JP2001119036A - Method for manufacturing thin-film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve reliability without changing the characteristics of a thin- film transistor by forming SiNx with small fixed electric charge between a transparent substrate and a polycrystalline silicon film in the polycrystalline silicon thin-film transistor on the transparent substrate. SOLUTION: By selectively heating an undercoat SiO2 film or a semiconductor film after injecting nitrogen into an undercoat SiO2 film 20, injected nitrogen 30 is crystallized and SiNx with a small fixed electric charge is formed, thus obtaining a polycrystalline thin-film transistor having improved reliability without causing the transistor characteristics to change.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a polycrystalline thin film transistor.

[0002]

2. Description of the Related Art In recent years, polycrystalline silicon thin film transistors have been actively developed. One of the great attractions is that a polycrystalline silicon thin film transistor can be formed at a temperature of 600 ° C. or less at which a glass substrate can be used by a technique such as laser annealing. In addition, since a polycrystalline silicon thin film transistor has much higher mobility than an amorphous silicon thin film transistor using amorphous silicon for a semiconductor layer, not only a pixel transistor used for liquid crystal switching but also a driving circuit for driving the pixel transistor is made of glass. It can be formed on a substrate. By forming the drive circuit on a glass substrate, the number of external circuits can be reduced, which leads to cost reduction. Further, by reducing the number of external circuits, the number of connection points with external circuits is reduced, and reliability is improved. Furthermore, since there is no limitation due to mounting technology and pixels can be formed at a narrow pitch, a high-definition image can be realized. As described above, an active matrix type liquid crystal display device using a polycrystalline thin film transistor as a switching element can realize high reliability and high definition image at low cost. And is widely used in notebook computers.

On the other hand, in an active matrix type liquid crystal display device, a polycrystalline thin film transistor is formed on a large-area glass substrate in order to increase the screen size and reduce the cost of the display. Undercoat S for protection because it contains many impurities
An iO2 film was formed on a glass substrate, and a thin film transistor was formed thereon.

[0004]

However, since the SiO ₂ film is not as dense as the SiN _x film, impurities such as alkali metals diffuse due to long-time annealing or electric stress at a high temperature, and the characteristics of the thin film transistor are reduced. affect. In order to avoid this, when SiN _x is formed as an undercoat insulating film by plasma CVD, diffusion of impurities from the glass substrate can be prevented.
A large amount of positive fixed charges are contained in the iN _x film, and the characteristics of the thin film transistor are greatly changed by the fixed charges.

Therefore, an object of the present invention is to form a SiN _x film having a small fixed charge and prevent the diffusion of impurities from a glass substrate without changing the characteristics of a thin film transistor.
An object of the present invention is to provide a method of manufacturing a thin film transistor with improved reliability.

[0006]

Means for Solving the Problems In order to solve this problem, in the present invention, in the step after injecting nitrogen into the undercoat SiO ₂ film performs lamp annealing or excimer laser annealing, an undercoat SiO ₂ film Direct heating or indirect heating by heat absorbed by the semiconductor film crystallizes the injected nitrogen. As a light source for lamp annealing, an excimer lamp is suitable for directly heating an SiO ₂ film, and a halogen lamp, a UV lamp, and an excimer lamp are suitable for heating an amorphous silicon film or a polycrystalline silicon film.

Hereinafter, the respective manufacturing methods will be described.

In the manufacturing method of the first aspect, nitrogen is injected after forming an undercoat SiO ₂ film on a transparent substrate,
By performing lamp annealing with a light source adapted to the wavelength region absorbed by the SiO ₂ film, the undercoat SiO 2
_{The two} films are selectively heated to crystallize the injected nitrogen to form a SiN _x film.

According to a second aspect of the present invention, after nitrogen is injected into the undercoat SiO ₂ film, a polycrystalline silicon film is formed by a plasma CVD method, and a light source adapted to a wavelength region absorbed by the polycrystalline silicon film. Lamp annealing is performed. The polycrystalline silicon is heated by the lamp annealing, the heat is conducted to the undercoat SiO ₂ film, the injected nitrogen is crystallized, and the SiN _x film is formed.

According to a third aspect of the present invention, the implanted nitrogen is crystallized by lamp annealing in an atmosphere containing a hydrogen nitride compound, a nitrogen oxide compound, or a mixture thereof, and simultaneously the oxynitride of the polycrystalline silicon film is performed. I do. As a result, dense Si
Simultaneously it makes a N _x as a protective film, low interface state polycrystalline silicon film / oxide film interface is formed.

According to a fourth aspect of the present invention, lamp annealing is performed by converting an atmospheric gas into plasma so that the polycrystalline silicon film is more easily oxynitrided.

According to a fifth aspect of the present invention, after injecting nitrogen into the undercoat SiO ₂ film, a polycrystalline silicon film is formed by a plasma CVD method, and excimer laser annealing is performed. The excimer laser light is absorbed by the polycrystalline silicon film, and a large grain size of the polycrystalline silicon film is realized. At the same time, the heat absorbed by the polycrystalline silicon film is conducted to the undercoat SiO ₂ film,
Nitrogen injected into the O ₂ film is crystallized to form a SiN _x film.

[0013] In the manufacturing method according to the sixth aspect, the under-
SiO_TwoAfter injecting nitrogen into the film, plasma CVD method
Amorphous silicon is deposited by excimer
Of amorphous silicon by laser annealing
To form a polycrystalline silicon film,
Undercoat SiO by heat conduction from recon film _Two
The film is heated and the undercoat SiO_TwoNitrogen injected into the membrane
Crystallization of silicon and SiN _xForm a film.

According to a seventh aspect of the present invention, the under-
SiO_TwoAfter injecting nitrogen into the film, plasma CVD method
To form amorphous silicon
Run with a light source compatible with the wavelength region absorbed by the silicon film
Pre-anneal is performed. This makes amorphous silicon
Absorbs the lamp light and heats the amorphous silicon
You. And by heat conduction from amorphous silicon
Undercoat SiO _TwoIs heated and undercoat S
iO_TwoThe nitrogen injected into the film is crystallized and _xFormed
Is done.

In the manufacturing method according to the present invention, the lamp annealing is performed in two stages. First, after annealing at a first temperature, annealing is performed at a second temperature. This is because when amorphous silicon is recrystallized by, for example, lamp annealing, the concentration of hydrogen contained in the amorphous silicon film must be reduced to about 1 atomic% before recrystallization. Therefore, first, dehydrogenation is performed by annealing at a first temperature, and then recrystallization is performed at a second temperature.

According to a ninth aspect of the present invention, the first temperature is set to 400 ° C. to 550 ° C., and the second temperature is set to 600 ° C.
C. to 750.degree.

According to a tenth aspect of the present invention, the substrate is preliminarily heated in order to suppress a rapid temperature change of the substrate and reduce the shape deformation. Thereby, cracks in the thin film can also be suppressed.

In the manufacturing method according to the eleventh aspect, the light source of the lamp annealing is a UV lamp such as a high-pressure mercury lamp, a metal halide lamp, and a xenon lamp. These lamps contain a lot of near-infrared to ultraviolet light that is absorbed by polycrystalline silicon or amorphous silicon and not absorbed by the glass substrate, so that the semiconductor film can be selectively heated.

According to a twelfth aspect of the present invention, the light source for lamp annealing is a halogen lamp. Halogen lamps have a broad spectrum with a peak at a wavelength of about 1 μm, a small amount of long-wavelength components of about 3 μm or more absorbed by a glass substrate, and a large amount of components from near infrared to ultraviolet. It can be selectively heated. In terms of selective heating, UV lamps and excimer lamps are better, but halogen lamps are more stable.

In the manufacturing method according to the thirteenth aspect, the light source of the lamp annealing is an excimer lamp. An excimer lamp has one emission peak, and emits light only in a very narrow region around the peak. There are various types of peak wavelengths from ultraviolet to vacuum ultraviolet (VUV), and the SiO ₂ film can be heated. Since there is only one emission peak, a specific film can be more selectively heated.
Inferior to lamps and halogen lamps.

In a step after nitrogen is injected into the undercoat SiO ₂ film, the glass substrate is selectively heated by lamp annealing or excimer laser annealing to selectively heat the polycrystalline silicon film, the amorphous silicon film, or the undercoat SiO _2. While maintaining the temperature low enough not to soften, the undercoat SiO ₂ is temporarily
By setting the temperature to be higher than or equal to 00 ° C., the implanted nitrogen can be crystallized to form a SiN _x film. As a result, it is possible to form a dense SiN _x film with a small fixed charge without causing a change in the shape of the glass substrate, and a protective film that prevents diffusion of impurities from the glass substrate without changing the characteristics of the thin film transistor. It is formed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS.

(Embodiment 1) Embodiment 1 according to the present invention will be described with reference to FIG. First, the glass substrate 10
Undercoat SiO ₂ by plasma CVD
A film 20 is deposited from 2000 to 4000 degrees. And
Nitrogen is ion-implanted into the undercoat SiO ₂ film 20 by an ion implantation method or an ion doping method at an acceleration voltage of 5 to 15 kV into an extremely shallow place of about 5E14 to 5E15 / cm ² . Then, lamp annealing is performed with an Ar excimer lamp having a peak wavelength of 126 nm. Since the lamp light is almost absorbed by the undercoat SiO ₂ film 20 and does not reach the glass substrate 10, the undercoat SiO ₂ film 20 is selectively heated. Thus, while maintaining the temperature of the glass substrate 10 at a temperature equal to or lower than the softening point, the nitrogen 30 injected into the undercoat SiO ₂ film 20 is crystallized to form Si.
The _Nx film 50 can be formed. A polycrystalline silicon film 60 is formed thereon by a plasma CVD method from 500 ° to 100 °.
After depositing and patterning at 0 °, a SiO ₂ film is formed as the gate insulating film 70 by plasma CVD or normal pressure CVD at about 500 ° to 1000 °. Then, for example, Ta is formed as the gate electrode 80 by a 3000 ° sputtering method, and patterning is performed. After the gate electrode 80 is formed, an impurity imparting N conductivity type or P conductivity type in a self-aligned manner is added to the polycrystalline silicon film 60 by an ion doping method.
a and the drain region 60b are formed. After depositing SiO ₂ as an interlayer insulating film 90 by a plasma CVD method,
A contact hole is opened, a source electrode 100 and a drain electrode 110 are formed, and a polycrystalline silicon thin film transistor is completed.

(Embodiment 2) Embodiment 2 according to the present invention will be described with reference to FIG. First, the glass substrate 10
Undercoat SiO ₂ by plasma CVD
A film 20 is deposited from 2000 to 4000 degrees. And
Nitrogen is implanted into the undercoat SiO ₂ film 20 by ion implantation or ion doping at an acceleration voltage of 5 to 15 kV into an extremely shallow place at about 5E14 to 5E15 / cm ² . Thereafter, a polycrystalline silicon film is deposited at a thickness of 500 to 1000 ° by a plasma CVD method. Then, lamp annealing is performed with a light source suitable for the wavelength region absorbed by the polycrystalline silicon film 60, for example, a metal halide lamp. The metal halide lamp has a continuous spectrum of 250 ° to 450 ° and is absorbed by the polycrystalline silicon film 60 but not absorbed by the glass substrate 10. Therefore, the polycrystalline silicon film 60 can be selectively heated, and the undercoating SiO ₂ film is formed by heat conduction from the polycrystalline silicon film 60 at the same time as increasing the grain size and the crystallinity of the polycrystalline silicon film 60. Nitrogen 30 injected by heating 20
Is crystallized to form SiN _x 50. Thus, diffusion of impurities from the glass substrate 10 can be prevented, change in transistor characteristics due to thermal stress or electric stress can be prevented, and reliability can be improved. If lamp annealing is performed in an atmosphere containing a hydrogen nitride, a nitrogen oxide compound, or a mixture thereof, for example, in an NH ₃ atmosphere, the polycrystalline silicon film 60 can be oxynitrided. Thereby, a good polycrystalline silicon film / insulating film interface can be obtained simultaneously with the crystallization of the implanted nitrogen. Further, when lamp gas annealing is performed by converting the atmospheric gas into plasma, oxynitridation is further promoted.

After patterning the polycrystalline silicon 60, an SiO ₂ film is formed as a gate insulating film 70 by a plasma CVD method or a normal pressure CVD method from 500 ° to 10 °.
A film is formed at about 00 °. Then, for example, Ta is formed as the gate electrode 80 by a 3000 ° sputtering method,
Perform patterning. After the gate electrode 80 is formed, an impurity imparting an N conductivity type or a P conductivity type is added to the polycrystalline silicon film 60 in a self-aligning manner by an ion doping method to form a source region 60a and a drain region 60b. Plasma CVD of SiO2 as interlayer insulating film 90
After the deposition by the method, a contact hole is opened, a source electrode 100 and a drain electrode 110 are formed, and a polycrystalline silicon thin film transistor is completed.

In this embodiment, the SiN _x 50 is formed by lamp annealing. However, after the polycrystalline silicon film 60 is formed by the plasma CVD method, the polycrystalline silicon film 60 is heated by excimer laser annealing, and heat conduction is performed. The injected nitrogen 30 is crystallized by heating the undercoat SiO ₂ film 20 with SiN _x 50.
Can also be formed.

(Embodiment 3) Embodiment 3 according to the present invention will be described with reference to FIG. First, the glass substrate 10
Undercoat SiO ₂ by plasma CVD
A film 20 is deposited from 2000 to 4000 degrees. And
Nitrogen is implanted into the undercoat SiO ₂ film 20 by ion implantation or ion doping at an acceleration voltage of 5 to 15 kV into an extremely shallow place at about 5E14 to 5E15 / cm ² . Then, an amorphous silicon film is deposited at 500 to 1000 ° by a plasma CVD method. Thereafter, the amorphous silicon film 130 is melted by irradiating an excimer laser, and recrystallized to form the polycrystalline silicon film 60. At the same time, the undercoat SiO 2 is formed by heat conduction from the amorphous silicon film 130.
₂ Heat the film 20, crystallize the injected nitrogen 30 and
Forming an N _x 50. When recrystallizing the amorphous silicon film 130 by lamp annealing, lamp annealing is performed by a light source suitable for the wavelength region absorbed by the amorphous silicon film 130, for example, a metal halide lamp. Metal halide lamp 250 ~ 450
It has a continuous spectrum of Å, and is absorbed by the amorphous silicon film 130 and not absorbed by the glass substrate 10. Therefore, the amorphous silicon film 130 can be selectively heated, and the amorphous silicon film 130 can be recrystallized while the temperature of the glass substrate 10 is kept below the softening point. At the same time, the undercoat SiO ₂ film 20 is heated by heat conduction from the amorphous silicon film 130, the injected nitrogen 30 is crystallized, and SiN _x 50 is formed.

Since the amorphous silicon film 130 contains a large amount of hydrogen, when it is melted, the hydrogen evaporates and the film peels off. Therefore, it is necessary to reduce the hydrogen concentration to about 1 atomic% by dehydrogenation before recrystallization. Must. Dehydrogenation is 4
This is performed by furnace annealing at about 50 ° C.
By performing lamp annealing in two stages, dehydrogenation and recrystallization can be performed continuously. For example, first
Anneal at 400 ° C. to 550 ° C. for about 30 seconds to 2 minutes to perform dehydrogenation, and then anneal at 600 ° C. to 750 ° C. for about several seconds to several tens of seconds to recrystallize the amorphous silicon film 130, The silicon film 60 can be formed.

As the gate insulating film 70, plasma CVD
The SiO ₂ film is deposited at 500
From about 1000 °. Then, for example, Ta is formed as the gate electrode 80 by a 3000 ° sputtering method, and patterning is performed. After the gate electrode 80 is formed, an impurity imparting N conductivity type or P conductivity type in a self-aligned manner is added to the polycrystalline silicon film 60 by an ion doping method, so that the source region 60a and the drain region 60 are formed.
b is formed. After depositing SiO ₂ as an interlayer insulating film 90 by a plasma CVD method, a contact hole is opened, a source electrode 100 and a drain electrode 110 are formed, and a polycrystalline silicon thin film transistor is completed.

In the embodiments 2 and 3, the metal halide lamp was used as the light source when the polycrystalline silicon film 60 and the amorphous silicon film 130 were subjected to lamp annealing, but other UV lamps such as a xenon lamp and a mercury lamp were used. The same effect can be obtained by using an excimer lamp or a halogen lamp as a light source.

Further, by heating the substrate in advance before lamp annealing, a rapid temperature change of the substrate can be suppressed to reduce the shape deformation, and the crack of the thin film can be suppressed.

[0032]

As described above, according to the present invention, by selectively heating the undercoat SiO ₂ film or the semiconductor film thereon, the injected nitrogen is crystallized to form SiNx having a small fixed charge. be able to. This has the advantageous effect of preventing the diffusion of impurities from the glass substrate without changing the transistor characteristics and improving the reliability of the thin film transistor.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment according to the present invention.

FIG. 2 is a diagram showing a second embodiment according to the present invention.

FIG. 3 is a diagram showing a third embodiment according to the present invention.

[Explanation of symbols]

10 glass substrate 20 undercoat SiO ₂ 30 implanted nitrogen 40 lamp light 50 SiN _x 60 polycrystalline silicon 60a source region 60b drain region 70 a gate insulating film 80 gate electrode 90 interlayer insulating film 100 source electrode 110 drain electrode 120 laser beam 130 Amorphous silicon

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 29/78 627G (72) Inventor Masumi Ido 1006 Ojidoma, Kazuma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. Terms (reference) 2H092 KA04 KA07 KA12 KA16 KA18 KB21 MA03 MA08 MA13 MA17 MA22 MA29 MA30 MA35 MA37 NA25 NA27 NA29 PA01 5F058 BA05 BA20 BB04 BB07 BC08 BF76 BF78 BF80 BJ10 5F110 AA26 BB01 GG17 FF30 DD02 DD02 DD13 DD14 PP02 PP03 PP35

Claims (13)

[Claims] 1. A method of manufacturing a polycrystalline silicon thin film transistor on a transparent substrate, comprising: a step of forming an undercoat SiO ₂ film; and a step of injecting nitrogen into the undercoat SiO ₂ film. A method of manufacturing a polycrystalline silicon thin film transistor, comprising performing lamp annealing with a light source adapted to a wavelength region absorbed by an SiO ₂ film. 2. A method for producing polycrystalline silicon thin film transistor on a transparent substrate, forming an undercoat SiO ₂ film, a step of injecting nitrogen into the undercoat SiO ₂ film, the polycrystalline silicon by a plasma CVD method Forming a film, and after forming the polycrystalline silicon film, performing lamp annealing with a light source suitable for a wavelength region absorbed by the polycrystalline silicon film. 3. The method according to claim 2, wherein the lamp annealing is performed in an atmosphere containing a hydrogen nitride compound, a nitric oxide compound or a mixture thereof. 4. A method for manufacturing a polycrystalline silicon thin film transistor according to claim 3, wherein an atmosphere gas containing a hydrogen nitride compound, a nitrogen oxide compound or a mixture thereof is plasma-decomposed and lamp-annealed. 5. A method of manufacturing a polycrystalline silicon thin film transistor on a transparent substrate, comprising: a step of forming an undercoat SiO ₂ film; a step of injecting nitrogen into the undercoat SiO ₂ film; Forming a polycrystalline silicon film, followed by excimer laser annealing after forming the polycrystalline silicon film. 6. The method for producing polycrystalline silicon thin film transistor on a transparent substrate, forming an undercoat SiO ₂ film, a step of injecting nitrogen into the undercoat SiO ₂ film, an amorphous silicon film by a plasma CVD method Forming a polycrystalline silicon thin film, after forming the amorphous silicon film, performing excimer laser annealing. 7. The method for producing polycrystalline silicon thin film transistor on a transparent substrate, forming an undercoat SiO ₂ film, a step of injecting nitrogen into the undercoat SiO ₂ film, an amorphous silicon film by a plasma CVD method Forming a polycrystalline silicon thin film transistor, wherein after the amorphous silicon film is formed, lamp annealing is performed with a light source adapted to a wavelength region absorbed by the amorphous silicon film. 8. The method according to claim 7, wherein the lamp annealing comprises annealing at a first temperature and annealing at a second temperature. 9. The method according to claim 1, wherein the first temperature is between 400 ° C. and 550 ° C.
9. The method according to claim 8, wherein the second temperature is in a range of 600 [deg.] C. to 750 [deg.] C. 10. The lamp annealing step includes a step of preheating the substrate before annealing.
10. The method for manufacturing a polycrystalline silicon thin film transistor according to any one of the above items. 11. A light source for lamp annealing is a UV lamp such as a high-pressure mercury lamp, a metal halide lamp, and a xenon lamp.
The method for manufacturing a polycrystalline silicon thin film transistor according to any one of the above. 12. The method of manufacturing a polycrystalline silicon thin film transistor according to claim 1, wherein a light source of the lamp annealing is a halogen lamp. 13. The method of manufacturing a polycrystalline silicon thin film transistor according to claim 1, wherein a light source of the lamp annealing is an excimer lamp.