JP2006344844A - Laser processing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laser processing device which is capable of reducing its thermal load imposed on a substrate to a small extent and suitably applied to an annealing process carried out for a semiconductor thin film. <P>SOLUTION: The laser processing device is equipped with a stage 1 where a substrate W as an object of processing is placed, a light source 2 which is equipped with a semiconductor laser oscillator 2a and irradiates the surface of the substrate W placed on the stage 1 with a laser beam Lh from a normal direction, an object lens 3 which is arranged on the optical path of the laser beam Lh that radiates from the light source 2 making the normal direction of the surface of the substrate W placed on the stage 1 serve as an axial direction, and a biaxial device driver (scanning control unit) 4 which enables the laser beam Lh to scan the substrate W placed on the stage 1 by moving the object lens 3 in a direction vertical to the axis. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a laser processing apparatus, and more particularly to a laser processing apparatus suitably used for annealing a semiconductor thin film in the manufacture of a thin film semiconductor device.

  In a flat display device such as a liquid crystal display device or an organic EL display device, a thin film transistor (TFT) is used as a switching element for performing an active matrix display of a plurality of pixels. For thin film transistors, TFTs using polycrystalline silicon (poly-Si) or microcrystalline silicon (μc-Si) in the active region (polycrystalline silicon TFTs) and amorphous silicon (amorphous Si) are used in the active region. TFT (amorphous silicon TFT). Among these, the polycrystalline silicon TFT has a feature that the carrier mobility is about 10 to 100 times larger than that of the amorphous silicon TFT, and has a very excellent characteristic as a constituent material of the switching element. Yes. Therefore, in the flat type display device described above, in order to achieve high functionality by providing various functions and circuits on a display substrate called a system-on-panel as well as high-definition of a display image, as a switching element The use of polycrystalline silicon TFTs has become an essential technology.

  As a manufacturing technique of the polycrystalline silicon TFT as described above, a so-called low temperature polysilicon process using only a low temperature process of approximately 600 ° C. or less has been developed and put into practical use. By using a low-temperature polysilicon process, it is not necessary to use a high heat-resistant but expensive substrate such as quartz or single crystal silicon, and a flat display device with high definition can be realized at low cost.

  Here, in the low-temperature polysilicon process, first, a semiconductor thin film is formed by a plasma decomposition CVD method. Since the semiconductor thin film thus formed contains hydrogen, in the next step, dehydrogenation annealing is performed in which hydrogen contained in the semiconductor thin film is released by heating at a temperature of 450 ° C. or higher for several hours. I do. Thereafter, laser annealing by excimer laser light irradiation is performed for crystallization of the semiconductor thin film. At this time, for a large substrate, the irradiation area of the laser beam formed into a long linear shape is shifted, and a plurality of pulse irradiations are performed on each irradiation position, so that the entire surface of the substrate is uniform. A laser beam is irradiated with energy to make the crystal grain size uniform (see Patent Document 1 below).

  By the way, the excimer laser light source conventionally used as the laser light source of the laser processing apparatus used for the laser annealing described above is a device that lacks output stability and is very difficult to handle. Therefore, from the viewpoint of output stability, it is desirable to use a solid-state laser light source or a semiconductor laser light source in the ultraviolet region, in which the energy of the laser light is stable and has a long lifetime.

  However, in a laser processing apparatus using a solid laser light source or a semiconductor laser light source, it is difficult to obtain sufficient power with only one light source. In view of this, it is conceivable to combine laser beams emitted from a plurality of light sources to generate a laser beam that has a wide irradiation region and is capable of obtaining a necessary irradiation energy density. However, in the case of manufacturing the above-described polysilicon film, if laser annealing is not performed with laser light having a uniform intensity distribution within the beam diameter, the crystal grain size will vary and the characteristics of the thin film transistor will deteriorate. End up. For this reason, when combining laser beams emitted from a plurality of light sources, it is also necessary to make the intensity distribution in the irradiation region uniform. As an example of an apparatus that meets these demands, a two-beam configuration including two light sources that emit laser light is disclosed. Then, by driving the stage on which the substrate is mounted, the substrate is moved in the XY direction, and the surface of the substrate is pulsed with laser light in synchronization with this (see Patent Document 2 below).

JP 2000-340506 A (see paragraph 21) International Publication No. WO03049175 (see fig15)

  However, any of the laser processing apparatuses for laser annealing typified by the above-described configuration aims to irradiate the laser beam uniformly over a wider range, and irradiates the laser beam in pulses in synchronization with the step movement of the substrate. It is a configuration. Then, in the annealing using such an apparatus, as described above, a plurality of pulse irradiations are performed on each irradiation position while shifting the irradiation region of the laser beam formed into a long linear shape. Processing is performed. Therefore, for example, in the process of annealing a part of the elements arranged for the drive substrate of the display device, most of the irradiating energy is expended in a region where it is not used, which is wasteful.

  In recent years, in the manufacture of flat display devices, a process using a plastic substrate that is easy to handle instead of a glass substrate has been studied. In particular, by using a plastic substrate that bends flexibly, a roll-to-roll process becomes possible, and a great merit can be expected in reducing equipment costs. However, the configuration in which laser light is irradiated over a wide range as described above has a large thermal load on the substrate, and is not suitable for application to a process using a plastic substrate.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a laser processing apparatus that can be suitably used for annealing a semiconductor thin film with a small thermal load on the substrate.

  In order to achieve such an object, a laser processing apparatus of the present invention includes a stage on which a substrate to be processed is placed. Moreover, the light source part which irradiates a laser beam from the normal line direction with respect to the substrate surface mounted on the stage is provided. An objective lens is arranged on the optical path of the laser light emitted from the light source unit with the normal direction of the substrate surface placed on the stage as the axial direction. Furthermore, a scanning control unit is provided for scanning the laser beam on the substrate placed on the stage by moving the objective lens in a direction perpendicular to the axis thereof.

  In the laser processing apparatus having such a configuration, a scanning control unit that scans the laser beam by moving the objective lens with respect to the substrate placed on the stage is provided. For this reason, compared with the case where the irradiation position of a laser beam is scanned by the drive of a stage, a laser beam can be scanned with respect to a board | substrate at high speed. As a result, for example, the substrate is irradiated with the laser beam while scanning the substrate with the laser beam at a high speed exceeding 0.1 m / second. And the annealing process said to reduce the thermal load with respect to the said board | substrate with the moving speed of the laser beam with respect to a board | substrate can be performed. Moreover, the thermal load on the substrate is further reduced by selectively performing such laser light irradiation only on a necessary portion of the substrate.

  In particular, the scanning control unit provided in the laser processing apparatus moves the objective lens in the direction perpendicular to the optical axis of the laser beam, so that the optical axis of the laser beam is maintained in a constant direction. The laser beam is scanned. Therefore, processing by irradiation with laser light with no aberration, that is, constant energy is performed.

  As described above, according to the present invention, it is possible to perform an annealing process in which the thermal load on the substrate is reduced by adjusting the moving speed of the laser light at a high speed. Therefore, for example, in an annealing process for crystallizing a semiconductor thin film on a substrate, it is possible to use a plastic substrate having lower heat resistance. As a result, for example, in the manufacturing process of the thin film semiconductor device, it is possible to realize a mass production process with reduced roll-to-roll facility costs.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The laser processing apparatus of the embodiment described here is for crystallizing and activating an amorphous semiconductor film such as silicon or germanium formed on a substrate in a process such as crystallization activation of a semiconductor thin film. The device used.

<First Embodiment>
FIG. 1 is a block diagram showing the laser processing apparatus of the first embodiment. The laser processing apparatus shown in this figure includes a stage 1 on which a substrate to be processed is placed, and a light source unit 2 for irradiating a laser beam Lh used for processing. An objective lens 3 is provided between the stage 1 and the light source unit 2, and the objective lens 3 is provided with a scanning control unit 4 for scanning the laser beam Lh. Further, the laser processing apparatus includes an inspection light source unit 6 for irradiating the inspection light fh, a focus control unit 7, and a position control unit 8.

  Of these, the stage 1 is provided with a slider that can keep the substrate W placed on the stage 1 horizontal, and can move and scan the substrate W freely in the XY directions in the horizontal plane. It has become. Here, when the substrate W placed on the stage 1 has flexibility and bends flexibly, the stage 1 is provided with a roll-to-roll substrate winding mechanism at the end thereof, and the substrate W The substrate W may be configured to be wound up in one direction (for example, ± Y direction) for scanning the substrate. In the drawing, the Y direction is the depth direction on the drawing.

  The light source unit 2 is provided with a semiconductor laser oscillator 2a. As the semiconductor laser oscillator 2a, one that oscillates a laser beam Lh having an appropriate wavelength is selected depending on what kind of processing is performed using this laser processing apparatus. For example, when this laser processing apparatus is used for crystallization and activation of a semiconductor thin film made of amorphous silicon, a compound semiconductor laser including Ga and N having an oscillation wavelength of 350 nm to 470 nm is used. In addition, a semiconductor laser resonator whose active layer is a so-called II-VI group semiconductor material such as zinc oxide, Zn, Cd, Se, and S, or a so-called III such as Al, Ga, In, As, and P It is also possible to use a laser resonator that is a combination of a laser resonator including a group V semiconductor as a main component of the active layer and a second harmonic using quasi-phase matching or Cherenkov light emission. In particular, a GaN-based compound semiconductor laser oscillator having a high power necessary for crystallization and activation (for example, a rating of 40 mW or more by continuous irradiation) is preferably used.

  The light source unit 2 includes a plurality of members arranged on the optical path of the laser beam Lh oscillated from the semiconductor laser oscillator 2a. The normal direction of the light source unit 2 with respect to the surface of the substrate W arranged on the stage 1 Is configured to be irradiated with laser light Lh. The structure of such a light source part 2 is demonstrated along the optical path order of the laser beam Lh.

  That is, the laser beam Lh oscillated from the semiconductor laser oscillator 2a spreads with a large spread angle. For this reason, a collimator lens 2b having a large numerical aperture NA is disposed at the subsequent stage of the semiconductor laser oscillator 2a, and the laser light Lh enters the collimator lens 2b and becomes parallel light. Further, the laser light Lh oscillated from the semiconductor laser oscillator 2a has different divergence angles between the crystal growth direction of the semiconductor laser and the direction parallel to the crystal growth direction. It has become. For this reason, an anamorphic prism 2c in which two prisms are combined is disposed after the collimator lens 2b, and the laser light Lh is incident on the anamorphic prism 2c and the beam shape is converted into a circular beam.

A polarizing beam splitter 2d designed to have a P-wave transmittance T _p = 100% and an S-wave reflectance R _s = 100% is disposed downstream of the anamorphic prism 2c. Here, when a plane parallel to the paper surface is used as a refracting surface, the orientation of the laser light Lh oscillated from the semiconductor laser oscillator 2a is previously set so as to be polarized in a direction parallel to the paper surface. . Thereby, the laser beam Lh (for example, wavelength 405 nm) converted into a circular beam is configured to pass through the polarization beam splitter 2d.

  A λ / 4 plate 2e is disposed after the polarization beam splitter 2d, and the laser light Lh becomes circularly polarized light by passing through the λ / 4 plate 2e. Further, a dichroic prism 2f is disposed at the subsequent stage of the λ / 4 plate 2e, and the dichroic prism 2f irradiates the surface of the substrate W disposed on the stage 1 with laser light Lh from its normal direction. It is the composition which becomes.

  The laser beam Lh reflected by the substrate W is further reflected by the dichroic prism 2f and is incident on the λ / 4 plate 2e. The λ / 4 plate 2e becomes linearly polarized light orthogonal to the incident time, is reflected by the polarizing beam splitter 2d, and is absorbed by the beam damper 2g. With such an optical path, light returning to the semiconductor laser oscillator 2a can be minimized, and the laser oscillation can be kept stable.

  And the objective lens 3 arrange | positioned between the light source part 2 of the above structures and the stage 1 makes the normal direction of the surface of the board | substrate W mounted on the stage 1 an axial direction (lens axial direction). In this state, it is arranged on the optical path of the laser beam Lh emitted from the light source unit 2 toward the stage 1.

  The objective lens 3 is preferably made of glass or resin, and is preferably corrected for chromatic aberration with respect to laser light Lh (for example, wavelength 405 nm) and inspection light (for example, wavelength 830 nm) described below. In addition, compared with a plurality of combination lenses, the design for reducing the aberration when the focal spot size is to be reduced is easy and inexpensive.

  In particular, it is assumed that the objective lens 3 is provided in a state of being mounted on a biaxial actuator not shown here. Thereby, the objective lens 3 is configured to move in two axial directions, that is, a lens axis (optical axis) direction and a direction perpendicular to the lens axis (optical axis) direction by a drive signal from the outside of the scanning control unit 4 described below. The biaxial actuator may be a voice coil, a piezo actuator, or the like, and its form is not limited.

  The scanning control unit 4 provided in the objective lens 3 is provided as a biaxial device driver (scanning control unit) 4 that controls driving of the biaxial actuator on which the objective lens 3 is mounted. The biaxial device driver (scanning control unit) 4 also serves as a part of a focus control unit 7 and a position control unit 8 described below.

  Here, the laser light Lh incident on the objective lens 3 is collimated light, and the beam shape at the focal point is represented by a sinc function. When the numerical aperture NA of the objective lens 3 and the wavelength λ of the laser light Lh are used, the beam diameter (minimum circle diameter with an amplitude of 0) φ is expressed by the following equation (1). φ = 2.44 × λ / (2 × NA) (1)

  In such laser light Lh, the intensity in the direction perpendicular to the optical axis (lens axis) has a Gaussian distribution in the collimated portion. For this reason, the movement of the objective lens 3 in the direction perpendicular to the optical axis by the biaxial device driver (scanning control unit) 4 is performed within a range in which the power density at the focal point formed by the objective lens 3 changes within 5%. It is assumed that it is set as follows. Thereby, when the laser beam Lh is scanned by the movement of the objective lens 3, a change in the irradiation intensity of the laser beam Lh at each scanning position can be suppressed to be small. As an example, when the objective lens 3 having a numerical aperture NA of 0.85 is used, the objective lens 3 is moved so that the laser light Lh is incident within a range of ± 50 μm from the lens axis (center position) of the objective lens 3. Thus, the change in power density at the focal point formed by the objective lens 3 can be suppressed to 5% or less. It is preferable that the intensity distribution of the laser beam Lh and the size of the aperture of the objective lens are designed so that the scanning range of the laser beam Lh due to the movement of the objective lens 3 is expanded as much as possible.

  Next, the inspection light source unit 6 is provided with an inspection light oscillator 6a that oscillates the inspection light fh. Here, as the inspection light fh, light having a wavelength that is not absorbed by the material to be processed is used. For this reason, for example, when a laser processing apparatus is used for crystallization and activation of a semiconductor thin film made of amorphous silicon, a laser having a wavelength of 650 nm or more, preferably a wavelength of 830 nm, in which absorption in the silicon-based semiconductor film becomes small. Light is used as inspection light fh. Thereby, the influence on the substrate W surface by the irradiation of the inspection light fh is prevented. As the inspection light source unit 6 that oscillates such inspection light fh, for example, a laser oscillator that oscillates laser light having a wavelength of 830 nm as inspection light fh is used.

  The inspection light source unit 6 includes a plurality of members disposed on the optical path of the inspection light fh oscillated from the inspection light oscillator 6a, and is disposed on the stage 1 through the objective lens 3 together with the laser light Lh described above. The surface of the substrate W is irradiated so as to be irradiated. The configuration of the inspection light source unit 6 is almost the same as that of the light source unit 2 described above.

In other words, the inspection light fh oscillated from the inspection light oscillator 6a is incident on the collimator lens 6b to be parallel light, and is incident on the anamorphic prism b to be converted into a circular beam. The inspection light fh is transmitted through the polarization beam splitter 6d designed to have a P-wave transmittance T _p = 100% and an S-wave reflectance R _s = 100%, and passes through the λ / 4 plate 6e. It passes through and becomes circularly polarized light. Then, the light passes through the dichroic prism 2 f of the light source unit 2, is combined with the laser light Lh, and enters the objective lens 3.

  The inspection light fh reflected by the substrate W passes through the dichroic prism 2f and enters the λ / 4 plate 6e. The λ / 4 plate 6e becomes linearly polarized light orthogonal to the incident time, is reflected by the polarizing beam splitter 6d, and is guided to the focus control unit 7 and the position control unit 8.

  Then, the cylindrical lens 7a, the condensing lens 7b, and the quadrant detector 7c are arranged in this order toward the focus control unit 7 to which the inspection light fh reflected by the polarization beam splitter 6d is guided. Has been placed.

  The cylindrical lens 7a is for generating astigmatism. The quadrant detector 7c is in an imaging relationship with the substrate W placed on the stage 1 as a processing object. Therefore, when the objective lens 3 is focused on the substrate W, the inspection light fh is focused at the center of the quadrant detector 7c. On the other hand, when the focus of the objective lens 3 is above or below the surface of the substrate W, astigmatism occurs due to the cylindrical lens 7a, and the longitudinal axis or the horizontal direction has a long axis on the quadrant detector 7c. An elliptical beam is projected.

  Therefore, when the output signals A to D from the respective detector portions of the quadrant detector 7c are defined as described below, the signal (A + C) − (B + D) indicates whether the focus of the objective lens 3 is above or below the object. Change the sign of plus and minus, and this signal becomes zero when the focus is on the object. Therefore, this signal is used as an error signal (focus error signal) when focus servo is performed, and this error signal is fed back to the scanning control unit 4 of the objective lens 3 so that the signal becomes zero. Is moved in the lens axis direction (vertical direction in the drawing) to perform focus servo.

  The position control unit 8 to which the inspection light fh reflected by the polarizing beam splitter 6d is guided includes the focus control unit 7 and the image signal position recognition unit 8a in the traveling direction of the inspection light fh. Arranged in order. Here, it is assumed that the focus control unit 7 also serves as a part of the position control unit 8.

  Then, the image signal position recognition unit 8a provided at the subsequent stage of the focus control unit 7 is based on the information on the surface of the substrate W to be processed and the output signals A to D from the respective detector portions of the quadrant detector 7c. Thus, the position where the inspection light fh is irradiated through the objective lens 3 is recognized.

  That is, when the output signals A to D from the detector portions of the quadrant detector 7c are defined, the sum signal (A + B + C + D) is a signal indicating a change in the reflectance of the exposure object. Therefore, an alignment mark serving as the same reference point in a two-dimensional plane on the substrate W is formed in a pattern on the substrate W to be processed. Then, the image signal position recognition unit 8a is obtained by scanning the inspection light fh on the surface of the substrate W by moving the stage 1 and the shape information (alignment mark arrangement information) of the surface of the substrate W obtained in advance. Further, the irradiation position of the inspection light fh on the surface of the substrate W is recognized from the change of the sum signal.

  In this laser processing apparatus, a reference point for annealing using the laser processing apparatus is obtained from the irradiation position of the inspection light fh recognized by the image signal position recognition unit 8a. Then, by moving the stage 1 based on this reference point, the arrangement state of the substrate W in the laser processing apparatus is set to a predetermined state. That is, the substrate W is moved with respect to the objective lens 3 by driving the stage 1 so that the part of the surface of the substrate W to be annealed is the irradiation position of the laser light Lh.

  Further, the position controller 8 turns on / off the oscillation of the laser beam Lh from the semiconductor laser oscillator 2a in a state where the stage 1 is driven so that the laser beam Lh is at a predetermined irradiation position as described above. By controlling the laser beam Lh, only the target portion on the surface of the substrate W is irradiated. Then, in a state where the laser beam Lh is irradiated, the objective lens 3 is moved in the direction perpendicular to the axis by the biaxial device driver (scanning control unit) 4, so that the substrate W placed on the stage 1 is moved. On the other hand, the laser beam Lh is scanned.

  In the above laser processing apparatus, the stage 1 is repeatedly moved by moving the irradiation position of the laser beam Lh by driving the stage 1 and scanning the laser beam Lh by moving the objective lens 3 at the irradiation position. A process of irradiating the laser beam Lh to an arbitrary position on the surface of the substrate W placed thereon can be performed.

  Among the configurations described above, the processing unit 10 is configured by the light source unit 2, the objective lens 3, the scanning control unit 4, the inspection light source unit 6, the focus control unit 7, and the position control unit 8, and one laser processing apparatus. A plurality of processing units 10 may be provided for one stage 1 in FIG.

  According to the laser processing apparatus configured as described above, the scanning control unit 4 that scans the laser light Lh by moving the objective lens 3 with respect to the substrate W placed on the stage 1 is provided. For this reason, compared with the case where the irradiation position of the laser beam Lh is scanned by driving the stage 1, the laser beam Lh can be scanned with respect to the substrate W at a higher speed. As a result, for example, the substrate W is irradiated with the laser light Lh while the substrate W is scanned with the laser light Lh at a high speed exceeding 0.1 m / second. And the annealing process of reducing the thermal load with respect to the board | substrate W by the moving speed of the laser beam Lh with respect to the board | substrate W can be performed. Further, by selectively performing such irradiation of the laser light Lh only on a necessary portion with respect to the substrate W, the thermal load on the substrate W is further reduced.

  As a result, by adjusting the moving speed of the laser beam Lh at a high speed, it is possible to perform an annealing process that reduces the thermal load on the substrate W. For example, to crystallize a semiconductor thin film on the substrate W In this annealing process, it is possible to use a plastic substrate or the like having lower heat resistance. Thereby, for example, in the manufacturing process of the thin film semiconductor device, it is possible to realize a mass production process in which the cost of equipment in roll-to-roll is suppressed.

  Further, by adjusting the intensity of the laser beam Lh by adjusting the output of the laser beam Lh oscillated from the semiconductor laser oscillator 2a and changing the duty in the case of AC driving, an arbitrary laser intensity can be placed in the XY two-dimensional region on the substrate. It is also possible to form a distribution pattern.

  In addition, the provision of the semiconductor laser oscillator 2a makes it possible to reduce the size of the entire apparatus by reducing the size of the light source unit 2 as compared with an excimer laser device or a YAG laser. In addition, since the light source unit 2 is downsized, a plurality of processing units 10 including the light source unit 2 may be provided to irradiate each position of the substrate W with multiple points of laser light. Thereby, it becomes possible to shorten the process of laser irradiation and improve productivity.

  When this laser processing apparatus is used for crystallization and activation of a semiconductor thin film made of amorphous silicon, the continuous irradiation of the laser beam Lh onto the substrate W is completely continuous without any interruption during the movement of the laser beam Lh. And a case where there is a pause that does not completely complete solidification of the melted semiconductor thin film portion by irradiation with the laser beam Lh. For this reason, if such a condition is satisfied, the case where a pause time shorter than the irradiation time is included is included in the continuous irradiation. As an example, a pause of about 10 to 20 ns is included with respect to the irradiation time of 100 ns to the semiconductor thin film portion. In some cases, it is included in continuous irradiation. Note that the pause time with respect to the irradiation time is appropriately designed according to the material and thickness of the semiconductor thin film, the energy density of the laser light Lh, and the like. By providing such a pause time, the thermal influence on the substrate W due to the laser light Lh irradiation can be suppressed. The excimer laser light is a complete pulse wave, and if it is a pulse wave of about 300 Hz, a pause of about 3300 ns will occur for an irradiation time of 25 ns. For this reason, in the excimer laser light, the next pulse irradiation is performed in a state where the solidification of the melted semiconductor thin film 5 portion by the irradiation of the laser light Lh is completed. Can not.

  Next, as an example of the annealing process using the laser processing apparatus described above, an annealing process for crystallizing a semiconductor thin film made of amorphous silicon covering the surface of the substrate W will be described. Here, as the substrate W, for example, a plastic substrate is used in which a semiconductor thin film made of amorphous silicon is formed through a heat insulating buffer layer. This semiconductor thin film is formed with a film thickness of 50 nm by PE-CVD (plasma enhancement-chemical vapor deposition) which can keep the film formation temperature low. The semiconductor thin film thus formed is made of so-called hydrogenated amorphous silicon (a-Si: H) containing a large amount of hydrogen.

  The semiconductor thin film as described above is usually subjected to laser annealing for crystallization after hydrogen removal by dehydrogenation annealing in a heat treatment furnace. This prevents so-called ablation, in which hydrogen ions are gasified and expand to break the film during laser annealing.

  However, here, by using the above laser processing apparatus, crystallization can be performed only by the following laser annealing treatment without performing dehydrogenation annealing at a temperature of 450 ° C. or higher for several hours as a pretreatment. It becomes possible. That is, the laser processing apparatus is used to irradiate the semiconductor thin film with laser light Lh having a wavelength of 350 nm to 470 nm while moving the irradiation position at a predetermined speed. At this time, the laser beam irradiation is continuous irradiation. Thereby, together with crystallization of the semiconductor thin film, excess hydrogen is removed from the irradiated portion of the laser light Lh without gasifying and expanding hydrogen ions in the semiconductor thin film.

  Thereby, it is possible to crystallize only the irradiated part of the laser beam Lh and to activate this part.

  In such laser annealing treatment, by using the laser processing apparatus, it is possible to move the irradiation position of the laser beam on the semiconductor thin film at a predetermined high speed, and the semiconductor thin film is heated by the laser beam irradiation. This prevents the substrate from being affected. Further, in this annealing step, the semiconductor thin film is moved while being continuously irradiated with laser light. As a result, surplus hydrogen in the laser light irradiation portion continues to move in the semiconductor thin film as the laser light moves, so that surplus hydrogen is removed from the crystallization region. Therefore, it is not necessary to perform dehydrogenation annealing for several hours at a temperature of 450 ° C. or higher in a separate process. In addition, although excess hydrogen is removed from the laser beam irradiation portion, an appropriate amount of hydrogen remains. Therefore, by this laser annealing treatment, dehydrogenation and hydrogenation treatment in the crystallization region in the semiconductor thin film are simultaneously performed.

  As a result, the heat generation of the semiconductor thin film due to the laser light irradiation is prevented from affecting the substrate, and the dehydrogenation annealing process for several hours at a temperature of 450 ° C. or higher is not performed in a separate process. Dehydrogenation can be performed simultaneously in the annealing step for crystallization. As a result, it is possible to use a material having lower heat resistance as a substrate of a highly functional thin film semiconductor device using a crystallized semiconductor thin film. As a result, it becomes possible to use a plastic substrate, and for example, it is possible to realize a mass production process with reduced equipment costs in roll-to-roll. In addition, since the hydrogenation process is performed at the same time as the crystallization and dehydrogenation of the semiconductor thin film, the manufacturing process of the thin film semiconductor device using the crystallized semiconductor thin film is simplified and the productivity is thereby improved. Is possible.

  In the laser processing apparatus having the above-described configuration, when the effective Na of the objective lens is 0.4, for example, and the substantial optical efficiency is 0.25, the average energy density is 2.6 mW / cm 2. When the scanning speed is adjusted to about 1.2 m / s, the passing time of the beam diameter passing through one point on the film is about 100 ns, and it can be seen that energy equivalent to a maximum of 2.6 J / cm 2 can be irradiated. .

Therefore, the laser beam Lh is applied to the semiconductor thin film 5a (a-Si: H) having a film thickness of 50 nm formed by PE-CVD method with an energy equivalent to 1 J / cm ² at a moving speed vt = 8.2 m / sec. When irradiated, as shown in FIG. 2, crescent-shaped crystal grains a that are convex in the moving direction of the laser beam Lh indicated by the arrows in the drawing are arranged along the moving direction (arrow direction) of the laser beam Lh. It was confirmed. The crystal grain a was about 800 nm wide × 100 nm long in the moving direction. Further, at the end of irradiation with the laser beam, a defect in which excess hydrogen was precipitated in the form of voids at the end of the crystal region A of the semiconductor thin film was observed. In addition, a similar defect was partially observed in the region where solidification progressed in the direction opposite to the movement of the laser beam at the irradiation start end of the laser beam Lh.

  Here, in a laser apparatus using a GaN laser oscillator having a rating of 60 mW designed with an effective Na of the objective lens set to 0.6, for example, when the substantial optical efficiency is 0.5, an average of 17. An energy density of 7 MW / cm 2 is possible. Therefore, if the scanning speed of the laser beam can be increased to about 8.2 m / S, the passing time (that is, the irradiation time) of the laser beam passing through one point of the semiconductor thin film is about 100 ns, which corresponds to a maximum of 1.77 J / cm 2. It can be seen that energy can be irradiated. Even in this case, when an energy equivalent to 1 J / cm 2 is applied to a semiconductor thin film made of amorphous silicon having a thickness of 50 nm formed by a CVD method using this apparatus, crystallization may be possible. confirmed.

Second Embodiment
FIG. 3 is a configuration diagram illustrating a laser processing apparatus according to the second embodiment. The difference between the laser processing apparatus shown in this figure and the laser processing apparatus of the first embodiment described with reference to FIG. 1 is the configuration of the position control unit 8 ′, and the other configurations are the same.

  That is, the position control unit 8 ′ provided in the laser processing apparatus of the second embodiment shown in FIG. 3 includes an illumination light source that is not shown here. The illumination light source irradiates the surface of the substrate W placed on the stage 1 with transmitted or incident illumination light. The dichroic prism 6f that reflects part of the illumination light H and the inspection light fH transmitted through the objective lens 3 and the dichroic prism 2f from the surface of the substrate W and transmits the inspection light fh that does not reflect the illumination light H and the inspection light. It is arranged in the optical path fh.

  A condensing lens 8a ′, a CCD 8b ′, and an image signal position recognition unit 8c ′ constituting the position control unit 8 ′ are arranged in this order on the optical path of the illumination light H reflected by the dichroic prism 6f. . An object and a focal position on the surface of the substrate W placed on the stage 1 are imaged on the CCD 8b 'by the objective lens 3 and the condenser lens 8a'. Then, by processing the image information of the CCD 8b ', the position on the surface of the substrate W on the stage 1 where the laser beam Lh is irradiated is specified. Further, based on the image information of the CCD 8b ′, a signal is sent to the biaxial device driver (scanning control means) 4 and the driver of the semiconductor laser oscillator 2a, and the laser beam Lh is moved by moving the objective lens 3 at a specific location on the substrate W. , And the surface of the substrate W is processed while adjusting the focal position.

  In the laser processing apparatus configured as described above, the processing unit 10 ′ is configured by the light source unit 2, the objective lens 3, the scanning control unit 4, the inspection light source unit 6, the focus control unit 7, and the position control unit 8 ′. A plurality of processing units 10 ′ may be provided for one stage 1 in one laser processing apparatus.

  Even in the laser processing apparatus configured as described above, the laser beam Lh is scanned by moving the objective lens 3 with respect to the substrate W placed on the stage 1. Similarly, by adjusting the moving speed of the laser beam Lh at a high speed, it is possible to perform an annealing process in which the thermal load on the substrate W is reduced.

It is a block diagram of the laser processing apparatus of 1st Embodiment. It is a top view explaining the crystal grain obtained by the laser annealing process using this invention processing apparatus. It is a block diagram of the laser processing apparatus of 2nd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Stage, 2 ... Light source part, 3 ... Objective lens, 4 ... Biaxial device driver (scanning control part), 6 ... Inspection light source part, 7 ... Focus control part, 8, 8 '... Position control part, 10, 10 '... Processing unit, Lh ... Laser light, fh ... Inspection light, W ... Substrate

Claims (7)

A stage on which a substrate to be processed is placed;
A light source unit that emits laser light from the normal direction to the substrate surface placed on the stage;
An objective lens disposed on the optical path of the laser light emitted from the light source unit with the normal direction of the substrate surface placed on the stage as the optical axis direction;
A laser control unit that scans the laser beam with respect to the substrate placed on the stage by moving the objective lens in a direction perpendicular to the optical axis thereof; apparatus. The laser processing apparatus according to claim 1,
The light source unit includes a semiconductor laser oscillator. The laser processing apparatus according to claim 2,
A plurality of processing units including the light source unit, the objective lens, and the scanning control unit,
The laser processing apparatus, wherein the plurality of processing units irradiate the laser light at multiple points to each position of the substrate placed on the stage. The laser processing apparatus according to claim 1,
The light source section includes a compound semiconductor laser oscillator including Ga and N, a compound semiconductor laser oscillator including Zn and O, a compound semiconductor laser oscillator including Zn, Cd, Se, and S, or Al, Ga, In, As, and A laser processing apparatus comprising a compound semiconductor laser oscillator including P and a second harmonic generator. The laser processing apparatus according to claim 1,
A test light having a wavelength that is not absorbed by the material to be processed, or a wavelength that has a small absorption in a range that does not raise the temperature to the extent that the object to be processed causes a physical and chemical change even if absorbed, is emitted from the light source unit. An inspection light source unit for irradiating the substrate placed on the stage together with the laser beam to be irradiated. The laser processing apparatus according to claim 5, wherein
A focus control unit that adjusts the focus of the laser light by moving the objective lens in the optical axis direction based on the inspection light reflected and detected by the surface of the substrate placed on the stage; A laser processing apparatus characterized by that. The laser processing apparatus according to claim 5, wherein
The stage is moved so that the laser beam is selectively irradiated to a predetermined position on the substrate surface based on the inspection light reflected and detected by the substrate surface placed on the stage. A laser irradiation apparatus comprising a position control unit.

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