JP2001320056A - Manufacturing method for thin-film transistor and thin- film semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a process for crystallizing a semiconductor thin-film by laser irradiation which is used for an active layer of a bottom gate type thin-film transistor. SOLUTION: This manufacturing method comprises a gate electrode forming process where a gate electrode 5 is formed on an insulating substrate 1, a gate insulating film forming process where gate insulating films 3 and 4 are so formed as to cover the gate electrode 5, a semiconductor thin-film forming process for forming a semiconductor thin-film 2 on the gate insulating films 3 and 4, a crystallizing process where the semiconductor thin-film 2 is irradiated with laser beam 50 for crystallization, and an impurity introducing process where an impurity is selectively introduced into the semiconductor thin-film 2. In the crystallizing process, the laser beam 50 of wavelength 300 nm or shorter is projected to crystallize the semiconductor thin-film 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a thin film transistor and a thin film semiconductor device. More specifically,
The present invention relates to a technique for manufacturing a thin-film semiconductor device in which a bottom-gate thin-film transistor using polycrystalline silicon or the like as an active layer is integrated on an insulating substrate.

[0002]

2. Description of the Related Art Thin-film semi-semiconductor devices are suitable for driving substrates such as active matrix type liquid crystal displays for display, and are currently being actively developed. In particular, polycrystalline silicon thin film transistors have been attracting attention because they can realize small and high-definition active matrix color liquid crystal display devices. In order to form a thin film transistor as a pixel switching element on an insulating substrate made of a transparent glass or the like, in the conventional semiconductor technology, a polycrystalline silicon thin film that has been used only as an electrode material or a resistance material is used as an active layer. This is the only technology that can realize a high-performance thin film transistor for a switching element that can be designed with high density to achieve the image quality required in the market. At the same time, it has also become possible to form a peripheral circuit portion using an external IC in the same process on the same substrate as the pixel array portion. It is possible to realize an active matrix liquid crystal display with high definition and a peripheral circuit unit integrated type, which cannot be realized with an amorphous silicon thin film transistor.

Since polycrystalline silicon has a higher carrier mobility than amorphous silicon, the current driving capability of the polycrystalline silicon thin film transistor is increased, and peripheral circuit portions such as a horizontal scanning circuit and a vertical scanning circuit which require high-speed driving are required. It can be simultaneously formed on the same substrate as the pixel switching thin film transistor. Therefore, the number of signal lines to be taken out from the display thin film semiconductor device to the outside can be significantly reduced. Also, a CMOS circuit in which N-channel and P-channel thin film transistors are integrated can be formed on-chip, a level shift circuit can be built in, and low-voltage driving of timing signals can be performed.

As a thin film transistor device technology and a process technology, a high temperature process technology employing a processing temperature of 1000 ° C. or higher has been established. The feature of this high temperature process is that a semiconductor thin film formed on a high heat resistant substrate such as quartz is modified by solid phase growth.
The solid phase growth method is a method in which a semiconductor thin film is heat-treated at a temperature of 1000 ° C. or higher. In a film formation stage, individual crystal grains contained in polycrystalline silicon, which is a collection of minute silicon crystals, are enlarged. The polycrystalline silicon obtained by this solid-phase growth method is 100 cm ² / v. A high carrier mobility of about s can be obtained. In order to carry out such a high-temperature process, it is essential to use a substrate having excellent heat resistance, and conventionally expensive quartz or the like has been used. However, quartz is disadvantageous from the viewpoint of reducing manufacturing costs.

[0005] Instead of the high temperature process described above,
Low temperature processes employing the following processing temperatures have been developed. Laser annealing using a laser beam has attracted attention as a part of a method for making a manufacturing process of a thin film semiconductor device a low-temperature process. This involves irradiating a laser beam onto a non-single-crystal semiconductor thin film such as amorphous silicon or polycrystalline silicon formed on a low heat-resistant insulating substrate such as glass, and then locally heating and melting it, and then cooling it. In the process, the semiconductor thin film is crystallized. Using the crystallized semiconductor thin film as an active layer (channel region), a polycrystalline silicon thin film transistor is integrated and formed. Since the crystallized semiconductor thin film has high carrier mobility, the performance of the thin film transistor can be improved to some extent.

[0006] By the way, conventionally, the thin film transistor mainly has a top gate type structure. In the top gate structure, a semiconductor thin film is formed on an insulating substrate, and a gate electrode is formed above via a gate insulating film. In the low-temperature process, a low-cost large glass plate is used as an insulating substrate. Since this glass plate contains a lot of impurity metals such as Na,
Na and the like are localized according to the voltage for driving the thin film transistor. There is a reliability problem that the characteristics of the thin film transistor fluctuate due to the electric field. On the other hand, in recent years, a bottom gate type structure suitable for a low-temperature process has been developed. In this method, a gate electrode made of a metal film or the like is arranged on an insulating substrate such as a glass plate, and a semiconductor thin film is formed thereon via a gate insulating film. The gate electrode has an effect of shielding the electric field in the glass plate, and the bottom gate type is superior to the top gate type in terms of reliability from a structural point of view.

[0007]

However, the bottom gate structure has a serious problem when performing crystallization by laser annealing. In the semiconductor thin film to be recrystallized, a portion to be a channel region is located directly above a gate electrode, and portions to be a source region and a drain region are on a glass plate. For this reason, when energy is given by laser beam irradiation, a difference appears in the heat conduction state and the heat dissipation state on the glass plate and on the metal gate electrode. Therefore, the optimal laser energy differs between the channel region, the source region, and the drain region, so that laser irradiation with the optimal energy at which large carrier mobility is obtained cannot be performed. That is, when recrystallization is performed by laser annealing, both the semiconductor thin film on the metal gate electrode and the semiconductor thin film on the glass plate are irradiated with a laser beam at the same time. In addition, on the metal gate electrode, heat is transmitted in the gate wiring and dissipated in the horizontal direction, so that the heat is solidified in a relatively short time. For this reason, the crystal grain of the recrystallized semiconductor thin film differs between the metal gate electrode and the glass plate, and the carrier mobility is not uniform. In an extreme case, when attempting to increase the crystal grain size of the semiconductor thin film on the metal gate electrode, the semiconductor thin film on the glass plate may have too high irradiation energy and evaporate. Conversely, if the crystal state of the semiconductor thin film on the glass plate is to be made normal, the semiconductor thin film on the metal gate electrode has a small crystal grain size.
In other words, at the time of laser annealing, if a semiconductor thin film is irradiated with laser light at an optimum energy on both a metal gate electrode and an insulating substrate such as glass, the process margin becomes extremely narrow. is there. Here, the process margin indicates an allowable range of the irradiation energy density of the laser beam in the manufacturing process. Conventionally, since the process margin is narrow, it is necessary to severely suppress the fluctuation of the irradiation energy density of the laser beam, which has been accompanied by great difficulty.

[0008]

SUMMARY OF THE INVENTION In view of the above-mentioned problems of the prior art, an object of the present invention is to improve a crystallization process of a semiconductor thin film used for an active layer of a bottom gate type thin film transistor by laser light irradiation. . The following measures were taken in order to achieve this purpose. That is, the present invention provides a gate electrode forming step of forming a gate electrode on an insulating substrate,
Forming a gate insulating film so as to cover the gate electrode; forming a semiconductor thin film on the gate insulating film; and irradiating the semiconductor thin film with laser light. In a method for manufacturing a thin film transistor comprising a crystallization step for crystallization and an impurity introduction step for selectively introducing an impurity into the semiconductor thin film, the crystallization step is performed by irradiating a laser beam having a wavelength of 300 nm or less. The method is characterized in that a semiconductor thin film is crystallized. Preferably, in the crystallization step, the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source. In the gate electrode forming step, a gate electrode having a thickness of 10 nm or more is formed.
In the gate electrode forming step, a gate electrode made of metal aluminum is formed.

According to the present invention, a semiconductor thin film of a bottom-gate thin film transistor is crystallized by irradiating a laser beam having a wavelength of 300 nm or less. For example, a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source is used. On the other hand, conventionally, laser light having a wavelength of 308 nm emitted from a XeCl excimer laser light source has been frequently used for crystallization of a semiconductor thin film. As the wavelength of the laser beam becomes shorter, the absorption at the surface of the semiconductor thin film increases, and the laser beam hardly penetrates into the inside. Therefore, as the wavelength is shorter, the heat generated by the absorption of the laser light is also limited to the surface of the semiconductor thin film, and it is difficult to transmit the heat to the metal gate electrode and the insulating substrate made of glass or the like located therebelow. In other words, as the wavelength becomes shorter, the thermal effect of the laser light irradiation does not reach the back side of the semiconductor thin film, and the difference between the metal gate electrode and the glass substrate disappears. Therefore, the wavelength is 300 nm
By using the following laser light, the difference in crystal state between the channel region on the metal gate electrode and the source / drain region on the glass substrate is reduced, and uniform polycrystal is obtained. On the other hand, when a laser beam having a wavelength of 300 nm or more is used, the laser beam is absorbed not only at the surface of the semiconductor thin film but also inside the semiconductor thin film. In other words,
Since the crystallization state is different between the metal gate electrode and the glass substrate, it is difficult to integrally form thin film transistors with uniform characteristics.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic diagram illustrating the basic concept of the present invention. (A) shows a method for manufacturing a thin film transistor according to the present invention. Basically, a thin film transistor is formed by a gate electrode forming step, a gate insulating film forming step, a semiconductor thin film forming step, a crystallization step, and an impurity introducing step. First, in the gate electrode forming step,
A gate electrode 5 is formed on an insulating substrate 1 made of glass or the like. Specifically, a metal film is formed by, for example, sputtering, and is etched according to the shape of the gate electrode. Next, a gate insulating film forming step is performed, and a gate insulating film is deposited so as to cover the gate electrode 5. For example, plasma CVD
A gate nitride film 3 is deposited to a thickness of about 50 nm by the method, and a gate oxide film 4 is deposited to a thickness of 100 nm by the plasma CVD method. The gate nitride film 3 is made of, for example, silicon nitride, and the gate oxide film 4 is made of, for example, silicon oxide. Subsequently, a semiconductor thin film forming step is performed, and the gate nitride film 3 is formed.
The semiconductor thin film 2 is formed on a gate insulating film having a laminated structure of the gate oxide film 4 and the gate oxide film 4. For example, a semiconductor thin film 2 made of amorphous silicon is deposited to a thickness of 40 nm by a plasma CVD method. Thereafter, a crystallization step is performed, and the semiconductor thin film 2 is irradiated with a laser beam 50 to achieve crystallization. Specifically, amorphous silicon is converted to polycrystalline silicon. Thereafter, an impurity introducing step is performed, and the crystallized semiconductor thin film 2 is formed.
To selectively introduce impurities.

[0011] As a feature of the present invention, the crystallization step comprises:
The semiconductor thin film 2 is crystallized by irradiating a laser beam 50 having a wavelength of 300 nm or less. For example, the semiconductor thin film 2 is crystallized by irradiating laser light having a wavelength of 248 nm emitted from a KrF excimer laser light source. In some cases, an Ar ₂ excimer laser light source having an oscillation wavelength of 126 nm, an ArCl excimer laser light source having an oscillation wavelength of 175 nm, an ArF excimer laser light source having an oscillation wavelength of 193 nm, a KrCl excimer laser light source having an oscillation wavelength of 222 nm, and an oscillation wavelength of 282 nm A XeBr excimer laser light source can be used. Each laser light source is of a pulse oscillation type.
On the other hand, a XeCl excimer laser light source having an oscillation wavelength of 308 nm and a XeF excimer laser light source having an oscillation wavelength of 353 nm are all excluded from the technical scope of the present invention since the wavelengths exceed 300 nm. Most of the laser light 50 having a wavelength of 300 nm or less is absorbed by the surface of the semiconductor thin film 2 made of silicon or the like, so that the semiconductor thin film 2 can be uniformly crystallized without being affected by the base. For this reason,
The gate electrode 5 located under the semiconductor thin film 2 does not need to have a small heat capacity, and can have a thickness of 10 nm or more. Since the electrical resistance decreases as the gate electrode 5 becomes thicker, it is preferable in terms of a circuit. In an actual product, the gate electrode 5
Is set to 30 to 150 nm. Also, if the wavelength is 3
When a laser beam 50 having a thickness of 00 nm or less is used, heat generation is limited to the surface of the semiconductor thin film 2, so that the underlying gate electrode 5 does not become overheated, and aluminum can be used instead of the high melting point metal. Aluminum is preferable in terms of circuit because it has lower electric resistance than the high melting point metal. Needless to say, a high melting point metal such as Mo, Mo / Ta, or Cr may be used as the material of the gate electrode 5.

In FIG. 2A, a portion where the gate electrode 5 is arranged is represented by a region MTL. A portion where the gate electrode 5 is not provided and the surface of the substrate 1 made of glass or the like is directly located under the semiconductor thin film 2 is represented by a region GLS. Here, (b) is a graph showing the relationship between the laser beam (KrF) energy and the crystal grain size for the regions MTL and GLS. As shown in the figure, in the region MTL where the gate electrode 5 is disposed immediately below, when the laser beam energy is set to 270 mJ / cm ² , a maximum crystal grain size of about 1000 nm is obtained. On the other hand, immediately below the glass substrate 1
In the region GLS where the surface is located, the maximum crystal grain size can be obtained by setting the laser light energy to about 260 mJ / cm ² . There is no significant difference in the range of the laser beam energy at which the maximum crystal grain diameter can be obtained between the regions MTL and GLS, and the optimum crystal state can be obtained in any of the regions MTL and GLS under almost the same laser beam irradiation conditions. KrF laser light has a wavelength of 24
Since it is as short as 8 nm, it is almost absorbed on the surface of the semiconductor thin film 2 and is less affected by the underlayer. Therefore, the area M
The difference in the optimum laser beam irradiation conditions between TL and GLS is reduced, and a relatively large process margin can be obtained. For example, a grain size of 500 nm is secured in the region MTL and the region GL is secured.
In order to secure a particle diameter close to 1000 nm in S, the laser beam energy may be controlled in the range of 250 to 270 mJ / cm ² .

(C) shows a XeCl excimer as a reference example.
This shows a case where a laser light source is used. XeCl exci
The oscillation wavelength of the laser light source is 308 nm. As shown
As described above, in the region GLS, there is no much difference from the KrF laser beam,
Energy is 260mJ / cm ²Around 1000nm
Is obtained. In contrast, the gate
In the region MTL where the electrode 5 is arranged, the maximum crystal grain size is
The resulting laser light energy shifts significantly upwards
290 mJ / cm in the illustrated example.²It has become.
If the wavelength exceeds 300 nm, the laser light
Heat is absorbed not only on the surface but also inside
This also occurs in the lower portion near the gate electrode 5. Therefore, metal
The heat loss flowing out to the gate electrode 5 increases,
Large laser light energy to obtain suitable grain size
turn into. As described above, the region MTL and the GLS
If the optimum irradiation conditions of the light are different, the process margin will be narrow.
And control becomes difficult. For example, 100 in the area GLS
500 in region MTL while maintaining a crystal grain size close to 0 nm
When trying to secure a crystal grain size of
Energy range from 255 to 275 mJ / cm²About
It is much narrower than the case shown in (b).
U.

FIG. 2 is a process chart showing an example of a method for manufacturing a thin film transistor according to the present invention. First, as shown in (a), Al, T is placed on an insulating substrate 1 made of glass or the like.
a, Mo, W, Cr, Cu or an alloy thereof is formed in a thickness of 30 to 150 nm, and is patterned to be processed into the gate electrode 5.

Next, as shown in FIG.
A gate insulating film on the substrate. In this example, the gate insulation
The film is a gate nitride film 3 (SiN_x) / Gate oxide film 4 (S
iO _Two) Was used. The gate nitride film 3 is made of SiH
_FourGas and NH_ThreeUse a gas mixture as the source gas
The film was formed by a plasma CVD method (PCVD method). In addition, Plas
Normal pressure CVD or reduced pressure CVD may be used instead of
No. In this embodiment, the gate nitride film 3 has a thickness of 50 nm.
Deposited. Gate oxidation is performed successively after the formation of the gate nitride film 3.
The film 4 is formed with a thickness of about 100 nm. Further gate acid
Semiconductor thin film made of amorphous silicon continuously on the oxide film 4
The film 2 was formed with a thickness of about 40 nm. Double-layer gate
The insulating film and the amorphous semiconductor thin film 2 are connected to a vacuum system of a film forming chamber.
A continuous film was formed without breaking. Plasma CVD method with the above film formation
If used, a nitrogen atmosphere at a temperature of 400 to 450 ° C.
Heat treatment in air for about 1 hour to form amorphous semiconductor thin film 2
Releases the hydrogen contained. So-called dehydrogenation annie
Do Next, a laser beam 50 is applied to the amorphous semiconductor.
The body thin film 2 is crystallized. Oscillation wavelength as laser light 50
Use a 248 nm KrF excimer laser beam.
Can be. What is called laser annealing is 600 ° C or less.
A powerful tool for crystallizing semiconductor thin films at process temperatures
It is a step. In this embodiment, a laser excited in a pulse
Light 50 is applied to the amorphous semiconductor thin film 2 to perform crystallization.
U. Specifically, the laser light 50 emitted from the laser light source is
Rays that are shaped and have a predetermined intensity distribution in a predetermined irradiation area
A shaping step for forming the light;
Run so that the irradiation area partially overlaps the conductor thin film 2
Irradiation step of repeatedly irradiating the laser beam 50 while inspecting
Do.

As shown in FIG. 1C, SiO ₂ is formed to a thickness of about 100 nm to 300 nm on the polycrystalline semiconductor thin film 2 crystallized in the previous step, for example, by a plasma CVD method. This SiO ₂ is patterned into a predetermined shape and processed into a stopper film 16. In this case, the stopper film 16 is patterned so as to be aligned with the gate electrode 5 using the back surface exposure technique. The portion of the polycrystalline semiconductor thin film 2 located immediately below the stopper film 16 is protected as a channel region Ch. Subsequently, impurities (for example, P + ions) are implanted into the semiconductor thin film 2 by ion doping using the stopper film 16 as a mask to form an LDD region. The dose at this time is, for example, 6 × 10 ^{12 to} 5 × 10 ¹³ / cm ^2.
It is. Further, the stopper film 16 and the LDD on both sides thereof
After patterning a photoresist so as to cover the region, impurities (for example, P + ions) are implanted at a high concentration using the photoresist as a mask to form a source region S and a drain region D. For example, ion doping can be used for the impurity implantation. This is to implant impurities by electric field acceleration without applying mass separation. In this embodiment, the impurities are implanted at a dose of about 1 × 10 ¹⁵ / cm ² to form the source region S and the drain region D. .
Although not shown, in the case of forming a P-channel thin film transistor, after the region of the N-channel thin film transistor is covered with a photoresist, the impurity is switched from P + ions to B + ions and the dose is about 1 × 10 ¹⁵ / cm ^2. Ion doping.

Thereafter, the impurities implanted in the polycrystalline semiconductor thin film 2 are activated. For example, laser activation annealing using a KrF excimer laser light source is performed. That is, the glass substrate 1 is irradiated with the pulse of the KrF excimer laser while scanning, thereby activating the impurities injected into the polycrystalline semiconductor thin film 2.

Finally, as shown in FIG. 1D, a film of SiO ₂ is formed to a thickness of about 200 nm to form an interlayer insulating film 6. After the formation of the interlayer insulating film 6, SiN _x is applied for about 2
The passivation film (cap film) 8 is formed to a thickness of 00 to 400 nm. At this stage, heat treatment at about 350 ° C. is performed for one hour in an atmosphere of nitrogen gas, forming gas, or vacuum to diffuse hydrogen atoms contained in the interlayer insulating film 6 into the semiconductor thin film 2. Thereafter, a contact hole is opened, and Mo, Al, or the like is sputtered with a thickness of 200 to 400 nm, and then patterned into a predetermined shape to process the wiring electrode 7. Further, after a flattening layer 10 made of an acrylic resin or the like is applied with a thickness of about 1 μm, a contact hole is opened. ITO or IX on the flattening layer 10
After sputtering a transparent conductive film made of O or the like, it is patterned into a predetermined shape and processed into the pixel electrode 11.

FIG. 3 schematically shows crystallization annealing using a linear laser beam (line beam). The line beam has a longitudinal dimension of, for example, 300 mm and a width dimension of, for example, 0.1 mm.
38 mm. A laser beam 50 shaped into a line along the Y direction of the insulating substrate 1 made of glass or the like is irradiated from the surface side of the insulating substrate 1 on which a semiconductor thin film has been formed in advance.
At this time, the insulating substrate 1 is moved in the X direction (scanning direction) relatively to the irradiation area. Here, the line beam 50 emitted from the KrF excimer laser light source is emitted intermittently and partially overlapping. That is, the insulating substrate 1 is scanned via the stage in the X direction relative to the line beam 50. The stage is moved for each one shot at a pitch smaller than the width dimension of the line beam 50, and crystallization annealing is performed so that the line beam 50 can be applied to the entire substrate 1.

FIG. 4 is a schematic view showing an example of a laser irradiation apparatus used in the present invention. This laser irradiation device uses KrF
A laser beam 50 oscillated by a laser oscillator (laser light source) 51 is adjusted to an appropriate energy intensity using an attenuator 52. Further, an optical system 53 including a homogenizer and the like
Thereby, the laser beam 50 is shaped into, for example, a long shape.
Then, the insulating substrate 1 placed on the XY stage 55 in the chamber 54 is irradiated with the laser beam 50. Note that a semiconductor thin film 2 to be processed is formed on the insulating substrate 1 in advance. The inside of the chamber 54 is a nitrogen atmosphere, an air atmosphere, another gas atmosphere, or a vacuum atmosphere created by a dry pump or the like. In some cases, the crystallization annealing may be performed in the air atmosphere using only the XY stage 55 without using the chamber 54. Insulating substrate 1
When a semiconductor thin film 2 made of, for example, amorphous silicon is formed thereon by an appropriate method, the amorphous silicon is converted into polycrystalline silicon by irradiation with the laser beam 50. The output of this laser irradiation device is 1 J or more, preferably 2
J or more. The oscillation frequency is 200Hz to 300Hz.
Hz. The time width of the pulsed laser light is, for example, several tens of nsec. For example, assuming that the output is 1 J and the oscillation frequency is 200 Hz, the output of the laser irradiation apparatus is 200
W. With this degree, a relatively large-area semiconductor thin film can be efficiently crystallized.

Next, an example of a liquid crystal display device using a thin film transistor manufactured according to the present invention will be described with reference to FIG. As shown in the figure, the present liquid crystal display device has a panel structure including a pair of insulating substrates 101 and 102 and an electro-optical material 103 held between the pair. As the electro-optical material 103, a liquid crystal material is used. Lower insulating substrate 10
In 1, a pixel array unit 104 and a drive circuit unit are integrally formed. The drive circuit is divided into a vertical scanner 105 and a horizontal scanner 106. Further, a terminal portion 107 for external connection is formed at an upper end of a peripheral portion of the insulating substrate 101. The terminal unit 107 is connected to a vertical scanner 105 and a horizontal scanner 106 via a wiring 108. A row-shaped gate wiring 109 and a column-shaped signal wiring 110 are formed in the pixel array unit 104. A pixel electrode 111 and a thin film transistor 112 for driving the pixel electrode 111 are formed at the intersection of the two wires. The gate electrode of the thin film transistor 112 is connected to the corresponding gate wiring 109, the drain region is connected to the corresponding pixel electrode 111, and the source region is connected to the corresponding signal wiring 110. Gate wiring 10
9 is connected to the vertical scanner 105 while the signal wiring 11 is connected.
0 is connected to the horizontal scanner 106. Pixel electrode 11
1 and the thin film transistors included in the vertical scanner 105 and the horizontal scanner 106 are manufactured according to the present invention.

FIG. 6 is a schematic partial sectional view showing an example of an electroluminescent display device according to the present invention. In this embodiment, an organic electroluminescent element OLED is used as a pixel. OLED is anode A,
The organic layer 210 and the cathode K are sequentially stacked. The anode A is separated for each pixel, and is made of, for example, chromium and is basically light-reflective. The cathode K is commonly connected between the pixels, and has a laminated structure of, for example, a metal layer 211 and a transparent conductive layer 212, and is basically light transmissive. When a forward voltage (about 10 V) is applied between the anode A and the cathode K of the OLED having such a configuration, carriers such as electrons and holes are injected, and light emission is observed. The operation of the OLED is
It is considered that the light is emitted by excitons formed by holes injected from the cathode and electrons injected from the cathode K.

On the other hand, a thin film transistor TFT for driving an OLED is provided with a gate electrode 5 formed on an insulating substrate 1 made of glass or the like, a gate insulating film 43 overlaid thereon, and Gate electrode 5
And a semiconductor thin film 2 overlaid on top of the semiconductor thin film. The semiconductor thin film 2 is made of, for example, a silicon thin film crystallized by KrF excimer laser annealing. The thin film transistor TFT includes a source region S, a channel region Ch, and a drain region D that serve as a path for a current supplied to the OLED. The channel region Ch is located just above the gate electrode 5. The thin film transistor TFT having the bottom gate structure is covered with an interlayer film 6, on which a wiring 7 is formed. On top of these is another interlayer film 1
The OLED described above is formed via Oa. The anode A of the OLED is connected to a thin film transistor T
It is electrically connected to the FT. Also in this embodiment, the wavelength is 3
A laser beam of not more than 00 nm is used, and a process margin in laser annealing of the semiconductor thin film 2 is expanded.

[0024]

As described above, according to the present invention, the method for manufacturing a thin film transistor has a wavelength of 300 nm.
The semiconductor laser is irradiated with the following laser light to crystallize the semiconductor thin film. Thereby, the process margin in the crystallization step is increased. In addition, since the grain size of the semiconductor thin film forming the channel region located immediately above the gate electrode can be increased, a transistor having high mobility can be obtained. In addition, the influence of the base such as the gate electrode in the crystallization step is reduced, so that the degree of freedom in designing the pattern of the gate wiring including the gate electrode is increased.
Further, since a low-resistance metal material such as aluminum can be used instead of a high-melting-point metal for the gate wiring, the resistance of the wiring can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view illustrating a method for manufacturing a thin film transistor according to the present invention.

FIG. 2 is a process chart of a method for manufacturing a thin film transistor according to the present invention.

FIG. 3 is a schematic view showing a crystallization step.

FIG. 4 is a block diagram showing a laser irradiation device used for a crystallization step.

FIG. 5 is a schematic perspective view showing a liquid crystal display device according to the present invention.

FIG. 6 is a schematic partial sectional view showing an electroluminescent display device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Substrate, 2 ... Semiconductor thin film, 3 ... Gate nitride film, 4 ... Gate oxide film, 5 ... Gate electrode, 5
0 laser light (KrF)

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G09F 9/30 365 H01L 29/78 627G 5G435 H01L 21/20 G02F 1/136 500 21/28 301 H01L 29/78 617K 617M (72) Inventor Masato Takatoku 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo F-term in Sony Corporation (reference) 2H092 JA26 JA33 JA34 JA35 JA36 JA37 JA39 JB36 JB57 JB58 KA04 KA05 KA10 KA12 KA18 KB04 KB22 KB24 KB25 MA08 MA27 MA30 MA35 MA37 NA28 4M104 AA09 BB02 BB13 BB16 CC05 DD16 DD17 DD37 EE03 EE17 GG20 5C094 AA13 AA25 AA31 AA43 AA53 BA03 BA27 BA43 CA19 DA09 DA13 DB01 DB04 EA04 EA05 EB02 FA01 FA02 FB02 BA07 FB02 DA02 DB03 JA02 5F110 AA30 BB02 CC08 DD02 EE02 EE03 EE04 EE06 EE14 EE44 FF02 FF03 FF09 FF29 FF30 FF32 GG02 GG13 GG25 GG45 HJ01 HJ04 HJ12 HJ23 HL03 HL04 HL23 HM15 NN16 PP13 NN15 PP04 QQ23 5G435 AA14 AA16 AA17 BB05 BB12 CC09 KK05 KK10

Claims (24)

[Claims] A gate electrode forming step of forming a gate electrode on an insulating substrate; a gate insulating film forming step of forming a gate insulating film so as to cover the gate electrode; and a semiconductor thin film on the gate insulating film. Forming a semiconductor thin film, a crystallization step of irradiating the semiconductor thin film with laser light to crystallize the semiconductor thin film, and an impurity introducing step of selectively introducing impurities into the semiconductor thin film. 3. The method for manufacturing a thin film transistor according to claim 1, wherein in the crystallization step, the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 300 nm or less. 2. The method of manufacturing a thin film transistor according to claim 1, wherein in the crystallization step, the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source. . 3. The method according to claim 1, wherein the step of forming the gate electrode has a thickness of 10
2. The method according to claim 1, wherein a gate electrode having a thickness of not less than nm is formed. 4. The method according to claim 1, wherein said gate electrode forming step forms a gate electrode made of metal aluminum. 5. A thin film semiconductor device in which a thin film transistor having a bottom gate structure in which a gate electrode, a gate insulating film, and a semiconductor thin film are laminated in order from the bottom is formed on an insulating substrate, wherein the semiconductor thin film has a wavelength of 300 nm or less. A thin film semiconductor device which is crystallized by irradiating a laser beam. 6. The thin film semiconductor device according to claim 5, wherein the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source. 7. The gate electrode has a thickness of 10 nm.
The thin film semiconductor device according to claim 5, wherein: 8. The thin film semiconductor device according to claim 5, wherein said gate electrode is made of metallic aluminum. 9. A method for manufacturing a liquid crystal display device in which liquid crystal is arranged in a gap between a pair of substrates joined to each other, a pixel electrode and a thin film transistor for driving the pixel electrode are formed on one substrate, and a counter electrode is formed on the other substrate. In the thin film transistor, a gate electrode forming step of forming a gate electrode on the one substrate; a gate insulating film forming step of forming a gate insulating film so as to cover the gate electrode; A semiconductor thin film forming step of forming a semiconductor thin film on the semiconductor thin film, a crystallization step of irradiating the semiconductor thin film with laser light to crystallize the semiconductor thin film, and an impurity introducing step of selectively introducing impurities into the semiconductor thin film. A crystallization step of irradiating a laser beam having a wavelength of 300 nm or less to crystallize the semiconductor thin film. 10. The liquid crystal display device according to claim 9, wherein in the crystallization step, the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source. Production method. 11. The method according to claim 11, wherein the step of forming the gate electrode has a thickness of 1
10. The method according to claim 9, wherein a gate electrode having a thickness of 0 nm or more is formed. 12. The method for manufacturing a liquid crystal display device according to claim 9, wherein said gate electrode forming step forms a gate electrode made of metallic aluminum. 13. A liquid crystal display device comprising: a liquid crystal disposed in a gap between a pair of substrates joined to each other; a pixel electrode and a thin film transistor for driving the pixel electrode formed on one substrate; and a counter electrode formed on the other substrate. The thin film transistor has a bottom gate structure in which a gate electrode, a gate insulating film, and a semiconductor thin film are sequentially stacked on the one substrate from the bottom, and the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 300 nm or less. A liquid crystal display device, characterized in that: 14. The liquid crystal display device according to claim 13, wherein the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source. 15. The gate electrode has a thickness of 10 n.
14. The liquid crystal display device according to claim 13, wherein m is not less than m. 16. The liquid crystal display device according to claim 13, wherein said gate electrode is made of metallic aluminum. 17. A method of manufacturing an electroluminescence display device in which an electroluminescent element and a thin film transistor for driving the same are formed on an insulating substrate, wherein the thin film transistor has a gate electrode forming step of forming a gate electrode on the insulating substrate. Forming a gate insulating film so as to cover the gate electrode; forming a semiconductor thin film on the gate insulating film; and irradiating the semiconductor thin film with laser light. The semiconductor thin film is formed by a crystallization process for achieving crystallization and an impurity introducing process for selectively introducing an impurity into the semiconductor thin film. The crystallization process includes irradiating a laser beam having a wavelength of 300 nm or less to crystallize the semiconductor thin film. A method for manufacturing an electroluminescent display device, comprising: 18. The electroluminescent display device according to claim 17, wherein in the crystallization step, the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source. Manufacturing method. 19. The method according to claim 19, wherein the step of forming the gate electrode has a thickness of 1
The method according to claim 17, wherein a gate electrode having a thickness of 0 nm or more is formed. 20. The method according to claim 17, wherein said gate electrode forming step forms a gate electrode made of metal aluminum. 21. An electroluminescent display device comprising an electroluminescent element and a thin film transistor for driving the electroluminescent element formed on an insulating substrate, wherein the thin film transistor includes a gate electrode, a gate insulating film, and a semiconductor thin film on the insulating substrate in order from the bottom. An electroluminescent display device having a stacked bottom gate structure, wherein the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 300 nm or less. 22. The electroluminescent display device according to claim 21, wherein the semiconductor thin film is crystallized by irradiating a laser beam having a wavelength of 248 nm emitted from a KrF excimer laser light source. 23. The gate electrode has a thickness of 10 n.
22. The electroluminescent display device according to claim 21, wherein m is not less than m. 24. The electroluminescent display device according to claim 21, wherein said gate electrode is made of metallic aluminum.