JP2005129889A - Beam homogenizer, laser irradiator, and method of manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a beam homogenizer capable of forming a rectangular shaped beam spot whose energy distribution in the long side direction is uniform on a surface to be irradiated without using optical lens to which high manufacturing accuracy is required. <P>SOLUTION: In a beam homogenizer, a beam spot on a surface to be irradiated is formed in a rectangular shape having an aspect ratio of ≥ 10, preferably, ≥ 100. The beam homogenizer has an optical waveguide for uniformizing the rectangular shaped energy distribution in the long side direction. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a beam homogenizer that makes a beam spot on an irradiated surface uniform in a specific region. The present invention also relates to a laser irradiation apparatus that irradiates the irradiated surface with the beam spot. Further, the present invention relates to a method for manufacturing a semiconductor device using a crystalline semiconductor film formed using the laser irradiation apparatus.

  In recent years, an amorphous semiconductor film or a crystalline semiconductor film (not a single crystal, a semiconductor film having crystallinity such as polycrystalline or microcrystal) formed over an insulating substrate such as glass, that is, a semiconductor that is not a single crystal A technique for performing laser annealing on a film (referred to as a non-single-crystal semiconductor film) to improve crystallization and crystallinity has been widely studied. A silicon film is often used as the semiconductor film.

  A glass substrate is cheaper and more workable than a quartz substrate that has been frequently used in the past, and has an advantage that a large-area substrate can be easily manufactured. For this reason, the above research has been actively conducted. Lasers are preferred for crystallization because the glass substrate has a low melting point. The laser can give high energy only to the non-single-crystal semiconductor film without significantly changing the temperature of the substrate.

  A crystalline silicon film formed by laser annealing has high mobility. Therefore, a thin film transistor (TFT) using this crystalline silicon film is actively used. For example, it is actively used for a monolithic liquid crystal electro-optical device or the like in which TFTs for pixels and driving circuits are formed on a single glass substrate. Since the crystalline silicon film is made of a large number of crystal grains, it is called a polycrystalline silicon film or a polycrystalline semiconductor film.

  Further, a pulse oscillation type laser beam having a high output, such as an excimer laser, can be shaped by an optical system so as to be a square spot of several cm square or a linear shape having a length of 10 cm or more on the irradiated surface. (For example, Patent Document 1). A method of performing laser annealing by scanning the irradiation position of such a beam spot relative to the surface to be irradiated is preferable because it is excellent in mass productivity and industrially excellent.

  In particular, when a linear beam spot is used, unlike in the case of using a spot beam spot that requires scanning in the front, rear, left, and right, irradiation is performed only in a direction perpendicular to the longitudinal direction of the linear beam spot. Since the entire surface can be irradiated with a laser beam, high productivity can be obtained. Here, the linear beam spot is a rectangular beam spot having a large aspect ratio. The reason for scanning in the direction perpendicular to the long width direction is that it is the most efficient scanning direction. Due to this high productivity, it is becoming more common for laser annealing to use a linear beam spot obtained by shaping a beam spot of a pulsed excimer laser with an appropriate optical system.

  FIG. 6 shows an example of an optical system for processing the cross-sectional shape of the beam spot into a linear shape on the irradiated surface. The optical system shown in FIG. 6 is very general. The optical system not only converts the cross-sectional shape of the beam spot into a linear shape, but also at the same time achieves uniform energy of the beam spot on the irradiated surface. In general, an optical system that makes beam energy uniform is called a beam homogenizer. The optical system shown in FIG. 6 is also a beam homogenizer.

  First, the side view of FIG. The laser beam emitted from the laser oscillator 1201 divides the laser beam spot in one direction by cylindrical lens arrays 1202a and 1202b. The direction will be referred to as the vertical direction. The vertical direction is bent in the direction of light bent by the mirror when the mirror enters the middle of the optical system. In this configuration, there are four divisions. These divided spots are once combined into one spot by the cylindrical lens 1204. The spot separated again is reflected by the mirror 1207 and then condensed again into one spot on the irradiated surface 1209 by the doublet cylindrical lens 1208. The doublet cylindrical lens refers to a lens composed of two cylindrical lenses. Thereby, the energy in the vertical direction of the beam spot shaped linearly is made uniform, and the length in the vertical direction is determined.

  Next, the plan view of FIG. 6B will be described. The laser beam emitted from the laser oscillator 1201 divides the spot of the laser beam in a direction perpendicular to the vertical direction by a cylindrical lens array 1203. The perpendicular direction is referred to as a lateral direction. The horizontal direction is bent in the direction of light bent by the mirror when the mirror enters the middle of the optical system. In this configuration, there are seven divisions. After that, the spots divided into seven by the cylindrical lens 1205 are combined into one at the irradiated surface 1209. The mirror 1207 and the subsequent lines are indicated by broken lines. The broken line indicates the exact optical path and the position of the lens and the irradiated surface when the mirror 1207 is not disposed. Thereby, the horizontal energy distribution of the beam spot shaped into a linear shape is made uniform, and the length in the horizontal direction is determined.

  As described above, the cylindrical lens array 1202a, the cylindrical lens array 1202b, and the cylindrical lens array 1203 are lenses that divide the laser beam spot. The uniformity of the energy distribution of the obtained linear beam spot is determined by the number of divisions.

  The above lenses are made of synthetic quartz in order to be compatible with the XeCl excimer laser. In addition, the surface is coated so as to transmit the excimer laser well, whereby the transmittance of the excimer laser per lens becomes 99% or more.

  The linear beam spot shaped in the above configuration is irradiated while being gradually shifted in the line width direction of the beam spot. Then, for example, laser annealing can be performed on the entire surface of the non-single-crystal silicon film to improve crystallization and crystallinity.

Next, a typical method for manufacturing a semiconductor film to be irradiated with a laser beam is described. First, a glass substrate having a thickness of 0.7 mm and a 5-inch square is used as the substrate. A SiO ₂ film (silicon oxide film) having a thickness of about 200 nm is formed on the substrate using a plasma CVD apparatus, and an amorphous silicon film (hereinafter referred to as an a-Si film) having a thickness of about 50 nm is formed on the surface of the SiO ₂ film. (Denoted) is formed. When the substrate is exposed to a nitrogen atmosphere at a temperature of 500 ° C. for 1 hour, the hydrogen concentration in the film is reduced. This significantly improves the laser resistance of the film.

  The laser oscillator uses a XeCl excimer laser (wavelength 308 nm, pulse width 30 ns). The spot size of the laser beam is 15 × 35 mm (both half-value width) at the exit of the laser beam. The exit of the laser beam is defined by a plane perpendicular to the traveling direction of the laser beam immediately after the laser beam is emitted from the laser oscillator.

  The shape of the laser beam generated by the excimer laser is generally rectangular and falls within the range of 1 to 5 when expressed in terms of aspect ratio. The intensity of the laser beam spot shows a Gaussian distribution that is stronger toward the center of the laser beam spot. The spot size of the laser beam is converted into a spot shape with a uniform energy distribution, for example, a linear beam spot of 300 mm × 0.4 mm, by the optical system shown in FIG.

In the case of irradiating the above-described semiconductor film with a laser beam, the overlapping pitch is most suitable around 1/10 of the short width (half-value width) of the linear beam spot. Thereby, the uniformity of crystallinity in the semiconductor film can be improved. In the above example, since the half width is 0.4 mm, the excimer laser pulse frequency is 300 Hz, the scanning speed is 10 mm / s, and the laser beam is irradiated. At this time, the energy density on the surface irradiated with the laser beam is set to 450 mJ / cm ² . The method described so far is a very general method used for crystallizing a semiconductor film using a linear beam spot.

JP-A-9-234579

  The manufacturing of the cylindrical lens array requires a high processing accuracy.

  The cylindrical lens array is a lens in which cylindrical lenses are arranged in a curvature direction. Here, the curvature direction is a direction perpendicular to the generatrix of the cylindrical surface of the cylindrical lens. In the cylindrical lens array, there is always a junction between the cylindrical lenses constituting the cylindrical lens array. Since the junction does not have a curved surface as a cylindrical lens, the laser beam incident on the junction is transmitted without being affected by the cylindrical lens. A laser beam that reaches the irradiated surface without receiving the above action can cause non-uniformity in the energy distribution of the rectangular beam spot on the irradiated surface.

  In addition, all the cylindrical lenses constituting the cylindrical lens array must be manufactured with the same accuracy. If the cylindrical lens has a different curvature, the laser beam divided by the cylindrical lens array is not superimposed on the same position on the irradiated surface by the condenser lens. That is, the area where energy is attenuated by the rectangular beam spot on the irradiated surface increases. This leads to a decrease in energy use efficiency.

  The cause of the non-uniformity of the energy distribution of the beam spot on the irradiated surface lies in the structural problem and manufacturing accuracy of the cylindrical lens array constituting the optical system. That is, one of the causes of the non-uniformity is that all the laser beams divided by the cylindrical lens array are not superimposed at the same position.

  Further, when the semiconductor film is irradiated with a rectangular beam spot whose energy distribution in the long side direction of the rectangle is non-uniform on the irradiated surface and scanned, the crystallinity reflecting the non-uniform distribution on the semiconductor film is obtained. Inhomogeneity occurs. The non-uniformity of crystallinity is synchronized with the non-uniformity of characteristics such as the electric mobility of the semiconductor film. For example, it appears as variations in electrical characteristics of TFTs formed using the semiconductor film, and a light and dark pattern is displayed on a panel using the TFTs.

  In the present invention, in view of the above problems, a rectangular beam spot having a uniform energy distribution in the long side direction can be formed on the irradiated surface without using an optical lens that requires high manufacturing accuracy. A possible beam homogenizer is provided. In addition, a laser irradiation apparatus capable of irradiating a laser beam having a rectangular beam spot with a uniform energy distribution in the long side direction is provided. Furthermore, the present invention provides a method for manufacturing a semiconductor device, which can improve the uniformity of crystallinity in a substrate surface and produce a TFT having high operating characteristics.

  The present invention uses an optical waveguide as an optical system for uniforming the energy distribution in the long side direction of the rectangular beam spot on the irradiated surface in the optical system for forming the rectangular beam spot. An optical waveguide is a circuit that has the capability of confining radiated light in a certain region and guiding and transmitting the energy flow parallel to the axis of the path.

  The beam homogenizer disclosed in this specification is a beam homogenizer for making a beam spot on an irradiated surface into a rectangular shape with an aspect ratio of 10 or more, preferably 100 or more, and has an energy distribution in a long side direction of the rectangle. It is characterized by having a uniform optical waveguide.

  In the present invention, the reason why the optical waveguide is used for the beam homogenizer is as follows. When a laser beam is incident on the optical waveguide, the laser beam repeatedly reflects in the optical waveguide and reaches the exit surface. That is, the laser beam incident on the optical waveguide is superimposed on the exit surface at the same position so as to be folded. Therefore, the laser beam incident on the optical waveguide is divided and is subjected to the same effect as when the divided laser beams are superimposed at the same position, and the laser beam is emitted at the exit surface where the laser beam is superimposed. The energy distribution is made uniform.

  The configuration of the present invention is a beam homogenizer for forming a beam spot on an irradiated surface in a rectangular shape having an aspect ratio of 10 or more, preferably 100 or more, and uniformizes the energy distribution in the long side direction of the rectangle. A beam homogenizer having an optical waveguide and one or a plurality of cylindrical lenses for condensing light emitted from the optical waveguide in a long side direction of a rectangular shape on an irradiated surface.

  Another configuration of the present invention is a beam homogenizer for forming a beam spot on a surface to be irradiated into a rectangular shape having an aspect ratio of 10 or more, preferably 100 or more, and has an energy distribution in the short side direction of the rectangle. The beam homogenizer includes means for making uniform on the irradiation surface and an optical waveguide for making the energy distribution in the long side direction of a rectangular shape uniform, and the means has at least a cylindrical lens array.

  Another configuration of the present invention is a beam homogenizer for forming a beam spot on an irradiated surface in a rectangular shape having an aspect ratio of 10 or more, preferably 100 or more, and has a uniform energy distribution in the long side direction of the rectangle. It is a beam homogenizer characterized by having an optical waveguide to be converted and an optical waveguide to make the energy distribution in the rectangular short side direction uniform.

  In the above-mentioned configuration of the invention of the beam homogenizer, the optical waveguide has two reflecting surfaces facing each other.

  A light pipe can be used as the optical waveguide. The light pipe is usually for transmitting light from one end to the other end by reflection, and has a shape such as a cone, a pyramid, a cylinder, or a prism. In addition, the reflection by a mirror may be used for optical transmission, and what has two reflective surfaces which face each other is considered.

  The laser irradiation apparatus disclosed in this specification is a laser irradiation apparatus having a rectangular shape with an aspect ratio of a beam spot on an irradiated surface of 10 or more, preferably 100 or more, and includes a laser oscillator and a beam homogenizer. The beam homogenizer is a laser irradiation apparatus characterized by having an optical waveguide that makes the energy distribution in the long side direction of a rectangular shape uniform.

  Another configuration of the present invention is a laser irradiation apparatus having a rectangular shape with an aspect ratio of a beam spot on an irradiated surface of 10 or more, preferably 100 or more, which includes a laser oscillator and a beam homogenizer, and a beam homogenizer. Is a laser irradiation apparatus having an optical waveguide that equalizes the energy distribution in the long side direction of the rectangular shape and an optical waveguide that equalizes the energy distribution in the short side direction of the rectangular shape.

  In the above-described configuration of the laser irradiation apparatus, the optical waveguide has two reflecting surfaces facing each other.

  A light pipe can be used as the optical waveguide.

In the above-described configuration of the laser irradiation apparatus, the laser oscillator is any one of an excimer laser, a YAG laser, a glass laser, a YVO ₄ laser, a GdVO ₄ laser, a YLF laser, and an Ar laser.

  In the above-described configuration of the laser irradiation apparatus, the laser irradiation apparatus includes a moving stage that moves the irradiated object of the beam spot relative to the beam spot, and transports the irradiated object to the stage. It has the conveyance apparatus which performs.

  A manufacturing method of a semiconductor device disclosed in the present invention includes a step of forming a non-single-crystal semiconductor film on a substrate, and a laser beam generated by a laser oscillator using a non-single-crystal semiconductor film as an irradiated surface to form a cylindrical lens array And an optical waveguide to shape the beam spot into a uniform beam spot having a rectangular energy distribution with an aspect ratio of 10 or more, preferably 100 or more on the irradiated surface, and the position of the beam spot with respect to the non-single crystal semiconductor film. A step of laser annealing the non-single crystal semiconductor film while relatively moving, the cylindrical lens array acting in the short side direction of the rectangular beam spot, and the optical waveguide being the long side of the rectangular beam spot It is characterized by acting in the direction.

  Another structure of the present invention includes a step of forming a non-single-crystal semiconductor film on a substrate and a laser beam generated by a laser oscillator using a plurality of optical waveguides with the non-single-crystal semiconductor film as an irradiated surface. While shaping to a rectangular beam distribution with a rectangular energy distribution having an aspect ratio of 10 or more, preferably 100 or more, on the surface to be irradiated, and moving the position of the beam spot relative to the non-single crystal semiconductor film, A step of laser annealing the non-single crystal semiconductor film, and at least one of the plurality of optical waveguides acts in a long side direction of the rectangular beam spot, and at least one of the optical waveguides has a rectangular shape. It is characterized by acting in the short side direction of the beam spot.

A light pipe can be used as the optical waveguide.

In the above-described structure of the method for manufacturing a semiconductor device, the laser oscillator is any one of an excimer laser, a YAG laser, a glass laser, a YVO ₄ laser, a GdVO ₄ laser, a YLF laser, and an Ar laser.

  The laser irradiation apparatus disclosed in the present invention includes a beam homogenizer provided with an optical waveguide. The optical waveguide has two reflecting surfaces facing each other, and the energy distribution in the long side direction of the rectangular shape can be made uniform on the irradiated surface.

  If a beam homogenizer that forms a rectangular beam spot using an optical waveguide disclosed in the present invention is used, a rectangular shape with a uniform energy distribution in the long side direction is used without using an optical lens that requires high manufacturing accuracy. A beam spot can be formed on the irradiated surface. In addition, the optical waveguide is more preferable because it acts in the rectangular short-side direction, and the energy distribution in that direction can be made uniform on the irradiated surface. When a rectangular beam spot emitted from a laser irradiation device using this beam homogenizer is scanned in the short side direction of the rectangle on the semiconductor film, the crystallinity non-uniformity due to the non-uniformity of the energy distribution of the beam spot And the uniformity of crystallinity in the semiconductor film surface can be improved. Further, if the present invention is applied to a mass production line for low-temperature polysilicon TFTs, TFTs with high operating characteristics can be efficiently produced. Further, when low-temperature polysilicon is applied to a liquid crystal display device or a light-emitting device using a light-emitting element typified by an organic EL element, a display device with extremely small display unevenness can be manufactured.

First, a method for equalizing the energy distribution of the beam spot by the optical waveguide will be described with reference to FIG. First, the plan view of FIG. 1A will be described. An optical waveguide 102 having two reflecting surfaces 102a and 102b facing each other and an irradiated surface 103 are prepared, and a laser beam is incident from the left side of the drawing. The laser beam when the optical waveguide 102 exists is indicated by a solid line 101a, and the laser beam when the optical waveguide 102 does not exist is indicated by a broken line 101b. When the optical waveguide 102 does not exist, the laser beam incident from the left side of the drawing reaches the areas of the irradiated surfaces 103a, 103b, and 103c as indicated by the broken line 101b.

  On the other hand, when the optical waveguide 102 exists, the laser beam is reflected by the reflecting surface of the optical waveguide 102 as shown by the laser beam 101a, and all the laser beams reach the region of the irradiated surface 103b. That is, when the optical waveguide 102 exists, all the laser beams that reach the irradiated surfaces 103a and 103c when the optical waveguide 102 does not exist reach the irradiated surface 103b. Accordingly, when a laser beam is incident on the optical waveguide 102, reflection is repeated in the optical waveguide and reaches the exit. That is, it is superimposed on the irradiated surface 103b at the same position so that the incident laser beam is folded. In this example, the length of the light spread 103a, 103b, 103c on the irradiated surface 103 when there is no optical waveguide is A, and the light spread 103b on the irradiated surface 103 when there is an optical waveguide. When the length is B, A / B corresponds to the number of divisions of the homogenizer described in the prior art. In this way, by dividing the incident laser beam and superimposing the divided laser beams on the same position, the energy distribution of the laser beam at the superimposed position is made uniform.

  In general, the homogenizer has a higher uniformity of energy distribution at a position where the divided laser beams are superimposed as the number of divided laser beams is increased. In the optical waveguide 102, the number of divisions of the laser beam can be increased by increasing the number of reflections in the optical waveguide 102. That is, it is preferable to increase the length of the two reflecting surfaces of the optical waveguide in the laser beam incident direction. Also, the number of divisions can be increased by reducing the interval between the reflecting surfaces facing each other. Alternatively, the number of divisions can be increased by increasing the NA (numerical aperture) of the incident laser beam.

  A rectangular beam spot forming optical system using the beam homogenizer disclosed in the present invention will be described with reference to FIG. In the plan view of FIG. 2A, the direction perpendicular to the paper surface is the short-side direction of the rectangular beam spot. Hereinafter, a light pipe can be used as the optical waveguide.

  First, the plan view of FIG. 2A will be described. The laser beam emitted from the laser oscillator 201 is propagated in the direction of the arrow in FIG. 2 and is incident on the cylindrical lens 202. The laser beam is narrowed down in the long side direction of the rectangular shape by the cylindrical lens 202 and enters the optical waveguide 203 having two reflecting surfaces 203a and 203b facing each other. The laser beam incident on the optical waveguide 203 is repeatedly reflected in the optical waveguide 203 and reaches the exit. At the exit of the optical waveguide 203, a surface having a uniform energy distribution is formed in the long side direction of the rectangular beam spot. As the shape of the optical waveguide 203, one having a length of 300 mm in the incident direction of the laser beam and a distance of 2 mm between the reflecting surfaces can be considered.

  The longer the length of the optical waveguide 203 in the incident direction, and the shorter the focal length of the cylindrical lens 202, the more uniform the energy distribution. However, since the actual system must be manufactured in consideration of the size of the optical system, the length of the optical waveguide and the focal length must be practical according to the size of the system.

  A surface having a uniform energy distribution in the long side direction of the rectangular beam spot formed at the exit of the optical waveguide 203 is projected onto the irradiated surface 208 by the cylindrical lens 204. That is, the uniform surface and the irradiated surface 208 are in a conjugate position with respect to the cylindrical lens 204. Thereby, the energy distribution in the long side direction of the rectangular beam spot is made uniform, and the length in the long side direction is determined.

The present invention having an optical waveguide 203 is a structural problem and manufacturing accuracy of a cylindrical lens array, a divided laser, which causes non-uniformity of energy distribution of a rectangular beam spot on an irradiated surface in a conventional optical system. It is possible to improve the problem of manufacturing accuracy of a cylindrical lens which is a beam condensing lens.

  Next, the side view of FIG. 2B will be described. The laser beam emitted from the laser oscillator 201 is divided in the short-side direction of the rectangular beam spot by the cylindrical lens arrays 205a and 205b. The laser beams divided by the cylindrical lens arrays 205a and 205b are superimposed on the same surface by the cylindrical lens 206, and the energy distribution in the short side direction of the rectangular beam spot is made uniform.

  A surface formed by the cylindrical lens 206 and having a uniform energy distribution in the short side direction of the rectangular beam spot is projected onto the irradiated surface 208 by a doublet cylindrical lens composed of the cylindrical lenses 207a and 207b. Thereby, energy distribution is made uniform in the short side direction of the rectangular beam spot on the irradiated surface 208, and the length in the short side direction is determined. The doublet cylindrical lens may not be used, but by using the doublet cylindrical lens, a distance can be secured between the optical system and the irradiation surface, so that a spatial margin can be obtained. Note that a singlet cylindrical lens may be used when the uniformity of the beam spot on the irradiated surface is not so required, or when the F-number (focal length / aperture ratio) of the doublet cylindrical lens is very large.

  By using the optical system having the above configuration, a rectangular beam spot having a uniform energy distribution in both the long side direction and the short side direction can be formed on the irradiated surface.

  The laser oscillator combined with the rectangular beam spot forming optical system using the beam homogenizer disclosed in the present invention preferably has a wavelength region that has a large output and is well absorbed by the semiconductor film. When a silicon film is used as the semiconductor film, the wavelength of the laser beam emitted from the laser oscillator to be used is preferably 600 nm or less in consideration of the absorption rate. Examples of a laser oscillator that emits such a laser beam include an excimer laser, a YAG laser (harmonic), and a glass laser (harmonic).

In addition, although the current technology has not yet obtained a large output, as a laser oscillator that oscillates a laser beam having a wavelength suitable for crystallization of a silicon film, for example, a YVO ₄ laser (harmonic), a GdVO ₄ laser (harmonic) Wave), YLF laser (harmonic), and Ar laser.

  Hereinafter, a method for manufacturing the semiconductor device of the present invention using the beam homogenizer and the laser irradiation apparatus of the present invention will be described. First, as a substrate, for example, a 600 × 720 × 0.7 mm substrate is prepared. This substrate has sufficient durability at temperatures up to 600 ° C., and typically, an alkali-free glass substrate such as aluminoborosilicate glass, barium borosilicate glass, aluminosilicate glass, or the like can be used. A silicon oxide film having a thickness of 200 nm is formed on the glass substrate as a base film. Further, an amorphous silicon film is formed thereon to a thickness of 55 nm. Both films are formed by sputtering. Alternatively, the film may be formed by a plasma CVD method.

The film-formed substrate is placed in a nitrogen atmosphere at 450 to 500 ° C. for 1 to 3 hours. This step is a step for reducing the hydrogen concentration in the amorphous silicon film. If there is too much hydrogen in the semiconductor film, the film cannot withstand the laser energy, so this step can be performed. The hydrogen concentration in the film is suitably on the order of 10 ²⁰ / cm ³ . Here, 10 ²⁰ / cm ³ means that 10 ²⁰ hydrogen atoms exist per 1 cm ³ .

  In the embodiment of the present invention, for example, a XeCl excimer laser is used as the laser oscillator. In this example, a XeCl excimer laser (wavelength: 308 nm, pulse width: 30 ns) STEEL1000 manufactured by Lambda is used. The excimer laser is a pulse laser. The maximum energy of the excimer laser is 1000 mJ per pulse, the oscillation wavelength is 308 nm, and the maximum frequency is 300 Hz. During the laser treatment of one substrate, uniform crystallization can be performed if the energy fluctuation for each pulse of the pulse laser is within ± 10%, preferably within ± 5%.

  The fluctuation of the laser energy described here is defined as follows. That is, the average value of the laser energy during the period during which one substrate is irradiated is used as a reference, and the difference between the minimum energy or the maximum energy during the period and the average value is expressed in%.

  As a laser oscillator, for example, a XeCl excimer laser (oscillation wavelength 308 nm, pulse width 170 ns) VEL1520 manufactured by Sopra may be used. The excimer laser has a maximum energy of 15 J per pulse and a frequency of 20 Hz. When the excimer laser is used, the energy fluctuation per pulse can be kept within ± 2.5% during laser processing of one substrate, and more uniform crystallization can be performed. Further, when the optical system using the optical waveguide of the present invention is used, the position of the beam spot on the irradiated surface is not affected at all by the fluctuation of the laser beam, so that the output stability is extremely high like the optical waveguide and the VEL 1520. When combined with a laser, very uniform laser annealing can be performed.

The laser beam irradiation is performed, for example, while scanning the stage with the irradiated surface 208 shown in FIG. 2 in the short side direction of the rectangular beam spot. At this time, the practitioner may appropriately determine the energy density of the beam spot on the irradiated surface and the scanning speed. Rule of thumb is the range of the energy density of ^{200mJ / cm 2 ~1000mJ / cm 2} . If an appropriate scanning speed is selected in a range where the width of the rectangular beam spot in the short side direction is about 90% or more and overlaps each other, there is a high possibility that uniform laser annealing can be performed. The optimum scanning speed depends on the frequency of the laser oscillator and may be considered to be proportional to the frequency.

  Thus, the laser annealing process is completed. A large number of substrates can be processed by repeating the above steps. In addition, it is possible to process a substrate more efficiently by preparing a substrate holder that can store a plurality of substrates and a transfer device that automatically conveys the substrate between the substrate holder and the stage. Become. For example, an active matrix type liquid crystal display device can be manufactured according to a known method using the substrate.

In the above example, an excimer laser is used as the laser oscillator. An excimer laser has a very small coherence length of several μm and is suitable for the optical system in the above example. Some of the lasers shown below have a long coherent length, but when using such a laser, it is possible to generate interference by combining optical beams with different optical paths before combining the divided laser beams. Can be suppressed. Alternatively, before passing through the optical system, an optical fiber or the like is passed through and the coherent length is artificially changed and then introduced into the homogenizer. Even if a harmonic of a YAG laser or a harmonic of a glass laser is used, the same large output can be obtained, and the energy of the laser beam is well absorbed by the silicon film, which is preferable. Other laser oscillators suitable for crystallization of the silicon film include YVO ₄ laser (harmonic), GdVO ₄ laser (harmonic), YLF laser (harmonic), and Ar laser. The wavelength range of these laser beams is well absorbed by the silicon film.

  In the above example, an amorphous silicon film is used as the non-single crystal semiconductor film, but it can be easily estimated that the present invention can be applied to other non-single crystal semiconductors. For example, a compound semiconductor film having an amorphous structure such as an amorphous silicon germanium film may be used as the non-single-crystal semiconductor film. Alternatively, a polycrystalline silicon film may be used for the non-single-crystal semiconductor film.

  FIG. 3 shows an example of an optical system using an optical waveguide described in this embodiment. A light pipe can be used as the optical waveguide. First, the plan view of FIG. 3A will be described. The laser beam emitted from the laser oscillator 301 is propagated in the direction of the arrow in FIG. In the plan view of FIG. 3A, the direction perpendicular to the paper surface is the short-side direction of the rectangular beam spot.

  First, the laser beam is expanded by the spherical lenses 302a and 302b. This configuration is not necessary when the beam spot emitted from the laser oscillator 301 is sufficiently large. In addition, like the spherical lenses 302a and 302b, an optical system that expands the shape of the beam spot is generally called a beam expander.

  The laser beam expanded by the beam expander is focused in the long-side direction of the rectangular beam spot by a cylindrical lens 303 having a first surface with a radius of curvature of 194.25 mm, a second surface with a flat surface, and a thickness of 20 mm. The sign of the radius of curvature is positive when the center of curvature is on the laser beam exit side with respect to the lens surface and negative when the center of curvature is on the incident side with respect to the lens surface. The lens surface is defined as a first surface that is incident on the laser beam and a second surface that is emitted.

  The optical waveguide 304 composed of the two reflecting surfaces 304 a and 304 b facing each other is arranged so that the entrance position of the optical waveguide 304 is the focal position of the cylindrical lens 303. The laser beam incident on the optical waveguide 304 is repeatedly reflected in the optical waveguide 304, the energy distribution is made uniform, and reaches the exit. A plane having a uniform energy distribution in the long side direction of the rectangular beam spot is formed at the exit of the optical waveguide 304. The optical waveguide 304 has a length in the traveling direction of the laser beam of 200 mm and a distance between the reflecting surfaces of 2 mm.

  A rectangle formed at the exit of the optical waveguide 304 by a cylindrical lens 305 having a radius of curvature of 9.7 mm on the first surface, a flat second surface, and a thickness of 5 mm disposed at a position 20 mm from the exit of the optical waveguide 304. A surface having a uniform energy distribution in the long side direction of the beam spot is projected onto an irradiated surface 309 arranged at a position 3600 mm behind the cylindrical lens 305. That is, the uniform surface and the irradiated surface 309 are in a conjugate position with respect to the cylindrical lens 305. Thereby, the energy distribution in the long side direction of the rectangular beam spot is made uniform, and the length in the long side direction is determined. In this embodiment, the cylindrical lens 305 is used as a lens for projecting the laser beam emitted from the optical waveguide 304 onto the irradiated surface 309. However, a doublet cylindrical lens may be used to reduce aberrations. The doublet cylindrical lens refers to a lens composed of two cylindrical lenses. Alternatively, a lens composed of three or more lenses may be used. It may be determined by the system to be designed and the required specifications.

  Next, the side view of FIG. 3B will be described. The laser beam emitted from the laser oscillator 301 is expanded by a beam expander composed of spherical lenses 302a and 302b. The laser beam expanded by the beam expander is disposed at 773.2 mm behind the cylindrical lens 305, and the first surface has a radius of curvature of 486 mm, the second surface is flat, and the cylindrical lens 306 has a thickness of 20 mm. Focus the beam spot in the side direction.

  The optical waveguide 307 composed of the two reflecting surfaces 307 a and 307 b facing each other is arranged so that the entrance position of the optical waveguide 307 is the focal position of the cylindrical lens 306. The laser beam incident on the optical waveguide 307 is repeatedly reflected in the optical waveguide 307, the energy distribution is made uniform, and reaches the exit. A surface having a uniform energy distribution in the short side direction of the rectangular beam spot is formed at the exit of the optical waveguide 307. The optical waveguide 307 has a laser beam traveling direction length of 250 mm and a distance between the reflecting surfaces of 2 mm.

  A rectangular beam spot formed at the exit of the optical waveguide 304 on the irradiated surface 309 disposed 237 mm behind the doublet cylindrical lens by the doublet cylindrical lenses 308a and 308b disposed 1250 mm behind the exit of the optical waveguide 307. A surface with a uniform energy distribution in the short side direction is projected.

  The two cylindrical lenses constituting the doublet cylindrical lens are one in which one has a curvature radius of 125 mm on the first surface, a curvature radius of 77 mm on the second surface, and a thickness of 10 mm, and the other is the first lens. This is a cylindrical lens having a radius of curvature of 97 mm, a radius of curvature of the second surface of -200 mm, and a thickness of 20 mm, and the interval between the two cylindrical lenses is 5.5 mm. Thereby, the energy distribution in the short side direction of the rectangular beam spot is made uniform, and the length in the short side direction is determined. The irradiation surface may be arranged immediately after the optical waveguide 307 without using the doublet cylindrical lens. However, since the distance between the optical system and the irradiation surface can be increased by using the doublet cylindrical lens, the space Can afford.

  With the optical system using the optical waveguide shown in FIG. 3, a rectangular beam spot having a uniform energy distribution having a length of 300 mm in the long side direction and a length of 0.4 mm in the short side direction can be formed. FIGS. 4A to 4C show the simulation results performed in the optical design software. FIG. 4A is a diagram showing the energy distribution of a beam spot formed on a plane of ± 200 mm in the long side direction and ± 0.3 mm in the short side direction from the center of the rectangular beam spot. 4 (b) and 4 (c) are cross-sectional views of the energy distribution along the lines A and B shown in FIG. 4 (a), where the vertical axis indicates the laser intensity (AU) and the horizontal axis indicates the length (mm). It is. From the result of FIG. 4A, the shape of the beam spot is very close to a rectangular shape, and the line width of the beam spot is uniform over a length of 300 mm, so uniform annealing can be expected.

  Using the optical system using the optical waveguide shown in this example, laser annealing of the semiconductor film is performed by the method according to the embodiment, for example. For example, an active matrix liquid crystal display device can be manufactured using the semiconductor film. The production may be performed by a practitioner according to a known method.

  In this example, an example of an optical system different from the optical system described in the embodiment is given. FIG. 5 shows an example of an optical system described in this embodiment. A light pipe can be used as the optical waveguide.

  In FIG. 5, the laser beam passes through the same optical path as the optical system shown in FIG. 3 except for the optical waveguide 504 and the optical waveguide 507. The optical waveguides 504 and 507 have two reflecting surfaces facing each other in the same manner as the optical waveguide 304. The space between the two reflecting surfaces facing each other in the optical waveguide 304 is hollow, while the space between the two reflecting surfaces facing each other in the optical waveguides 504 and 507 is filled with a medium having a refractive index n (> 1). . They are different in this respect. Based on the same principle as that of an optical fiber, when a laser beam is incident on the optical waveguides 504 and 507 at an angle greater than a critical angle, the laser beam is totally reflected on the reflecting surface. For example, an optical waveguide having a total reflection surface at the interface between the optical waveguide and air can be realized by disposing an optical waveguide made of quartz (refractive index of about 1.5) in the air. When the optical waveguide as described above is used, the transmittance of the laser beam is very high compared to the case where total reflection is not performed. Therefore, the laser beam from the laser oscillator 301 can be propagated to the irradiated surface 309 with higher efficiency.

  In place of the optical waveguides 504 and 507 in FIG. 5, an optical waveguide having a multilayer structure may be used. Typically, it is made of two materials as shown in FIG. 7A, and the refraction of the inner material 702 (for example, quartz containing germanium) is higher than the refractive index of the outer material 701 (for example, quartz). An optical waveguide with a higher rate can also be used.

FIG. 7B shows a cross-sectional view of the optical waveguide shown in FIG. FIG. 7C shows an enlarged view of the reflecting surface in FIG. When the incident angle θ of the laser beam 703 is incident on the optical waveguide at an angle equal to or larger than the critical angle θ ₀ , the incident light is totally reflected between the two reflecting surfaces facing each other.

  When the laser beams are incident on the optical waveguides 504 and 507, a coating for suppressing the reflectivity may be applied to the incident surface as appropriate in order to suppress the reflectivity of the laser beam on the incident surface of the optical waveguide.

With the optical system shown in FIG. 5, a rectangular beam spot having a uniform energy distribution with a length of 300 mm in the long side direction and a length of 0.4 mm in the short side direction can be formed.

  Utilizing the optical system shown in this example, laser annealing of the semiconductor film is performed by the method according to the embodiment of the invention, for example. For example, an active matrix liquid crystal display device or a light-emitting device can be manufactured using the semiconductor film. The production may be performed by a practitioner according to a known method.

The figure explaining equalization of the energy distribution of the beam spot by an optical waveguide. The figure which shows the example of the beam homogenizer using the optical waveguide which this invention discloses. The figure which shows the example of the beam homogenizer using the optical waveguide which this invention discloses. The energy distribution of the rectangular beam spot by the beam homogenizer presented in FIG. The figure which shows the example of the beam homogenizer using the optical waveguide which this invention discloses. The figure which shows the conventional beam homogenizer. The figure which shows the example of the optical waveguide which this invention discloses.

Claims (24)

Having an optical system that uniformizes the energy distribution in one direction of the beam spot formed on the irradiated surface;
The beam spot is rectangular,
The one direction is the long side direction of the rectangular shape,
The optical system includes an optical waveguide having two opposing reflecting surfaces that allow a laser beam to enter from one end face and emit the laser beam from the other end face. Having an optical system that uniformizes the energy distribution in one direction of the beam spot formed on the irradiated surface;
The beam spot is rectangular,
The one direction is the long side direction of the rectangular shape,
The optical system has an optical waveguide having two opposing reflecting surfaces that allow a laser beam to enter from one end face and emit the laser beam from the other end face, and a uniform energy distribution formed by the optical waveguide. A beam homogenizer comprising one or a plurality of cylindrical lenses that project and enlarge a surface in the long-side direction of the rectangular shape on the irradiated surface. A first optical system for homogenizing an energy distribution in a first direction of a beam spot formed on an irradiated surface;
A second optical system for uniformizing energy distribution in a second direction orthogonal to the first direction of the beam spot;
The beam spot is rectangular,
The first direction is the long side direction of the rectangular shape,
The second direction is the rectangular short-side direction,
The first optical system has an optical waveguide having two opposing reflecting surfaces that allow a laser beam to enter from one end face and emit the laser beam from the other end face,
The second optical system has a cylindrical lens array, and is a beam homogenizer. A first optical system for homogenizing an energy distribution in a first direction of a beam spot formed on an irradiated surface;
A second optical system for uniformizing energy distribution in a second direction orthogonal to the first direction of the beam spot;
The beam spot is rectangular,
The first direction is the long side direction of the rectangular shape,
The second direction is the rectangular short-side direction,
The first optical system and the second optical system have an optical waveguide having two opposing reflecting surfaces that allow a laser beam to enter from one end face and emit the laser beam from the other end face. A characteristic beam homogenizer. In any one of Claims 1 thru | or 4,
The beam homogenizer, wherein the optical waveguide is a light pipe. In any one of Claims 1 thru | or 5,
A beam homogenizer, wherein an aspect ratio of the beam spot is 10 or more. In any one of Claims 1 thru | or 5,
A beam homogenizer, wherein an aspect ratio of the beam spot is 100 or more. A laser oscillator;
A beam homogenizer,
The beam homogenizer homogenizes the energy distribution in at least one direction of the beam spot formed on the irradiated surface,
The beam spot is rectangular,
The one direction is the long side direction of the rectangular shape,
The beam homogenizer has an optical waveguide having two opposing reflecting surfaces that allow a laser beam to enter from one end face and emit the laser beam from the other end face. A laser oscillator;
A beam homogenizer,
The beam homogenizer includes a first optical system that uniformizes an energy distribution in a first direction of a beam spot formed on an irradiated surface;
A second optical system for uniformizing energy distribution in a second direction orthogonal to the first direction of the beam spot;
The beam spot is rectangular,
The first direction is the long side direction of the rectangular shape,
The second direction is the rectangular short-side direction,
The first optical system has an optical waveguide having two opposing reflecting surfaces that allow a laser beam to enter from one end face and emit the laser beam from the other end face,
The laser irradiation apparatus, wherein the second optical system has a cylindrical lens array. A laser oscillator;
A beam homogenizer,
The beam homogenizer includes a first optical system that uniformizes an energy distribution in a first direction of a beam spot formed on an irradiated surface;
A second optical system for uniformizing energy distribution in a second direction orthogonal to the first direction of the beam spot;
The beam spot is rectangular,
The first direction is the long side direction of the rectangular shape,
The second direction is the rectangular short-side direction,
The first optical system and the second optical system have an optical waveguide having two opposing reflecting surfaces that allow a laser beam to enter from one end face and emit the laser beam from the other end face. A featured laser irradiation device. In any one of Claims 8 to 10,
The laser irradiation apparatus, wherein the optical waveguide is a light pipe. In any one of Claims 8 thru | or 11,
The laser oscillator is one of an excimer laser, a YAG laser, and a glass laser. In any one of Claims 8 thru | or 11,
2. The laser irradiation apparatus according to claim 1, wherein the laser oscillator is any one of a YVO ₄ laser, a GdVO ₄ laser, a YLF laser, and an Ar laser. In any one of Claims 8 to 13,
A beam homogenizer, wherein an aspect ratio of the beam spot is 10 or more. In any one of Claims 8 to 13,
A beam homogenizer, wherein an aspect ratio of the beam spot is 100 or more. In any one of Claims 8 thru | or 15,
The laser irradiation apparatus includes a moving stage that moves an irradiation object having the irradiation surface relative to the beam spot. In claim 16,
The laser irradiation apparatus includes a transfer device that conveys an irradiation target having the irradiation surface to the moving stage. Forming a non-single crystal semiconductor film on the substrate;
Using the optical system having a cylindrical lens array and an optical waveguide, the beam spot generated on the irradiated surface is shaped into a rectangular shape using the single crystal semiconductor as the irradiated surface, and the beam spot is shaped into a rectangular shape. Laser annealing the non-single-crystal semiconductor film while moving the position of the spot relative to the non-single-crystal semiconductor film, and the cylindrical lens array has a short-side direction of the rectangular beam spot. And the optical waveguide acts in the long side direction of the rectangular beam spot. Forming a non-single crystal semiconductor film on the substrate;
Using the optical system having a cylindrical lens array and a plurality of optical waveguides, the laser beam generated by a laser oscillator is shaped into a rectangular shape using a cylindrical lens array and a plurality of optical waveguides as the irradiated surface of the single crystal semiconductor, Laser annealing the non-single-crystal semiconductor film while moving the position of the beam spot relative to the non-single-crystal semiconductor film, and at least one of the plurality of optical waveguides Acts on the long side direction of the rectangular beam spot, and at least one optical waveguide acts on the short side direction of the rectangular beam spot. The method for manufacturing a semiconductor device according to claim 18, wherein the optical waveguide uses a light pipe. In any one of claims 18 to 20,
The method for manufacturing a semiconductor device, wherein the laser oscillator uses any one of an excimer laser, a YAG laser, and a glass laser. In any one of claims 18 to 20,
The method for manufacturing a semiconductor device, wherein the laser oscillator uses any one of a YVO ₄ laser, a GdVO ₄ laser, a YLF laser, and an Ar laser. In any one of Claims 18 to 22,
A method for manufacturing a semiconductor device, wherein the beam spot has an aspect ratio of 10 or more. In any one of Claims 18 to 22,
A method for manufacturing a semiconductor device, wherein the beam spot has an aspect ratio of 100 or more.