KR20130035117A - Crystallization method and method of fabricating thin film transistor using thereof - Google Patents

Abstract

PURPOSE: A crystallizing method and a method for manufacturing a thin film transistor are provided to improve crystallization uniformity by using a laser beam with a step profile. CONSTITUTION: An amorphous silicon thin film(120) is formed on a substrate(110). A green laser beam with a first energy density is scanned. A grain is formed on the amorphous silicon thin film by a scanning process. A green laser beam with a second energy density is scanned on the amorphous silicon thin film. The grain is recrystallized to a seed by the scanning process.

Description

Crystallization method and manufacturing method of thin film transistor using the same {CRYSTALLIZATION METHOD AND METHOD OF FABRICATING THIN FILM TRANSISTOR USING THEREOF}

The present invention relates to a crystallization method and a method for manufacturing a thin film transistor using the same, and more particularly, to a crystallization method using a green laser and a method for manufacturing a thin film transistor using the same.

Recently, interest in information display has increased, and a demand for using portable information media has increased, and a light-weight flat panel display (FPD) that replaces a cathode ray tube (CRT) And research and commercialization are being carried out. Recently, a liquid crystal display device or an organic light emitting display device has been developed as a flat panel display device having excellent performance of thinness, light weight, and low power consumption, thereby replacing the existing CRT.

The active matrix (AM) method, which is a driving method mainly used in the liquid crystal display, has excellent resolution and video performance, and uses a thin film transistor (TFT) as a switching element for each pixel. This is to control the voltage on and off.

In addition, the organic light emitting device has a high brightness and low operating voltage characteristics, and because it is a self-luminous device that emits light by itself, it has a high contrast ratio, enables an ultra-thin display, and a low voltage of DC 5V to 15V. Since the drive circuit is easily manufactured and designed, it has attracted attention as a flat panel display device.

In such a liquid crystal display and an organic light emitting device, a thin film transistor, which is essentially a switching element, is used to control each pixel area on and off in common.

Generally, the thin film transistor uses amorphous silicon as an active layer. However, since the amorphous silicon has an atomic arrangement, the thin film transistor is changed into a metastable state when irradiated with light or applied with an electric field. This is a problem. In addition, the amorphous silicon thin film transistor has a low mobility of 0.1 cm ² / Vs to 1.0 cm ² / Vs in a channel, which makes it difficult to use it as an element for a driving circuit.

In order to solve this problem, a polycrystalline silicon thin film transistor having a higher mobility than the amorphous silicon thin film transistor has been developed, and a crystallization method using an excimer laser (EL) has been proposed as the crystallization of the amorphous silicon. .

Crystallization using the excimer laser generates a laser beam having a wavelength of 308 nm by a gas medium, and is used for crystallization. However, using a gas as a source medium for generating a laser beam, a laser beam having an optimal power for melting amorphous silicon is generated, and the generated laser beam has a large error range of its energy density. When the amorphous silicon is irradiated, the energy density difference of the laser beam irradiated for each position is generated, and thus the characteristics of the thin film transistor itself are uneven for each position. In addition, there is a disadvantage in that the maintenance cost is large, such as expensive gas medium to be replaced at any time.

An object of the present invention is to provide a crystallization method using a green laser and a method of manufacturing a thin film transistor using the same, which are intended to solve the above problems.

Another object of the present invention is to provide a crystallization method for improving crystallization uniformity and a method for manufacturing a thin film transistor using the same in crystallization using a green laser.

Other objects and features of the present invention will be described in the following description of the invention and claims.

In order to achieve the above object, the crystallization method of the present invention comprises the steps of forming an amorphous silicon thin film on a substrate; Scanning the green laser beam having a first energy density on the amorphous silicon thin film to perform solid phase crystallization to form uniform grains; And recrystallizing the grains by seeding the amorphous silicon thin film by scanning a green laser beam having a second energy density higher than the first energy density.

At this time, the first energy density is characterized in that it is set to 300mJ / cm ² ~ 450mJ / cm ² .

The second energy density is characterized in that 500mJ / cm ² ~ 800mJ / cm ^{2 It is} set.

Another crystallization method of the present invention comprises the steps of forming an amorphous silicon thin film on a substrate; And performing crystallization by scanning a green laser beam having a step profile on the amorphous silicon thin film.

In this case, the laser beam is characterized in that the two laser beams having a phase difference with respect to the beam width (width) direction has a different energy density to form a step profile.

In this case, the green laser beam having the step profile is formed by adjusting the energy density of the two laser beams after the two laser sources give a phase difference in the beam width direction through the optical system.

 The energy density of the front laser beam located in front of the scanning direction is set low, and the energy density of the rear laser beam in the rear is set high.

At this time, the energy density of the front laser beam is matched to the start of the crystallization, for example, characterized in that it is set to 300mJ / cm ² ~ 350mJ / cm ² .

In this case, the energy density of the rear laser beam uses an energy density region recrystallized by a pulse overlap shot, for example, it is set to 500mJ / cm ² ~ 800mJ / cm ² .

After the buffer layer is formed on the substrate, an amorphous silicon thin film is formed thereon.

After forming the amorphous silicon thin film, characterized in that it further comprises the step of performing a dehydrogenation process on the amorphous silicon thin film.

A method of manufacturing a thin film transistor of the present invention comprises the steps of forming an amorphous silicon thin film on a substrate; Scanning the green laser beam having a step profile on the amorphous silicon thin film to perform crystallization; And patterning the crystallized silicon thin film to form an active layer.

In this case, the laser beam is characterized in that the two laser beams having a phase difference with respect to the beam width direction has a different energy density to form a step profile.

In this case, the green laser beam having the step profile is formed by adjusting the energy density of the two laser beams after the two laser sources give a phase difference in the beam width direction through the optical system.

The energy density of the front laser beam located in front of the scanning direction is set low, and the energy density of the rear laser beam behind is set high.

As described above, the crystallization method and the manufacturing method of the thin film transistor using the same according to the present invention is crystallized using a green laser to reduce the maintenance cost compared to conventional excimer laser crystallization, thereby ensuring high productivity and price competitiveness Provide effect.

The crystallization method according to the present invention and the manufacturing method of the thin film transistor using the same in the crystallization using the green laser, the crystallization using a laser beam having a laser beam having a step profile (step profile) using two scans with different energy of the laser beam As a result, crystallization uniformity can be improved. The result is an effect applicable to large area displays. In addition, by improving grain size and crystallization uniformity, mura is suppressed, thereby providing an effect of improving the performance of the organic light emitting device.

1 and 2 show, for example, a green laser crystallization apparatus according to the present invention.
3 is a graph showing absorbance according to wavelength in amorphous silicon and polycrystalline silicon.
4A to 4D are cross-sectional views sequentially illustrating a crystallization method according to a first embodiment of the present invention.
5A to 5C are cross-sectional views sequentially illustrating a crystallization method according to a second embodiment of the present invention.
6A and 6B schematically show profiles of a first laser beam and a second laser beam;
7A, 7B and 8 schematically show profiles of a laser beam used in the crystallization method according to the second embodiment of the present invention.
9A to 9F are cross-sectional views sequentially illustrating a method of manufacturing a thin film transistor according to the present invention.
10 and 11 are graphs showing electrical characteristics of thin film transistors according to various positions of a panel.

Hereinafter, with reference to the accompanying drawings will be described in detail a preferred embodiment of the crystallization method and a method for manufacturing a thin film transistor using the same according to the present invention.

1 and 2 are views showing, for example, a green laser crystallization apparatus according to the present invention.

1 illustrates the configuration of the optical system in the green laser crystallization apparatus according to the present invention, but the present invention is not limited to the configuration of the optical system.

Referring to the drawings, the green laser crystallization apparatus according to the present invention may be largely composed of an optical system including a laser generator 150 and a beam splitter 185, the laser generator 150 The laser beam 155 generated by the laser beam is irradiated to the predetermined substrate 110 through the optical system in a scan method.

The laser generator 150 is a YAG (Yttrium Aluminum) that generates a substantial laser beam 155 by collecting a diode 152 that supplies light energy in an infrared form and light energy emitted from the diode 152. Garnet rod 151 and Second-Harmonic Generation (SHG) optical system 153.

In this case, the diode 152 serves to supply light energy to the YAG rod 151 in the form of infrared rays, and the YAG rod 151 opens the YAG rod 151 through the light energy incident therein. The atoms that make up the high energy state and returns to the original state serves to generate the laser beam 155. In addition, the second harmonic generating optical system 153 serves to double the wavelength of the laser beam 155 from the YAG rod 151 and then enters the YAG rod 151 from the diode 152. The laser beam 155 coming out still has a wavelength of 1064 nm, but as it passes through the second harmonic generating optical system 153, its part is still 532 nm whose length is halved to another with a wavelength of 1064 nm. The laser beam 155 having a wavelength of is made.

In addition, the laser beam 155 having two wavelength bands passing through the second harmonic generating optical system 153 is a laser beam 155 having a wavelength of 532 nm and infrared (IR) having a wavelength of 1064 nm through the wavelength separation mirror 154. Will be separated.

The laser beam 155 having a wavelength of 532 nm includes a plurality of reflection mirrors 171a, 171b, and 171c, an attenuator and a shutter 181, a telescope lens 172, It is irradiated onto the substrate 110 via a homogenizer 182, a wavelength separation mirror 155, and a focusing lens 175.

The laser beam 155 separated by the wavelength separation mirror 185 may include a charge coupled device (CCD) 175, an imaging lens 173, an attenuator 177, and a focusing lens. And enters a beam profiler / feedback control system 183 consisting of 174.

However, the present invention is not limited to the configuration of the optical system.

In the case of the green laser crystallization apparatus having the above-described configuration, the YAG rod 151, which is a solid medium for generating the diode 152 and the laser beam 155, which are used as energy sources, has a lifespan of about 15 to 18 hours a day. If used, it is about one year, which is three times longer than an excimer laser device using gas or liquid as a medium for generating a laser beam.

In addition, the laser crystallization apparatus using such a solid source is irradiated during the crystallization process because the error of the energy density per unit area of the generated laser beam 155 is much smaller than that generated through the excimer laser apparatus using gas as a medium source. Stripe unevenness generated by the energy density difference for each position of the laser beam 155 is hardly generated.

However, the crystallization method using the green laser has a disadvantage that a difference occurs in the light absorption of the amorphous silicon and the polycrystalline silicon due to the laser wavelength.

3 is a graph showing absorbance according to wavelength in amorphous silicon and polycrystalline silicon.

Referring to FIG. 3, it can be seen that the light absorption of the amorphous silicon and the polycrystalline silicon is different from each other according to the wavelength, and in the case of the green laser having a wavelength of about 532 nm, the difference in the light absorption of the amorphous silicon and the polycrystalline silicon is greatly generated. I can see that.

As such, the crystallization is uneven due to the difference in the light absorption between amorphous silicon and polycrystalline silicon and the green laser wavelength in which light absorption occurs at the entire depth of the silicon, resulting in random distribution of large and small grains.

That is, due to the characteristics of the green laser wavelength, as crystals grow by seeding the fine grain of the shoulder region of the first shot when the laser beam overlaps, the crystals grow uniformly in subsequent shots. This becomes difficult.

Accordingly, the first embodiment of the present invention proposes a crystallization method using two scans with different energy of the laser beam in order to improve such non-uniform crystallization.

4A to 4D are cross-sectional views sequentially illustrating a crystallization method according to a first embodiment of the present invention.

In this case, although the first embodiment of the present invention describes amorphous silicon as a thin film to be crystallized, the present invention is not limited thereto.

As shown in FIG. 4A, a buffer layer 111 having a predetermined thickness is formed on the entire surface of the substrate 110 made of a transparent insulating material such as glass.

The buffer layer 111 serves to block impurities such as sodium (natrium) from the substrate 110 from penetrating into the upper layer during the crystallization process.

Thereafter, amorphous silicon thin film 120 is formed by depositing amorphous silicon on the entire surface of the substrate 110 on which the buffer layer 111 is formed.

Representative methods of depositing the amorphous silicon thin film 120 include a low pressure chemical vapor deposition (LPCVD) method and a plasma enhanced chemical vapor deposition (PECVD) method. In the case of depositing the amorphous silicon thin film 120 by the plasma chemical vapor deposition method, the hydrogen atoms of about 20% are included in the amorphous silicon thin film 120 although there is a slight difference depending on the temperature of the substrate during deposition.

As shown in FIG. 4B, if necessary, a dehydrogenation process is performed on the amorphous silicon thin film 120 to remove hydrogen contained in the amorphous silicon thin film 120.

Then, the uniform scan of the laser generating apparatus 150, the amorphous silicon thin film 120, the laser beam (155 '), the low energy density of ^{300mJ / cm 2 ~ 450mJ / cm} 2 in the via, as shown in Figure 4c One solid phase crystallization is carried out. In this case, for example, the solid phase crystallization may form a first polycrystalline silicon thin film 130 ′ having a seed having a uniform grain in the first scan using the laser beam 155 ′ in the 350 mJ / cm ² region.

Then, as shown in Fig. 4d, by scanning the first polycrystalline silicon thin film ^{(130 ') 500mJ / cm 2} ~ 800mJ / cm 2 of the laser beam (155 ") of a high energy density in the formed of a first scan Recrystallization is carried out using the uniform grain as a seed, for example, the recrystallization is performed by recrystallization using the uniform grain formed from the first scan using a laser beam in the 650 mJ / cm ² region as a seed. Proceeding to form the secondary polycrystalline silicon thin film 130.

While the crystallization method according to the first embodiment of the present invention improves the crystallization uniformity, productivity is somewhat lowered because two scans are required for seed formation and recrystallization.

Accordingly, the second embodiment of the present invention proposes a crystallization method using a laser beam having a step profile in order to improve such productivity decrease.

To form uniform and large grains, it is necessary to form a uniform seed at a low energy density and then recrystallize by pulse overlap shot at a high energy density. In the case of the first embodiment of the present invention, the productivity is reduced, but by changing the laser beam profile to overcome this limitation, it is possible to form grain of uniform and large size in one scan.

5A to 5C are cross-sectional views sequentially illustrating a crystallization method according to a second embodiment of the present invention.

In this case, although the second embodiment of the present invention describes amorphous silicon as a thin film to be crystallized, the present invention is not limited thereto.

As shown in FIG. 5A, a buffer layer 211 having a predetermined thickness is formed on the entire surface of the substrate 210 made of a transparent insulating material such as glass.

Thereafter, amorphous silicon thin film 220 is formed by depositing amorphous silicon on the entire surface of the substrate 210 on which the buffer layer 211 is formed.

As described above, representative methods of depositing the amorphous silicon thin film 220 include low pressure chemical vapor deposition and plasma chemical vapor deposition. In the case of depositing the amorphous silicon thin film 220 by the plasma chemical vapor deposition method, a hydrogen atom of about 20% is included in the amorphous silicon thin film 220 although there is a slight difference depending on the temperature of the substrate during deposition.

And, as shown in Figure 5b, if necessary dehydrogenation process to the amorphous silicon thin film 220 to remove the hydrogen contained in the amorphous silicon thin film 220.

Subsequently, as shown in FIG. 5C, the amorphous silicon thin film 220 is irradiated with the laser beam 255 having a step profile to the amorphous silicon thin film 220 through the laser generator 250 to have a uniform and large grain of the polycrystalline silicon thin film 230. To form.

For reference, FIGS. 6A and 6B schematically illustrate profiles of a first laser beam and a second laser beam.

7A, 7B and 8 are diagrams schematically showing a profile of a laser beam used in the crystallization method according to the second embodiment of the present invention.

7A schematically illustrates a lower surface of the laser beam having a step profile, and FIG. 7B schematically illustrates a side surface of the laser beam having the step profile.

Referring to the drawings, the laser beam 255 may have a step profile by varying energy densities of two laser beams 255a and 255b having a phase difference with respect to a beam width (W) direction.

The laser beam 255 having such a step profile can be formed by adjusting the energy densities of the two laser beams 255a and 255b after retarding two laser sources with respect to the beam width W direction through the optical system. . For example, the energy density of the front laser beam 255a located in front of the scanning direction can be lowered, and the energy density of the rear laser beam 255b in the rear can be made high. The energy density of the front laser beam 255a may be adjusted to a portion where crystallization starts, and may be, for example, about 300 mJ / cm ² to 350 mJ / cm ² . The energy density of the back of the laser beam (255b) is used and the energy density region in which re-crystallization by a shot pulses overlap, for example, be about ^{500mJ / cm 2 ~ 800mJ / cm} 2.

For example, when the thickness of the amorphous silicon thin film 220 is about 500 Hz, the energy density of the front laser beam 255a is about 350 mJ / cm ² , and the energy density of the rear laser beam 255b is 750 mJ / cm ² ~ 800 mJ. / cm ² can be.

In addition, when the thickness of the amorphous silicon thin film 220 is about 600 Hz, the energy density of the front laser beam 255a is about 300 mJ / cm ² , and the energy density of the rear laser beam 255b is 500 mJ / cm ² to 600 mJ /. I can do it about cm ² .

In this way, a uniform seed is formed using a region having a low energy density of the front laser beam 255a with respect to the scanning direction, and then recrystallized in a region having a high energy density of the rear laser beam 255b to achieve uniform and large grain. Can be formed in one scan.

In this case, the polycrystalline silicon thin film crystallized in accordance with the present invention can be used in the fabrication of semiconductor devices such as thin film transistors, solar cells, image sensors, and the like. For example, it is as follows.

9A to 9F are cross-sectional views sequentially illustrating a method of manufacturing a thin film transistor according to the present invention.

First, as shown in FIG. 9A, a buffer layer 211 having a predetermined thickness is formed on a substrate 210 made of a transparent insulating material such as glass.

In this case, the buffer layer 211 is composed of a silicon oxide film (SiO ₂ ) to block impurities such as sodium present in the substrate 210 from penetrating into the upper layer during the crystallization process.

Thereafter, an amorphous silicon thin film is deposited to a predetermined thickness on the substrate 210 on which the buffer layer 211 is formed, and then the amorphous silicon thin film is crystallized using the crystallization method of the present invention to form a polycrystalline silicon thin film.

At this time, as described above, representative methods for depositing the amorphous silicon thin film include a low pressure chemical vapor deposition method and a plasma chemical vapor deposition method. In the case of depositing the amorphous silicon thin film by the plasma chemical vapor deposition method, the hydrogen atoms of about 20% are included in the amorphous silicon thin film although there is a slight difference depending on the temperature of the substrate during deposition.

Then, if necessary, a dehydrogenation process is performed on the amorphous silicon thin film to remove hydrogen contained in the amorphous silicon thin film.

The amorphous silicon thin film is irradiated with a laser beam having a step profile to form a polycrystalline silicon thin film having uniform and large grains. At this time, for example, a uniform seed is formed by using a region having a low energy density of the front laser beam in the scanning direction, and then recrystallized in a region having a high energy density of the rear laser beam. It can be formed by scanning.

Thereafter, the polycrystalline silicon thin film is patterned through a photolithography process to form a predetermined active layer 224.

Thereafter, as illustrated in FIG. 9B, a gate oxide layer 215a is formed by depositing a silicon oxide layer or a silicon nitride layer SiNx on the entire surface of the substrate 210 on which the active layer 224 is formed.

In addition, a gate line (not shown) extending in one direction is formed on the substrate 210 on which the gate insulating layer 215a is formed, and a gate electrode 221 connected to the gate line is formed on the active layer 224. Form.

In this case, the gate electrode 221 and the gate line are formed by depositing a first conductive layer on the entire surface of the substrate 210 and then selectively patterning the same by a photolithography process.

Here, the first conductive layer may include aluminum (Al), aluminum alloy (Al alloy), tungsten (W), copper (Cu), chromium (Cr), molybdenum (Mo), and Low resistance opaque conductive materials such as molybdenum alloys can be used. The first conductive layer may have a multilayer structure in which two or more low resistance conductive materials are stacked.

For example, in the case of forming an N-type thin film transistor, a high concentration of n + ions is implanted into a predetermined region of the active layer 224 using the gate electrode 221 as a mask so that the source region 224a and the drain region ( 224b). In this case, the gate electrode 221 serves as an ion stopper to prevent the dopant from penetrating into the channel region 224c of the active layer 224.

Subsequently, as shown in FIG. 9C, after depositing the interlayer insulating film 215b on the entire surface of the substrate 210, a portion of the gate insulating film 215a and the interlayer insulating film 215b is selectively selected using a photolithography process. Patterning to form a first contact hole 240a and a second contact hole 240b exposing portions of the source region 224a and the drain region 224b, respectively.

Subsequently, as illustrated in FIG. 9D, a source electrode 222 electrically connected to the source region 224a and the drain region 224b through the first contact hole 240a and the second contact hole 240b, respectively. ) And the drain electrode 223 are formed.

In this case, a data line (not shown) defining a pixel region is formed to cross the gate line, and the source electrode 222, the drain electrode 223, and the data line form a second conductive layer on the entire surface of the substrate 210. After deposition on the photolithography process is selectively patterned to form.

Here, a low resistance opaque conductive material such as aluminum, aluminum alloy, tungsten, copper, chromium, molybdenum and molybdenum alloy may be used as the second conductive film. The second conductive layer may have a multilayer structure in which two or more low resistance conductive materials are stacked.

Subsequently, as shown in FIG. 9E, after the protective film 215c is deposited on the entire surface of the substrate 210, a portion of the protective film 215c is selectively patterned using a photolithography process to thereby drain the drain electrode 223. A third contact hole 240c exposing a portion of

As shown in FIG. 9F, a third conductive layer is formed on the entire surface of the substrate 210. In this case, the third conductive layer includes a transparent conductive material having excellent transmittance such as indium tin oxide (ITO) or indium zinc oxide (IZO) to form a pixel electrode.

Thereafter, the third conductive film is selectively removed through a photolithography process, and the third conductive film is formed on the array substrate 210 and electrically connected to the drain electrode 223 through the third contact hole 240c. The pixel electrode 218 to be connected is formed.

Meanwhile, the thin film transistor manufactured as described above may improve crystallization uniformity by crystallizing using two scans having different energy of the laser beam or using a laser beam having a step profile. As a result, it is possible to apply to large-area display, and the mura is suppressed by the improvement of grain size and crystallization uniformity, thereby improving the performance of display devices such as organic light emitting devices.

For reference, FIGS. 10 and 11 are graphs showing electrical characteristics of thin film transistors according to various positions of the panel, and for example, electrical characteristics measured at eight points in the panel.

10 illustrates electrical characteristics of a thin film transistor crystallized through a green laser having a general Gaussian flow profile, and FIG. 11 illustrates a step profile according to the second embodiment of the present invention. The electrical characteristics of the thin film transistor crystallized by the excitation green laser are shown.

Referring to FIG. 10, it can be seen that the thin film transistor crystallized through a Gaussian-type green laser having an energy density of 750 mJ / cm ² is not uniform in electrical characteristics. For example, the average mobility is about 55.9 cm ² / Vs, where uniformity is measured to be about 69%.

Referring to FIG. 11, the energy density of the front is 350mJ / cm ² energy density of the back it can be seen that the electrical characteristics even if the thin film transistor crystallization through the green laser with 780mJ / cm ² in the step profile . For example, the average mobility is about 62.4 cm ² / Vs, with a uniformity of about 82%.

Compared to the result measured in FIG. 10, the mobility was increased by about 10%, and the uniformity was improved by about 13%.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be construed as limited to the embodiments described, but should be determined by equivalents to the appended claims and the claims.

110,210: substrate 111,211: buffer layer
120,220: amorphous silicon thin film 130,230: polycrystalline silicon thin film
150,250: laser generator 155,255: laser beam

Claims (15)

Forming an amorphous silicon thin film on the substrate;
Scanning the green laser beam having a first energy density on the amorphous silicon thin film to perform solid phase crystallization to form uniform grains; And
And recrystallizing the grains with seeds by scanning a green laser beam having a second energy density higher than the first energy density on the amorphous silicon thin film. Forming an amorphous silicon thin film on the substrate; And
And crystallizing the amorphous silicon thin film by scanning a green laser beam having a step profile. The method of claim 1, wherein the first energy density of the crystallization method characterized in that it is set to ^{300mJ / cm 2 ~ 450mJ / cm} 2. The method of claim 1, wherein the second energy density of the crystallization method characterized in that the set ^{500mJ / cm 2 ~ 800mJ / cm} 2. The crystallization method of claim 2, wherein the laser beam forms a step profile by having two energy beams having a phase difference with respect to a beam width direction having different energy densities. The crystallization method according to claim 5, wherein the green laser beam having the step profile is formed by adjusting the energy densities of the two laser beams after giving two laser sources with respect to the beam width direction through an optical system. . 6. The crystallization method according to claim 5, wherein the energy density of the front laser beam located in front of the scanning direction is set low and the energy density of the rear laser beam in the rear is set high. 8. The crystallization method according to claim 7, wherein the energy density of the front laser beam is matched to a portion where crystallization starts, for example, 300 mJ / cm ² to 350 mJ / cm ² . 9. The method of claim 8 wherein the energy density of the back of the laser beam is a crystallization method characterized in that it uses an energy density region in which re-crystallization by a shot pulses overlap, for example, set to ^{500mJ / cm 2 ~ 800mJ / cm} 2 . The crystallization method according to any one of claims 1 and 2, wherein after forming a buffer layer on the substrate, an amorphous silicon thin film is formed thereon. The method of claim 10, further comprising, after forming the amorphous silicon thin film, performing a dehydrogenation process on the amorphous silicon thin film. Forming an amorphous silicon thin film on the substrate;
Scanning the green laser beam having a step profile on the amorphous silicon thin film to perform crystallization; And
And patterning the crystallized silicon thin film to form an active layer. The method of claim 12, wherein the laser beam forms a step profile in which two laser beams having a phase difference with respect to a beam width direction have different energy densities. The thin film transistor according to claim 13, wherein the green laser beam having the step profile is formed by adjusting energy density of the two laser beams after giving two laser sources with respect to the beam width direction through an optical system. Manufacturing method. The method of claim 13, wherein the energy density of the front laser beam located in front of the scanning direction is set low and the energy density of the rear laser beam in the rear is set high.

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