JP2009218524A - Manufacturing method of flat display device, and flat display device - Google Patents

Abstract

By subjecting only a desired region of a hydrogenated amorphous silicon film to microcrystallization by laser irradiation without causing damage without passing through an annealing (dehydrogenation) step using a furnace or the like, the same substrate is formed. Hydrogenated amorphous silicon TFTs and polycrystalline (microcrystalline) silicon TFTs are formed.
Irradiation of continuous wave laser light by shaping a continuous wave laser beam into a rectangular beam having a uniform power density distribution only in a desired region (drive circuit formation region) of a hydrogenated amorphous silicon film. Irradiation is performed while scanning at a constant speed under the condition that the time is 5 milliseconds or more. As a result, the non-laser irradiated region remains as a hydrogenated amorphous silicon film, and the laser irradiated portion is converted into a polycrystalline silicon film without causing damage due to dehydrogenation. In the flat display device manufactured from this substrate, the channel portion of the pixel portion transistor is constituted by a hydrogenated amorphous silicon film, and the channel portion of the drive circuit portion transistor is constituted by a dehydrogenated polycrystalline (microcrystalline) silicon film.
[Selection] Figure 3

Description

  The present invention relates to a method for manufacturing a flat display device, and more particularly, to a manufacturing method for forming a drive circuit having a semiconductor element outside a display region composed of a set of pixels having TFT elements, and a technique effective when applied to a flat display device. It is about.

  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 area of the TFT substrate is amorphous silicon (a-Si), which is sufficient in terms of performance, but is insufficient in terms of dynamic characteristics to form a drive circuit. For this reason, it is necessary to locally crystallize the amorphous silicon in the region where the drive circuit is formed.

  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, when dehydrogenation is performed by heat treatment in an electric furnace or the like, amorphous silicon on the entire surface of the substrate is dehydrogenated, which is inconvenient for forming a TFT element in the pixel region. (If amorphous silicon does not contain a large amount of hydrogen, it is difficult to contact the electrode.)
On the other hand, if polycrystallization is performed by laser irradiation without performing heat treatment (dehydrogenation) in an electric furnace or the like, hydrogen is suddenly released from the amorphous silicon film during laser light irradiation, and the silicon film is damaged due to hydrogen release. Specifically, there has been a problem that peeling or scattering of the silicon film occurs.

  For this reason, when the TFT elements in the pixel region are made of amorphous silicon and the TFTs in the drive circuit region are made of crystallized silicon, it is necessary to create them in different processes, which requires many processes and causes an increase in price. It was.

  As a method of dealing with this problem, a method of dehydrogenating amorphous silicon using a laser beam instead of heat treatment using an electric furnace or the like is disclosed in, for example, Patent Document 1, Patent Document 2, Patent Document 3, and Patent Document 4. Has been.

  Patent Document 1 discloses a method in which dehydrogenation is performed with a first excimer laser and polycrystallization is performed with a second excimer laser.

  Patent Document 2 discloses a method in which a pulsed laser beam is divided into two, dehydrogenation is performed with the preceding beam, and polycrystallization is performed with the subsequent beam.

  Patent Document 3 discloses a method for polycrystallizing only the drive circuit portion, not polycrystallizing the entire surface of the amorphous silicon film, that is, for forming a pixel with hydrogenated amorphous silicon and a drive circuit with polycrystalline silicon. Irradiate only the drive circuit with a pulse laser, gradually increase the energy of the pulse of the laser beam to dehydrogenate the hydrogenated amorphous semiconductor, and finally irradiate with an energy larger than the crystallization energy. A method of performing crystallization is disclosed.

  Patent Document 4 discloses a method for removing hydrogen gas in a semiconductor film without expanding it by continuously irradiating a laser beam focused to about 10 μm while moving it.

JP 2002-158173 A JP 2002-64060 A JP-A-8-129189 JP 2006-1000066 A

  The present invention improves the above-described prior art. In other words, the methods described in Patent Documents 1, 2, and 3 all perform dehydrogenation by irradiating a pulse laser typified by an excimer laser. Become very large. In addition, the excimer laser has a problem that the energy variation for each pulse is large and the process window is small. Further, when crystallization is performed with a pulse laser, the surface of the obtained polycrystalline film has large irregularities, and when a gate insulating film is formed on the polycrystalline film (in the case of a top gate), the breakdown voltage is lowered. There was a problem.

  In addition, the method described in Patent Document 4 discloses a method of performing dehydrogenation and crystallization by scanning a laser spot focused to 10 μm or less. Since the process window is narrow and the transistor regions are annealed sequentially, the throughput is low.

  An object of the present invention is to provide stable and stable dehydrogenation and conversion into a polycrystalline silicon film only for the amorphous silicon film outside the pixel region (display region) of the substrate and in the region where the drive circuit is formed. The object is to provide a technique that can be performed at low cost and with high throughput.

  Another object of the present invention is to use amorphous silicon for the semiconductor layer of the TFT element in the display area, and polycrystalline (microcrystalline) silicon for the semiconductor layer of the semiconductor element of the driving circuit outside the display area. It is another object of the present invention to provide a technique capable of manufacturing a TFT substrate using strip-shaped polycrystalline silicon.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  In order to achieve the above object, the flat display device manufacturing method of the present invention irradiates both dehydrogenation and polycrystallization while scanning a desired region in a lump with a CW laser. At that time, in order to achieve the heating time necessary for dehydrogenation by laser irradiation, irradiation is performed while scanning the CW laser while adjusting the width of the laser beam in the scanning direction and the scanning speed. Furthermore, when it is necessary to enlarge the crystal grains in the dehydrogenated and polycrystallized region, the CW laser beam shaped and condensed into a linear shape can be scanned without causing damage to the silicon film. It is converted into a band-like polycrystalline film. Both the dehydrogenated / polycrystalline silicon film and the band-shaped polycrystalline silicon film obtained by the present invention have a flat surface.

  According to the present invention, the pixel portion is made of amorphous silicon, the drive circuit portion is made of polycrystalline silicon having a flat surface, and if necessary, a TFT made of a band-like polycrystalline silicon film at a lower cost than when an excimer laser is used. A flat display device can be manufactured stably. Further, according to the present invention, a flat display device in which an amorphous silicon TFT and a polycrystalline silicon TFT are mixed in the same substrate is obtained.

  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 dehydrogenation / polycrystallization (microcrystallization) apparatus suitable for carrying out the method of manufacturing a flat display device 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 amplitude-modulating laser light 3 to realize pulsing and temporal modulation of energy, beam expander for adjusting the beam diameter of laser light 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. An imaging lens 14 for projecting a laser beam shaped into a rectangular shape on the 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 transmission 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. The continuous wave laser beam 3 preferably has a wavelength that is absorbed by the hydrogenated amorphous silicon thin film to be dehydrogenated, that is, an ultraviolet wavelength and a visible wavelength, and more specifically, an LD (laser diode) that oscillates the visible wavelength. ), Ar laser or Kr laser and its second harmonic, Nd: YAG laser, Nd: YVO4 laser, Nd: YLF laser, second harmonic and third harmonic, etc. are applicable. Among these, considering the output size and stability, the second harmonic (wavelength 532 nm) of the LD (laser diode) pumped Nd: YAG laser or the second harmonic (wavelength 532 nm) of the Nd: YVO4 laser or An LD (laser diode) that oscillates a visible wavelength is most desirable. In the following description, 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 top-flat rectangular beam. Normally, a gas laser or a solid-state laser has a Gaussian energy distribution and cannot be used as it is for the laser dehydrogenation of the present invention. 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 desired energy distribution 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 portion is shielded from light by the rectangular opening slit 11 so that a rectangular beam with an arbitrary rise and a sudden rise can be obtained.

The state of the amorphous silicon thin film when it is irradiated while scanning with continuous wave laser light that has been amplitude-modulated and shaped into a rectangular beam shape of a desired size will be described with reference to FIG. In the target substrate here, an amorphous silicon 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 substrate is scanned in the direction of the arrow shown in the figure while being irradiated with the laser beam. By irradiating with the laser beam 3, the amorphous silicon thin film 33 is heated to near the melting point, and hydrogen in the amorphous silicon thin film 33 is desorbed at the same time to be polycrystallized to become a dehydrogenated polycrystalline silicon thin film 34. . This dehydrogenated polycrystalline silicon thin film 34 has small crystal grains, and a so-called microcrystal whose surface is as flat as that of an amorphous silicon thin film can be obtained. It is about 100 times the quality of 0.1 cm ² / Vs, and the TFT may be formed as it is. When a silicon film having a higher mobility (100 cm ² / Vs or more, typically 300 cm ² / Vs) is required, the amorphous silicon thin film 33 is dehydrogenated polycrystalline silicon thin film 34 as shown in FIG. The linear laser beam 38 having a beam width in the scanning direction that is focused to 10 μm or less (typically about 5 μm) is irradiated to the portion that has changed. As a result, the film is converted into a band-like polycrystalline silicon film 35 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. In other words, dehydrogenation / polycrystallization (microcrystallization) and band-like polycrystallization may be performed while switching the beam shaper with a single device, or a dehydrogenation / polycrystallization (microcrystallization) device. A band-like polycrystallization apparatus may be separately prepared, and dehydrogenation / polycrystallization and band-like crystallization may be sequentially performed.

  In the dehydrogenation / polycrystallization (microcrystallization) by laser irradiation, if the power density of the laser light 36 is too small, the silicon thin film in the irradiation region 41 of the laser light 36 is incompletely dehydrogenated / multiple as shown in FIG. A crystalline silicon film 42 is formed. When the power density is increased or the scanning speed is decreased, the entire irradiation region 41 is satisfactorily dehydrogenated and polycrystallized (microcrystallized) under a certain condition range, and the dehydrogenated polycrystalline silicon film 34 is shown in FIG. It becomes.

  When the power density is further increased, as shown in FIG. 6, most of the film remains as the dehydrogenated / polycrystalline silicon thin film 34, but the silicon film is partially peeled off in a region close to the irradiation start portion. Circular peeling 44 occurs. The peeled silicon film (not shown) scatters and adheres to the periphery. When the power density of the laser beam 36 is further increased, the silicon film in the entire irradiation region 41 of the laser beam 36 is peeled and scattered as shown in FIG. The film 47 is exposed. The state shown in FIGS. 6 and 7 is defective.

  After dehydrogenation / polycrystallization (microcrystallization), laser light 38 for zonal polycrystallization is irradiated as necessary. The irradiation region 50 of the laser beam 38 is set to be narrower than the dehydrogenation region 41, and the well-dehydrogenated silicon film shown in FIG. 5 is subjected to melting and re-solidification as shown in FIG. The film 51 is converted. If the laser power density at the time of dehydrogenation / polycrystallization (microcrystallization) is too low or the scanning speed is too high and the laser beam 38 is irradiated in an incomplete dehydrogenation state, the remaining hydrogen will be rapidly increased. As a result, the silicon film is peeled off and scattered. For this reason, the base insulating film 46 or the gate insulating film 47 is exposed in the irradiation region of the laser light 38 and becomes defective.

  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. 10, the substrate is formed of an insulating film made of SiO2 film and / or SiN film on a transparent substrate 61 such as glass, and after the gate electrode is patterned, the gate insulating film and amorphous silicon are formed. A film 62 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 61 is placed and fixed on the stage 12 of the apparatus shown in FIG.

  First, a plurality of alignment marks 63 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 61 is positioned by moving the stage 12 or converting coordinates. Dehydrogenation of a desired region (forming a drive circuit) is sequentially performed according to design coordinates with the alignment mark position as a reference. In FIG. 10, the pixel region 64 and the drive circuit region 65 are indicated by broken lines. The laser beam is shaped into a top-flat rectangular beam by the beam shaper 10. Normally, the drive circuit region 65 is designed to have a width of 0.5 to 1 mm and a length similar to that of the pixel region 64. Here, as an example, the width of the drive circuit region is set to 0.8 mm, a rectangular shape (square) of 1 mm in the laser beam scanning direction and 1 mm in the direction orthogonal to the scanning direction, and a uniform power density distribution of ± 5% or less. Shape into a distributed beam shape.

  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 drive circuit area. After passing through the drive circuit regions 65, 66, 67, 68 and 69, the laser irradiation is stopped when the beam center has passed about 1.5 to 2 mm. Thereby, as shown in FIG. 11, the region 70 including the drive circuit regions 65, 66, 67, 68, and 69 is dehydrogenated and polycrystallized (microcrystallized). Next, the stage 12 is moved in a direction orthogonal to the scanning direction of the laser beam, and the region 70 ′ is dehydrogenated. When the width of the drive circuit region 65 is larger than the dimension in the direction orthogonal to the laser beam scanning direction, dehydrogenation and polycrystallization (microcrystallization) may be performed by a plurality of scans.

  By this dehydrogenation and polycrystallization (microcrystallization), most of the hydrogen in the amorphous silicon film is desorbed. When the hydrogen concentration of the silicon film before and after laser irradiation was measured by SIM analysis, it was confirmed that the hydrogen concentration was reduced to 1/10 or less by irradiating laser light under appropriate conditions. With this process, the silicon thin film in the substrate remains as an amorphous silicon film containing 8 to 15 atomic% of hydrogen in the pixel portion, and the portion irradiated with the laser has a polycrystalline (microscopic) concentration of hydrogen of 1.5% or less. Crystalline) is converted into a silicon film. This polycrystalline (microcrystalline) silicon film has a surface flatness comparable to that of an amorphous silicon film.

  After dehydrogenation and microcrystallization of necessary parts, the beam shaper 10 is switched to the beam shaper 20 as necessary, the scanning direction (short axis direction) is 5 μm, and the direction perpendicular to the scanning direction (long axis direction) A drive circuit region 65, 66, 67 corresponding to each panel while scanning at a scanning speed of 500 mm / s in the minor axis direction with a power density sufficient to cause re-solidification at 0.9 mm. 68, 69 are irradiated with continuous wave laser light 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 light and converted into a band-like polycrystalline film. Similarly, for the dehydrogenation region 70 ', the drive circuit region is converted into a strip-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, as shown in FIG. 11, among the amorphous silicon thin film 62 formed on the glass substrate 61, only the region where the drive circuit is formed is dehydrogenated by laser irradiation and is a polycrystalline (or microcrystalline) silicon thin film. 70 and 70 ′. Further, if necessary, scanning is performed while irradiating a laser beam shaped into a linear shape, and as shown in FIG. 12, a polycrystalline silicon thin film laterally grown in the scanning direction, that is, strip-shaped polycrystalline silicon thin films 65, 65 Converted to '.

  On the other hand, the pixel region 64 is left as an amorphous silicon thin film without being irradiated with the laser. After this step, the amorphous silicon thin film and the strip-like polycrystalline silicon film are patterned into a desired shape, and the source / drain electrodes are formed to form the TFTs, so that the switching transistor of the pixel is an amorphous silicon film. The drive circuit transistor is a liquid crystal display device composed of a strip-like polycrystalline silicon film. Here, it goes without saying that the channel portion of the pixel switching transistor is amorphous silicon having a hydrogen concentration of 8 to 15 atomic%, and the channel portion of the drive circuit transistor is polycrystalline silicon having a hydrogen concentration of 1.5% or less. Yes.

  10 to 12, 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. 10 to 12, the driving circuit is formed on one side of the panel, but may be arranged on two sides as necessary. In that case, the substrate may be rotated 90 degrees, the laser may be scanned in a direction orthogonal to the above-described scanning, and dehydrogenation / polycrystallization (microcrystallization) and strip-shaped polycrystallization may be performed as necessary.

  Conditions under which laser can be satisfactorily dehydrogenated and polycrystallized (microcrystallized) can be defined by the power density of the irradiated laser light and the irradiation time. As a result of experiments on an amorphous silicon thin film having a thickness of 50 nm, dehydrogenation and polycrystallization (microcrystallization) were possible within the range shown by hatching in FIG. In FIG. 13, the thick solid line indicates the upper limit of dehydrogenation / polycrystallization (microcrystallization), and damage occurs in the silicon film under the condition above the thick solid line. A thick broken line indicates a lower limit of dehydrogenation / polycrystallization (microcrystallization), and proper dehydrogenation can be realized under conditions above the broken line, and dehydrogenation is insufficient under conditions below the broken line. That is, proper dehydrogenation and polycrystallization (microcrystallization) could be realized within the range of conditions surrounded by a thick solid line and a broken line. A thick one-dot chain line indicates a threshold for polycrystallization, and an amorphous silicon thin film is converted into polycrystal (microcrystal) under conditions above the one-dot chain line. In other words, it is presumed that under conditions where dehydrogenation can be realized, the silicon film melts or rises to a temperature close to the melting point. However, the polycrystal obtained here has an extremely small crystal grain size of 10 to 100 nm, and the surface is kept flat enough to show no change before laser irradiation.

  As is apparent from FIG. 13, the irradiation power density when the irradiation time of the continuous wave laser beam (the time from when the rectangular beam reaches an arbitrary point until it finishes passing) is 5 ms or more, preferably 10 ms or more. Therefore, a sufficiently practical process window can be secured. The laser irradiation time of 10 ms here corresponds to, for example, scanning a beam shaped to a width of 1 mm in the scanning direction at 100 mm / s by adjusting the laser output so that the relative power density is 1.2. When a beam shaped to 0.5 mm was irradiated in the scanning direction, the same result was obtained even when scanning at 50 mm / s. In addition, when a beam shaped to 0.5 mm was irradiated in the scanning direction, almost the same result was obtained even if it was scanned twice at 100 mm / s.

  Under the condition immediately above the upper limit of dehydrogenation / polycrystallization (microcrystallization) indicated by the thick solid line in FIG. 13, the circular silicon film peeling occurs at the irradiation start portion as shown in FIG. This is because the rise of the laser beam ON by the EO modulator is 100 ns or less, so that the laser beam is rapidly heated at the irradiation start portion (the laser power increases rapidly from 0 to a set value). Subsequent parts are preheated by heat conduction from the laser-heated part and then irradiated with the laser, so the temperature rises more slowly than the irradiation start part, and hydrogen desorption also occurs accordingly. To do. For this reason, the silicon film does not peel in a circle except at the irradiation start portion, and the upper limit of dehydrogenation shown in FIG. 13 is shifted to the condition indicated by a thin solid line in FIG. That is, the conditions for properly dehydrogenating are expanded. Naturally, when the laser power density is further increased (or the scanning speed is made lower), the silicon film is damaged and peels off even if preheating is caused by heat conduction.

  As described above, in order to prevent circular peeling and to expand the range of appropriate dehydrogenation / polycrystallization (microcrystallization) conditions, a laser is used in an area that requires dehydrogenation / polycrystallization (microcrystallization). Irradiation starts at a low power density before the light arrives, and the power density is gradually increased so that a predetermined power density is obtained in areas where dehydrogenation and polycrystallization (microcrystallization) are required. The power density of the laser beam to be adjusted may be adjusted. That is, as shown in FIG. 14 which shows the relationship between the position of the laser beam in the scanning direction and the power density at the beam center, the power density is gradually increased from before the region where dehydrogenation / polycrystallization (microcrystallization) is required. Then, when a region requiring dehydrogenation / polycrystallization (microcrystallization) is reached, more precisely, when the center of the beam reaches 1/2 or more of the beam width, it is fixed at a desired power density. The region requiring dehydrogenation and polycrystallization (microcrystallization) is maintained at a constant power density, and when passing through the laser irradiation region, more precisely from when the beam center passes through half the beam width. The power density is gradually reduced, and finally the irradiation is stopped. During this time, the scanning speed is kept constant. The size of the power density increasing region and decreasing region can be set as appropriate, but a sufficient effect can be obtained with a beam width in the scanning direction. Note that a procedure for gradually decreasing the power density after the laser light passes through the laser irradiation region is not necessarily required.

  The increase / decrease in power density can be realized by continuously adjusting the transmittance of the transmittance variable filter 6 or by continuously changing the voltage applied to the modulator 7. Of course, it is also possible to continuously change the output of the excitation LD, but this is not desirable from the viewpoint of stabilizing the laser output.

  By the above-described method, stable and inexpensive dehydrogenation / polycrystallization (microcrystallization) was performed only in a desired region, and high-quality band-like polycrystalline silicon was obtained as needed. In addition, high hydrogen concentration amorphous silicon is used for the semiconductor layer of the TFT element in the display region, and the pixel region and the drive circuit region are outside the display region without passing through extra steps such as making the pixel region and the drive circuit region in separate steps. A TFT substrate using low hydrogen concentration polycrystalline silicon for the semiconductor layer of the semiconductor element of the driving circuit or, if necessary, band-like crystalline silicon can be manufactured.

  Next, FIG. 15 shows an optical system configuration of another laser dehydrogenation apparatus 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.

  Here, as the oscillation wavelength of the LD, UV to visible wavelength absorbed by the amorphous silicon film is desirable. The cross-sectional shape perpendicular to the optical axis of the kaleidoscope 103 continuously changes so that the laser beams from the plurality of LDs incident on the kaleidoscope 103 are mixed and the energy density at the exit becomes uniform. Finally, the shape is irradiated onto the substrate. 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 square with a side of 10 mm, the imaging lens 106 projects the same size (1 ×) onto the surface of the slit 107, and the slit image is further reduced to 1/10 on the substrate 113 by the projection lens 108. By projecting, the irradiation area can be made into a square having a side of 1 mm, and the same dehydrogenation and polycrystallization (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 blue semiconductor laser having an oscillation wavelength of 445 nm and an oscillation output of 1 W can be used. By inputting the 50 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. Since the power density is reduced in the peripheral part of the beam, a beam having a substantially uniform power density distribution is obtained as a transmitted beam by cutting out with the rectangular slit 107. 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 the flat display device using the manufacturing apparatus having the configuration shown in FIG. 15 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. 10, the substrate is formed of an insulating film made of SiO ₂ film and / or SiN film on a transparent substrate 61 such as glass, and the gate electrode is patterned. A silicon film 62 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 61 is placed and fixed on the stage 112 of the apparatus shown in FIG.

  First, a plurality of alignment marks 63 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 61 is positioned by moving the stage 112 or converting coordinates. Dehydrogenation of a desired region (forming a drive circuit) is sequentially performed according to design coordinates with the alignment mark position as a reference. In FIG. 10, the pixel region 64 and the drive circuit region 65 are indicated by broken lines. The laser light is shaped into a top-flat rectangular beam by the kaleidoscope 103. Normally, the drive circuit region 65 is designed to have a width of 0.5 to 1 mm and a length similar to that of the pixel region 64. Here, as an example, the width of the drive circuit region is 0.8 mm, a rectangular shape (square) of 1 mm in the laser beam scanning direction and 1 mm in the direction orthogonal to the scanning direction, and a uniform power density distribution of ± 5% or less. Shape into a distributed beam shape.

  After the substrate is positioned, the stage 112 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 drive circuit area. After passing through the drive circuit regions 65, 66, 67, 68 and 69, the laser irradiation is stopped when the beam center has passed about 1.5 to 2 mm. Thereby, as shown in FIG. 11, the region 70 including the drive circuit regions 65, 66, 67, 68, and 69 is dehydrogenated and polycrystallized (microcrystallized). Next, the stage 112 is moved in a direction perpendicular to the scanning direction of the laser light, and the region 70 ′ is dehydrogenated. When the width of the drive circuit region 65 is larger than the dimension in the direction orthogonal to the laser beam scanning direction, dehydrogenation and polycrystallization (microcrystallization) may be performed by a plurality of scans.

  By this dehydrogenation and polycrystallization (microcrystallization), most of the hydrogen in the amorphous silicon film is desorbed. When the hydrogen concentration of the silicon film before and after the laser irradiation is measured by SIM analysis, it can be confirmed that the hydrogen concentration is reduced to 1/10 or less by irradiating the laser beam under appropriate conditions. By this treatment, the pixel portion of the silicon thin film in the substrate remains as an amorphous silicon film containing 8 to 15 atomic% of hydrogen, and the portion irradiated with the laser has a polycrystalline ( Microcrystalline) converted into a silicon film. This polycrystalline (microcrystalline) silicon film has a surface flatness comparable to that of an amorphous silicon film.

  After dehydrogenation and microcrystallization of necessary parts, the apparatus shown in FIG. 1 is switched to the beam shaper 20 as necessary, and the scanning direction (short axis direction) is 5 μm, and the direction orthogonal to the scanning direction ( A drive circuit region 65 corresponding to each panel is shaped into a linear beam of 0.9 mm in the major axis direction and scanned at a scanning speed of 500 mm / s in the minor axis direction with a power density sufficient to cause melting and re-solidification. , 66, 67, 68, and 69 are irradiated with continuous-wave laser light 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 light to form a band-shaped polycrystalline film Convert. Similarly, for the dehydrogenation region 70 ', the drive circuit region is converted into a strip-like polycrystalline film. In the apparatus shown in FIG. 15, ON / OFF of the continuous wave laser beam is performed by directly driving the LD.

  As a result of the above procedure, only the region where the drive circuit is formed in the amorphous silicon thin film 62 formed on the glass substrate 61 as shown in FIG. 11 is dehydrogenated and polycrystalline (microcrystalline) silicon thin film 70 by laser irradiation. , 70 ′. Further, if necessary, scanning is performed while irradiating a laser beam shaped into a linear shape, and as shown in FIG. 12, a polycrystalline silicon thin film laterally grown in the scanning direction, that is, strip-shaped polycrystalline silicon thin films 65, 65 Converted to '.

  On the other hand, the pixel region 64 is left as an amorphous silicon thin film without being irradiated with the laser. After this step, the amorphous silicon thin film and the belt-like polycrystalline silicon film are patterned into a desired shape, and a source / drain electrode is formed to form a TFT. Thus, a liquid crystal display device is formed in which the switching transistor of the pixel is an amorphous silicon film, and the drive circuit transistor is a polycrystalline (microcrystalline) silicon film or a band-shaped polycrystalline silicon film. Here, it goes without saying that the channel portion of the pixel switching transistor is amorphous silicon having a hydrogen concentration of 8 to 15 atomic%, and the channel portion of the drive circuit transistor is polycrystalline silicon having a hydrogen concentration of 1.5% or less. Yes.

  10 to 12, 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. 10 to 12, the driving circuit is formed on one side of the panel, but may be arranged on two sides as necessary. In that case, the substrate may be rotated 90 degrees, the laser may be scanned in a direction orthogonal to the above-described scanning, and dehydrogenation / polycrystallization (microcrystallization) and strip-shaped polycrystallization may be performed as necessary.

  As is clear from the description of the above-described embodiments, the gist of the present invention is to provide a method capable of realizing a high yield with a stable process when simultaneously performing dehydrogenation and microcrystallization in only a desired region by laser irradiation. It is. If necessary, the dehydrogenated and microcrystallized region is formed into a band-like polycrystal so that the pixel portion is made of an amorphous silicon film and the drive circuit portion is made of a microcrystal or a band-like polycrystalline silicon film. The flat display apparatus comprised by these and its manufacturing method are provided. It is obvious that the process order can be changed without departing from the spirit of the present invention.

  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 perspective view which shows a mode that dehydrogenation and polycrystallization are performed with the manufacturing apparatus of the flat display apparatus which is an Example of this invention. It is a perspective view which shows a mode that it converts into strip | belt polycrystal after performing dehydrogenation and polycrystallization with the manufacturing apparatus of the flat display apparatus which is an Example of this invention. It is a figure which shows the board | substrate surface which performed incomplete dehydrogenation and polycrystallization with the manufacturing apparatus of the flat display apparatus shown in FIG. It is a figure which shows the board | substrate surface which performed favorable dehydrogenation and polycrystallization with the manufacturing apparatus of the flat display apparatus shown in FIG. It is a figure which shows the substrate surface which dehydrogenated and polycrystallized on the manufacturing apparatus of the flat display apparatus shown in FIG. It is a figure which shows the substrate surface which dehydrogenated and polycrystallized on the conditions with excess laser power density with the manufacturing apparatus of the flat display apparatus shown in FIG. It is a figure which shows the board | substrate surface after irradiating the laser for converting into strip | belt polycrystal after performing favorable dehydrogenation and polycrystallization with the manufacturing apparatus of the flat display apparatus shown in FIG. It is a figure which shows the board | substrate surface after irradiating the laser for converting into strip | belt polycrystal after performing incomplete dehydrogenation and polycrystallization with the manufacturing apparatus of the flat display apparatus shown in FIG. 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 dehydrogenated and polycrystallized only the drive circuit area | region. It is a top view of the board | substrate irradiated with the laser for implementing the manufacturing method of the flat display apparatus which is this invention, dehydrogenating and polycrystallizing only a drive circuit area | region, and converting into a strip | belt-shaped polycrystal. It is a figure which shows the state of dehydrogenation and polycrystallization obtained with respect to irradiation time and irradiation power density as laser irradiation conditions. It is a figure which shows the relationship between the scanning direction position of a laser beam and relative power density in another Example of the manufacturing method of the flat display apparatus of this invention. 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.

  DESCRIPTION OF SYMBOLS 1 ... Laser diode, 2 ... Optical fiber, 3 ... Laser beam, 4 ... Laser oscillator, 6 ... Transmission continuously variable filter, 7 ... Modulator, 9 ... Beam Diameter adjuster, 10 ... Beam shaper, 14 ... Objective lens, 13 ... Substrate, 12 ... Stage, 17 ... CCD camera, 18 ... Image processing device, 19 ... Control device 33... Amorphous silicon film 34... Dehydrogenated / polycrystalline (microcrystalline) silicon film 35... Strip-shaped polycrystalline silicon film 42. Membrane, 44... Circular peeling portion, 47... Ablation peeling portion, 51... Strip-like polycrystalline silicon film, 63... Alignment mark, 64... Pixel region, 65, 66, 67, 68 69 ... Drive circuit region, 70 ... Dehydrogenation / polycrystallization region, 1 1 ... LD, 102 ... optical fiber, 103 ... kaleidoscopes, 105 ... shutter, 117 ... CCD camera, 114 ... control device

Claims (7)

In a method of manufacturing a flat display device comprising an annealing step of crystallizing a desired region of the semiconductor thin film by irradiating the hydrogenated amorphous semiconductor thin film with laser light,
Using a continuous wave laser as a laser source, shaping the laser beam into a rectangular shape with a uniform power density, and irradiating the hydrogenated amorphous semiconductor thin film while moving the irradiation position at a constant speed, A method for manufacturing a flat display device, wherein the hydrogenated amorphous semiconductor thin film is simultaneously dehydrogenated and polycrystallized (microcrystallized). In the manufacturing method of the flat display device according to claim 1,
When irradiating the rectangular laser beam with a uniform power density to the hydrogenated amorphous semiconductor thin film while moving the irradiation position at a constant speed, the irradiation time (passing time) of the laser beam The method of manufacturing a flat display device, wherein the hydrogenated amorphous semiconductor thin film is dehydrogenated and polycrystallized (microcrystallized) simultaneously by irradiating under a condition that is 5 milliseconds or longer. In the manufacturing method of the flat display device according to claim 1 or 2,
The laser beam shaped into a rectangular shape with a uniform power density is gradually increased before reaching the desired laser irradiation region, and is irradiated at a constant power density in the desired laser region, thereby the hydrogen A method for producing a flat display device, characterized in that dehydrogenation and polycrystallization (microcrystallization) of the amorphous semiconductor thin film are simultaneously performed. In the manufacturing method of the flat display device according to claim 1 to claim 3,
A method for manufacturing a flat panel display device, comprising: forming a band-shaped polycrystalline film by scanning linearly shaped continuous wave laser light in a region where dehydrogenation and polycrystallization (microcrystallization) are performed simultaneously. A flat display device having a transistor composed of a silicon thin film,
The channel part of the pixel part transistor is composed of a hydrogenated amorphous silicon film, and the channel part of the drive circuit part transistor is a continuous power laser beam of uniform power density shaped into a rectangle on the hydrogenated amorphous silicon film, A flat display device comprising a microcrystalline silicon film crystallized simultaneously with dehydrogenation by irradiating while moving an irradiation position at a constant speed. A flat display device having a transistor composed of a silicon thin film,
The channel portion of the transistor of the pixel portion and the driver circuit portion is a silicon thin film formed in the same process, and the channel portion of the pixel portion transistor is composed of a hydrogenated amorphous silicon film having a hydrogen concentration of 8 to 15 atomic%. A flat display device comprising a polycrystalline silicon film having a hydrogen concentration of 1.5 atomic% or less in a channel portion of a driver circuit portion transistor. A flat display device having a transistor composed of a silicon thin film,
The channel portion of the transistor of the pixel portion and the driver circuit portion is a silicon thin film formed in the same process, and the channel portion of the pixel portion transistor is composed of a hydrogenated amorphous silicon film having a hydrogen concentration of 8 to 15 atomic%. A flat display device comprising a band-like polycrystalline silicon film having a hydrogen concentration in a channel portion of a drive circuit portion transistor of 1.5 atomic% or less.

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