JP2000077333A - Manufacture of thin-film transistor and laser annealing apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high productivity, high mobility and less variations when a semiconductor thin film for use in a thin-film transistor array of a liquid crystal display is crystallized. SOLUTION: A laser beam from a laser device 1 using a YLF crystal is passed through a harmonics conversion device 3 including a reflecting mirror 2 and two sheets of KDP crystal to convert the wavelength of the laser beam from the laser device 1 to triple thereof, and the laser beam 9 subjected to the harmonics conversion is attenuated down to a predetermined energy with use of an optical attenuator 4. Thereafter, the attenuated laser beam 9 is passed through a uniformalizing device 5 for performing shaping and uniformalizing operations over the attenuated laser beam 9 to form a laser beam 9 having a uniform intensity distribution, to melt and crystallize an amorphous Si film formed on a glass substrate 8, and to form a polycrystalline Si film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for manufacturing a thin film transistor and a laser annealing apparatus for a semiconductor film.

[0002]

2. Description of the Related Art As a method for manufacturing a semiconductor film of a thin film transistor, an amorphous semiconductor film formed on a substrate such as glass is irradiated with a laser beam, melted and crystallized to obtain a crystalline semiconductor film. An annealing method has been used. At this time, an argon laser, a KrF or XeCl excimer laser is generally used as a laser light source.
A method using a YAG laser as a light source has also been devised (for example, Japanese Patent Laid-Open No. 6-45272).

Further, even when the film quality of the crystalline semiconductor film deteriorates due to ion doping of impurities into the semiconductor film, the film quality is improved by the above-described laser beam irradiation.

[0004]

The laser light source for laser annealing as described above is required to have at least the following three performances.

The first point is that it is necessary to process a large area at a time from the viewpoint of productivity and the output is high. The second point is that the output of the laser beam is stable because the variation in transistor characteristics is suppressed. The third point is the stability of the device and the ease of maintenance when the laser device is operated for a long time.

Here, although the output of the argon laser is relatively stable, the output is about 4 W at the maximum and there is a problem in productivity. Further, although the excimer laser has a high output of 200 W at the maximum, there is a problem that there is a large variation between emitted pulses. Further, a normal YAG laser has a high output of up to 1800 W, but has a wavelength of 1064 nm.
And the absorptance of the commonly used amorphous Si film is 40%
However, there is a problem that the efficiency is low (see FIG. 6), and distortion occurs due to heating the glass substrate.

[0007] Conventionally, a TFT for a liquid crystal display is used.
Is generally formed by scanning a linear beam of an excimer laser to form polycrystalline Si. However, this method has the following problems.

FIG. 7 is a perspective view showing a state in which a laser beam is scanned and irradiated. In FIG.
i and 8 denote a substrate (glass), and 9 denotes a laser beam.

When the beam is scanned, variations in the TFT characteristics occur at the joint of the laser pulses, and as shown in FIG.
As shown in (1), a distribution 18 corresponding to a linear pulse of polycrystalline Si occurs. On the other hand, when the large area cannot be irradiated by one scan, the irradiation is divided into several degrees. In this case, variations in TFT characteristics also occur at the joints, and as shown in FIG. A distribution 19 corresponding to the divisional scanning of Si occurs. Note that FIG. 7B shows an example in which divided irradiation is performed twice vertically.

Furthermore, the pulse width of the excimer laser is about 3
Since it is as short as 0 nS, the amorphous Si thin film is rapidly heated and cooled, so that the grain size of the obtained polycrystalline Si becomes fine, and as a result, TFT characteristics (particularly mobility) do not become very high.

Further, polycrystalline S by impurity ion doping or the like is used.
In the process of improving the film quality by irradiating the laser light when the film quality of the i film is deteriorated, the stability, productivity, maintainability, and pulse of the laser light are similar to the case of the crystallization of the Si film. There is a problem of variation due to optical scanning.

[0012]

In order to solve the above-mentioned problems, YL is used as a base material crystal as a light source for laser annealing.
It is possible to anneal a large area at a time by using twice, three or four times higher harmonics of laser light emitted from a laser device using F, YVO ₄ , alexandrite crystal, garnet crystal or sapphire crystal. And improved productivity. In addition, since light having a wavelength having a high absorptivity to the silicon film is used, efficiency is improved.

Further, by using a harmonic twice, triple or quadruple the laser light of a glass laser as a light source for laser annealing, it is possible to anneal a large area at once with a high output laser light. Productivity has improved. In addition, since light having a wavelength having a high absorptivity to the silicon film is used, efficiency is improved.

Further, by using the above-mentioned light source as a light source for laser annealing and irradiating a plurality of laser lights having different energy densities to the non-single crystalline semiconductor film to form a polycrystalline semiconductor film, the uniformity of transistor characteristics can be improved. Improved.

Further, after the non-single-crystal semiconductor film is irradiated with laser light to form a polycrystalline semiconductor film using the above-mentioned light source as a light source for laser annealing, a laser light having a higher energy density than the laser light is applied to the polycrystalline semiconductor film. By irradiating the polycrystalline semiconductor film, the uniformity of transistor characteristics was improved.

Further, a base material is used as a light source for laser annealing.
YAG, YLF, YVO as crystals _Four, Alexandra
Using lite, garnet or sapphire crystals
Twice, three times or more than the laser light emitted from the laser device
Melts the polycrystalline semiconductor film by irradiating the fourth harmonic.
Melt and recrystallize to improve and modify polycrystalline semiconductor film quality
The quality of the semiconductor film of the thin film transistor
Improved and stable.

Further, the polycrystalline semiconductor film is melted and recrystallized by irradiating a laser beam of a laser beam of a glass laser with twice, triple or quadruple harmonics as a light source of the laser annealing, and the film quality of the polycrystalline semiconductor film is improved. By improving and reforming, the film quality of the semiconductor film of the thin film transistor was improved and stabilized.

Further, at least YAG,
A laser annealing apparatus including a laser device using YLF, YVO ₄ , an alexandrite crystal, a garnet crystal, or a sapphire crystal, a lens for shaping a laser beam, and a device for homogenizing the laser beam.
By using a laser annealing apparatus characterized in that it is equipped with a device for converting the harmonics into double, triple and quadruple harmonics, it is possible to irradiate a large area with a laser beam having a required energy density at a time, thereby improving productivity. And the uniformity of the film quality of the irradiated semiconductor film was improved. In addition, maintenance of the device is easier than in a device using a gas laser such as an excimer laser.

At least a glass laser oscillator;
What is claimed is: 1. A laser annealing apparatus comprising: a lens for shaping laser light; and a device for homogenizing the laser light, comprising: a device for converting laser light into harmonics of 2, 3, and 4 times. By using a laser annealing apparatus, a large area can be irradiated with laser light having a required energy density at a time, thereby improving the productivity and the uniformity of the film quality of the irradiated semiconductor film. In addition, maintenance of the device is easier than in a device using a gas laser such as an excimer laser.

Further, by using the laser light amplifier, it is possible to use a laser beam having a higher output, and to irradiate a large area with a laser beam having a required energy density at a time, thereby improving productivity. The uniformity of the film quality of the irradiated semiconductor film was improved. Further, it is possible to irradiate the area corresponding to the screen of the liquid crystal display or the entire substrate at one time, and the uniformity of transistor characteristics is dramatically improved.

Further, by forming the resonator portion of the laser device as a multi-rod, the output of laser light is further increased, and a large area can be irradiated with laser light having a required energy density at a time, thereby improving productivity. .

Further, since the resonator portion of the laser device has a slab structure in which rods are arranged in a zigzag manner, a laser beam having a higher output and a more stable output can be used, and a large area is required at a time. A laser beam having a high energy density can be irradiated, thereby improving the productivity and improving the uniformity of the film quality of the irradiated semiconductor film.

Further, by using the Q switch, a laser beam having a higher output can be used, and a laser beam having a required energy density can be radiated to a large area at a time. The uniformity of the film quality of the obtained semiconductor film was improved.

The irradiation time of one pulse of the laser beam is 2 hours.
0 nSec or more, preferably 50 nSec or more and 5 m
By being S or less, the film quality of the irradiated semiconductor film was improved.

Further, since the laser light is continuous light, feedback laser output control is easier and the uniformity of the film quality of the irradiated semiconductor film is improved as compared with the method using pulsed laser light.

The oscillation wavelength of the YLF laser is a high output laser with a wavelength of 1053 nm, the second harmonic is 527 nm, the third harmonic is 351 nm, and the fourth harmonic is 263 nm. By converting into harmonics, the absorption to Si is increased by orders of magnitude (FIG. 6), so that the efficiency of annealing is improved and energy and processing time are reduced. Lasers using YAG, alexandrite crystals, garnet crystals, sapphire crystals (generally ruby lasers), silicate-based laser glasses, or phosphate-based laser glasses are also high-output infrared lasers. It becomes suitable as a light source for annealing. By using, for example, KDP as a crystal for harmonic conversion and reducing loss such as phase matching, the conversion efficiency from the original laser light to the third harmonic reaches a maximum of 60%.

By using these laser light sources,
Compared with the laser annealing of a semiconductor film using an excimer laser, which is generally used at present, it has a large output and a controllable pulse width, and thus has the following features.

First, a large area can be processed at a time, and the productivity is excellent. Second, it is possible to irradiate a large area with one pulse, and there is no non-uniformity of transistor characteristics due to a joint of irradiation for each pulse. Third, the stability of the laser is high, and the uniformity of transistor characteristics is improved. Fourth, maintenance of the laser device is easy,
Long maintenance intervals. Fifth, the mobility is improved by increasing the pulse width.

By using a laser amplifier or a Q switch such as a lot amplifier or a disk amplifier, an ultra-high output laser is obtained, and the advantage of using the above high output laser is increased. A substrate having a large area (55 cm × 65 cm or the like) can enter a laser beam irradiation area without being moved and be irradiated collectively, and the uniformity of transistor characteristics is further improved.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. In addition, as a semiconductor film, a III-V semiconductor such as Si, Ge, and GaAs, Zn
It has been confirmed that the semiconductor crystallization method of the present invention is similarly effective even when using II-VI semiconductors such as Se. However, in the embodiment described below, silicon, which is the most common, is taken as an example. Will be explained. The crystal or glass used for the laser resonance medium is usually doped with Nd or the like.

(Embodiment 1) A method of manufacturing a TFT according to Embodiment 1 of the present invention will be described below.

First, for the purpose of preventing impurities from glass, a SiO ₂ film having a thickness of 300 nm is formed on a glass substrate as a substrate having optical transparency by, for example, TEOS CVD.
An underlayer is formed. The thickness of this underlayer is 300 n.
Not limited to m, various settings are possible.

Next, an amorphous Si film having a thickness of, for example, 85 nm is formed by a plasma CVD method. In forming the amorphous Si film, a low pressure CVD method may be used, and the thickness of the amorphous Si film is not limited to 85 nm, and various settings can be made.

Next, as shown in FIG. 1, YLF (LiYF
₄ ) Laser annealing is performed using laser light emitted from the laser device 1 using a crystal. The laser device used in this embodiment is a slab laser, and the emitted laser light has a wavelength of 1053 nm and an output of 500 W. Further, the wavelength of the laser beam emitted from the laser device was converted into a triple harmonic through a reflecting mirror 2 and a harmonic converter 3 composed of two KDP crystals. At this time, the wavelength of the laser light after harmonic conversion is 351 nm, the power is 300 W, and the pulse width is 200 μS. The harmonic-converted laser light 9 is attenuated to a predetermined energy using the optical attenuator 4. The attenuated laser light 9 is shaped into a predetermined shape through a homogenizing device 5 for shaping and uniformizing the beam, and is converted into a laser light 9 having a uniform intensity distribution. Note that the above laser device 1 may use a laser device using an alexandrite crystal, a garnet crystal, or a sapphire crystal as a resonance medium instead of YLF. The power density of the laser beam may be any power density sufficient to crystallize the amorphous Si film, for example, 200 to 400 mJ / cm ² ,
Preferably, it may be set to 280 to 380 mJ / cm ² or the like. The irradiation of the laser beam causes the amorphous Si film formed on the glass substrate 8 to melt and crystallize, forming a polycrystalline Si film. In FIG. 1, reference numeral 6 denotes polycrystalline Si irradiated with the laser light 9, and reference numeral 7 denotes amorphous Si before the irradiation with the laser light 9.

After that, since a large number of dangling bonds are formed in the polycrystalline Si film, the film is left in a hydrogen plasma, for example, at 450 ° C. for 2 hours.

Hereinafter, the following steps are performed similarly to the conventional TFT. First, by dry etching, polycrystalline Si
Pattern the layer. Next, for example, TEOS CVD
SiO ₂ is formed to a thickness required as a gate insulating film, for example, 100 nm by a method. Next, the aluminum film is sputtered and patterned into a predetermined shape by etching to form a gate electrode. Thereafter, a necessary kind of dopant is implanted into the source and drain regions by using the gate electrode as a mask by an ion doping apparatus. Further, an interlayer insulating film made of silicon oxide is formed by atmospheric pressure CVD.
Film, cover the gate electrode, and etch
A contact hole reaching the source region or the drain region of the polycrystalline Si film is opened in the interlayer insulating film and the Si oxide film. Next, a titanium film and an aluminum film are sputtered and patterned into a predetermined shape by etching to form a source electrode and a drain electrode.

The mobility of the TFT thus formed is 3.5 times higher than that of a TFT formed by a conventional process using an excimer laser in a laser annealing process. The mobility variation of the conventional TFT is about 15%, whereas the mobility variation of the TFT formed in this embodiment is 9%, which is excellent in uniformity.

Since the irradiation power of the laser beam used in the present embodiment is 300 W, the conventional irradiation power of 20 W is used.
Compared to the case of using an excimer laser of 0 W,
Tact was improved 1.5 times.

(Embodiment 2) Hereinafter, a method of manufacturing a TFT according to Embodiment 2 of the present invention will be described.

As in the first embodiment, a SiO ₂ underlayer and an amorphous Si film are formed on a glass substrate.

Next, as shown in FIG. 1, laser annealing is performed using laser light emitted from a laser device 1 using glass as a resonance medium. The laser device used in this embodiment is a system using glass, for example, phosphate glass LHG5 as a resonance medium, and has a pulse width of 300 μS. In addition, as a kind of glass, silicate type, phosphoric acid type,
A phosphoric acid type or the like can be used. Using the laser light emitted from the glass laser device, the light passes through the harmonic converter 3 in the same manner as in the first embodiment, converts the wavelength to a triple harmonic, passes through the optical attenuator 4, and the homogenizer 5. A laser beam having a predetermined wavelength, shape, and intensity is obtained. Conversion to harmonics is
Double and quadruples can also be used. The power density of the laser light is the same as in the first embodiment. The irradiation of the laser beam causes the amorphous Si film formed on the glass substrate 8 to melt and crystallize, forming a polycrystalline Si film.

After that, since a large number of dangling bonds are formed on the polycrystalline Si film, the film is left at, for example, 450 ° C. for 2 hours in hydrogen plasma.

Hereinafter, through the same steps as in the first embodiment, T
Form FT. The TFT thus formed is:
The mobility is 3.7 compared to a TFT formed by a conventional process using an excimer laser for a laser annealing process.
Improved by a factor of two. The mobility variation of the conventional TFT is about 15%, whereas the mobility variation of the TFT formed in this embodiment is 9%, which is excellent in uniformity.

Since the irradiation power of the laser beam used in this embodiment is 720 W, the conventional irradiation power of 20 W is used.
Compared to the case of using an excimer laser of 0 W,
Tact time improved by 3.6 times.

Embodiment 3 Hereinafter, a method of manufacturing a TFT according to Embodiment 3 of the present invention will be described.

As in the first embodiment, an SiO ₂ underlayer and an amorphous Si film are formed on a glass substrate. Next, the amorphous Si film formed on the glass substrate 8 is melted and crystallized by the irradiation of the laser beam used in Embodiment 1, and a polycrystalline Si film is formed. Thereafter, in the same manner as in the first embodiment, hydrogenation treatment, patterning of a polycrystalline Si layer, formation of a gate insulating film, formation of a gate electrode,
And ion doping.

This doping step damages the polycrystalline Si layer and causes defects. Therefore, by irradiating the polycrystalline Si film formed on the glass substrate 8 with laser light of the laser device used in the first embodiment, the polycrystalline Si film is melted and recrystallized to reduce defects in the polycrystalline Si film. Let it. The power density of the laser beam at this time may be a power density sufficient to melt the amorphous Si film, for example, 200 to 400 mJ / cm ² , preferably 200 to 400 mJ / cm ² .
It may be set to 310 mJ / cm ² or the like.

Thereafter, the same film forming process and etching process as those in the first embodiment were repeated to form a driving TFT of the liquid crystal display device.

The mobility of the TFT thus formed is 1.2 times that of the TFT formed by the method of the first embodiment. Also, in a conventional TFT,
The variation in mobility is about 15%, while the variation in mobility of the TFT formed in this embodiment is 7%, which is excellent in uniformity.

Further, since the irradiation power of the laser beam used in the present embodiment is 300 W, the tact time is smaller than that in the case of using an excimer laser having a conventional irradiation power of 200 W in the polycrystalline Si reforming step. Was improved 1.5 times.

(Embodiment 4) Hereinafter, a method of manufacturing a TFT according to Embodiment 4 of the present invention will be described.

In the same manner as in the third embodiment, an SiO ₂ underlayer and an amorphous Si film are formed on a glass substrate, a polycrystalline Si film is formed, hydrogenation treatment, patterning of the polycrystalline Si layer, A gate insulating film is formed, a gate electrode is formed, and ion doping is performed.

This doping step damages the polycrystalline Si layer and causes defects. Therefore, by irradiating the polycrystalline Si film formed on the glass substrate 8 with laser light of the laser device used in the second embodiment, the polycrystalline Si film is melted and recrystallized, thereby reducing defects in the polycrystalline Si film. Let it. The power density of the laser beam at this time may be a power density sufficient to melt the amorphous Si film, for example, 200 to 400 mJ / cm ² , preferably 200 to 400 mJ / cm ² .
It may be set to 310 mJ / cm ² or the like.

Thereafter, the same predetermined film forming process and etching process as in Embodiment 1 were repeated to form a driving TFT of the liquid crystal display device.

The mobility and the variation of the mobility of the TFT thus formed have substantially the same effects as in the third embodiment. In addition, since the irradiation power of the laser beam used in the present embodiment is 720 W, the tact is 3 times as compared with the case where an excimer laser having a conventional irradiation power of 200 W is used in the polycrystalline Si reforming process. 6 times improved.

The case where the excimer laser annealing is used to reduce defects generated at the time of impurity implantation for forming source / drain regions has been described in the third and fourth embodiments. FIG. Show.

In FIG. 2, reference numeral 8 denotes a substrate made of glass or the like;
Indicates polycrystalline Si, 12 indicates a gate insulating film, 11 indicates a gate electrode, 13 indicates damaged polycrystalline Si,
Defects caused by impurity implantation as shown in FIG. 3A can be obtained by irradiating excimer laser light from the gate electrode side as shown in FIG. 3B or by using the back surface (glass) as shown in FIG. It is reduced by irradiating excimer laser light from the substrate side).

(Fifth Embodiment) Hereinafter, a method of manufacturing a TFT according to a fifth embodiment of the present invention will be described.

In the same manner as in the first embodiment, an SiO ₂ underlayer and an amorphous Si film are formed on a glass substrate.

Next, as shown in FIG. 1, laser annealing is performed using laser light emitted from a laser device 1 using a YAG crystal as a resonance medium. As the crystal of the resonance medium, besides YAG, YLF, YVO ₄ , alexandrite crystal, garnet crystal or sapphire crystal can be used. With respect to the laser light emitted from the YAG laser device, the intensity of the laser light is increased using a rod-type laser light amplifier and a disk-type laser light amplifier. The amplified laser light passes through the harmonic conversion device 3, the optical attenuator 4, and the equalization device 5 in the same manner as in the first embodiment to obtain laser light having a predetermined wavelength, shape, and intensity. In addition,
The power density of the laser light is the same as in the first embodiment. The irradiation of the laser beam causes the amorphous Si film formed on the glass substrate 8 to melt and crystallize, forming a polycrystalline Si film.

Hereinafter, through the same steps as in the first embodiment, T
Form FT. The laser device used in the laser annealing step of the present embodiment will be described more specifically. The laser device used in this embodiment is a pulse laser using a Q switch, and is a multi-rod type. The emitted laser light has a wavelength of 1064 nm and an output of 2 kW. Further, as shown in FIG. 3, by arranging a plurality of rod-type and disk-type laser light amplifiers in series, the laser light is amplified, the amplified laser light output is 200 MW, the pulse width is 200 nS, and The power of the laser beam that can be converted and shaped and irradiated is 100 MW. Note that FIG.
In the figure, 15 is a beam shaping optical system, 16 is a rod type amplifier, and 17 is a disk type amplifier.

Conventionally, when a TFT for a liquid crystal display is formed, polycrystalline Si is formed by scanning a linear beam of an excimer laser. However, variations in TFT characteristics occur at the connection of laser pulses, In the case where the irradiation cannot be performed by one scanning of the area, the irradiation is performed in several degrees. However, there is a problem that a variation in the TFT characteristics occurs at a joint in that case. Therefore, as described above, by using a high-power laser, it is possible to irradiate the area (FIG. 4B) corresponding to the screen of the liquid crystal display or the entire substrate (FIG. 4A) at once, and the uniformity of the transistor characteristics is improved. Dramatically improved.

The TFT formed by the method of the present embodiment
Has a mobility of 3 compared to a TFT manufactured by a conventional process using an excimer laser for a laser annealing process.
Improved by a factor of two. In addition, the mobility variation of the conventional TFT is about 15%, whereas the mobility variation of the TFT formed in this embodiment is 3%, which is excellent in uniformity.

Further, since the irradiation power of the laser beam used in the present embodiment is as high as 200 MW, the tact is almost zero except for the transport time.

(Embodiment 6) A method of manufacturing a TFT according to Embodiment 6 of the present invention will be described below.

As in the first embodiment, an SiO ₂ underlayer and an amorphous Si film are formed on a glass substrate.

Next, laser annealing is performed using a laser beam described later. By the irradiation of the laser beam, the amorphous Si film formed on the glass substrate 8 is melted and crystallized to form a polycrystalline Si film.

Hereinafter, through the same steps as in the first embodiment, T
Form FT. The laser device used in the laser annealing step of the present embodiment will be specifically described. The pulse width of the pulsed solid-state laser can be controlled from about 100 fS to about 20 mS depending on the excitation light source, the type of the Q switch, the oscillation frequency, the presence or absence of pulse compression, the dose of Nd, and the like.

Using the third harmonic of the YAG laser, the dependence of the polycrystalline Si formation on the laser pulse width was reduced from 10 ns to 10 ns.
Investigated to mS. From 10nS to 50nS, use a Pockels Q switch with xenon flash lamp excitation, from 50nS to 200nS, use an ultrasonic Q switch with krypton arc lamp excitation, and from 200nS to 10mS use a Q switch with xenon flash lamp excitation. The pulse width was controlled by a method that was not used.

The laser beam passes through the third harmonic converter 3, optical attenuator 4, and homogenizer 5 in the same manner as in the first embodiment, and a laser beam having a predetermined wavelength, shape, and intensity is obtained. .

FIG. 5 shows the pulse width dependence of the field effect mobility of the TFT manufactured by the above manufacturing method. Field effect mobility is 20nS or more and 100c which is a standard of high performance TFT
m ² / V · S or more, and 200 cm ² /
When the pulse width exceeds VS and the pulse width becomes longer, the mobility tends to be improved. It is considered that when the pulse width is short, the crystal growth of Si is inhibited by rapid heating and rapid cooling.

However, it monotonically reaches a plateau from about 1 μS and reaches 200 cm ² / V · S for a pulse width of 5 mS or more.
It falls to below. This is considered to be because if the heating time is too long, heat is excessively transmitted to the base or the substrate, which causes problems such as diffusion of impurities.

In consideration of the experimental result shown in FIG. 5 and the fact that the mobility is about 60 cm ² / V · S in continuous light such as an argon laser, the irradiation time of one pulse is 20 nS.
By performing laser annealing using laser light having a value of ec or more, preferably 50 nSec or more and 5 mS or less, a polycrystalline Si film with high mobility can be formed.

[0074]

As described above, according to the present invention, as a light source for laser annealing, YAG, YLF,
A laser device using YVO ₄ , an alexandrite crystal, a garnet crystal, or a sapphire crystal, or a laser device using a silicate laser glass or a phosphoric acid laser glass, which is twice, three or four times higher harmonics. By using, a large output can be obtained as compared with a conventional excimer laser or the like, so that it is possible to anneal a large area at once, and the productivity is improved.

Further, the productivity is improved by using the harmonics of the solid-state laser in the step of irradiating a polycrystalline Si film having many defects and the like with a laser beam to melt and recrystallize the film.

Further, by using a laser light amplifier in addition to the above-mentioned solid-state laser device, the laser light intensity can be dramatically increased, thereby improving the productivity and supporting the screen of the liquid crystal display. It is possible to irradiate the entire area or the entire substrate at once, and the uniformity of transistor characteristics is improved.

The pulse width of the solid-state laser can be selected depending on the configuration. Laser annealing is performed by using a laser beam having a pulse irradiation time of 20 nSec or more, preferably 50 nSec or more and 5 mS or less. By doing so, the mobility of the TFT was increased.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a laser light irradiation method used in an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a step of modifying a polycrystalline semiconductor film by laser light irradiation in Embodiments 3 and 4 of the present invention.

FIG. 3 is a sectional view showing a configuration of a laser annealing apparatus used in a fifth embodiment of the present invention.

FIG. 4 is a perspective view showing a polycrystalline Si film formed in a fifth embodiment of the present invention.

FIG. 5 is a diagram showing the pulse width dependence of the TFT field-effect mobility described in Embodiment 6 of the present invention.

FIG. 6 is a diagram showing a spectral transmittance of an amorphous Si film;

FIG. 7 is a perspective view showing a polycrystalline Si film formed by a conventional laser irradiation method.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser oscillator 2 reflector 3 harmonic generator (eg KDP crystal) 4 attenuator 5 homogenizer 6 polycrystalline Si 7 amorphous Si 8 substrate (glass) 9 laser light 10 ionized impurity 11 metal for gate wiring Film 12 Insulating film 13 Damaged polycrystalline Si layer 14 Reflector 15 Beam shaping optical system 16 Rod type amplifier 17 Disk type amplifier 18 Polycrystalline Si, distribution corresponding to linear pulse 19 Polycrystalline Si, divided scanning Distribution corresponding to

Continued on the front page F term (reference) 2H092 JA24 KA04 MA30 NA24 NA27 NA29 NA30 PA01 5F052 AA02 AA11 BA07 BB03 BB07 CA10 DA02 DB03 HA01 JA10

Claims (15)

[Claims] 1. A laser beam emitted from a laser device using YLF, YVO ₄ , alexandrite crystal, garnet crystal or sapphire crystal as a base material crystal.
A method for manufacturing a thin film transistor, comprising a step of irradiating a non-single-crystal semiconductor film by irradiating double-, triple-, or quadruple-order harmonics to crystallize and form a polycrystalline semiconductor film. 2. A step of irradiating a laser beam of a glass laser with twice, three or four times higher harmonics to melt and crystallize the non-single-crystal semiconductor film to form a polycrystalline semiconductor film. A method for manufacturing a thin film transistor, comprising: 3. The method according to claim 1, further comprising irradiating the non-single-crystal semiconductor film with a plurality of laser beams having different energy densities to form a polycrystalline semiconductor film. Method. 4. A method for irradiating a non-single crystalline semiconductor film with laser light to form a polycrystalline semiconductor film and irradiating the polycrystalline semiconductor film with laser light having an energy density higher than that of the laser light. The method for manufacturing a thin film transistor according to claim 1 or 2, wherein: 5. A base material crystal of YAG, YLF, YVO
_{4. The} polycrystalline semiconductor film is melted and recrystallized by irradiating a laser beam emitted from a laser device using an alexandrite crystal, a garnet crystal, or a sapphire crystal with twice, three times, or four times the harmonic, thereby forming a polycrystal. A method for manufacturing a thin film transistor, comprising a step of improving and modifying the quality of a semiconductor film. 6. The polycrystalline semiconductor film is melted and recrystallized by irradiating a laser beam of twice, three times or four times higher than a laser beam of a glass laser to improve and modify the quality of the polycrystalline semiconductor film. A method for manufacturing a thin film transistor, comprising the steps of: 7. YAG, YL at least as a base material crystal
A laser device using F, YVO ₄ , alexandrite crystal, garnet crystal or sapphire crystal, a lens for shaping the laser beam, and a device for homogenizing the laser beam;
A laser annealing apparatus for converting laser light into harmonics of two, three and four times. 8. A system comprising at least a glass laser oscillator, a lens for shaping a laser beam, a device for homogenizing the laser beam, and a device for converting the laser beam into two, three and four times higher harmonics. Laser annealing equipment. 9. The laser annealing apparatus according to claim 7, wherein a laser light amplifier is used. 10. The laser annealing apparatus according to claim 7, wherein the resonator portion of the laser device is a multi-rod. 11. The laser annealing apparatus according to claim 7, wherein a resonator portion of the laser apparatus has a slab structure in which rods are arranged in a zigzag manner. 12. The laser annealing apparatus according to claim 7, wherein a Q switch is used. 13. An irradiation time of one pulse of laser light is 20 times.
The laser annealing apparatus according to claim 7, wherein nSec is equal to or more than nSec. 14. The laser annealing apparatus according to claim 7, wherein the laser light is continuous light. 15. The laser annealing apparatus according to claim 12, further comprising a laser beam feedback output stabilizing apparatus.