JP2001110803A - Method for forming oxide film, and method for manufacturing thin-film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form an oxide film with improved quality on a semiconductor thin film containing silicon in a low-temperature process where a substrate temperature is at 600 deg.C or lower, and to provide a reliable thin-film transistor with improved performance while keeping the substrate temperature at a low temperature. SOLUTION: A catalyst element for accelerating oxidation is added to a semiconductor thin film containing silicon, heat treatment is made in oxidation atmosphere, and also the operation between oxygen radical and oxygen ion is utilized, thus forming an oxide film with improved quality on the semiconductor thin film containing silicon in a low-temperature process where the substrate temperature is at 600 deg.C or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an oxide film used for various semiconductor devices and a method for manufacturing a thin film transistor applied to a liquid crystal display device and a sensor array.

[0002]

2. Description of the Related Art Hereinafter, TEOS (Tetraethyl)
Orthosilicate: As a conventional thin film transistor using a silicon oxide formed by a plasma CVD method using (C ₂ H ₅ O) ₄ Si) as a source gas as a gate oxide film, development for a liquid crystal display device has been advanced. A low-temperature polycrystalline silicon thin film transistor (hereinafter abbreviated as “low-temperature Poly-Si TFT”) will be described with reference to the drawings.

A large-sized liquid crystal display device of the 10-inch class using a polycrystalline silicon thin film transistor requires a large area, and therefore uses an inexpensive glass substrate. However, when glass is used as the substrate, the heat resistance is not sufficient, so that a thin film transistor must be manufactured at a relatively low temperature (about 600 ° C. or lower). A conventional example will be briefly described with reference to FIG.

In this conventional method of manufacturing a low-temperature Poly-Si TFT, first, glass (Corning # 1737) is used.
Etc.) On the surface of the substrate 11, an undercoat film 12 made of silicon oxide for preventing diffusion of impurities in the glass substrate
(About 400 nm) on a substrate provided with silane (SiH
₄ ) Amorphous silicon 13 is formed to a thickness of 50 nm by a plasma CVD method using ( ₄ ) as a source gas (FIG. 5A).

Next, the amorphous silicon is crystallized by irradiating a XeCl excimer laser 15 to form a polycrystalline silicon 14 (FIG. 5B). Irradiation conditions at this time depend on conditions such as the film thickness and film quality of the amorphous silicon, but the energy density is 150 to 450 mJcm ^-2 and the number of times of irradiation is 1 to 500 times.

The polycrystalline silicon is patterned into an island shape by known photolithography and etching (FIG. 5C).

After that, TEOS (Tetraethyl)
orthosilicate: (C _TwoH_FiveO)_FourSi)
By plasma CVD method used as source gas, island-shaped
900 絶 縁 gate insulating film 51 formed on polycrystalline silicon
(FIG. 5D).

Then, a gate electrode 31 is formed using a molybdenum-tungsten alloy (MoW), and the gate insulating film 51 and the gate electrode 31 are patterned into an island shape by known photolithography and etching. Then, a hydrogen-diluted phosphine (PH ₃ ) plasma is generated, and ion doping is performed under the conditions of an acceleration voltage of 70 kV and a dose of 10 ¹⁵ cm ⁻² to form a source region 32 and a drain region 33 (FIG. 5E). )).

Thereafter, heat treatment is performed to activate the implanted ions. And TEOS (Tetraethy)
lorthosilicate: (C ₂ H ₅ O) ₄ Si)
Silicon dioxide (SiO ₂ ) is deposited on the entire surface as an interlayer insulating film 34 by a plasma CVD method using as a source gas, a contact hole is formed, and a source electrode 35 is formed.
For example, aluminum (A
l) is deposited by a sputtering method and then patterned by photolithography and etching,
The thin film transistor is completed (FIG. 5F).

[0010] TE is used as a gate insulating film of a thin film transistor.
OS (Tetraethylorthosilicate)
As an example of using silicon dioxide formed by a plasma CVD method using e: (C ₂ H ₅ O) ₄ Si) as a source gas, see Japanese Journal of Applied Physics, 1992, p. 4570. Page 4573 (Japanes Journal)
l of Applied Physics p. p.
4570-4573).

As a conventional example of a method of forming an oxide film,
Japanese Patent Application Laid-Open No. 9-45679 describes a method for forming an oxide film, which comprises depositing a catalyst metal after forming an oxide film on a semiconductor thin film, and performing heat treatment in an oxidizing atmosphere at 600 ° C. or lower.

[0012]

When the conventional low-temperature Poly-Si TFT shown in FIG. 5 is manufactured, the following problems occur.

In the example shown in FIG. 5, a TEOS (Tetraet) is formed on a polycrystalline silicon layer obtained by crystallization.
hylorthosilicate: (C ₂ H ₅ O) ₄ S
By the plasma CVD method using i) as a source gas,
A silicon dioxide layer is formed as a gate insulating film.
However, TEOS (Tetraethylortho)
Silicate: A film of silicon dioxide obtained by a plasma CVD method using (C ₂ H ₅ O) ₄ Si) as a source gas contains many dangling bonds of carbon and silicon. The amount varies depending on the film forming method, conditions, and the presence or absence of heat treatment, but reaches as high as 10 ¹⁹ cm ^-3 when the amount is larger than 10 ¹⁶ cm ^-3 . These dangling bonds cause carrier traps and have a great effect not only on the characteristics of the thin film transistor but also on the reliability of the device. Further, in the plasma CVD method, since plasma for decomposing a source gas damages polycrystalline silicon as an active layer, an interface state of the order of 10 ¹¹ to 10 ¹² cm ⁻² eV ^{−1 is present at the} silicon dioxide / polycrystalline silicon interface. Place occurs. As a result, there is a problem that carrier trapping and scattering occur and the characteristics of the thin film transistor deteriorate.

Further, in the conventional method of forming an oxide film, since the surface of the semiconductor thin film is covered with the oxide film and the catalytic metal, there is a problem that the reaction between the semiconductor thin film and oxygen hardly occurs and the oxidation rate is reduced. .

In view of the foregoing, it is an object of the present invention to provide a method of manufacturing a highly reliable insulating film and a method of manufacturing a thin film transistor having high throughput and excellent characteristics while keeping a substrate temperature low. I do.

[0016]

Means for Solving the Problems To solve these problems, the inventors of the present invention have made various studies, and found that the formation of an oxide film requires the addition of a catalytic element that promotes oxidation to a semiconductor thin film. It is effective. However, since the formation of an oxide film does not proceed simply by simply adding a catalyst element, heat treatment in an oxidizing atmosphere after addition of a catalyst element that promotes oxidation to a semiconductor thin film can also produce oxygen radicals and oxygen ions. By utilizing the function, a high-quality thermal oxide film is formed on a semiconductor thin film containing silicon.

In order for the reaction between oxygen and silicon to occur efficiently, it is effective to use a catalytic element that promotes oxidation. However, instead of simply forming a catalytic element on a semiconductor thin film, it is characterized by adding a catalytic element to the semiconductor thin film to efficiently form a high-quality thermal oxide film on the surface of the semiconductor thin film at a low temperature. It is.

Further, a method of manufacturing a thin film transistor according to the present invention includes a step of forming an oxide film by using the above-described method of forming an oxide film.

[0019]

According to a first aspect of the present invention, there is provided a method for forming an oxide film, wherein a catalytic element for promoting oxidation is added to a semiconductor thin film containing silicon and an atmosphere containing at least an oxidizing substance at 600 ° C. or lower. A step of forming an oxide film on the surface of the silicon-containing semiconductor thin film by performing a heat treatment therein. According to the present invention, it is possible to form a high-quality oxide film while keeping the substrate temperature low.

According to a second aspect of the present invention, there is provided a method of forming an oxide film, comprising adding a catalytic element for promoting oxidation to a semiconductor thin film containing silicon and leaving it in a plasma atmosphere containing at least oxygen radicals and oxygen ions. Forming an oxide film on the surface of the semiconductor thin film containing silicon. According to the present invention, since a reaction by excited oxygen atoms having high energy is used, a high quality oxide film can be formed while the substrate temperature is kept lower.

According to a third aspect of the present invention, there is provided a method of forming an oxide film, comprising a step of performing heat treatment in an atmosphere containing a halogen element to getter the catalyst element which promotes the oxidation. Item 3 is a method for forming an oxide film according to Item 1 or 2. According to the present invention, contamination due to a catalytic element can be removed after the formation of an oxide film, so that a high-quality and highly reliable oxide film can be formed while the substrate temperature is kept low.

According to a fourth aspect of the present invention, there is provided a method for forming an oxide film, wherein the method of adding a catalytic element for promoting oxidation is a method of implanting ions containing an accelerated catalytic element. Item 4. A method for forming an oxide film according to items 1, 2 and 3. According to the present invention, since the catalytic element is added to the semiconductor thin film, it has an effect that a high-quality oxide film can be formed at a high throughput while keeping the substrate temperature low.

According to a fifth aspect of the present invention, there is provided a method of manufacturing a thin film transistor, comprising: a semiconductor thin film containing silicon comprising a channel region and a source / drain region containing an impurity serving as a donor or an acceptor; A thin film transistor having at least a gate electrode and a source / drain electrode, wherein a catalytic element for promoting oxidation is added to the silicon-containing semiconductor thin film;
A step of forming an oxide film on the surface of the semiconductor thin film containing silicon by performing a heat treatment in an atmosphere containing at least an oxidizing substance at a temperature of not more than ° C. According to the present invention, there is an effect that a thin film transistor having excellent performance can be manufactured while keeping the substrate temperature low.

According to a sixth aspect of the present invention, there is provided a method of manufacturing a thin film transistor, comprising: a semiconductor thin film containing silicon comprising a channel region and a source / drain region containing an impurity serving as a donor or an acceptor; And a thin film transistor having at least a gate electrode and a source / drain electrode, by adding a catalytic element that promotes oxidation to the semiconductor thin film containing silicon and leaving it in a plasma atmosphere containing at least oxygen radicals and oxygen ions, A step of forming an oxide film on the surface of the semiconductor thin film containing silicon. According to the present invention, since a reaction by excited oxygen atoms having high energy is used, it has an effect that a thin film transistor having excellent performance can be manufactured while keeping the substrate temperature lower.

In the method of manufacturing a thin film transistor according to a seventh aspect of the present invention, a step of forming an oxide film on the silicon-containing semiconductor thin film before adding a catalytic element promoting oxidation to the silicon-containing semiconductor thin film is performed. 7. The method of manufacturing a thin film transistor according to claim 5, wherein the method includes: According to the present invention, since the oxide film formed on the semiconductor thin film containing silicon functions as a buffer layer, the semiconductor thin film containing silicon has an effect of not being damaged by addition of a catalyst element that promotes oxidation. .

According to a eighth aspect of the present invention, the method of manufacturing a thin film transistor includes a step of gettering the catalytic element which promotes the oxidation by performing a heat treatment in an atmosphere containing a halogen element. 8. A method for manufacturing a thin film transistor according to 5, 6, and 7. According to the present invention, contamination due to a catalytic element can be removed after the formation of an oxide film, so that a highly reliable thin film transistor can be manufactured while keeping the substrate temperature low.

According to a ninth aspect of the present invention, in the method of manufacturing a thin film transistor, the method of adding a catalytic element that promotes oxidation is a method of implanting ions containing the accelerated catalytic element. 9. The method for forming an oxide film according to 5, 6, 7, and 8. According to the present invention, since a catalytic element is added to a semiconductor thin film, a highly reliable thin film transistor can be manufactured with high throughput while maintaining a low substrate temperature.

Hereinafter, embodiments of the present invention will be specifically described.

(Embodiment 1) FIG. 1 is a process sectional view for explaining a method of forming an oxide film according to a first embodiment of the present invention, and will be described in order.

First, glass (Corning # 1737, etc.)
An undercoat film 12 (40) of silicon oxide is formed on the surface of the substrate 11 to prevent diffusion of impurities in the glass substrate.
For example, silane (SiH
₄ ) Amorphous silicon 13 is formed to a thickness of 30 nm to 200 nm by a plasma CVD method using ₄ ) as a source gas (FIG. 1A).

Next, as a laser, for example, XeCl
Irradiation with an excimer laser 15 crystallizes amorphous silicon to form polycrystalline silicon 14.
(B)). The irradiation conditions at this time depend on the conditions such as the film thickness and film quality of the amorphous silicon, but the energy density is 15%.
The irradiation is performed in the range of 0 to 450 mJcm ^-2 and the number of irradiations is in the range of 1 to 500 times.

Next, for example, platinum (Pt) ions as a catalyst element for promoting oxidation are added to polycrystalline silicon by an ion implantation method (FIG. 1C). The concentration of the added ions at this time is 1.0 × 10 ¹⁷ cm ^{−3 to} 1.0 × 10 ²³ cm ^−3.
Perform within the range.

Thereafter, an oxide film having a thickness of 2 nm to 120 nm is formed by performing a heat treatment in an oxygen atmosphere at 200 ° C., for example (FIG. 1D).

By the action of the platinum injected into the polycrystalline silicon as a catalyst, an oxide film having a thickness of 0.9 nm per minute could be formed by heat treatment at a low temperature of 200 ° C. The interface state density is 6.2 × 10 ¹¹ cm ⁻² eV ⁻¹ near the mid-gap of the polycrystalline silicon, and the interface state density existing at the interface between the insulating film formed by the plasma CVD method and the polycrystalline silicon. This is a lower level than the density. This indicates that the oxide film formed according to this embodiment has sufficient interface characteristics to be used as a gate insulating film of a thin film transistor.

In the first embodiment, the catalytic element generated after forming the oxide film by the catalytic action is left. However, as a compound containing a halogen element, for example, HCl,
HF, NF ₃ , HBr, Cl ₂ , ClF ₃ , BCl ₃ ,
It may be removed by heat treatment at a temperature of 600 ° C. or lower in an atmosphere containing F ₂ , Br, or the like.

In the first embodiment, the catalyst element which promotes oxidation is injected after the polycrystalline silicon is formed. However, before the catalyst element is injected, an oxide film serving as a buffer layer is formed on the polycrystalline silicon. May be. By forming the buffer layer in advance, there is an advantage that damage to polycrystalline silicon caused at the time of implanting catalytic element ions can be reduced.

In the first embodiment, amorphous silicon formed by plasma CVD is used as a base when an oxide film is formed.
It may be formed by a method or a sputtering method. Alternatively, microcrystalline silicon, polycrystalline, or single-crystal silicon may be used as a starting material in addition to amorphous silicon. Further, it may be processed into a desired shape using a known photolithography step and etching step.

Although silicon oxide is used as the undercoat film in the first embodiment, an insulating film such as silicon nitride may be used, or the undercoat film may not be formed.

In the first embodiment, a XeCl excimer laser is used as a laser.
An excimer laser such as F or KrF or an argon laser may be used.

In the first embodiment, platinum is used as a catalyst element that promotes oxidation, but palladium, copper, or the like may be used.

In the first embodiment, an ion implantation method is used as a method for adding an element that promotes oxidation. However, an ion doping method or a FIB method (ion focus beam method) is used.
Etc. may be used.

In the first embodiment, the heat treatment is performed in an oxygen atmosphere at 200 ° C., but the temperature may be 600 ° C. or less, and an atmosphere containing an oxidizing substance such as a nitrogen oxide atmosphere or an ozone atmosphere. It only has to be inside.

In the first embodiment, the catalyst element that promotes oxidation is added after polycrystalline silicon is formed. However, polycrystalline silicon may be formed after adding the catalyst element to amorphous silicon.

(Embodiment 2) FIG. 2 is a process sectional view for illustrating a method of forming an oxide film according to a second embodiment of the present invention, and will be described in order.

As in the first embodiment, for example, polycrystalline silicon 14 is formed on a substrate as a semiconductor thin film containing silicon (FIGS. 2A and 2B). Next, for example, platinum (Pt) ion as a catalyst element for promoting oxidation is added to polycrystalline silicon by an ion implantation method (FIG. 2).
(C)). The added ion concentration at this time was 1.0 × 10 ¹⁷
It is performed in a range of cm ^{−3 to} 1.0 × 10 ²³ cm ⁻³ . afterwards,
An oxygen plasma atmosphere is created using a plasma CVD apparatus, the sample is left in the atmosphere, and an oxide film having a thickness of 2 nm to 120 nm is formed on polycrystalline silicon (FIG. 2).
(D)).

By the action of the platinum injected into the polycrystalline silicon as a catalyst, an oxide film having a thickness of 1.8 nm was formed per minute. The interface state density is 7.4 × 10 ¹¹ cm ⁻² eV ⁻¹ near the mid-gap of polycrystalline silicon,
This level is lower than the interface state density existing at the interface between the insulating film and the polycrystalline silicon formed by the plasma CVD method. This indicates that the oxide film formed according to this embodiment has sufficient interface characteristics to be used as a gate insulating film of a thin film transistor.

In the second embodiment, the catalytic element generated after the oxide film is formed by the catalytic action is left. However, as a compound containing a halogen element, for example, HCl,
HF, NF ₃ , HBr, Cl ₂ , ClF ₃ , BCl ₃ ,
It may be removed by performing a heat treatment at a temperature of 600 ° C. or less in an atmosphere containing F ₂ , Br, or the like.

Further, in the second embodiment, after the polycrystalline silicon is formed, a catalytic element for promoting oxidation is injected. However, before the catalytic element is injected, an oxide film serving as a buffer layer is formed on the polycrystalline silicon. May be. By forming the buffer layer in advance, there is an advantage that damage to polycrystalline silicon caused at the time of implanting catalytic element ions can be reduced.

In the second embodiment, amorphous silicon formed by a plasma CVD method is used as a base when a thermal oxide film is formed.
It may be formed by the D method or the sputtering method. Alternatively, microcrystalline silicon, polycrystalline, or single-crystal silicon may be used as a starting material in addition to amorphous silicon. Further, it may be processed into a desired shape using a known photolithography step and etching step.

Although silicon oxide is used as the undercoat film in the second embodiment, an insulating film such as silicon nitride may be used, or the undercoat film may not be formed.

In the second embodiment, the XeCl excimer laser is used as the laser.
An excimer laser such as F or KrF or an argon laser may be used.

In the second embodiment, platinum is used as a catalyst element for promoting oxidation, but palladium or copper may be used.

In the second embodiment, an ion implantation method is used as a method for adding an element that promotes oxidation, but an ion doping method or a FIB method (an ion focus beam method) is used.
Etc. may be used.

In the second embodiment, a catalyst element for promoting oxidation is added after polycrystalline silicon is formed. However, polycrystalline silicon may be formed after adding a catalyst element to amorphous silicon.

In the second embodiment, the plasma CV
Although an oxygen plasma atmosphere was created using the D apparatus, oxygen may be excited by light or the like to create an oxygen radical atmosphere, or an ECR-CVD apparatus or a remote plasma CV
An oxygen radical or oxygen ion atmosphere may be created using a D apparatus or the like. Further, nitrogen ions, argon ions, or the like may be contained in an oxygen radical or oxygen ion atmosphere.

(Embodiment 3) FIG. 3 is a process sectional view for illustrating a method of forming a thin film transistor according to a third embodiment of the present invention, and will be described in order.

First, glass (Corning # 1737 etc.)
On the surface of the substrate, an undercoat film 12 (400 nm) made of silicon oxide for preventing diffusion of impurities in the glass substrate.
Polycrystalline silicon 14 is formed on substrate 11 provided with (about m) by the same method as in the first embodiment, and this polycrystalline silicon is patterned into an island shape by known photolithography etching (FIG. 3A )).

Then, for example, platinum ion as a catalyst element for promoting oxidation is added to polycrystalline silicon by an ion implantation method (FIG. 3B). The concentration of the added ions at this time is in the range of 1.0 × 10 ¹⁷ cm ^{−3 to} 1.0 × 10 ²³ cm ⁻³ .

Thereafter, a high-quality oxide film 18 as a gate insulating film is formed on the island-like polycrystalline silicon by heat treatment in an oxygen atmosphere at, for example, 200 ° C. for about 900 minutes.
(4) The formed platinum is heat-treated at 600 ° C. for 1 hour in an atmosphere containing HCl gas to remove the remaining platinum (FIG. 3C).

Thereafter, a gate electrode 31 is formed using, for example, an alloy of molybdenum and tungsten (MoW), and the oxide film 18 and the gate electrode 31 are patterned into an island shape by known photolithography and etching.

Then, hydrogen-diluted phosphine (PH ₃ )
Plasma at an accelerating voltage of 70 kV and a dose of 10
^The source region 32 and the drain region 33 are formed by ion doping under the condition of ¹⁵ cm ⁻² (FIG. 3).
(D)).

Thereafter, for example, RTA (Rapid Th)
In this case, local heating is performed by thermal annealing to activate the implanted ions. And, for example, T
EOS (Tetraethylorthosilica)
te: Silicon dioxide (SiO ₂ ) is deposited on the entire surface as an interlayer insulating film 34 by a plasma CVD method using (C ₂ H ₅ O) ₄ Si) as a source gas, then a contact hole is formed, and a source electrode 35 is formed. For example, aluminum (Al) is deposited as a drain electrode 36 by a sputtering method, and then patterned by photolithography and etching to complete a thin film transistor (FIG. 3E).

The sub-threshold swing (S value) of the TFT obtained by the manufacturing method of the third embodiment is 0.2
5 V / decade, which is superior to the case where a gate insulating film is formed by a plasma CVD method.

In the third embodiment, only one oxide film is formed on polycrystalline silicon as the gate insulating film, but the gate insulating film is not necessarily required to be one layer. The throughput of the gate oxide film forming step may be increased by reducing the thickness of the oxide film described in Embodiment 3 and stacking another insulating film. For example, TEO is formed on an oxide film (approximately 100 °) formed by using the method of the third embodiment.
A stacked structure formed by forming an insulating film using an S-CVD method, an NCVD method, an ECR-CVD method, a remote plasma CVD method, or the like may be used. At this time, the insulating film formed on the oxide film is made of SiO ₂ , SiN _x , TaO.
_x or the like can be used.

In the third embodiment, platinum is used as a catalyst element for promoting oxidation, but palladium or copper may be used.

In the third embodiment, an ion implantation method is used as a method for adding an element that promotes oxidation. However, an ion doping method or a FIB method (ion focus beam method) is used.
Etc. may be used.

In the third embodiment, the heat treatment is performed in an oxygen atmosphere at 200 ° C., but the temperature may be 600 ° C. or less, and an atmosphere containing an oxidizing substance such as a nitrogen oxide atmosphere or an ozone atmosphere. It only has to be inside.

In the third embodiment, the platinum remaining after forming the oxide film is removed. However, platinum may be used as the gate electrode or may be used as a part of the gate electrode. Further, HCl is used as a compound containing a halogen element.
Although an example in which platinum is removed using a gas has been described, HF, NF ₃ , HBr, Cl ₂ , ClF ₃ ,
It may be removed by heat treatment at a temperature of 600 ° C. or less in an atmosphere containing BCl ₃ , F ₂ , Br, or the like.

In the third embodiment, a catalyst element for promoting oxidation is implanted after polycrystalline silicon is formed. However, an oxide film serving as a buffer layer is formed on polycrystalline silicon before implanting the catalyst element. May be. By forming the buffer layer in advance, there is an advantage that damage to polycrystalline silicon caused at the time of implanting catalytic element ions can be reduced.

In the third embodiment, the active layer
Although amorphous silicon formed by the plasma CVD method is used, it may be formed by a low-pressure CVD method other than the plasma CVD method, a sputtering method, or the like. Alternatively, microcrystalline silicon, polycrystalline, or single-crystal silicon may be used as a starting material in addition to amorphous silicon.

In the third embodiment, silicon oxide is used as the undercoat film. However, an insulating film such as silicon nitride may be used, or the undercoat film may not be formed.

In the third embodiment, RTA is used to activate the implanted ions. However, annealing may be performed in an atmosphere of 400 ° C. or more, or self-activation by simultaneously implanted hydrogen may be performed. It is not necessary to intentionally activate in anticipation of activation.

In the third embodiment, MOW and Al are used for the gate electrode, the source electrode, and the drain electrode. However, aluminum (Al), tantalum (Ta), molybdenum (Mo), chromium (Cr), titanium A metal such as (Ti) or an alloy thereof may be used, or a transparent conductive layer such as ITO may be used.

In the third embodiment, TEOS (Tetraethylorthosil) is used as the interlayer insulating film.
icate: silicon dioxide produced by a plasma CVD method using (C ₂ H ₅ O) ₄ Si) as a source gas was used. However, an AP-CVD method or an ECR-CVD method may be used. An insulating film may be used.

In the third embodiment, phosphorus ions are used as ions to be implanted, but aluminum or the like may be used, or boron or the like serving as an acceptor may be used.

In the third embodiment, the oxide film is formed after the polycrystalline silicon is formed. However, a catalytic element that promotes oxidation is added to the amorphous silicon first, and then the polycrystalline silicon is formed. Then, an oxide film may be formed.

(Embodiment 4) FIG. 4 is a process sectional view for explaining a method of forming a thin film transistor according to a fourth embodiment of the present invention, and will be described in order.

First, glass (Corning # 1737 etc.)
On the surface of the substrate, an undercoat film 12 (400 nm) made of silicon oxide for preventing diffusion of impurities in the glass substrate.
Polycrystalline silicon 14 is formed on substrate 11 provided with (about m) by the same method as in the second embodiment, and this polycrystalline silicon is patterned into an island shape by known photolithography etching (FIG. 4A )).

Then, for example, platinum ion as a catalyst element for promoting oxidation is added to polycrystalline silicon by an ion implantation method (FIG. 4B). The concentration of the added ions at this time is in the range of 1.0 × 10 ¹⁷ cm ^{−3 to} 1.0 × 10 ²³ cm ⁻³ .

Thereafter, an oxygen plasma atmosphere is created using a plasma CVD apparatus, the sample is left in the atmosphere, and a high-quality oxide film 18 is formed on the island-like polycrystalline silicon as a gate insulating film at a thickness of approximately 900 °. The remaining platinum is removed by heat treatment at 600 ° C. for 1 hour in an atmosphere containing HCl gas (FIG. 4C).

Thereafter, a gate electrode 31 is formed using, for example, a molybdenum-tungsten alloy (MoW), and the oxide film 18 and the gate electrode 31 are patterned into an island shape by known photolithography and etching. Then, a hydrogen-diluted phosphine (PH ₃ ) plasma is generated and ion-doped under the conditions of an acceleration voltage of 70 kV and a dose of 10 ¹⁵ cm ⁻² , thereby forming a source region 32 and a drain region 33 (FIG. 4D). )).

Thereafter, for example, RTA (Rapid Th)
In this case, local heating is performed by thermal annealing to activate the implanted ions. And, for example, T
EOS (Tetraethylorthosilica)
te: Silicon dioxide (SiO ₂ ) is deposited on the entire surface as an interlayer insulating film 34 by a plasma CVD method using (C ₂ H ₅ O) ₄ Si) as a source gas, then a contact hole is formed, and a source electrode 35 is formed. For example, aluminum (Al) is deposited as a drain electrode 36 by a sputtering method, and then patterned by photolithography and etching to complete a thin film transistor (FIG. 4E).

The sub-threshold swing (S value) of the TFT obtained by the manufacturing method of the fourth embodiment is 0.2
8 V / decade, which is superior to the case where a gate insulating film is formed by a plasma CVD method.

In the fourth embodiment, only one oxide film is formed on polycrystalline silicon as the gate insulating film, but the gate insulating film is not necessarily required to be one layer. The throughput of the gate oxide film forming step may be increased by reducing the thickness of the oxide film described in Embodiment 4 and stacking another insulating film. For example, TEO is formed on an oxide film (approximately 100 °) formed by using the method of the fourth embodiment.
A stacked structure formed by forming an insulating film using an S-CVD method, an NCVD method, an ECR-CVD method, a remote plasma CVD method, or the like may be used. At this time, the insulating film formed on the oxide film is made of SiO2, SiNx, Ta.
Ox or the like can be used.

Further, in the fourth embodiment, platinum is used as a catalyst element for promoting oxidation, but palladium or copper may be used.

In the fourth embodiment, an ion implantation method is used as a method of adding an element which promotes oxidation. However, an ion doping method or a FIB method (an ion focus beam method) is used.
Etc. may be used.

In Embodiment 4, a catalyst element for promoting oxidation is added after polycrystalline silicon is formed. However, polycrystalline silicon may be formed after adding a catalyst element to amorphous silicon.

In the fourth embodiment, the plasma CV
Although an oxygen plasma atmosphere was created using the D apparatus, oxygen may be excited by light or the like to create an oxygen radical atmosphere, or an ECR-CVD apparatus or a remote plasma CV
An oxygen radical or oxygen ion atmosphere may be created using a D apparatus or the like. Further, nitrogen ions, argon ions, or the like may be contained in an oxygen radical or oxygen ion atmosphere.

In the fourth embodiment, the platinum remaining after forming the oxide film is removed. However, platinum may be used as a gate electrode, or may be used as a part of the gate electrode. Further, HCl is used as a compound containing a halogen element.
Although an example of removing platinum using a gas has been described, other gases such as HF, NF ₃ , HBr, Cl ₂ , ClF ₃ ,
It may be removed by heat treatment at a temperature of 600 ° C. or less in an atmosphere containing BCl ₃ , F ₂ , Br, or the like.

Further, in the fourth embodiment, after the polycrystalline silicon is formed, a catalytic element for promoting oxidation is injected. However, before the catalytic element is injected, an oxide film serving as a buffer layer is formed on the polycrystalline silicon. May be. By forming the buffer layer, there is an advantage that damage to polycrystalline silicon caused when the catalyst element ions are implanted can be reduced.

In the fourth embodiment, the active layer
Although amorphous silicon formed by the plasma CVD method is used, it may be formed by a low-pressure CVD method other than the plasma CVD method, a sputtering method, or the like. Alternatively, microcrystalline silicon, polycrystalline, or single-crystal silicon may be used as a starting material in addition to amorphous silicon.

Further, in the fourth embodiment, silicon oxide is used as the undercoat film. However, an insulating film such as silicon nitride may be used, or the undercoat film may not be formed.

In the fourth embodiment, RTA is used to activate the implanted ions. However, annealing may be performed in an atmosphere of 400 ° C. or more, or self-activation by simultaneously implanted hydrogen may be performed. It is not necessary to intentionally activate in anticipation of activation.

In the fourth embodiment, MOW and Al are used for the gate electrode, source electrode and drain electrode. However, aluminum (Al), tantalum (Ta), molybdenum (Mo), chromium (Cr), titanium A metal such as (Ti) or an alloy thereof may be used, or a transparent conductive layer such as ITO may be used.

In the fourth embodiment, TEOS (Tetraethylorthosil) is used as the interlayer insulating film.
icate: silicon dioxide produced by a plasma CVD method using (C ₂ H ₅ O) ₄ Si) as a source gas was used. However, an AP-CVD method or an ECR-CVD method may be used. An insulating film may be used.

Further, in the fourth embodiment, phosphorus ions are used as ions to be implanted. However, aluminum or the like may be used, or boron or the like serving as an acceptor may be used.

In the fourth embodiment, the oxide film is formed after the polycrystalline silicon is formed. However, a catalytic element which promotes oxidation is added to the amorphous silicon first, and then the polycrystalline silicon is formed. Then, an oxide film may be formed.

[0098]

As described above, according to the method for forming an oxide film of the present invention, an oxide film can be formed by thermal oxidation by the action of a catalytic element that promotes oxidation. Can be cleaned. Further, by adding a catalytic element to the semiconductor thin film, an oxide film can be efficiently formed at a low temperature.

Further, according to the method for manufacturing a thin film transistor of the present invention, a highly reliable thin film transistor having excellent performance can be provided while the substrate temperature is kept low.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of each main process for describing a method of forming an oxide film according to a first embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of each main process for describing a method of forming an oxide film according to a second embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view showing main steps for describing a method for manufacturing a thin film transistor according to a third embodiment of the present invention;

FIG. 4 is a schematic cross-sectional view of each main process for describing a method for manufacturing a thin film transistor according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view for explaining a conventional method of manufacturing a thin film transistor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Substrate 12 Undercoat film 13 Amorphous silicon 14 Polycrystalline silicon 15 Laser beam 16 Platinum ion implantation 17 Polycrystalline silicon containing platinum 18 Oxide film formed by catalysis 21 Oxygen ion 31 Gate electrode 32 Source region 33 Drain region 34 interlayer insulating film 35 source electrode 36 drain electrode 51 gate insulating layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H01L 21/336 H01L 29/78 627G F-term (Reference) 2H092 JA25 JA29 JA38 JA42 JA44 JB13 JB23 JB32 JB33 JB38 KA04 KA07 KA12 KA16 KA18 MA05 MA08 MA14 MA15 MA16 MA18 MA19 MA20 MA22 MA27 MA30 MA35 MA37 MA41 NA22 NA25 PA06 QA07 4M104 AA10 BB02 BB16 CC05 DD79 DD80 EE03 FF06 GG20 5F058 BA20 BB04 BB07 BC02 BC04 ABF12B17B02A EE06 FF01 FF02 FF03 FF09 FF23 FF25 FF29 FF31 FF35 FF36 GG02 GG13 GG43 GG45 GG47 HJ01 HJ13 HL03 HL04 HL07 NN23 NN35 PP03

Claims (9)

[Claims] An oxide film is formed on the surface of a semiconductor thin film containing silicon by adding a catalytic element for promoting oxidation to a semiconductor thin film containing silicon and performing heat treatment in an atmosphere containing at least an oxidizing substance at a temperature of 600 ° C. or less. Forming an oxide film. 2. An oxide film is formed on the surface of the silicon-containing semiconductor thin film by adding a catalyst element that promotes oxidation to the silicon-containing semiconductor thin film and leaving it in a plasma atmosphere containing at least oxygen radicals and oxygen ions. Forming an oxide film. 3. The method for forming an oxide film according to claim 1, further comprising a step of performing a heat treatment in an atmosphere containing a halogen element to getter the catalyst element that promotes the oxidation. 4. The oxidation according to claim 1, wherein the method of adding a catalyst element that promotes oxidation is a method of implanting ions containing an accelerated catalyst element. Method of forming a film. 5. A thin film transistor having, on an insulating substrate, at least a semiconductor thin film containing silicon comprising a channel region and a source / drain region containing an impurity serving as a donor or an acceptor, a gate insulating film, a gate electrode, and a source / drain electrode. The method for producing a semiconductor thin film containing silicon by adding a catalytic element promoting oxidation to the semiconductor thin film containing silicon and performing heat treatment in an atmosphere containing at least an oxidizing substance at 600 ° C. or lower. Forming a thin oxide film on the thin film transistor. 6. A thin film transistor comprising a silicon semiconductor thin film comprising a channel region and a source / drain region containing impurities serving as donors or acceptors, a gate insulating film, a gate electrode, and a source / drain electrode on an insulating substrate. A method of adding a catalytic element that promotes oxidation to the silicon-containing semiconductor thin film and leaving it in a plasma atmosphere containing at least oxygen radicals and oxygen ions to oxidize the silicon-containing semiconductor thin film. A method for manufacturing a thin film transistor, comprising a step of forming a film. 7. The method according to claim 5, further comprising the step of forming an oxide film on the silicon-containing semiconductor thin film before adding a catalyst element for promoting oxidation to the silicon-containing semiconductor thin film. A method for manufacturing the thin film transistor according to the above. 8. The thin film transistor according to claim 5, further comprising a step of performing a heat treatment in an atmosphere containing a halogen element to getter a catalytic element that promotes oxidation. Production method. 9. The method according to claim 5, wherein the method of adding a catalyst element that promotes oxidation is a method of implanting ions containing the accelerated catalyst element. Method for manufacturing thin film transistor.