxidation chamber 30 is separated by a partition.
Then, the pressure in the photo-oxidation chamber 30 is reduced, and the substrate 6 is heated by the heater 3. Next, the oxidizing gas and the rare gas are both flown into the photo-oxidizing chamber 30, and the ultraviolet light 5 is emitted from the lamp 1 onto the substrate 6.
Of the Si film is irradiated. As a result, the Si film on the substrate 6 is photooxidized to form a SiO ₂ film (first-layer gate insulating film).

Next, the substrate 6 on which the SiO ₂ film is formed is transferred from the photooxidation chamber 30 to the transfer chamber 31 with the partition removed. The transfer chamber 31 is depressurized to the same degree as the photooxidation chamber 30 in advance. The transfer chamber 31 is separated by a partition to reduce the pressure.

Then, the substrate 6 is transferred from the transfer chamber 31 to the CVD film forming chamber 32 with the partition removed. This CV
The D film forming chamber 32 is separated by a partition and is depressurized. next,
A raw material gas is caused to flow into the CVD film forming chamber 32, and plasma is generated by the plasma generator 33. The SiO ₂ film (first layer) formed on the substrate 6 by this plasma CVD method
A SiO ₂ film (second layer gate insulating film) is further formed on the layer gate insulating film).

Thus, the gate insulating film 13 (first layer gate insulating film 13a and second layer gate insulating film 13a) is formed.
Can be formed.

Noble gas used in the photo-oxidation chamber 30,
The conditions such as oxidizing gas, temperature, and ultraviolet light are the same as the conditions used in the above photo-oxidizer.

Since the transfer chamber 31 is evacuated, C
It is possible to prevent impurities from being brought into the VD film forming chamber 32. Further, since it is not exposed to the outside air, it is possible to prevent impurities from adhering between the first-layer gate insulating film and the second-layer insulating film.

In the CVD film forming chamber 32, SiH ₄ (monosilane) gas: 5 sccm and N ₂ O (nitrous oxide) gas: 700 sccm can be used as a source gas. In addition, TEOS (Tetr
a Ethyl Ortho Silicate) gas and O ₂ gas may be flowed. The atmosphere in the CVD film forming chamber 32 is 30 Pa-100.
It may be kept at 0 Pa. The plasma discharge is, for example, 0.1
The power density may be about 0.2 W / cm ² . In the CVD film forming chamber 32, an example in which plasma is generated by RF glow discharge has been described, but plasma may be generated by microwave discharge.

In the CVD film forming chamber 32, plasma C
Although the example of forming the second-layer gate insulating film by the VD method has been described, the second-layer gate insulating film may be formed by using another film forming method, for example, the PVD method or the like.

The characteristics of the low temperature polysilicon TFT having the gate insulating film formed by the photo-oxidation method of the present invention will be described below.

In the process of manufacturing a low temperature polysilicon TFT, when the gate insulating film was formed by the conventional deposition, the interface state density and the fixed charge density could not be reduced. Further, after the Bias temperature test (BT test), the deviation of the flat band voltage (Vfb) was large, and thus it was difficult to realize the MOS structure.

Further, when the TFT is formed, a threshold voltage (Vth) having a small absolute value in the current-voltage characteristic, a steep rise characteristic, and a BT test or a continuous operation test are performed. Threshold voltage (Vth)
It was not possible to reduce the deviation of the ON current and the change in the ON current and the OFF current.

Therefore, the current-voltage characteristics of the low temperature polysilicon TFT provided with the gate insulating film formed by the photo-oxidation method of the present invention were examined.

The polysilicon TFT has Vth = 1.0.
It had a small value of about V. Further, the TFT is
The subthreshold slope showing the steep rising characteristic of the current was 150 to 300 mV / dec. Further, even after the BT test, the deviation of Vth: ΔV
th was 0.5 V or less. That is, the polysilicon TFT had extremely excellent characteristics.

Also formed by the photo-oxidation method of the present invention.
Using the gate insulating film, create a sample of MOS structure,
C-V characteristics are measured to determine the interface state density and fixed charge density.
evaluated. As a result, the interface state density is 10¹¹cm^-2eV
^-1Below, the fixed charge density is 10 ¹¹cm^-2Silicon below
A gate insulating film interface could be obtained. In Figure 5, p-type
Single crystal silicon wafer ((100) plane, about 10 Ωcm)
On top of the insulating film (the insulating film of the present invention
Film) and a conventional plasma-enhanced CVD method.
About the insulation film (conventional insulation film) formed by one method
Then, an Al electrode is formed on each insulating film to form a MOS structure.
The high frequency C-V characteristics (1MHz) of the fabricated sample
A comparison of data is shown. The insulating film of the present invention is a rare gas assist
A photo-oxide film (corresponding to the first layer gate insulating film) of 3 nm,
And SiH_Four+ N₂Shaped by PECVD method using O gas
SiO made₂System insulating film (corresponding to second insulating oxide film)
Was formed to a thickness of 97 nm. The conventional insulating film is SiH_Four+
N₂SiO by PECVD method using O gas₂System insulation film
100 nm was formed).

It can be seen that the insulating film of the present invention has a sharp C-V characteristic curve and exhibits excellent characteristics. In FIG. 5, the flat band voltage Vfb is the sample according to the present invention: -1.4V, the sample according to the conventional method: -4.8V.
Met. In addition, BT test (150 ° C ± 2 MV / cm
Even after the DC energization test), the deviation ΔVfb of the flat band voltage was 0.5 V or less, which had excellent characteristics.

That is, by stacking the first layer gate insulating film formed by the photo-oxidation method of the present invention from the surface layer of the polysilicon film and the second layer gate insulating film formed by the plasma CVD method, excellent current- A TFT having a voltage characteristic can be obtained.

That is, by applying the photo-oxidation method of the present invention to the step of forming the insulating film of the polysilicon TFT, T
In the current-voltage characteristics of FT, Vth having a small absolute value is obtained, and a TFT exhibiting a sharp change in current value is obtained. Further, even when a BT test or a continuous energization test is performed, a TFT with a small change in the above characteristics can be obtained. As a result, a stable polysilicon TFT having a low operating voltage can be operated.

[0074]

As described above, the photo-oxidation method of the present invention heats an object to be oxidized under reduced pressure, exposes it to an oxidizing gas containing oxygen and a rare gas, and irradiates it with ultraviolet light. It is a composition.

According to the above arrangement, the rare gas is excited by irradiating it with ultraviolet light under reduced pressure. Then, the excited rare gas transfers excitation energy to oxygen molecules to generate oxygen atom radicals.
Since this oxygen atom radical has high reactivity, the object to be oxidized can be quickly oxidized. That is, there is an effect that the rate of photooxidation can be increased.

The wavelength of the ultraviolet light is 120 ± 10.
It is preferably nm. Further, the oxidizing gas is
It is preferable that the oxygen content is 5% to 15% and the rare gas content is 85% to 95%. The rare gas is preferably krypton. According to the above configuration, there is an effect that the rate of photooxidation can be further increased.

Further, the photooxidation method of the present invention is carried out at 100 ° C.
It is preferable to heat to a temperature of 400 ° C.

The method of manufacturing a semiconductor device according to the present invention uses SiO.
_A method of manufacturing a semiconductor device having an insulating film made of ₂ , wherein the insulating film is manufactured by photo-oxidizing a Si film by the photo-oxidation method described above.

According to the above structure, since the Si film is photo-oxidized, there is no fear that impurities or the like will remain between the Si film and the formed SiO ₂ film. Therefore, the interface state density and the fixed charge density at the interface between the Si film and the SiO ₂ film can be suppressed. As a result, a semiconductor device having excellent current-voltage characteristics can be manufactured. Further, a dense and uniform insulating film can be formed. Also,
Since the photo-oxidation method is used, throughput can be increased and mass productivity can be improved.

The photo-oxidation device of the present invention is a photo-oxidation device for photo-oxidizing an object to be oxidized, which comprises a decompression chamber in which the object to be oxidized is exposed to an oxidizing gas containing a rare gas and oxygen under reduced pressure. A heating device that heats the oxidation target and an ultraviolet irradiation device that irradiates the oxidation target with ultraviolet light.

According to the above arrangement, the rare gas is excited by irradiating it with ultraviolet light under reduced pressure. Then, the excited rare gas transfers excitation energy to oxygen molecules to generate oxygen atom radicals.
Since this oxygen atom radical has high reactivity, the object to be oxidized can be quickly oxidized. That is, it is possible to provide an apparatus having a high photooxidation rate.

The semiconductor device manufacturing apparatus of the present invention is made of SiO.
A semiconductor device manufacturing apparatus having an insulating film consisting of ₂ is provided with the photo-oxidizing device for photo-oxidizing a Si film to form the insulating film.

According to the above structure, since the Si film is photo-oxidized, there is no fear that impurities or the like will remain between the Si film and the formed SiO ₂ film (insulating film). Therefore, the interface state density and the fixed charge density at the interface between the Si film and the SiO ₂ film (insulating film) can be suppressed. As a result, it is possible to provide a device capable of manufacturing a semiconductor device having excellent current-voltage characteristics. In addition, the above-described apparatus has an effect that a dense and uniform insulating film can be formed.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a photo-oxidation device according to an embodiment of the present invention.

FIG. 2 is a polysilicon TF according to one embodiment of the present invention.
It is sectional drawing of the principal part of T.

FIG. 3 is a graph showing a spectral radiation distribution of an Ar excimer lamp, which is an example of a light source used in the photooxidation device.

FIG. 4 is a sectional view showing an apparatus for manufacturing a gate insulating film of the polysilicon TFT.

FIG. 5 is a graph showing high-frequency CV measurement data of a gate insulating film manufactured by the photo-oxidizing apparatus of the present invention and an insulating film manufactured by a conventional method.

[Explanation of symbols]

1 Lamp (ultraviolet light irradiation device) 2 Vacuum chamber (decompression chamber) 3 Lamp heater (heating device) 4 Installation table 5 Vacuum ultraviolet light (ultraviolet light) 6 Substrate (oxidation target) 10 Substrate 11 Undercoat layer 12 Polysilicon channel Part 13 Gate insulating film 13a First layer gate insulating film 13b Second layer gate insulating film 14 Gate electrode 16 n ⁺ type silicon part 17 p ⁺ type silicon part 18 Interlayer insulating film 19 Source metal 20 Drain metal 21 Passivation film 22 Transparent electrode Film 30 Photooxidation chamber 31 Transfer chamber 32 CVD film forming chamber

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toshimasa Hamada             22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka             Inside the company F-term (reference) 5F048 AC04 BA16 BB09 BB11 BE08                       BG07                 5F058 BA05 BB07 BC02 BF78 BJ04                 5F110 AA14 AA17 BB02 BB04 CC02                       DD02 DD11 EE06 EE44 FF02                       FF09 FF22 FF27 FF30 GG02                       GG13 GG25 HJ01 HJ04 HJ12                       HL03 HL04 HL11 NN03 NN04                       NN23 NN24 NN35 NN72 PP03                       PP04 QQ09 QQ11

Claims (8)

[Claims] 1. A photooxidation method comprising heating an object to be oxidized under reduced pressure, exposing it to an oxidizing gas containing oxygen and a rare gas, and irradiating it with ultraviolet light. 2. The photooxidation method according to claim 1, wherein the wavelength of the ultraviolet light is 120 ± 10 nm. 3. The oxidizing gas contains 5% to 15% of oxygen,
The photooxidation method according to claim 1 or 2, wherein the rare gas is contained in a proportion of 85% to 95%. 4. The photooxidation method according to claim 1, wherein the rare gas is krypton. 5. The photooxidation method according to claim 1, wherein heating is performed to a temperature of 100 ° C. to 400 ° C. 6. A method of manufacturing a semiconductor device having an insulating film made of SiO ₂ , wherein the insulating film is photooxidized by a method according to any one of claims 1 to 5. A method for manufacturing a semiconductor device, which comprises manufacturing the semiconductor device. 7. A photooxidation apparatus for photooxidizing an oxidation target, the decompression chamber exposing the oxidation target to an oxidizing gas containing oxygen and a rare gas under reduced pressure, and the oxidation target. A photo-oxidation device, comprising: a heating device for heating the object; and an ultraviolet irradiation device for irradiating the object to be oxidized with ultraviolet light. 8. A device for manufacturing a semiconductor device having an insulating film made of SiO ₂ , comprising the photo-oxidizing device according to claim 7, wherein the Si film is photo-oxidized to form the insulating film. Semiconductor device manufacturing equipment.