JP2010056433A - Method of manufacturing flat panel display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To manufacture a flat panel display device comprising transistors having reduced characteristic dispersion and no direction dependency of the characteristic, by irradiating a desired region of an amorphous silicon film formed on a glass substrate with continuous oscillation laser light directly, to convert into a fine crystal silicon film, without a process of forming and removing a buffer film and a photo-thermal conversion film. <P>SOLUTION: The continuous oscillation laser light is shaped into a beam having a rectangular and uniform power density distribution, and the desired region of the amorphous silicon thin film 33 formed on a transparent substrate 31 is irradiated with the laser light 36 with the irradiation time (a transit time of any point) of the continuous oscillation laser light set not smaller than 0.5 msec while being run at a constant speed, to convert into the fine crystal silicon film 34. At this point, the wavelength of the laser light to be irradiated is selected so that the penetration depth (reciprocal number of the absorption coefficient) to the amorphous silicon is larger than the film thickness of the amorphous silicon film, and the absorption coefficient to the amorphous silicon is larger than the absorption coefficient to a crystal silicon. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a flat display device, and more particularly to a technique that is effective when applied to a method for manufacturing a flat display device having TFT elements with small characteristic variations in the flat display device.

  Conventionally, a liquid crystal display device having a liquid crystal display panel in which a liquid crystal material is sealed between a pair of substrates includes an active matrix TFT liquid crystal display device. An active matrix TFT liquid crystal display device is widely used, for example, in a television receiver, a display of a personal computer (PC), a display unit of a mobile phone terminal or a personal digital assistant (PDA).

  In a liquid crystal display panel used in an active matrix TFT liquid crystal display device, a plurality of scanning signal lines, a plurality of video signal lines, TFT elements, pixel electrodes, and the like are provided on one substrate. In a conventional liquid crystal display device, for example, a driver IC for inputting a video signal (sometimes referred to as gradation data) to a plurality of video signal lines or a scanning signal to a plurality of scanning signal lines is input. In general, a flexible circuit board such as TCP or COF on which a driver IC is mounted is connected to a liquid crystal display panel, or each of the driver ICs is mounted directly on the liquid crystal display panel. In recent years, for example, a drive circuit (peripheral circuit) having a function equivalent to that of the driver IC is formed outside a display region of a substrate (hereinafter referred to as a TFT substrate) on which the scanning signal lines are formed. Liquid crystal display panels have been proposed.

  The drive circuit formed outside the display area of the TFT substrate is mainly composed of semiconductor elements such as transistors and diodes, and each semiconductor element is formed when forming the scanning signal lines and the video signal lines. The semiconductor layer of the semiconductor element is formed when the semiconductor layer (channel layer) of the TFT element in the display region is formed. The semiconductor layer of the TFT element formed in the display region of the TFT substrate may be insufficient in terms of dynamic characteristics when using amorphous silicon (a-Si: amorphous silicon). For this reason, it is necessary to crystallize amorphous silicon as a semiconductor layer.

  In recent years, a technique for crystallizing an amorphous silicon film by irradiating a laser has been established and applied to products. In general, amorphous silicon is dehydrogenated by heat treatment in an electric furnace or the like at 450 ° C. for several hours, and a pulse laser such as an excimer laser is irradiated to the dehydrogenated amorphous silicon a plurality of times. In this way, a method is employed in which the amorphous silicon film on the substrate is polycrystallized by irradiating while moving step by step. Above all, TFTs composed of a strip-like polycrystalline film obtained by shaping and condensing continuous wave laser light into a linear or rectangular shape and scanning in the direction of the minor axis width of the beam are crystals formed by a pulsed laser. It is much better in terms of dynamic characteristics than the constructed TFT.

  However, the polycrystalline silicon formed by these methods has the following problems. That is, polycrystalline silicon obtained by irradiation with a pulsed laser such as an excimer laser has a crystal grain size of several hundred nm to several μm, and its characteristics greatly vary depending on the number of crystal grain boundaries included in the channel region of the TFT. In addition, the polycrystalline film formed by the pulse laser irradiation is prone to have protrusions at the grain boundary portions, and in the top gate structure TFT, these protrusions also cause the breakdown voltage of the gate insulating film to decrease. In addition, the band-like polycrystalline film obtained by scanning with continuous wave laser light has a large mobility in the scanning direction of laser light (crystal growth direction), but the mobility is perpendicular to the scanning direction. The problem is that the direction dependency of the characteristics is large, such as halving.

  As a method for coping with this problem, for example, Patent Document 1 discloses a method of forming a TFT channel layer with a polycrystalline silicon film (microcrystalline silicon film) having a crystal grain size of 100 nm or less.

  In Patent Document 1, a gate electrode is formed on a substrate, and a gate insulating film, an amorphous silicon film, a buffer film, and a light-heat conversion film are formed in this order so as to cover the gate electrode. The conversion film is irradiated with semiconductor laser light to crystallize the amorphous silicon film into a microcrystalline silicon film, and then the light-to-heat conversion film and the buffer film are removed, and an amorphous silicon film is formed on the microcrystalline silicon film. A method of manufacturing a thin film transistor by forming a film and further forming a source / drain electrode is disclosed.

JP 2007-005508 A

  The present invention improves the above-described prior art. That is, in the method described in Patent Document 1, an originally unnecessary buffer film and a light-heat conversion film are formed on an amorphous silicon film, and the amorphous silicon film is microcrystallized by laser irradiation. In other words, extra steps such as removal of the buffer film and the light-heat conversion film are included, resulting in an increase in manufacturing cost and a decrease in throughput.

  An object of the present invention is to manufacture a flat display device having TFTs with little variation in characteristics and having no direction dependency by eliminating the process of forming and removing a buffer film and a light-heat conversion film at low cost and high yield. It is to provide a method.

  In order to achieve the above object, the flat display device manufacturing method of the present invention shapes a continuous wave laser beam into a linear or rectangular beam having a uniform energy density distribution in one direction, and projects the beam into a projection optical system. Thus, direct irradiation is performed by projecting onto the surface of the amorphous silicon film, and scanning is performed relatively in a direction orthogonal to one direction. At that time, the wavelength of the laser to be irradiated can be sufficiently transmitted through the amorphous silicon film thickness to be irradiated to uniformly heat the entire film, and the wavelength of the absorption coefficient of amorphous silicon is larger than that of polycrystalline silicon. Selected. Further, the laser beam is irradiated so that the amorphous silicon film is not melted and is kept at a temperature close to the melting point for a certain time. As a result, the amorphous silicon film is heated uniformly in the thickness direction for a predetermined time, and is stably converted into a microcrystalline silicon film.

  According to the present invention, a flat display device having a TFT with no characteristic variation and no direction dependency of characteristics is manufactured at low cost and with a high yield without the need for forming and removing a buffer film and a light-heat conversion film. be able to.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the best embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a diagram showing an optical system configuration of a laser microcrystallization apparatus suitable for carrying out the flat display device manufacturing method according to the present invention. In order to adjust the energy of the laser beam 3, a laser oscillator 4 that generates a continuous wave laser beam 3 coupled with an excitation LD (laser diode) 1 and a fiber 2, a shutter 5 that shields the laser beam 3 when it is not necessary, and the like. Continuously variable ND filter 6, modulator 7 for realizing pulse modulation or temporal modulation of energy by modulating laser beam 3, beam expander for adjusting the beam diameter of laser beam 3 ( Or a beam reducer 9, a beam shaper 10 for shaping the laser light 3 into a top-flat rectangular beam, a rectangular slit 11 for adjusting the dimension of the shaped laser light 3, the beam shaper 10 and the rectangular slit 11. A projection lens 14 for projecting a laser beam shaped into a rectangular shape onto a substrate 13 placed on the XY stage 12, and the substrate 13 Dichroic mirror 15, imaging lens 16, CCD camera 17, image processing device 18, excitation LD1 ON / OFF, shutter 5 open / close, transmittance continuously variable ND filter 6 for observation or alignment mark detection, etc. It comprises a control device 19 that controls rate adjustment, ON / OFF of the modulator 7, driving of the stage 12, detection of alignment marks by the image processing device 18, and switching of the beam shapers 10, 20 as necessary. Yes.

Next, the operation and function of each unit will be described in detail. First, consider the wavelength of the laser beam to be irradiated. FIG. 2 shows the spectral absorption coefficient (α) of amorphous silicon and crystalline silicon. The horizontal axis represents wavelength (nm), and the vertical axis represents absorption coefficient α (cm ⁻¹ ). In order to microcrystallize the amorphous silicon film, it is necessary to irradiate the amorphous silicon thin film with an absorbing wavelength. However, if the absorption coefficient is too large, the laser beam cannot be transmitted through the amorphous silicon film and only the surface is heated. Of course, it is heated to the side in contact with the substrate by heat conduction, but it is not preferable because the temperature is different from the surface and the crystallization state is also different. That is, it is desirable that the penetration depth of laser light (the reciprocal of the absorption coefficient) be equal to or greater than the film thickness of the amorphous silicon film. For example, if the film thickness of the amorphous silicon film is 40 nm, the penetration depth is preferably about 40 nm or more (= absorption coefficient is 2.5 × 10 ^ 5 (cm ⁻¹ ) or less). Is equivalent to 445 nm or more. The absorption coefficient of silicon varies depending on the impurity concentration or defect density in the silicon, but can be considered to be approximately 440 nm or more. When the film thickness of the amorphous silicon film is large, it shifts to a longer wavelength side. For example, when the film thickness of the amorphous silicon film is 100 nm, it is approximately 520 nm or more.

  On the other hand, it is not desirable that the absorption coefficient increases when the amorphous silicon film is irradiated with laser light to be microcrystallized. That is, the absorption coefficient increases at the moment when the amorphous silicon film is microcrystallized by irradiating a laser under appropriate conditions, and the microcrystal film melts or crystal grains grow greatly, Cannot be formed. On the other hand, if the absorption coefficient decreases at the moment when the amorphous silicon film is microcrystallized by irradiating a laser under appropriate conditions, the microcrystalline film is preserved. From this viewpoint, the absorption coefficient of amorphous silicon with respect to the wavelength of the laser beam to be irradiated needs to be larger than the absorption coefficient of crystalline silicon. The wavelength at which the absorption coefficient is reversed varies depending on the manufacturing process, impurity concentration, and defect density of the silicon film, but is in the range of 650 to 750 nm, and corresponds to 670 nm in the case of FIG. It is necessary to irradiate laser light having a wavelength shorter than this wavelength. This wavelength does not depend on the film thickness of the silicon film.

From the above, the wavelength of the laser light applied to the present invention needs to be 440 nm or more and 700 nm or less when the amorphous silicon film thickness is about 40 nm, and more preferably 445 to 670 nm. Lasers that satisfy this condition include LDs (laser diodes) that oscillate visible wavelengths, Ar lasers or Kr lasers, second harmonics of Nd: YAG lasers, second harmonics of Nd: YVO ₄ lasers, Nd: YLF lasers The second harmonic can be applied. In the description of this embodiment, the case where the second harmonic of the LD-pumped Nd: YVO ₄ laser is mainly used will be described.

  The laser beam 3 oscillated from the laser oscillator 4 is shielded by the shutter 5 except when the laser is necessary. That is, the laser oscillator 4 is always in a state of oscillating the laser beam 3 with a constant output, the shutter 5 is normally in the OFF state, and the laser beam 3 is blocked by the shutter 5. Only when the laser beam 3 is irradiated, the laser beam 3 is output by opening (turning on) the shutter 5. Although it is possible to turn on / off the laser beam 3 by turning on / off the pumping laser diode 1, it is not desirable for ensuring the stability of the laser output. In addition, the shutter 5 may be closed when it is urgently desired to stop the irradiation of the laser beam 3 from the viewpoint of safety.

  The laser beam 3 that has passed through the shutter 5 passes through a continuously variable transmittance ND filter 6 used for output adjustment and is incident on a modulator 7. The continuously variable transmittance ND filter 6 is preferably one that transmits laser light and does not rotate its polarization direction. However, this is not the case when an AO modulator that is not affected by the polarization direction is used as the modulator 7 as will be described later. The EO modulator 7a rotates the polarization direction of the laser beam 3 transmitted through the crystal by applying a voltage to a Pockels cell (crystal) (shown as 7a in the figure) via a driver (not shown). The polarization beam splitter 8 placed behind the crystal passes only the P-polarized light component and deflects the S-polarized light component by 90 degrees, so that the ON / OFF of the laser light 3 and the output adjustment can be performed.

  A voltage V1 for rotating the polarization direction of the laser light 3 so as to be incident on the polarization beam splitter 8 as P-polarized light, and a voltage V2 for rotating the polarization direction of the laser light 3 so as to be incident as S-polarized light. The amplitude of the laser beam 3 is modulated by applying a voltage that changes alternately or between V1 and V2. In FIG. 1, the EO modulator 7 a has been described by combining a Pockels cell and the polarizing beam splitter 8, but various polarizing elements can be used as an alternative to the polarizing beam splitter 8. In FIG. 1, the portion up to the Pockels cell is described as the EO modulator 7a. However, since there are cases where various polarization elements are included, the Pockels cell and the polarization beam splitter 8 are commercially available. An entire combination of (or various polarizing elements) may be referred to as an EO modulator.

  As another example of the modulator 7, an AO (acousto-optic) modulator can be used. In general, the AO modulator has a lower driving frequency than the EO modulator and has a diffraction efficiency of 70 to 90%, which is inefficient compared to the EO modulator. However, the AO modulator is ON / OFF even when the laser beam is not linearly polarized light. Even when a continuously variable transmittance ND filter 6 having a rotating polarization direction of the transmitted laser beam is used, no problem occurs. In this way, by using the modulator 7 such as the EO modulator 7a (and the polarization beam splitter 8) or the AO modulator, laser light having an arbitrary waveform (temporal energy change) from the continuous wave laser light at an arbitrary timing. Obtainable. That is, desired amplitude modulation can be performed.

  The amplitude-modulated laser light 3 is adjusted in beam diameter by a beam expander (or beam reducer) 9 for adjusting the beam diameter, and enters the beam shaper 10. The beam shaper 10 is an optical element for shaping the laser light 3 into a linear or rectangular beam that is top flat in at least one direction. Normally, a gas laser or a solid-state laser has a Gaussian energy distribution and cannot be used for the microcrystallization of the present invention as it is. If the output of the oscillator is sufficiently large, it is possible to obtain a substantially uniform energy distribution by sufficiently widening the beam diameter and cutting out only a relatively uniform part of the central part, but the peripheral part of the beam is discarded. , Most of the energy is wasted. The beam shaper 10 is used to solve this drawback and convert the Gaussian distribution into a desired distribution.

  A diffractive optical element can be used as the beam shaper 10. The diffractive optical element forms a fine step in a photoetching process on a substrate such as quartz, and synthesizes a diffraction pattern formed by laser light that passes through each step portion on the imaging surface (surface of the rectangular aperture slit 11). Thus, it is created so as to obtain a uniform energy distribution in at least one direction on the image plane (the surface of the rectangular aperture slit 11). When a diffractive optical element is used, a uniform distribution of about ± 3% is obtained. If necessary, the peripheral part is shielded by the rectangular opening slit 11 so that a linear or rectangular beam having a desired rise and a rapid rise can be obtained.

A continuous wave laser beam, which has been amplitude-modulated and shaped into a linear or rectangular beam having a desired size, is projected as a linear or rectangular beam onto the amorphous silicon film on the substrate 13 by the projection optical system 14. The state of the amorphous silicon thin film when irradiated while scanning will be described with reference to FIG. In the target substrate here, an amorphous silicon thin film 33 is formed on a transparent substrate 31 such as glass via a base insulating film 32 made of a SiO ₂ film and / or a SiN film. Alternatively, a gate electrode film (not shown) patterned on a transparent substrate 31 such as glass via a base insulating film 32 made of a SiO ₂ film and / or a SiN film, or a gate insulating film (see FIG. An amorphous silicon thin film 33 is formed thereon. At this time, the film thickness of the amorphous silicon is 30 to 150 nm. The case where the former board | substrate is used is demonstrated below.

The substrate 13 is placed and fixed on the stage 12, and the laser beam 36 is scanned in the direction of the arrow shown in the drawing as the substrate 13 moves together with the stage 12. By irradiating the laser beam 36, the amorphous silicon thin film 33 is heated to near the melting point, and the amorphous silicon thin film 33 is microcrystallized to become a microcrystalline silicon thin film 34. At that moment, the absorption coefficient for the irradiating laser beam 36 decreases, and the microcrystalline state is preserved. The microcrystalline silicon thin film 34 has a crystal grain size as small as 30 to 70 nm, and the surface is the same level as the amorphous silicon thin film before laser irradiation. When a TFT is formed with this microcrystalline silicon thin film, carrier mobility of several to 20 times that of amorphous 0.5 cm ² / Vs can be obtained. Further, when a silicon film having a high mobility (100 cm ² / Vs or more, typically 300 cm ² / Vs) is required, the beam width in the scanning direction is 10 μm or less at the portion changed to the microcrystalline silicon thin film 34 ( A linear laser beam focused to about 5 μm is irradiated. Thereby, the film is converted into a band-shaped polycrystalline silicon film composed of crystals laterally grown in the scanning direction of the laser beam. The surface of the obtained band-like polycrystalline silicon film is also very flat. As an apparatus suitable for carrying out this band-like polycrystallization, the beam shaper 10 of the apparatus shown in FIG. 1 may be replaced with a beam shaper 20 that converts it into a linear beam. That is, microcrystallization and band-like polycrystallization may be performed while switching the beam shaper with a single device, or a microcrystallizer and a band-like polycrystallizer are prepared separately, and the And band-like crystallization may be performed.

  FIG. 4 shows how the amorphous silicon film changes when the irradiation power density and the scanning speed are changed with the beam width in the scanning direction constant in the microcrystallization by laser irradiation. . The horizontal axis represents relative scanning speed, and the vertical axis represents relative irradiation power density. If the irradiation power density is too high and the scanning speed is too low (the region above the solid line in FIG. 4), the amorphous silicon film melts and the liquid state is long, so the surface tension causes the laser beam to scan in the scanning direction. Aggregation into rod-shaped silicon or scattering (ablation) occurs when the energy density is higher. On the other hand, in a region surrounded by a solid line and a broken line in FIG. 4, a band-like crystal is formed in which the amorphous silicon film is laterally grown in the scanning direction of the laser light through a process of melting and recrystallization. Also, under the conditions surrounded by the broken line and the one-dotted line, the molten silicon cannot be continued in the lateral direction and becomes a granular crystal. Further, under the conditions surrounded by the alternate long and short dash line, the amorphous silicon film does not melt, and microcrystals having a crystal grain size of 100 nm or less, typically 20 to 70 nm are formed. Under the condition below the two-dot line, the amorphous silicon remains unchanged.

  Hereinafter, a first embodiment of a method for manufacturing a flat display device using the manufacturing apparatus having the configuration shown in FIG. 1 will be described in detail with reference to the drawings. Here, the case where the bottom gate structure is targeted will be described, but the case of the top gate structure can also be basically manufactured by the same process.

As shown in FIG. 5, the substrate is formed of an insulating film made of a SiO ₂ film and / or a SiN film on a transparent substrate 41 such as glass, and after the gate electrode is patterned, the gate insulating film and amorphous A silicon film 42 is formed. The amorphous silicon film thickness is in the range of 30 to 150 nm and is used for TFT fabrication. Here, the case where the amorphous silicon film thickness is 50 nm will be described. The amorphous silicon film 42 is formed by a technique such as plasma CVD, but a large amount of hydrogen is typically contained at a concentration of 8 to 15 atomic%, and is also referred to as a hydrogenated amorphous silicon film. Is done. The amorphous silicon film 42 is first dehydrogenated by furnace annealing at 450 degrees for about 2 hours. By this step, the hydrogen concentration in the amorphous silicon thin film is reduced to about 1 atomic%, and even if laser irradiation is performed thereafter, the silicon film is not peeled off or damaged due to rapid hydrogen desorption. The substrate 41 is placed and fixed on the stage 12 of the apparatus shown in FIG.

  First, a plurality of alignment marks 43 formed simultaneously with the formation of the gate electrode are picked up by the CCD camera 17 and detected by the image processing device 18, and the substrate 41 is positioned by moving the stage 12 or converting coordinates. A desired region is irradiated with continuous wave laser light sequentially according to design coordinates with the alignment mark position as a reference. In FIG. 5, the pixel region 44 and the drive circuit region 54 are indicated by broken lines, and a gate electrode is formed in these regions. Further, the laser light is shaped into a rectangular beam having a top flat shape in at least one direction by the beam shaper 10. For example, a uniform energy density distribution of 2 mm in the longitudinal direction (direction perpendicular to the scanning direction), a uniform energy density distribution of 0.1 mm in the lateral direction (scanning direction), or a trapezoidal energy density distribution or a Gaussian distribution. Shaped into a beam.

  After the substrate is positioned, the stage 12 starts scanning at a speed of 100 mm / s, and the irradiation of the continuous wave laser beam 3 is started from a position where the beam center is about 1.5 to 2 mm before the pixel region 44. After passing through the pixel regions 45, 46, 47, and 48, the laser irradiation is stopped when the beam center has passed about 1.5 to 2 mm. Thereby, as shown in FIG. 6, the region 50 including each part of the pixel regions 44, 45, 46, 47, 48 is microcrystallized. Next, the stage 12 is moved by 2 mm in a direction perpendicular to the scanning direction of the laser beam, and the stage 12 is moved in the opposite direction to the previous direction, whereby the region 50 ′ is microcrystallized. By repeating this, the region including the pixel region and the drive circuit region in the substrate is microcrystallized. Since this microcrystalline silicon film has not undergone a melting process, it has a surface flatness comparable to that of an amorphous silicon film.

  After microcrystallizing necessary portions, the beam shaper 10 is switched to the beam shaper 20 as necessary, and the scanning direction (short axis direction) is 5 μm, and the direction perpendicular to the scanning direction (long axis direction) is 1 mm. While shaping into a linear beam and scanning at a scanning speed of 500 mm / s in the minor axis direction with a power density sufficient to cause melting and re-solidification, the drive circuit regions 54, 55, 56, 57, 58 corresponding to each panel are scanned. The continuous wave laser beam is irradiated while being turned on and off, and the irradiated portion is melted and recrystallized, whereby the crystal is laterally grown in the scanning direction of the laser beam and converted into a band-like polycrystalline film. Similarly, the drive circuit region of the microcrystallized region 50 'is converted into a band-like polycrystalline film. The surface of the band-like polycrystalline film is also a flat film with irregularities of about 10 nm.

  By the above procedure, the region 60 including the pixel region and the drive circuit region in the amorphous silicon thin film 42 formed on the glass substrate 41 as shown in FIG. 7 is converted into a microcrystalline silicon thin film by laser irradiation. Further, if necessary, scanning is performed while irradiating a laser beam shaped into a linear shape, so that drive circuit regions 54, 54 ′, 55, 55 ′, 56, 56 ′, 57, Only 57 ′, 58 and 58 ′ are converted into a polycrystalline silicon thin film laterally grown in the scanning direction, that is, a band-shaped polycrystalline silicon thin film.

  After these steps, an amorphous silicon film is formed on the entire surface of the substrate as necessary, and has a two-layer structure of a microcrystalline silicon thin film and an amorphous silicon film, and a band-shaped polycrystalline silicon film and an amorphous silicon film. The silicon film is patterned into a desired shape as a channel region, and source / drain electrodes are formed to form TFTs. That is, a liquid crystal display device is formed in which the transistors of the pixel circuit and the drive circuit are formed of a microcrystalline silicon film and an amorphous silicon film, or only the transistors of the drive circuit are formed of a band-shaped polycrystalline silicon film and an amorphous silicon film. .

  5 to 8, the inside of the substrate is composed of 10 panels of 2 rows and 5 columns, but several to hundreds of panels can be manufactured depending on the size of the substrate and the size of the panel. 5 to 8, the driving circuit is formed on one side of the panel. However, it can be arranged on two sides as necessary. In that case, if necessary, the substrate is rotated by 90 degrees, the laser is scanned in the direction orthogonal to the above-described scanning, and only a desired region is subjected to band-like polycrystallization.

  Conditions under which fine microcrystallization can be achieved by laser irradiation can be defined by the power density and irradiation time of the laser beam to be irradiated. As a result of experiments on an amorphous silicon thin film having a thickness of 50 nm, microcrystallization was possible within the range shown in FIG. That is, in FIG. 9, the solid line indicates the lower limit of microcrystallization, and crystallization cannot be performed under conditions below the solid line. An alternate long and short dash line indicates the upper limit of microcrystallization. Under conditions above the alternate long and short dash line, crystal grains grow large, or silicon melts and aggregates due to surface tension. Appropriate microcrystallization was realized within the condition range surrounded by the solid line and the alternate long and short dash line. Under these conditions, it is estimated that the silicon film has risen to a temperature close to the melting point, but has not melted and has been microcrystallized in a solid state. The microcrystal obtained here has a crystal grain size of 100 nm or less, typically 30 to 80 nm, which is extremely small, and the surface is kept flat enough to show no change from that before laser irradiation.

  As is clear from FIG. 9, the longer the irradiation time of the continuous wave laser beam (the time from the arrival of the rectangular beam at an arbitrary point to the end of passage) is, the wider the margin for microcrystallization is. Here, the margin for microcrystallization is defined by a value obtained by dividing the upper limit of power density of the microcrystal by the lower limit of power density. Uniformity in the direction perpendicular to the scanning direction of the beam shaped into a linear or rectangular shape and ± 10% variation in power density due to variation between the substrate and the projection lens, and amorphous silicon film thickness between and within the substrate Assuming that the fluctuation of the power density required for the microcrystallization due to the fluctuation is ± 10%, the crystallization margin is preferably 1.4 or more. From this point of view, if the laser irradiation time is 0.5 ms or longer, preferably 1 ms or longer, the condition range of the irradiation power density is wide and a sufficiently practical process window can be secured. Microcrystallization is possible even when the irradiation time is 0.1 ms or less. However, as described above, it is affected by fluctuations in laser output, nonuniformity in power density distribution, and variations in film thickness of the amorphous silicon film. Therefore, it cannot be formed so stably that it can be applied to mass production. The laser irradiation time of 1 ms here corresponds to, for example, scanning a beam shaped to a width of 0.1 mm in the scanning direction at 100 mm / s. When a beam shaped to 0.5 mm is irradiated in the scanning direction, the same result can be obtained even if scanning is performed at 500 mm / s. Note that even if the region once microcrystallized was irradiated again with laser under the same conditions, no change occurred. This is because, as discussed with respect to the laser wavelength, the absorption coefficient decreases by microcrystallization, and the temperature does not increase until the crystal growth proceeds at the second irradiation. In addition, even in the overlapping portion of the previous scanning region and the subsequent scanning region, the portion once microcrystallized does not change even when irradiated again, so that the portion where the beam overlaps can be almost distinguished from the portion where the beam does not overlap. Absent. For this reason, when the longitudinal dimension of the rectangular beam is smaller than the substrate dimension, even if the front surface of the substrate is irradiated by a plurality of scans, uniform microcrystals can be obtained regardless of whether or not the irradiation regions are superimposed.

  Next, when performing scanning while directly irradiating the amorphous silicon thin film with laser light using FIGS. 11 to 14, the state of the irradiated region is monitored and the output of the laser light is controlled within an appropriate range. Explain that you can.

  By monitoring the crystal state immediately after laser irradiation and correcting the laser condition when the crystal state is not appropriate, it can be converted into a more stable microcrystalline film. For example, the optical system shown in FIG. 11 is provided before and after the projection lens 14, and the crystal state is monitored by the optical system opposite to the scanning direction (the side already irradiated with laser light). This optical system includes projectors 73 and 73 ′ that illuminate a region including a laser irradiation region at a shallow angle, a linear sensor 75 for capturing a substrate surface as a dark field image, an image processing device 76, and a display device 77. Yes. When the amorphous silicon film 72 formed on the glass substrate 71 and the laser irradiation region 74 are picked up as a dark field image by the optical system, the surface of the amorphous silicon 72 is very flat, so that the linear sensor 75 has no surface. Scattered light from the surface of the crystalline silicon 72 does not enter and the brightness is low. If the power density of the irradiated laser beam is too low to crystallize, the surface state of the laser irradiation region 74 is the same as the surface of the amorphous silicon 72 and cannot be distinguished. The state is shown in FIG.

  On the other hand, when laser light is irradiated under conditions suitable for microcrystallization, the laser irradiation region is microcrystallized and a slight amount of scattered light is generated as shown in FIG. Although the brightness is slightly higher than the surface of the silicon 72, it is sufficiently low. However, when irradiation is performed under conditions where the laser power density is too high, the amorphous silicon 72 becomes granular crystals or protrusions are formed, and scattered light is generated. For this reason, the brightness of the laser irradiation region 74 is increased as shown in FIG. In this case, since the brightness exceeding the threshold A shown in FIG. 12 is detected, it is determined that the laser output is too high (the power density is too large), and the laser output is adjusted by the variable transmittance filter.

  Further, the optical system shown in FIG. 13 is provided in front of and behind the projection lens 14, and the crystal state is monitored by the optical system opposite to the scanning direction (already irradiated with laser light). This optical system includes a light projector 81 for irradiating light having a wavelength with a large difference in absorption coefficient between amorphous silicon and crystalline silicon, and a light detector 82 for detecting light transmitted through the laser irradiation region (one-time transmitted light), or When the surface of the stage on which the glass substrate 71 is placed is coated with white alumina or zirconia, the amount of reflected / scattered light from the stage surface that has passed through the silicon film twice, avoiding regular reflection on the silicon film surface It is comprised from the photodetector 83 for detecting. The output from the photodetector 82 or 83 is compared with an output value set by an output determination circuit (not shown) to determine whether or not the crystal state is appropriate.

  FIG. 14 shows the relationship between the laser output to be irradiated and the detected light amount of transmitted or reflected light in the laser irradiated region. Since the amorphous silicon remains before the laser irradiation or irradiation with low output, the amount of light transmitted from the projector 81 is small. As the laser output is increased, the amorphous silicon film is microcrystallized and the amount of light detected increases. Further, even if the laser output is increased and the granular polycrystal is formed, the change in the detected light amount is small and almost constant. From this, it is determined that the crystallization is insufficient, that is, the laser output is insufficient when the detected light amount becomes 0.9 or less when the detected light amount becomes constant relative value 1. Can do. If it is determined that the laser output is insufficient based on this result, the laser output is adjusted by increasing the transmittance of the transmittance continuous wave variable filter.

  As described above, it is possible to determine whether the laser output is excessive or not based on the size of scattered light from the surface of the laser irradiation region, and whether the laser output is excessive or not based on the amount of light transmitted through the laser irradiation region. By adjusting the laser output applied to the amorphous silicon film according to the above determination, conversion to an appropriate microcrystalline film can be realized with a high yield.

  By the above method, microcrystalline silicon could be stably obtained in a desired region. The transistor formed of this microcrystalline silicon film has less mobility than a transistor formed from a polycrystalline silicon film formed by so-called excimer laser annealing, but has less characteristic variation, and the direction of transistor characteristics on a glass substrate There is no dependency.

  Next, FIG. 10 shows an optical system configuration of an apparatus for manufacturing another flat display device suitable for carrying out the flat display device manufacturing method according to the present invention. Laser beams emitted from a plurality of LDs housed in the casing 101 are incident on the kaleidoscope 103 through optical fibers 102, 102 ′, 102 ″,... Each incident laser beam is incident on the kaleidoscope. The laser beam 104 is mixed and transmitted through the safety shutter 105, the imaging lens 106, the rectangular slit 107, and the projection lens 108 as the laser light 104, and is reduced and projected onto the substrate 113 placed on the XY stage 112. , A dichroic mirror 115 for performing observation on the substrate 113 or detection of an alignment mark, an imaging lens 116, a CCD camera 117, and an image processing device 118. The control device 114 turns on / off the LD, drives the stage 112, Controls the detection of alignment marks.

First, consider the wavelength of the laser beam to be irradiated. FIG. 2 shows the spectral absorption coefficient (α) of amorphous silicon and crystalline silicon. The horizontal axis represents wavelength (nm), and the vertical axis represents absorption coefficient α (cm ⁻¹ ). In order to microcrystallize the amorphous silicon film, it is necessary to irradiate the amorphous silicon thin film with an absorbing wavelength. However, if the absorption coefficient is too large, the laser beam cannot be transmitted through the amorphous silicon film and only the surface is heated. Of course, it is heated to the side in contact with the substrate by heat conduction, but it is not preferable because the temperature is different from the surface and the crystallization state is also different. That is, it is desirable that the penetration depth of laser light (the reciprocal of the absorption coefficient) be equal to or greater than the film thickness of the amorphous silicon film. For example, if the film thickness of the amorphous silicon film is 40 nm, the penetration depth is preferably about 40 nm or more (= absorption coefficient is 2.5 × 10 ^ 5 (cm ⁻¹ ) or less). Is equivalent to 445 nm or more. The absorption coefficient of silicon varies depending on the impurity concentration or defect density in the silicon, but can be considered to be approximately 440 nm or more. When the film thickness of the amorphous silicon film is large, it shifts to a longer wavelength side. For example, when the film thickness of the amorphous silicon film is 100 nm, it is approximately 520 nm or more.

  On the other hand, it is not desirable that the absorption coefficient increases when the amorphous silicon film is irradiated with laser light to be microcrystallized. That is, the absorption coefficient increases at the moment when the amorphous silicon film is microcrystallized by irradiating a laser under appropriate conditions, and the microcrystal film melts or crystal grains grow greatly, Cannot be formed. On the other hand, if the absorption coefficient decreases at the moment when the amorphous silicon film is microcrystallized by irradiating a laser under appropriate conditions, the microcrystalline film is preserved. From this viewpoint, the absorption coefficient of amorphous silicon with respect to the wavelength of the laser beam to be irradiated needs to be larger than the absorption coefficient of crystalline silicon. The wavelength at which the absorption coefficient is reversed varies depending on the manufacturing process, impurity concentration, and defect density of the silicon film, but is in the range of 650 to 750 nm, and corresponds to 670 nm in the case of FIG. It is necessary to irradiate laser light having a wavelength shorter than this wavelength. This wavelength does not depend on the film thickness of the silicon film.

  From the above, the wavelength of the laser light applied to the present invention needs to be approximately 750 nm or less, and more preferably 445 to 670 nm. In the description of this embodiment, a case where an LD having an oscillation wavelength of 670 nm is used will be described.

  Laser light 104 emitted from a plurality of LDs is transmitted through the fiber 102 and is incident on the kaleidoscope 103. The incident laser light is mixed while being multiple reflected in the kaleidoscope 103, and the energy density at the exit is made uniform. Further, the cross-sectional shape perpendicular to the optical axis of the kaleidoscope 103 changes continuously, and finally becomes the shape of the beam irradiated onto the substrate. The size of the exit depends on the magnification of the projection optical system. The material may be made of a material that is transparent to the laser beam 104, such as quartz, or may be a hollow structure having an inner surface with a high reflectivity with respect to the laser beam 104. When the shape of the exit is a rectangle having a side of 20 mm × 1 mm, the imaging lens 106 projects the same size (1 ×) onto the surface of the slit 107, and the slit image is projected onto the substrate 113 by the projection lens 108. By projecting the image at a reduced size, the irradiation area can be made into a 2 mm × 0.1 mm rectangular shape, and the same microcrystallization as that by the optical system shown in FIG. 1 can be performed.

  Next, the operation and function of each unit will be described in detail. As the LD, a red semiconductor laser having an oscillation wavelength of 670 nm and an oscillation output of 5 W can be used. By inputting the 10 LD outputs into the kaleidoscope 103 through fibers, 50 W is obtained as a total output. If further output is required, an LD may be added. The laser light is turned on / off by directly controlling the LD.

  The laser beam is normally blocked by the shutter 105, and only when the laser beam is irradiated, the laser beam is output by opening (turning on) the shutter 105. In addition, the shutter 105 may be closed when it is urgently desired to stop the laser beam irradiation from the viewpoint of safety.

  The laser light that has passed through the shutter 105 is projected onto the rectangular slit 107 by the imaging lens 106, for example, one to one. Thereby, the power density distribution at the exit of the kaleidoscope 103 is stored on the rectangular slit 107. If necessary, the rectangular slit 107 is adjusted to a desired longitudinal dimension to obtain a beam having a uniform power density distribution and a substantially uniform desired dimension as a transmitted beam. This beam is reduced and projected on the substrate 113 by a projection lens 108 to 1/10. In this example, the imaging lens 106 is 1/1 and the projection lens 108 is 1/10, and the overall reduction projection is 1/10. However, the magnification may be changed as necessary. What is necessary is just to select a magnification according to the dimension required on a board | substrate and the dimension of the kaleidoscope 103 exit.

  Hereinafter, a second embodiment of the method for manufacturing a flat display device using the manufacturing apparatus having the configuration shown in FIG. 10 will be described in detail with reference to the drawings. Here, the case where the bottom gate structure is used will be described. However, the top gate structure can also be basically manufactured by the same process.

As shown in FIG. 5, the substrate is formed of an insulating film made of a SiO ₂ film and / or a SiN film on a transparent substrate 41 such as glass, and after the gate electrode is patterned, the gate insulating film and amorphous A silicon film 42 is formed. The amorphous silicon film is formed by a method such as plasma CVD, but a large amount of hydrogen is typically contained at a concentration of 8 to 15 atomic%, and is also called a hydrogenated amorphous silicon film. The The amorphous silicon film thickness is in the range of 30 to 150 nm and is used for TFT fabrication. Here, the case where the amorphous silicon film thickness is 50 nm will be described. The substrate 41 is preliminarily dehydrogenated by annealing at 450 ° C. for 2 hours by furnace annealing, and is placed and fixed on the stage 112 of the apparatus shown in FIG.

  First, a plurality of alignment marks 43 formed simultaneously with the formation of the gate electrode are picked up by the CCD camera 117 and detected by the image processing device 118, and the substrate 41 is positioned by moving the stage 112 or converting coordinates. In accordance with the design coordinates with the alignment mark position as a reference, a desired region is sequentially microcrystallized. In FIG. 5, the pixel region 44 and the drive circuit region 54 are indicated by broken lines, and a gate electrode is formed in these regions. The laser light is shaped into a top-flat rectangular beam by the kaleidoscope 103. For example, a uniform energy density distribution of 2 mm in the longitudinal direction (perpendicular to the scanning direction), a uniform energy density distribution of 0.1 mm in the lateral direction (scanning direction), or a trapezoidal or Gaussian energy density distribution. Shaped into a beam.

  After the substrate is positioned, the stage 12 starts scanning at a speed of 100 mm / s, and the irradiation of the continuous wave laser beam 3 is started from a position where the beam center is about 1.5 to 2 mm before the pixel region 44. After passing through the pixel regions 45, 46, 47, and 48, the laser irradiation is stopped when the beam center has passed about 1.5 to 2 mm. Thereby, as shown in FIG. 6, the region 50 including each part of the pixel regions 44, 45, 46, 47, 48 is microcrystallized. Next, the stage 12 is moved 2 mm in a direction perpendicular to the scanning direction of the laser beam, and the stage 112 is moved in the opposite direction to the previous direction, whereby the region 50 ′ is microcrystallized. By repeating this, a region including the pixel region and the drive circuit region in the entire surface of the substrate is microcrystallized. Since this microcrystalline silicon film has not undergone a melting process, it has a surface flatness comparable to that of an amorphous silicon film. In the apparatus shown in FIG. 10, the continuous wave laser light is turned on / off by directly driving the LD.

  After the necessary portion is microcrystallized, the substrate is unloaded and proceeds to the next step. If necessary, the apparatus shown in FIG. 10 has a power density sufficient to cause melting and re-solidification of a linear beam of 5 μm in the scanning direction (short axis direction) and 1 mm in the direction orthogonal to the scanning direction (long axis direction). While driving at a scanning speed of 500 mm / s in the minor axis direction, the drive circuit regions 54, 55, 56, 57, and 58 corresponding to each panel are irradiated with continuous oscillation laser light ON / OFF, and the irradiated portions are irradiated. By melting and recrystallization, the crystal is laterally grown in the scanning direction of the laser beam and converted into a band-like polycrystalline film. Similarly, for the microcrystalline region 50 ', the drive circuit region is converted into a band-like polycrystalline film. The surface of the band-like polycrystalline film is also a flat film with irregularities of about 10 nm.

  By the above procedure, the region 60 including the pixel region and the drive circuit region in the amorphous silicon thin film 42 formed on the glass substrate 41 as shown in FIG. 7 is converted into a microcrystalline silicon thin film by laser irradiation. Further, if necessary, scanning is performed while irradiating a laser beam shaped into a linear shape, so that drive circuit regions 54, 54 ′, 55, 55 ′, 56, 56 ′, 57, Only 57 ′, 58 and 58 ′ are converted into a polycrystalline silicon thin film laterally grown in the scanning direction, that is, a band-shaped polycrystalline silicon thin film.

  After the microcrystallization process, an amorphous silicon film is formed on the entire surface of the substrate as necessary. A two-layer structure of a microcrystalline silicon thin film and an amorphous silicon film, and a band-shaped polycrystalline silicon film and an amorphous silicon film The silicon film is patterned into a desired shape, and the source-drain electrodes are formed to form TFTs, respectively, so that the transistors of the pixel circuit and the driving circuit are microcrystalline silicon film and amorphous silicon film, or the driving circuit A liquid crystal display device composed of a band-like polycrystalline silicon film and an amorphous silicon film is formed only with the transistor.

  5 to 8, the inside of the substrate is composed of 10 panels of 2 rows and 5 columns, but several to hundreds of panels can be manufactured depending on the size of the substrate and the size of the panel. 5 to 8, the driving circuit is formed on one side of the panel. However, it can be arranged on two sides as necessary. In that case, if necessary, the substrate is rotated by 90 degrees, the laser is scanned in the direction orthogonal to the above-described scanning, and only a desired region is subjected to band-like polycrystallization.

  In the flat panel display manufacturing apparatus shown in FIG. 10, the laser output can be easily increased by adding LD. For example, by installing 100 LDs with an output of 5 W, the oscillator output becomes 500 W, and the width that can be crystallized in one scan can be increased. Alternatively, the scanning speed can be increased by increasing the width in the scanning direction. Thereby, even when the entire surface of the substrate is microcrystallized, a sufficient throughput can be obtained.

  In addition, as described in the description of the first embodiment, the surface roughness of the already irradiated region is irradiated while the amorphous silicon film is irradiated with the laser beam, and the amorphous silicon film and the crystalline silicon film. The crystal state is monitored by detecting the transmittance of light with a wavelength with a large difference in absorption coefficient, and the laser output irradiated to the amorphous silicon film is adjusted as necessary to achieve fine crystallization. It is clear that can be realized. In addition, since these contents were demonstrated in detail in Example 1, description is abbreviate | omitted here.

  As is apparent from the above description of the embodiments, the gist of the present invention is to provide a method for performing microcrystallization by directly irradiating an amorphous silicon film with continuous wave laser light without adding an extra step. To do. As a result, a transistor formed of a microcrystalline film has a small variation in characteristics, and a transistor having characteristics independent of the source-drain direction in the substrate can be obtained, and a flat display device including these transistors is manufactured. Can do.

  The method for producing a flat display device of the present invention can be applied to the production of a flat display device such as a liquid crystal display device or an organic EL display device.

It is a figure which shows the structure of an apparatus suitable for implementing the manufacturing method of the flat display apparatus which is this invention. It is a figure which shows the spectral absorption coefficient of an amorphous silicon and a crystallized silicon. It is a perspective view which shows a mode that microcrystallization is performed with the manufacturing apparatus of the flat display apparatus which is an Example of this invention. It is explanatory drawing which shows how it changes with the conditions of the laser which an amorphous silicon film irradiates. It is a top view of the board | substrate which enforces the manufacturing method of the flat display apparatus which is this invention. It is a top view of the board | substrate which implemented the manufacturing method of the flat display apparatus which is this invention, and was microcrystallized to the middle. It is a top view of the board | substrate after enforcing the manufacturing method of the flat display apparatus which is this invention, and the pixel part and the drive circuit area | region were microcrystallized. FIG. 6 is a plan view of a substrate in which a driving circuit region is formed into a belt-like polycrystal as necessary after a pixel portion and a driving circuit region are microcrystallized by performing the flat display device manufacturing method according to the present invention. It is a figure which shows the irradiation power density condition range and microcrystallization margin which can obtain a microcrystal when changing irradiation time as laser irradiation conditions. It is a figure which shows the structure of another apparatus suitable for implementing the manufacturing method of the flat display apparatus which is this invention. It is a figure which shows the structure of the optical system which monitors a crystalline state suitable for implementing the manufacturing method of the flat display apparatus which is this invention. It is a figure which shows the example of the signal detected with the optical system shown in FIG. It is a figure which shows the structure of another optical system which monitors a crystal state suitable for implementing the manufacturing method of the flat display apparatus which is this invention. It is a figure which shows the example of the detected light quantity with respect to the laser output detected with the optical system shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Laser diode, 2 ... Optical fiber, 3 ... Laser light, 4 ... Laser oscillator, 6 ... Transmission continuously variable ND filter, 7 ... Modulator, 9 ... Beam diameter regulator, 10 ... Beam shaper, 12 ... Stage , 13 ... substrate, 14 ... projection lens, 17 ... CCD camera, 18 ... image processing device, 19 ... control device, 33 ... amorphous silicon thin film, 34 ... microcrystalline silicon thin film, 43 ... alignment mark, 44 ... pixel region 45, 46, 47, 48, 49 ... drive circuit region, 50, 60 ... microcrystallization region, 73, 81 ... projector, 75 ... linear sensor, 76 ... image processing device, 77 ... display device, 82, 83 ... Photodetector 101 ... Case, 102 ... Optical fiber, 103 ... Calidoscope, 105 ... Shutter, 114 ... Control device, 117 ... CCD camera

Claims (13)

A method of manufacturing a flat panel display device including a step of irradiating an amorphous silicon thin film formed on an insulating substrate with a laser beam to convert it into a microcrystalline silicon thin film,
The above process inputs the laser beam oscillated from the laser source into a linear or rectangular beam having a uniform energy distribution in at least one direction and converts it into a uniform energy distribution. While directly irradiating the surface of the amorphous silicon thin film with the laser beam, the laser beam is scanned relatively in the direction orthogonal to the one direction, so that the amorphous silicon thin film has a crystal grain size of 100 nm or less. A method for manufacturing a flat display device, characterized by converting to a microcrystalline silicon thin film.   2. The method of manufacturing a flat display device according to claim 1, wherein the laser beam is a continuous wave laser beam oscillated from a laser source, and the amorphous laser beam is converted into a uniform energy distribution by the projection optical system. A method of manufacturing a flat display device, characterized by direct irradiation by projecting onto the surface of a silicon thin film.   2. The method for manufacturing a flat display device according to claim 1, wherein the laser beam is a continuous wave laser beam oscillated from a plurality of laser sources and has a linear or rectangular shape and a uniform energy distribution in at least one direction. Is input to a multi-beam combining / homogenizing optical system for conversion into a single beam, and laser light combined into a single beam and converted into a uniform energy distribution is projected onto the surface of the amorphous silicon thin film by a projection optical system. A method of manufacturing a flat display device, wherein direct irradiation is performed by projection.   2. The method of manufacturing a flat display device according to claim 1, wherein the wavelength of the laser beam is in a wavelength region in which an absorption coefficient for amorphous silicon is larger than an absorption coefficient for crystalline silicon. Method.   2. The method for manufacturing a flat display device according to claim 1, wherein the laser beam has a wavelength in a wavelength range shorter than 700 nm.   2. The method for manufacturing a flat display device according to claim 1, wherein the wavelength of the laser beam is a wavelength region in which a penetration depth (reciprocal of an absorption coefficient) into amorphous silicon is larger than a film thickness of the amorphous silicon thin film. A method for manufacturing a flat display device.   2. The method for manufacturing a flat display device according to claim 1, wherein the wavelength of the laser beam is a wavelength region longer than 440 nm.   2. The method of manufacturing a flat display device according to claim 1, wherein the wavelength of the laser light is a wavelength region in which an absorption coefficient for amorphous silicon is larger than an absorption coefficient for crystalline silicon, and the penetration depth with respect to amorphous silicon. A method of manufacturing a flat display device, wherein (the reciprocal of the absorption coefficient) is in a wavelength region larger than the film thickness of the amorphous silicon thin film.   2. The method for manufacturing a flat display device according to claim 1, wherein the wavelength of the laser beam is shorter than 700 nm and longer than 440 nm.   2. The method for manufacturing a flat panel display device according to claim 1, wherein when the laser beam is scanned while directly irradiating the amorphous silicon thin film, the irradiation time of the laser beam (the time during which the width of the laser beam in the scanning direction passes). ) Is scanned under the condition of 0.5 ms or longer.   2. The method for manufacturing a flat display device according to claim 1, wherein when the laser beam is scanned while directly irradiating the amorphous silicon thin film, the state of the already irradiated region is monitored, and the output of the laser beam is within an appropriate range. A method of manufacturing a flat panel display device, characterized by controlling to:   12. The method of manufacturing a flat display device according to claim 11, wherein an image including at least a laser irradiation region is taken under dark field illumination in order to detect surface roughness (unevenness) of the already irradiated region. A method for manufacturing a flat panel display device, comprising: determining whether the already irradiated region is a microcrystal based on whether the brightness of the laser irradiation region is smaller than a threshold value, and controlling the output of the laser beam.   12. The method of manufacturing a flat display device according to claim 11, wherein the amorphous silicon and the crystalline silicon are detected in order to detect the transmittance for light having different absorption coefficients of the amorphous silicon and the crystalline silicon in the irradiated region. The amount of light having a different absorption coefficient is detected by detecting the amount of light that passes through the irradiated region once or twice, and whether the irradiated region is amorphous depending on whether the amount of light is greater than a specified amount of light. A method for manufacturing a flat panel display device, comprising: determining whether the material is crystalline and controlling the output of the laser beam.

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